Problems of Centralized Depuration Systems

Abstract

Sewage management produces one of the worse impacts on our environment. The current technology applied is obsolete, which results in a huge public spent on installation and maintenance, with very negative consequences on the health of people and environment. The administration and the water companies try to hide these consequences, but the impacts are everyday more and more evident. This situation blocks any development of new technology that can solve the problem in a few years, changing the management, with strict control of every cubic meter of treated water and mud produced, saving an enormous quantity of money from public administration and avoiding a huge negative sanitary and environmental impact. New technologies can change the centralized depuration for decentralized depuration, avoiding the current problems, with a certificate control and saving between 80 and 90% of public inversion, and with the possibility to reuse the mud and treated water in place.

1. Introduction

Wastewater management is one of the best indicators of the low health and environmental awareness prevalent at different levels of society today. Except for some examples of efficient treatment systems implemented, most of the world uses highly inadequate technology that requires centralized management of wastewater treatment. This produces a series of associated problems well known to public administrations, which put the health of the public at risk and lead to a huge environmental impact that is reducing the quality of inland aquatic systems and coastal waters.

The vast majority of wastewater treatment plants currently being built and operated around the world are based on technology that has not seen an appreciable development in more than 100 years. This produces purification systems with a low capacity to eliminate contaminants from water as well as numerous associated problems that make it necessary to move treatment plants away from urban centers due to the danger to human health they pose [1, 2, 3].

The need to move treatment plants away from wastewater production areas makes it necessary to create an entire sewage infrastructure, with pumping stations and kilometers of pipes; and this represents one of the main problems in wastewater management throughout the world. Only by taking into account the losses from this sewage network can we get an idea of the scale of the problem of this management.

The best example demonstrating the precariousness of purification technology in a standard wastewater management system is the obligatory marine outfall in coastal areas, or discharge pipes to aquifers, lakes, and rivers in inland environments; these provide little confidence in being able to manage wastewater properly. They are totally necessary because purification processes under normal conditions produce an effluent with a high concentration of pollutants, which makes it very difficult to achieve the health guarantees for its reuse; so, the most widely used solution is to discharge it into the aquatic environment.

Sludge produced from purification is another of the major problems associated with these systems since the high concentrations of pollutants it contains exceed the capacity of the system and make it extremely dangerous to manage properly. Most of the time, this sludge ends up in the environment: discharged through outfalls, accumulated in landfills, dumped into the sea from ships, or unfortunately scattered over crop fields [4, 5, 6, 7, 8].

All of this bleak panorama—which can be summarized only briefly in this chapter—costs an enormous amount of public money, both for initial investment and for maintenance and management of the systems in our cities that treat wastewater; yet this water mostly ends up in the environment.

2. The danger of urban wastewater

Increasingly universally accepted, urban wastewater represents one of the main problems for coastal ecology. These are liquid residues that are not taken into sufficient consideration, as it is assumed they only contain organic matter and its degradation products.

As a brief introduction to the danger of urban wastewater, it should be highlighted that, in addition to organic matter, it contains all the toxic products from different industries, for example, heavy metals, chemical products, and micro and macro plastics. These are primarily responsible for over half of hydrocarbon discharges into the marine environment; this applies to the so-called emerging and dangerous compounds, which the public administration has recently begun to take into account as compounds to monitor [4, 5, 6, 7, 9, 10, 11, 12].

Another of the contents of these wastewaters are pharmaceutical products, which when dumped uncontrollably into the sewer, end up in all aquatic systems, whether inland or coastal [13].

It should be remembered that wastewater also contains the entire sum of pathogenic microorganisms for humans, which when cultivated with sublethal doses of antibiotics in the sewage system and in the bioreactors of purification systems, are an ideal culture medium for the creation of drug-resistant pathogenic microorganisms, which are inevitably released into the environment [14, 15, 16, 17].

3. Types of discharge into the environment

Having outlined the danger that urban wastewater poses, not only for the environment but for public health, what follows is a description of the routes of entry into the environment of this dangerous waste.

3.1 Discharges from treatment plants

It should be pointed out that this section describes how wastewater is generally managed throughout the world; however, there are a few places where the management is better than in others and may be acceptable, but this is after huge investment in civil works and maintenance that most countries cannot or will not address.

There is not enough space in this summary to address Membrane Biological Reactor (MBR) systems or plant filters, but their results are not very satisfactory either. So, this introduction will focus on traditional purification systems that consist of several chain treatments, where the most common is a so-called primary treatment followed by a secondary one, which is a combination of filtering, biological reactor (bacteria culture), and sedimentation process.

In general, pollutant removal from currently used treatment plants operates at low efficiency, despite their enormous size, initial investment, and maintenance costs, leaving the projects with very little capacity. A typical situation is due to the large civil works required which take several years on average, the plant is normally undersized when it is opened because of the population increase.

One of the main problems of these plants is their extreme fragility, which cannot withstand changes in effluent conditions. The quality of the treated water is affected by changes in the concentrations of initial wastewater, such as organic matter, suspended sediments, nutrients, and numerous parameters, which make management a continuous headache; even the weather can modify the treatment process [18].

Consequently, their management is very complex and depends on the ability of the management team. However, they are not always adequately trained in maintaining a culture of living organisms (biological reactor), and engineers are generally overwhelmed since these do not depend on precise parameters of pressure, flow, pumping, and temperatures, as happens in desalination plants. Here, the recommended plant conditions can be achieved quite well, but the growth of living organisms depends on their inter-relationship, biogeochemical cycles, stratification, denitrification, foaming, etc. [19].

One of the most critical parameters that need to be controlled, especially in coastal places, is the salinity of the effluent. Small levels of salinity affect drastically the biological reactor, the core of the treatment [20].

All these changes and variations in the effluent can produce a total collapse of the system. This is when it is necessary to empty tanks to the environment and restart the cultivation. This period can last several weeks, and lead to even worse quality of treated water during this time.

The sewage system does not separate rainwater from wastewater, which overwhelms the purification system in heavy rain, and then has to be directly discharged without purifying. Of all the wastewater management deficiencies, this one-off wastewater malfunction is the only one that is admitted within the management control system, and yet there are rarely any statistics on it or independent assessment of the impact that occurs in these cases [21].

The different public administrations in charge of controlling water treatment, whether private or public, do not use to admit these problems and try to hide them. Therefore, it is not so easy to have reliable statistics on the frequency with which systems are overcome; how long they take to restart; how much is sent to submarine outfall or directly into the environment and under what conditions, and for how long. It is typically admitted that discharges occur at night, as detected by the bad odors suffered in our cities, near the points of discharge.

