Combination of a UASB reactor and a curtain type DHS (downflow hanging sponge) reactor as a cost-effective sewage treatment system for developing countries

The second generation of our originally proposed sewage treatment system. w hich consists of a UASB reactor as an anaerobic pre-treatment unit and curt ain-type DHS (downflow hanging sponge) reactor as an aerobic post-treatment unit, was installed at a municipal sewage treatment site. A 550-day contin uous experiment demonstrated that the whole combined system successfully ac hieved 94-97% of unfiltered-BOD removal, 81-84% of unfiltered-GOD removal, and 63-79% of SS removal. at an overall HRT of 8 h (6 h for UASB and 2 h fo r 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: requ iring neither external aeration input nor excess sludge withdrawal.