Down-flow Hanging Sponge Reactor Research Articles

Aerobic–anaerobic DHS reactor for enhancing denitrification in municipal wastewater treatment

Providing anaerobic environments can enhance the denitrification capacity of wastewater treatment systems. This study developed an aerobic–anaerobic downflow hanging sponge (DHS) reactor to increase denitrification. A siphon tube was integrated with a conventional DHS to create anaerobic conditions by controlling a water column inside the reactor. The siphon heights were set in the middle of the reactor, representing 2/5 of the total volume. Anaerobic conditions were maintained at the bottom (1/5), whereas aerobic conditions were maintained at the top (2/5). The middle part experienced alternating aerobic–anaerobic conditions within a siphon cycle. The hydraulic retention time (HRT) was 3 h, and the temperature was maintained at 30 °C. The study was divided into the low-loading and standard phases based on the influent soluble chemical oxygen demand (sCOD) concentration. During the low-loading phase, the aerobic–anaerobic DHS exhibited a higher sCOD removal rate (53.6 ± 26.6 %) than the control aerobic DHS (35.6 ± 31.9). However, the removal efficiencies for NH₄+–N and total nitrogen (TN) were lower, averaging 37.1 ± 24.7 % and 31.5 ± 21 %, respectively. In the standard phase, the aerobic–anaerobic DHS achieved an sCOD removal rate of 69.3 ± 14.8 % and an NH₄+–N removal rate of 17.2 ± 11.4 %. The control aerobic DHS showed higher sCOD and NH₄+–N removal at 84.7 ± 10.8 % and 54.1 ± 12.8 %, respectively, possibly due to the reduced aerobic zone volume in the aerobic–anaerobic DHS. The TN removal rates were also lower in the aerobic–anaerobic DHS (17.1 ± 11.4 %) than in the control DHS (25 ± 12.3 %). However, based on the ratio of nitrification to TN removal, the aerobic–anaerobic DHS showed a high denitrification rate of 85 %–100 %. The highest number of denitrifiers was in the middle section of the aerobic–anaerobic DHS, with Rhodocyclaceae the most prominent, followed by Comamonadaceae. Maintaining an anaerobic zone improved the denitrification capacity, indicating the potential of the aerobic–anaerobic DHS for efficient municipal wastewater treatment.

Application of Biofloc-Down flow hanging sponge system to remove nitrogen components in recirculating zero water exchange aquaculture system

This study presents a novel approach to sustainable aquaculture by integrating biofloc technology (BFT) with a compact down-flow hanging sponge (DHS) reactor. The integrated BFT-DHS system effectively removed nitrogen compounds while maintaining ammonia–nitrogen (NH4+-N) concentrations below 1 mg-N L-1 without water exchange. Application of this system in a tank bred with juvenile Oreochromis niloticus showed a high NH4+-N removal rate of up to 97 % and nitrite (NO2– −N) concentrations were maintained at 0.1 ± 0.1 mg-N L-1. Microbial analysis revealed Gordonia as the predominant genus in the biofloc contributing to heterotrophic nitrification, while the Peptostreptococcaceae family dominated the DHS reactor. Heterotrophic nitrification seemed to be the primary process for enhanced nitrogen removal. Pathogenic bacteria, Vibrio sp. was absent throughout the study. This study highlights the potential integration of BFT and DHS system for sustainable aquaculture practice with effective nitrogen removal.

Distinct comammox Nitrospira in high-rate down-flow hanging sponge reactor treating municipal wastewater

A down-flow hanging sponge (DHS) reactor is a trickling filter system used for wastewater treatment, which employs sponges to retain biomass. This study assessed the process performance of a compact DHS combined with a sedimentation tank with seven phases at varying hydraulic retention times (HRT) over 500 days. The BOD of the DHS effluent was maintained at 4.0 ± 0.5 mg·L-1 for the shortest HRT 0.3 ± 0.1 h. The nitrification efficiency was considerably impacted by the reduced HRT, with NH4+-N and NO3–-N concentrations of 9.0 ± 1.2 mgN·L-1 and 2.2 ± 0.5 mgN·L-1, respectively. Nevertheless, the effluent complied with effluent discharge standards throughout the trial period. The number of comammox 16S rRNA gene copies ranged from 5.58 to 13.2 × 107 copies·mL−1, indicating that sponges biomass retained carrier can provide favorable conditions for comammox growth and could contribute to nitrification in the high-rate DHS reactor.

