Municipal Sewage Treatment Research Articles

Sorption of Co2+, Zn2+, Cd2+ and Cs+ ions by activated sludge of sewage treatment plant

Sludges are byproducts of sewage treatment process. Land application of sewage sludge is one of the final steps of waste water treatment, but solubilization of toxic metals restricts this method of sludge disposal. In our paper cobalt, zinc, cadmium and cesium sorption by suspension of non-treated activated sewage sludge (14 g/dm3, dry wt.) from waste water spiked with 60CoCl2, 65ZnCl2, 109CdCl2 or 137CsCl were determined in laboratory experiments at 20°C. Activated sludge supplied by the municipal sewage treatment plant in Zeleneč (Trnava region, Slovakia) showed high efficiency to sorb Co2+, Zn2+, Cd2+ and Cs+ ions from waste water pH 6-7. The process can be characterized by the concentration equilibrium (Csolid/Cliquid) typical for sorption processes. Efficiency of the sorption increased in the order Cs < Co < Zn < Cd. Metal sorption process was not inhibited by pretreatment of the sludge with 0.2% formaldehyde or thermal inactivation at 60°C, what confirms that the process was not dependent on metabolic activity of the sludge. Cobalt, zinc, cadmium and cesium were easily removable from the
 sludge by washing with diluted HCl, EDTA or water solutions of the corresponding metal ions, but with low efficiency by deionized water.

An innovative biofilter technology for reducing environmental spreading of emerging pollutants and odour emissions during municipal sewage treatment

Wastewater treatment plants (WWTPs) are known sources of contaminants of emerging concern (CECs) spreading into the environment, as well as, of unpleasant odors. CECs represent a potential hazard for human health and the environment being pharmaceutical or biologically active compounds and they are acquiring relevance in European directives. Similarly, the public concern about odour emissions from WWTPs is also increasing due to the decreasing distance between WWTP and residential areas. This study focuses on the effectiveness of the recently developed MULESL technology (MUch LEss SLudge; WO2019097463) in removing CECs and limiting odour emissions from WWTPs. MULESL technology has been developed for its ability to reduce up to 80% the sludge production from WWTPs. However, it is ought to evaluate if the benefits coming from sludge production reduction do not invalidate CECs removal or negatively affect odour emissions. Thus, the performances of a MULESL and a conventional WWTP (flow rate of 375 m3/d and 3600 m3/d, respectively) were compared while treating the same municipal sewage.Whereas both plants succeeded in removing the traditional gross parameters characterizing wastewaters (e.g. chemical oxygen demand, nitrogen), the MULESL was much more effective than the conventional one in terms of CECs removal for about 60% of the identified compounds showing, however, the same or lower effectiveness for about 30% and 10% of them, respectively. This result was attributed to the high sludge retention time and biomass concentration in the MULESL (enabling enrichment of slow growing microorganisms and forcing biomass to use unusual substrates, respectively), and to the biomass feature to grow in the form of biofilm and granules (favoring micropollutants absorption on biomass).Furthermore, odour impact analysis has shown that the MULESL was characterized by a much lower impact, i.e. 45% lower than that of primary and secondary treatments of the conventional WWTP.

Simultaneous partial nitritation, anammox, and denitrification process for the treatment of simulated municipal sewage in a single-stage biofilter reactor

This study provides a feasible scheme for the treatment of municipal sewage through simultaneous partial nitritation, anammox, and denitrification (SNAD) process, which was realized in a single-stage biofilter reactor (BFR). First, the BFR was started up to enrich the anaerobic ammonium-oxidizing bacteria (AnAOB) in the upper part of the reactor through the operation mode of the top influent and bottom effluent. Then, the BFR was inoculated with activated sludge and aerated continuously at the bottom to realize the coupling of SNAD, which was accompanied by a two-point influent from the bottom and top effluent. Results indicated that the high removal efficiency of NH4+-N (93.40%), total nitrogen (TN, 89.95%), and soluble chemical oxygen demand (SCOD, 92.68%) were achieved with an air–water ratio of 4.29 and hydraulic retention time (HRT) of 6 h. During the SNAD steady phase for the treatment of simulated municipal sewage with a soluble chemical organic demand to nitrogen (C/N) ratio of 2.31, low concentrations of NH4+-N (4.13 mg/L), TN (6.44 mg/L), and SCOD (11.29 mg/L) were attained in the effluent. High-throughput sequencing analysis indicated that the relative abundance of Nitrosomonas, Candidatus Brocadia, and Denitratisoma were 0.77%, 0.43%, and 4.07% in the biofilm at the 0–12.5 cm zone, respectively, suggesting successful implementation of the SNAD process.

