Pilot-scale study of biomass reduction in wastewater treatment.

Pilot-scale experiments were continuously carried out for more than 9 months to study the excess biomass reduction effect using a biophase-separation bioreactor, which was designed based on food-chain theory. By separating the biophase in the wastewater treatment system, bacteria, protozoa, and metazoa could be separated from each other and dominated in different microbial communities. After degrading organic matter, bacteria were consumed by protozoa or metazoa in the following process in such a reactor. Thus, both chemical oxygen demand (COD) and biomass were reduced. During the process of treating restaurant wastewater, the excess biomass yield in this biophase-separation technique varied from 0.13 to 0.22 kg/kg COD removed, 50% lower than that from the reference system. Apart from low biomass production, this biophase-separation technique can simultaneously achieve a high COD removal efficiency and improve settleability of biosolids at a hydraulic retention time of 6 to 13 hours.