Isolation and physiological properties of methanogenic archaea that degrade tetramethylammonium hydroxide.

Tetramethylammonium hydroxide (TMAH) is a known toxic chemical used in the photolithography process of semiconductor photoelectronic processes. Significant amounts of wastewater containing TMAH are discharged from electronic industries. It is therefore attractive to apply anaerobic treatment to industrial wastewater containing TMAH. In this study, a novel TMAH-degrading methanogenic archaeon was isolated from the granular sludge of a psychrophilic upflow anaerobic sludge blanket (UASB) reactor treating synthetic wastewater containing TMAH. Although the isolate (strain NY-STAYD) was phylogenetically related to Methanomethylovorans uponensis, it was the only isolated Methanomethylovorans strain capable of TMAH degradation. Strain NY-STAYD was capable of degrading methylamine compounds, similar to the previously isolated Methanomethylovorans spp. While the strain was able to grow at temperatures ranging from 15 to 37°C, the cell yield was higher at lower temperatures. The distribution of archaeal cells affiliated with the genus Methanomethylovorans in the original granular sludge was investigated by fluorescence in situ hybridization (FISH) using specific oligonucleotide probe targeting 16S rRNA. The results demonstrated that the TMAH-degrading cells associated with the genus Methanomethylovorans were not intermingled with other microorganisms but rather isolated on the granule's surface as a lone dominant archaeon. KEY POINTS: • A TMAH-degrading methanogenic Methanomethylovorans strain was isolated • This strain was the only known Methanomethylovorans isolate that can degrade TMAH • The highest cell yield of the isolate was obtained at psychrophilic conditions.

Enhanced sulfide removal by gas stripping in a novel reactor for anaerobic wastewater treatment.

Removal of sulfide by gas stripping using biogas produced in an internal phase-separated reactor (IPSR) was evaluated during anaerobic treatment. The IPSR consisted of upper and lower segments with a gas-liquid partitioning (GLP) valve between the sections. Wastewater was fed to the upper segment in the first stage and then to the lower segment in the second stage. The GLP valve separated the liquid phase from the gaseous phase and supplied biogas from the lower segment to the upper segment. The IPSR and a control reactor were fed with synthetic wastewater and operated in parallel under an organic loading rate of 12 kg COD/(m3 day) at 35 °C. The sulfide concentration increased to 400-600 mg S/L, which is above the previously reported 50% inhibition level for methanogenic activity. The IPSR showed higher H2S removal performance than the control reactor and removed approximately twice the H2S as the control reactor at 400 mg S/L, indicating that it can be used for the stable treatment of wastewater containing high concentrations of sulfide.

Effect of formic acid inflow on microbial properties of the anaerobic granular sludge in a UASB reactor.

In the production of natural rubber, formate or acetate is added to the latex solution to coagulate the rubber; therefore, the wastewater contains high concentrations of organic acids, requiring the application of anaerobic treatment technology. In this study, a two-phase continuous flow experiment using a laboratory-scale upflow anaerobic sludge blanket (UASB) was conducted to investigate the influence of formate inflow on the microbial and physical characteristics of the retained granular sludge. In phase 1, acetate-based wastewater was used as feed, while in phase 2, formate-based wastewater was used as feed. In phase 1, the UASB exhibited high COD removal efficiency (97.2%); in addition, the retained sludge showed increased methane production from acetate and proliferation of acetate-utilizing Methanosaeta species. In phase 2, the UASB performed as well as phase 1, with 98.2% COD removal efficiency. Microbial community structure analysis confirmed that relatives of Methanobacterium formicicum present in the retained sludge were responsible for the degradation of formate in phase 2. However, decreased diameter and slight deterioration of granular sludge settleability were observed. In conclusion, formate inflow has low risk of interference with the process performance of the UASB, but it has negative effects on the physical properties of the granular sludge.

Sequence-Specific Capture of Oligonucleotide Probes (SCOPE): a Simple and Rapid Microbial rRNA Quantification Method Using a Molecular Weight Cutoff Membrane.

