Efficiency of Forage Crops for Domestic Wastewater Treatment by Vertical Subsurface Flow Constructed Wetland

Abstract

The objective of this study was to investigate application of forage crop for domestic wastewater treatment using vertical subsurface flow constructed wetland (VSF CW). Pangolar grass (Digitaria decumbens), Atratum grass (Paspalum atratum) and Buffalo grass (Brachiaria mutica) were planted in VSF CW. Efficiencies of these species for pollutant removal were evaluated. In addition, growth, nutrient accumulation rate and yield of each species were also examined at each harvest period. This work gave promising result that the VSF CW fed with domestic wastewater at 20 cm/day or 100.6 l/day of HLR had potential for domestic wastewater
treatment. Average efficiencies of the VSF CW for removal of COD, TSS, TKN, NH₃-N, NO_x-N and TP were 70.42, 32.31, 80.48, 24.54, -932.48 and 41.66 %, respectively. Atratum grass showed the highest efficiency for COD, TKN and NO_x-N removal and Buffalo grass showed the highest efficiency for TSS, TP and NH₃-N removal. However, statistical analysis showed that efficiency of each grass species for removal of all types of the pollutants was not significantly different at P 0.05. Average nutrient accumulation rate of root of Pangolar grass, Atratum grass and Buffalo grass was 0.0061, 0.0142 and 0.0110 g N/m2/d and 0.0041, 0.0095 and 0.0048 g P/m²/d, respectively. The nutrient accumulation rate of root of each grass species was not significantly different at P 0.05. For above ground part, average nutrient accumulation rate of Pangolar grass, Atratum grass and Buffalo grass at each harvest period was 0.0273-0.0285, 0.0410-0.0496 and 0.0238-0.0423 g N/m²/d, and 0.0146-0.0208, 0.0220-0.0326 and 0.0167-0.0216 g P/m²/d, respectively. There were significant differences between studied species at 1st and 2nd harvest for nitrogen accumulation rate, and 1^st and 3^rd harvest for phosphorus accumulation rate (P < 0.05). Moreover, there were significant differences between harvest period for nitrogen accumulation rate of Buffalo grass and phosphorus accumulation rate of Pangolar grass (P < 0.05). Average
relative growth rate (RGR) of Pangolar grass, Atratum grass and Buffalo grass at each harvest period was 0.098-0.149, 0.107-0.171 and 0.109-0.160 per day, respectively. There were not significant differences between RGR of each studied species and RGR of each harvest period. Average dry yield of Pangolar grass, Atratum grass and Buffalo grass at 1st harvest was 372.2, 608.8 and 673.0 kg/rai, respectively. The average dry yield of those at 2nd and 3rd harvest was 388.9, 560.3 and 429.9 kg/rai, and 318.4, 965.5 and 602.0 kg/rai, respectively. It was found that average dry yield was not significantly different (P0.05) between studied species and also harvest period.