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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. HIGHLIGHTS A full-scale down-flow hanging sponge reactor was evaluated in India.; The DHS reactor was exposed to double organic rate for 400 min.; The DHS reactor produced stable effluent quality under shock loadings.; The DHS achieved a steady state soon after shock loadings under summer and winter.; The full-scale experiment verify that the DHS was resilient to shock-loadings.;

Wastewater pollution will continue to grow as the population and community activities continue to increase. Various techniques have been applied for domestic waste treatment, but generally these processes require relatively high operation and maintenance costs. Down Flow Hanging Sponge (DHS) has been proposed as a solution to the problem of handling domestic waste for developing countries. DHS bioreactor is a biological waste treatment that does not require an aerator and is easy to operate. This study aims to evaluate DHS bioreactors that can be applied in Indonesia. DHS bioreactor is operated with 4 hours hydraulic retention time (HRT). The results showed that DHS bioreactor is able to reduce up to 34% Chemical Oxygen Demand (COD) total, 33% soluble Chemical Oxygen Demand (COD), 80% Biological Oxygen Demand (BOD) total, and 65% Ammonia.ABSTRAK Pencemaran air limbah akan terus bertambah dengan meningkatnya jumlah penduduk dan aktifitas masyarakat. Berbagai proses telah diaplikasikan untuk pengolahan limbah domestik, tetapi umumnya proses-proses tersebut membutuhkan biaya operasi dan perawatan yang relatif mahal. Downflow Hanging Sponge (DHS) telah diusulkan sebagai pemecahan persoalan penanganan limbah domestik untuk negara-negara berkembang. DHS bioreaktor adalah pengolahan limbah secara biologis yang tidak membutuhkan aerator dan mudah dalam pengoperasian. Penelitian ini bertujuan untuk mengevaluasi bioreaktor DHS sehingga dapat diterapkan di Indonesia. Bioreakor DHS dioperasikan dengan hydraulic retention time (HRT) 4 jam. Hasil penelitian menunjukkan DHS bioreaktor mampu mengurangi hingga 34% Chemical Oxygen Demand (COD) total, 33% soluble Chemical Oxygen Demand (COD), 80% Biological Oxygen Demand (BOD) total, dan 65% ammonia.

A stand-alone down-flow hanging sponge (DHS) system with a two-stage configuration was operated for 700 days to treat synthetic soft drink wastewater at 3000 mg/L chemical oxygen demand (COD). Throughout the operation, >90% COD and total organic carbon (TOC) removal efficiency was obtained by the first stage, and a final effluent of COD <60 mg/L (TOC <20 mg/L) was consistently maintained with the second stage. Lower organic removal efficiency was observed to closely correlate with lower pH, higher volatile fatty acid (VFA) concentration, and higher suspended solid (SS) in the effluent. Occasionally, biomass sloughing was observed as a cause to unstable reactor performance in the first stage. The microbial community of the retained biomass on the sponges differed significantly based on spatial locations of sponges, sampling time points, and loading shocks. In general, Proteobacteria were found to be more abundant in the reactor at an organic removal efficiency >80% than that at <50%. Specifically, operational taxonomic units closely related to Tolumonas auensis and Rivicola pingtungensis were identified as important populations that were responsible for degrading the major substrate in the soft drink wastewater toward to the end of the reactor operation. In addition, high abundance of Bacteroidetes in the reactor was speculated to be responsible for the VFA accumulation in the effluent. This study demonstrated that stand-alone DHS reactor could be used in treating high-strength wastewater efficiently. [ABSTRACT FROM AUTHOR]

Resilience to process outages is an essential requirement for sustainable wastewater treatment systems in developing countries. In this study, we evaluated the ability of a full-scale down-flow hanging sponge (DHS) reactor to recover after a 10-day outage. The DHS tested in this study uses polyurethane sponge as packing material. This full-scale DHS reactor has been tested over a period of about 4 years in India with a flow rate of 500 m 3 /day. Water was not supplied to the DHS reactor that was subjected to the 10-day outage; however, the biomass did not dry out because the sponge was able to retain enough water. Soon after the reactor was restarted, a small quantity of biomass, amounting to only 0.1% of the total retained biomass, was eluted. The DHS effluent achieved satisfactory removal of suspended solids, chemical oxygen demand, and ammonium nitrogen within 90, 45, and 90 min, respectively. Conversely, fecal coliforms in the DHS effluent did not reach satisfactory levels within 540 min; instead, the normal levels of fecal coliforms were achieved within 3 days. Overall, the tests demonstrated that the DHS reactor was sufficiently robust to withstand long-term outages and achieved steady state soon after restart. This reinforces the suitability of this technology for developing countries. [ABSTRACT FROM AUTHOR]

