Synergistic ferrate(VI) and chlorine for reclaimed water disinfection: Microbial control and chlorine decay mitigation.

Chlorination is the most widely used disinfection technology due to its simplicity and continuous disinfection ability. However, the drawbacks of disinfection by-products and chlorine-resistant bacteria have gained increasing attention. Nowadays, ferrate (Fe(VI)) is a multifunctional and environmentally friendly agent which has great potential in wastewater reclamation and reuse. This study investigated synergistic Fe(VI) and chlorine technology for reclaimed water disinfection in terms of microbial control and chlorine decay mitigation. Specifically, synergistic disinfection significantly improved the inactivation efficiency on total coliform, Escherichia coli and heterotrophic bacteria compared to sole chlorination. Synergistic disinfection also exhibited superior performance on controlling the relative abundance of chlorine-resistant bacteria and pathogenic bacteria. In addition, the decay rate of residual chlorine was relatively lower after Fe(VI) pretreatment, which was beneficial for microbial control during the reclaimed water distribution process. Technical and economic analyses revealed that synergistic Fe(VI) and chlorine disinfection was suitable and feasible. Results of this study are believed to provide useful information and alternative options on the optimization of reclaimed water disinfection.

Effects of water quality on bacterial inactivation by ferrate(VI).

Ferrate (Fe(VI)) is an emerging green oxidant which has great potential and prospect in water disinfection. However, the effects of water quality on Fe(VI) disinfection remain unclear. This study systematically investigated the effects of pH, organic matters and inorganic ions on Fe(VI) inactivation of Escherichia coli (E. coli). Results showed that pH was the dominant influencing factor and the inactivation efficiency as well as inactivation rate constant was negatively correlated with pH (6.8-8.4). HFeO4- was found to be the critical Fe(VI) species contributing to the inactivation. As for organic matters (0-5 mg C/L), protein and humic acid significantly accelerated the decay of Fe(VI) and had negative effects on the inactivation efficiency, while polysaccharide slightly inhibited the inactivation due to the low reactivity with Fe(VI). As for inorganic ions, bicarbonate (0-2 mM) could stabilize Fe(VI) and decreased the inactivation rate constant, while ammonium (0-1 mM) had little effect on the inactivation of E. coli. In addition, the comprehensive effects of water quality on Fe(VI) disinfection in actual reclaimed water were also evaluated. The inactivation of E. coli in secondary effluent and denitrifying effluent was found to be inhibited compared to that in phosphate buffer. Overall, this study is believed to provide valuable information on Fe(VI) disinfection for water and wastewater treatment practices.

Inactivation of Bacteria in Water by Ferrate(VI): Efficiency and Mechanisms.

Ferrate (Fe(VI)) is an emerging green disinfectant and has received increasing attention nowadays. This study conducted systematic analyses of Fe(VI) disinfection on six typical bacteria in different water matrices. The results showed that Fe(VI) was more effective in inactivating Gram-negative (G-) bacteria than Gram-positive (G+) bacteria, and the disinfection performance of Fe(VI) was better in a phosphate buffer than that in a borate buffer and secondary effluent. The inactivation rate constants of G- bacteria were significantly higher than those of G+ bacteria. The cell membrane damage of G- bacteria was also more severe than that of G+ bacteria after Fe(VI) treatment. The cell wall structure, especially cell wall thickness, might account for the difference of the inactivation efficiency between G- bacteria and G+ bacteria. Moreover, it is revealed that Fe(VI) primarily reacted with proteins rather than other biological molecules (i.e., phospholipids, peptidoglycan, and lipopolysaccharide). This was further evidenced by the reduction of bacterial autofluorescence due to the destruction of bacterial proteins during Fe(VI) inactivation. Overall, this study advances the understanding of Fe(VI) disinfection mechanisms and provides valuable information for the Fe(VI) application in water disinfection.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES).

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

Modeling and optimization of synergistic ozone-ultraviolet-chlorine process for reclaimed water disinfection: From laboratory tests to software simulation.

