Using advanced control, post-denitrification and equalisation to improve the performance of a submerged filter

In 1998, the capacity of the BIOSTYR(R) submerged biofilter at Nyborg WWTP was extended from 48,000 PE to 60,000 PE including advanced sensor based co ntrol, post-denitrification in BIOSTYR(R) and equalization of side flows. The existing configuration with 8 BIOSTYR(R) DN/N cells is based on pre-den itrification and an infernal recirculation of 600-800 %. The extended plant comprises 7 BIOSTYR(R) DN/N cells with 50-225% recirculation followed by 3 BIOSTYR DN cells for post-denitrification. The advanced control loops incl ude blower control, control of the number of active cells (stand-by), autom atic switch to high load configuration, control of the side flow equalizati on, control of the internal recirculation and control of the external carbo n source dosing. In this paper, the achieved improvements are documented by comparing influe nt and effluent data, methanol and energy consumption from comparable perio ds before and after the extension. Although the nitrogen load to the plant was increased by 20% after the extension, the effluent quality has improved significantly with a reduction of Total-N from 7-8 mg/l to 3-4 mg/l. Simul taneously, the methanol consumption has been reduced by more than 50% per k g removed nitrogen. The energy consumption remained constant although the n itrogen load was increased by 20% and the inflow by 80%.