Study on the Impact of Artificial Recharge on Treated Domestic Sewage

Abstract

The proposed research will look into, and study the impact of artificial recharge of treated sewage in the unconfined aquifer. In order to enhance the focus on the development and planning for wastewater management, finding a solution for the disposal of treated sewage has become an important priority. As a result, a quantitative study is necessary to bring out the solution for the disposal of treated sewage. There are two types of artificial recharge of treated sewage practiced globally (a) confined aquifer recharge and (b) unconfined aquifer recharge. Artificial recharge in a confined aquifer may not be sufficient to meet the need for pollutant removal, but artificial recharge practice in an unconfined aquifer will meet the needs of pollutant removal as per the review of the literature. At the moment, treated sewage after tertiary treatment is reused in a variety of ways, such as landscapes in educational institutions, cooling towers in industry, and so on. However, the pollution control board insists zero disposal, then the disposal of treated sewage remaining after reusing will become a burning issue to handle and to dispose it. The idea of the recharge will serve the purpose of replenishment and also a solution for disposal in all-time weathering conditions.

1. Introduction

Water is a vital source of life for all creatures on the planet earth. Indians have developed various lifestyles as a result of the country’s diverse culture and because of the constant growth in population, wastewater management has become a time-consuming procedure, especially in urban areas. The demand for water is increasing every day, and so is the quantity of water squandered. Furthermore, due to a lack of adequate wastewater disposal management, the issue has gained momentum in virtually all cities inside the present environment.

The focus is on driving away sustainable development as a result of increased urbanization and the government’s smart city program. In the current situation, adopting a systematic approach to achieve sustainability is critical, since pollution, climate change, and deforestation are on the rise on the one hand, while natural existing water supplies are decreasing day by day on the other end. After China, India is second of the leading populated countries in the globe. Currently, 61,754 million liters of water per day (MLD) of sewage is generated per day, 22,963 MLD of sewage is processed, and 62% of sewage is discharged straight into water bodies without treatment, according to the estimates.

Water consumption for business and home use might reach 29.2 billion cubic meters by 2025 and the population is expected to cross 1.5 billion mark by 2050 [1]. Therefore, the aim has to be to utilize the treated sewage as an alternative source to replenish and conserve it for future purposes by employing an artificial recharge technique. This may increase the efficiency in the use of water by employing the conjunctive use of groundwater thereby reducing the demand for freshwater sources. Though the practice of stormwater recharge is adopted, the significant effects are still unknown after recharge for seasonal emerging pollutants. The artificial recharge system of treated sewage is a promising technique that has significant research potential to understand the mechanism with preliminary hydrogeological investigation to evaluate the impact on unconfined aquifer. This study will head into a new form of disposal for all weathering conditions and more importantly, the potential of the land to adopt this method needs to be addressed.

2. Aquifers

Aquifers are bodies of rock and/or sediment that contain groundwater. The term “groundwater” refers to rainwater that penetrated through the soil and accumulated in voids of the subsurface of the soil. Aquifers naturally filter groundwater by forcing it to travel through tiny pores and between sediments, which aids in the removal of contaminants. However, this natural filtration process may not be sufficient to remove all of the pollutants. Aquifers are classified into two types: confined and unconfined.

Confined aquifers are also known as “Artesian aquifers” since they are located mainly above the base of confined rock strata. Water levels in punctured wells derived from artesian aquifers fluctuate owing to pressure changes rather than the quantity of stored water. The ruptured wells function primarily as conduits for water transfer from replenishment regions to natural or artificial end destinations.

Unconfined aquifers, in contrast to restricted aquifers, are typically found near the ground surface above the water table, although sitting comparatively above impervious clay rock strata. The water table is the highest barrier of groundwater inside an unconfined aquifer. Groundwater in an unconfined aquifer is more sensitive to contamination by surface pollution than groundwater in confined aquifers due to simple groundwater penetration by terrestrial contaminants. The level of groundwater fluctuates and is determined by the amount of groundwater stored in the aquifer, which impacts the rise or fall of water levels in wells that draw their water from aquifers (Figure 1).

Figure 1.

Unconfined and confined aquifer systems.

