Secondary Wastewater Treatment Research Articles

A Comprehensive Review on Use of Wastewater in the Manufacturing of Concrete: Fostering Sustainability through Recycling

The primary aim of this review article is to find the influence of wastewater and its characteristics on recycling as an alternative to potable water for concrete preparation. On the other hand, scarcity, and the demand for freshwater for drinking are also increasing day by day around the globe. About a billion tons of freshwater is consumed daily for concrete preparation for various operations such as mixing and curing, to name a few. The rapid development of certain industries such as textile, casting, stone cutting, and concrete production has caused the water supply to be severely affected. Recycling wastewater in concrete offers various potential benefits like resource conservation, environmental protection, cost savings, and enhanced sustainability. This article reviews the effect of various types of wastewater on various physical and chemical properties of wastewater, rheological characteristics, strength, durability, and microstructure properties of concrete. It also explores the potential effects of decomposing agents on enhancing concrete properties. Currently, limited research is available on the use of various types of wastewater in concrete. Hence, there is a need to develop various methods and procedures to ensure that the utilization of wastewater and treated wastewater is carried out in the production of concrete in a sustainable manner. Although wastewater can reduce the workability of fresh concrete, it can also increase its strength and long-term performance of concrete. The use of various types of wastewater, such as reclaimed water and tertiary-treated wastewater, was found to be superior compared to those using industrial- or secondary-treated wastewater. Researchers around the globe agree that wastewater can cause various detrimental effects on the mechanical and physical properties of concrete, but the reductions were not significant. To overcome limited scientific contributions, this article reviews all the available methods of using various types of wastewater to make concrete economically and environmentally friendly. This research also addresses possible challenges with respect to the demand for freshwater and the water crisis.

Integrated toxicity of secondary, tertiary, wetland effluents on human stem cells triggered by ERα and PPARγ agonists

Residual pollutants in discharged and reused water pose both direct and indirect human exposure. However, health effects caused by whole effluent remain largely unknown due to the lack of human relevant model for toxicity test. Effluents from four secondary wastewater treatment plants (SWTPs), a tertiary wastewater treatment plant (TWTP) and a constructed wetland (CW) were evaluated for the integrated toxicity of the organic extractions. Multiple-endpoint human mesenchymal stem cells (MSCs) assay was used as an in vitro model relevant to human health. The effluents caused cytotoxicity, oxidative stress and genotoxicity in MSCs. The osteogenic and neurogenic differentiation were inhibited and the adipogenic differentiation were stimulated by some of the effluent extractions. The SWTP, TTP and CW treatments reduced integrated biomarker response (IBR) by 26.3 %, 17.5 % and 33.3 % respectively, where the integrated biomarker response values of final CW (8.3) and TWTP (8.2) effluents were relatively lower than SWTPs (9.1). Among multiple biomarkers, the inhibition of osteogenesis was the least reduced by wastewater treatment. Besides, ozone disinfection in tertiary treatment increased cytotoxicity and differentiation effects suggesting the generation of toxic products. The mRNA expressions of estrogen receptor alpha (ERα) and peroxisome proliferator-activated receptor gamma (PPARγ) were significantly upregulated by effluents. The inhibitory effects of effluents on neural differentiation were mitigated after antagonizing ERα and PPARγ in the cells. It is suggested that ERα and PPARγ agonists in effluents were largely accountable for the impairment of stem cell differentiation. Besides, the concentrations of n-C29H60, o-cresol, fluorene and phenanthrene in the effluents were significantly correlated with the intergrated stem cell toxicity. The present study provided toxicological evidence for the relation between water contamination and human health, with an insight into the key toxicity drivers. The necessity for deep water treatment and the potential means were suggested for improving water quality.

Lessons in Legacies: Treatment Plant Expansion Under the Clean Water Act

The US Clean Water Act of 1972 required cities to build secondary wastewater treatment plant capacity to improve the environment and protect public health. The expansion of the Southeast Pollution Control Plant in San Francisco’s Bayview-Hunters Point, a historically Black neighborhood, illustrates how planners employed rational-comprehensive approaches as the bases for their decision-making, worsening the community’s environmental burdens. This occurred even as the community used recently adopted environmental policy frameworks to mitigate the plant’s consequences. The Clean Water Act should be evaluated on clean water objectives and in terms of how communities were harmed to achieve these environmental goals.

