Surfactant-assisted thermal hydrolysis off waste activated sludge for improved dewaterability, organic release, and volatile fatty acid production.

The surfactant-assisted thermal hydrolysis pretreatment (THP) of waste activated sludge (WAS) was investigated, focusing on the effect of the surfactant addition on the results of sludge disintegration, dewaterability, organic release, and production of volatile fatty acids (VFAs) via fermentation. Typical anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyl trimethyl ammonium bromide (CTAB) were used for the THP experiments. The supernatant of the THP-treated sludge was anaerobically fermented to determine its potential VFAs yield. The results showed that the surfactant addition, particularly CTAB, enhanced the hydrolysis and organic solubilization of the sludge during THP. CTAB addition led to a 36% increase of dissolved organic and a 27% increase of VFAs production. For the THP-treated sludge with the surfactant addition, its dewaterability was also greatly improved. When the CTAB dosage increased from 0 to 0.10 g/g VSS, the minimum capillary suction time (CST) of the sludge decreased from 205 to 50 s/g TSS, and the sludge particles became smaller and less negative with the zeta potential changing from -12.4 to -8.2 mV. Analysis of extracellular polymeric substances (EPS) of the sludge revealed that the surfactant addition increased the sludge disintegration and organic dissolution during the THP process. The surfactant-assisted THP is shown to be a promising technology to enhance the WAS treatment for improved sludge dewaterability, waste reduction, and resource recovery.

Stable nitrogen removal by anammox process after rapid temperature drops: Insights from metagenomics and metaproteomics.

This study investigated the impacts of rapid temperature drops on anammox process performance and the metabolism of its core microbial populations through proteomic analysis. Over a 50-day period, the temperature of an up-flow granular bed anammox reactor was stepwise decreased from 35 °C to 15 °C and resulted in repeated transient increases in effluent nitrite concentrations. At 15 °C, a nitrogen removal rate of 2.71 ± 0.23 gN/(L·d) was maintained over 100 days operation. Total AnAOB population abundance (20.9%±4.9%) and AnAOB protein abundances (75.7% ± 3.3%) remained stable with decreased temperature. Key proteins of Ca. Brocadia for nitrogen metabolism, as well as for carbohydrate metabolism and primary metabolite biosynthesis were less expressed at 15 °C than 35 °C, while several proteins of heterotrophic Chloroflexi spp. involved in carbohydrate and metabolites metabolisms were expressed to a higher degree at 15 °C. Overall, metabolism of AnAOB responded at a higher degree to low temperatures than that of heterotrophs.

Two-stage anaerobic digestion of food waste coupled with in situ ammonia recovery using gas membrane absorption: Performance and microbial community.

A two-stage GAs Membrane Absorption anaerobic Reactor (GAMAR) was developed by combining the gas membrane absorption (GMA) system with two-stage anaerobic digestion. The two-stage configuration consisted of an acidogenic reactor (AR) and a methanogenic reactor (MR) with GMA. With the application of GMA, the ammonia concentration of MR was maintained at 2200 mgN L-1 to alleviate potential ammonia inhibition. The setup of AR enhanced hydrolysis and acidogenesis of FW and alleviated volatile fatty acids (VFA) accumulation in MR. Two-stage GAMAR could be operated stably at 6.1 kg VS m-3 d-1 and the volumetric biogas production rate was 3.21 m3 m-3 d-1. The different environmental conditions caused a significant shift in the microbial community. Lactobacillus and Aeriscardovia became predominant in AR under low pH, while Syntrophomonas was dominant in MR when the reactor was stable. The dominant archaea genus in MR was Methanothrix and it greatly decreased when MR was acidified.

Enhanced biogas production and in situ ammonia recovery from food waste using a gas-membrane absorption anaerobic reactor.

A novel GAs-Membrane Absorption anaerobic Reactor (GAMAR) was developed by combining gas-membrane absorption system with anaerobic digestion. A gas-permeable expanded polytetrafluoroethylene (ePTFE) membrane was submerged in the anaerobic reactor. Free ammonia could transfer through the gas-permeable membrane and be recovered by acidic solution. The free ammonia concentration was lower than 40 mgN L-1 in GAMAR, which alleviated ammonia inhibition. Meanwhile free ammonia concentration up 70 mgN L-1 in the reference reactor inhibited methanogens and led to unstable operation. The volumetric biogas production rate of GAMAR was 2.83 m3 m-3 d-1, and 58% higher than the reference reactor. Long term use of membrane led to membrane fouling and hydrophobicity loss. The contact angle of membrane decreased from 105.9 ±â€¯1.2° to 97.6 ±â€¯6.3° after 43 d. The abundance of methanogens in GAMAR was 1.8-2.1 times higher than that in the reference reactor, which was in accordance with the higher biogas production rate in GAMAR.