A method named sequence-specific capture of oligonucleotide probes (SCOPE) was developed for quantification of microbial rRNA molecules in a multiplex manner. In this method, a molecular weight cutoff membrane (MWCOM) was used for the separation of fluorescence-labeled oligonucleotide probes hybridized with rRNA from free unhybridized probes. To demonstrate proof of concept, probes targeting bacteria or archaea at different taxonomic levels were prepared and were hybridized with rRNAs. The hybridization stringency was controlled by adjusting reaction temperature and urea concentration in the mixture. Then, the mixture was filtered through the MWCOM. The rRNA and hybridized probes collected on the MWCOM were recovered and quantified using a spectrophotometer and fluorospectrometer, respectively. The method showed high accuracy in detecting specific microbial rRNA in a defined nucleic acid mixture. Furthermore, the method was capable of simultaneous detection and quantification of multiple target rRNAs in a sample with sensitivity up to a single-base mismatch. The SCOPE method was tested and benchmarked against reverse transcription-quantitative PCR (RT-qPCR) for the quantification of Bacteria, Archaea, and some key methanogens in anaerobic sludge samples. It was observed that the SCOPE method produced more reliable and coherent results. Thus, the SCOPE method allows simple and rapid detection and quantification of target microbial rRNAs for environmental microbial population analysis without any need for enzymatic reactions. IMPORTANCE Microorganisms play integral roles in the Earth's ecosystem. Microbial populations and their activities significantly affect the global nutrient cycles. Quantification of key microorganisms provides important information that is required to understand their roles in the environment. Sequence-based analysis of microbial population is a powerful tool, but it provides information only on relative abundance of microorganisms. Hence, the development of a simpler and quick method for the quantification of microorganisms is necessary. To address the shortcomings of a variety of molecular methods reported so far, we developed a simple, rapid, accurate, and multiplexed microbial rRNA quantification method to evaluate the abundance of specific microbial populations in complex ecosystems. This method demonstrated high specificity, reproducibility, and applicability to such samples. The method is useful for quantitative detection of particular microbial members in the environment.

Detection of potentially pathogenic Arcobacter spp. in Bangkok canals and the Chao Phraya River.

The management of pathogenic bacteria in waterways is a public health issue. Here, we investigated the concentrations of potentially pathogenic bacteria, Arcobacter spp. and Campylobacter spp., and Escherichia coli, by quantifying species-specific genes in surface water samples from canals and the Chao Phraya River from June 2017 to June 2018 in Bangkok, Thailand. We assessed the relationship between the specific bacterial concentrations, water quality, and seasonal changes. Arcobacter spp. were detected at high density in all samples and showed seasonal fluctuations according to analyses based on 16S rDNA and the invasion gene ciaB. High levels of 16S rDNA and dut gene of E. coli were detected in the polluted drainage canals. A high correlation was observed between E. coli and chemical and biochemical oxygen demand (COD and BOD), suggesting that untreated domestic wastewater was the source of the E. coli. In contrast, Arcobacter spp. were detected with high density even in water samples with relatively low COD, suggesting that Arcobacter spp. are more likely than E. coli to survive in the water environment. The analysis of 16S rDNA and ciaB gene sequence analyses indicated that the Arcobacter spp. isolated from the drainage canals were A. butzleri and A. cryaerophilus.

Differences in the isotopic signature of activated sludge in four types of advanced treatment processes at a municipal wastewater treatment plant.

