Combining Nutrient Removal With Protein Synthesis Using A Water Hyacinth Freshwater Prawn Polyculture Wastewater Treatment System

A two-stage polyculture wastewater treatment system, using water hyacinth, Eichhornia crassipes, in the first-stage and a combination of Azolla and the freshwater prawn, Macrobrachium rosenbergii, in the second-stage, was developed at the pilot plant scale to provide tertiary treatment of municipal wastewater. A conceptual three-compartment nitrogen model was also developed to simulate the first-stage of the system.

The results of the analysis of the first-stage water hyacinth system indicated that for NH3-N loadings ranging from 11.6 to 76.1 kg NH3-N/ha-d, NH3-N removals averaged 76.8 percent. Nitrate and ORG-N removals ranged from 24 to 80 percent and 75 to 95 percent, respectively. The first-stage effluent NH3-N, NO3-N, and ORG-N concentrations ranged from 0.3 to 25.0 mg/L, 0.5 to 2.3 mg/L, and 0.3 to 0.8 mg/L, respectively.

The results from monitoring the second-stage Azolla-prawn system indicated that at NH3-N loadings between 115 to 10,360 gm-N/ha-d, system performance for NH3-N varied between a 14 percent increase to a 90 percent removal. Nitrate and ORG-N removals in the Azolla-prawn system were highly variable through the system.

Overall performance of the polyculture system for the removal of total COD, TSS, total coliforms (MPN), and turbidity (NTU) indicated removals of 58, 98, 99.9, and 94 percent, respectively. Other parameters for the two stage system were monitored including temperature, Ortho-P, biomass, productivity, alkalinity, pH, and specific conductance. In addition, prawn growth studies were performed in the field and laboratory.