AN OVERVIEW ON THE SYNTHESIS OF PHOSPHORYLATED CHITOSAN DERIVATIVES FOR THE ADSORPTION OF EMERGING CONTAMINANTS IN WATER

Safe water for human consumption and for aquatic life is of paramount importance. The emergence of new kinds of contaminants like surfactants, pharmaceutical drugs, hormones, foods and additives, laundry detergents, etc., are posing new and serious challenges to the conventional primary and secondary waste water treatment, because of the inability to remove or degrade these toxic pollutants efficiently and hence, the need for cost effective tertiary treatment method. Adsorption is a promising method worldwide for the removal of emerging contaminants, since it is highly-efficient and has a simple operating system. This review seeks to investigate the suitable preparation methods of soluble phosphorylated chitosan derivatives as efficient adsorbent for effective removal of emerging contaminants in water. Hence, the goal of this study, is to review some synthesis of the phosphates of chitosan under various chemical conditions to produce soluble chitosan derivatives which can be effectively used for the removal of emerging contaminants in water by adsorption technique.

Organic carbon utilisation by the filamentous alga Tribonema

AbstractFilamentous algae have potential application to wastewater treatment, in particular for efficient recovery of nutrients into biomass. However, supplying inorganic carbon is a major limiting factor. The utilisation of organic carbon present in wastewater may reduce the constraints in carbon supply, however there is little knowledge of mixotrophic growth amongst filamentous algae. This study investigated the utilisation of organic carbon sources relevant to wastewater by the filamentous xanthophyte alga Tribonema. Algae growth was compared in the absence of organic carbon (autotrophic) and in presence of 0.2 g-C L-1 glucose, ethanol or acetate under mixotrophic (presence of organic carbon and light) or heterotrophic (presence of organic carbon and absence of light) conditions. To investigate direct utilisation of organic carbon and indirect utilisation via bacterial CO2-genesis, cultivation was performed under both axenic and non-axenic conditions. Tribonema was found to directly utilise glucose, which increased mixotrophic productivity and maintained growth under heterotrophic conditions. In contrast, acetate was only indirectly utilised mixotrophically in the presence of bacteria, whereas ethanol was not utilised under any conditions. The underlying mechanisms of glucose utilisation by Tribonema were also investigated by analysing its photosynthetic rate and respiration rate under glucose concentrations ranging from 0 – 100 g L-1. Based on the results, enhancements to metabolic pathways and reduced CO2 requirements provided by glucose utilisation were proposed. Despite the positive results with respect to glucose utilisation, out competition for this resource by bacteria suggest that Tribonema is more suitable for treatment of wastewater with low organic carbon concentrations, such as secondary-treated wastewater effluent.

Retention of nine micropollutants covering a wide range of physical-chemical properties using polyelectrolyte multilayer hollow fiber NF membranes

Our work investigates the efficiency of two polyelectrolyte multilayer hollow fiber nanofiltration (NF) membranes for the removal of nine micropollutants (MPs) from pre-treated wastewater. The Square Latin method was used to select the contaminants to study according to their molecular weight, hydrophilicity (log Kow), and charge at environmental pH. NF experiments were carried out in batch mode at 20 °C with a crossflow velocity of 1 m.s−1, and a transmembrane pressure of 3 bar. Retentions of MPs and salts were evaluated at various volume reduction ratios (1, 3 or 6), membrane molecular weight cut-off (400 or 800 Da) and fouling potential of the matrix (ultrapure water, synthetic water, or real pre-treated wastewater). Our study identified the 400 Da membrane as the best option as balance between MPs and salts retention was the most acceptable. With this membrane, two thirds of the investigated MPs showed a retention above 90 %, two MPs had a retention around 60 % and only one MP was retained less than 20 % while monovalent salts had a retention lower than 30 %. Our work identified size exclusion and electrostatic interactions as the main mechanisms involved in MPs retention by the negatively charged membrane. This membrane showed its efficiency to maintain high permeation flux during 24 h-filtration of stream with organic matter content comparable to secondary-treated wastewater to a volume reduction ratio up to 6. At this content, organic matter did not modify retention of micropollutants or salts. The selected membrane is an encouraging tool to produce MPs-free water from pre-treated wastewater without producing a highly saline retentate. In the future, permeate would possibly be employed for REUSE purposes.

