Permeable reactive barrier technology for the remediation of groundwater contaminated with nitrate and phosphate resulted from pit-toilet leachate

Abstract

In this study, different by-product wastes, i.e., fly ash (FA) and rice husk (RH), were analyzed in various proportions with other materials, i.e., activated carbon (AC), activated alumina (AA) and quartz sand (QS), for the remediation of NO3− and PO43- using Permeable Reactive Barrier (PRB) generated from pit-toilet leachate. Initially, a batch analysis was conducted for finding the optimum material composition considering various significant parameters, viz., pH, temperature, initial concentration, and dosage. The experimental results suggest that NO3− and PO43- were successfully removed, following the adsorption mechanism, with an efficiency of more than 95 %. This removal efficiency was obtained with a mixture of AC, RH, AA, QS, and FA in a weight proportion of 1:2:1:2:4 at a controlled pH value of 6. Langmuir isotherm model showed the most effective results with a coefficient of determination (R2) of 0.975 with a maximum sorption capacity of 32.6 mg g-1 and 46.5 mg g-1 for removal of NO3− and PO43- respectively. The adsorption kinetic data, for both NO3−and PO43-, provided better relationships with the pseudo-first-order model. Further, continuous fixed-bed column analysis manifested that at 10 mL min-1 flow rate and 600 mg L-1 initial concentration of both NO3− and PO43-, the reaction zone of the barrier provides a higher saturation time. Similarly, the retention time of contaminant water was also found to be higher at 45 cm bed depth. Furthermore, an adsorption-desorption regeneration test observed a decent amount of material recovery after full exhaustion of reactive bed.