Reuse of Sintered Sludge from Municipal Sewage Treatment Plants for the Production of Lightweight Aggregate Building Mortar

In recent years, the sludge produced by municipal sewage treatment plants has become an important recyclable resource for producing green building materials. After the systematic processing of incineration and particle formation, the sintered sludge can be processed into fine lightweight aggregate to produce building mortar with the controlled leaching of heavy metals and radioactivity. In this paper, to increase its economic and environmental benefits, mortar with sintered sludge aggregate was made by cement admixing of fly ash or limestone powder. The water-to-binder ratio was set at three levels—0.82, 0.68, and 0.62—and either flay ash or limestone powder was used to replace equal masses of cement at 10%, 20%, or 30%. Eighteen groups of mortar were studied to evaluate their workability, air content, compressive strength, tensile adhesive strength, dry density, and thermal conductivity. The results indicate that with a proper water-to-binder ratio, and the replacement ratio of fly ash or limestone powder, the mortar can be produced with good workability, consistency, water-retention rate, layering degree, and setting time. The mortar made with sintered sludge lightweight aggregate, designated by the mix-proportion method for conventional lightweight aggregate mortar, did not meet the target strength, although the compressive strength of mortar was no less than 3.0 MPa, which meets the strength grade M2.5. The tensile adhesive strength reached 0.18 MPa. The mortar was super lightweight with a dry density less than 400 kg/m3, and a thermal conductivity within 0.30~0.32 W/(m⋅K). The effects of water-to-binder ratio and replacement ratio of fly ash or limestone powder on the above properties are discussed with test results. The study provides a basis for using sintered sludge lightweight aggregate for building mortar.

A Technoeconomic Approach to Solid Waste Disposal and Handling in Dakhlia Governorate. (Dept. P)

Due to the rapid increase of population in rural areas, specifically in Dakhlia Governorate, and the limited dwelling areas, the solid waste emanating either from stables, large animal stocks or agricultural waste causes hygienic problems, air pollution, water pollution, effects on the ecological balance and greater risk of dangerous fire. Anaerobic digestion is considered as one of the new trends in solid waste disposal. The anaerobic fermentation processes employed in/or by : 1- Industrial and municipal sewage treatment facilities. 2- Agricultural and animal biogas systems. 3- Garbage dumps/landfills. For industrial and municipal waste water treatment plants the prime objective is to stabilize the sludge and exploit the biogas as an energy carrier for fueling the thermal process. The anaerobic treatment of liquid manure from intensive livestock units should be carried out for the following reasons : (1) Breakdown of smells. (2) Production of biogas. (3) Improvement of fertilizer properties. For sanitary landfills/dump sites, utilization of anaerobic treatment permits the collection of the inevitably produced biogas in a beneficial form. The objective of this paper is to introduce the framework of the feasibility study for the evaluation of the biogas, produced from biofermentation of agricultural and animal waste and sewage sludge either for electricity generation or direct combustion. Also, the sludge produced from biofermentation would be evaluated as fertilizer or fodder additives as compared to its use in the raw form.

Pilot study on the treatment of low carbon and nitrogen ratio municipal sewage by A1/O2/A3/A4/O5 sludge-membrane coupling process with multi-point inflow.

