Maize industry wastewater physicochemical composition.
In this research, an innovative physicochemical strategy is presented to address the problem of nejayote, from two perspectives: the first focusing on sanitation and reuse of nejayote using waste from shrimp shells, thereby adding value to the recovered solids of nejayote. Zeta potential measurements are a proactive electrochemical tool to define the strategy to allow integral use of nejayote in the industry nixtamalization. The treated water can be discharged from the municipal sewer system using a process of coagulation-flocculation, with an optimal dose of 1250 mg/L chitosan at pH 5, achieving removal of up to 80% of total suspended solids and turbidity. Moreover, zeta potential measurements show that the anionic biopolyelectrolyte obtained from nejayote has potential to be applied in the area of water treatment as a green chelating agent.
- zeta potential
Nixtamalized products such as maize tortillas originated in Mexico, are the main sources of energy, protein, calcium and other important nutrients and are considered the national breads and consumed with other fillings such as beans, meats, eggs and vegetables [1–3].
The ancient, laborious or traditional process (nixtamalization) to obtain tortillas is a process widely used by indigenous people in Mexico (41%), the Southern United States, Central America, Asia and parts of Europe, that consumes significant amounts of water, energy and time . Traditional maize is lime-cooked in clay pots over a fire, followed by steeping for 8–16 h (generally overnight), the supernatant called maize wastewater or commonly known as “
Nixtamalization causes a loss of about 5% by weight dry basis of corn; 3% is suspended and the remaining 2% is dissolved. The suspended matter can be separated easily and inexpensively by sedimentation and the dissolved substance should “precipitate” to separate solids which is also done by sedimentation [2, 11–16].
A typical maize nixtamalization facility, processing 50 kg of maize everyday, uses over 75 L of water per day and generates nearly the equivalent amount of alkaline wastewater on a daily basis . The estimated monthly volume of
In this research, an innovative physicochemical strategy is presented to address the problem of
It is shown in Figure 1 that zeta potential measurements were used to interconnect the physicochemical characteristics of
Commercial testing water-quality reagents from HACH® were used. Milli-Q grade water was used in all the experiments. All other reagents were of analytical grade and were used without further purification.
2.1.1. Wastewater sampling in the nixtamalization industry
2.1.2. Chitosan extraction from waste shrimp shells
Chitosan is obtained from waste shrimp shells using the method proposed by the authors Goycoolea et al. .
2.1.3. Maize gum extraction of
Maize gum was obtained by fractional separation, using hexane, ethanol and hydrochloric acid, isopropanol, acetone, methanol formed by the steps of desalmidonado, deproteinization, delipidation, delignification which are proposed by the authors of [8, 18, 19].
2.2.1. Physicochemical characterization of
The main parameters of quality wastewater used in this research were performed following the Mexican standard procedures to determine the biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total nitrogen (TN), the solids content, total organic carbon (TOC), total phosphorus (TP), and other parameter fields such as pH, electrical conductivity (EC) and temperature were carried out based on the Hach methods.
2.2.2. Profiles of
ζ = f(pH) of nejayote, maize gum and chitosan
The charge density, isoelectric point and chitosan-dosing strategy for treating
Nejayote treatability tests by coagulation-flocculation using chitosan
A sample of 20 mL of
2.2.4. Evaluation of the capacity of polyelectrolyte maize gum for decontaminating wastewater
The anionic BPE obtained from
3. Results and discussion
3.1. Physicochemical characterization of
In this investigation the
As shown in Table 1, the physicochemical characteristics of
|Parameter||Maximum permissible limit|
|Suspended Solids, SS (mL/L)||800–900||1b|
|Total Solids, TS (mg/L)||46,523.00||200b|
|Total Dissolved Solids, TDS (mg/L)||46,339.70||NI|
|Total Suspended Solids, TSS (mg/L)||2000.00||NI|
|Alkalinity (mg/L CaCO3)||1020–1050||NI|
|Electric conductivity, EC (mS/cm)||4.29–6.42||NI|
|Particle size of the dissolved part (nm)||100–600||NI|
|Chemical Oxygen Demand, COD (mg O2/L)||9800–28,450||NI|
|Total Organic Carbon, TOC (mg C/L)||7337–9836||NI|
|Inorganic Carbon, IC (mg/L)||23–28||NI|
|Total Carbon, TC (mg C/L)||7360–9864||NI|
|Biochemical Oxygen Demand, BOD5 (mg O2/L)||2700||200b|
|Total Phosphorus, TP (mg P/L)||905–1321||30b|
|Total Nitrogen, TN (mg N/L)||303–418||60b|
For this research the measurement of other nonregulatory parameters was performed, and they are key to evaluate the performance of coagulation-flocculation process and determine the best operating conditions.
3.2. Profiles of
ζ = f(pH) of nejayote and chitosan
The zeta potential is a parameter by electrochemical nature that allows to study and predict the interactions occurring at the molecular level between the colloidal particles
Surface charge of chitosan and
In Figure 4, chitosan shows an amphoteric behavior, in the region of pH = 2–5.5 has a positive surface charge (
Nejayote treatability tests by coagulation-flocculation using chitosan
Dosing strategy for chitosan was determined by
Since the best wastewater clarification was at pH = 5.5 for chitosan, a turbidity-dosage profile was performed near the same pH to determine the optimal quantity of chitosan needed to flocculate
The coagulation-flocculation window of
Figure 5 shows the behavior of the zeta potential and turbidity with respect to the concentration of chitosan. In the region of low doses (250 and 750 mg/L), a decrease in turbidity (1590–500 FAU) is achieved, and the variation of zeta potential ζ = −10 mV to more positive values (ζ = −5.4 mV) shows that the mechanism of destabilization of
The coagulation-flocculation window was obtained from 1000 to 1500 mg/L chitosan with optimal dosage of 1250 mg/L chitosan, obtaining with this removal turbidity and suspended solids of about 80% (see Figure 6). At this dose, the surface charges of
3.4. Evaluation of the polyelectrolyte capacity of maize gum for decontaminating wastewater
The behavior of zeta potential vs pH of anionic BPE obtained from
This negative surface charge is very interesting for the treatment of wastewater containing high concentration of heavy metal. In the FTIR spectrum (see Figure 8) shows that the BPE has the characteristic functional groups of a polysaccharide (3400 cm−1 corresponding to stretching of the OH groups and 2900 cm−1 corresponding to the CH2 groups) which give the negative surface charge and that can interact with oppositely charged species, such as heavy metal ions .
Figure 9 shows the morphology of anionic BPE and analysis of chemical composition, indicating that its content is primarily carbon, oxygen and calcium, because lime is used in the nixtamalization.
Zeta potential measurements are a proactive electrochemical tool to define the strategy of chitosan dosage that allows sanitation and water reuse industry nixtamalization. The use of chitosan allows the use and reuse of byproducts recovered from
The authors gratefully acknowledge support from Consejo Nacional de Ciencia y Tecnologia, México (CONACyT) Project Ciencia Básica 2015 No. 237032, Project Problemas Nacionales No. 247236.
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