Down-flow Hanging Sponge Reactor Research Articles

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.

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 sixth-generation down-flow hanging sponge (DHS) reactor using rigid sponge media for post-treatment of UASB treating municipal sewage

A sixth-generation down-flow hanging sponge reactor (DHS-G6), using rigid sponge media, was developed as a novel aerobic post-treatment unit for upflow anaerobic sludge blanket (UASB) treating municipal sewage. The rigid sponge media were manufactured by copolymerizing polyurethane with epoxy resin. The UASB and DHS system had a hydraulic retention time (HRT) of 10.6 h (8.6 h for UASB and 2 h for DHS) when operated at 10-28 °C. The system gave reasonable organic and nitrogen removal efficiencies. The final effluent had a total biochemical oxygen demand of only 12 mg/L and a total Kjeldahl nitrogen content of 6 mg/L. The DHS reactor gave particularly good nitrification performance, which was attributed to the new rigid sponge media. The sponge media helped to provide a sufficient HRT, and retained a high biomass concentration, extending the solids retention time. The DHS reactor maintained a high dissolved oxygen concentration under natural ventilation.

Microbial community composition of a down-flow hanging sponge (DHS) reactor combined with an up-flow anaerobic sludge blanket (UASB) reactor for the treatment of municipal sewage

The microbial community composition of a down-flow hanging sponge (DHS) reactor in an up-flow anaerobic sludge blanket (UASB)-DHS system used for the treatment of municipal sewage was investigated. The clone libraries showed marked differences in microbial community composition at different reactor heights and in different seasons. The dominant phylotypes residing in the upper part of the reactor were likely responsible for removing organic matters because a significant reduction in organic matter in the upper part was observed. Quantification of the amoA genes revealed that the proportions of ammonia oxidizing bacteria (AOB) varied along the vertical length of the reactor, with more AOB colonizing the middle and lower parts of the reactor than the top of the reactor. The findings indicated that sewage treatment was achieved by a separation of microbial habitats responsible for organic matter removal and nitrification in the DHS reactor.

Enhancement of denitrification in a down-flow hanging sponge reactor by effluent recirculation

A down-flow hanging sponge reactor, constructed by connecting three identical units in series, was applied to the treatment of artificial wastewater containing phenol and ammonia under high salinity conditions (10.9 g-Cl(-)/L). The theoretical hydraulic retention time (HRT) of each unit was 4 h (total HRT = 12 h). To enhance denitrification by effluent recirculation, the effluent recirculation ratio was increased in increments ranging from 0.0 to 2.0. The concentration of total ammonia nitrogen (TAN), NO2-N, and NO3-N in the final effluent as a proportion of the TAN in the influent was determined to calculate the unrecovered, or denitrification, proportion. The denitrification proportion of the reactor was equivalent to 19.1 ± 14.1% with no effluent recirculation; however, this was increased to 58.6 ± 6.2% when the effluent recirculation ratio was increased to 1.5. Further increasing the effluent recirculation ratio to 2.0 resulted in a decrease in the denitrification proportion to 50.9 ± 9.3%. Activity assays of nitrification and denitrification, as well as 16S rRNA gene sequence analysis, revealed that denitrification occurred primarily in the upper sections of the reactor, while nitrification increased in the lower sections of the reactor. Gene sequence analysis revealed that denitrification by Azoarcus-like species using phenol as an electron donor was dominant.

Characterization of the retained sludge in a down-flow hanging sponge (DHS) reactor with emphasis on its low excess sludge production

Experiments to characterize retained sludge in a down-flow hanging sponge (DHS) reactor fed with upflow anaerobic sludge blanket (UASB) treated sewage under moderate conditions were conducted. Plenty of oxygen was supplied through the DHS reactor without aeration and the effluent qualities after the reactor were comparable to activated sludge processes. The average excess sludge production rate was 0.09g SS g−1 COD removed. The DHS reactor maintained a high sludge concentration of 26.9g VSS L−1 sponge, resulting in a low loading rate of 0.032g COD g−1 VSS day−1. The endogenous respiration rate of DHS sludge was comparable to previously reported aerobic sludges. The numbers of microfauna were one order of magnitude greater than those in activated sludge. The results indicated that low excess sludge production was attributable to the high sludge concentration, sufficient oxygen supply, adequate endogenous respiration rate, and a high density and diversity of microfauna.

