Iron-mediated DAMO-anammox process: Revealing the mechanism of electron transfer.

The nitrate denitrifying anaerobic methane oxidation-anaerobic ammonia oxidation (DAMO-anammox) can accomplish nitrogen removal and methane (CH4) reduction. This process greatly contributes to carbon emission mitigation and carbon neutrality. In this study, we investigated the electron transfer process of functional microorganisms in the iron-mediated DAMO-anammox system. Fe3+ could be bound to several functional groups (-CH3, COO-, -CH) in extracellular polymeric substance (EPS), and the functional groups bound were different at different iron concentration. Fe3+ underwent reduction reactions to produce Fe2+. Most Fe3+ and Fe2+ react with microorganisms and formed chelates with EPS. Three-dimensional fluorescence spectra showed that Fe3+ affected the secretion of tyrosine and tryptophan, which were essential for cytochrome synthesis. The presence of Fe3+ accelerated c-type cytochrome-mediated extracellular electron transfer (EET), and when more Fe3+ existed, the more cytochrome C expressed. DAMO archaea (M. nitroreducens) in the system exhibited a high positive correlation with the functional genes (resa and ccda) for cytochrome c synthesis. Some denitrifying microorganisms showed positive correlations with the abundance of riboflavin. This finding showed that riboflavin secreted by functional microorganisms acted as an electron shuttle. In addition, DAMO archaea were positively correlated with the hair synthesis gene pily1, which indicated that direct interspecies electron transfer (DIET) may exist in the iron-mediated DAMO-anammox system.

Strategies to attenuate ciprofloxacin inhibition on enhanced biological phosphorus removal from wastewater and its recoverability.

The inhibiting effects of ciprofloxacin (CIP) on enhanced biological phosphorus removal (EBPR) were investigated with no change in reactor operation and with increased aeration rate and sludge retention time (SRT) to explore inhibition-alleviating solutions. Additionally, performance recoverability was evaluated. The results showed that the phosphorus removal efficiency in the presence of 0.002-0.092 mg/L CIP for 7 days was only 12.5%. Increasing the aeration rate relieved inhibition (33.5% phosphorus removal efficiency on Day 7), and increasing SRT slowed EBPR performance deterioration. The EBPR performance recovered from CIP inhibition and increases in the aeration rate and SRT resulted in different recovery phenomena. The maximum PO43--P release rate continued to decrease in the first 2 days of the recovery stage and then gradually increased. However, the maximum PO43--P uptake rate immediately increased at different rates among reactors, which might be attributed to variations in the microbial community structure, decreased poly-P content, and enhanced abundances of ABC transporters and quorum sensing. It was found that some microorganisms associated with phosphorus removal were more tolerant to CIP than glycogen accumulating organisms. Moreover, the increased relative abundance of the qepA gene indicated that the microorganisms in the EBPR system had strong antibiotic resistance capacity. The bacterial community structure was significantly affected by CIP and could not recover to the initial structure. The results help to provide technical support for the operation of the EBPR process in the presence of CIP and to increase the understanding of system recoverability.

Machine learning-based model construction and identification of dominant factor for simultaneous sulfide and nitrate removal process.

Accurate water quality prediction models are essential for the successful implementation of the simultaneous sulfide and nitrate removal process (SSNR). Traditional models, such as regression and analysis of variance, do not provide accurate predictions due to the complexity of microbial metabolic pathways. In contrast, Back Propagation Neural Networks (BPNN) has emerged as superior tool for simulating wastewater treatment processes. In this study, a generalized BPNN model was developed to simulate and predict sulfide removal, nitrate removal, element sulfur production, and nitrogen gas production in SSNR. Remarkable results were obtained, indicating the strong predictive performance of the model and its superiority over traditional mathematical models for accurately predicting the effluent quality. Furthermore, this study also identified the crucial influencing factors for the process optimization and control. By incorporating artificial intelligence into wastewater treatment modeling, the study highlights the potential to significantly enhance the efficiency and effectiveness of meeting water quality standards.

Interaction between Cr(VI) and Tubificidae in sludge reduction system: effect, reduction, and redistribution of Cr(VI).

