Scaling of ammonia stripping towers in the treatment of groundwater polluted by municipal solid waste landfill leachate: study of the causes of scaling and its effects on stripping performance.

This paper documents the causes of the scaling of stripping towers used for the treatment of groundwater polluted by the leachate from an old municipal solid waste (MSW) landfill in northern Italy. The effects of the scaling on the stripping performance are also reported. The whole process consists of a coagulation-flocculation pre-treatment at pH > 11, followed by an ammonia stripping stage, after heating the water to 38°C in order to improve removal efficiency. The stripped ammonia is recovered by absorption with sulfuric acid, producing a 30% solution of ammonium sulfate (reused as a base fertilizer). The effluent air stream is recirculated to the stripping towers (closed loop systems) in order to avoid an excessive temperature drop inside the packings, mainly in winter, with consequent loss of efficiency and risk of icing. The progressive scaling of the packing has resulted in a loss of ammonia removal efficiency from an initial value of 98% (clean packing) down to 80% after six months of continuous operation, necessitating a chemical cleaning. Optimum conditions for design and operation of the stripping process are also documented.