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The production of sodium hypochlorite (NaOCl) from salty wastewater using an electrochemical cell has several advantages over other methods that often require hazardous chemicals and generate toxic waste, being more sustainable and environmentally friendly. However, the process of producing sodium hypochlorite using an electrochemical cell requires careful control of the operating conditions, such as the current density, flow rate, inert electrode spacing, and electrolyte concentration, to optimize the conversion efficiency and prevent electrode fouling and degradation. In this study, NaOCl was produced via a bench-scale electrochemical cell using a flowing porous graphite electrode in a continuous flow system from salty wastewater collected from the Suez Canal in Egypt. The aim of the investigation was to examine the factors that affect the concentration of NaOCl and energy consumption, such as anodic current density, salinity, inert electrode spacing, and influent feed flow rate. A lab-scale reactor with two electrodes was used to conduct the experiments. The highest NaOCl yield of 20.6% was achieved with a graphite electrode, which had high current efficiency and rigidity at a flow rate of 4.5 mL/min, a current density of 3.183 mA/cm2, an electrode space of 0.5 cm, salinity of 40,000 ppm, and a pH of 6.4. The power consumption under these conditions was 0.0137 kwh. Additionally, a statistical and least square multivariate regression technique was employed to establish a correlation for predicting the % NaOCl production. The obtained correlation had an R2 value of 98.4%. Overall, this investigation provides valuable insights into the production of NaOCl using a continuous flow system from salty wastewater, which could have potential for industrial applications in various sectors such as textiles, detergents, paper, and pulp. [ABSTRACT FROM AUTHOR]

Untreated wastewater released into rivers can result in water pollution, the spread of waterborne diseases, harm to ecosystems, contamination of soil and groundwater, as well as air pollution and respiratory problems for nearby humans and animals due to the release of greenhouse gases. The current study aims to investigate the recent input of anthropogenic loads into the rivers using linear alkylbenzene (LAB), which is one of the molecular chemical markers with application of sophisticated model statistical analyses. In order to determine the compositions of LABs, which act as wastewater pollution molecular indicators, surface sediment samples from the Muar and Kim Kim rivers were collected. Gas chromatography-mass spectrometry (GC-MS) was utilized to identify LABs and investigate their sources and degradation. ANOVA and the Pearson correlation coefficient were employed to determine the significance of differences between sampling locations, with a threshold of p < 0.05. To assess the degradation degree and efficacy of wastewater treatment plants (WWTPs), LABs were identified based on chains ranging from long to short (L/S), C13/C12 homolog, and internal to external (I/E) congeners. The results indicated that LAB concentrations in the studied areas of the Muar River ranged from 87.4 to 188.1 ng g−1dw. There were significant differences in LAB homology at p < 0.05, and a significant percentage of sampling stations contained C13-LAB homology. Based on the LAB ratios (I/E) determined, which ranged from 1.7 to 2.2 in the studied areas, it was concluded that effluents from primary and secondary sources are being discharged into the marine ecosystem in those areas. The degradation of LABs was up to 43% in the interrogated locations. It can be inferred that there is a requirement for enhancing the WWTPs, while also acknowledging the efficacy of LAB molecular markers in identifying anthropogenic wastewater contamination. [ABSTRACT FROM AUTHOR]

• Tannery industry generates a large amount of Cr(III)-contaminated wastewater. • Composite had a higher Cr(III) removal (97%) than chitosan at 20 mg/L of Cr concentration. • Optimum conditions: 4 g/L of dose, pH 6.5, 200 rpm of speed, and 1 h of reaction time. • Treated effluents could not meet the limit of Cr(III) discharge standards of less than 0.5 mg/L. Tannery industry generates a large amount of Cr(III)-contaminated wastewater daily. Unless properly treated, not only this effluent contaminates the water body, but also damages the environment and threatens public health. This batch study investigates the feasibility of chitosan-coated coconut shells as a low-cost material for removing Cr(III) from tannery wastewater. Both chitosan and coconut shell (CS) waste are abundantly available from local agricultural and fishery industries. To enhance its treatment performance for Cr(III) removal, the CS was coated with chitosan as a composite. To sustain its cost-effectiveness, the saturated composite was regenerated with HNO 3. Its performance for Cr(III) removal was evaluated and compared to other low-cost adsorbents in previous work. At the same initial concentration of 20 mg/L, it was found that the composite had a higher Cr(III) removal (97%) than the chitosan alone under the optimized conditions of 4 g/L of dose, pH 6.5, 200 rpm of agitation speed, and 1 h of reaction time. The isotherm of Cr(III) removal by the adsorbents followed the Langmuir model, while the pseudo-second order reaction was representative to simulate the adsorption data. The Cr(III) removal by the composite was based on attractive columbic forces between the negative charge of the adsorbent's surface and the positive charge of the metal cation. The negative value of ΔG thermodynamic parameter suggests the spontaneous nature of adsorption. The efficiency of machine learning regression (MLR) model was assessed in predicting the experimental data of adsorption. In spite of promising results, treated effluents still could not comply with the required limit of discharge standards of less than 0.5 mg/L mandated by local legislation. Therefore, a subsequent treatment using activated sludge is required. Overall, this work reveals a contribution of unused resources from the coconut and shrimp industries in the form of composite for protecting the aquatic environment. [Display omitted] [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is one of the gases with the greatest impact in the atmosphere due to its persistence and significant contribution to the greenhouse effect. This study provides an insight into the dynamics of N2O production in wastewater nitrogen removal systems. A 10 L sequencing batch reactor containing enriched anammox biomass was subjected to different operational conditions, i. e., temperature, feed time, NO2-/NH4+ ratio and the initial concentrations of NH4+ and NO2-. Tests showed no significant differences in maximum N2O production when the system was operated with a shorter feed time and no increase in the operating temperature. A higher N2O production was observed when the initial NO2-/NH4+ ratio increased from 1.3 to 1.7 and 1.9. The highest initial concentration of NO2- was linked to an increase in residual N2O at the end of the batch cycle, probably due to heterotrophic denitrifying metabolism. [ABSTRACT FROM AUTHOR]

