Achieving zero fouling in the ultrafiltration for secondary water supply systems in the absence of residual chlorine.

Ultrafiltration (UF) technology is widely used in secondary water supply systems (SWSS) to provide high-quality drinking water. However, the challenge of severe membrane fouling, which leads to frequent cleaning requirements, makes UF maintenance intensive. In this study, we tried to validate the feasibility of achieving zero fouling without the need for cleaning in the UF for SWSS, i.e., the fouling resistance can be maintained for a very long time without any increase. We operated dead-end UF systems at different fluxes, both with and without residual chlorine, and monitored the formation of fouling layers during filtration. The results demonstrated the successful achievement of zero fouling under a flux of 10 L/(m2 h) in the absence of chlorine, evidenced by no increase in transmembrane pressure for three months. This zero-fouling phenomenon was attributed to the formation of a self-regulating biofouling layer. This biofouling layer could degrade the deposited foulants and featured a loose morphology, facilitated by microbial activities in the cake layer. Although residual chlorine reduced the fouling rate by half at a flux of 30 L/(m2 h), it hindered the achievement of zero fouling at the lower flux of 10 L/(m2 h), due to its inhibitory effect on microbial activity. Intermittent operation of UF was effective in achieving zero fouling at higher fluxes (e.g., 30 L/(m2 h)). This benefit was primarily ascribed to the biodegradation of accumulated foulants and the expansion of biofouling layer during the pause of the intermittent filtration, which prompted the formation of biofouling layers with loose structure and balanced composition. To the best of our knowledge, this study is the first attempt to achieve zero fouling in UF for SWSS, and the findings may offer valuable insights for the development of cleaning-free and low-maintenance membrane processes.

Potential roles of acyl homoserine lactones (AHLs) in nitrifying bacteria survival under certain adverse circumstances.

Potential roles of quorum sensing (QS) in nitrifying bacteria activity and ecology, particularly under adverse circumstances have been rarely reported. Herein, eight lab-scale nitrification sequencing batch reactors, with or without adding acyl homoserine lactones (AHLs) were operated under adverse circumstances respectively. The results indicated that the introduction of AHLs significantly enhanced the nitrogen removal efficiency in the presence of nitrification inhibitors (dicyandiamide, DCD), accelerated the low temperature (10 °C) group into stable stage, and improved the utilization efficiency of AHLs in these two groups. Community analysis and qPCR further confirmed that AHLs significantly increased the abundance of nitrifying bacteria in low temperature group and DCD group, especially AOB. For normal condition (28 °C, pH = 8) or low pH level (5.5), however, the AHLs had no significant effect. Canonical correspondence analysis showed that nitrifying bacteria positively responded to AHLs, indicating that adding AHLs was an effective strategy to regulate nitrification process. However, under acid conditions, the effect of this regulatory mechanism was not significant, indicating that the influence of pH on the system was greater than that of AHLs. This study demonstrated that exogenous AHLs could enhance the competitiveness of nitrifying bacteria to utilize more resource and occupy space under some adverse environmental conditions.

Stable and rapid partial nitrification achieved by boron stimulating autoinducer-2 mediated quorum sensing at room & low temperature.

The stable and rapid initiation of partial nitrification is a long-term interest of researchers. In this study, boron, an activator of autoinducer-2 (AI-2), was first proposed to promote partial nitrification and improve sludge properties. Two concentrations of boron were added to six laboratory-scale nitrification reactors to study the effects of boron stimulated AI-2-mediated quorum sensing on nitrification at room and low temperature. Boron could significantly increase the concentration of AI-2 in the reactor (p < 0.05), and the high concentration of boron showed better performance at two temperatures. The realization of partial nitrification was mainly due to the accumulation of NO2-- N promoted by the increase of AI-2 concentration. NO2-- N accumulation occurred in all the boron-treated reactors, while no NO2-- N accumulation occurred in the reactor without boron at room temperature or the accumulation efficiency was 14% lower at low temperature. Community analysis and qPCR further confirmed that exogenous boron had no significant effect on AOB, but inhibited NOB, especially at room temperature. The changes of EPS were slightly different at the two temperatures: at room temperature, boron increased the total EPS production, while at low temperature it mainly changed the PN/PS value of EPS. It was worth noting that the effect of boron on partial nitrification depended not only on its concentration, but also on NH4+-N concentration and temperature. This study provided a new strategy for the rapid and stable initiation of partial nitrification process.

Function of quorum sensing and cell signaling in wastewater treatment systems.