The biggest problem of this treatment system, in addition to achieving quite poor purification results after the secondary treatment, is that the composition of the resulting effluent is tremendously variable [22].

This great variability makes it very difficult to design an adequate disinfection system or tertiary treatment. As the dosage of hypochlorite or ultraviolet radiation intensity, for example, should depend on the concentration of bacteria; and the same happens with filtration systems, which find it impossible with this great unpredictability.

In addition, these discharges from treatment plants also include products added in plant management processes, such as substances to promote decantation, cleaning of pipes, disinfectants, and other chemicals, all of which end up dumped into the environment. For instance, the impact of hypochlorite when it reacts with organic matter is well known.

Figure 1 shows the result of the water treatment plant in the Mar Menor (Murcia, Spain) with the best traditional technology (activated sludge, prolonged aeration, coagulation processes, flocculation, ring filter, and ultraviolet treatment) with tertiary treatment. However, what cannot be seen in the figure is the bad smell from the treatment plant discharge, which is proof of the serious difficulties in meeting the minimum purified water parameters.

Figure 1.

The outlet from the Torre Pacheco treatment plant into the Rambla de Albion, which ends up in the nearby lagoon after passing through the flowmeter located downstream. The bad smell of decomposing organic matter dominates the area (Mar Menor, Murcia, Spain).

In addition to the bad smell from the same discharge, several dead fish, apparently, mullets (Mugil cephalus) of about 15 or 20 cm could be seen, with other smaller, unidentified ones, marked with red circles in Figure 2. This gives an idea of the impact that this discharge has when it reaches the coastal lagoon of Mar Menor.

Figure 2.

View of the dead fish at the treatment plant outlet from Figure 1, marked with red circles for easier identification; and at the entrance to the treatment plant from which the emanation of foul smells was already evident. This is all indicative of the limitations of the technology.

The light foam accumulating on the edges of the discharge is a sign of a significant concentration of surfactants. The toxicity of these compounds for the life of water courses is well known, as they disturb gaseous exchange between the water surface and atmosphere, among other conditions [23].

This is only a small example of the most common day-by-day management, but it is also very indicative of the weakness of this technology.

3.2 Discharges from the sewerage and cesspools

The risk of treatment plants means they must be located away from population centers, which implies a huge sewerage system is required. This kilometric net is almost impossible to control, leading to a large number of problems, including an important number of leaks into the soil and aquifer.

This enormous net of pipes needs pumping stations to impulse the effluent to the treatment plants. Pumping increases the pressure within the tubes and elevates drastically the leaks to the soil, also the turbulence washes the sediments accumulation, producing a variability of the effluent quality, which the treatment plants do not support easily. Because of the bad smells effluent pumping produce, this maneuver used to be developed during the night.

It must be taken into account that it is estimated that between 8% and more than 50% of the sewerage effluent is lost by leaks during its travel to the treatment plants, which represents an enormous quantity of pollution and sanitary risk that gives it an idea about the size of the problem [24, 25, 26, 27, 28].

There are numerous works to replace the drinking water system, also due to the fact that the danger for human health as a result of these losses in sewerage used to be great, if one takes into account that the two pipes usually run parallel and losses from the wastewater pipes can seep into drinking water pipes, create a serious health problem over the world. Taking into account that the standard consumes of water per person in Europe is about 250 liters per day, which approximately means leaks of about 20 liters per day per person of wastewater to the aquifer, applying the lower rate of leaks (8%), is easy to reckon the size of the problem [29].

Figure 3 shows an example of how the sewage reaches the sand itself and its low tightness, producing a continuous discharge that quickly reaches the shore. These losses provide a continuous nutrient flow that feeds the primary producers of any aquatic system.

Figure 3.

Sewage leaks make a significant contribution to nutrients, in addition to numerous more dangerous pollutants. This can be seen in this figure and is directly related to the algae growth on the shore of the beaches. (Mar Menor, Murcia, Spain).

Fixing this problem is a very complicated matter because the budgets to carry out this work are sky-high and require a large amount of time. In addition, the high cost of sewerage means many homes are not connected to the general network of pipes and are forced to use filtering cesspools. The municipalities are realizing the problem, but there is not enough budget to solve it and the long deadlines needed to place them at a dead end.

The sewage system contaminates not only when the wastewater leaks into aquifers and the shoreline but also when salt water penetrates pipelines in coastal places. Together with the discharges from pumps in flood-prone areas in buildings, this increases the salinity of water reaching the purification plants, as explained above, which hinders the purification processes and makes the quality and purification capacity drop even more, as we discuss in the previous chapter.

The sewage system also collects rainwater, which causes the entire treatment system to break down, producing a general discharge throughout the hydraulic basin made up of sewage system wastewater, washing of the sediments accumulated in the sewer system, discharges from the blocked treatment plants, and rainwater, which produces a significant polluting effluent. Then, it is necessary to understand that the majority of human settlements are a continuous source of a big amount of wastewater to the soil, which finished in continental and coastal waters.

The processes of water movement in porous media and the amount of effluent spilled by the sewerage and filtering cesspools are difficult to follow and any approximation must be carried out carefully using a series of data that, usually, do not exist. It is very difficult to find the hydraulic model of wastewater spread in the aquifer, where speed, quality, and flow, for example, could be estimated [30, 31, 32].

However, the filtering will retain mainly larger particles or groups in the form of flocs, they can also retain fats and oils that will be adsorbed to the soil particles; similar to the effect sought in sand filters from sewage treatment plants [33].

In the case at hand, it should be stated that highly soluble compounds will pass through this filtrate to reach the aquifer, while those that precipitate, and form crystals or flocs will be retained.

Is typical to the behavior of nitrogen that due to it elevated solubility moves almost freely with the effluent through the soil and aquifer, arriving to the coastal areas, lagoons, rivers, etc., producing a continuous increment of nitrogen in those places.

As will be seen in the section on the effects of pollution, the arrival of soluble phosphorus compounds is one of the novelties that has changed the response of the lagoon ecosystem in Europe; producing the possibility of new growth that was not possible until 2015–2016, due to the change in the formulations of laundry and dishwashing detergents [34, 35].

The phosphorus compounds that were used prior to the European Union regulation of 2012 formed precipitate crystals that were relatively easily retained in the ground and most phosphorus did not reach the coastal areas or continental waters. However, the high solubility of current phosphorus compounds has led to this being an important pathway for the change in speciation.

