Pilot-scale development of a bioreactor for the treatment of dairy dirty water

Dirty water arising on dairy farms may have a biochemical oxygen demand (BO D,) of 3000-5000 mg/l and an ammoniacal nitrogen content of 500 mg/l. It ca n be a significant cause of river pollution. An 'on-farm' treatment scheme is being developed by The University of Birmingham, integrating a bioreacto r and reed beds, that aims to treat dairy dirty water so that it can be dis charged to a water course. The paper describes pilot-scale trials of a submerged aerated filter biorea ctor to assess its suitability for adoption in the treatment scheme. A subm erged aerated filter employs a packed bed immersed in the wastewater underg oing treatment to provide a surface for microbial colonization. The process is well suited to performing nitrification in a farming context but is les s appropriate if bulk BOD5 removal is its principal function. Nitrification in the pilot plant has been remarkably resilient following process upset a nd nitrification rates in the region of 0.25 kg [N]/m(3) d at 150 degreesC have been observed. Results relating to the plant's capacity for BOD5 removal and nitrification are presented. The influences of temperature, organic loading and various chemical species on nitrification are discussed and the costs of a full-sca le bioreactor are estimated. (C) 2000 Silsoe Research Institute.