Integration of down-flow hanging sponge reactor to oreochromis niloticus − Brassica oleracea aquaponics system

Aquaponics is a promising solution for addressing food security concerns. Nonetheless, an effective water-purification system is necessary to achieve high and stable yields of fish and vegetables. This study aimed to evaluate the nitrification and oxygen transfer performance of a laboratory-scale down-flow hanging sponge (DHS) reactor with a Brassica oleracea aquaponics system to treat water in an Oreochromis niloticus closed-aquaculture system. The DHS reactor showed a higher oxygen transfer coefficient (KLa) than the conventional aerator and provided an adequate dissolved oxygen (DO) concentration of approximately 5.5 mg/L essential for O. niloticus growth throughout the experimental period. The evaluated DHS-based aquaponic system maintained high water quality in an aquaculture tank, with a survival rate of 97%. The O. niloticusgrew at a low feed conversion ratio of 1.5–2.1 and a low feeding rate of 0.5% at high stocking densities of 17.5–22.2 kg-fish-weight/m3. 16S rRNA gene sequencing indicated that the DHS sponge carrier effectively retained nitrifying bacteria such as Nitrosomonas and Nitrospira. This study demonstrated that the DHS reactor provided a high DO concentration and that a simultaneous DHS reactor with a hydroponic tank provided a low-cost aquaponic system that could be applied for food production in the aquaculture industry.

Escherichia coli removal in down-flow hanging sponge reactors: insights from laboratory reactor studies

Down-flow hanging sponge (DHS) reactors, employed in domestic wastewater treatment, have demonstrated efficacy in eliminating Escherichia coli and other potentially pathogenic bacteria. The aim of this study was to elucidate the mechanism of removal of E. coli by employing a cube-shaped polyurethane sponge carrier within a compact hanging reactor. An E. coli removal experiment was conducted on this prepared sponge. Escherichia. coli level was found to decrease by more than 2 logs after passing through five nutrient-restricted DHS sponges. Conversely, a newly introduced sponge did not exhibit a comparable reduction in E. coli level. Furthermore, under conditions of optimal nutritional status, the reduction in E. coli level was limited to 0.5 logs, underscoring the crucial role of nutrient restriction in achieving effective elimination. Analysis of the sponge-associated bacterial community revealed the presence of a type VI secretion system (T6SS), a competitive mechanism observed in bacteria. This finding suggests that T6SS might play a pivotal role in contributing to the observed decline in E. coli level.

Restart performance of prolonged stopped down-flow hanging sponge reactor for treating of low-strength domestic sewage

The down-flow hanging sponge (DHS) reactor, a type of trickling filter used as a sponge, is a promising treatment system for low-cost sewage treatment. However, the performance of dried sponges that have been non-operational for 8 months has not been evaluated. Accordingly, herein, the re-startup process performance of a DHS reactor treating low-strength domestic sewage in Thailand that had stopped operation for over eight months was investigated. The dried sponge carrier immediately retained water in the sponge biomass-retained carrier and absorbed organic compounds. High nitrification activity of the DHS reactor was observed after 13 d, which was the same as that of the pure sponge biomass-retained carrier start-up. The tracer test results showed that the restarted DHS reactor had a high hydraulic retention time (HRT)/theoretical HRT ratio of 134.2 % at the beginning of the operation from the water retention property of the sponge carrier. Microbial community analysis showed that nitrifying microorganisms were effectively recovered in the biomass-retained sponge carrier. These results demonstrate that the sponge carriers in the DHS reactor that were left into dry condition are available for reuse and has high potential for rapid re-startup.

