Evaluation of three lignocellulosic wastes as a source of biodegradable carbon for denitrification in treatment wetlands

Abstract

Lignocellulosic wastes are a good alternative to provide biodegradable carbon in treatment wetlands to promote denitrification, specifically in partially saturated subsurface vertical flow wetlands in which such residues can be added both in the free-drainage zone and in the saturated zone. Although the composition of lignocellulosic wastes is similar (lignin, cellulose and hemicellulose), the rate of releasing biodegradable carbon, recalcitrant compounds, color, etc., could be different. Furthermore, their degradation rate may be different under unsaturated and saturated conditions Therefore, in order to optimize their use in treatment wetlands, the aim of this study was to evaluate three lignocellulosic wastes (corncob, pine wood shavings and agave bagasse) with respect to their capacity to generate biodegradable carbon, as well as the release of recalcitrant compounds, total suspended solids and color, in unsaturated and saturated conditions. It was found that corncob and pine wood shavings were the most suitable wastes to be used as a carbon source in partially saturated subsurface vertical flow wetlands. Corncob released low content of biochemical oxygen demand in unsaturated conditions but high content in saturated conditions, while pine-wood shavings released a moderate-low content in both conditions. In contrast, agave bagasse increased the concentrations of biochemical oxygen demand, chemical oxygen demand, total suspended solids and color in the effluents indicating a very fast degradation, which was confirmed with its weight loss in around 44% in both unsaturated and saturated conditions.