Disinfection for decentralized wastewater reuse in rural areas through wetlands and solar driven onsite chlorination

Treatment of real laundry wastewater using vertical flow constructed wetland planted with the ornamental climbing plant Trachelospermum jasminoides: assessing the removal of conventional pollutants and benzotriazoles

This study investigates the effectiveness of vertical flow constructed wetlands (VFCWs) planted with a climbing ornamental plant for on-site treatment of real laundry wastewater. Specifically, the presence or absence of Trachelospermum jasminoides was evaluated for the removal performance of conventional pollutants (turbidity, TSS, COD, TP) and benzotriazoles (BTRs): 1H-benzotriazole (BTR), 5-methyl-1H-benzotriazole (5-TTR), 5-chlorobenzotriazole (CBTR), and xylytriazole (XTR). Results revealed that high removal efficiencies ranging from 92 to 98% were presented in both planted and unplanted systems for turbidity, TSS, and COD. Moreover, high removal rates were observed for CBTR and XTR, which were the only compounds found in real laundry wastewater, in both VFCW systems (planted: 100%; 94%; unplanted: 87%; 92%, respectively). The contribution of plants to the pollutant's removal was not statistically significant for all examined parameters. However, T. jasminoides demonstrated the ability to survive and grow without any visible symptoms under the harsh conditions of laundry wastewater, enabling the development of green facade. According to the findings, the application of VFCWs for on-site laundry wastewater treatment in buildings seems to be a highly promising solution, not only for primarily removing conventional pollutants but also for addressing emerging contaminants, specifically BTRs.

Potential pathogenic microorganisms in rural wastewater treatment process: Succession characteristics, concentration variation, source exploration, and risk assessment

Pathogenic microorganisms can cause infection, sepsis, and other diseases in humans. Although municipal wastewater plants are important sources and sinks for potential pathogenic microorganisms, data on rural wastewater treatment processes are limited. The proximity of rural wastewater facilities to human settlements and the trend toward wastewater resourcing could pose risks to humans. Here, a typical village in southern China was selected to analyze potential pathogenic microorganisms in wastewater, sewage sludge, and aerosols during the collection, treatment, and discharge of domestic wastewater. The succession characteristics and concentration variations of potential pathogenic microorganisms throughout the wastewater treatment process were identified using high-throughput sequencing and culture methods. Bacteria-associated health risks in facility aerosols were estimated based on average daily dose rates from inhalation and dermal exposure. Lower amounts of pathogenic bacteria and pathogenic fungi were detected in the effluent of the 1-ton treatment scale and the 10-ton treatment scale facilities, compared to those in the influent. Pathogen effluent concentrations were significantly lower than influent concentrations after treatment in rural wastewater facilities. 16 and 29 potential pathogenic bacteria and fungi were detected in aerosols from wastewater treatment facilities, respectively. Furthermore, the potential pathogen concentrations were higher than those in the background air. Aerobic units are the main source of pathogen emissions from aerosols. There were 42 potential pathogenic bacteria and 34 potential pathogenic fungi in the sewage sludge. Biochemical units were the main source of potential pathogens in sewage sludge, and more potential airborne pathogens originated from wastewater. In rural wastewater resourcing processes with greater pollutant exposure, the effluent of rural wastewater treatment facilities (WWTFs), downstream rivers, and facility aerosols, could be important potential sources of microbial risk. Inhalation is the main pathway of human exposure to airborne bacteria. Therefore, more attention should be focused on microbiological risk in rural wastewater treatment processes.

Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?

Electrochlorination has gained research interest for its potential application as decentralized water treatment. A number of studies have displayed promising efficiency for water disinfection. However, a comprehensive comparison of in situ electrodisinfection to existing disinfection techniques, particularly under realistic water composition and flow rates, still needs additional research efforts. The aim of this study is to evaluate in situ electrochlorination while comparing the treatment with conventional chemical chlorination for point-of-entry decentralized disinfection at the household level. An electrochemical flow cell reactor was operated in a single pass mode considering water flow and water consumption for a household of four family members. Disinfection efficiency assessment of both electrochemical and chemical chlorination was conducted using bacterial and viral surrogates, E. coli and MS2 bacteriophage. Furthermore, a techno-economic analysis was conducted, using the levelized cost of water, to compare two electrochemical chlorination scenarios (i.e., electrical grid energy use, and solar panel powered system) and benchmarked against the baseline treatment of chemical chlorination. The findings revealed increased inactivation efficiency of in situ electrochlorination over conventional chlorination (p-value < 0.05). The synergetic impact of radicals and chlorine, and/or contribution of high chlorine concentration at acidic pH near anode surface were identified as key factors that could enhance disinfection performance of in situ electrochlorination. The techno-economic analysis demonstrated that electrochemical treatment, when operated using renewable energy sources, is not only a more environmentally sustainable approach, but also emerges as a more economically feasible solution for decentralized water treatment application. The results highlight that in situ electrochlorination is a more advanced alternative to decentralized water chlorination. However, further fundamental research on products and by-products formation under various water matrices is required.