Genomic dynamics of full-scale temperature-phased anaerobic digestion treating waste activated sludge: Focusing on temperature differentiation.

A robust microbial community is essential for the overall stability and performance of the anaerobic digestion process. In this study, two digesters of a full-scale temperature-phased anaerobic digestion plant treating waste activated sludge were sampled for one year. The acidogenesis reactor (AR) was run at 45 ±â€¯2 °C for six months in Period I and was run at 38 ±â€¯2 °C for six months in Period II. While the methanogenesis reactor (MR) was run at 36 ±â€¯3 °C throughout the year. 16S rRNA amplicon sequencing and GeoChip 5.0 results showed that samples were clearly differentiated by reactors and periods. The elevated temperature in AR during Period I improved the effects of phase separation between the AR and MR. In AR, Fervidobacterium, assigned to Class Thermotogae, had a higher relative abundance of 8.9% in Period I. The abundance of genes involved with carbon degradation was significantly higher in Period I than Period II. In MR, the relative abundance of Methanosarcina increased from 19.8% in Period I to 30.6% in Period II. In addition, the influent characteristics, reactor performance, and operating parameters were determined as the key variables shaping the microbial community, contributing to a total of 76.3% and 69.5% of the variance of the AR and MR, respectively. Combined, this study enriches our understanding of genomic dynamics in full scale temperature-phased anaerobic digestion process.

High variations of methanogenic microorganisms drive full-scale anaerobic digestion process.

Anaerobic digestion is one of the most successful waste management strategies worldwide, wherein microorganisms play an essential role in reducing organic pollutants and producing renewable energy. However, variations of microbial community in full-scale anaerobic digesters, particularly functional groups relevant to biogas production, remain elusive. Here, we examined microbial community in a year-long monthly time series of 3 full-scale anaerobic digesters. We observed substantial diversification in community composition, with only a few abundant OTUs (e.g. Clostridiales, Anaerolineaceae and Methanosaeta) persistently present across different samples. Similarly, there were high variations in relative abundance of methanogenic archaea and methanogenic genes, which were positively correlated (r2 = 0.530, P < 0.001). Variations of methanogens explained 55.7% of biogas producing rates, much higher than the explanatory percentage of environmental parameters (16.4%). Hydrogenotrophic methanogens, especially abundant Methanomicrobiales taxa, were correlated with biogas production performance (r = 0.665, P < 0.001) and nearly all methanogenic genes (0.430 < r < 0.735, P < 0.012). Given that methanogenic archaea or genes are well established for methanogenesis, we conclude that high variations in methanogenic traits (e.g. taxa or genes) are responsible for biogas production variations in full-scale anaerobic digesters.

Realizing stable operation of anaerobic ammonia oxidation at low temperatures treating low strength synthetic wastewater.

The low activity of Anammox bacteria at low temperatures and competition from nitrite oxidation bacteria (NOB) when treating low strength wastewater have been major bottlenecks in implementing Anammox in mainstream wastewater treatment. By intermittent high strength feeding (IHSF) and stepwise temperature reduction, stable operation of a granular Anammox reactor was realized at low temperatures (down to 15°C) for 28days when treating low strength synthetic wastewater. The nitrogen loading rate reached 1.23-1.34kgN/m3/day, and the total nitrogen removal rate reached 0.71-0.98kgN/m3/day. The IHSF enriched the Anammox sludge in high strength cycles and compensated for sludge loss in low strength cycles, and the high concentration of ammonium in high strength cycles inhibited NOB. The 16SrRNA gene sequencing results revealed that Candidatus Kuenenia was predominant in the reactor at low temperatures.

Quantification of multi-antibiotic resistant opportunistic pathogenic bacteria in bioaerosols in and around a pharmaceutical wastewater treatment plant.

Pharmaceutical wastewater treatment plants (WWTPs) are thought to be a "seedbed" and reservoirs for multi-antibiotic resistant pathogenic bacteria which can be transmitted to the air environment through aeration. We quantified airborne multi-antibiotic resistance in a full-scale plant to treat antibiotics-producing wastewater by collecting bioaerosol samples from December 2014 to July 2015. Gram-negative opportunistic pathogenic bacteria (GNOPB) were isolated, and antibiotic susceptibility tests against 18 commonly used antibiotics, including 11 ß-lactam antibiotics, 3 aminoglycosides, 2 fluoroquinolones, 1 furan and 1 sulfonamide, were conducted. More than 45% of airborne bacteria isolated from the pharmaceutical WWTP were resistant to three or more antibiotics, and some opportunistic pathogenic strains were resistant to 16 antibiotics, whereas 45.3% and 50.3% of the strains isolated from residential community and municipal WWTP showed resistance to three or more antibiotics. The calculation of the multiple antibiotic resistance (MAR) index demonstrated that the air environment in the pharmaceutical WWTP was highly impacted by antibiotic resistance, while the residential community and municipal WWTP was less impacted by antibiotic resistance. In addition, we determined that the dominant genera of opportunistic pathogenic bacteria isolated from all bioaerosol samples were Acinetobacter, Alcaligenes, Citrobacter, Enterobacter, Escherichia, Klebsiella, Pantoea, Pseudomonas and Sphingomonas. Collectively, these results indicate the proliferations and spread of antibiotic resistance through bioaerosols in WWTP treating cephalosporin-producing wastewater, which imposed a potential health risk for the staff and residents in the neighborhood, calling for administrative measures to minimize the air-transmission hazard.