3.3 Direct discharges

As we have already discussed above, purification systems are often too small, very fragile, and with a low capacity to remove pollutants, then a standard sewage management organization requires direct discharge points to evacuate raw effluent before reaches the treatment system, and partially treated effluent with poor quality, by spillways or submarine outfalls.

Spillways are normally used for this purpose, which is discharge points that in theory should be used to evacuate excess water in the event of floods. These spillways use to be operating all the time when the system is too small, at most, a bar screen is usually used, more to prevent the piping infrastructure from clogging than for the purpose of reducing environmental impact. However, even an adequately sized system that in theory could absorb all the effluent, commonly produces effluent quality not suitable for purification, then needs to be evacuated as well.

Storm tanks have an interesting use in these operations. In principle, they are meant floodwater but are used to accumulate effluent during the day that can then be discharged at night, or pumped into the treatment plant, depending on the effluent quality.

Clearly, these storm tanks are usually placed at the head of the start of marine outfalls or in spillway pipes, since they need a discharge point to manage this accumulation of wastewater that often has significant odor problems. They are usually found in the middle of cities, promenades, squares, or recreational spaces with an admirable combination of recklessness and lack of professionalism.

4. Connivance of the public administrations

This state of affairs is only possible due to collusion between wastewater managers and public administrations that should closely monitor the entire system, aware of the enormous problems, but they simply do not carry out this function.

The complicity between administrations and water managers begins with drafting legislation that is extremely benign and condescending to managing companies. The list of flagrant cases of laxness in the legislation of various countries around the world would fill this introductory summary.

To give an idea of the legislative problem, it should suffice to point out that until 1999 the European Union authorized and recommended the discharge of treated wastewater into the sea together with the sludge. In other words, after a multimillion investment with equally high maintenance costs, continuous discomfort for the public due to unpleasant odors, insects, rodents, pests, noise from pumps at night, the facilitation of disease transmission, and exposing the public to contact with the dangerous effluent, in the end, the treated water is discharged into the sea, with the sludge as well. This process occurs in other parts of the world, and it seems to have been the general solution for many years, continuing to be so today due to minimal control from the administration [36, 37].

The only way to control the water management system would be to monitor each process of management and movement of water and sludge, so that the impact the wastewater is having can be at least approximately evaluated. This would be important not only for the environment, but also to see the impact on the proliferation of resistant bacteria, the return of diseases that had already been overcome, and the incidence of parasites, or malnutrition problems in affected populations as a result of these diseases from this wastewater mismanagement [8].

The cost of such a control system, for example, with adequate sensors, would be negligible compared to the amount of money already spent in this sector on the construction of conventional treatment plants, the pipes to carry wastewater to these points, and the construction of pumping stations, not to mention their maintenance [38].

The results of a sensor system could be offered to the public, so that management was transparent. For example, users could know and limit their use of the coast, by not fishing when dumping in a submarine outfall occurs; or safe bathing areas or freshwater courses affected by a spill could be properly segregated. But anybody with a small experience in this sector believes that this transparency will be real in the next 20 years.

Other examples of the ineffective control of the public administrations are submarine outfalls, which are lucky to be visited once a year, with totally irrelevant surface sampling taken. Also, the specific sampling in treatment plants is carried out in accordance with the operators, and both samplings are carried out in full agreement with the operating companies [39].

The increasing privatization of wastewater management together with this poor control by public administrations, augment the still huge problems we have. Private management means that the purification quality is varied to save money, probably the most common way is to reduce energy consumption in the process. Firstly, as much effluent as possible is removed, by direct discharges before it reaches the treatment plant, and the biological tank aeration flow rates are decreased, constituting practically the biggest expense a traditional treatment plant has. This is very easy to see in sewage treatment plants with agitator aeration, with a reduction in stirring speed during the night leading to an award for the plant manager for the energy savings achieved. This decrease in the already low purification result goes unnoticed, since everything goes through submarine outfall, which is not controlled, much less at night.

5. Sanitation and environmental impact

To understand the impact on the environment of this wastewater management, a short introduction about the evolution of effluents is needed. There is a greater emphasis on marine processes since they are less known and perhaps more difficult to understand than continental water systems.

Produced through submarine outfalls, spillways, or streams that discharge on the shore or a few meters below sea level, the maximum depth should be around 50 meters depth. This chapter will describe the fundamental processes that control the development of these effluents and will summarize their impact, which is very important in the phenomena being studied.

Marine and especially coastal processes are very complicated to differentiate as established academic subjects. However, in this chapter, we will try to differentiate between physical, chemical, and biological processes that occur after the direct discharge of wastewater into the sea. It is undoubtedly necessary to repeat some concepts in various sections, as there may be various points to be discussed.

5.1 Physical evolution of wastewater discharges

5.1.1 Evolution in the water column

From the moment it leaves the pipe, the discharge encounters certain conditions of depth, density, salinity, nutrients, marine life, temperature, waves, wind, and coastal currents, which establish their mixing and movement processes with respect to the point of discharge and coast. This determines the environmental impact on the coast and in the area near the discharge point.

The evolution of the discharge on the water column is part of what is technically called the Near Field, where the physical processes of evolution are dominated by the discharge system design [40, 41, 42].

From the point of view of the movement of effluent, when leaving the pipe, it will feel several forces, for example, density difference, with the discharge coming up against water of greater density since wastewater is less dense, giving it a tendency to float toward the surface. It is also found in an environment of slow-moving water, as the speeds of marine currents are very weak near the bottom; the discharge normally has a higher speed and will run into the seawater until it is stopped (Figure 4).

Figure 4.

The view of a spillway on the surface of the water. These discharge points are well known to seagulls, for which they are often an easy source of food.

This decrease in speed causes the turbulence to decrease, so that the particles that were kept in suspension with this turbulent energy within the effluent begin to precipitate as the effluent loses speed.

At the outlet to the sea, there will be a sum of these two forces, one floating and the other as a jet in the direction of the outlet, which will lead to a result as determined by the Froude number for the jet:

$$Fr=\frac{\text{U}}{\sqrt{{\text{g}}^{’}\text{D}}}$$E1

where U is the exit velocity g’ is a modified gravity that takes into account the density difference $\left(g^{´}=g\left(\frac{\rho 1-\rho 2}{\rho 1}\right)\right)$, and D is the pipe diameter.