Long term Evaluation of the Effect of Salinity on Organic Removal and Ammonium Oxidation in a down-flow Hanging Sponge Reactor

The effect of salinity on organic removal and ammonium oxidation in a down-flow hanging sponge reactor was investigated by conducting a long-term continuous experiment over a period of 800 days. The DHS reactor, constructed by connecting three identical units, was fed with artificial wastewater containing 500 mg-N/L of ammonium nitrogen and 1400 mg- COD/L of phenol. Salinity of the influent was controlled by the addition of 8.0 to 25 g-Cl-/L of NaCl. The DHS reactor was operated at a hydraulic retention time of 12 h in a temperature controlled room at 25oC. No significant inhibition of organic removal and ammonium oxidation was observed at salinities of up to 20 g-Cl-/L, at which levels ammonium oxidation and COD removal both exceeded 90%, respectively. However, at a salinity of 25 g-Cl-/L, organic removal and ammonium oxidation were both severely inhibited. In addition, the ratio of effluent nitrite nitrogen to influent ammonium nitrogen increased from 3.4% at salinities of 8.0 g-Cl-/L to 33% at salinities of 20 g-Cl-/L.

The effect of salinity on nitrite accumulation in a down‐flow hanging sponge reactor

AbstractBACKGROUND: In this study, the inductive effect of salinity on nitrite accumulation in a down‐flow hanging sponge (DHS) reactor, developed as a novel and cost‐effective wastewater treatment process, was evaluated by conducting a long‐term continuous experiment lasting more than 1400 days.RESULTS: The influent salinity was controlled by adding NaCl at concentrations ranging from 0 to 25 g Cl− L−1. The effluent nitrite increased with increases in salinity, i.e. the fraction of nitrite to total nitrogen in the effluent increased from 1.6% at 0 g Cl− L−1 to 87.6% at 25 g Cl− L−1. Fluorescence in situ hybridization (FISH) analysis revealed that as salinity increased, the nitrifying bacterial community in the DHS changed markedly at the species level. In particular, the dominant nitrite‐oxidizing bacteria changed from Nitrospira‐sublineage I at 0 g Cl− L−1 to Nitrobacter spp. at 15 g Cl− L−1. At 25 g Cl− L−1, no nitrite‐oxidizing bacteria were detected.CONCLUSION: Our findings suggest that the DHS reactor is suitable for cost‐effective nitrite production processes and that salinity control using NaCl is an effective method for inducing nitrite accumulation. Copyright © 2012 Society of Chemical Industry

Direct Treatment of Settled Sewage by DHS Reactors with Different Sizes of Sponge Support Media

The down-flow hanging sponge (DHS) reactor, which was developed for post-treatment of effluent from up-flow anaerobic sludge blanket (UASB) process treating sewage, uses polyurethane sponge as media to retain biomass. Wastewater is trickled from the top of the reactor and purified by microorganisms retained both inside and outside of the sponge media as the wastewater flows vertically down through the reactor. Three DHS reactors employing different sizes of sponge media with the same total sponge volume were used for the direct treatment of settled sewage. All the reactors exhibited excellent performance in removal of COD, ammonium nitrogen, and fecal coliform at a fixed hydraulic retention time of 2.0 h based on the sponge volume. It was shown that smaller sponge media produced better removal efficiencies for all the parameters listed above. The most reasonable explanation for this might be that smaller sponge media allows better oxygen uptake in the stream flowing down through the reactors.

Dissolved methane oxidation and competition for oxygen in down-flow hanging sponge reactor for post-treatment of anaerobic wastewater treatment

Post-treatment of anaerobic wastewater was undertaken to biologically oxidize dissolved methane, with the aim of preventing methane emission. The performance of dissolved methane oxidation and competition for oxygen among methane, ammonium, organic matter, and sulfide oxidizing bacteria were investigated using a lab-scale closed-type down-flow hanging sponge (DHS) reactor. Under the oxygen abundant condition of a hydraulic retention time of 2h and volumetric air supply rate of 12.95m3-airm−3day−1, greater than 90% oxidation of dissolved methane, ammonium, sulfide, and organic matter was achieved. With reduction in the air supply rate, ammonium oxidation first ceased, after which methane oxidation deteriorated. Sulfide oxidation was disrupted in the final step, indicating that COD and sulfide oxidation occurred prior to methane oxidation. A microbial community analysis revealed that peculiar methanotrophic communities dominating the Methylocaldum species were formed in the DHS reactor operation.