2.1 Artificial recharge

Artificial recharge is a strategy for replenishing an unconfined aquifer by sending additional surface water into the earth by distributing it on the surface, using recharge wells, or modifying natural conditions to enhance penetration. Artificial recharge is also known as planned recharge, which is described as the storage of water underground. During periods of water scarcity, the requirement of additional water is been provided as per demand. Artificial groundwater replenishment with treated wastewater is a crucial and necessary practice with several benefits. It helps to avoid groundwater depletion first and foremost. Second, it maintains water in a certain basin or watershed (i.e., the water is not lost to surface water outflow from the watershed or discharge to the ocean). Third, it may save a lot of money when compared to alternative water sources (Figure 2) [3].

Figure 2.

Different types of aquifer recharge [2].

With recovered water, three methods of groundwater recharge are typically used: subsurface injection into the vadose zone, surface spreading, and direct injection into the aquifer. Figure 3 illustrates these three ways.

Figure 3.

Different methods in groundwater recharge [4].

2.2 Selection of recharge system

The most frequent technique of groundwater recycling with recharge basins is the surface spread, although it is constrained to aquifers having vadose areas. Injection wells, which have developed recently, are less prevalent in the vadose zone in unconfined aquifers. With confined or unconfined aquifers, direct injection wells may be employed; they may be used to inject a variety of aquifers at various depths (Table 1).

Characteristic	Recharge basins	Vadose zone (shallow) wells	Direct injection wells
Location where treatment occurs	Vadose zone and saturated zone	Vadose zone and saturated zone	Saturated zone
Aquifer type	Unconfined	Unconfined	Unconfined or confined
Pre-treatment Requirement	Secondary treatment	Secondary treatment & Filtration	Advanced filtration
Maintenance Requirements	Drying and scraping	Drying and Disinfection	Disinfection and flow reversal

Table 1.

Characteristics of aquifer recharge for different [4].

2.3 Simulation study

This work is carried out to track contaminant movement in a horizontal direction and is analyzed using a 2D model of pollutant transport in a porous medium with regulated discharge. COMSOL Multiphysics generated a soil matrix for water recharging of treated household sewage. With a 2D analysis, the diffusion is positioned in the center of the recharge as it flows downhill and horizontally through the soil matrix. The soil column dimensions are 1.5 × 1.2 m. The flow pattern in lateral direction was investigated in COMSOL to study the transport of recharge water as well as its pollutant constituents such as completely dissolved solids with adsorption and desorption characteristics in soil. This research was carried out by developing and running domestic wastewater subsurface infiltration systems. It was discovered that this work discusses the significance of purifying substrates and the types of structures for optimizing diverse operation modes such as HLR, PLR, intermittent operation, aeration, and shunting distribution operation [5]. Metabolomics analysis of a subsurface wastewater infiltration system subjected to organic load fluctuations and current microbiology [6]. Depending on the size of the pores involved, the transport of pollutants in porous media equation was utilized for saturated porous medium. The primary goal of the research is to comprehend the concentration distribution and find the impact after infiltration in the porous medium. Variations in concentration are seen at the outflow based on the study time from the physical model study (Figure 4).

Figure 4.

Flow diagram of pollutant transport modeling.

Governing equation for the contaminant transport in porous media

$$\frac{\partial \left({\epsilon }_{\text{p}}{c}_i\right)}{\partial t}+\frac{\partial \left(\rho c_{\text{P}\text{}j}\right)}{\partial t}+\nabla \cdot J_i+u\cdot \nabla c_i=R_i+S_i$$

$$J_i=-\left(D_{\text{D}\text{}j}+D_{\text{e}\text{}j}\right)\nabla c_i$$

$\theta ={\epsilon }_{\text{p}}$ Under no flux condition with the associated boundary conditions.

$$\theta ={\epsilon }_{\text{p}}$$

$$-n\cdot \left(J_i+u{c}_i\right)=0$$

The model for the best results, we must partition the entire model into discrete portions. Depending on the intended effects, this meshing can be further split in a variety of ways. Because the emphasis is on the model’s inlet and outflow, a small mesh was chosen based on the geometry of the model. Table 4 shows the statistics used to solve the mesh (Figure 5).

Property	Minimum element quality	Average element quality	Triangle	Edge element	Vertex element
Value	0.7128	0.9294	1154	72	8

Figure 5.