Figure 5 shows a couple of examples of the exit from the final mouth of a discharge through an underwater outlet without a diffuser section, where the distance traveled by the effluent from the mouth depends on the exit speed, where the tendency to rise from the bottom is dependent on the difference in density of the effluent and seawater.

Figure 5.

Pictures show a coupled of examples of physical behavior of two different submarine outflows. For the administration both are considered as depurated wastewater without any environmental impact, despite the awful visual appearance.

At this moment, which is represented in the photos, the exit velocity and the difference in density cause the discharge to travel a distance in the jet mode, so that after losing the exit velocity, its evolution is in the form of a plume, where the forces of buoyancy dominate the movement, producing those volutes that grow and incorporate water from the environment into the effluent.

In this ascent, the phenomenon of dilution occurs through very specific mixing processes that form increasingly larger eddies or volutes, according to the interface between the effluent and seawater. In a limited mixture of the effluent with water with less concentration of contaminants, causing the difference between the two waters to decrease.

During the ascent, important sedimentation phenomena take place due to the change in conditions. This sedimentation is enhanced by the effect of aggregates, a mixture of different compounds (bacteria, organic matter, flocculant products, detergents, and other pollutants) that form small flocs that are ingested by fish and other filtering organisms. This is perhaps the most direct process of damage to the environment and to people’s health, since these fish incorporate contaminants directly into their tissues in a rapid bioaccumulation process [43, 44, 45].

The formation of flocs that gives rise to the phenomenon of “Marine Snow” increases sedimentation, and also produces a very negative effect on the organisms that are attached to the bottom or depend on it to live. The high sedimentation in the areas impacted by the submarine discharge points covers the bottom and suffocates the benthic organisms in rocky or sandy systems. However, the ones that suffer the most from this abnormal sedimentation process are the filter feeders, whose mechanisms for capturing food are obstructed and are not able to survive in these conditions.

An indirect effect of sedimentation is the anoxia produced on the seabed where it is deposited. The marine snow flocs transport a large amount of organic matter mixed with bacteria to the bottom, which is consumed by them that need oxygen for their degradation. The amount of oxygen is not sufficient and the processes of oxygenation of the sediment stop with this layer of sediments, creating a layer with a high oxygen deficit that eliminates all aerobic life [46, 47].

Sedimentation depends as well on the hydrodynamic conditions of the area: the higher the current, the less sedimentation there is in each area since turbulence keeps the sediments in suspension. Flocs in this form will travel in the water column and settle when they encounter appropriate low turbulence conditions. They will be concentrated at these points and will be resuspended when the dynamics increase.

This happens in storms arrive or due to high-speed boats in small depths, which put a large amount of organic matter back into the water column along with the pollutants that have settled during the calm period.

5.1.2 Evolution on surface

When the discharge finally reaches the surface, it is still very buoyant and accumulates against the surface due to this thrust of the effluent density difference. This accumulation creates a gravity current that causes the spill to spread out horizontally and accelerate toward the surface currents that dominate the area, usually driven by the wind (video 1).

At this point, the dilution of the effluent depends on the natural conditions of the environment and is independent of the discharge type; the process that takes place from this moment on is called Far Field [40, 41, 42].

So, a surface “cloud” is created that remains continuously stationary, with slight side movements, which can be pushed in different directions only by energy processes, such as the wind, currents, or movement of boats in shallow places.

Figure 6 shows how the tidal ellipse gives shape to the spill on the surface, which remains stationary, with slight movements around the spill point, with the tail of this case being dragged by the coastal drift. In this case, it is to the right of the photo, which corresponds to the southern component. The slick remains stable in this situation for the duration of the spill and gradually loses its contamination tail.

Figure 6.

View of the slick of a discharge from a submarine outlet on the coast of the gran Canaria capital. The discharge stays on the surface in an elliptical shape, stationary at the mercy of the coastal currents, wind, and waves.

Figure 7 shows the output of a numerical simulation model for the dispersion of pollutants from the discharge at a depth of 42 m from an underwater outfall (corresponding to the spill in Figure 6 and the left picture in Figure 5).

Figure 7.

Numerical simulations were performed by a pollutant dispersion model of the discharge in Figure 6, produced by a submarine outlet at a depth of 42 m. firstly, the ascent to the surface can be verified, with accumulation when it reaches this point and a progression on the surface up to 2000 m away. The color code indicates the evolution of the concentration.

Figure 7 shows various images of a numerical model for the scenario shown in Figure 5 left and 6, where the discharge finds a denser medium once it leaves the tube and rises to the surface, due to the difference in buoyancy. On the surface, it accumulates and gives rise to the typical spill slick from underwater pipelines.

In coastal lagoons and close seas like the Mediterranean and Baltic, tidal currents are negligible, and the slick will grow around the outcrop point, which will be dragged by the coastal drift current, although the wind is mainly responsible for the movement.

As a summary of the dynamic evolution of the discharge when it comes out of the mouth of a submarine drainage conduit, initially, it rises to the surface where significant sedimentation and dilution take place, which continues until it reaches the surface. During this ascent, the dynamics of the currents lift this plume to the seepage point. Here, there is a process of concentration of the discharge pushed by the buoyancy against the surface of the water, more or less above the outlet (Figure 8) (video 2).

Figure 8.

View of an experiment carried out in the fluid mechanics’ laboratory of the physics department, Las Palmas university, gran Canaria. It is a scale model of an underwater outlet discharge. An experiment was conducted to determine the distribution of effluent with a lower density than the receiving medium and thus calibrate a numerical model of contaminant distribution (video 1).

This is why the odor produced by gases from decomposing organic matter is easily detectable, especially in a shallow system, such as the Mar Menor and other coastal lagoons along the world, since the initial dilution, that is, in the Near Field, is reduced and the effluent appears on the surface with practically the same properties as that circulating through the sewage system, where hydrogen sulfide clearly stands out from other gases in the putrefaction of organic matter.

These areas need to be more controlled by the administrations because is a very high dangerous places that are attractive by coastal users, like fishermen, because of the fish concentration, sailboat racers (especially kits with small boats like an optimist) because is a point to turn, or to berth, because use to have a big buoy to mark the end of outfall point.

Figure 8 shows a scale model experiment of the behavior of dilution and evolution in the water column and on the surface of wastewater discharge. This is one of the actions necessary to calibrate a numerical model of contaminant dispersion, for the case when the discharge is carried by a discharge pipe without a diffuser system.

