Yutaka Yoneyama

Denitrification characteristics of reject water in upflow biofiltration

Two types of bench-scale experiments using upflow biofilm reactors packed with granular floating polystyrene (GFP) or polyurethane foam cubes (PFC), were used to investigate the denitrification of reject water. A high denitrification rate was achieved in both upflow biofilm reactors since the highly concentrated volatile fatty acids in reject water served as effective hydrogen donors for denitrification. Of the two biofiltrations, the denitrification rate using GFP was 3.5 kg−1 N m−3 per day, and higher than that using PFC. The amount of total attached biomass and solid capture capacity were also greater in GFP than in PFC. Moreover, the backwashing of the GFP packed column was optimized with air and water agitation. Of the processes investigated in this study, upflow biofiltration using GFP was the most acceptable process for reject water treatment based on treatability and operation.

STUDY OF THE REDUCTION OF RETURNED PHOSPHORUS FROM A SLUDGE TREATMENT PROCESS

ABSTRACT Pilot plant experiments on biological phosphorus removal from municipal wastewater, sludge thickening and dewatering, were performed to investigate the quantity of released phosphorus from a sludge treatment process and a system for minimizing this phosphorus. A combination process of biological phosphorus removal with chemical phosphorus removal was very effective, not only for reducing the phosphorus but also for steadily removing phosphorus when the T-P/BOD ratio of the wastewater was over 0.08. An intermediate clarifier and fluidized phosphorus crystallization reactor were operated as a chemical phosphorus removal process, the soluble PO4-P removal was 80% and the packed phosphorus rocks were enlarged to twice the size of the initially packed rocks after one month of operation. From experimental results, it was clear that separate thickening of primary sludge and excess activated sludge was effective in reducing the quantity of phosphorus returning to the biological process. Precipitation removal of phosphorus from the filtrate of a sludge dewatering process, using a chemical precipitant, was also effective in reducing the returning phosphorus. When the excess activated sludge is dewatered alone, aerating the thickened sludge can be adopted effectively.