A new multi-point inflow pre-anoxic/oxic/anaerobic/anoxic/oxic (A1/O2/A3/A4/O5) sludge-membrane coupling process and pilot plant were developed and designed to solve the problem of nitrogen and phosphorus removal of low carbon and nitrogen (C/N) ratio domestic sewage in southern China. The removal effect and transformation rule of organic matter, nitrogen, and phosphorus in the system were studied by changing the distribution ratio of multi-point influent. The average C/N ratio of the influent was 2.09 and the influent distribution ratio was 1:1. When the temperature was 16-25 °C, the average concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH4+- N), total nitrogen (TN), and total phosphorus (TP) in the effluent were 21.31 (±2.65), 0.60 (±0.24), 12.76 (±1.09), and 0.34 (±0.05) mg/L, respectively, and their average removals are 87.3 (±1.2)%, 98.7 (±0.4)%, 74.1 (±1.3)%, and 88.1 (±0.4)% respectively. When the low temperature was 12-15 °C, the average removals were 78.6 (±1.1)%, 90.5 (±1.3)%, 73.7 (±1.13)%, and 86.6 (±1.7)%, respectively. Compared with the traditional anaerobic/anoxic/aerobic (A2O) process under the same conditions, the TN removal was increased by 15.4%, and the TP removal was increased by 22.2%. This system has obvious advantages in treating wastewater with low C/N ratio, thereby solving the problem wherein the effluent of biological phosphorus removal from low C/N ratio domestic sewage was difficult when it was lower than 0.5 mg/L.

Atmospheric dispersion and transmission of Legionella from wastewater treatment plants: A 6-year case-control study.

An atmospheric dispersion model was used to generate nationwide exposure maps of aerosols from 776 WWTPs in the Netherlands. Municipal sewage treatment plants and industrial WWTPs were both included. Exposure of LD cases and controls at the residential address was compared, in a matched case-control design using a conditional logistic regression. Cases were notified LD cases with onset of disease in the period 2013-2018 in the Netherlands (n=1604). Aerosols dispersed over a large part of the Netherlands, but modelled concentrations are estimated to be elevated in close proximity to WWTPs. A statistically significant association was found between LD and the calculated annual average aerosol concentrations originating from WWTPs (odds-ratio: 1.32 (1.06-1.63)). This association remained significant when the two outbreak-related WWTPs were removed from the analysis (odds-ratio: 1.28 (1.03-1.58)). LD cases were more exposed to aerosols from WWTPs than controls. This indicates that exposure to aerosols dispersed from WWTPs caused Legionnaires Disease in residents living near WWTPs in the period 2013-2018. In order to investigate which characteristics of WWTPs are associated with an increased LD risk, the WWTP database should be updated and more data is needed on the presence and survival of aerosolized Legionella bacteria to improve the Legionella dispersion modelling. Furthermore, it is recommended to further investigate how aerosol dispersion of WWTPs can effectively be reduced in order to reduce the potential health risk.

Water quality assessment and pollution source analysis of Yaojiang River Basin: a case study of inland rivers in Yuyao City, China

Abstract To fully understand the water quality status of the Yuyao section in the Yaojiang River Basin, we utilized the single factor and comprehensive water quality identification index methods, as well as factor analysis in this study. The single factor water quality assessment results showed that the common parameters exceeding the standard in both the wet and dry seasons included dissolved oxygen and total nitrogen, which were inferior to the target water quality grade III by 1–6 grades. The comprehensive water quality order reaching the target grade III was Hutang River (87.5%), Changling River (50.0%), Yaojiang River (43.8%), and Linzhou River (37.5%). The comprehensive water quality in the dry season (90.0% standard-achieving rate) was better than that in the wet season (25.0% standard-achieving rate). These results suggested that the surface runoff might considerably impact water quality. The factor analysis results showed that the basin surveyed in 2018 was mainly polluted by urban sewage and agricultural sources, while the primary pollution source in 2019 was agricultural pollution. Integrated with comprehensive water quality assessment results, in this study, we demonstrated that the series of water treatment projects carried out in Yuyao City positively impacted municipal sewage treatment.

