Tertiary Treatment Research Articles

Impact of Corona virus pandemic on wastewater characteristics, treatment, and water reuse in a municipal plant

The COVID-19 pandemic is considered one of the most significant threats to health. The effect of the pandemic on performance of wastewater treatment plants has not received much attention in the literature. This study assessed the impact of Coronavirus pandemic on the wastewater quantity, characteristics, treatment processes, and water reuse in Kuwait. It focused on three municipal wastewater treatment plants (WWTPs) with different design capacities, namely Sulaibiya (600,000 m3/d), Kabd (180,000 m3/d), and Umm Al-Hayman (27,000 m3/d), all using tertiary treatment. Daily data records were obtained on influent and effluent over the years 2018–2020 (before and during the pandemic). In addition, influent and effluent samples were collected from the Sulaibiya and Kabd plants for laboratory analysis to determine the effect of increase in the use of home disinfectants. The results indicate an increase (<50%) in the average daily flow rates received in WWTPs during the 2020 home quarantine lockdowns. Statistical analysis showed stability of the Sulaibiya in BOD5, COD, and TSS removal efficiency while a decrease in the Kabd and UAH plants removal efficiency was observed during the pandemic. During the lockdown period, GC-MS analysis showed a high probability of chloroxylenol (>90), one of the main components of Dettol disinfectant, existing in the raw wastewater samples while the GC-FID analysis indicated the presence of (PAH) as emerging contaminants, at higher concentrations in the influent and effluent samples. The pandemic adversely affected wastewater treatment plant performance and excessive use of Dettol disinfectant by homes resulted in the presence of objectionable organic pollutants in the tertiary-treated effluent which would impair water reuse. Reverse osmosis process used in Sulaibiya plant proved to be effective in removing residual organics and improving effluent quality for reuse during the pandemic.

Microalgae and co-culture for polishing pollutants of anaerobically treated agro-processing industry wastewater: the case of slaughterhouse

Anaerobically treated slaughterhouse effluent is rich in nutrients, organic matter, and cause eutrophication if discharged to the environment without proper further treatment. Moreover, phosphorus and nitrogen in agro-processing industry wastewaters are mainly removed in the tertiary treatment phase. The objective of this study is to evaluate the pollutant removal efficiency of Chlorella and Scenedesmus species as well as their co-culture treating two-phase anaerobic digester effluent through microalgae biomass production. The dimensions of the rectangular photobioreactor used to conduct the experiment are 15 cm in height, 20 cm in width, and 30 cm in length. Removal efficiencies between 86.74–93.11%, 96.74–97.47%, 91.49–92.91%, 97.94–99.46%, 89.22–94.28%, and 91.08–95.31% were attained for chemical oxygen demand, total nitrogen, nitrate, ammonium, total phosphorous, and orthophosphate by Chlorella species, Scenedesmus species, and their co-culture, respectively. The average biomass productivity and biomass yield of Chlorella species, Scenedesmus species, and their co-culture were 1.4 ± 0.1, 1.17 ± 0.12, 1.5 ± 0.13 g/L, and 0.18, 0.21, and 0.23 g/L*day, respectively. The final effluent quality in terms of chemical oxygen demand, total nitrogen, and total phosphorous attained by Chlorella species and the co-culture were below the permissible discharge limit for slaughterhouse effluent standards in the country (Ethiopia). The results of the study showed that the use of microalgae as well as their co-culture for polishing the nutrients and residual organic matter in the anaerobically treated agro-processing industry effluent offers a promising result for wastewater remediation and biomass production. In general, Chlorella and Scenedesmus species microalgae and their co-culture can be applied as an alternative for nutrient removal from anaerobically treated slaughterhouse wastewater as well as biomass production that can be used for bioenergy.Graphical