As already explained initial process is dominated by the effluent outlet velocity and the difference in buoyancy between the receiving medium and discharge, or the water of the sea and the effluent of a wastewater discharge.

However, the starting situation can change when there is stratification due to heavy rain flood processes, estuary, or river presence when the freshwater from the continental streams enters the sea and produces a surface layer of water less dense than that of the sea.

In this case, wastewater discharge poses a greater risk, since it can be trapped between these two water layers, leading to a totally underwater discharge situation.

This discharge makes no contact with the surface of the water, that is, there is no possibility of oxygen entering from the atmosphere. It cannot undergo the energetic mixing processes, produced by wind and waves at the surface (See Figure 9) (videos 1, 2).

Figure 9.

View of a video frame of a physical simulation of a single point discharge in a receiving medium with strong stratification. The discharge rises until it finds the corresponding density and evolves between the two layers of water due to the difference in density from the point of accumulation where the effluent arrives (video 2).

Figure 9 shows a laboratory simulation using a physical scale model, where the effluent discharged between two layers of water is seen to develop. The spill evolves between the two layers, almost exclusively by density difference processes and with limited dilution, produced solely by friction between the layers of water.

This process is very likely to be taking place in coastal lagoons when there are discharges under these conditions of strong stratification after a rain flood of water, where it is very easy for it to produce large general oxygen deficits in the two layers, since it tends to sequester oxygen from both, further impeding oxygenation of the bottom layer.

The effluent can travel in this way, without mixing, for long distances and seep out at any point, either on the shoreline or propelled to the surface by powerful storms or vessels, which causes it to reach the surface creating a serious foul smell nuisance.

5.2 Chemical evolution of wastewater discharge

When urban wastewater discharges, it meets water from marine coastal areas, which has a different chemical composition. In this encounter, in addition to the mixing processes already mentioned, chemical changes are produced in the composition of the mixing effluent.

Perhaps the most important change is that of acidity or pH. Seawater has a basic pH, above 8, while wastewater maintains a pH of around 7, depending on the chemical compounds diluted in it [48].

This change in pH favors a process previously established as marine snow, which is the product of the transformation of species that are dissolved at acidic pH (around 7), which when they encounter a basic pH become insoluble compounds. The most common example is the change from oxides (soluble) to hydroxides (insoluble). Inorganic contaminants, such as heavy metals and trace elements, experience this change the most.

Acidity modification affects the ecosystem because, while the dilution occurs and since the discharge is continuous, it creates a differential gradient of acidity that compromises the normal development of marine life, which is dependent on Ph, that is, it prevents, for example, the growth of shells and tissues made of calcium carbonate, which poses a danger to the ecosystem and especially to organisms with a shell or exoskeleton.

Figure 10 shows a clear example of sedimentation and turbidity processes, while in Figure 11, a detail of the consequences of this sedimentation on the seabed is shown. The flocs most visible in this photo are the light-colored ones, but the abundance of dark flocs is much higher and they appear in the photo as dark turbidity.

Figure 10.

Photograph of a spill on the coast where you can see the fall of marine snow, in the form of white dots, which transports a lot of pollution to the seabed. You can also see the turbidity that obscures the photo in broad daylight and at a relatively shallow depth. (Sta Cruz de Tenerife, Canary Islands, Spain).

Figure 11.

Photograph of a coastal seabed affected by an underwater discharge. You can see the dark color of muddy sediment, which indicates sedimentation and anaerobic degradation processes. In addition, you can see the microplastic particles that cover this sludge where a higher life is not found.

This high organic load provides this effluent with a high content of nitrogen, phosphorus, and other compounds, which are responsible for the problems that these effluents produce when they are discharged into the environment. They cause growth above usual levels of macro or microalgae and bacteria of species in coastal waters.

A large part of organic contaminants are associated with these flocs (Figure 10) and remain in suspension. They are ingested by marine organisms or precipitate, as described above. Many dissolve in the water, where they are absorbed by the respiratory organs (gills), incorporated into the bloodstream directly, and quickly injected into the food chain.

Another material dumped into the sea by wastewater is microplastic, mainly due to the discharge of water from industry and washing synthetic textiles, but also due to the discharge of numerous hygiene products. Plastics not only increase turbidity and leave annoying-colored grains on beaches; they also chemically degrade and release highly toxic products into the environment that add to the series of pollutants outlined in this study.

For example, bisphenols, vinyl, and carbamates, among others, are compounds (monomers) of high toxicity and are released into the environment from the degradation of the polymers in objects made of plastic materials [49, 50, 51, 52, 53, 54, 55, 56].

Some of the monomers that act chemically with very toxic biological effects are called endocrine disruptors because when organisms assimilate them in their tissues, they modify their metabolic and endocrine processes, as their structure is similar enough to replace them; they are all highly active carcinogens [57].

Chemical components of wastewater have been shown to have a catalytic effect on the populations of opportunistic competitor organisms. They stand out among all the vitamins and hormones, and their kinetics are described in the scientific literature as being responsible for bacterial emergence [58].

These organic substances are part of a group called persistent compounds since, in rapid purification cycles, they do not degrade and even less during their passage through the sewage system, poor technology treatment plants, and of course, in untreated discharge. In fact, these persistent molecules end up degrading into smaller compounds (CO2, N2, and H2O) after at least 96 hours and, during this long period, they can be incorporated into the tissues of marine organisms as the complete compound or a degradation product [59].

Over time, the remaining nutrients end up mineralizing, which can lead to the growth of sulfate-reducing or methanogenic bacteria in increasingly tropical seas that are being related to local changes in the pH and sulfur content of these seabeds [60].

All these processes are accentuated in coastal lagoons, or places where accumulation conditions are greater and renewal rates are low.

Thus, in a short time, these areas can no longer support life, as shown in Figure 11, of the bed in the vicinity of an underwater discharge pipeline. The dark-colored bottom confirms the existence of these processes with oxygen deficit; the fact that it is mud instead of sand, also indicates large fine particulate sedimentation, which covers an initial bed of light sand, located just underneath, which leaves the upper sediment lifeless.

This sediment devoid of oxygen and with a large amount of partially degraded organic matter produces anaerobic processes that can be divided into two broad categories:

1. Closed and reducing or hydrogenating anaerobic environments, in which hydrogen is produced and digested by hydrogenotrophic bacteria. Organic acid and polysaccharide chains break down to CH4 and CO2. Purines and amino acids break down to NH3 or NH4+ ammonium anions [61].