The treatment of heavy metals in sewage treatment systems has gained more attention with the increase in heavy metal hazards. Tubificidae in sludge reduction have been widely studied; however, little is known about the effect of Tubificidae in the treatment of Cr-containing wastewater. In this study, the mechanism of Tubificidae in the sludge reduction system with Cr stress was studied. Predation experiments by Tubificidae in a Cr-containing sludge reduction system were conducted to investigate the changes in enzyme activities in the Tubificidae under different concentrations of Cr, and the distribution of Cr in the sludge reduction reactor was analyzed. The kinetic model of uptake and elimination of Cr in Tubificidae was established. The results showed that the maximum activation multiplier factor of superoxide dismutase (SOD) activity was 1.95 under the low concentration of Cr(VI), which indicated that Tubificidae had a certain detoxification. After the effect of Tubificidae on Cr(VI) experiments, the Cr concentrations in Tubificidae, sludge, and feces increased first and then decreased with exposure time, and the proportion of total Cr and Cr(VI) in the sludge decreased from 71.98% and 42.7% to 29.18% and 6.82%, respectively. The detoxification mechanism of the Tubificidae could be activated with Cr stress, and 63.22% of the Cr(VI) was converted to Cr(III). The bioconcentration factor (BCF) for theoretical equilibrium was 446, the maximum bioaccumulation factor (BAF) reached 0.97 on the 15th day. It can be seen that Tubificidae could be considered a good scavenger of environmental Cr(VI). The hyperbolic model fits the process of Cr uptake and elimination well and can be used as a predictive tool for Tubificidae accumulation.

Production and characteristics of elemental sulfur during simultaneous nitrate and sulfide removal.

The production and characteristics of elemental sulfur were examined during simultaneous sulfide and nitrate removal, with abiotic assays as control. The biotic assay showed good sulfide and nitrate removal, with the respective removal percentage of which were 90.67-96.88% and 100%. Nitrate reduction resulted in the production of nitrogen gas, while sulfate formed due to sulfide oxidation. The concentration of elemental sulfur in the effluent was greater than that in the sludge, which accounted for 73.70-86.28% of total elemental sulfur produced. Furthermore, the elemental sulfur of the effluent and sludge from the biotic assays was orthorhombic crystal S8. Elemental sulfur was normally distributed in the effluent, but its average diameter increased with the increasing influent sulfide concentration (60-300 mg S/L), where the average diameter increased from 10 (60 mg S/L) to 29 µm (300 mg S/L).

The effect of sulfate on nitrite-denitrifying anaerobic methane oxidation (nitrite-DAMO) process.

Sulfate is generally found in natural water and wastewater. Nitrite-DAMO bacteria live in natural water or wastewater containing different sulfates. To determine the effect of sulfate on the nitrite-DAMO process, we conducted batch tests and continuous tests to investigate the performance and microbial structure of the nitrite-DAMO system at different sulfate concentrations. The results indicated that the nitrogen removal performance of the nitrite-DAMO system was initially promoted and then inhibited at 0-200 mg SO42-/L, and the denitrification rate was highest at 80 mg SO42-/L which was 1.26 mgN/(L·d). When stimulated by sulfate, protein stabilized nitrite-DAMO bacteria. The denitrification kinetics conformed to the Edward equation, and the initial inhibitory concentration of the nitrite-DAMO system was 189.70 mg SO42-/L. Changes in the proportion of unclassfied_c_ABY1 of the phylum Patescibacteria and norank_f_LD-RB-34 of the phylum Bacteroidetes were the main factors influencing how the nitrogen removal rate of the nitrite-DAMO system responded to sulfate.

Coupled substrate removal and electricity generation in microbial fuel cells simultaneously treating sulfide and nitrate at various influent sulfide to nitrate ratios.

The current work coupled simultaneous sulfide and nitrate removal in a Microbial Fuel Cell (MFC). The substrate removal and electricity generation were coupled at influent Sulfide to Nitrate molar ratios (S/N ratios) of 5:0, 5:1, 5:2 and 5:3. The sulfide concentrations used included: 60 mg S/L, 300 mg S/L, 540 mg S/L, 780 mg S/L and 1020 mg S/L. The effect of S/N ratio on the performance of substrate removal was greater at higher influent sulfide concentration. The electricity generation also varied at different influent sulfide concentrations and S/N ratios. The number of electrons generated at S/N ratio of 5:2 was the largest at any fixed influent sulfide concentration. The Pearson correlation showed that effluent sulfate concentration and nitrogen gas had significant positive correlations with steady state voltage (or electronic quantity). Moreover, the simulation models were developed to establish the relation between substrate removal and electricity generation at various S/N ratios.

The short- and long-term effects of nitrite on denitrifying anaerobic methane oxidation (DAMO) organisms.