Quantitative balance and analysis of fulvic acids changes in the process of municipal sewage treatment

The latest researches show that large amounts of humic substances (HS) are discharged by municipal facilities, including sewage treatment plants, therefore this paper covers characteristics of a soluble HS fraction, i.e. fulvic acids (FAs) contained in municipal sewage and balance of their amounts introduced to and discharged from a biological reactor.FAs were extracted from samples collected from mechanically and biologically treated sewage and from sewage and activated sewage sludge, from the following cells of a biological reactor: predenitrification, dephosphatation, denitrification and nitrification, according to the flow through sewage treatment plant's section.The paper discussed quantitative (concentrations and 24-h loads of FAs introduced to and discharged from the biological reactor) and qualitative (basic composition, share of selected non-organic pollutants, including heavy metals, thermo-gravimetric analysis and infra-red spectroscopy) research. Additional, atomic quotients (C/O, C/H, C/N and O/H) of basic composition were defined, which made possible to conduct analysis of FAs chemical and biochemical changes in the process of sewage treatment in the biological reactor. The conducted quantitative balance of FAs, extracted from raw sewage and activated sewage sludge indicated that these substances are not subjects to biodegradation but, to a large extent, they are precipitated and absorbed on activated sewage sludge. The remaining quantities are discharged from a sewage treatment plant together with treated sewage.

The impact of hydraulic retention time on the performance of two configurations of anaerobic pond for municipal sewage treatment

ABSTRACT Anaerobic ponds have the potential to contribute to low carbon wastewater treatment, however are currently restricted by long hydraulic residence time (HRT) which leads to large land requirements. A two-stage anaerobic pond (SAP) design was trialled against a single-stage control (CAP) over four HRTs down to 0.5 days, to determine the lowest HRT at which the ponds could operate effectively. No statistical differences were observed in particulate removal between the ponds over all four HRTs, suggesting solids loading is not a critical factor in AP design. Significantly higher biogas production rates were observed in the SAP than the CAP at 1.5 d and 1.0 d HRT, and microbial community profiling suggests the two-stage design may be facilitating spatial separation of the anaerobic digestion process along reactor length. Hydrogenotrophic methanogensis dominated over aceticlastic, with acetate oxidisation a likely degradation pathway. Experimental tracer studies were compared to CFD simulations, with the SAP showing greater hydraulic efficiency, and differences more pronounced at shorter HRTs. Greater flow recirculation between baffles was observed in CFD velocity profiles, demonstrating baffles can dissipate preferential flow patterns and increase effective pond volume, especially at high flow rates. The study demonstrates the potential of APs to be operated at shorter HRTs in psychrophilic conditions, presenting an opportunity for use as pre-treatments (in place of septic tanks) and primary treatment for full wastewater flows. Two-stage designs should be investigated to separate the stages of the anaerobic digestion process by creating preferential conditions along the pond length.

Biodegradation and metabolism of tetrabromobisphenol A in microbial fuel cell: Behaviors, dynamic pathway and the molecular ecological mechanism

Tetrabromobisphenol A (TBBPA) has aroused widespread pollution in industrial wastewater. Microbial fuel cell (MFC) was proved powerful in organics degradation and simultaneous resource recovery during wastewater treatment. However, the TBBPA biotransformation potential, pathway and the related molecular mechanism remain poorly understood. In this study, the enhanced degradation and detoxification performance of TBBPA in MFC anode was confirmed, evidenced by the shorter degradation period (2.3 times shorter) and less generation of bisphenol A. UPLC-QTOF-MS analysis verified TBBPA metabolism went through reductive debromination, hydrolytic debromination, oxidative ring cleavage and o-methylation. Accompanied with those biochemical processes, the metabolites underwent dynamic changes. The distinctly decreased abundance and fewer interactions with other functional genera for the potential reductive dehalogenators (Pseudomonas, etc.) possibly led to the suppressed reductive debromination (5.1%) in the closed bioanode. Otherwise, the more abundant potential function bacteria with more collaborated interrelations, including hydrolytic dehalogenators (Acinetobacter, etc.), aromatics degrading bacteria (Geobacter, Holophaga, etc.) and electroactive bacteria (Geobacter, Desulfovibrio, etc.) made great sense to the enhanced hydrolytic debromination and detoxification of TBBPA. This study revealed that MFC anode was beneficial to TBBPA degradation and provided theoretical support for the decomposition and transformation of micro-pollutants in the municipal sewage treatment coupled with MFC process.

