The small-tonnage oleo-chemical plant processing wastewater treatment and agro-utilization

Abstract

The paper presents a developed method of pretreating wastewaters coming from small-tonnage oleochemical production and also the research results on variability of concentrations of nickel (Ni) in the soil irrigated and fertilized with wastewater from this production. The processing wastewater pretreatment was carried out at two stages. The first stage eliminated fatty substances by using dispersed air flotation aided with hydrogen peroxide as an oxidizer. The second stage included coagulation and chemical precipitation with milk of lime, flocculation, final dissolved air flotation (DAF) and also oxidation with hydrogen peroxide. Field experiments, the aim of which was to compare variability levels for speciation fractions of heavy metal, were carried out according to Tessier’s method for four years. Doses of wastewater directed on experimental plots were limited by total nitrogen concentration in final portions, not exceeding the maximal amount of 170 kgN/ha×year. The study revealed that total average concentration of metal did not significantly change during the experiment, including samples of soil treated with either the defatted raw wastewater or the pretreated wastewater. Analyzing the fractional content of individual metal in soil samples irrigated with the studied wastewater, a significant diversification of variabilities for individual fractional plots was found, which evidently justifies the necessity of two-stage physical-chemical pretreatment and further agro-utilization of wastewater from the oleo-chemical production with no risk of soil environment degradation.