Ammonia inhibition of waste degradation in landfills – A possible consequence of leachate recirculation in arid climates

Abstract

Ammonia inhibition of anaerobic waste degradation has been extensively investigated on a laboratory scale. It is hence well known that at ammonium levels above 2500 mg/l, methanogenic bacteria are inhibited, which leads to both reduced methane (CH₄) production and increased organic pollution of the leachate. In the present paper, and for the first time, data on a full-scale landfill indicating ammonia inhibition of waste degradation is presented. The leachate of the landfill is characterized by extremely high concentrations of chloride (up to 70,000 mg/l) and ammonium–nitrogen (up to 20,000 mg/l). These high pollution levels are explained by the following facts: first, the landfill is located in an arid climate (annual precipitation of 200 mm), resulting in low fresh water infiltration; and second, leachate or concentrate resulting from reverse osmosis treatment at the site has been recirculated. The high ammonium levels obviously caused inhibitory effects on the anaerobic degradation, which resulted in chemical oxygen demand concentrations in the leachate of far above 300,000 mg/l. Furthermore, a comparatively low level of landfill gas (LFG) generation and a shift towards higher carbon dioxide and lower CH₄ contents in the collected LFG was observed. Based on the gas compositional data, the overall reduction in CH₄ generation was assessed to be 50%. In order to reduce organic leachate pollution and to enhance LFG production at the site investigated, fresh (rain) water infiltration should be enhanced and the recirculation of leachate or treatment residues derived thereof should be terminated.