Oxidation of sulfides following anaerobic municipal wastewater treatment for non-potable reuse applications

Anaerobic secondary biological wastewater treatment could increase energy efficiency by avoiding energy-intensive aeration while producing methane that could be harvested for energy production.

Characteristics and removal efficiency of microplastics at secondary wastewater treatment plant in Lithuania.

Wastewater treatment plants (WWTPs) are the most significant barrier between anthropogenic microplastics and environmental ecosystems. The distribution and characteristics of microplastics in WWTPs remain uncertain and incompletely understood, particularly in northeastern Europe (Baltic States), where there is a lack of data on microplastic pollution and distribution. This study presents the removal efficiency and variation in characteristics of microplastics in different stages of the secondary WWTP during a 3-month sampling campaign in Lithuania. The abundance, size, shape, color, and chemical composition of microplastics in the wastewater at different treatment stages were thoroughly examined, in a size range from 20 to 1000 μm. On average, 2962 ± 25 particles/L of microplastic enter the studied WWTP. The obtained microplastic removal efficiency was 55.4% ± 3.9%, highlighting the necessity to enhance wastewater treatment strategies focusing on microplastic removal. Fragment-type microplastics smaller than 100 μm were removed from wastewater samples with the highest removal efficiency. Furthermore, our study includes recommendations to improve microplastic removal efficiency and contribute to mitigating microplastic pollution. PRACTITIONER POINTS: A large number of MPs in the size range of 20-1000 μm enter Lithuanian WWTP. Small-sized MPs within a range of 20-50 μm and 50-100 μm were removed with the highest efficiency of 54.07 ± 1.68% and 56.4 ± 2.43%, respectively. The shape and size of MPs have a major impact on the efficiency of their removal. Future research should prioritize the development of economical and energy-efficient systems, specifically designed for the removal of MPs in WWTPs.

Investigating the applicability of waste foam concrete for phosphorus recovery in real pig wastewater based on the effect of organic matter on the HAP crystallisation method

HAP crystallization use waste foam concrete as a calcium source, studied the impact of typical organic compounds in simulated pig wastewater on phosphorus recovery, and applied them to actual wastewater. Energy dispersive X-ray spectrometer(EDS) and SEM indicate: citric acid had a stronger inhibitory effect on crystallization compared to humic acid. Citric acid chelated Ca2+ ions, competing with crystallization ions and interfering with crystal nucleation. Humic acid hindered crystal growth through adsorption and ion exchange mechanisms. When citric acid and humic acid were added together, they competitively interacted, reducing the inhibition of phosphorus recovery. HAP crystallization alone reduced phosphorus content and turbidity in secondary pig wastewater, while combining 2 mL(5 g/L)PAM yielded favorable outcomes. Effluent phosphorus concentration was only 1.0 mg/L, with turbidity below 25. here was a noticeable reduction in Pseudomonas pathogenic bacteria from the Aspergillus phylum, along with a significant downward trend in the CL500_29_marine_group, which represents water body eutrophication. The combined method cost RMB 1.15 yuan/ton of water treated, a 26 % decrease compared to the original treatment plant. This method is suitable as an add-on unit for secondary pig wastewater treatment.

Catalyst-free persulfate activation by UV/visible radiation for secondary urban wastewater disinfection

