Nitrogen and aerobic treatment of slurry

Abstract

The effects on slurry nitrogen of the aerobic treatment of pig and cattle excreta under various aerotion regimes are described. They were: high-rate aeration with dissolved oxygen >15% of saturation; low-rate aeration with dissolved oxygen 1–15% of saturation; and minimal aeration with dissolved oxygen <1% of saturation by control of redox potential at values <0mV E_cal. These had important effects upon the mineralised nitrogen components of the excreta. This nitrogen could be conserved as ammoniacal nitrogen, lost via ammonia stripping, oxidised to nitrate and conserved, or lost via denitrification. They also had important implications for energy conservation and odour regeneration. The energy requirement for aerobic treatment was minimal when the dissolved oxygen level was as low as possible and still consistent with adequate treatment. Conservation of the mineralised nitrogen as nitrate may prevent odour regeneration subsequent to treatment, but a dissolved oxygen level > 15% of saturation was required. In addition, the oxygen requirement for nitrification was equivalent to about 30–80% of the heterotrophic oxygen demand. Thus, with minimal aeration the efficiency was maximised, the extra oxygen demand for nitrification prevented and the nitrogen conserved as ammonia, but odour regeneration could be fairly rapid during storage.