The denitrifying anaerobic methane oxidation (DAMO) process can achieve methane oxidation and denitrification at the same time by using nitrate or nitrite as an electron acceptor. The short- and long-term effects of nitrite on DAMO organisms were studied from macro (such as denitrification) to micro (such as microbial structure and community) based on two types of DAMO microbial systems. The results showed that the inhibitory effects of nitrite on the two DAMO microbial systems increased with rising concentration and prolonged time. In the short-term inhibitory phase, nitrite with concentrations below 100 mg N L-1 did not inhibit the two distinct DAMO enrichments. When nitrite concentration was increased to 950 mg N L-1, the nitrogen removal performance was completely inhibited. However, in the long-term inhibition experiment, when nitrite concentration was increased to 650 mg N L-1, the nitrogen removal performance was completely inhibited. In addition, in acidic conditions, the real inhibitor of nitrite is FNA (free nitrous acid), while in alkaline conditions, the real inhibitor is the ionized form of nitrite. By using high-throughput sequencing technology, the species abundance and diversity of the two DAMO microbial systems showed an apparent decrease after long-term inhibition, and the community structure also changed significantly. For the enrichment culture dominated by DAMO bacteria, the substantial drop of Methylomonas may be the internal cause of the decreased nitrogen removal rate, and for the coexistence system that hosted both DAMO bacteria and archaea, the reduction of Nitrospirae may be an internal reason for the decline of the denitrification rate.

Long-term effect of low concentration Cr(VI) on P removal in granule-based enhanced biological phosphorus removal (EBPR) system.

In light of the fact that most wastewater in China contained both industrial and domestic wastewater, a 52-d systematical investigation was conducted on the long-term effect of low concentration Cr(VI) (0.3-0.8 mg L(-1)) on P removal performance of granule-based EBPR system in this study. The mechanisms were likewise discussed. Results showed that high Cr(VI) concentration (⩾0.5 mg L(-1)) could significantly inhibit P removal, while this phenomenon was not found when Cr(VI) concentration was less than (or equal to) 0.4 mg L(-1). Most of the granules was disintegrated and filamentous bacteria overgrew inducing sludge bulking occurred at 0.7 mg L(-1) Cr(VI). During the exposure test, the abundance of poly-phosphate-accumulating organisms (PAOs) significantly decreased while the populations of glycogen accumulating organisms (GAOs) and other bacteria increased. Both production and degradation of poly-ß-hydroxyakanoates (PHAs) were apparently inhibited. An improved polysaccharide/protein (PS/PN) ratio was observed with the increasing Cr(VI) concentration, implying excessive polysaccharide was secreted by microorganisms to support its resistance to the toxicity of Cr(VI). Besides, good linear regression between PS/PN ratio and the granule size (R(2)=-0.86, p<0.01) was obtained, indicating that high PS/PN was adverse to granule stability. Correlation analysis indicated that the accumulation of granules intracellular Cr was directly responsible for the observed inhibitory effect on P removal process. The long-term Cr(VI) treatment had irreversible effects on granule-based EBPR system as it could not revive after a 16-d recovery process.

[Physiological responses of tubificidae to heavy metal chromium stress].

Tubificidae is now used in the wastewater treatment systems to successfully minimize the sludge production, which has been proved an effective, economical and sustainable technology. But the excess sludge inevitably contains a variety of heavy metals, especially the sludge from industrial wastewater treatment plant. In order to apply tubificidae to these systems, Chromium was selected as pollutant object and the physiological responses of tubificidae to Chromium were studied in this paper. Acute toxicity was analyzed and Median lethal concentrations (LC50) were determined over 96 h periods for Cr. Results indicated that 24 h LC50 and 96 h LC50 were 7.94 mg x L(-1) and 0.49 mg x L(-1), respectively. The duration f tubificidae in Cr solution decreased with increasing Cr concentration. Under the Cr stress, a highest respiration rate was obtained when the concentration of Cr(VI), temperature, pH and DO was 2.50 mg x L(-1), 26 degrees C, 6.0 and 6.0 mg x L(-1), respectively. The order of these factors was the concerntration of Cr(VI), temperature, DO and pH. The respiration experiments demonstrated that low concentration (< 2.50 mg x L(-1)) of Cr could promote the respiration rate of tubificidaes. On the other hand, when the concentration of Cr was 8.00 mg x L(-1), it could remarkably inhibit the respiratory rates of tubificidae.

The effects of operational conditions on the respiration rate of Tubificidae.