The natural abundance of stable isotopes is a powerful tool for evaluating biological reactions and process conditions. However, there are few stable isotope studies on the wastewater treatment process. This study carried out the first investigation on variations in natural abundance of carbon and nitrogen stable isotope ratios (δ13C and δ15N) of activated sludge in four types of advanced treatment process (extended aeration activated sludge (EAAS), aerobic-anoxic-aerobic (A2O), recycled nitrification-denitrification (RND), and modified Bardenpho (MB)) at a municipal wastewater treatment plant. The δ13C and δ15N values of influent suspended solids settled in the primary sedimentation tank (i.e., primary sludge) ranged from -25.4‰ to -24.6‰ and 0.5‰-2.9‰, respectively, during monitoring periods. The δ13C values of the activated sludge were -24.6‰ to -23.6‰ (EAAS), -25.4‰ to -24.3‰ (A2O), -25.7‰ to -24.9‰ (RND), and -25.7‰ to -24.3‰ (MB). The δ13C values of the activated sludge were similar to those of influent suspended solids. However, the δ13C values of activated sludge in EAAS was significantly higher than in A2O, RND, and MB. Meanwhile, the δ15N values of activated sludge were obviously higher than influent suspended solids; 5.8‰-7.5‰ (EAAS), 6.6‰-8.1‰ (A2O), 5.5‰-7.5‰ (RND), and 5.3‰-7.6‰ (MB). Changes in δ13C and δ15N values of the activated sludge within the treatment system were also found. These findings indicate that changes in δ13C and δ15N values of the activated sludge rely on important function for biological wastewater treatment such as nitrification, denitrification, and methane oxidation through wastewater treatment over time.

Microbial properties of the granular sludge in a psychrophilic UASB reactor fed with electronics industry wastewater containing organic chemicals.

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to the treatment of artificial electronics industry wastewater containing tetramethylammonium-hydroxide (TMAH), monoethanolamine (MEA), and isopropyl-alcohol (IPA) in order to evaluate process performance and degradation properties. During 800 days of operation, 96% efficiency of chemical oxygen demand (COD) removal was stably achieved at an organic loading rate of 8.5 kgCOD/m3/day at 18-19 °C. MEA degradation, carried out by acid-forming eubacteria, was confirmed within a week. The physical properties of the retained granular sludge were degraded by feeding with TMAH wastewater, but maintained by feeding with MEA wastewater due to an accumulation of species from the genus Methanosaeta and family Geobacteraceae. Analysis of the microbial community structure via SEM and 16S rRNA genes showed a proliferation of Methanomethylovorans-like cells and Methanosaeta-like cells at the surface and in the core of the granular sludge with TMAH, MEA and IPA acclimation. Furthermore, a batch degradation experiment confirmed that process inhibition due to increasing chemical concentration was relatively stronger for TMAH than for MEA or IPA. Thus, controlling the TMAH concentration of the influent to below 1 gCOD/L will be important for the stable treatment of electronics industry wastewater by UASB technology.

Performance evaluation of a down-flow hanging sponge (DHS) reactor as a decentralized domestic wastewater treatment system in tropical regions.

In this study, a pilot-scale down-flow hanging sponge (DHS) reactor was operated in the community plant of Bangkok for the treatment of domestic wastewater (COD 285 mg/L, BOD 105 mg/L) collected by separate sewer to evaluate the reactor's feasibility as a decentralized treatment system. The DHS reactor was operated for 600 days at ambient temperatures of 25-30 °C, both with constant flow conditions and with fluctuating flow conditions that simulated wastewater discharge patterns of the community. The results indicate that under constant flow at an HRT of 5 h, the volumetric loading rates of 0.36 kgBOD/m3-sponge/day and 0.16 kgN/m3-sponge/day were the optimum operational conditions of the DHS reactor in order to satisfy the effluent discharge standards. The DHS achieved removal rates of 89, 95, 91 and 90% for COD, BOD, TSS and NH4-N. Under the fluctuating flow condition, improvement of denitrification was confirmed at volumetric loading rates of 0.50 kgBOD/m3-sponge/day and 0.18 kgN/m3-sponge/day. The fluctuating flow of wastewater positively affects retained sludge activities in terms of homogenizing sludge concentration and stimulating oxygen uptake rates. These results suggest that the DHS reactor can be applied as a decentralized treatment system for domestic wastewater with fluctuating flow rates in tropical regions.

Biological treatment of electronic industry wastewater containing TMAH, MEA and sulfate in an UASB reactor.

