Process design of a treatment system to reduce conductivity and ammoniacal nitrogen content of landfill leachate

Abstract

An innovative combination of computational modelling and laboratory testing was applied to address the challenge of reducing conductivity and ammoniacal nitrogen in landfill leachate. The hypothesis was that accelerated selection of an appropriate treatment process could be achieved by application of new water process engineering software termed AqMB. Several scenarios were investigated incorporating settling ponds, clarifiers, lime softening, ion exchange, pH adjustment and degassing unit operations. Settling ponds reduced the lime demand if a lime softening process was tested, albeit ponds involved greater expense and needed space. Alternately, a clarifier using aluminium chlorohydrate removed suspended solids. Use of a single cation resin bed in series with a strong base anion (SBA) resin column was not able to meet regulatory targets. However, employment of a weak acid cation (WAC) and strong acid cation (SAC) resin combination achieved very low ammoniacal nitrogen levels. To satisfy conductivity limits both a degassing unit and a strong base anion (SBA) resin were also necessary. Bench top testing of actual leachate confirmed that the software predicted the trends in water quality. Final solution conductivity of ca. 250 μS/cm and ammoniacal nitrogen content of <1 mg/l were recorded which were compliant with target values of <1600 μS/cm and <100 mg/l ammoniacal nitrogen. Process economics encompassing power, chemicals, and resin costs were calculated to be A$10.50 per kL leachate.