Quorum sensing (QS) is a communication mode between microorganisms to regulate bacteria ecological relations and physiological behaviors, thus achieve the physiological function that single bacteria cannot complete. This phenomenon plays important roles in the formation of biofilm and granular sludge, and may be related to enhancement of some functional bacteria activity in wastewater treatment systems. There is a need to better understand bacterial QS in engineered reactors, and to assess how designs and operations might improve the removal efficiency. This article reviewed the recent advances of QS in several environmental systems and mainly analyzed the regulation mechanism of QS-based strategies for biofilm, granular sludge, functional bacteria, and biofouling control. The co-existences of multiple signal molecules in wastewater treatment (WWT) processes were also summarized, which provide basis for the future research on the QS mechanism of multiple signal molecules' interaction in WWT. This review would present some prospects and suggestions which are of practical significance for further application.

Delineating the key virulence factors and intraspecies divergence of Vibrio harveyi via whole-genome sequencing.

Vibrio harveyi is one of the major pathogens in aquaculture. To identify the key virulence factors affecting pathogenesis of V. harveyi towards fish, we conducted a field investigation for three representative fish farms infected with V. harveyi. Multilocus sequence typing (MLST) and whole-genome sequencing were conducted to delineate the phylogenetic relationship and genetic divergence of V. harveyi. A total of 25 V. harveyi strains were isolated from the diseased fish and groundwater and were subtyped into 12 sequence types by MLST. Five virulence genes, mshB, pilA, hutR, ureB, and ureG, were variably presented in the sequenced strains. The virulence gene profiles strongly correlated with the distinct pathogenicity of V. harveyi strains, with a strain harboring all five genes exhibiting the highest virulence towards fish. Phenotype assay confirmed that reduced virulence correlated with decreased motility and biofilm formation ability. Additionally, three types of type VI secretion system, namely T6SS1, T6SS2, and T6SS3, were identified in V. harveyi strains, which can be classified into six, four, and 12 subtypes, respectively. In conclusion, the results indicated that the virulence level of V. harveyi is mainly determined by the above virulence genes, which may play vital roles in environmental adaptation for V. harveyi.

Quantifying the impacts of climate variability and human interventions on crop production and food security in the Yangtze River Basin, China, 1990-2015.

Food security has become a global policy concern due to its important role in sustaining development and human well-being. Using spatial autocorrelation analysis of statistical data at the county-level, this study quantifies the change in spatial and temporal patterns of crop production in the Yangtze River Basin of China since 1990 and draws out policy implications for food security in the country. Four panel models were constructed to examine in what ways and to what extent four major factors (climate variation, sown area, fertilizer use intensity, and population size) influence the capacity for crop production. The results show that total crop production increased by 15.2% in 1990-2015, while there exists significant spatial heterogeneity in crop output across the upper, middle and lower sections of the Basin. The spatial agglomerations of crop production (hotspots) in the Basin have varied significantly over time, with the hotspots in the lower section having disappeared since 2000. Over a quarter of the total number of counties (649) in the region have experienced a high risk of food shortages, with 19.4-27.4% of counties having experienced severe or moderate shortages of per capita food availability since 1990. This percentage increased from 9.3% to 16.2% in the lower section, while it declined from 53.9% in 1990 to 41.9% in 2015 in the upper section and remained unchanged in the middle section. The variables of sown area, fertilizer use intensity, total precipitation in the growing seasons and time (Year) have significant positive effects on the growth of crop production, but mean temperature in the growing seasons of crops and total population have significant and negative relationships with crop outputs. Establishing a reliable food supply system, safeguarding high-quality cultivated land and increasing fertilizer use efficiency are suggested as imperative countermeasures to mitigate food security risks in the Yangtze River Basin.

Ecosystem services trade-offs and determinants in China's Yangtze River Economic Belt from 2000 to 2015.