In deammonification systems, nitrite-oxidizing bacteria (NOB) suppression and nitrous oxide (N 2 O) mitigation are two important operational objectives. To carry out this multivariable analysis of response, a comprehensive model for the N cycle was developed and evaluated against experimental data from a laboratory-scale deammonification granular sludge sequencing batch reactor. Different aeration strategies were tested, and the manipulated variables comprised the dissolved oxygen (DO) set point in the aerated phase, aeration on/off frequency (F), and the ratio (R) between the non-aerated and aerated phase durations. Experimental results showed that a high ammonium utilization rate (AUR) in relation to the low nitrate production rate (NPR) (NPR/AUR = 0.07-0.08) and limited N 2 O emissions ( E N 2 O < 2%) could be achieved at the DO set point = 0.7 mg O 2 /L, R ratio = 2, and F frequency = 6-7 h -1 . Under specific operational conditions (biomass concentration, NH 4 + -N loading rate, and temperature), simulation results confirmed the feasible aeration strategies for the trade-offs between the NOB suppression and N 2 O emission. The intermittent aeration regimes led to frequent shifts in the predominating N 2 O production pathways, that is, hydroxylamine (NH 2 OH) oxidation (aerated phase) versus autotrophic denitrification (non-aerated phase). The inclusion of the extracellular polymeric substance mechanism in the model explained the observed activity of heterotrophs, especially Anaerolineae , and granule formation.

Nitrous oxide (N 2 O) is one of the gases with the greatest impact in the atmosphere due to its persistence and significant contribution to the greenhouse effect. This study provides an insight into the dynamics of N 2 O production in wastewater nitrogen removal systems. A 10 L sequencing batch reactor containing enriched anammox biomass was subjected to different operational conditions, i.e., temperature, feed time, NO 2 - /NH 4 + ratio and the initial concentrations of NH 4 + and NO 2 - . Tests showed no significant differences in maximum N 2 O production when the system was operated with a shorter feed time and no increase in the operating temperature. A higher N 2 O production was observed when the initial NO 2 - /NH 4 + ratio increased from 1.3 to 1.7 and 1.9. The highest initial concentration of NO 2 - was linked to an increase in residual N 2 O at the end of the batch cycle, probably due to heterotrophic denitrifying metabolism.

A mechanistic model was developed as an extension of the Activated Sludge Model No. 1 to describe three nitrous oxide (N 2 O) production pathways in a laboratory-scale anammox-enriched granular sequencing batch reactor. Heterotrophic denitrification and two processes mediated by ammonia oxidizing bacteria (AOB), that is, ammonia (NH 4 + ) oxidation via hydroxylamine (NH 2 OH) and autotrophic denitrification, were considered. A systematic model calibration and validation protocol was developed to obtain a unique set of kinetic parameters in the extended model. The dynamic nitrate (NO 3 - ), nitrite (NO 2 - ), NH 4 + and N 2 O behaviors were accurately predicted (R 2 ≥ 0.81) under five different nitrogen loading conditions. The predicted N 2 O production factor ranged from 1.7 to 2.9%. The model-based analysis also revealed the dominant N 2 O production mechanisms in terms of the actual process conditions, that is, NH 4 + oxidation via NH 2 OH when only NH 4 + was supplied, heterotrophic denitrification when only NO 2 - was supplied, and a shift of the dominant mechanism when a mixture of NH 4 + and NO 2 - was supplied.