This study investigated the feasibility of the methanogenic treatment of electronic industry wastewater containing tetramethylammonium hydroxide (TMAH), monoethanolamine (MEA) and sulfate in a lab-scale mesophilic up-flow anaerobic sludge blanket reactor. Feeding a mixture of electronic industry wastewater and co-substrate organics to the reactor for smooth acclimatization of sludge gave complete degradation of each organics within five days. When the reactor was fed only electronic industry wastewater, total COD removal, TMAH removal and MEA removal were achieved over 80, 99 and 99%, respectively, at an organic loading rate of 11.5 kg-COD m-3 day-1. 173 mg-S L-1 of influent sulfate was almost reduced simultaneously with the COD removal. In order to evaluate performance stability, the TMAH shock load event was performed under the conditions of 11,000 mg-COD L-1 for 24 h. Inflow of high TMAH concentration inhibited TMAH degradation and sulfate reduction for more than one month, however, not MEA. The batch feeding experiment and specific activity measurement revealed degradation pathways of each organics. TMAH was degraded via methanogenic pathway without sulfate reduction, MEA was degraded via methanogenic pathway with sulfate reduction. The results indicated that methanogenic treatment was applicable to electronic industry wastewater by appropriate reactor handling.

Evaluation of process performance and retained sludge properties of a psychrophilic UASB reactor for treatment of iso-plophyl alcohol (2-propanol)-containing wastewater.

In this study, a continuous feeding experiment was conducted with synthetic iso-plophyl alcohol (2-propanol)-containing wastewater using a lab-scale psychrophilic UASB reactor to evaluate process performance and retained sludge properties. For smooth acclimation, methanogenic granular sludge was seeded and a proportion of 2-propanol in the synthetic wastewater containing sucrose and volatile fatty acids was increased stepwise from 0% to 30%, 60% and then 90% of COD (chemical oxygen demand). As a result, after a 4-week period for acclimation to 2-propanol degradation, a COD removal rate of 95% was achieved at an organic loading rate (OLR) of 8.4 kg COD/m3/day. Additionally, the physical properties of the retained granular sludge were maintained even when the reactor was supplied with 2-propanol-rich wastewater for more than 200 days. From the batch assays using serum bottles, methanogenic degradation of 2-propanol was observed with acetone accumulation. By comparison, 2-propanol degradation was clearly inhibited in the presence of chloroform as a specific inhibitor of methanogen. A domain archaeal community structure analysis targeting 16S rRNA genes showed the relative abundance of the genus Methanospillium was increased in the 2-propanol acclimated sludge. These results suggested Methanospillium related species in the granular sludge appreciably contributed to the direct degradation of 2-proapanol into acetone under an anaerobic condition.

Influence of tetramethylammonium hydroxide (TMAH) on the microbial properties of anaerobic granular sludge acclimated to isoplophyl alcohol (IPA) wastewater under psychrophilic conditions.

In this study, a continuous flow experiment was conducted in which a lab-scale upflow anaerobic sludge blanket (UASB) reactor at psychrophilic conditions (18-19°C) was fed with artificial wastewater, containing tetramethylammonium hydroxide (TMAH) and isoplophyl alcohol (IPA), from the electronics industry. This was done to evaluate process performance and microbial properties of the granular sludge that was retained in the reactor. The inoculated granular sludge was precultured with IPA containing wastewater but not TMAH; as a result, no degradation was observed in 30 days of operation. To enhance degradation, the reactor was seeded with 2% weight of the TMAH-enriched sludge, after which TMAH was enhanced. Consequently, the total COD removal efficiency reached 90% at an organic loading rate of 7.5 kg COD/m3/day. The TMAH inflow decreased the diameter of the retained granular sludge, but the sludge retained its settleability. The proliferation of the Methanometylovorans microorganisms present in the enrichment culture was confirmed by analysis of the 16 S rRNA gene in the retained sludge. In addition, TMAH degradation was inhibited by addition chloroform, a methanogen inhibitor. These results suggested species in the genus Methanometylovorans in the granular sludge contributed significantly to methanogenic TMAH degradation.

