A mathematical model for predicting the reduction of nitrogen and phosphorus concentrations in horizontal subsurface flow constructed wetlands was developed. The model considered the piggery wastewater input, storage, plant use and nutrient output to the environment is predominantly through nitrogen denitrification. Nutrient release from plant litter was not considered an influence on the constructed wetland because the young plants were picked for fodder and, contamination from rainfall and groundwater was considered insignificant. The adjustment and authentication of the model was carried out by separate data sets. Nutrient attenuation followed exponential trend during the period followed by stability contingent on the decay coefficient. Simulated parameters correlated highly with the observed values with R= 0.8940 for nitrogen and 0.9518 for phosphorus respectively. ME of 0.211 and 0.139, RMSE of 0.32 and 0.18, RE of 24 and 12%, model efficiencies of 64 and 37% and index of agreements of 0.6527 and 0.8676 for nitrogen and phosphorus respectively. The linear regression coefficients appear good for a natural system under environmental influences.

Keywords : Piggery Wastewater, Horizontal-Subsurface- Flow-Constructed-Wetlands, Pollution, Water Quality, Nutrients.