Effect of external carbon sources on nitrate removal in constructed wetlands treating industrial wastewater: woodchips and ethanol addition

The present chapter assessed the effect of ethanol and woodchips addition on nitrate removal in free water surface/vertical flow wetland microcosms operated at a 6 day hydraulic retention time, one received increasing ethanol concentrations (COD varying from 58 to 336mgfL) and the other received 2140g (9.3 kg/rn2) of dry woodchips. After the addition of COD both system had increased percentage removal of nitrate. COD:N03 ratios applied here with external carbon (16:1 minimum) were higher than the experimental 7:1 reported in the literature for complete denitrification. Excess COD, however, was successfully removed. Parallel to the wetland microcosm, the COD released from woodchips was measured by placing 1OOg woodchips in IL of water, COD was measured and the I L water batch changed weekly. After 65 days the 1OOg of woodchips released a total of 2262mg COD. These trials were preliminary to a large scale constructed wetland receiving up to 2,000 rn3/day of industrial wastewater with high nitrate and low COD. Woodchips, as a low cost biological waste product, can be considered as an alternative to expensive ethanol. Alternatively, the feasibility of using high COD wastewaters from nearby industries is being assessed.