Microplastic removal and management strategies for wastewater treatment plants

Discharging microplastics into the environment with treated wastewater is becoming a major concern around the world. Wastewater treatment plants (WWTPs) release microplastics into terrestrial and aquatic habitats, mostly from textile, laundry, and cosmetic industries. Despite extensive research on microplastics in the environment, their removal, and WWTP management strategies, highlighting their environmental effects, little is known about microplastics' fate and behaviour during various treatment processes. Microplastics interact with treatment technologies differently due to their diverse physical and chemical characteristics, resulting in varying removal efficiency. Microplastics removed from WWTPs may accumulate in soil and harm terrestrial ecosystems. Few studies have examined the cost, energy use, and trade-offs of large-scale implementation of modern treatment methods for the removal of microplastics. To safeguard aquatic and terrestrial habitats from microplastics' contamination, focused and efficient management techniques must bridge these knowledge gaps. This review summarizes microplastic detection, collection, removal and management strategies. A compilation of treatment process studies on microplastics’ removal efficiency and their destiny and transit paths shows recent improvement. Bioremediation, membrane bioreactor (MBR), electrocoagulation, sol-gel technique, flotation, enhanced filtering, and AOPs are evaluated for microplastic removal. The fate and behaviour of microplastics in WWTPs suggest they may be secondary suppliers of microplastics to receiving ecosystems. Innovative microplastic removal strategies and technologies such as nanoparticles, microorganism-based remediation, and tertiary treatment raise issues. These new WWTP technologies are examined for feasibility, limitations, and implementation issues. Pretreatment modifies microplastic size, adsorption potential, and surface morphology to remove microplastics from WWTPs. Membrane bioreactors (MBR) can remove 99.9% of microplastics more efficiently than other approaches. MBR systems require membrane cleaning and fouling control, which raises operational and capital costs. To reduce MPs, plastic alternatives and strict controls, including microplastic waste transformation, should be prioritized. Microplastics must be controlled through monitoring policy execution and awareness.

In the quest for sustainable management of liquid fraction of manure - Insights from a life cycle assessment

To mitigate the risk of eutrophication and minimize adverse environmental impacts, surplus manure in nitrate-vulnerable zones is frequently divided into a liquid and solid fraction. Managing the liquid fraction (LF) typically presents a greater challenge due to its substantial volume. This study aimed to assess the environmental impacts by region and trade-offs of managing surplus LF with inventory data from pilot facilities using a life cycle assessment (LCA). The LF-treatment technologies assessed were (i) nitrification-denitrification (NDN) with field application of effluent (ii) NDN with ammonia stripping and nitric acid scrubbing as a pre-treatment step followed by polishing in constructed wetlands, and (iii) nutrient up-concentration using vacuum evaporation and/or membrane filtration.The LCA results suggested that 60 to 80 % of the environmental impacts occurred locally. Nutrient up-concentration from LF via membrane filtration (reverse osmosis) and vacuum evaporation indicated a better environmental performance, albeit with high uncertainty when compared to the other scenarios. Although ammonia stripping-scrubbing showed environmental benefits, these were offset by high environmental burdens from fugitive N2O emissions and energy demand during NDN. Furthermore, the study identified that managing the effluent after NDN, a source of potassium (K), requires a nuanced approach from policymakers. Firstly, when K fertilization requirements are not met, direct land application of the effluent as a fertigation source can be a viable option. This minimizes the need for synthetic K fertilizer production and its ensuing freshwater ecotoxicity impacts. However, tertiary treatment of NDN effluent via constructed wetlands can be considered to prevent deterioration of soil from the influx of K. Policymakers are encouraged to engage with local stakeholders to tailor solutions based on these trade-offs. Furthermore, future research should focus on the implications of K on soil quality as well as the life span of nutrient up-concentration technologies for LF.

Leachate management in medium- and small-sized sanitary landfills: a Greek case study

The sustainable management of landfill leachates remains a matter of important concern in many countries. We used as case study a medium-sized Greek landfill, and we initially investigated the performance of the existing secondary leachate treatment system. The activated sludge process removed chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH4-N, and PO4-P by 55%, 84%, 94%, and 14%, respectively, but the effluents did not meet the legislation requirements for discharge or reuse. Afterwards, different management options of these effluents (co-treatment with sewage in the centralized treatment plant, onsite tertiary treatment with reverse osmosis, granular activated carbon (GAC), ozonation, photo-Fenton, or constructed wetlands) were evaluated regarding their operational costs and environmental footprint. The use of constructed wetlands presented the lower operational cost, energy requirements, and greenhouse gas (GHG) emissions, not exceeding 21.5 kg CO2eq/day. On the other hand, the power consumption and the GHG emissions of the other on-site technologies ranged from 0.37 kWh/m3 and 5.56 kg CO2eq/day (use of GAC) to 39.19 kWh/m3 and 588.6 kg CO2eq/day (use of ozonation), respectively. The co-treatment of the leachates with municipal wastewater required 0.6 kWh/m3 and emitted 30.18 kg CO2eq/day. For achieving zero-discharge of the treated leachates, a system consisting of constructed wetlands and evaporation ponds in series was designed.