Ecosystem services (ES) play an important role in sustaining ecological security, sustainable development and human well-being. This study investigates spatio-temporal changes in five key ES in the Yangtze River Economic Belt of China in 2000-2015-water conservation (WC), soil retention (SR), carbon sequestration (CS), biodiversity conservation (BC) and food supply (FS), by applying three ecological models (InVEST, RUSLE, CASA). Employing scenario simulations, the study quantifies distinct effects of significant factors on ES changes. Using spatial overlapping and Spearman's rank correlation respectively, the study distinguishes spatial patterns of synergies and trade-offs between five ES at the grid and city-scales. The results show that CS, FS, WC and SR presented an overall upward trend, increasing by 22.7%, 16.9%, 6.4% and 4.7%, respectively, while BC remained steady with a marginal degradation. Change in these five ES exhibited dramatic spatial heterogeneity. Across 131 cities, 98.5% of which increased in CS, 87.7% in WC, 68.5% in FS, and 53.1% in SR, while more than half experienced slight degradation in BC. There is high heterogeneity and a great diversity among spatial distributions of ES synergies and trade-offs, which is largely dependent on ES pairs and spatial patterns of land use. Land use/land cover change was the dominant force driving changes in SR, BC and CS, while meteorological factors exhibited a greater effect on WS change than land use/land cover change. The paper examines the synergies between WC-SR, CS-BC and BC-FS on the city level, while WC-BC exhibits significant trade-offs, and no significant relationships for other ES pairs. It is imperative that ES trade-offs at different scales are incorporated to strengthen ecological protection and management policies in project implementation, maintaining ES within vital regions in China. More sophisticated methods and more ES indicators need to be incorporated to enhance the robustness and completeness of assessment.

Removal of heavy metal from sludge by the combined application of a biodegradable biosurfactant and complexing agent in enhanced electrokinetic treatment.

In this work, the heavy metal removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent Tetrasodium of N, N-bis (carboxymethyl) glutamic acid (GLDA) also in combination with a biodegradable biosurfactant (rhamnolipid) was investigated to decontaminate heavy metals from the sludge. The main results explored that the nature of sludge and their interactions with different improving agents significantly influenced the electrokinetic removal processes. A general increase of pH values from anode to cathode in the sludge-cell was observed due to the strong buffering capacity of carbonates. Compared with the deionized water, the use of GLDA as an electrolyte, Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 53.2 ± 3.12%, 67.4 ± 3.45%, 59.2 ± 4.78%, 45.4 ± 4.15%, 72.8 ± 3.68% and 45.0 ± 4.85%, respectively, whereas a further improvement heavy metals removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 64.8 ± 2.34%, 56.8 ± 4.12%, 49.4 ± 4.45%, 46.6 ± 2.35%, 60.4 ± 3.45% and 69.6 ± 3.54%, respectively) were achieved by repalcing rhamnolipid as the electrolyte. Significantly higher removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 70.6 ± 3.41%, 82.2 ± 5.21%, 89.0 ± 3.34%, 60.0 ± 4.67%, 88.4 ± 4.43% and 70.0 ± 3.51%, respectively) were obtained by the simultaneous use of GLDA and rhamnolipid due to their synergic action in electrokinetic process.

Biofouling control by biostimulation of quorum-quenching bacteria in a membrane bioreactor for wastewater treatment.

Bacterial quorum quenching (QQ) has been shown to be effective in controlling biofouling in membrane bioreactors (MBRs) for wastewater treatment. However, the encapsulation of a sufficient level of QQ bacteria is complicated and difficult. In plant research, gamma-caprolactone (GCL), which is structurally similar to the quorum signal, N-acyl homoserine lactone (AHL), was successfully used to specifically stimulate AHL-degrading bacteria (biostimulation) in hydroponic systems to control blackleg and soft rot diseases in potato. In this study, the feasibility of enriching QQ bacteria from activated sludge by GCL was examined, and the effect of biostimulation on biofouling control in MBR treating domestic wastewater was investigated. The results showed that after enrichment with GCL, activated sludge could effectively degrade AHLs, and a QQ gene (qsdA) was augmented. The proposed biostimulation QQ strategy, by introducing and continuously dosing GCL, could significantly increase QQ activity, decrease AHL, control the secretion of extracellular polymeric substances (EPS), and thus, effectively control biofouling in an MBR. This biostimulation QQ strategy provides a more convenient option for biofouling control in MBR applications. Biotechnol. Bioeng. 2016;113: 2624-2632. © 2016 Wiley Periodicals, Inc.

Biofilm activity and sludge characteristics affected by exogenous N-acyl homoserine lactones in biofilm reactors.

This study verified the effect of N-acyl homoserine lactone (AHL) concentrations on mature biofilm systems. Three concentrations of an AHL mixture were used in the batch test. Introducing of 5nM AHLs significantly increased biofilm activity and increased sludge characteristics, which resulted in better pollutant removal performance, whereas exogenous 50nM and 500nM AHLs limited pollutant removal, especially COD and nitrogen removal. To further identify how exogenous signal molecular affects biofilm system nitrogen removal, analyzing of nitrifying bacteria through real-time polymerase chain reaction (RT-PCR) revealed that these additional signal molecules affect nitrifying to total bacteria ratio. In addition, the running state of the system was stable during 15days of operation without an AHL dose, which suggests that the changes in the system due to AHL are irreversible.