Heterotrophic nitrifying bacteria from activated sludge in DHS reactor for ammonium removal of natural rubber processing wastewater treatment

Two heterotrophic nitrifying bacterial strains, D2 and D7 were isolated from an activated sludge of sponges in a laboratory-scale downflow hanging sponge reactor. Both strains exhibited efficient ammonium removal ability over a wide range of ammonium loads. At the initial concentration of 100 mg/L, NH4+-N was completely degraded within 20 h by both strains. When the initial concentration was increased to 200 mg/L, the NH4+-N removal efficiency was 99.6 % within 20 h by the strain D2 and 61.3 % by the strain D7. In natural rubber processing wastewater, the ammonium removal efficiencies of strain D2 and D7 were 38 % and 99 % with the initial N-NH4+ concentration of 280 and 380 mg/L after 88 h, respectively. The 16S rRNA gene sequence of D2 and D7 showed the highest similarity to the Pseudomonas aeruginosa and Glutamicibacter nicotianae, respectively. This is the first report to demonstrate the ability to remove ammonium in NRPW by ​heterotrophic nitrifying bacteria isolated from activated sludge in DHS reactor.

A series anaerobic-aerobic down-flow hanging sponge (DHS) reactor for the treatment of palm oil mill effluent (POME)

Palm oil mill effluent (POME) contains very high organic compounds that must be treated before being discharged into the environment. Pond technology has been widely used for the treatment of POME; however, it requires a huge area of land. Down-flow hanging sponge (DHS) reactor has shown a high pollutant removal efficiency, less energy, and land area requirement. This study aimed to investigate the performance of a series of anaerobic (R3) and aerobic (R4) DHS reactors in treating POME. The reactor was continuously supplied with POME in three different phases for 165 days. The COD loading rate was set at 3.06, 6.12, and 12.24 kg-COD/m³·day in Phase 1, Phase 2, and Phase 3, respectively. Hydraulic retention time (HRT) was set at 47 min and 50 min, in R3 and R4, respectively. The reactors showed good performance for pollutant removal efficiency, especially COD. In Phase 1, the average COD removal rate was 2.68 and 0.27 kg-COD/m³·d in R3 and R4, respectively. In Phase 2, when the COD loading rate was increased, the average COD removal rate achieved 4.12 and 1.53 kg-COD/m³·d in R3 and R4, respectively. In Phase 3, the COD loading rate was doubled to 12.24 kg-COD/m³·day and the average COD removal rate of 5.81 and 2.90 kg-COD/m³·d was achieved in R3 and R4, respectively. During operation, the concentration of nitrate fluctuated in R4, which indicated that nitrification had occurred. Phosphate could be reduced in R3, but only a small portion could be removed in R4. Total suspended solids (TSS) could be effectively removed in R4. These results revealed that a combination of anaerobic-aerobic DHS reactors showed good performance in removing pollutants such as COD and TSS. Therefore, DHS technology can be used as a polishing treatment for treated POME.

Palm oil mill effluent (POME) treatment using a combined anaerobic-microalgae down-flow hanging sponge (DHS) reactor