This study focuses on the treatment of secondary urban wastewater (W) to improve the effluent quality aiming at the reduction of pathogenic microorganisms for the safe reuse of the treated wastewater (TW). Catalyst-free persulfate activation by radiation-based oxidation was applied as a treatment technology. A parametric study was carried out to select the best operating conditions. Total enterobacteria inactivation (quantified by the log reduction (CFU/100 mL)) was achieved when using [S2O82−] = 1 mM, pH = 8.5 (natural pH of W), T = 25 °C, and I = 500 W/m2. However, storing TW for 3 days promoted the regrowth of bacteria, risking its reutilization. Therefore, in this study, and for the first time, the potential beneficial role of inoculation of wastewater treated by the radiation-activated persulfate process with a diverse bacterial community was evaluated in order to control the regrowth of potentially harmful microorganisms through bacterial competition. For this, TW was diluted with river water (R) in the volume percentages of 5, 25, and 50 (percentages refer to R content), and enterobacteria and total heterotrophs were enumerated before and after storage for 72 h. The results showed total heterotrophs and enterobacteria regrowth for TW and R + TW diluted 5 and 25% after storage. However, for R + TW diluted 50%, only the total heterotrophs regrew. Hence, the treated wastewater generated by the oxidative process diluted with 50% river water complies with the legislated limits for reuse in urban uses or irrigation.

Partitioning and inactivation of enveloped and nonenveloped viruses in activated sludge, anaerobic and microalgae-based wastewater treatment systems

Anaerobic and microalgae-based technologies for municipal wastewater treatment have emerged as sustainable alternatives to activated sludge systems. However, viruses are a major sanitary concern for reuse applications of liquid and solid byproducts from these technologies. To assess their capacity to reduce viruses during secondary wastewater treatment, enveloped Phi6 and nonenveloped MS2 bacteriophages, typically used as surrogates of several types of wastewater viruses, were spiked into batch bioreactors treating synthetic municipal wastewater (SMWW). The decay of Phi6 and MS2 in anaerobic and microalgae-based reactors was compared with the decay in activated sludge batch reactors for 96 h (Phi6) and 144 h (MS2). In each reactor, bacteriophages in the soluble and solids fractions were titered, allowing the assessment of virus partitioning to biomass over time. Moreover, the influence of abiotic conditions such as agitation, oxygen absence and light excess in activated sludge, anaerobic and microalgae reactors, respectively, was assessed using dedicated SMWW control reactors. All technologies showed Phi6 and MS2 reductions. Phi6 was reduced in at least 4.7 to 6.5 log10 units, with 0 h concentrations ranging from 5.0 to 6.5 log10 PFU mL−1. Similarly, reductions achieved for MS2 were of at least 3.9 to 7.2 log10 units, from starting concentrations of 8.0 to 8.6 log10 PFU mL−1. Log-logistic models adjusted to bacteriophages’ decay indicated T90 values in activated sludge and microalgae reactors of 2.2 and 7.9 h for Phi6 and of 1.0 and 11.5 h for MS2, respectively, all within typical hydraulic retention times (HRT) of full-scale operation. In the case of the microalgae technology, T99 values for Phi6 and MS2 of 12.7 h and 13.6 h were also lower than typical operating HRTs (2–10 d), while activated sludge and anaerobic treatment achieved less than 99 % of Phi6 and 50 % of MS2 inactivation within 12 h of typical HRT, respectively. Thus, the microalgae-based treatment exhibited a higher potential to reduce the disinfection requirements of treated wastewater.

Exploring advanced phycoremediation strategies for resource recovery from secondary wastewater using a large scale photobioreactor

This study aimed to investigate the operation of a 1000L microalgae-based membrane photobioreactor system in a greenhouse for continuous secondary wastewater treatment using Desmodesmus sp., a green microalgae strain originally isolated from a German sewage plant. The research spanned both summer and winter seasons, seeking to comprehend key trends and optimization strategies. Maintaining low cell concentrations in the photobioreactor during periods of light inhibition proved advantageous for nutrient uptake rates. Effective strategies for enhancing algae-based wastewater treatment included cell mass recycling, particularly during periods of high light availability. In comparison to conventional continuous cultivation methods, employing cell recycling and high dilution rates during times of abundant light, alongside using low cell concentrations and dilution rates during light inhibition, resulted in an 80 % and 10 % increase in overall biomass productivity during summer and winter, respectively. Furthermore, nitrogen/phosphorus (N/P) removal rates exhibited a 23 % improvement during winter, while remaining unchanged in summer.

