Full scale parallel operation of a biological aerated filter (BAF) and activated sludge (AS) for nitrogen removal

In connection with the reconstruction and capacity extension of the Frederikshavn Central Wastewater Treatment Plant in the period between 1989 and 1995 the existing activated sludge plant (AS) was supplemented with a biological aerated filter (BAF). The parallel operation with two wastewater flows has made a comparison of the two plants possible in relation to operating data, operating costs and experience. For the purpose of optimizing the operation, tests were conducted to increase the hydraulic capacity of the plant during rain and control strategies for the plants were considered for dry weather as well as wet weather situations. This paper discusses the experience gained from the plant operation as well as the considerations made in relation to future control strategies and possibilities of increasing the total hydraulic capacity during rain.