A pilot scale experiment of intermittently aerated sequencing batch reactor process (SBR) was carried out during 5 months to investigate the removal characteristics of BOD and nitrogen from a piggery wastewater. The pilot plant was set to operate in automatic control. The SBR pilot plant was operated on a 24h cycle, as mix of 5h, aeration of 15h, sedimentation of 3.5h and withdraw of 0.5h. The concentration of MLSS was highly controlled as 6,000-7,000mg·l-1. The operation of the SBR pilot plant was conducted with low BOD volumetric loading (mean value is 0.26 BODkg·m-3·d-1), and very long sludge age (57d).
The percentage removals of BOD and CODMn during the experimental period were 99.5% (< 37mg·l-1) and 89.9% (< 170mg·l-1), respectively. The mean NH4-N concentration of effluent was 10mg·l-1 and any ammonia accumulation was not observed during the operational period except for the conditions that pH value of treated water was less than 5.5. This nitrate accumulation was because the carbon sources for denitrification was deficient. The maximal NO3-N concentration of effluent increased up to 250mg·l-1 at BOD/T-N 1.0. The percentage removal of T-N decreased remarkably when BOD/T-N ratio was less than 3.0. This result indicates that to maintain BOD/T-N ratio of piggery wastewater suitably is important for the treatment performance of nitrogen. Filamentous microorganisms were always observed in activated sludge, however settling control problems by filaments were not seen during the experimental period. The influence of BOD-MLSS loading on the settling process was more significant rather than the occurrence of filamentous microorganisms in activated sludge.