2. Nonreducing open anaerobic environment, in which the hydrogen produced escapes. In these cases, the organic chains degrade to acetic acid:

$$C{H}_3-\text{COOH}+H{R}_2{\text{R}}_3\text{N}=C{H}_3-{\text{CONR}}_2{\text{R}}_3\left(\text{Toxic Amide}\right)+{\text{H}}_2\text{O}.$$

The seabed is usually type (b) since it is an open and nonreducing system, which produces short-chain acids that, in turn, react with amines to produce highly toxic amides [62].

The generation of these toxins also finds an absorbent medium through which they can percolate, as if they were leachate, eliminating species capable of photosynthesis on that bed. They can be resuspended, however, by especially energetic storms or much more efficiently by high-speed sports boats with high-power motors and propellers near the bottom, which put new toxins into the water column until they settle elsewhere or are ingested by marine life. Thus, there is continuous pollution from different sources, from which it has no ability to recover its balance; so-called chronic action.

The layer of small, brightly colored, microplastic particles on the seabed, as seen in Figure 11, can end up having absorbent spongy properties when degraded, constituting ideal niches for the stabilization of bacteria provided by fecal water, in particular Clostridium prefigens, which causes skin and soft tissue infections in humans and fish. Proof of this is the excoriations, infections, and ulcers that fish have that live in the environments of the discharge pipe [63, 64].

In addition, there is the dangerous genus of Cryptosporidium protozoa that live in wastewater and are one of the most dangerous parasites worldwide, and are very difficult to eradicate with common disinfection systems. These are just two examples of the dangers to which users of coastal areas polluted by sewage are exposed, and they are cited here so that sewage receives attention as a toxic product, with increased control over these effluents [65, 66].

In the same way that these microorganisms can affect humans, they also affect these phenomena of accumulation of pathogens and other pests in fisheries, and the rest of marine organisms.

A clear example is the increase of ciguatera (which produces an accumulation of ciguatera toxin in the fatty parts of the fish), which is related to the opportunistic growth of populations of bacteria, such as dinoflagellates and some species of cyanobacteria that produce hepatotoxins and neurotoxins, in contaminated environments. Wastewater especially favors this growth, and it is found in coastal waters with increasing frequency [67].

Many of these plastic granules are ingested by living beings so, although in theory, they are inert chemically, they are vectors of diseases spread by bacteria. Even if the granule is subsequently returned or defecated, the bacteria will affect the fish, mollusk, or mammalian host [52, 53, 54, 55, 56].

And wastewater impacts in more ways. One of the clearest that gives an idea of the enormous damage caused in coastal waters is the oxygen consumption in the water column, an environment with a limited amount of oxygen.

Seawater has on average about 6 mg/l of dissolved oxygen. This is consumed by bacteria that degrade organic matter, and so can cause anoxia situations that produce degradation of organic matter with more harmful by-products.

A good measure of the impact is to calculate how much volume of water will be affected by the discharge only in Ref. to the dissolved oxygen to be consumed by the degradation of organic matter [68].

A flow of wastewater of one cubic meter, with an average BOD5 of 360 mg/l has an impact on approximately 60 m³ of seawater, which will be left without oxygen to be able to degrade organic matter.

5.3 Biological evolution of wastewater discharges

As briefly described in the previous section, the discharge carries a large number of polluting compounds, in addition to appearing in various forms and undergoing different processes, such as sedimentation and dilution.

The sedimentation process and formation of flocs generally called marine snow, evolves in two fundamental ways within the ecosystem. These flocs are either ingested by fish before reaching the bottom, or they are deposited and otherwise impact the coastal ecosystem.

During the descent of this particulate material, the fish are strongly attracted by these flocs since they are made up of organic matter of terrestrial origin, upon which bacterial colonies are developing; providing energy to move and proteins to grow without making any significant effort.

In addition to fish, there is a type of organism that is especially affected by these particles before they reach the bottom, which specifically concerns protected species that normally inhabit all marine ecosystems; these are filtering organisms [69, 70].

Filter feeders capture these particles, which also have a negative effect on their body, assimilating contaminants in a similar way, but at a faster rate than fish. If the amount of sediment or the size of the flocs is greater than the dimensions or capacity of the filtering system, these organisms have their feeding mechanisms obstructed and disappear from the areas affected by the discharges.

To understand the global impact of this process, it is enough to remember that coral reefs disappear due to this same problem, but other filtering organisms, such as oysters, will also be affected [71, 72, 73].

The enormous increase in suspended particles produced by a discharge pipe decreases the transparency of the water, and sunlight has more difficulty reaching the bottom. It is not difficult to understand that sunlight is essential for the development of another of the most important systems in the coastal waters, such as the Cymodocea nodosa meadows, or any seabed plant. However, in this area, they also have a negative influence on the development of the coastal rocky areas, since the algae that form the basis of this habitat need sunlight to develop, reducing their habitat depth as the turbidity caused by suspended sediments increases [74, 75, 76].

Once it reaches the bottom, the sediment can be ingested by detritivore organisms that incorporate the pollutants. Normally, the amount of sediment is very large, and they end up accumulating rapidly, exceeding the capacity of the detritivores [77, 78].

However, the marine ecosystem goes against the intention of the discharges which is to dilute the concentration of pollutants, through a process called bioaccumulation.

Bioaccumulation is a process by which marine organisms living in a contaminated environment concentrate in their tissues a greater number of pollutants, than in the medium, increasing its concentration at each step in the food chain [79, 80].

Wastewater discharges also produce numerous indirect effects in the coastal areas, one of the most recognized is their responsibility in the eutrophication process because they are by far the largest contributors of both N and P in many places. This process of fertilization produces an increase in different opportunistic vegetables in water [81, 82, 83].

The abnormal and widespread growth of plants is evidence of this excess of nutrients. The specific abundance of species and their growth also depend on other factors, such as the dynamic regime, salinity, and availability of consistent substrate.

The larger these algal growths, the more pollution the coast is suffering from, and in the images, it can be seen that these coastal algae are extensive and enormously widespread (see Figure 12). These abnormal growths of algae alter the entire ecosystem, where opportunistic species dominate over specialists, changing the ecosystem from its baseline status [84, 85].

Figure 12.

The problems suffered by the area due to an overabundance of nutrients are shown. In this case, they are taken advantage of by opportunistic macroalgae specializing in assimilating nutrients in enormous quantities and growing rapidly. Mar Menor (Murcia, Spain).