Antibiotics in the municipal solid waste incineration plant leachate treatment process

ABSTRACT At present, the distribution of antibiotics in wastewater is mainly concentrated in municipal sewage treatment plants, and little attention is paid to the distribution and removal of antibiotics in landfill leachate. The concentrations of five sulfonamide, three tetracycline, and two macrolide antibiotics in leachate from a solid waste incineration plant were measured and the efficiency of the leachate treatment process in removing them was investigated. All target antibiotics were detected in the raw leachate samples. The total sulfonamide, tetracycline, and macrolide concentrations in the raw leachate ranged from 0.98 to 90.25, 1.90 to 50.64, and 146.41 to 382.90 ng/L, respectively. The leachate treatment process simultaneously removed all ten antibiotics with high removal efficiencies ranged from 96.0% to 100%. Biological and physical processes affected the removal of different types of antibiotics differently, with macrolides being more difficult for microorganisms to degrade than the other two categories. Leachate contaminants correlated to antibiotics suggesting environmental factors impact the removal of antibiotics. The accumulation of antibiotics in the leachate treatment process may create environmental problems.

Simultaneous enhancement of power generation and chlorophenol degradation in nonmodified microbial fuel cells using an electroactive biofilm carbon felt anode

Microbial fuel cells (MFCs) are an emerging technique presenting remarkable potential. In the current MFC, an electroactive biofilm anode was inoculated with activated sludge from a local municipal sewage treatment plant. The output voltage peaked at 0.60 V and 0.56 V in MFCs cultured with 2-chlorophenol (MFC-2-CP) and 2,4-dichlorophenol (MFC-2,4-DCP), respectively. The degradation and mineralization efficiency in MFC-2-CP were 100.0% and 82.0%, respectively. Based on the bacterial 16S rRNA gene sequence analysis, abundant Acinetobacter and Azospirillum existed during both the bioelectricity and biodegradation stages in MFC-2-CP, but different patterns were exhibited in MFC-2,4-DCP. The electrogenic bacteria relied on the electron transfer pathway of nicotinamide adenine dinucleotide dehydrogenase, succinate dehydrogenase and terminal oxidase, while the electrons were transferred to the extracellular electrode by cytochrome C, riboflavin, degradation products of CPs and flagella. 2-CP and 2,4-DCP were biodegraded into less toxic cyclohexanol via dichlorination, hydroxylation, and hydrogenation; hereafter, the ring was opened to generate long-chain hydrocarbons, and finally mineralized into CO2 and H2O. This work provided a new strategy for MFCs in power generation and contaminant treatment.

Occurrence, Profiles and Ecological Risk of Bisphenol Analogues in a Municipal Sewage Treatment Plant.

Due to the strict control on bisphenol A (BPA) in many countries, bisphenol analogues (BPs) are being widely used as alternative materials to manufacture epoxy resins and polycarbonate plastics, resulting in their occurrence in sewage treatment plants (STPs). In this study, the occurrence and distribution of 7 BPs in a large-scale STP in Beijing China was investigated. Wastewater samples were collected from the influents and effluents of each processing unit, and extracted by solid-phase extraction. Target compounds were quantified by ultra-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The total concentrations of seven BPs (ΣBPs) were 400.42 ± 48.12ng/L in the raw sewage, 438.60 ± 46.50ng/L in the primary effluent, 17.21 ± 13.12ng/L in the secondary effluent, and 11.33 ± 4.84ng/L in the tertiary effluent, respectively. Bisphenol S (BPS) and BPA were the predominant congener in raw sewage with an overall contribution of 29.32% and 70.22% to the ΣBPs, indicating that there was a large amount of BPS and BPA consumption in the study area. During a one-week sampling period, ΣBPs changed slightly at the same sampling site. It was found that high removal efficiencies were achieved for BPs in anoxic and oxic secondary clarifier treatment units, suggesting that biodegradation and sorption played major roles in BPs elimination in the STP. After tertiary treatment, all BPs except BPA were completely removed, suggesting the necessity to investigate the fate and toxicity of BPA in the aquatic environment.

