Takashi ONODERA

Real-scale experiment of a novel sewage treatment system combined with UASB and DHS in India

Hideki HARADA, Akiyoshi OHASHI

Application of upflow anaerobic sludge blanket (UASB) technology to municipal sewage treatment has been increasingly recognized as a cost-effective option in some developing countries. However, treatment of sewage by UASB alone cannot meet the effluent discharge standards. Therefore, an appropriate post-treatment to polish up the UASB effluent is urgently needed. Our proposed a novel post-treatment system called, bench-scale downflow hanging sponge (DHS) reactor has been exercised excellent performance of organic removal (95%) and nitrification (50%) used actual municipal sewage during long experiment period for 5 years. In this study, I evaluate the performance of full-scale DHS reactor in India. The research has been carried out at Karnal STP (Sewage Treatment Plant) treating actual domestic sewage. This STP is consisted of a UASB and a Stabilization pond of which is called gFinal Polishing Unit g(FPU). The design hydraulic retention time (HRT) of UASB and FPU were 8.6 h and 1 day, respectively. A portion of the UASB effluent is fed to full-scale DHS reactor at a feeding rate of 500 m3 per day. A total amount of the sponge volume is 31.1m3 and HRT based on the sponge volume is 1.5 h.
The overall organic removal rate of the DHS-Biotower is 2.76 kgCOD/m3 per day and 0.88 kgBOD/m3 per day. The average effluent concentration of BOD and COD are only 5 mg/l and 32 mg/l, and overall removal rate (UASB + DHS) are above 96% and 92%, in respectively. Thus, the full-scale DHS reactor almost completes the removal of organic compounds with very short retention time of 1.5 hours and produces excellent effluent quality. Nutrient removal by DHS was also satisfactory. Fecal coliform were removed by 1.9 log with final count of 104 to 105 MPN/100ml. Moreover, excess sludge production from full-scale DHS reactor was negligible. DHS system could be maintained on high performance even long operational period of 1100 days without regular maintenance. Therefore, the DHS system can be recommended as a cost effective and high performance technology for post-treatment of UASB effluent.