Performance of down-flow hanging sponge (DHS) reactor coupled with up-flow anaerobic sludge blanket (UASB) reactor for treatment of onion dehydration wastewater

In this study, a promising system consisting of up-flow anaerobic sludge blanket (UASB) reactor followed by down-flow hanging sponge (DHS) reactor was investigated for onion dehydration wastewater treatment. Laboratory experiments were conducted at two different phases, i.e., phase (1) at overall hydraulic retention time (HRT) of 11h (UASB reactor: 6h and DHS reactor: 5h) and phase (2) at overall HRT of 9.4h (UASB reactor: 5.2h and DHS reactor: 4.2h). Long-term operation results of the proposed system showed that its overall TCOD, TBOD, TSS, TKN and NH4N removal efficiencies were 92±5, 95±2, 95±2, 72±6 and 99±1.3%, respectively (phase 1). Corresponding values for the 2nd phase were 85.4±5, 86±3, 87±6, 65±8 and 95±2.8%. Based on the available results, the proposed system could be more viable option for treatment of wastewater generated from onion dehydration industry in regions with tropical or sub-tropical climates and with stringent discharge standards.

Use of down-flow hanging sponge (DHS) reactor as a promising post-treatment system for municipal wastewater

The aim of the present study was the treatment of municipal wastewater to be used for irrigation using a technology that is robust and simple to operate with minimum energy consumption. In order to achieve these objectives, two treatment schemes have been investigated. The first scheme consisted of a hybrid up-flow anaerobic sludge blanket (HUASB) reactor followed by a down-flow hanging sponge (DHS) reactor. The second one consisted of a primary sedimentation tank (PST) followed by a DHS reactor. Both systems were fed continuously with raw municipal wastewater. The study lasted for more than 140 days, the results of which revealed that the efficiency of both systems was comparable with regard to carbonaceous and nitrogenous compounds removal. The average removal values of COD total, COD soluble, BOD 5total, TSS and TN in the first scheme were 90 ± 4, 78 ± 8, 95 ± 2, 96 ± 5 and 72 ± 8%, respectively. However, the residual geometric mean of faecal coliform counts in the final effluent of the first treatment scheme was only 2.7 × 10 2 MPN/100 ml compared to 6.5 × 10 3 MPN/100 ml in the second treatment scheme. In general, available data proved that the DHS reactor can cope with higher organic loads. The performance of DHS reactor was quite good for carbonaceous organic matter and nitrogen removal even at high OLR of 4.8 kg COD/m 3 d.

Quantification of organic and nitrogen removal in downflow hanging sponge (DHS) systems as a post-treatment of UASB effluent

The aim of this research was to investigate the nature and composition of organic substrate in two down-flow hanging sponge (DHS) systems using mixed fungal (FDHS) and bacterial (BDHS) cultures treatment for UASB effluent of tapioca starch wastewater, evaluated by COD fractionations and two material balances. The random type DHS reactors were operated as modular columns consisting of four identical segments connected vertically. Results of the wastewater characterization showed that carbonaceous fractions were varied on a function of DHS height. Two balances applied to experimental data were for chemical oxygen demand (COD) and nitrogen (N). Results of mass balance calculations can also be used to examine the process behavior of two DHS systems to improve the organic and nitrogen removal mechanisms.