Eukaryotic Community Shift in Response to Organic Loading Rate of an Aerobic Trickling Filter (Down-Flow Hanging Sponge Reactor) Treating Domestic Sewage.

In this study, changes in eukaryotic community structure and water quality were investigated in an aerobic trickling filter (down-flow hanging sponge, DHS) treating domestic sewage under different organic loading rates (OLRs). The OLR clearly influenced both sponge pore water quality and relative flagellates and ciliates (free-swimming, carnivorous, crawling, and stalked protozoa) abundances in the retained sludge. Immediately after the OLR was increased from 1.05 to 1.97 kg chemical oxygen demand (COD) m-3 day-1, COD and NH4+-N treatment efficiencies both deteriorated, and relative flagellates and ciliates abundances then increased from 2-8 % to 51-65 % total cells in the middle-bottom part of the DHS reactor. In a continuous operation at a stable OLR (2.01 kg COD m-3 day-1), effluent water quality improved, and relative flagellates and ciliates abundances decreased to 15-46 % total cells in the middle-bottom part of the DHS reactor. This result may indicate that flagellates and ciliates preferentially graze on dispersed bacteria, thus, stabilizing effluent water quality. Additionally, to investigate eukaryotic community structure, clone libraries based on the 18S ribosomal ribonucleic acid (rRNA) gene of the retained sludge were constructed. The predominant group was Nucletmycea phylotypes, representing approximately 29-56 % total clones. Furthermore, a large proportion of the clones had <97 % sequence identity in the NCBI database. This result indicates that phylogenetically unknown eukaryotes were present in the DHS reactor. These results provide insights into eukaryotic community shift in the DHS reactor treating domestic sewage.

Development of downflow hanging sponge (DHS) reactor as post treatment of existing combined anaerobic tank treating natural rubber processing wastewater.

Conventional aerated tank technology is widely applied for post treatment of natural rubber processing wastewater in Southeast Asia; however, a long hydraulic retention time (HRT) is required and the effluent standards are exceeded. In this study, a downflow hanging sponge (DHS) reactor was installed as post treatment of anaerobic tank effluent in a natural rubber factory in South Vietnam and the process performance was evaluated. The DHS reactor demonstrated removal efficiencies of 64.2 ± 7.5% and 55.3 ± 19.2% for total chemical oxygen demand (COD) and total nitrogen, respectively, with an organic loading rate of 0.97 ± 0.03 kg-COD m-3 day-1 and a nitrogen loading rate of 0.57 ± 0.21 kg-N m-3 day-1. 16S rRNA gene sequencing analysis of the sludge retained in the DHS also corresponded to the result of reactor performance, and both nitrifying and denitrifying bacteria were detected in the sponge carrier. In addition, anammox bacteria was found in the retained sludge. The DHS reactor reduced the HRT of 30 days to 4.8 h compared with the existing algal tank. This result indicates that the DHS reactor could be an appropriate post treatment for the existing anaerobic tank for natural rubber processing wastewater treatment.

Evaluation of the process performance of a down-flow hanging sponge reactor for direct treatment of domestic wastewater in Bangkok, Thailand.

This study assesses the performance of an aerobic trickling filter, down-flow hanging sponge (DHS) reactor, as a decentralized domestic wastewater treatment technology. Also, the characteristic eukaryotic community structure in DHS reactor was investigated. Long-term operation of a DHS reactor for direct treatment of domestic wastewater (COD = 150-170 mg/L and BOD = 60-90 mg/L) was performed under the average ambient temperature ranged from 28°C to 31°C in Bangkok, Thailand. Throughout the evaluation period of 550 days, the DHS reactor at a hydraulic retention time of 3 h showed better performance than the existing oxidation ditch process in the removal of organic carbon (COD removal rate = 80-83% and BOD removal rate = 91%), nitrogen compounds (total nitrogen removal rate = 45-51% and NH4+-N removal rate = 95-98%), and low excess sludge production (0.04 gTS/gCOD removed). The clone library based on the 18S ribosomal ribonucleic acid gene sequence revealed that phylogenetic diversity of 18S rRNA gene in the DHS reactor was higher than that of the present oxidation ditch process. Furthermore, the DHS reactor also demonstrated sufficient COD and NH4+-N removal efficiency under flow rate fluctuation conditions that simulates a small-scale treatment facility. The results show that a DHS reactor could be applied as a decentralized domestic wastewater treatment technology in tropical regions such as Bangkok, Thailand.