Structural and functional changes in bacterial communities during sludge foaming in the sub-plateau MSTPs

Sludge foaming has been a persistent ailment in worldwide municipal sewage treatment plants (MSTPs). In particular, this problem frequently occurs and lasts throughout the winter and spring season in the sub-plateau MSTPs. Aims to explore the causes of sludge foaming under sub-plateau circumstance, the correlation between the structural and functional changes in bacterial communities and sewage properties was conducted using Illumina high-throughput sequencing technology. The results from 16S rRNA gene sequencing shown that the relative abundances of Actinobacteria (39.5 % ± 4.8 %) and Firmicutes (10.5 % ± 1.0 %) in the foaming sludge were remarkably higher than that in the non-foaming sludge. The abundances of Candidatus Microthrix parvicella (29.8 % ± 6.9 %), Trichococcus (6.5 % ± 1.0 %), and Ornithinibacter (3.5 % ± 0.6 %) were increased after sludge foaming, and which are considered as the dominated foaming-causative bacterial assemblages by the linear discriminant analysis (LDA). Spearman’s correlation analysis and redundancy analysis (RDA) also agreed that lower temperature and dissolved oxygen (DO) levels, higher lipid and protein contents were significantly correlated with sludge foaming. In addition, the predictive functional profiling indicated that the enzymes and their coding genes of the bacterial communities are mainly involved in the fast proliferation and lipid metabolism, and which abundance are highly upregulated during foaming period. These results suggested that the sludge foaming was strongly linked to the Actinobacteria and Firmicutes communities and higher lipid and protein content in the sewage under sub-plateau circumstance. The findings might be important for developing operating strategies to maintain the desired microbial community pattern and improve the performance of MSTPs.

Effects of Anaerobic Digestion on Antibiotic Resistance Genes in Sludge

Sludge treatment and reuse in municipal sewage treatment plants is beneficial to improve economic effect and reduce environmental pollution. Sludge is an important source of contamination of antibiotic resistance genes. Anaerobic fermentation is an important way to treat activated sludge. Effective treatment of municipal sludge can avoid the release of pathogenic microorganisms and resistance genes (ARGs) into the environment and cause secondary pollution. The research results will be of certain guiding significance to the resource utilization of sludge.

Aeration and non-aeration cycles (AE/NA) time: influence in combined organic matter and nitrogen removal and features of biofilm

ABSTRACT This research aimed the performance evaluation of a structured bed reactor with different cycles of Intermittent Aeration (IA)(SBRRIA) in the municipal sewage treatment and the verification of the effect of IA cycles on the total nitrogen (TN) removal and organic matter (COD). Three IA cycles were evaluated: phase I (4 h AE (aeration on) – 2 h NA (aeration off)); II (2 h AE–1 h NA) and III (2 h AE–2 h NA), with Hydraulic Retention Time of 16 h. The best nitrogen removal was obtained during phase II, with the lowest non-aeration time: efficiency of nitrification, denitrification, TN and COD removal of 80 ± 15%, 82 ± 12%, 67 ± 6% and 94 ± 7%, respectively. The mean cell residence time was 19, 26 and 33 d in phases I, II and III, respectively. The statistical analysis applied to the AE/NA profiles showed that the time of AE and NA in the cycles did not influence nitrogen and organic matter removal. Thus, this indicates the recirculation and the gradient formed in the support material facilitate the process of Simultaneous Nitrification and Denitrification. The lowest concentration of nitrifying and denitrifying microorganisms was obtained in effluent and sludge at the end of phase III. From the TP (Total Proteins)/TPS (Total Polysaccharides) ratio obtained (0.8 ± 0.1, 1.3 ± 0.1 e 1.5 ± 0.1 in phases I, II and III), it was possible to conclude that the biofilm in phase I was more porous, with a thin layer if compared to that in phase II and III.