Column-based removal of high concentration microplastics in synthetic wastewater using granular activated carbon

ABSTRACTMicroplastic (MP) is an emerging contaminant of concern due to its abundance in the environment. Wastewater treatment plant (WWTP) can be considered as one of the main sources of microplastics in freshwater due to its inefficiency in the complete removal of small MPs. In this study, a column-based MP removal which could serve as a tertiary treatment in WWTPs is evaluated using granular activated carbon (GAC) as adsorbent/filter media, eliminating clogging problems commonly caused by powder form activated carbon (PAC). The GAC is characterized via N2 adsorption–desorption isotherm, field emission scanning electron microscopy, and contact angle measurement to determine the influence of its properties on MP removal efficiency. MPs (40–48 μm) removal up to 95.5% was observed with 0.2 g/L MP, which is the lowest concentration tested in this work, but still higher than commonly used MP concentration in other studies. The performance is reduced with further increase in MP concentration (up to 1.0 g/L), but increasing the GAC bed length from 7.5 to 17.5 cm could lead to better removal efficiencies. MP particles are immobilized by the GAC predominantly by filtration process by being entangled with small GAC particles/chips or stuck between the GAC particles. MPs are insignificantly removed by adsorption process through entrapment in GAC porous structure or attachment onto the GAC surface.

Phosphorus removal from ore waste in aqueous solution with different mass of ore waste adsorbent from the Johor mine site

Abstract Mine waste management is becoming a growing global environmental concern for mining industries all over the world. Due to the abundance of ore waste from mining industries, this study aimed to observe the possibility of using ore waste to remove phosphorus from a solution. Although phosphorus is one of the essential elements for plant life, excessive phosphorus in water becomes one of the environmental issues, e.g., eutrophication. This study analysed the prediction contour of removal efficiency with the mass of adsorbent needed under different initial concentrations of solution. The batch experiment used an aqueous solution of 5 mg/L using potassium dihydrogen phosphate (KH2PO4) at different masses of adsorbent (2, 4, 6, 8, 10 g). The highest removal efficiency for phosphorus using 10 g of adsorbent is 54.3%. The data verified that the pseudo-second-order model (0.9976) fitted well. The adsorption between ore waste adsorbent and phosphorus was chemical sorption, whereas the analysis of isotherm models fitted the Freundlich model, with the occurrence of multilayer adsorption on the adsorption surface. The ability of ore waste to remove phosphorus was successful. This approach is one of the alternatives to enhance tertiary wastewater treatment technologies.

Ultrasonication-flotation-advanced oxidation tertiary treatment of oil-based drilling cuttings

The treatment of oil-based drilling cuttings (OBDCs) with high oil content is difficult. In this study, a tertiary treatment of ultrasonication–flotation–advanced oxidation for treating OBDCs with a high oil content of 20.10 wt% was proposed for the first time. All stages of the treatment processes were optimised. The recommended parameters for ultrasonication at room temperature were a mass ratio of OBDCs to the degreaser of 1:8, an ultrasonication power of 600 W and treatment time of 30 min. After the ultrasonication treatment, the oil content of the OBDCs decreased from 20.10 wt% to 5.00 wt%. Flotation was performed at room temperature with a mass ratio of OBDCs to the degreaser of 1:10, a stirring speed of 400 rpm, an aeration head aperture of 3 μm and airflow rate of 400 mL/min under N2 injection for 60 min. After the flotation treatment, the oil content of the OBDCs decreased from 5.00 wt% to 2.01 wt%. Advanced oxidation was performed at room temperature with a mass ratio of OBDCs to water of 1:10, 3.57 wt% sodium persulphate in water, 4.17 wt% ferrous sulphate heptahydrate in water and ultrasonication power of 1000 W for 100 min. Following the advanced oxidation treatment, the oil content of the OBDCs decreased from 2.01 wt% to 0.58 wt%. The results of this study provide a new method and idea for treating OBDCs with high oil content.