Tubificidae is often used in the wastewater treatment systems to minimize the sludge production because it can be fed on the activated sludge. The process conditions have effect on the growth, reproduction, and sludge reduction efficiency of Tubificidae. The effects of the water quality, density of worms, pH, temperature and dissolved oxygen (DO) concentration on the respiration rate of Tubificidae were investigated to determine the optimal conditions for the growth and metabolism of the worms and reveal the mechanisms involving the efficient sludge reduction in terms of these conditions. It was observed that the respiration rate was highest in the water discharged from an ecosystem that included symbiotic Tubificidae and microbes and was lowest in distilled water. Considering density of the worms, the highest rate was 81.72±5.12 mg O2/g(dry weight)·h·L with 0.25 g (wet weight) of worms in 1 L test flask. The maximum Tubificidae respiration rate was observed at a pH of 8.0±0.05, a rate that was more than twice as high as those observed at other pH values. The respiration rate increased in the temperature range of ∼8°C-22°C, whereas the rate declined in the temperature range of ∼22°C-30°C. The respiration rate of Tubificidae was very high for DO range of ∼3.5-4.5 mg/L, and the rates were relatively low for out of this DO range. The results of this study revealed the process conditions which influenced the growth, and reproduction of Tubificidae and sludge reduction at a microscopic level, which could be a theoretical basis for the cultivation and application of Tubificidae in wastewater treatment plants.

Inhibition of free ammonia to the granule-based enhanced biological phosphorus removal system and the recoverability.

The inhibition of free ammonia (FA) to the granule-based enhanced biological phosphorus removal (EBPR) system and the recoverability from macro- to micro-scale were investigated in this study. FA was found to seriously deteriorate the EBPR performance and sludge characteristic (settleability and morphology). The FA inhibitory threshold of 17.76 mg NL(-1) was established. Acclimation phenomenon took place when poly-phosphate accumulating organisms (PAOs) were exposed for long time to constant FA concentration (8.88 mg NL(-1)). The repressed polysaccharides excretion could lead to breaking the stability and integrity of the granules. Therefore, the reduced particle size and granule disintegration were observed. The molecular analysis revealed that FA had a significant influence on the microbial communities and FA inhibition may provide a competitive advantage to glycogen accumulating organisms (GAOs) over PAOs. Interestingly, the community composition was found irreversible by recovery (Dice coefficients, 36.3%), although good EBPR performance was re-achieved.

Nitrogen removal from wastewater by coupling anammox and methane-dependent denitrification in a membrane biofilm reactor.

This work demonstrates, for the first time, the feasibility of nitrogen removal by using the synergy of anammox and denitrifying anaerobic methane oxidation (DAMO) microorganisms in a membrane biofilm reactor (MBfR). The reactor was fed with synthetic wastewater containing nitrate and ammonium. Methane was delivered from the interior of hollow fibres in the MBfR to the biofilm that grew on the fiber's outer wall. After 24 months of operation, the system achieved a nitrate and an ammonium removal rate of about 190 mgN L(-1) d(-1) (or 86 mgN m(-2) d(-1), with m(2) referring to biofilm surface area) and 60 mgN L(-1) d(-1) (27 mgN m(-2) d(-1)), respectively. No nitrite accumulation was observed. Fluorescence in situ hybridization (FISH) analysis indicated that DAMO bacteria (20-30%), DAMO archaea (20-30%) and anammox bacteria (20-30%) jointly dominated the microbial community. Based on the known metabolism of these microorganisms, mass balance, and isotope studies, we hypothesize that DAMO archaea converted nitrate, both externally fed and produced by anammox, to nitrite, with methane as the electron donor. Anammox and DAMO bacteria jointly removed the nitrite produced, with ammonium and methane as the electron donor, respectively. The process could potentially be used for anaerobic nitrogen removal from wastewater streams containing ammonium and nitrate/nitrite.

[Effect of simulated heavy metal leaching solution of electroplating sludge on the bioactivity of Acidithiobacillus ferrooxidans].

An Acidithiobacillus ferrooxidans strain WZ-1 was isolated from the tannery sludge in Wenzhou, Zhejiang Province in China. The cell of WZ-1 strain is Gram negative and rod-shaped, its 16S rDNA sequence is closely related to that of Acidithiobacillus ferrooxidans ATCC23270 with 99% similarity. These results reveal that WZ-1 is a strain of Acidithiobacillus ferrooxidans. The effects of Ni2+, Cr3+, Cu2+, Zn2+ and 5 kinds of simulated leaching solutions of electroplating sludge on the bioactivity of Fe2+ oxidation and apparent respiratory rate of WZ-1 were investigated. The results showed that Ni2+ and Cr3+ did not have any influence on the bioactivity of WZ-1 at concentrations of 5.0 g x L(-1) and 0.1 g x L(-1), respectively. WZ-1 showed tolerance to high levels of Ni2+, Zn2+ (about 30.0 g x L(-1)), but it had lower tolerance to Cr3+ and Cu2+ (0.1 g x L(-1) Cr3+ and 2.5 g x L(-1) Cu2+). Different kinds of simulated leaching solution of electroplating sludge had significant differences in terms of their effects on the bioactivity of WZ-1 with a sequence of Cu/Ni/Cr/Zn > Cu/Ni/Zn > Cu/Cr/Zn > Cu/Ni/Cr > Ni/Cr/Zn.

