ABSTRACT
Pilot scale continuous-culture experiments are described, which determine the oxygen requirements for controlling odour from pig slurry. Odour control and the stability of the treated slurries were measured using volatile fatty acids (VFA) as indicators of odour offensiveness. Oxygen consumption was measured by the changes in chemical oxygen demand (COD), NO2 −1 and NO3 −. Biodegradation was measured by the changes in total solids, volatile solids, biochemical oxygen demand (BODw), VFA and COD. Increasing the residence time from 1 to 4.8 d significantly (P=0.001) increased biodegradation, oxygen consumption and the stability of the treated slurry. Increasing the aeration level from a redox potential of +50 mV Eh to +200 mV Eh and further to 0.5–2.0 mg/l dissolved oxygen had no significant effect on carbonaceous oxygen consumption or solids destruction, but nitrification was inhibited when redox cotrol was used and the residual BODw of the treated slurries were higher. The stability of the treated slurry was related to the content of residual biodegradable COD, when an allowance was made for NO2 − and NO3 −. The energy requirements for treating slurry from a standard fattening pig ranged from 110–225 Wh/d to obtain stabilities after treatment of 18–56 days.