Combining large-scale investigation and quantum chemical calculation of pharmaceuticals: Spatiotemporal patterns of occurrence and structural insights into removal

This study investigated the spatiotemporal distribution of 17 pharmaceuticals in wastewater treatment plants (WWTPs) from 17 provinces across China, and explored structural insights into their removal in full-scale wastewater treatment processes by quantum chemistry. Briefly, 10 pharmaceuticals were detected in above 85 % of samples, of which ibuprofen and sulfamethoxazole dominated with concentrations up to the μg/L level. Seasonally, concentrations of psychoactive drugs (PDs) were 1.3–2.6 times higher in summer than in other seasons. Spatially, higher average concentrations were detected in northern WWTPs, and regions with similar economic levels exhibited similar contamination patterns. Pharmaceutical removal in WWTPs ranged from 41.4 % (carbamazepine) to 87.2 % (sulfamethizole), with the secondary treatment segment, especially aerobic treatment units, maintaining an important position. Molecular structural mechanisms behind these removal performances were further revealed. Firstly, we demonstrated a significant association of pharmaceutical overall removal with electrophilicity index (ωcubic) as well as the lowest unoccupied molecular orbital energy (ELUMO). Highly electrophilic pharmaceuticals may persist in WWTPs and their sensitivity to electron exchange reactions accounted for the discrepant removal. In terms of treatment segments, pharmaceuticals with reaction sites masked in molecular structure, such as ibuprofen and venlafaxine, showed a propensity for tertiary treatment suitability. Furthermore, enzymes of aerobic units exhibited excellent docking affinity to pharmaceutical molecules with an average affinity of −7.2 kcal/mol, and hydrogen-bond interactions played an important factor in promoting biodegradation. Our results emphasize the necessity of assessing pharmaceutical contamination on a larger spatiotemporal scale. Moreover, the structural insights into removal phenomena offer scientific molecular-level justification for the design and optimization of pharmaceutical treatment technologies in WWTPs.

Tertiary/quaternary treatment of urban wastewater by UV/H2O2 or ozonation: Microplastics may affect removal of E. coli and contaminants of emerging concern

The aim of this study was to investigate the interference of polyethylene microplastics (MPs) on ultraviolet irradiation/hydrogen peroxide (UV/H2O2) and ozonation processes in the inactivation of E. coli bacteria (tertiary treatment) and removal of contaminants of emerging concern (CECs) (quaternary treatment) from simulated and real secondary treated urban wastewater. Three pharmaceuticals were investigated as model CECs, namely carbamazepine, sulfamethoxazole and trimethoprim. Experimental results showed that disinfection efficiency of UV/H2O2 treatment decreased (2.4, 1.8 and 1.3 log reductions of E. coli, initial H2O2 dose of 30 mg/L, 2.5 min treatment) as the initial concentration of MPs was increased (0.25, 0.5 and 1.0 g/L, respectively). Similarly, an increase in MPs concentration (0.25, 0.5 and 1.0 g/L) reduced the inactivation (4.7, 4.1 and 3.7 log reductions) of the target bacteria after 60 min of ozonation treatment. Although the disinfection efficiency of both treatment processes was negatively affected by the presence of MPs, UV/H2O2 was more effective than the ozonation, despite ozonation being investigated at high doses to better discriminate the effect of MPs. Noteworthy, CECs degradation by UV/H2O2 under realistic operating conditions was affected to some extent by MPs, while a lower effect was observed for ozonation, at not realistic ozone dose.

Tertiary treatment using ultrafiltration in an existing sewage treatment plant for industrial reuse: a modelling approach using artificial neural network with uncertainty estimation

Abstract Navi Mumbai Municipal Corporation of Maharashtra state, India, unified a tertiary treatment plant (TTP) of 20 × 103 m3/day capacity with ultrafiltration technology in an existing Koparkhairane sewage treatment plant (STP) for producing effluent quality usable for industrial purposes. As prior art, an artificial neural network-genetic algorithm (ANN-GA) along with uncertainty estimation using prediction interval is employed to model secondary treated effluent (STE) flow rate (QT) and other quality parameters such as biochemical oxygen demand, chemical oxygen demand, and total suspended solids (TSS) to conclude the reliability of the range in which the input available to TTP. ANN-GA model provides a coefficient of determination above 0.90 for all STE parameters modelled other than TSS. Inferring that a good quantity and quality of 20 × 103 m3/day STP treated water is currently available, where a decreasing trend of QT is also noticed and highlighted. Further, the Wilcoxon signed-rank test on the quality parameter of effluent TTP for industrial reuse standard infers TSS shows infringement during the initial period but started adhering to standards over time. The research delineates at the outset of exploring water reuse policy in India, emphasizing Maharashtra state, modelling STE using ANN-GA and performance evaluation of TTP.

