The overall objective of this research activity is the development of a fixed-film biological nutrient removal (BNR) biofilter system for the reuse and discharge of a selected aquaculture water. The three stage biofilter system used in the study provided alternating aeration/non-aeration cycles for phosphorus removal in two of the three biofilters. The removal of TOC and ammonia improved as the cycle duration (CD) increased as a result of the reduction in the frequency of the transition periods between the cycles. The system achieved limited net phosphorus removal due to the limited sludge wasting and lack of external organic carbon supplies during phosphorus uptake. However, the phosphorus activity in the system was significant and was modified by the CD. The denitrification activity was coupled with phosphorus uptake and both activities appeared to have been supplied by an internal organic carbon source.
The major challenges of achieving phosphorus removal in the system include: (1) overcoming the deterioration in the performance of the system during the transition period following the start of each new cycle; and (2) wasting the excess biomass following the aeration cycle. Without active sludge wasting, the system behaves as a phosphorus reservoir with a limited storage capacity. On the other hand, frequent sludge wasting may disrupt the performance of the system.