Water treatment and reclamation by implementing electrochemical systems with constructed wetlands

Seasonal or permanent water scarcity in off-grid communities can be alleviated by recycling water in decentralized wastewater treatment systems. Nature-based solutions, such as constructed wetlands (CWs), have become popular solutions for sanitation in remote locations. Although typical CWs can efficiently remove solids and organics to meet water reuse standards, polishing remains necessary for other parameters, such as pathogens, nutrients, and recalcitrant pollutants. Different CW designs and CWs coupled with electrochemical technologies have been proposed to improve treatment efficiency. Electrochemical systems (ECs) have been either implemented within the CW bed (ECin-CW) or as a stage in a sequential treatment (CW + EC). A large body of literature has focused on ECin-CW, and multiple scaled-up systems have recently been successfully implemented, primarily to remove recalcitrant organics. Conversely, only a few reports have explored the opportunity to polish CW effluents in a downstream electrochemical module for the electro-oxidation of micropollutants or electro-disinfection of pathogens to meet more stringent water reuse standards. This paper aims to critically review the opportunities, challenges, and future research directions of the different couplings of CW with EC as a decentralized technology for water treatment and recovery.

Membrane-Assisted Electrochlorination for Zero-Chemical-Input Point-of-Use Drinking Water Disinfection

Due to the challenges of providing centralized drinking water infrastructure in low-income and rural settings, point-of-use (POU) disinfection systems are an attractive option for enhancing access to safe drinking water. Electrochlorinators offer an easily scalable and adaptable alternative to POU disinfection systems that require frequent replenishment and accurate dosing of chlorine, but they also require addition of salts on a regular basis. To address this need, we developed an electrochemical disinfection system that efficiently produces chlorine without any chemical inputs. To convert the low concentration of chloride in source waters (i.e., 10-200 mg L^-1) to free chlorine (i.e., HOCl/OCl^-), an anion exchange membrane was positioned between two electrodes, creating two separate chambers. By providing continuous water flow through the catholyte while operating the anolyte in the batch mode, chloride was concentrated into the anolyte, where it was more efficiently converted into chlorine. This approach allowed us to produce chlorine at rates that were about 50% faster than that of an undivided cell operating under similar conditions. Chlorate production was approximately 20% slower in the separated cell compared to an undivided cell; concentrations in finished water never exceeded the World Health Organization's provisional guideline value of 0.7 mg L^-1. The performance of the system was further improved by retaining some of the anolyte between operating cycles. This helped avoid periods of high cell potential before salts were concentrated in the anolyte chamber. Use of an anion exchange membrane and a recycled anolyte mode of operation reduced energy consumption by 30%-70% relative to an undivided cell. The energy required to disinfect water ranged from approximately 0.05 to 1 kWh m^-3, depending on the chloride content and conductivity of the source water.

Preparation of Copper-Decorated Activated Carbon Derived from Platamus occidentalis Tree Fiber for Antimicrobial Applications

This study focuses on a greener approach to synthesizing activated carbon by carbonizing Platamus occidentalis tree fibers (TFSA) with 98% H₂SO₄ at 100 °C. The resulted TFSA was employed as an effective adsorbent for copper ions in aqueous media, yielding copper decorated TFSA (Cu@TFSA). The successful adsorption of copper onto the TFSA was proven through extensive characterization techniques. Herein, the TEM and XPS showed that copper nanoparticles were formed in situ on the TFSA surface, without the use of additional reducing and stabilizing agents nor thermal treatment. The surface areas of TFSA and Cu@TFSA were 0.0150 m²/g and 0.3109 m²/g, respectively. Applying the Cu@TFSA as an antimicrobial agent against Escherica coli ( E. coli) and Salmonella resulted in the potential mitigation of complex secondary pollutants from water and wastewater. The Cu@TFSA exhibited outstanding antimicrobial activity against E. coli and Salmonella in both synthetic and raw water samples. This demonstrated a complete growth inhibition observed within 120 min of exposure. The bacteria inactivation took place through the destruction of the bacteria cell wall and was confirmed by the AFM analysis technique. Cu@TFSA has the potential to be used in the water and wastewater treatment sector as antimicrobial agents.