Treatment of Sugar Containing-Low Strength Wastewater at 20°C by Anaerobic Granular Sludge Bed Reactor

To investigate the feasibility of anaerobic wastewater treatment technology for low strength sugar refinery wastewater (0.4 - 0.5 g COD/L), an 8.8 L volume of anaerobic granular sludge bed reactor was operated at 20°C for 400 days. The operation mode was combination of one pass flow (UASB, 50 min) and effluent-recirculation (EGSB, 10 min) mode. The aerobic down-flow hanging sponge (DHS) reactor was installed as a post-treatment. During the started-up period, reactors were fed with synthetic wastewater at overall HRT of 3 hours (anaerobic 2 hours, aerobic 1 hour). After day 85, feed was changed to real wastewater together with supplement of nutrients, trace elements and NaHCO3. The sufficient COD removal efficiency (85% SD±6.2) and stable process performance were elicited from the granular sludge bed reactor.Also, post-treatment (DHS reactor) offered good quality of effluent (45 mg COD/L, 7 mg BOD/L) and it achieved the discharge standard. Increasing of sulfate concentration of wastewater caused higher contribution of sulfate reducing bacteria for COD removal. The sludge concentration and settleability were well maintained thoroughly. However, floatation of large size granule was observed in the later part of experiment. This phenomenon may attribute to the high growth yield of retained sludge at 20°C.

Closed DHS system to prevent dissolved methane emissions as greenhouse gas in anaerobic wastewater treatment by its recovery and biological oxidation

Anaerobic wastewater treatment has been focused on its eco-friendly nature in terms of the improved energy conservation and reduction in carbon dioxide emissions. However, the anaerobic process discharges unrecovered methane as dissolved methane. In this study, to prevent the emission of dissolved methane from up-flow anaerobic sludge blanket (UASB) reactors used to treat sewage and to recover it as useful gas, we employed a two-stage down-flow hanging sponge (DHS) reactor as a post-treatment of the UASB reactor. The closed DHS reactor in the first stage was intended for the recovery of dissolved methane from the UASB reactor effluent; the reactor could successfully recover an average of 76.8% of the influent dissolved methane as useful gas (containing methane over 30%) with hydraulic retention time of 2 h. During the experimental period, it was possible to maintain the recovered methane concentrations greater than 30% by adjusting the air supply rate. The remaining dissolved methane after the first stage was treated by the next step. The second closed DHS reactor was operated for oxidation of the residual methane and polishing of the remaining organic carbons. The reactor had a high performance and the influent dissolved methane was mostly eliminated to approximately 0.01 mgCOD L(-1). The dissolved methane from the UASB reactor was completely eliminated--by more than 99%--by the post-treatment after the two-stage closed DHS system.

塩分によるDHSリアクター内の硝化細菌群の菌叢変化と亜硝酸化の促進

The effect of salinity on nitritation in a Down-flow Hanging Sponge (DHS) reactor was evaluated through a long-term continuous experiment for 700 days. The DHS reactor was fed with artificial wastewater containing 100 mg-N·L-1 ammonium nitrogen (HRT = 2 h, 20-25°C). The salinity of the influent was controlled by adding NaCl at concentrations of 5 to 18 g-Cl-·L-1. The effluent nitrite concentration increased with increasing of salinity, i.e., the nitrite concentration increased up to approximately 60% of the total nitrogen in the effluent at 18 g-Cl-·L-1. The nitrifying bacterial community in the DHS markedly changed at the species level. For example, the dominant nitrite-oxidizing bacteria changed from Nitrospira-sublineage I at 0 g-Cl-·L-1 to Nitrobacter spp. at 18 g-Cl-·L-1.

Biological oxidation of dissolved methane in effluents from anaerobic reactors using a down-flow hanging sponge reactor

Anaerobic wastewater treatment plants discharge dissolved methane, which is usually not recovered. To prevent emission of methane, which is a greenhouse gas, we utilized an encapsulated down-flow hanging sponge reactor as a post-treatment to biologically oxidize dissolved methane. Within 3 weeks after reactor start-up, methane removal efficiency of up to 95% was achieved with a methane removal rate of 0.8 kg COD m −3 day −1 at an HRT of 2 h. After increasing the methane-loading rate, the maximum methane removal rate reached 2.2 kg COD m −3 day −1 at an HRT of 0.5 h. On the other hand, only about 10% of influent ammonium was oxidized to nitrate during the first period, but as airflow was increased to 2.5 L day −1, nitrification efficiency increased to approximately 70%. However, the ammonia oxidation rate then decreased with an increase in the methane-loading rate. These results indicate that methane oxidation occurred preferentially over ammonium oxidation in the reactor. Cloning of the 16S rRNA and pmoA genes as well as phylogenetic and T-RFLP analyses revealed that type I methanotrophs were the dominant methane oxidizers, whereas type II methanotrophs were detected only in minor portion of the reactor.