The ozone-ultraviolet (UV)-chlorine process is a highly effective method of disinfection in water reuse system, but currently still lacks precise quantification and accurate control. It is difficult to determine the dosage of each disinfectant because of the complex interactions that occur between disinfection units and the complicated mathematical calculation required. In this study, we proposed a dosage optimization model for ozone-UV-chlorine synergistic disinfection process. The model was able to identify the cost-effective doses of the disinfectants under the constraints of microbial inactivation, decolorization, and residual chlorine retention requirements. Specifically, the simulation of microbial inactivation rates during synergistic disinfection process was accomplished through quantification of the synergistic effects between disinfection units and the introduction of enhancement coefficients. In order to solve this optimization model rapidly and automatically, a MATLAB-based software program with graphical user interface was developed. This software consisted of calibration unit, prediction unit, assessment unit, and optimization unit, and was able to simulate synergistic ozone-UV-chlorine process and identify the optimal dose of ozone, UV, and chlorine. Validation experiments revealed good agreements between the experimental data and the results calculated by the developed software. The developed software is believed to help the water reclamation plants improve disinfection efficiency and reduce the operational costs of synergistic disinfection processes.

Identification of significant live bacterial community shifts in different reclaimed waters during ozone and chlorine disinfection.

Ozone and chlorine are the most widely used disinfectants for water and wastewater disinfection. They play important role in microbial inactivation but could also pose a considerable selection effect on the microbial community of reclaimed water. Classical culture-based methods that rely on the assessment of conventional bacterial indicators (e.g., coliform bacteria) could hardly reflect the survival of disinfection residual bacteria (DRB) and hidden microbial risks in disinfected effluents. Hence, this study investigated the shifts of live bacterial community during ozone and chlorine disinfection in three reclaimed waters (i.e., two secondary effluents and one tertiary effluent), adopting Illumina Miseq sequencing technology in combination with a viability assay, propidium monoazide (PMA) pretreatment. Notably, statistical analyses of Wilcoxon rank-sum test confirmed the existance of distinct differences in bacterial community structure between samples with or without PMA pretreatment. On the phylum level, Proteobacteria commonly dominated in three undisinfected reclaimed waters, while ozone and chlorine disinfection posed varied effects on its relative abundance among different influents. On the genus level, ozone and chlorine disinfection significantly changed the bacterial composition and dominant species in reclaimed waters. Specifically, the typical DRB identified in ozone disinfected effluents were Pseudomonas, Nitrospira and Dechloromonas, while for chlorine disinfected effluents, Pseudomonas, Legionella, Clostridium, Mycobacterium and Romboutsia were recognized as typical DRB, which call for much attention. The Alpha and Beta diversity analysis results also suggested that different influent compositions greatly affected the bacterial community structure during disinfection processes. Since the experiments in present study were conducted in a short period and the dataset was relatively limited, prolonged experiment under different operational conditions are needed in future to illustrate the potential long-term effects of disinfection on the microbial community structure. The findings of this study could provide insights into microbial safety concern and control after disinfection for sustainable water reclamation and reuse.

Comparison of the disinfection efficacy between ferrate(VI) and chlorine in secondary effluent.

Disinfection is essential for the microbial safety of reclaimed water. Traditional chlorine disinfection leads to secondary problems such as disinfection by-products and chlorine-resistant bacteria. Ferrate (Fe(VI)) is a novel green disinfectant. However, research on the disinfection characteristics of Fe(VI) remains insufficient. This study compared the disinfection efficacy between Fe(VI) and chlorine in secondary effluent, including the inactivation efficiency of coliforms and heterotrophic bacteria and the control effect on typical chlorine-resistant bacteria. The results showed that Fe(VI) was more effective than chlorine in inactivating Escherichia coli and total coliforms at low doses, whereas chlorine was more effective than Fe(VI) in inactivating heterotrophic bacteria. A severe trailing phenomenon was observed in Fe(VI) disinfection. Based on bacterial community structure analysis, Fe(VI) was also found to be capable of controlling the relative abundance of some chlorine-resistant bacteria such as Sphingomonas, Bacillus, Mycobacterium and Legionella except for Pseudomonas. The results of this study could have implications in evaluating Fe(VI) disinfection ability and optimizing Fe(VI) dosing for disinfection.

The noteworthy chloride ions in reclaimed water: Harmful effects, concentration levels and control strategies.