Implications of COD analysis use in the peracetic acid-based wastewater treatment

Peracetic acid (PAA) stands out as a safe and environmental-friendly oxidant and disinfectant which has been effectively used in wastewater treatment. Chemical oxygen demand (COD) is a very popular analysis in wastewater treatment; however, the interference of residual PAA on the COD measurement is still unknown. In this context, this study investigated the implications of applying the COD analysis in PAA-based treatment. Each 1 mg·L^-1 of PAA increased the COD concentration around 13.5 mg O₂·L^-1. Residual PAA and hydrogen peroxide (H₂O₂) were efficiently neutralized by sodium metabisulfite (SMBS) at the optimal SMBS/PAA ratio of 10.2:1 in a wide pH range (5 to 9). The effect of PAA addition on the COD concentration was evaluated in different water matrices (potassium hydrogen phthalate and wastewater solutions). The COD results with the SMBS addition at optimal SMBS/PAA ratio were lower than the ones without it. It may happen due to the neutralization of residual H₂O₂/PAA and the complexity of the water matrices which can interfere in the COD results. This study discussed the impact of the residual H₂O₂/PAA neutralization before the COD analysis, and this investigation can be used as a practical guideline for the correct COD measurement in PAA-based treatment.

Mitigation of emerging pollutants and pathogens in decentralized wastewater treatment processes: A review

Emerging pollutants (such as micropollutants, microplastics) and pathogens present in wastewater are of rising concern because their release can affect the natural environment and drinking water resources. In this decade, with increasing numbers of small-scale decentralized wastewater systems globally, the status of emerging pollutant and pathogen mitigation in the decentralized wastewater treatment processes has received more attention. This state-of-the-art review aims to discuss the mitigation efficiencies and mechanisms of micropollutants, microplastics, and pathogens in single-stage and hybrid decentralized wastewater treatment processes. The reviewed results revealed that hybrid wastewater treatment facilities could display better performance compared to stand-alone facilities. This is because the multiple treatment steps could offer various microenvironments, allowing incorporating several mitigation mechanisms (such as sorption, degradation, filtration, etc.) to remove complicated emerging pollutants and pathogens. The factors (such as system operation conditions, environmental conditions, wastewater matrix) influencing the removals of emerging pollutants from wastewater in these systems have been further identified. Nevertheless, it was found that very limited research work focused on synergised or conflicted effects of operation conditions on various emerging pollutants naturally present in the wastewater. Meanwhile, effective, reliable, and rapid analysis of the emerging pollutants and pathogens in the complicated wastewater matrix is still a major challenge.

Where do we stand to oversee the coronaviruses in aqueous and aerosol environment? Characteristics of transmission and possible curb strategies

By 17 October 2020, the severe acute respiratory syndrome coronavirus (SARS-CoV-2) has caused confirmed infection of more than 39,000,000 people in 217 countries and territories globally and still continues to grow. As environmental professionals, understanding how SARS-CoV-2 can be transmitted via water and air environment is a concern. We have to be ready for focusing our attention to the prompt diagnosis and potential infection control procedures of the virus in integrated water and air system. This paper reviews the state-of-the-art information from available sources of published papers, newsletters and large number of scientific websites aimed to provide a comprehensive profile on the transmission characteristics of the coronaviruses in water, sludge, and air environment, especially the water and wastewater treatment systems. The review also focused on proposing the possible curb strategies to monitor and eventually cut off the coronaviruses under the authors' knowledge and understanding.