Evaluation of antibiotic resistant lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria and blaTEM-2 gene in cephalosporin wastewater and its discharge receiving river.

This study investigated the concentration of cephalosporin, the resistant levels of lactose fermentative opportunistic pathogenic Enterobacteriaceae bacteria (LFOPEB) against seven antibiotics and one cephalosporin-resistant gene in cephalosporin wastewater (CPWW) treatment plant and its discharge receiving river. Although large numbers of bacteria have been removed during the CPWW treatment process, the antibiotic resistant rates of the isolates to ß-lactam antibiotics significantly increased (p = 0.032) after treatment, while the percentage of resistant LFOPEB to non-ß-lactam antibiotics did not change dramatically. Furthermore, the discharge of the effluent of CPWW treatment plant (CPWWeff) led to an obvious increase in the percentages of ß-lactam antibiotic-resistant LFOPEB and relative abundance of the blaTEM-2 gene in the downstream receiving river (RWdown) in comparison with those in the upstream receiving river (RWup). The antibiotic resistant phenotypes of isolates in the influent of CPWW treatment plant (CPWWin), CPWWeff and RWdown appeared to be seriously affected by the cephalosporin residues, which suggested that main antibiotic resistance phenotypes in antibiotic contaminated water were closely associated with its antibiotic composition. Therefore, CPWW treatment process has been proved to result in selective growth of ARB and proliferation of ARG. Besides, CPWWeff was also proved to be an important supplier of ARB and ARG to the receiving river.

Inhibition by free nitrous acid (FNA) and the electron competition of nitrite in nitrous oxide (N2O) reduction during hydrogenotrophic denitrification.

Hydrogenotrophic denitrification is a promising technology for nitrate removal from organic-deficient wastewater or groundwater, and the attention of nitrous oxide (N2O) emission during this process is required. Both nitrite and free nitrous acid (FNA or HNO2) were reported to exert significant effects on N2O reduction in heterotrophic denitrification, whereas, little knowledge has been obtained in hydrogenotrophic denitrification. In this study, we conducted a series of batch tests to comprehensively investigate the effects of nitrite, pH and FNA on N2O production and reduction in a hydrogenotrophic denitrification process. The results showed that N2O reduction rate decreased under both conditions of low pH and presence of nitrite, which would exert synergetic inhibition on N2O reduction. The potential mechanisms that give rise to the results included electron competition and FNA inhibition. Electron competition between nitrite and N2O reductases occurred when both nitrite and N2O were added, which might contribute to the decrease in the N2O reduction rate. The electron supply, which was obtained from the uptake of molecular hydrogen, declined with increasing FNA concentration according to a logarithmic model (R2 = 0.9240). Additionally, the electron consumption rate of N2O reductase to nitrite reductase ratio was initially stable and then decreased with increasing FNA concentration. The inhibition of N2O reduction by FNA was determined to be reversible. The study suggested that both of the electron supply and N2O reduction in hydrogenotrophic denitrification could be inhibited by FNA.

A comparative study of thermophilic and mesophilic anaerobic co-digestion of food waste and wheat straw: Process stability and microbial community structure shifts.