The long-term effect of nitrite on the granule-based enhanced biological phosphorus removal system and the reversibility.

This study investigated the long-term effect of nitrite on the granule-based enhanced biological phosphorus removal (EBPR) system and the reversibility from macro- to micro-scale. Nitrite was found to seriously deteriorate the EBPR performance and result in severe sludge bulking. The inhibited polysaccharides excretion could lead to breaking the stability and integrity of the granules. Therefore, the reduced particle size and granule disintegration were observed. In this study, granules with lower ratio of proteins to polysaccharides (1.76) had better structure and function than the higher (3.84). Experimental results demonstrated that the microbial community structure was largely changed due to the presence of nitrite. In comparison, glycogen accumulating organisms (GAOs) had stronger resistibility and higher recovery rate than poly-phosphate accumulating organisms (PAOs). Interestingly, the community composition was unable to recover (Dice coefficients, 33.0%), although good EBPR performance was achieved only by propagating other types of PAOs.

Impact of Cr(VI) on P removal performance in enhanced biological phosphorus removal (EBPR) system based on the anaerobic and aerobic metabolism.

Influence of Cr(VI) on P removal in enhanced biological phosphorus removal (EBPR) system was investigated with respect to the composition of poly-phosphate-accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), the transformation of poly-ß-hydroxyalkanoates (PHA) and glycogen, enzymes' activities, and the intracellular Cr. Whether EBPR system could revive after Cr(VI) shock was also explored. Results showed P removal performance was completely inhibited by Cr(VI) with the concentration more than 5 mg L(-1). PAOs were more sensitive to Cr(VI) than GAOs and the other bacteria were. PHA consumption, glycogen synthesis and adenylate kinase's activity had been inhibited by 5 mg L(-1) Cr(VI). Both adenylate kinase's activity and P removal efficiency were negatively correlated with the intracellular Cr. Recovery experiments revealed that P removal performance with 5 mg L(-1) Cr(VI) shock could revive after a 2-day recovery treatment, while systems with high level Cr(VI) (20 and 60 mg L(-1)) shock could not.

Simultaneous sludge reduction and nutrient removal (SSRNR) with interaction between Tubificidae and microorganisms: a full-scale study.

A symbiotic ecosystem between Tubificidae and microorganisms was established at a full-scale wastewater treatment plant (WWTP). In this ecosystem Tubificidae were inoculated, and then adhered to the outer layers of carrier materials in an oxidation tank. During the long-term treatment of sewage volumes of 20,000 m(3)d(-1), the excess sludge production rate was reduced from 0.21 to 0.051 kg m(-3) and sludge settleability was significantly improved. When the influent concentrations of COD, NH(4)(+)-N, PO(4)(-)-P, and SS were in the ranges of 130.0-459.0 mg L(-1), 14.2-27.5 mg L(-1), 1.6-7.0 mg L(-1), and 60.0-466.0 mg L(-1), respectively, the COD and SS removal efficiency was increased by 8.7% and 13.6% within the symbiotic system compared to the control without Tubificidae. In addition, NH(4)(+)-N and phosphorus removal efficiency can also be improved. The results showed that both sludge reduction and nutrient removal were enhanced simultaneously significantly within the system utilizing the symbiotic interactions of Tubificidae and microorganisms.

[Full-scale experiments of municipal sewage treated by symbiotic system consisting of tubifex and microbes].

A symbiotic system consisting of tubifex and microbe was formed when tubifex was incubated in the biological contact oxidation process,the tubifex attached to the outer layer of the carriers. When the density of tubifex was about 31.3 g/L, a recycling food chain between corpse of tubifex and excrement and wastewater and microbe and sludge was formed and it could reach balance. The large scale control experimental system for treating 20,000 m3 x d(-1) municipal sewage was carried out for a long time. The result showed that tubifex could improve water quality in the effluent. When the concentration in the influent of COD,NH4+ -N,TP and SS were 130-459, 14.21-27.46, 1.60-6.93, 60-466 mg x L(-1), respectively,the removal rates of COD and SS can be improved by 8.7% and 13.6%. However, tubifex can also increase the concentration of NH4+ -N in the system,but a proper operation can make the effluent concentration of NH4+ -N below 5 mg x L(-1) stably. The symbiotic system consisting of tubifex and microbe has very good phosphorus removal efficiency. The reactor has a high toleration to loading shock and it could keep the effluent quality stable.