Assessment of sulfide production risk in soil during the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification process.

Abstract

This study aimed to determine the potential of sulfide generation during infiltration through soil of domestic wastewater treated by a sulfur-utilizing denitrification process. Three types of soil with different permeability rates (K s = 0.028, 0.0013, and 0.00015cm/s) were investigated to evaluate the potential risk of sulfur generation during the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification system. These soils were thoroughly characterized and tested to assess their capacity to be used as drainages for wastewaters. Experiments were conducted under two operating modes (saturated and unsaturated). Sulfate, sulfide, and chemical oxygen demand (COD) levels were determined over a period of 100days. Despite the high concentration of sulfates (200mg/L) under anaerobic conditions (ORP = -297mV), no significant amount of sulfide was generated in the aqueous (<0.2mg/L) or gaseous (<0.15ppm) phases. Furthermore, the soil permeability did not have a noticeable effect on the infiltration of domestic wastewater treated by a sulfur-utilizing denitrification system due to low contents of organic matter (i.e., dissolved organic carbon, DOC). The autotrophic denitrification process used to treat the domestic wastewater allowed the reduction of the concentration of biochemical oxygen demand (BOD5) below 5mg/L, of DOC below 7mg/L, and of COD below 100mg/L.