Palm oil mill effluent (POME) generated from the production of palm oil contains organic and inorganic contaminants that can be a nutrient source for microorganisms such as bacteria, fungi, and microalgae. In this study, POME was treated using a combined anaerobic (R1) and microalgae (R2) in down-flow hanging sponge (DHS) reactor. Chlorella pyrenoidosa was immobilized in sponge carriers of R2 and LED lights were used for 12 hours per day to support microalgae growth. The DHS reactors were continuously operated for 165 days in three phases with different COD loading rates, namely 3, 6, and 12 kg-COD/m³·day in Phase 1, Phase 2, and Phase 3, respectively. The hydraulic retention time (HRT) was set at 46 min and 52 min in R1 and R2, respectively. The highest COD removal rate was achieved at 6.93 kg-COD/m³·day and 4.85 kg-COD/m³·day in R1 and R2, respectively. In addition, maximum phosphate removal was 68% in both reactors. Increased concentration of nitrate in R-2 indicated that nitrification may occur in the reactor. The pH of R1 effluent was relatively stable at neutral conditions, while the pH value of R2 effluent slightly increased. Based on visual observation, bacteria biofilm also grew in the microalgae reactor (R2). Synergistic bacteria-microalgae may play an important role in pollutant removal. The results of this study show that a combined anaerobic and microalgae DHS reactor can be used as an alternative for POME treatment because they have a shorter HRT and can be applied in a small area.

A syphon-downflow hanging sponge (DHS) reactor for improving the denitrification efficiency of sewage water treatment

The study focused on developing a low-cost down-flow hanging sponge (DHS) to enhance denitrification. The DHS reactor was modified by connecting with a syphon tube to maintain aerobic and anaerobic conditions. This method can simultaneously achieve nitrification and denitrification, requiring no extra energy for pumping. The study had two phases to evaluate the denitrification efficiency of the syphoned reactor at different reactor configurations. In the first phase, the syphon height was equal to the reactor height, and a water column was developed inside the DHS to create an anaerobic zone. The sCOD removal rates of syphon–DHS and conventional-DHS (control) were 75 ± 20% and 73 ± 19%, respectively, and the removal rates were almost similar in both reactors. However, the total nitrogen (TN) removal rate of syphon–DHS was 19 ± 3%, six folds greater than that of the conventional-reactor. In phase II, the syphon height of the developed DHS was changed to 3/5 of the DHS height. The sCOD and NH4+-N removal of syphon–DHS in the second phase were 62 ± 33% and 62 ± 31%, respectively, and approximately similar to the convectional DHSs’ performance. The anaerobic zone of the reactor facilitated enhancing the TN removal two folds than the conventional-reactor and was measured as 18 ± 16%. Nitrifiers, denitrifiers and anammox bacteria were present in the sludge samples of syphon–DHS as nitrogen-removing bacteria. The developed anaerobic conditions in the syphon–DHS enhanced denitrification without using extra energy for operation.

Environmental and Economic Evaluation of Downflow Hanging Sponge Reactors for Treating High-Strength Organic Wastewater

This study evaluated the performance of a downflow hanging sponge (DHS) in reducing the concentrations of chemical oxygen demand (COD), ammonia (NH3), total suspended solids (TSS), and total dissolved solids (TDS) in high-strength organic wastewater (HSOW). The DHS unit was composed of three segments connected vertically and operated under different organic loading rates (OLRs) between 3.01 and 12.33 kg COD/m3sponge/d at a constant hydraulic retention time (HRT) of 3.6 h. The results demonstrated that the DHS system achieved COD, NH3, TSS, and TDS removal efficiencies of 88.34 ± 6.53%, 64.38 ± 4.37%, 88.13 ± 5.42%, and 20.83 ± 1.78% at an OLR of 3.01 kg COD/m3sponge/d, respectively. These removal efficiencies significantly (p < 0.05) dropped to 76.39 ± 6.58%, 36.59 ± 2.91%, 80.87 ± 5.71%, and 14.20 ± 1.07%, respectively, by increasing the OLR to 12.33 kg COD/m3sponge/d. The variation in COD experimental data was well described by the first-order (R2 = 0.927) and modified Stover–Kincannon models (R2 = 0.999), providing an organics removal constant (K1) = 27.39 1/d, a saturation value constant (KB) = 83.81 g/L/d, and a maximum utilization rate constant (Umax) = 76.92 g/L/d. Adding another DHS reactor in a secondary phase improved the final effluent quality, complying with most environmental regulation criteria except those related to TDS concentrations. Treating HSOW with two sequential DHS reactors was economically feasible, with total energy consumption of 0.14 kWh/m3 and an operating cost of about 7.07 USD/m3. Accordingly, using dual DHS/DHS units to remove organics and nitrogen pollutants from HSOW would be a promising and cost-efficient strategy. However, a tertiary treatment phase could be required to reduce the TDS concentrations.