Nature-Based Solution to Eliminate Cyanotoxins in Water Using Biologically Enhanced Biochar.

Climate change and high eutrophication levels of freshwater sources are increasing the occurrence and intensity of toxic cyanobacterial blooms in drinking water supplies. Conventional water treatment struggles to eliminate cyanobacteria/cyanotoxins, and expensive tertiary treatments are needed. To address this, we have designed a sustainable, nature-based solution using biochar derived from waste coconut shells. This biochar provides a low-cost porous support for immobilizing microbial communities, forming biologically enhanced biochar (BEB). Highly toxic microcystin-LR (MC-LR) was used to influence microbial colonization of the biochar by the natural lake-water microbiome. Over 11 months, BEBs were exposed to microcystins, cyanobacterial extracts, and live cyanobacterial cells, always resulting in rapid elimination of toxins and even a 1.6-1.9 log reduction in cyanobacterial cell numbers. After 48 h of incubation with our BEBs, the MC-LR concentrations dropped below the detection limit of 0.1 ng/mL. The accelerated degradation of cyanotoxins was attributed to enhanced species diversity and microcystin-degrading microbes colonizing the biochar. To ensure scalability, we evaluated BEBs produced through batch-scale and continuous-scale pyrolysis, while also guaranteeing safety by maintaining toxic impurities in biochar within acceptable limits and monitoring degradation byproducts. This study serves as a proof-of-concept for a sustainable, scalable, and safe nature-based solution for combating toxic algal blooms.

Adsorption–Desorption Process to Separate Dyes from Tanning Wastewaters

Wastewater production is a major environmental issue for the leather and textile industries: in a modern plant, several synthetic dyes are used in separated coloring batches whose wastewaters are usually mixed, diluted with other process water streams, and sent to a unique wastewater treatment plant. This includes specific physical and biochemical tertiary treatments to remove dyes efficiently. One of the main difficulties of these processes is the presence of multiple dyes, which cannot be treated with the same efficiency as a “wide-spectrum” process. This work explores the possibility of using conventional granular activated carbon (GAC) and a new polyurethane foam (PUF) for the adsorption of an acid red dye in the wastewater of a specific coloring batch of the tanning industry. The aim of this work is twofold: on the one hand, we aim to explore the performance of the new PUF sorbent; on the other hand, we aim to explore the possibility of using adsorption as an optimized pre-treatment for single-dye batches, which may take advantage of the presence of a single type of target dye and its higher concentration. The effluent is then sent to the wastewater treatment plant for further depuration.

Thyroidkeeper: a healthcare management system for patients with thyroid diseases.

Thyroid diseases, especially thyroid tumors, have a huge population in China. The postoperative patients, under China's incomplete tertiary diagnosis and treatment system, will frequently go to tertiary hospitals for follow-up and medication adjustment, resulting in heavy burdens on both specialists and patients. To help postoperative patients recover better against the above adverse conditions, a novel mobile application ThyroidKeeper is proposed as a collaborative AI-based platform that benefits both patients and doctors. In addition to routine health records and management functions, ThyroidKeeper has achieved several innovative points. First, it can automatically adjust medication dosage for patients during their rehabilitation based on their medical history, laboratory indicators, physical health status, and current medication. Second, it can comprehensively predict the possible complications based on the patient's health status and the health status of similar groups utilizing graph neural networks. Finally, the employing of graph neural network models can improve the efficiency of online communication between doctors and patients, help doctors obtain medical information for patients more quickly and precisely, and make more accurate diagnoses. The preliminary evaluation in both laboratory and real-world environments shows the advantages of the proposed ThyroidKeeper system.

