Ozone treatment and adsorption with granular activated carbon for the removal of organic compounds from agricultural soil leachates

Abstract

In this study, some laboratory experiments were carried out to evaluate the performance of ozonation treatment alone or combined with granular activated carbon (GAC) adsorption for leek fields’ leachate (in Tehran, Iran). The removal of the recalcitrant contaminants from the leachate was improved by oxidizing the GAC surface with ozone before the treatment. Based on ozone concentration and GAC density, TDS, COD, and BOD removal was investigated for ozonation alone and in combination with GAC (integrated ozone-GAC adsorption). Next, the results were compared with those of other physicochemical treatments reported in some previous studies. By designing the central composite design with response surface methodology (RSM), the interaction and association between operating variables (i.e., ozone concentration, GAC density, and reaction time) were evaluated while determining optimal operating conditions. According to statistical analysis and experience, quadratic models for three responses (COD, TDS, and BOD) were suitable and efficient because of their low probability values (0.0001). The achieved optimal conditions included 100 mg/l ozone concentration, 1.00 gr/cm3 of GAC density, and 33.77 min of reaction time. The model outcomes were 46, 44.81, and 44.13% removal for TDS, COD, and BOD, respectively. Among the purification methods studied, integrating the ozone-GAC adsorption utilizing ozone-modified GAC (COD (55.2%), TDS (54.4%), and BOD (56.5%)) compared with the ozonation-alone method (COD (25.1%), TDS (25.7%), and BOD (43.6%)) showed an acceptable performance. However, other biological treatments like activated nitrification or sludge are still necessary to complete leachate degradation and comply with environmental regulations because the treated effluent did not meet the discharge standards.