Polymeric materials used for immobilization of microalgae for the bioremediation of palm oil mill effluent

The immobilization of microalgae on polymeric materials such as polyurethane foam (PUF) has shown distinct advantages over non-immobilized technique with significant pollutants degradation efficiency. However, the effect of volume and pore size of PUF on the microalgae performance to remove organics and ammonium has not been extensively investigated. In this study, a down flow hanging sponge (DHS) reactor packed with PUF carrier for the immobilization of microalgae was utilized in treating palm oil mill effluent. The result of chemical oxygen demand (COD) degradation indicates that smaller pore size (0.56 mm) and higher PUF volume (38.0 %) increased the total performance of DHS reactor. In addition, this study also found that the growth of microalgae was greatly influenced by different pore sizes and volumes of PUF.

A pilot-scale study of a down-flow hanging sponge reactor as a post-treatment for domestic wastewater treatment system at short hydraulic retention times

This study proposes a down-flow hanging sponge (DHS) reactor as a post-treatment process for sewage treatment systems. A pilot-scale DHS reactor was operated over 1000 days under relatively short hydraulic retention times (HRT) of 1–3 h to evaluate its effectiveness as a post-treatment technology. The DHS reactor consistently achieved superior effluent water quality with total suspended solid <10 mg/L, biochemical oxygen demand < 10 mg/L, and ammonium nitrogen < 5 mg/L. The effective removals (> 2-log10 reduction) of Escherichia coli, a fecal contaminant indicator, and Arcobacter spp., a potentially pathogenic bacterial group, were achieved. The treatment performance was compared with the previous operation treating raw domestic wastewater under long HRTs of 4 and 5 h. As a result, the DHS reactor under short HRT conditions showed advantages for biological oxidation and fecal contaminant removal. These results indicate that the DHS reactor could be a compact post-treatment technology.

Evaluation of an anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system in treatment of black wastewater from a closed recirculating aquaculture system

This study focused on evaluating the nitrogen and solids removal performance of a laboratory-scale anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system for treating black wastewater from a closed recirculating aquaculture system (RAS) under a salinity of 15‰. The system was investigated under a controlled temperature (35 °C) with total organic carbon/total nitrogen (TOC/TN) ratios of 1.8, 2.5, 0.3, and 3.0, which corresponded to Phases 1, 2, 3, and 4, respectively, for 500 days. The ABR achieved a nitrate removal efficiency of 95–99 % at TOC/TN ratios higher than 1.8. The nitrate removal efficiency significantly decreased from 98 % to 12 % when the TOC/TN ratio decreased from 3.0 to 0.3. The highest TN removal efficiency (94 ± 4 %) was achieved with a TOC/TN ratio of 3.0. The ABR could remove 97 ± 6 % of the suspended solids during the entire experimental period. The DHS reactor achieved a nitrification efficiency of 70 % with short hydraulic retention times of 0.11–0.28 min. Total ammonia nitrogen in the DHS effluent was less than 1.0 mg N/L in the stable condition. The denitrifying Thauera genera predominant in the ABR reactor led to a high degree of denitrification. Methanogenic organisms such as Methanobacterium and Methanosaeta contributed to methane production of 0.8 ± 0.4 L/d in the ABR at a TOC/TN ratio of 3.0. Microbial community structure analysis showed that nitrifying microorganisms, such as Nitrosomonas, Nitrospira, and Candidatus Nitrosopumilus, were detected in the DHS-retained sludge. These results indicate that the ABR–DHS system evaluated could be applied for the removal of nitrogen and solids from RAS derived black wastewater to meet the water quality level needed for production-scale RAS.

