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.

Transcriptomics and metabolomics profiling reveals involvement of flavonoids in early nodulation of Caucasian clover (Trifolium ambiguum).

Caucasian clover (Trifolium ambiguum) is a perennial rooted and tillering leguminous forage with strong adaptability, outstanding stress tolerance and other preferable traits. However, the specificity with rhizobia limits the extended application of Caucasian clover. Therefore, it is important to study the changes of genes and metabolites in the early process of nodulation in Caucasian clover to improve its nodulation and nitrogen fixation ability. In this study, we used Caucasian clover as the experimental material to investigate its nodulation mechanism using transcriptomic and metabolomic approaches, such that to break the nitrogen fixation barrier for the promotion of Caucasian clover. Metabolomic and transcriptomic profiling revealed that both DAMs and DEGs were significantly enriched in the phenylpropanoid and flavonoid biosynthetic pathways, with DEGs showing up-regulation at 3 days and 6 days post inoculation (dpi) with rhizobia, and some DEGs showing down-regulation at 9 dpi. Accumulation of flavonoids was significantly increased at both 3 dpi and 6 dpi, and some compounds were significantly decreased at 9 dpi. A total of 35 DEGs were involved in flavonoid synthesis by WGCNA analysis, among which HCT, CCR, COMT and F3H played an important role. This study provides insights in understanding the molecular mechanism of nodulation and nitrogen fixation in Caucasian clover.

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.

Comparison of inactivation characteristics between Gram-positive and Gram-negative bacteria in water by synergistic UV and chlorine disinfection.

Disinfection is essential in water and wastewater treatment process as a guarantee for microbial safety. This study systematically investigated: (i) the inactivation characteristics of bacteria widely existed in water, including Gram-negative bacteria (Escherichiacoli) and Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis spores), by sequential UV and chlorine disinfection processes (UV-Cl and Cl-UV), simultaneous UV and chlorine disinfection process (UV/Cl); and (ii) the disinfection mechanisms on different bacteria. The combination of UV and chlorine disinfection could inactive bacteria at lower doses, but showed no synergistic effect on E. coli. Contrarily, disinfection results indicated that UV/Cl performed an obvious synergistic effect on highly disinfectant-resistant bacteria (e.g. S. aureus and B. subtilis spores). Specifically, UV/Cl at the UV dose of 9 mJ/cm2 and chlorine dose of 2 mg-Cl/L could inactivate S. aureus completely. Moreover, the effectiveness of UV/Cl on the removal of indigenous bacteria in actual water conditions was also confirmed. In short, the study provides significant theoretical and practical implications for ensuring microbial safety during water treatment and use.

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.

Quantitative models and potential surrogates for rapid evaluation and surveillance of chlorine disinfection efficacy in reclaimed water.

Chlorine disinfection has become the most widely applied and indispensable technology in wastewater treatment and reuse to mitigate microbial risk and guarantee water safety. However, owing to complexities and high concentrations of contaminants in reclaimed water, rapid evaluation of chlorine disinfection efficacy is a crucial but challenging issue. Based on intensive experimental and statistical analyses, this study has established kinetic models and potential surrogates for rapid indication of the inactivation of microbial indicators and opportunistic pathogens during chlorine disinfection in different reclaimed waters. Overall, the constructed Selleck models performed very well to simulate log removal values (LRVs) of fecal coliforms, Pseudomonas aeruginosa and heterotrophic plate counts in all reclaimed water samples (R2 = 0.877-0.990). Moreover, total and Peak A fluorescence intensity as well as fluorescence integral intensities in Regions II and IV were found to have high response sensitivities during the chlorination process. Nevertheless, their effectiveness to act as potential surrogates of LRVs of microbial indicators needs to be further validated. The results from this study can provide valuable information on microbial safety surveillance of disinfection toward sustainable and long-term water reuse.

Synergistic effects of UV and chlorine in bacterial inactivation for sustainable water reclamation and reuse.

Disinfection is a necessity in water and wastewater treatment and reclamation. This study examined the inactivation of a disinfectant resistant but widely existed opportunistic pathogen in reclaimed water, Staphylococcus aureus (S. aureus), by sequential UV and chlorine disinfection or simultaneous UV and chlorine disinfection (UV/Cl). It was identified that UV/Cl greatly promoted the inactivation efficacy and inhibited photoreactivation of S. aureus by the generation of free radicals (i.e. OH and Cl), which reached a 7-log10 reduction at UV and chlorine doses of 18 mJ/cm2 and 2 mg-Cl/L, respectively. The changes of bacterial viability and morphology and the increase of extracellular ATP concentration confirmed the enhancement of cell membranes damages (>21.4 %) due to free radicals generated in UV/Cl process, which caused a dramatic reduction in metabolic activity and suppressed the photoreactivation. Furthermore, this study demonstrated that UV/Cl effectively removed heterotrophic plate count bacteria and aromatic organic fluorophores in reclaimed water samples. This study is of significant theoretical and applicable importance in guaranteeing safe microbial levels for 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.

Photosynthetic bacteria wastewater treatment with the production of value-added products: A review.

Wastewater resource recovery can generate environmental and economic benefits; especially, value-added substance recovery from wastewater can create profits. Photosynthetic bacteria (PSB) can produce protein, coenzyme Q10, 5-ALA, carotenoids, bacteriochlorin, and polyhydroxyalkanoates while treating wastewaters. This review consists of four parts: (1) PSB wastewater treatment, including influence factors and enhancement methods for value-added substances production; (2) downstream processing, including cell separation from effluent, extraction of value-added substances, and purification; (3) comparison among different wastewater resource recovery technologies and brief economic analysis; (4) future development. The focus of this review is the whole procedure of PSB value-added substance production from wastewater. Recent progress of theoretical researches, practical researches and economic issues were systematically summarized and critically analyzed with the scope of promoting PSB technology from concept to practice.

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.