Augmentation of self-purification capacity of sewer pipe by immobilizing microbes on the pipe surface

Abstract

For the development of a sewer pipe that removes dissolved organic carbon (DOC) and nitrogen, a rectangular channel with a fabricated porous ceramic bed was investigated. The experimental channel was 1 m long, 2.0×10 −2 m wide, and 2.5×10 −2 m deep, the total volume being 0.81 l. Blocks of the ceramic bed with 2.0×10 −2 m 2 total surface area and 5.0×10 −3 m thickness were installed along the channel bed for the immobilization of microorganisms. Synthetic wastewater was used as the model sewage. Removal of organic carbon and nitrogen was carried out with or without aeration. Dissolved oxygen (DO) and pH microelectrodes were employed to analyze structure of the biofilm, which played an important role in the removal of both organic carbon and nitrogen. The results give evidence that the combination of aeration and biofilm development enhanced the simultaneous removal of organic carbon and nitrogen. Microelectrode study revealed that the biofilm was rough and heterogeneous in both vertical and horizontal directions and had an average thickness of 2.5–5 mm. The biofilm, consisting of an aerobic/anaerobic layer, was suggested to be responsible for the nitrification/denitrification process, while the aeration accelerated the removal of total organic carbon (TOC), NH 4 or NO 2 from the model sewage. Sequential nitrification/denitrification proceeded in the biofilm even when aeration was carried out. This study suggests that the immobilization of microbes inside the sewer pipe may be effective for the simultaneous removal of organic carbon and nitrogen in the sewage line.