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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel sewage treatment system was proposed, which consists of a UASB anaerobic pretreatment unit and the following DHS (downflow hanging sponge-cubes) aerobic posttreatment 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. (c) 1997 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]