Impact of aluminum chloride on process performance and microbial community structure of granular sludge in an upflow anaerobic sludge blanket reactor for natural rubber processing wastewater treatment.

In this study, granular sludge formation was carried out using an aluminum chloride supplement in an upflow anaerobic sludge blanket (UASB) reactor treating natural rubber processing wastewater. Results show that during the first 75 days after the start-up of the UASB reactor with an organic loading rate (OLR) of 2.65 kg-COD·m(-3)·day(-1), it performed stably with a removal of 90% of the total chemical oxygen demand (COD) and sludge still remained in small dispersed flocs. However, after aluminum chloride was added at a concentration of 300 mg·L(-1) and the OLR range was increased up to 5.32 kg-COD·m(-3)·day(-1), the total COD removal efficiency rose to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, and the flocs began to form granules. Massively parallel 16S rRNA gene sequencing of the sludge retained in the UASB reactor showed that total sequence reads of Methanosaeta sp. and Methanosarcina sp., reported to be the key organisms for granulation, increased after 311 days of operation. This indicates that the microbial community structure of the retained sludge in the UASB reactor at the end of the experiment gave a good account of itself in not only COD removal, but also granule formation.

Recovery and biological oxidation of dissolved methane in effluent from UASB treatment of municipal sewage using a two-stage closed downflow hanging sponge system.

A two-stage closed downflow hanging sponge (DHS) reactor was used as a post-treatment to prevent methane being emitted from upflow anaerobic sludge blanket (UASB) effluents containing unrecovered dissolved methane. The performance of the closed DHS reactor was evaluated using real municipal sewage at ambient temperatures (10-28 °C) for one year. The first stage of the closed DHS reactor was intended to recover dissolved methane from the UASB effluent and produce a burnable gas with a methane concentration greater than 30%, and its recovery efficiency was 57-88%, although the amount of dissolved methane in the UASB effluent fluctuated in the range of 46-68 % of methane production greatly depending on the temperature. The residual methane was oxidized and the remaining organic carbon was removed in the second closed DHS reactor, and this reactor performed very well, removing more than 99% of the dissolved methane during the experimental period. The rate at which air was supplied to the DHS reactor was found to be one of the most important operating parameters. Microbial community analysis revealed that seasonal changes in the methane-oxidizing bacteria were key to preventing methane emissions.

Protection of biomass from snail overgrazing in a trickling filter using sponge media as a biomass carrier: down-flow hanging sponge system.

This study investigated down-flow hanging sponge (DHS) technology as a promising trickling filter (TF) using sponge media as a biomass carrier with an emphasis on protection of the biomass against macrofauna overgrazing. A pilot-scale DHS reactor fed with low-strength municipal sewage was operated under ambient temperature conditions for 1 year at a sewage treatment plant in Bangkok, Thailand. The results showed that snails (macrofauna) were present on the surface of the sponge media, but could not enter into it, because the sponge media with smaller pores physically protected the biomass from the snails. As a result, the sponge media maintained a dense biomass, with an average value of 22.3 gVSS/L sponge (58.1 gTSS/L sponge) on day 370. The snails could graze biomass on the surface of the sponge media. The DHS reactor process performance was also successful. The DHS reactor requires neither chemical treatments nor specific operations such as flooding for snail control. Overall, the results of this study indicate that the DHS reactor is able to protect biomass from snail overgrazing.

Pilot-scale experiment of down-flow hanging sponge for direct treatment of low-strength municipal wastewater in Bangkok, Thailand.