3D and 2D boundary layer meshing and mesh extrusion make it possible to efficiently discretize.

3. Results and observation

The quality of the treated effluent of the sewage treatment plant (STP) is studied and used as an influent (Recharge water) for research work. The samples were collected after the secondary treatment and were tested for parameters such as BOD and COD.

The table below shows the average results of the recharge water used.

Parameter	Raw sewage	Treated effluent
BOD (mg/l)	140	39.24
COD (mg/l)	300	114.00
pH	6.65	6.8

4. Media characteristics

Soil is used as media for the recharge in the physical model developed. The media characteristics such as permeability, porosity, grain size, specific gravity, and density are the parameters determined.

Parameters (units)	Soil
Permeability (cm/s)	1.79 × 10^−5
Grain size	1.44
Specific gravity	2.54
Porosity	0.3
Density (gm/cm^3)	1.46

The table indicates the.

Parameter	Influent	Effluent	% Removal
BOD (mg/l)	53.33	23.85	58.02
COD (mg/l)	103.00	53.61	46.75
TDS (mg/l)	246.10	140.60	58.00
Alkalinity (mg/l)	220.00	105.00	52.06
Acidity (mg/l)	135.00	98.00	28.04
pH	7.90	7.56	—
Chloride (mg/l)	12.50	6.20	49.15

From the results, it was observed that there is a considerable reduction in the pollutant concentration from inlet to outlet which shows the impact of artificial recharge. Further, it is observed that the pollutant removal efficiency is higher in soil media than in sand media. Hence for the prediction analysis, the properties of soil are considered in the simulation model (COMSOL Multiphysics) [7].

5. Regression analysis

The validation of results from physical and simulation models is further strengthened using linear regression analysis for soil media.

5.1 Prediction analysis of pollutant removal using COMSOL multiphysics

Prediction analysis is carried out using COMSOL Multiphysics in order to determine the pollutant travel distance i.e., (zero concentration at the outlet). For the analysis based on the observation from the physical model used, the radius and time of flow were suitably assumed. By varying the radius of the model and on the basis of the time required from inlet to outlet for the analysis, the parameter BOD is considered with the inlet value of 26.66 and 53.33 mg/l. Following are the boundary conditions used for the prediction analysis.

Infiltration pipe: 0.15 m.

Permeability: 1.79 × 10⁻⁵ cm/s.

Discharge: 2.5 lpm.

Porosity: 0.3.

Materials used = soil media.

Density = 1.46 gm/cm³ (Table 2)

Radial distance (m)	Time (h)	Inlet BOD =26.66 mg/l	Inlet BOD =53.33 mg/l
		Outlet BOD mg/l	Outlet BOD mg/l
0.52	0.5	11.80	23.00
1.05	1	9.50	19.50
2.11	2	8.50	17.30
4.22	4	5.70	11.70
8.44	8	2.85	5.85
16.86	16	1.90	3.90
25.31	24	0.00	0.90
25.91	25	—	0.00

Table 2.

Simulated model output for pollutant removal (BOD).

From the prediction analysis, it is observed that the pollutant concentration decreases as the radius increases and reaches zero concentration at a certain distance. Hence, for the known quality of recharge water and site condition, it is possible to establish the pollutant travel distance.

6. Conclusion

Sewage management is a burning issue and there is a need for this should be addressed because of the disposal issue and nuisance most developing and underdeveloped countries face today. Each one of the counties has set up its own standards for disposal and degree of the treatment that needs to be provided based on the organic load in order to prevent environmental degradation. There is a lag in addressing the treated sewage disposal irrespective of the reuse for different purposes and needs. Since India is one of the countries where there is a large amount of fresh water available and the reuse of treated sewage has never been given importance and focus. But today, each continent is facing a drastic climate change and the global temperature is increasing, there is a need for addressing and promotig sustainable practice and conserving water. This will be one of the sustainability goal that can be reached by the United Nations by 2030.

Acknowledgments

I would like to thank the co-author Dr. Ganesha A for his support in preparing the report and reviewing the report. Also, I would like to thank Nealesh Dalal, managing trustee, JD school of design for giving me an opportunity to utilize the resources available in campus.

Conflict of interest

“The authors declare no conflict of interest.”