The effect of anaerobic pre-treatment on the performance of duckweed stabilization ponds.

The effect of anaerobic pre-treatment on the performance of a duckweed stabilization pond system was assed in a pilot plant located in the Ginebra Research Station-Colombia. The pilot plant consisted of two lines of seven duckweed ponds in series. One line received de-gritted domestic wastewater and the other received effluent of a UASB reactor. Both lines were operated at a total hydraulic retention time of 21 days. The systems were monitored for temperature, pH, oxygen, biochemical oxygen demand, chemical oxygen demand, total suspended solids, total phosphorus, and different forms of nitrogen and biomass production. No effect of anaerobic pretreatment was observed on pH and temperature in the two systems. Oxygen concentrations were higher in the system with UASB reactor. Although both systems complied with the Colombian regulation in terms of organic matter (> 85% removal), the pretreatment with UASB reactor may contribute to the reduction of area requirement. Effluent quality in terms of total suspended solids was excellent, 9 ± 2 and 4 ± 1 mg l -1 in system with and without pre-treatment, respectively. Total nitrogen removals were 63 % and 68% and phosphorus removals were 24% and 29% in the system with and without pre-treatment, respectively. The differences were found no significantly different. Biomass production was in the range of 54-90 g m -2 -d -1 (fresh weight) in the system with pre-treatment and 36-84 g m -2 -d -1 in the system without pre-treatment. Total biomass productions were significantly different at 92% level of confidence. Protein content was 35.1 % and 36.6% for the system with and without pre-treatment, respectively. Further research will be focused on understanding nitrogen transformations and removal mechanisms in duckweed covered sewage stabilization ponds.