Performance Comparison of Vertical Flow Treatment Wetlands Planted with the Ornamental Plant Zantedeschia aethiopica Operated under Arid and Mediterranean Climate Conditions

This work compares the performance of vertical subsurface flow treatment wetlands (VSSF TWs) for wastewater treatment, planted with Zantedeschia aethiopica (Za), here operated simultaneously under two different climate conditions, arid and Mediterranean. The experimental setup was divided into two treatment lines for each climate condition: three VSSF TWs planted with Schoenplectus californicus (Sc) (VSSF-S), as the control, and three VSSF TWs planted with Zantedeschia aethiopica (Za) (VSSF-Z), as the experimental unit. The four treatment systems were operated at a hydraulic loading rate of 120 mm/d during spring and summer seasons, in two locations, Iquique (Atacama Desert, Chile) and Talca (Central Valley, Chile). The water quality in effluents, plant development, and water balance were used as performance measures. In terms of the water quality, the influents’ characteristics were similar in both climates and classified as “diluted”. For the effluents, in both climate conditions, average COD and TSS effluent concentrations were below 50 mg/L and 15 mg/L, respectively. In both climate conditions, average TN and TP effluent concentrations were below 40 mg/L and 2 mg/L, respectively. Furthermore, only total nitrogen (TN) and total phosphorus (TP) in effluents to VSSF-Z had a significant effect (p < 0.05) in relation to the climate condition. Regarding plant development, Za showed a lower height growth in both climate conditions, with arid consistently 0.3 m and Mediterranean decreasing from 0.6 m to 0.2 m. However, the physiological conditions of the leaves (measured by chlorophyll content) were not affected during operation time in both climates. Water balance showed that it was not influenced by the climate conditions or plant, with water loss differences below 5%. Therefore, taking into account the water quality and water balance results, Zantedeschia aethiopica can be used in VSSF TWs in a way similar to traditional plants under arid and Mediterranean climates. However, its use has to be carefully considered because lower height could affect the esthetics for its implementation in the VSSF TWs.

Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

Conventional onsite wastewater treatment systems (OWTSs) could potentially contribute to the transmission of infectious diseases caused by waterborne pathogenic microorganisms and become an important human health concern, especially in the areas where OWTSs are used as the major wastewater treatment units. Although previous studies suggested the OWTSs could reduce chemical pollutants as well as effectively reducing microbial contaminants from onsite wastewater, the microbiological quality of effluents and the factors potentially affecting the removal are still understudied. Therefore, the design and optimization of pathogen removal performance necessitate a better mechanistic understanding of the hydrological, geochemical, and biological processes controlling the water quality in OWTSs. To fill the knowledge gaps, the sources of pathogens and common pathogenic indicators, along with their major removal mechanisms in OWTSs were discussed. This review evaluated the effectiveness of pathogen removal in state-of-art OWTSs and investigated the contributing factors for efficient pathogen removal (e.g., system configurations, filter materials, environmental and operational conditions), with the aim to guide the future design for optimized treatment performance.

Peracetic acid-based advanced oxidation processes for decontamination and disinfection of water: A review

Peracetic acid (PAA) has attracted growing attention as an alternative oxidant and disinfectant in wastewater treatment due to the increased demand to reduce chlorine usage and control disinfection byproducts (DBPs). These applications have stimulated new investigations on PAA-based advanced oxidation processes (AOPs), which can enhance water disinfection and remove micropollutants. The purpose of this review is to conduct a comprehensive analysis of scientific information and experimental data reported in recent years on the applications of PAA-based AOPs for the removal of chemical and microbiological micropollutants from water and wastewater. Various methods of PAA activation, including the supply of external energy and metal/metal-free catalysts, as well as their activation mechanisms are discussed. Then, a review on the usage of PAA-based AOPs for contaminant degradation is given. The degradation mechanisms of organic compounds and the influence of the controlling parameters of PAA-based treatment systems are summarized and discussed. Concurrently, the application of PAA-based AOPs for water disinfection and the related mechanisms of microorganism inactivation are also reviewed. Since combining UV light with PAA is the most commonly investigated PAA-based AOP for simultaneous pathogen inactivation and micropollutant oxidation, we have also focused on PAA microbial inactivation kinetics, together with the effects of key experimental parameters on the process. Moreover, we have discussed the advantages and disadvantages of UV/PAA as an AOP against the well-known and established UV/H₂O₂. Finally, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This critical review will facilitate an in-depth understanding of the PAA-based AOPs for water and wastewater treatment and provide useful perspectives for future research and development for PAA-based technologies.