Eichhornia crassipes Efficacy in Secondary Wastewater Treatment in the Western Highlands of Cameroon

Wastewater treatment using lagoons technology is recognised to have potential to protect the environment and preserve water resources. The implementation requires mastery of ecological conditions of operation and management of the plants used. We aimed to contribute to the implementation of macrophyte-based lagoons for wastewater treatment in the Western Highlands of Cameroon. We used two sets of four lagoons in series; one was vegetated with E. crassipes, while the other served as the control. Each set constituted an anaerobic, two facultative, and maturation lagoons. Each lagoon system was supplied with primary-treated domestic wastewater from the wastewater treatment plant of the University of Dschang, Cameroon, at a hydraulic loading rate of 1.13 m3/day. Monthly wastewater samples were collected from the inflow and outflow of each lagoon for physicochemical and bacteriological analyses, and plant growth was assessed biweekly for six months spanning the dry and rainy seasons. Macrophyte lagoons showed positive plant growth during both seasons. The highest plant height (10.67 and 25.21 cm), longer roots (11.3 and 37.41 cm), and the highest number of new buds (14 and 20 buds) were obtained during the dry and rainy seasons, respectively. Plants were significantly ( P < 0.0001) taller in facultative lagoons in the rainy season than in the dry season. Vegetated lagoons significantly ( P < 0.05) contributed to reducing TSS (−08.36% and 82.25%), true color (44.46% and 82.31%), orthophosphates (63.1% and 86.59%), and BOD5 (−56.79% and 56.06%) during the dry and rainy seasons, respectively. 100% elimination of fecal streptococci (FS) and 74.89% and 43.80% of fecal coliforms (FC) were observed in the dry and rainy seasons, respectively. Significant ( P = 0.0019) FS elimination was more in the dry season than in the rainy season. However, the average residual content of FC (190,000 UFC/100 ml) was still higher than WHO limits (≤1000 UFC/100 ml) for nonrestrictive reuse in agriculture. E. crassipes can be efficiently used in lagoon systems for domestic wastewater treatment in the Western Highlands of Cameroon.

Data-driven systematic analysis of waterborne viruses and health risks during the wastewater reclamation process

Waterborne viral epidemics are a major threat to public health. Increasing interest in wastewater reclamation highlights the importance of understanding the health risks associated with potential microbial hazards, particularly for reused water in direct contact with humans. This study focused on identifying viral epidemic patterns in municipal wastewater reused for recreational applications based on long-term, spatially explicit global literature data during 2000–2021, and modelled human health risks from multiple exposure pathways using a well-established quantitative microbial risk assessment methodology. Global median viral loads in municipal wastewater ranged from 7.92 × 104 to 1.4 × 106 GC L−1 in the following ascending order: human adenovirus (HAdV), norovirus (NoV) GII, enterovirus (EV), NoV GI, rotavirus (RV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Following secondary or tertiary wastewater treatment, NoV GI, NoV GII, EV, and RV showed a relatively higher and more stable log reduction value with medians all above 0.8 (84%), whereas SARS-CoV-2 and HAdV showed a relatively lower reduction, with medians ranging from 0.33 (53%) to 0.55 (72%). A subsequent disinfection process effectively enhanced viral removal to over 0.89-log (87%). The predicted event probability of virus-related gastrointestinal illness and acute febrile respiratory illnesses in reclaimed recreational water exceeded the World Health Organization recommended recreational risk benchmark (5% and 1.9%, respectively). Overall, our results provided insights on health risks associated with reusing wastewater for recreational purposes and highlighted the need for establishing a regulatory framework ensuring the safety management of reclaimed waters.

Enteric virus removal by municipal wastewater treatment to achieve requirements for potable reuse