多段嫌気性反応槽（ＵＡＳＢ）と下降流懸架式スポンジ（ＤＨＳ）反応槽を組み合わせた高濃度有機性廃水処理システムの開発

The processing performance of a high-strength-wastewater treatment system was investigated by feeding the system with sugar-containing synthetic wastewater for more than one year. The system consisted of a (35°C) mesophilic upflow anaerobic sludge blanket (UASB) reactor for pretreatment, and an ambient UASB reactor and a downflow hanging sponge (DHS) reactor for post-treatment. The DHS reactor was constructed using a liquid distributor and a packing material made with sponge cubes. A portion of the final effluent was recycled to the inlet of post-treatment with a recirculation ratio in the range of 2.0-0.3. The synthetic wastewater was made with organic waste from a food factory; it consisted of about 3,000mg of CODCr · l-1, 2,000mg of BOD · l-1 and 500mg of SS · l-1. The system exhibited excellent performance in organic removal, achieving 98% CODCr and 96% SS removal rates (final effluent: 43mgCODCr · l-1, 12mgBOD · l-1 and 15mgSS · l-1) with 75% of the methane recovered from the removed CODCr under conditions of 24hrs of HRT, a CODCr volumetric loading rate of 3.0 kg · m-3 · d-1 (35°C UASB as pretreatment, 1.4 kg · m-3 · d-1; post-treatment, 1.6 kg · m-3 · d-1), and low final effluent temperatures such as 1-10°C. The proposed system effectively saves energy and decreases the amount of excess sludge. It is considered as a novel process to treat high-strength wastewaters up to a discharge quality level.

Effective partial nitrification to nitrite by down-flow hanging sponge reactor under limited oxygen condition

Combining the processes of partial nitrification and anaerobic ammonium oxidation (ANAMMOX) is an attractive wastewater-treatment technology for nitrogen removal. In this study we investigated partial nitrification by implementing a closed down-flow hanging sponge (DHS) reactor operated at controlled oxygen concentrations. Basic concept of DHS process is similar to that of trickling filter, in which oxygen concentration can be easily manipulated by controlling airflow to the reactor. The closed reactor was fed with artificial wastewater containing NH 4Cl and operated with an HRT of 1.5 h at 30 °C. Oxygen inside the reactor was maintained below 3% (1.2 mg DO·L −1) (DO—dissolved oxygen) except during the startup periods. Five months of continuous operation showed that there was a strong relationship between oxygen concentration and nitrite production. The ratio of nitrite produced relative to ammonium oxidized increased by decreasing oxygen concentration. Partial nitrification was satisfactorily accomplished under oxygen limitation at around 0.5% in the gas phase (0.2 mg DO L −1). The system showed a high ammonium-removal rate, at a maximum of 1.46 kg NH 4 +–N m −3 day −1, even at limited oxygen concentration. We also found that oxygen concentration played an important role in the production of nitrous oxide, which increased with decreasing oxygen concentration.

Low strength wastewater treatment under low temperature conditions by a novel sulfur redox action process

The objective of this research is to make a novel wastewater treatment process activated by a sulfur-redox cycle action of microbes in low temperature conditions. This action is carried out by sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). The process was comprised of a UASB reactor as pre-treatment and an aerobic downflow hanging sponge (DHS) reactor as post-treatment. As the results of reactor operation, the whole process achieved that over 90% of CODcr removal efficiency, less than 30 mgCODcr/L (less than 15 mgBOD/L) of final effluent, at 12 h of HRT and at 8 degrees C of UASB reactor temperature. Acetobacterium sp. was detected as the predominant species by PCR-DGGE method targeting 16SrDNA with band excision and sequence analysis. In the UASB reactor, various species of sulfate-reducing bacterium, Desulfobulbus sp., Desulfovibrio sp., and Desulfomicrobium sp., were found by cloning analysis. In the DHS reactor, Tetracoccus sp. presented as dominant. The proposed sulfur-redox action process was considered as an applicable process for low strength wastewater treatment in low temperature conditions.