The second generation of our originally proposed sewage treatment system, which consists of a UASB reactor as an anaerobic pre-treatment unit and curtain-type DHS (downflow hanging sponge) reactor as an aerobic post-treatment unit, was installed at a municipal sewage treatment site. A 550-day continuous experiment demonstrated that the whole combined system successfully achieved 94–97% of unfiltered-BOD removal, 81–84% of unfiltered-COD removal, and 63–79% of SS removal, at an overall HRT of 8 h (6 h for UASB and 2 h for DHS units). The combined system performed an excellent organic removal as well as a fairly efficient nitrification, i.e. 52–61% of ammonia-nitrogen removal. Our proposed combined system possesses prominent advantages: requiring neither external aeration input nor excess sludge withdrawal.

A novel sewage treatment system was proposed, which consists of a UASB anaerobic pre-treatment unit and the following DHS (downflow hanging sponge-cubes) aerobic post-treatment unit, as a low-cost and easy-maintenance process for developing countries. Over six months experiment by feeding sewage our proposed system achieved 94% of total-COD removal, 81% of soluble-COD removal, and nearly perfect SS removal and total-BOD removal at the overall HRT of 8.3 hr (7 hr in UASB and 1.3 hr in DHS unit). Moreover, the DHS reactor was capable of performing high (73–78%) nitrification. Our whole system requires neither external aeration input nor withdrawal of excess sludge.

This paper presents an evaluation of the process performance of a pilot-scale "fourth generation" downflow hanging sponge (DHS) post-treatment system combined with a UASB pretreatment unit treating municipal wastewater. After the successful operation of the second- and third-generation DHS reactors, the fourth-generation DHS reactor was developed to overcome a few shortcomings of its predecessors. This reactor was designed to further enhance the treatment efficiency and simplify the construction process in real scale, especially for the application in developing countries. Configuration of the reactor was modified to enhance the dissolution of air into the wastewater and to avert the possible clogging of the reactor especially during sudden washout from the UASB reactor. The whole system was operated at a total hydraulic retention time (HRT) of 8 h (UASB: 6 h and DHS: 2 h) for a period of over 600 days. The combined system was able to remove 96% of unfiltered BOD with only 9 mg/L remaining in the final effluent. Likewise, F. coli were removed by 3.45 log with the final count of 10(3) to 10(4) MPN/100 ml. Nutrient removal by the system was also satisfactory.

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Fluorescence in-situ hybridization (FISH) and DO microelectrodes were applied to biofilms developed in a novel reactor named DHS (downflow hanging sponge-cubes), to investigate the mechanisms of simultaneous carbon removal and nitrification. The DHS reactor was employed as an aerobic post-treatment process after an UASB anaerobic pre-treatment process receiving a municipal sewage. The presence ratio of Nitrosomonas and Nitrobacter cells to total cells of the DHS biomass was estimated by FISH technique to be 1.4% and 0.18%, respectively. Cell concentrations of both nitrifying bacteria were in good agreement with the magnitudes of ammonia-oxidizing and nitrite-oxidizing activities evaluated from batch tests. The habitats of both nitrifiers were the interior space of sponge-cubes, rather than within the biofilms attached onto sponge-cube surfaces. DO microelectrodes verify that the sponge-cubes insides were kept aerobically throughout the whole reactor height excluding the inlet vicinity portion.

A novel sewage treatment system, which consists of an upflow anaerobic sludge blanket (UASB) pre-treatment unit and the following downflow hanging sponge (DHS) unit for polishing up the UASB effluent, was developed as a cost-effective and easy-maintenance sewage treatment system for developing countries. A long-term experiment with actual sewage was conducted in order to evaluate its treatment efficiency of organic substances, nutrients, and pathogen indicator microorganisms such as total coliphages, F+-specific RNA coliphages (RNA coliphages), and fecal coliforms. The main objective of this paper is to investigate the removal efficiency of those indicator microorganisms by the UASB-DHS combined system. The results obtained from the continuous flow experiment indicated a fairly promising removal of the indicator microorganisms, i.e., the log10 reductions of total coliphages, RNA coliphages, and fecal coliforms (based on sewage and DHS effluent) achieved were 2.01 log, 2.02 log, and 2.57 log, respectively. The UASB-DHS combined system was superior to the conventional activated sludge process in the reduction of fecal coliforms, but in the reductions of total and RNA coliphages, the system showed somewhat less removal efficiency. The vertical reducing patterns of the indicator microorganisms along the DHS reactor were also discussed.

The combination of baffled air flotation and a membrane system for the treatment of palm oil mill effluent (POME) was studied. The POME was obtained from a palm oil factory in PTPN I Tanjong Seumantoh, Aceh, Indonesia. Operation variables and conditions, such as the hydraulic retention time and air flow rates, were varied to find the optimum process. The air flotation process is able to reduce the concentration of suspended solids and fats/ oils contained in the wastewater, which increases the performance of the membrane by reducing clogging. The results showed that this method was promising for POME treatment. The optimum organic removal efficiency of the air flotation pretreatment was obtained at HRT = 5 days and at an air flow rate of 11 L/min. The effluent was subsequently passed through an anaerobic membrane system to achieve the highest removal efficiency treatment. The removal efficiency of chemical oxygen demand (COD), total suspended solids (TSS), turbidity, mixed liquor suspended solids (MLSS), mixed liquor volatile suspended solids (MLVSS), and fats/oils after passing through the membrane system were 97%, 93.9%, 99.8%, 94.5%, 96.2%, and 99.9%, respectively. The results also showed that the pH could be neutralized to 6.18, while a dissolved oxygen (DO) level of 1.60 mg/L could be achieved. A high quality of effluent was obtained, which met the standards for POME effluent.

The potential renewable energy from tofu processing industries in Banda Aceh city of Indonesia and their waste characteristics have been studied. There are 10 tofu processing industries in Banda Aceh with raw materials capacity ranging from 150-500 kg/day for each industry. Totally, about 45,900 kg of wastewater produced from 2,550 kg/day soybean in Banda Aceh. Currently, the waste has been disposed into the environment and river without any treatment, causing bad odours and pollution of the surface and ground water. The management of this waste with high water content represents an economic problem because of the high costs for disposal, treatment and/ or use. The concentration of chemical oxygen demand (COD) from the tofu processing industries of Banda Aceh city is ranging from 5000-8500 mg/L, indicated that the waste has potential for bio energy production. About 128.52 m 3 /day of CH4 could be produced from 10 tofu processing industries in Banda Aceh.