Primary and secondary treatment of municipal wastewater contributes to virus removal upstream of advanced purification to produce water for potable reuse. In this study, virus occurrence by cultivable and molecular methods was measured over a 24-month period in raw wastewater influents and secondary effluents from two municipal wastewater treatment plants that together provide the recycled water source for an advanced water purification facility. Using a rank-paired, covariance-based statistical approach, virus log removal values were determined for four wastewater treatment processes that operate in parallel at the two facilities (two activated sludge processes, trickling filter process, and trickling filter/solids contactor process). The trickling filter process exhibited the lowest observed removal of cultivable enteric virus with a median removal of 1.0 log10 (or 90% removal) and a 5th percentile log removal of 0.73 (or 82%), compared to the greatest removal observed for one of the activated sludge processes (median log removal of 2.4 or 99.6% and 5th percentile of 2.1 or 99.2%). Median log removal observed for male-specific (MS) and somatic (SOM) coliphage was 1.8 (98.6% removal) and 0.5 (70%), respectively, for trickling filter and 2.9 (99.9%) and 2.0 (99%) for activated sludge. Thus, coliphage removal was fairly similar to removal observed for cultivable enteric virus. The cultivable enteric virus 5th percentile removal (0.7) from the trickling filter treatment process was proposed to the state regulator for credit towards state requirements for virus removal related to groundwater augmentation with purified recycled water. Receiving pathogen removal credits for secondary wastewater treatment would allow for an improved margin (safety factor) of credits beyond the minimum required; and in this case may also increase the number of viable future groundwater recharge sites closer to drinking water production wells by reducing the underground travel time otherwise required to obtain sufficient credits.

Assessment of the in-situ electrogenerated chloramines damaging polyamide NF membrane during secondary wastewater treatment

Nanofiltration (NF) membrane is susceptible to chlorine damage during secondary wastewater treatment, rendering it critical to investigate the structure changes in polyamide membrane in chlorine-exposed environments. In this work, chlorinated secondary wastewater was pre-treated using an electro-oxidation (EO) process, and then the potential damage to polyamide membranes during the EO-NF process was assessed by the performance of NF90 nanofiltration membrane after exposure to the EO effluent. We observed a 90% reduction in the retention of Ca2+ and Mg2+ by the NF membrane at high concentration of chloramine (i.e., 20 mg/L), which was attributed to the formation of N-chloramides due to the binding of chloramine to the lone electron pair of the polyamide. Compared with the pristine membrane directly exposed to the chloramine-containing EO effluent, the NF membrane deposited with a biofouling layer did not exhibit any changes in chemical structure and compositions, probably because the biofouling layer blocked the chlorination of polyamide. Therefore, the biofouling layer formed by the deposition and development of microorganism on the membrane surface could prolong the lifetime of the polyamide membrane during the treatment of municipal wastewater in the EO-NF system.

Solar heterogeneous photo-Fenton for complete inactivation of Escherichia coli and Salmonella typhimurium in secondary-treated wastewater effluent

In this work, complete elimination of Escherichia coli and Salmonella typhimurium was achieved in 120 min using a heterogeneous photo-Fenton process under sunlight at pH 6.5 in distilled water. A face-centered composite central design 22 with one categoric factor and three replicates at the central point was used to evaluate the effect of iron (III) oxide concentration (0.8–3.4 mg L−1), H2O2 (2–10 mg L−1), and the type of iron oxide phase (maghemite and hematite) on the inactivation of both bacteria. The results showed that the amount of catalyst, H2O2 concentration and their interaction were significant factors (p < 0.05) in the elimination of the microorganisms. Thus, under the best conditions (3.4 mg L−1 of iron (III) oxide and 10 mg L−1 of H2O2) in the experimental ranges, complete inactivation of E. coli and S. typhimurium was achieved (6-log reduction) in 120 min using the photo-Fenton treatment with both iron-oxide phases. Furthermore, the photocatalytic elimination of both bacteria by the photo-Fenton process using hematite and maghemite in secondary-treated wastewater effluent was performed obtaining slower inactivation rates (1.2–5.9 times) than in distilled water due to the matrix effect of the effluent from a wastewater treatment plant. Nevertheless, the process continued to be effective in the effluent, achieving complete bacterial elimination in 150 min using the hematite phase. Additionally, the SEM images of the bacterial cells showed that the heterogeneous photo-Fenton treatment generated permanent and irreversible cell damage, resulting in complete cell death.

