Removal of soluble organic carbon from winery and distillery wastewaters by application to soil

A logistic model was used to describe the removal of water-soluble carbon from synthetic winery and distillery wastewaters containing ¹⁴C-labelled lactic acid and glycerol after their application to the top-soils of a brown earth and a solod. Decreases in the radioactivity of soil extracts during the first hour after application were ascribed to microbial uptake and adsorption. Oxidative microbial decay was responsible for the removal of the remaining ¹⁴C of the solution to concentrations of less than 5% of the applied ¹⁴C, with removal times dependent on the duration of a lag period (when present) and the rate of decay. Soils from existing wastewater disposal sites containing adapted populations of micro-organisms had shorter lag periods and faster rates of oxidative decay than newly exposed soils. When the loading of organic material was increased, higher concentrations of added ¹⁴C remained in the soil solution after initial microbial uptake or adsorption, and the lag periods were often prolonged. Their combined effects could not be fully offset by concurrent increased rates of oxidative microbial decay, which overall resulted in longer removal times. The disappearance of extractable ¹⁴C to concentrations of less than 5% of input ¹⁴C was used as the basis for determining the minimum times required between successive irrigations with wastewater, which increased in the order of acclimatised solod (0.3–1.4 d) < acclimatised brown earth (0.7–2.6 d) < non-acclimatised brown earth (1.1–4.5 d) < non-acclimatised solod (0.7–4.8 d). Estimates based on the evolution of ¹⁴CO₂were found to be less reliable, due to the continuous turnover of the ¹⁴C of the biomass after the extractable ¹⁴C had disappeared.