Development of a novel sewage treatment system for developing countries.

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Current sewage treatment system such as activated sludge is not suitable in developing counties due to high costs and high energy requirement. An "appropriate technology" of sewage treatment must be developed for developing countries. Recently UASB is attractive technology for sewage treatment in developing countries since it guarantees low construction and operational cost, produce energy as methane and less amount of sludge. However UASB alone can not meet discharge criteria, so that further option is needed to polish up UASB effluent without losing UASB strong point. As a proper system, we have proposed DHS (Down-flow Hanging Sponge) reactor. The principle of DHS is the use of a polyurethane sponge as a medium to retain biomass. The concept is similar to that of tricking filter, except that the packing material is sponge, which has a void space of more than 90%, resulting in a significant increase in entrapped biomass and thus longer solid retention time (SRT). As the sponge in a DHS is not submerged and freely hung in the air, oxygen is dissolved into the wastewater when it flows down the reactor. Therefore there is no need for external aeration or any other energy inputs. Moreover, production of excess sludge from DHS is negligible as longer SRT provides considerable time for autolysis of sludge in the system itself.Demonstration-scale DHS reactor with a treatment capacity of 1,000m^3・d^<-1> has been installed since 2002 by Indian government in India. We monitored this system as well as last year. DHS reactor has been operated at HRT of 1.49hr. As a long-term experimental period, we can see the excellent performance of DHS in terms of BOD, COD and fecal coliform removal which were 93%, 88% and 2 order, respectively without any problem. As a these result, a real scale DHS is planned on constructing in Agra city, India by Indian government.