Renewable energy recovery from organic solid waste via anaerobic digestion is a promising way to provide sustainable energy supply and eliminate environmental pollution. However, poor efficiency and operational problems hinder its wide application of anaerobic digestion. The effects of two key parameters, i.e. temperature and substrate characteristics on process stability and microbial community structure were studied using two lab-scale anaerobic reactors under thermophilic and mesophilic conditions. Both the reactors were fed with food waste (FW) and wheat straw (WS). The organic loading rates (OLRs) were maintained at a constant level of 3 kg VS/(m3·d). Five different FW:WS substrate ratios were utilized in different operational phases. The synergetic effects of co-digestion improved the stability and performance of the reactors. When FW was mono-digested, both reactors were unstable. The mesophilic reactor eventually failed due to volatile fatty acid accumulation. The thermophilic reactor had better performance compared to mesophilic one. The biogas production rate of the thermophilic reactor was 4.9-14.8% higher than that of mesophilic reactor throughout the experiment. The shifts in microbial community structures throughout the experiment in both thermophilic and mesophilic reactors were investigated. With increasing FW proportions, bacteria belonging to the phylum Thermotogae became predominant in the thermophilic reactor, while the phylum Bacteroidetes was predominant in the mesophilic reactor. The genus Methanosarcina was the predominant methanogen in the thermophilic reactor, while the genus Methanothrix remained predominant in the mesophilic reactor. The methanogenesis pathway shifted from acetoclastic to hydrogenotrophic when the mesophilic reactor experienced perturbations. Moreover, the population of lignocellulose-degrading microorganisms in the thermophilic reactor was higher than those in mesophilic reactor, which explained the better performance of the thermophilic reactor.

Evaluation of disinfection by-products (DBPs) formation potential in ANAMMOX effluents.

Disinfection by-products (DBPs), major health concerns in the potable reuse of municipal wastewater effluent, are process-related in wastewater treatment systems. Anammox is a promising and increasingly-applied technology for nitrogen removal in wastewater. In this study, the relationship between DBP formation potential and the anammox process has been investigated based on a lab-scale sequencing batch reactor (SBR). Excitation and emission matrix (EEM) fluorescence spectroscopy was employed to identify the compositions of the DBP precursors. The results showed that the effluents from the anammox SBR could yield both carbonaceous and nitrogenous DBPs after chlorination. Trichloromethane (TCM) was the dominant product among all DBPs detected. The anammox effluent has a low specific TCM formation potential of 0.778 µmol/mmol C and a trichloronitromethane (TCNM) formation potential of 0.0725 µmol/mmol C, leading to a TCM and TCNM formation potential ratio of 10.7. We found that substrate utilization of anammox did not enhance DBP yields, and the DBP formation potential decreased after 10 hour starvation. High pH conditions stimulated the production of TCM precursors in the anammox reactor. Humic acid-like and protein-like substances were identified in the EEM spectra of anammox effluents.

Effects of free ammonia on volatile fatty acid accumulation and process performance in the anaerobic digestion of two typical bio-wastes.

The effect of free ammonia on volatile fatty acid (VFA) accumulation and process instability was studied using a lab-scale anaerobic digester fed by two typical bio-wastes: fruit and vegetable waste (FVW) and food waste (FW) at 35°C with an organic loading rate (OLR) of 3.0kg VS/(m3·day). The inhibitory effects of free ammonia on methanogenesis were observed due to the low C/N ratio of each substrate (15.6 and 17.2, respectively). A high concentration of free ammonia inhibited methanogenesis resulting in the accumulation of VFAs and a low methane yield. In the inhibited state, acetate accumulated more quickly than propionate and was the main type of accumulated VFA. The co-accumulation of ammonia and VFAs led to an "inhibited steady state" and the ammonia was the main inhibitory substance that triggered the process perturbation. By statistical significance test and VFA fluctuation ratio analysis, the free ammonia inhibition threshold was identified as 45mg/L. Moreover, propionate, iso-butyrate and valerate were determined to be the three most sensitive VFA parameters that were subject to ammonia inhibition.

[Mesophilic and Thermophilic Anaerobic Co-Digestion of Food Waste and Straw].

The anaerobic co-digestion of food waste and straw is more efficient in avoiding the accumulation of volatile fatty acids and promoting the degradation of lignocellulose in comparison with their individual digestions. The co-digestion of food waste and straw was investigated under mesophilic(35℃) and thermophilic(55℃) condition, respectively. The results indicated that when feeding volatile solid concentration was 3 kg·m-3, the accumulated methane production yield of the mesophilic reactor reached the peak of 272.0 mL·g-1 at a food waste-to-straw ratio of 9:1, while it reached the peak of 402.3 mL·g-1 at a food waste-to-straw ratio of 5:5 for thermophilic reactor. These amounts were significantly higher than those of food waste digestion alone(218.6 mL·g-1 for mesophilic reactor and 322.0 mL·g-1 for thermophilic reactor). Co-digestion promoted the rate of carbon transfer to methane, and further, the rate of the thermophilic reactor was higher than that of the mesophilic reactor. Degradation rate for lignocellulose of thermophilic reactor was 34.7%-45.8%, higher than that of mesophilic reactor, 12.6%-42.2%. It was confirmed by 16S rRNA gene sequences of bacteria and archaea, ITS sequences of fungi based on high-throughput sequencing techniques, which showed the amounts of lignocellulose degrading bacteria and actinomycetes in the thermophilic reactor were both higher than those in the mesophilic reactor.