In an environment with the anthropomorphic input of nutrients, the formation of persistent foam is common, especially in large storm events or due to the beating of waves on the shores and motorboats. The beating of the water forms this foam from the emulsification of biological products associated with the growth and degradation of organic matter together with water. In Figure 13, you can see several places on the coast of the Mar Menor lagoon where this foam is formed [86, 87].

Figure 13.

Brown-colored persistent foam on the coast of the Mar Menor lagoon. (Spain).

The biological evolution of the discharge must include a reference to the very high concentration of microorganisms that are part of this waste, Escherichia coli values, of the order of 10⁸–10⁹ CFU/100 ml (1,000,000,000–100,000,000 formation units of colonies/in 100 ml of sample), are normal values in wastewater [88, 89].

But these bacteria are an indirect reference to the number of other species of microorganisms transported that are dangerous for the environment and human health. A large part of them are pathogens, which were briefly discussed in the chapter on chemical impacts [63, 64, 65, 66].

When the waste effluent comes into contact with the sea and this mixture is produced, the microorganisms find aggressive conditions, that is, high salinity, temperature differences, and when they reach the surface, great sunstroke.

These changes make it difficult for organisms from an environment of fresh water and darkness to progress. An indicative parameter for the Mediterranean Sea says that in 2 hours the concentration of bacteria has been reduced by 90%, which seems an important decrease; but not enough, considering the starting concentrations. As the mortality of microorganisms seems high, this process has led to incorrect speaking of the great purification capacity of the sea and associating this behavior in general with any pollutant (hydrocarbons, nutrients, and all the rest of chemical pollutants); this aspect is important because it is the basis of all legislation and wastewater management [90, 91].

5.4 Summary of the consequences of wastewater discharge

Everything described above shows that wastewater must be treated as a highly dangerous waste, which requires precise and extremely controlled management.

The controls that the legislation requires for a discharge pipeline are practically nonexistent and very inefficient. Thus, an underwater discharge pipeline or spillway becomes a dangerous point of contamination almost impossible to evaluate. The real impact it produces on the environment can only be approximated, in the face of a general lack of reliable and certified data.

Common management of discharges both for effluents and sludges is to concentrate them at night, which can be ease detected by the bad smells in our capitals or coastal population centers around the underwater discharge pipe or in the vicinity of the pipes that lead to their start on the coast.

Night discharges are especially serious for coastal areas, especially in lagoon or shallow and non-ventilated places, since, at that moment, the aquatic plants stop producing oxygen and begin to consume it to fulfill their respiratory metabolism. This produces a dangerous situation where oxygen consumption is generalized, and anoxic zones can quickly form if the movement of water is limited or is not capable of spreading the discharge quickly.

The first thing to mention is that the coastal lagoons are enclosed systems with limited connection to the coastal sea, so the dilution of pollutants is less, and they accumulate for a longer time. To this is added the low depth that makes the volume of waterless and so the water column can be quickly affected in its entirety. Also, the low depth means that the benthic system is accustomed to continuous lighting that promotes plant growth processes both on the bed and specializes in these conditions. However, at the same time, they are likely to produce exponential growth of phytoplankton when the right circumstances occur, which blocks the arrival of light to the bottom of the lagoon, in a system that is not prepared for low levels of lighting.

Sewage discharges produce a chronic impact because are continuous and it alters any marine area, which the ecological system is incapable of coping with, and which conditions it absolutely; thereby reducing the capacity of normal development of the ecosystem, no matter how small the discharge.

When considering dilution or dispersion or assimilation of discharge into the sea, as the final situation that solves the contamination problem, this is nothing more than the injection of pollutants into the marine environment. The incidence is direct and instantly affects organisms that in one way or another suffer the consequences.

Plastic may be a good example to understand the problem of pollution. It can be verified that it does not disappear but breaks into small pieces until it becomes part of the trophic web, so we are now aware that we are eating plastic even though it disappears from our sight in the sea. The same happens with pollutants, which become part of the food chain and ultimately end up on our tables as well as having a major impact on the coastal ecosystem.

It must be taken into account that treatment plants and the large movements of wastewater in sewers maintain cultures of all the pathogenic organisms that humans have plus sublethal doses of antibiotics, that is, it is the perfect breeding ground to produce resistant microscopic species which are discharged since the purification systems are not capable of retaining these microorganisms before discharge.

Having submarine discharges does not reduce pollution, it only dilutes the concentration of the discharge. This dilution is counteracted by the bioaccumulation effect of the contaminants, which are quickly incorporated and concentrated in the food chain; consequently, affecting all steps in the ecosystem and returning the concentrated contamination to our table in the form of fish.

The poor state of coastal ecosystems means that organisms are conditioned by pollution, having to use a significant part of their energy to defend themselves against this aggression, thus reducing their ability to grow, develop or, for example, fight against diseases and parasites. Parasites, especially microparasites, represent an increasingly worrying problem and the most worrying are those that prey on fish and can transmit themselves to us, such as Ciguatera or Anisakis.

This weakness means that the environment cannot recover from the changes we are experiencing, such as global warming, overfishing (both professional and recreational), coastal works, hydrocarbon spills, coastal erosion, and invasive species, are all part of the panorama of our bleak coastal waters.

This has led to an immense increase in pollution on the coast, which has been accumulating for decades, decreasing water quality dramatically. Therefore, today’s biodiversity is very poor, and the marine ecosystem is affected entirely. The system is so affected that it is changing the balance at important levels, and the idea that nitrogen is no longer a limiting nutrient for the growth of marine plants is finally beginning to be generalized, and it is increasingly accepted that phosphorus has also become the limiting nutrient in this environment.

Urban wastewater represents by far the greatest impact on the marine environment in general and on the coastal areas in particular. Both the management and the technology involved do not allow the control of the entire production or, of course, the elimination of pollutants in the effluent from our cities and urban settlements.

The list of pollutants that these effluents carry includes all the chemical products made in our society, plus a large amount of organic matter and chemical compounds from sewage treatment plants, which increase their toxic potential for the environment and, above all human health.

This effluent is a very dangerous toxic waste for people’s health and must be handled with great care. It also contains and concentrates all the organisms that cause diseases in human beings, some enhanced by its passage through the sewage system and by the treatments in sewage treatment plants.

6. Alternatives to centralized management of sewages

The alternative is decentralized treatment, based on having treatment plants arranged along the sewerage network to treat wastewater at the place it is produced and to make water available for reuse.

This system must necessarily be based on treatment plants that do not produce the usual problems, such as bad odors, noise, and proliferation of rodents and insects, and which can be installed even inside buildings in optimal health conditions.