A down-flow hanging sponge (DHS) reactor is a novel, unaerated, aerobic, biofilm reactor that is used to polish effluent received from an up-flow anaerobic sludge blanket (UASB) reactor for treating municipal sewage. A full-scale DHS reactor was constructed for post-treatment of a full-scale UASB reactor at a municipal sewage treatment plant in India. Performance of the DHS reactor was evaluated with respect to organic removal over 1800 days of continuous operation. The UASB + DHS system consistently produced effluent with chemical oxygen demand (COD), biochemical oxygen demand (BOD), and suspended solids (SS) values of 37, 6.0 and 19 mg L −1 , on average, respectively. The sludge yield of the DHS reactor was estimated to be 0.04 kg SS kg −1 COD removed or 0.12 kg SS kg −1 BOD removed, which is considerably lower than other aerobic treatment methods that have been employed for polishing UASB effluent. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] The microbial community composition of a DHS reactor was investigated. [•] Differences were observed at different reactor heights and in different seasons. [•] The dominant OTUs in the upper part were likely responsible for organic removal. [•] More AOB colonized in the middle and lower parts of the reactor. [•] A separation of microbial habitats was found in the DHS reactor. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: 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−3 day−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. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

This study determined the performance of upgraded sewage treatment plant (STP) based on an anaerobic-aerobic system consisting Up-flow Anaerobic Sludge Blanket (UASB) reactor, Final Polishing Unit (FPU) and Down-flow Hanging Sponge (DHS) system, treating municipal wastewater located at Dhandhupura, Agra, Uttar Pradesh (India). The performance evaluation of STP were based on the removal efficiency of parameters like Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Volatile Suspended Solids (VSS). The results exhibits improved BOD, COD, TSS and VSS removal efficiency for UASB-DHS system (92.01%, 82.26%, 91.02%, 92.88%) as compared to UASB-FPU (81.67%, 74.35%, 83.72%, 83.41%) respectively. In addition, this study compares the UASB-DHS system with other post-treatment methods based on their treatment cost and removal efficiency. The technology ranking analysis showed that the UASB-DHS system scored the highest desirability value of 6.77 followed by MBR and ASP technology having a score of 5.17 and 5.11 respectively. The results demonstrated that the UASB-DHS system outperformed the existing UASB-FPU system and met the Indian standards for effluent discharge i.e. BOD less than 30 mg/l. Therefore, the treated sewage can be considered for cultivation, irrigation purpose and safely discharged into water bodies. Moreover, the cost analysis indicates that the UASB-DHS system requires less energy in operation, low expenses in sludge handling and comparatively small area required for post-treatment operation. Hence, this work proposed an economical and efficient approach for the treatment of municipal wastewater particularly for developing countries. Image 1 • UASB-DHS integrated technology is sustainable approach for treatment developing countries. • UASB-DHS system has the highest removal efficiency with least laborious maintenance. • This study compares the UASB-DHS system with other post-treatment methods on cost and removal efficiency. • UASB-DHS integrated technology system exhibits an economical and efficient approach. • UASB-DHS system exhibits improved removal efficiency (max 93%) in reducing BOD, COD, TSS, VSS. [ABSTRACT FROM AUTHOR]

• A nitrifying bioreactor was continuously operated for 61 days. • Drastic changes in stable isotope ratios were observed in the bioreactor. • δ15N and δ18O of NO 3 − changed spatially with wastewater flow. • Sludge δ13C and δ15N spatially increased from −26‰ to −18‰ and from 5‰ to 30‰ • Isotopic signature of sludge and nitrate was related to process performance. This study determined the spatial and temporal changes in natural abundance of stable isotopes (δ13C, δ15N, and δ18O) with regard to nitrate (NO 3 −) and retained sludge in a nitrifying bioreactor. The bioreactor was continuously fed with synthetic wastewater including ammonium for 61 days at 20 °C. After the start-up period of the bioreactor, the NO 3 − concentration in the effluent gradually increased. The stable isotopes (δ15N and δ18O) of NO 3 − in the effluent also increased in a phase of incomplete nitrification. The profile experiments showed that the concentration and stable isotopes of NO 3 − changed simultaneously along the wastewater flow in the bioreactor. The stable isotope analysis revealed that nitrification efficiency seems to be strongly related to the δ15N of NO 3 −. Moreover, the δ13C and δ15N of the retained sludge drastically changed along the reactor length, from −26‰ to −18‰ and from 5‰ to 30‰, respectively, after 61 days of operation. The isotopic composition of the retained sludge might be affected by the isotope ratios (δ15N and δ18O) of NO 3 − in the bioreactor. Therefore, the isotope signatures of the retained sludge seem to closely reflect process performance such as nitrification efficiency throughout the operational period. Our findings suggest that the spatial distribution of the isotopic composition of the retained sludge can be used to detect process occurrence within the bioreactor over time. [ABSTRACT FROM AUTHOR]