Chloride ions (Cl-), which are omnipresent in reclaimed water, can cause various problems in water reuse systems, especially during water transmission and at end use sites. Although reverse osmosis (RO) is considered as an effective technology to reduce chloride, its high investment and complex maintenance requirements hinder its application in many water reclamation plants (WRPs). Recently, several technologies bringing new options to better deal with chloride have gained increased attention. This review provides detailed information on the harmful effects, concentration levels, and sources of chloride in reclaimed water and summarizes and discusses various chloride removal technologies, including non-selective methods (e.g., membrane filtration, adsorption and ion exchange, oxidation, and electrochemical methods) and selective methods (e.g. precipitation and specially designed electrochemical methods). Among these, Friedel's salt precipitation and capacitive deionization showed attractive development potential. This review also proposes a holistic framework for chloride control from aspects of "Fit-for-Purpose" planning, technical system development, and whole process optimization, which could facilitate the planning and operation of long-term sustainable water reuse practices.

An insight to sequential ozone­chlorine process for synergistic disinfection on reclaimed water: Experimental and modelling studies.

Water reclamation plants (WRPs) are facing the challenges of ensuring microbial safety and require efficient disinfection systems. Sequential ozone­chlorine disinfection is supposed to be a favorable alternative for reclaimed water disinfection. This study compared the inactivation efficiency of E.coli by single ozone, single chlorine, and sequential ozone­chlorine disinfection approaches. Notably, a single ozone or chlorine process could only achieve a log removal rate of up to 5 log, whereas the sequential ozone­chlorine disinfection could completely inactivate microorganisms (7.3 log). For sequential ozone­chlorine disinfection, the efficiency of chlorination was improved by 2.4%-18.5%. The synergistic effect mainly attributed to the elimination of chlorine consuming substances by ozone. Through the chlorine decay model (CRS) fitting and calculating the integral CT value, the enhancement ability of ozone to chlorine disinfection was quantified. By introducing an enhancement coefficient (ß), a succinct and accurate model was established to estimate the inactivation rate of sequential ozone­chlorine disinfection (mean absolute percentage error: 0.035). The results and methodology of this study are informative to optimize the disinfection units of WRPs.

[Discussion of Microbial Control Standards of Water Reclamation and Formulation Methods].

The key to water reclamation and reuse is water quality safety insurance and risk control. Microbial risk control is an important issue that requires priority during the safe reuse of reclaimed water. This paper systematically summarizes the control requirements for microbial indicators in China's current water reuse standards, focusing on the necessity and deficiencies of water quality targets and microbial indicator concentration control. The performance targets based on the removal requirements of microorganisms together with the methodology and implementation strategies are introduced in detail for the first time. In the future, it is necessary to further explore the microbial control method of water reclamation based on the combination of water quality targets and performance targets, which could provide support for the safe reuse of reclaimed water in China.

Formation of nanoscale Te0 and its effect on TeO32- reduction in CH4-based membrane biofilm reactor.

Formation and recovery of elemental tellurium (Te0) from wastewaters are required by increasing demands and scarce resources. Membrane biofilm reactor (MBfR) using gaseous electron donor has been reported as a low-cost and benign technique to reduce and recover metal (loids). In this study, we demonstrate the feasibility of nanoscale Te0 formation by tellurite (TeO32-) reduction in a CH4-based MBfR. Biogenic Te0 intensively attached on cell surface, within diameters ranging from 10 nm to 30 nm and the hexagonal nanostructure. Along with the Te0 formation, the TeO32- reduction was inhibited. After flushing, biofilm resumed the TeO32- reduction ability, suggesting that the formed nanoscale Te0 might inhibit the reduction by hindering substrate transfer of TeO32- to microbes. The 16S rRNA gene amplicon sequencing revealed that Thermomonas and Hyphomicrobium were possibly responsible for TeO32- reduction since they increased consecutively along with the experiment operation. The PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) analysis showed that the sulfite reductases were positively correlated with the TeO32- flux, indicating they were potential enzymes involved in reduction process. This study confirms the capability of CH4-based MBfR in tellurium reduction and formation, and provides more techniques for resources recovery and recycles.