A pilot-scale experiment of a down-flow hanging sponge (DHS) reactor for treatment of low-strength municipal wastewater was conducted over 1 year in Bangkok, Thailand, to establish an appropriate method for treatment under tropical climate conditions. Municipal wastewater with an average BOD of 19 mg/L was fed directly into the DHS reactor. Superior effluent quality (5.1 ± 3.4 mg/L TSS, 21.1 ± 9.0 mg/L COD, 2.8 ± 1.4 mg/L BOD, and 4.1 ± 1.0 mg/L TN) was achieved at a hydraulic retention time (HRT) of 1 h under an average temperature of 30 °C. The DHS reactor reached an actual HRT of 19.0 min, indicating good contact efficiency between wastewater and retained sludge. The DHS reactor retained dense sludge at 15.3-26.4 g VSS/L based on the sponge media volume. The sludge activity in terms of specific oxygen uptake rate was good. Excess sludge was produced as 0.051 g TSS/g COD removed (0.11 g TSS/g BOD removed), and a good SVI of 28 mL/g was observed. The sufficient performance was attributed to dense sludge with high activity, regardless of the low-strength wastewater. Overall, the DHS was advantageous owing to its simple operation, lack of operational problems, and low power consumption.

Development of a down-flow hanging sponge reactor for the treatment of low strength sewage.

The process performance of a down-flow hanging sponge (DHS) reactor for treating low strength sewage (biochemical oxygen demand (BOD) 20-50 mg/L) was investigated in Bangkok, Thailand. The hydraulic retention time (HRT) was set at 4 h during the start-up period and was reduced to 1.5 h in a stepwise manner. Throughout the 300-day operational period, the DHS reactor shows high performance with respect to the removal of total suspended solid (>90% total suspended solid removal efficiency). No clogging of sponge media was observed in response to the self-digestion phenomena of the biofilm. At a HRT of 1.5 h, the BOD removal efficiency was sufficiently high (about 85%). The pathogen Escherichia coli and other coliform bacteria were removed almost completely as well (removal was 99.4% and 98.1%, respectively). Regarding the retained sludge activity measurement, the nitrite oxidation rate was higher than the ammonium oxidation rate (0.031 and 0.022 gram of nitrogen per gram of volatile suspended solids per day, respectively). In the 300 days of operation, the amount of excess sludge production was negligible. Thus, no sludge treatment system is required. Introduction of the DHS system in developing countries is recommended because this system requires a relatively small area, and has low electricity consumption and operation costs.

Downflow sponge biofilm reactors for polluted raw water treatment: Performance optimisation, kinetics, and microbial community.

Water outages caused by elevated ammonium (NH4+-N) levels are a prevalent problem faced by conventional raw water treatment plants in developing countries. A treatment solution requires a short hydraulic retention time (HRT) to overcome nitrification rate limitation in oligotrophic conditions. In this study, the performance of polluted raw water treatment using a green downflow sponge biofilm (DSB) technology was evaluated. We operated two DSB reactors, DSB-1 and DSB-2 under different NH4+-N concentration ranges (DSB-1: 3.2-5.0 mg L-1; DSB-2: 1.7-2.6 mg L-1) over 360 days and monitored their performance under short HRT (60 min, 30 min, 20 min, and 15 min). The experimental results revealed vertical segregation of organic removal in the upper reactor depths and nitrification in the lower depths. Under the shortest HRT of 15 min, both DSB reactors achieved stable NH4+-N and chemical oxygen demand removal (≥95%) and produced minimal effluent nitrite (NO2--N). DSB system could facilitate complete NH4+-N oxidation to nitrate (NO3--N) without external aeration energy requirement. The 16S rRNA sequencing data revealed that nitrifying bacteria Nitrosomonas and Nitrospira in the reactor were stratified. Putative comammox bacteria with high ammonia affinity was successfully enriched in DSB-2 operating at a lower NH4+-N loading rate, which is advantageous in oligotrophic treatment. This study suggests that a high hydraulic rate DSB system with efficient ammonia removal could incorporate ammonia treatment capability into polluted raw water treatment process and ensure safe water supply in many developing countries.