Continuous-flow titration of low iron doses to promote photo-Fenton and photo-Fenton-like processes at neutral pH

Photo-Fenton (PF) is a promising process for degrading a wide range of contaminants of emerging concern (CECs) present in urban wastewater (UWW) after secondary treatment, mitigating their spread in aquatic systems. However, the near-neutral pH of UWW poses a challenge to PF performance. In this research, a tubular membrane photoreactor, designed for continuous “titration” of Fe2+, is explored to promote the PF process for the tertiary treatment of UWW. The application of persulfate (PF-like) as an alternative oxidant and the impact of phosphate (PO43−) content in UWW were also assessed. Process efficiency was evaluated in continuous mode, applying low residence times (RT: 6.1, 36.6, and 73.2 s) and low Fe2+ doses (1, 2, and 5 mg L−1), for the oxidation of 19 CECs (each spiked at 10 µg/L), in demineralized water (DW) and secondary-treated UWW. Despite the persistence of certain short-chain perfluoroalkyl substances (PFAS) and saccharine across all conditions tested, the PF-like process exhibited superior performance when compared with PF, attaining higher removals for most target CECs, especially for melamine. In UWW, for an RT = 73.2 s, [Fe2+] = 5 mg L−1, and [oxidant] = 1.2 mM, PF process removed 7 CECs > 60 % and PF-like 10 CECs > 60 %. Moreover, higher residual concentrations of Fe2+ and lower precipitation of PO43− were observed for PF-like treatments, evidencing its advantages for tertiary treatment. These results emphasize the importance of photoreactor design to achieve efficient PF/PF-like at neutral pH, avoiding the use of chelating agents while managing iron concentrations compatible with UWW discharge or reuse limits.

Enhancing the selective ciprofloxacin adsorption in urine matrices through the metal-doping of carbon sorbents

Pharmaceuticals excreted after administration can pollute water sources given their ineffective removal in conventional wastewater treatment plant. Among the techniques used during tertiary wastewater treatment, adsorption is an effective and cost-efficient method for removing antibiotics. This study aimed to investigate the adsorption of ciprofloxacin (CIP) on metal-doped granular activated carbon (GAC) and evaluate the impact of urine on CIP adsorption for pristine, pre-oxidized, and metal-doped GAC. The results showed that the uptake of CIP by iron (Fe)-doped GAC was higher than Ag-doped, pre-oxidized, and pristine GAC in single-solute isotherms (DI water). This higher uptake was attributed to the presence of Fe content (1.2%) on the carbon surface, which can strongly interact with zwitterionic CIP at a neutral pH. However, when synthetic human urine was introduced, the adsorption of CIP was negatively affected due to pore blockage and competition for available sorption sites on the GAC. Among the four types of GACs tested, the lowest reduction in CIP uptake in the urine solution was observed for Fe-doped GAC followed (%17) by pre-oxidized (64%), Ag-doped (%69), and pristine F400 (76%) carbon. These results suggested that the complexation between CIP and Fe-doped GAC in urine was stronger due to its higher functionalization compared to Ag-doped, pre-oxidized, and pristine GAC. As the equilibrium concentration of CIP increased, the competition between CIP and urine decreased on the surface of Fe-doped carbon, owing to the limited competition from urine for the available active sorption sites.

The benefits of restoring urban lakes in the tropics.

Lake restoration in developing economies, particularly in the tropics, is a major challenge given the severe levels of pollution from untreated wastewater and the warm climate conducive to microbial and algal growth. Restoration goals are often ill-defined or unachievable. Here we describe the successes that can be achieved through a control, compared with intervention case study of the two urban lakes in Bengaluru, India, one of the world's largest and fastest growing mega-cities. The unrestored control, Bellandur Lake, was severely polluted by 231 million litres per day (MLD) of untreated wastewater. The restoration site, Jakkur Lake, receives 10 MLD of treated wastewater and also receives some tertiary treatment by circulating the effluent through a constructed wetland before it enters the lake. The water quality of Bellandur Lake can only be described as extremely bad. Organic pollution levels in the main inflow were high (BOD5 of 199mg/l, faecal coliforms 6.9 Log MPN/100ml, total suspended solids (TSS) of 285mg/l) leading to the complete deoxygenation of lake even at the surface. The levels exceeded use-base standards for bathing water and fisheries. The high levels of organic pollution and low oxygen conditions also led to extreme levels of methane emissions that occasionally led to the lake surface catching fire. Total nitrogen (TN) and total phosphorus (TP) concentrations in the lake were extremely high (47mg/l and 6.3mg/l) respectively with low Secchi depth (SD). Despite the high nutrient levels, very little phytoplankton growth occurred (chlorophyll-a of 0mg/l), most likely due to the high TSS loads which restricted light availability. In comparison, the wastewater treatment and wetland at Jakkur Lake markedly reduced organic pollution of the main inflow (BOD5 of 32mg/l, faecal coliforms 4.1 Log MPN/100ml, TSS of 48mg/l). Levels of coliforms in the lake were above the standards for bathing waters. Total nitrogen (TN) and total phosphorus (TP) concentrations in the lake reduced (10.5mg/l, 2.4mg/l) but still classify the lake as extremely hypereutrophic. The lower TSS levels did, however, enable dense phytoplankton blooms to develop (max chlorophyll-a of 600 µg/l) which are in part responsible for the higher levels of dissolved oxygen in the lake water, albeit and as expected with large diurnal fluctuations. The comparison highlights the benefits that standard wastewater treatment provides to restore urban tropical lakes in context of rapidly urbanising catchments, and even though Jakkur Lake is by no means fully restored, it sustains water quality that allow propagation of fisheries and shore-based recreation. It also greatly contributes to greenhouse gas emission reductions. Further restoration measures are likely needed for urban tropical lakes, particularly to tackle pollutant loads in monsoon periods, but restoring community pride in the uses of a lake is an important milestone of the restoration efforts.

