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 (BOD,) of 3000-5000 mg/l and an ammoniacal nitrogen content of 500 mg/l. It can be a significant cause of river pollution. An 'on-farm' treatment scheme is being developed by The University of Birmingham, integrating a bioreactor and reed beds, that aims to treat dairy dirty water so that it can be discharged to a water course. The paper describes pilot-scale trials of a submerged aerated filter bioreactor to assess its suitability for adoption in the treatment scheme. A submerged aerated filter employs a packed bed immersed in the wastewater undergoing treatment to provide a surface for microbial colonization. The process is well suited to performing nitrification in a farming context but is less appropriate if bulk BOD5 removal is its principal function. Nitrification in the pilot plant has been remarkably resilient following process upset and 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-scale bioreactor are estimated. (C) 2000 Silsoe Research Institute.