Development of a post-treatment system using a downflow hanging sponge reactor – an upflow anaerobic reactor for natural rubber processing wastewater treatment

This study aimed to evaluate the nitrogen removal of a post-treatment system for natural rubber processing wastewater (NRPW) under low chemical oxygen demand to total nitrogen (COD/TN) ratios without any supplemental external carbon source. The system including a downflow hanging sponge (DHS) reactor and an upflow anaerobic reactor (UAR) was operated in two phases. In phase 1 (day 0–102), under a nitrogen loading rate (NLR) of 0.23 ± 0.06 kgN m−3 d−1 and COD/TN ratio of 0.63 ± 0.47, the DHS-UAR system removed 82.5 ± 11.8% and 83.9 ± 7.6% of TN and ammonium concentrations, respectively. In phase 2 (day 103–229), higher COD/TN ratio of 1.96 ± 0.28 was applied to remove increasing NLRs. At the highest NLR of 0.51 kgN m−3 d−1, the system achieved TN and ammonium removal efficiencies of 93.2% and 93.7%, respectively. Nitrogen profiles and the 16S rRNA high-throughput sequencing data suggested that ammonium, a major nitrogen compound in NRPW, was utilized by nitrifying and ammonium assimilation bacteria in DHS, then removed by heterotrophic denitrifying and anammox bacteria in the UAR. The predominance of Acinetobacter detected in both reactors suggested its essential role for the nitrogen conversion.

Biogas purification and ammonia load reduction in sewage treatment by two-stage down-flow hanging sponge reactor

In this study, a two-stage down-flow hanging sponge (TSDHS) reactor was used as biotrickling filter for biogas desulfurization by utilizing the anaerobic digester supernatant (ADS) of sewage sludge of an activated sludge process (ASP). The reactor comprises a closed-type first-stage down-flow hanging sponge (1st DHS) and an open-type second-stage down-flow hanging sponge (2nd DHS) reactors. In the 1st DHS, hydrogen sulfide in biogas was dissolved into the ADS, and then it was oxidized into elemental sulfur and sulfate by microbe using dissolved oxygen and nitrite in the ADS. More than 99.9 % of hydrogen sulfide was removed within 400 s of empty bed residence time, and >50 % of removed hydrogen sulfide was oxidized into elemental sulfur and accumulated at the surface of the sponge carrier in the 1st DHS. The 1st DHS effluent was fed into the 2nd DHS for nitrogen removal via nitrification and sulfur-based denitrification with the recirculation of the 2nd DHS effluent under nonaeration condition. In the 2nd DHS, 36.8 % of ammonia and 5.3 % of total inorganic nitrogen were removed. Sulfurimonas and Halothiobacillus were increased and contributed to the sulfur-based denitrification as well as the accumulation of elemental sulfur in the 1st DHS, respectively. In the 2nd DHS, Nitrosococcus, Nitrobacter, and Sulfuritalea were considered as the contributors of nitrogen removal via nitrification and sulfur-based denitrification. Further, this study shows that a TSDHS reactor can achieve not only desulfurization of biogas in the 1st DHS but also a 3.5 %–15 % reduction of the ammonia load in the 2nd DHS by effective utilization of the ADS during sewage treatment, assuming that the ADS is returned to the ASP.

Performance evaluation of quick and compact package-type down-flow hanging sponge system for domestic sewage treatment