The advantages of this new technology are great and largely solve the current purification problems, beginning with a change in sewage management, which will be used only for the transport of rainwater; so preventing the discharge of raw wastewater into the aquifer. The plants can achieve high purified water quality for complete reuse in the production area, without resorting to marine outfalls and discharges from pumping stations.

To manage this multiplication of treatment plants, sensor-based control systems connected to software that manages each part of the plant can be used. After calibration, they respond to changes in the variables monitored by the treatment plant automatically. The data can then be sent to a central station, where alarms and maintenance notices are managed and recorded to keep accurate statistics of all the water treated.

Plants can produce a totally degraded sludge that can be used without any hazard to health in electrical energy production to reduce consumption; hence, avoiding one of the biggest problems of the current purification of wastewater.

The investment necessary for the installation of these new technologies would save between 70% and 90% of the initial investment necessary for installing purification systems in places where these have not been installed. The same range of investment savings could be achieved when introducing these systems in cities where the traditional centralized purification systems are already installed. This is because only the reparation of the entire sewerage or the creation of a separate sewage network involves an investment of the order of two orders of magnitude superior to the installation of compact plants that do not need to use this network.

Energy consumption is higher in these plants but is between 1.8 and 2 kWh/m³ of treated water, which is not much higher than the consumption of traditional treatment plants where, in addition to the treatment cost, between 0.5 and 1 kWh, the cost of pumping wastewater from several kilometers to the treatment plant must be added.

The higher cost of energy consumption is offset by savings in management since the need for personnel, chemical products, sewage maintenance, and sludge purification treatment would be less; producing purified water that could be sold with all health guarantees.

When considering costs, the pollution parameter must also be considered; that is, how much does it cost to pollute? A system may consume slightly less energy, which could be compensated by maintenance savings, but where is the pollution produced? Clearly, a wastewater management system that produces a lot of pollution should be removed from the choice of systems. However, which is not something that is shared by the majority of water managers, who simply do not take this effect into account and continue as if nothing has happened, seeking to compare electricity consumption and justifying that the change is difficult, preventing even a debate or any objective evaluation.

These systems of small, high-efficiency, and low-price plants open up the possibility for minor municipalities or isolated communities to have a wastewater treatment solution, which until now has not been addressed with guarantees; preventing health and ecological hazards distributed throughout the world that has not even been evaluated. Only in Spain, there are thousands of municipalities without any type of purification, because the installation of alternative systems is not allowed.

There are enough examples for comparison; however, wastewater management in Venice, Italy is a good example. The difficulties in the area, the awareness of the water authorities and the conjunction of the private initiative led by applied research to solve problems have produced a decentralized system that is an example to follow. Over 100 treatment plants have been installed in the entire historic center of the island, specifically designed for each institution (hospitals and medical centers, chemical laboratories, grouped houses, hotels, sewage sludge treatment, mechanical workshops, theaters, universities, naval construction areas, etc.) and managed by eight people in 24-hour shifts.

There is also the Giniginamar plant, on the island of Fuerteventura, Canary Islands, which has been operating since 2008 for a coastal town of 200 inhabitants (smaller plants are more difficult to manage than large plants), where water has been reused in gardens and not discharged into the environment via the old filtering cesspools that were the solution adopted up to that moment. This has led to savings in the initial investment of several million euros compared with a standard solution. Despite having all the problems of a small, coastal system, with salinization of the effluent, seasonal variations in tourists, discharges from the chemical toilets of around 50 caravans, and all kinds of other discharges, including from a familiar craft cheese factory, output values are stable and, without changing membranes since 2008, the concentration of bacteria (Escherichia coli) has been zero during all the time and rest values under the limits of European water reuse legislation.

A typical bad case is a problem that has arisen in recent years in the Mar Menor lagoon, on the southeastern Mediterranean coast in Murcia, Spain. Here, water discharges with different degrees of purification along with other minor contributions of nutrients from agricultural and livestock activity have produced a spectacular growth of phytoplankton that has revealed the over-exploitation of tourism in the area, which caters to hundreds of thousands of people in the summer season.

Discharges that go unnoticed in other parts of the Mediterranean coast are more evident in a lagoon with these features. The poor state of the sewage system and the deficiencies of the technology explained above, together with the delicacy of the lagoon system, which is also visible to all and under the bright lights of the media have given rise to an enormous controversy where economic interests are intermingled with political ones, leading to a problem with no solution until contaminant inputs are addressed.

The high investment required and the enormous time it takes to improve the traditional purification system have given rise to a stalemate situation, where agriculture has received the full burden of responsibility for the degradation of the lagoon environment. This is because, as in the rest of the cases, the public administration is not capable of assuming responsibility for the real wastewater management situation. Since implementing only, the leaks of wastewater due to a sewage fault in the 1980s, without much care and in a hurry, both the contributions of organic matter and nutrients far exceed any contribution from other sources, together with other hazardous pollutants a pattern repeated all over the world.

7. Conclusions

Current wastewater management shows the failure of all sectors of our society. Beginning with a public administration that has no choice but to depend on the large water companies, with huge wastewater management businesses; as well as the hundreds of research centers that are incapable, not only of offering effective alternative solutions to the current management but of warning about the hazards entailed. In the end, it is clear that there is not the slightest awareness about health protection or, of course, about caring for the environment.

The increased concentration in the world population makes separating the contact between wastewater and the public much more complicated. There is increasing contact with wastewater, which reaches the dams from which we take drinking water, coasts, rivers, and lakes where we bathe, fish, and drink water, as well as aquifers and wetlands.

The saddest part of the situation is that the technology is available, capable of closing the water cycle for continuous reuse, with reduced initial investment and maintenance savings; managing to prevent the current health and environmental problem we suffer [92].

New relevant technology in our society is currently developed by small private companies, sometimes with associations of certain scientists from research centers. They have sufficient knowledge of reality and are promoting tangible alternatives to the great social problems we are facing at the moment. However, these developments are systematically blocked, and it is very difficult to generalize their use.

For improvement to be possible, we need independent, transparent public administrations associated with research institutes that are close to the real problems of our society.

The solution to the problem of water pollution is there, as with other contaminating sectors. We need to start thinking as a human species since our quality of life depends on it.

Videos

Video 1 https://www.youtube.com/watch?v=k3KTXtMGoIw.

Video 2 https://www.youtube.com/watch?v=F7k-xn11mBA&t=223s.