Modelling of a wastewater-treatment plant for process reliability and effluent reuse

Evaluation of wastewater-treatment plant (WWTP) performance is important to determine whether the plant produces an acceptable treated effluent satisfying the water quality standards for reuse. Modelling of WWTPs is required for optimising plant performance and choosing the optimum operation strategy. This study simulated the Kabd WWTP in Kuwait using the BioWin software. The plant receives 180 000 m3/day of domestic wastewater and comprises primary, secondary (activated sludge) and tertiary treatment stages. Daily data obtained from the WWTP during 2013–2018 were used for modelling plant performance under steady-state operation. The model could describe plant operation and accurately predict the effluent characteristics for the conditions examined. A high correlation (R 2 = 0.95–0.99) was obtained between the predicted and actual values of chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total suspended solids as main parameters characterising wastewater. The tertiary-treated effluent consistently satisfied the water quality criteria for reuse in irrigation. Using the model could aid in securing compliance of effluent quality with the local environmental standards. Factorial analysis revealed that COD and BOD are the most important parameters describing plant performance. Reliability analysis showed that the coefficient of variability was low (0.328) at a level of reliability of 95%, leading to a high coefficient reliability of 0.631, which indicates a highly stable plant performance. It is recommended to include reliability analysis in evaluating plant performance to demonstrate consistency in the ability of the plant to produce effluents satisfying requirements set by environmental authorities.

Performance of lagoon and constructed wetland systems for tertiary wastewater treatment and potential of reclaimed water in agricultural irrigation

Climate change poses challenges to agricultural water resources, both in terms of quantity and quality. As an adaptation measure, the new European Regulation (EU) 2020/741 establishes different water quality classes for the use of reclaimed water in agricultural irrigation. Italy is also working on the definition of a new regulation on reclaimed water reuse for agricultural irrigation (in substitution of the current one) that will also include the specific requirements imposed by the European one. Nature-based Solutions (NBS) can be a cost-effective and environmentally friendly way to facilitate water reclamation and reuse. The present study reports the outcomes of a long-term monitoring campaign of two NBS (e.g., a constructed wetland (CW) and a lagoon system (LS)) comparing influent and effluent concentrations of different contaminants (e.g., E. coli, BOD5, TSS, TN and TP) with the threshold values imposed by the new regulations. The results showed that in both the case studies, E. coli (about 100 CFU 100 mL−1) and BOD5 (lower than 25 mg L−1) mean effluent concentration need to be further reduced in reclaimed water to be suitable for unlimited reuse. As a negative aspect, in both the monitored NBS, an increase in TSS mean concentration in the effluent was observed, up to 40 mg L−1 in the case of the LS, making reclaimed water unsuitable for agricultural reuse. The CW has proven to be more effective in nitrogen removal (the effluent mean concentration was 3.4 mg L−1), whereas the LS was better at phosphorus removal (with an effluent mean concentration of 0.4 mg L−1). Based on the results, recommendations were made to further improve the performance of both systems in order to have adequate water quality, even for class A. Furthermore, the capacity of reclaimed water to meet crop water and nutrient needs was analyzed, and total nitrogen removal rate coefficients were calculated for the design of future LSs.

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.