Technical, Energetic and Economic Optimization Analysis of Selection of Heat Source for Municipal Sewage Sludge Dryer

The treatment of growing production of municipal sewage sludge has become a significant global problem. Drying of digested sewage sludge is a promising alternative to sludge disposal at dumping sites. The research objective of this study was to find the optimal heat source for a sludge drying plant in a large municipal sewage treatment plant (people equivalent: 250,000). Two boundary heat supply cases were analyzed in the paper: cogeneration of heat and power (CHP) units, internal combustion (IC) engines fired with natural gas, and plant supplied with a gas boiler. The aim of the research was to find the optimal size of the cogeneration unit cooperating with the gas boiler as heat sources for a given drying plant case with the maximum net present (NPV) value as the objective function. The results of the conducted optimization show higher profitability of cases with larger cogeneration unit. For the basic assumptions, the maximum NPV is obtained for the largest analyzed CHP unit: 1300 kW of thermal power output. Sensitivity analyses show that the varying gas and electricity prices can relocate the NPV maximum towards smaller CHP sizes. A supplementary energy analysis shows that implementing larger CHP units yields a higher energy efficiency of the system, up to 0.52.

Nitrogen removal from low COD/TIN real municipal sewage by coupling partial denitrification with anammox in mainstream

The application of partial denitrification coupling with anammox (PD/A) in municipal sewage treatment is one of the most promising research field, and it has just begun. In 548 days of experiment treating real domestic sewage, the continuous flow reactor was started up by adding biocarriers containing anammox bacteria and operated stably after acclimatization. The PD/A was successfully achieved in the step-feed AO system. Furthermore, mass balance of ammonium revealed that anammox could contribute 32–47% to nitrogen loss. Compared with no biocarriers addition phase, the nitrogen removal efficiency (NRE) increased to 77.8 ± 4.3% and the effluent total inorganic nitrogen (TIN) decreased to 11.0 ± 2.1 mg/L at the COD/TIN ratio of 2.9 from day 428 to day 548 under the condition of anammox biocarriers addition and without external carbon source. Quantitative polymerase chain reaction (qPCR) and high-throughput sequencing analysis showed that anammox bacteria on the biological carrier accounted for 3.06% of the total bacteria in the stable phase, which was much higher than the reported <0.003% in wastewater treatment plants (WWTPs). After 247 days of operation with anammox biocarriers addition, the abundance of anammox bacteria on the carriers tended to be stable at 3.36 × 1010 gene copies g−1 dry sludge. The activity of anammox decreased and maintained at 13.14 g NH4+-N m−3 d−1 under the biocarriers-only condition, while increased from 11.71 g NH4+-N m−3 d−1 to 25.65 g NH4+-N m−3 d−1 in the hybrid condition of biocarriers and flocs. This study indicated that PD/A is effective to strengthen nitrogen removal with low COD/TIN ratio.

Effect of low temperature on the performance of UASB reactor for municipal wastewater treatment: recent advances and future perspectives

Upflow anaerobic sludge blanket (UASB) reactor is a widely used anaerobic treatment technology, which is essential in municipal sewage treatment, in tropical and subtropical areas. However, UASB reactors have been underutilized in low-temperate zones due to the poor performance of UASB reactors under psychrophilic conditions. This study has three primary purposes: to review the performance of UASB reactors with different parameters, to describe the limiting factors at low temperatures, and to prospect the future solutions. In the low-temperature environment, lower COD removal efficiency and production of methane in the UASB reactor have been observed in various studies. The key limiting factors are increased dissolved methane, decreased activity of methanogens and hydrolytic bacteria. This article proposed that five technologies could reduce the impact of low temperature on the treatment of municipal wastewater by the UASB reactor, which are denitrifying anaerobic methane oxidation (DAMO), direct interspecies electron transfer (DIET), bio-electrochemical systems (BES), pre-hydrolysis, and degassing membrane (DM). These technologies are promising to be developed into highly-efficient engineering strategies for treating municipal wastewater in the UASB reactor at low temperatures in the future.