Water, sanitation, and hygiene implications of large-scale recycling of treated municipal wastewater in semi-arid regions

Access to water, sanitation, and hygiene (WaSH) is crucial for national development, as it improves human health and fulfills a fundamental need. This study examines the impact of a large-scale groundwater (GW) recharge scheme using secondary treated wastewater (STW) on WaSH characteristics and identifies the major determinants of improved WaSH charecteristics in drought-hit regions of Kolar district, southern India. The study quantifies improved WaSH practices by comparing WaSH characteristics between impacted areas (influenced by STW) and non-impacted areas (not influenced by STW) of Kolar, using household survey data. Pearson's chi-square and student's t-test are used to verify differences between WaSH characteristics. Furthermore, a composite WaSH score is formulated, and a hierarchical stepwise multiple linear regression model is constructed to identify major determinants of improved WaSH scores. The results show that impacted areas have better WaSH characteristics, including daily water supply by gram panchayat, enhanced toilet uses among all family members, bathing patterns, cloth washing practices, toilet cleaning patterns, and water consumption per capita per day. The maximum and minimum WaSH scores of impacted areas were 17.50 and 6.50, respectively, while those of non-impacted areas were 14 and 4.5. This study finds that improved water availability, quality, and security due to daily water supply at the household level are the major determinants of improved WaSH practices. These results can inform policymakers in designing sanitation and hygiene improvement policies that integrate water recycling projects in drought-hit areas.

A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment

Harvesting organic matter from wastewater, chemical enhanced primary treatment for instance, is widely applied to maximize energy recovery; however, it limits the applicability of secondary treatment for acceptable effluent discharge into surface water bodies. To turn this bottleneck issue into an opportunity, this study developed oxygen-induced thiosulfatE production duRing sulfATe reduction (ERATO) to provide efficient electron donor for denitrification or partial denitrification anammox in wastewater treatment. Typical pretreated wastewater was synthesized with chemical oxygen demand of 110 mg/L, sulfate of 50 mg S/L, ammonium of 30 mgN/L, and varying dissolved oxygen (DO) and was fed into a moving-bed biofilm reactor (MBBR) with a short hydraulic retention time of 40 min. The ORP maintained at − 311 mV in the bioreactor, indicating that the influent DO was vanished immediately when it enters the bioreactor. In 349 days’ continuous operation, the surface-specific sulfate reduction rate reached 0.42 g S/(m2·d). Notably, the formation rate of thiosulfate reached 0.12–0.18 g S/(m2·d) with a high thiosulfate-Sproduced/sulfide-Sproduced ratio of 38–73% when influent DO was 2.7–3.6 mg/L, much higher than 0–17% obtained in previously reported sulfate-reducing process. Then, batch tests and metabolism analysis were conducted to confirm the oxygen effect on thiosulfate formation, and to explore the mechanism of oxygen-induced thiosulfate formation in ERATO. Results examined that oxygen supply promoted the thiosulfate-Sproduced/sulfide-Sproduced ratio from 4% to 24–26%, demonstrated that S0 and sulfate were critical for thiosulfate production, and indicated that oxygen induces thiosulfate formation mainly through: sulfide first oxidized to S0 which then reacts with sulfite derived from oxygen-regulated biological sulfate reduction (S0 + SO32−→S2O32−). The proposed compact ERATO process with high thiosulfate production, supporting space- and energy-efficient secondary wastewater treatment.

Seasonal and depth variation of soil physical parameters irrigated with treated wastewater in the case of light textured soil

In places with scarce water supplies, treated wastewater (TWW) can be used for irrigation. This is the case in many places on the Mediterranean coast. In order to examine changes in soil physical proprieties irrigated with secondary-treated wastewater for &gt;38 years, a study was conducted under real agricultural conditions and three different sampling seasons (Summer, autumn and winter). Five soil depth distribution (0-20, 20-40, 40-60, 60-80 and 80-100 cm was also investigated. The soil parameters studied were: salinity (EC), permeablity (K) and structural stability (IS). The results demonstrate that K and IS depended significantly on the season and varied throught the soil profile. However, only the depth had an impact on the EC. The maximum EC and K were observed in summer at 0-60 and 0-20 cm, respectively. The highest IS, although, was detected during the winter at 40–60 cm depth layer. More interstingly, to take into consideration the interactions of both factors, a positive correlations were shown between K and EC, and IS (r =0.56***, r = 0.62***, respectively) and between EC and IS (r = 0.44**) in summer. In contrast, only K and EC showed a negative correlation (r = -0.35*) in the autumn, but no correlation was detected between all parameters in winter. The results indicate that treated wastewater is a suitable alternative during hot seasons, especially in sandy soils. Further research is required to investigate the effect of this wastwater on crops responses.