Wastewater treatment plants require long installation and start-up times. In this study, a compact package-type down-flow hanging sponge (DHS) operating system based on the trickling filter principle using polyurethane sponge media was designed and installed at a sewage treatment site in Thailand. The DHS system was installed within 14 d of material arrival and operated for 81 d without seed sludge inoculation. The T-BOD concentration of the DHS effluent reached 2.2 mg·L−1 after 6 d of operation. High nitrification activity of the DHS reactor, when operated with a hydraulic retention time of 3.7 ± 0.9 h, was observed after 13 d of operation. In addition, the DHS effluent achieved the discharge standard within 14 d of operation. The DHS reactor rapidly initiated the removal of organics and nitrogen and exhibited COD, TSS, and ammonia removal efficiencies of 58% ± 10%, 76% ± 21%, and 66% ± 32%, respectively. Parallel 16S rRNA gene sequencing of sludge revealed the rapid growth of nitrifying bacteria. The abundance of ammonia-oxidizing bacteria Nitrosomonas spp. ranged from 0.1% to 1.8% on day 18, indicating that the DHS sponge media effectively retained slow-growth nitrifying bacteria that were affected by the rapid start-up process. Nitrite-oxidizing Nitrospira sp. was mainly detected at the bottom of the reactor. These results show that the compact package-type DHS system is a novel and practical easy-contract sewage treatment method.

Full-scale application of a down-flow hanging sponge reactor combined with a primary sedimentation basin for domestic sewage treatment.

The down-flow hanging sponge (DHS) reactor is advantageous for sewage treatment since it produces an effluent quality that complies with the standards for reuse and there is little excess sludge. A full-scale DHS module was efficiently employed for the treatment of domestic sewage (200 m3day-1) flowing from a primary sedimentation basin (PSB), which was used to reduce the suspended solids loading rate and enhance the oxidation of organics by heterotrophs. The combined PSB-DHS was successfully operated at a total hydraulic retention time of 3.4h (2.4h for PSB and 1.0h for DHS) for the relatively long period of 600days at sewage temperatures of 10°C to 32°C. The PSB-DHS consistently produced an effluent quality with minimum values of chemical oxygen demand, biochemical oxygen demand, and suspended solids of 59 ± 15, 12 ± 3.0, and 15 ± 7mg L-1, respectively. The proposed system performed exceptionally well at removing organics and particulate matter over a short hydraulic retention time.

Environmental Factors Affecting the Community of Methane-oxidizing Bacteria.

Methane-oxidizing bacteria (MOB) are ubiquitous and play an important role in the mitigation of global warming by reducing methane. MOB are commonly classified into Type I and Type II, belonging to Gammaproteobacteria and Alphaproteobacteria, respectively, and the diversity of MOB has been examined. However, limited information is currently available on favorable environments for the respective MOB. To investigate the environmental factors affecting the dominant type in the MOB community, we performed MOB enrichment using down-flow hanging sponge reactors under 38 different environmental conditions with a wide range of methane (0.01–80%) and ammonium concentrations (0.001–2,000‍ ‍mg N L–1) and pH 4–7. Enrichment results revealed that pH was a crucial factor influencing the MOB type enriched. Type II was dominantly enriched at low pH (4–5), whereas Type I was dominant around neutral pH (6–7). However, there were some unusual cultivated biomass samples. Even though high methane oxidation activity was observed, very few or zero conventional MOB were detected using common FISH probes and primer sets for the 16S rRNA gene and pmoA gene amplification. Mycobacterium mostly dominated the microbial community in the biomass cultivated at very high NH4+ concentrations, strongly implying that it exhibits methane oxidation activity. Collectively, the present results revealed the presence of many unknown phylogenetic groups with the capacity for methane oxidation other than the reported MOB.

Evaluating the resilience of a full-scale down-flow hanging sponge reactor to shock-loadings

Abstract The effect of shock-loading on the performance of a full-scale down-flow hanging sponge (DHS), used to treat effluent from an up-flow anaerobic sludge blanket treating municipal sewage, was evaluated. This full-scale DHS reactor comprises a polyurethane sponge that retains the sludge. It has a capacity of 500 m3/day and, at the time of this study, had been operating at a sewage treatment plant in India for more than 1,300 days. The DHS reactor was exposed to shock loadings of organics at double the normal rate for 400 min under summer and winter conditions. The results showed that the DHS reactor maintained stable operation under the organic shock loading and that it returned to a steady state soon after restart, confirming that the reactor was resilient to organic shock loadings.