Abstract
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.
Highlights
Scientific literature documents many cases of groundwater pollution due to the leachate generated by landfills of municipal solid waste (MSW) and similar waste (Raboni et al, 2015; Rada et al, 2014b; Regadío et al, 2012; Torretta et al, 2014)
The scaling has mostly affected the upper zone of the tower because of three factors: higher concentrations of hardness and alkalinity in the water at the top of the stripping tower; inlet water temperature higher than the outlet one (38°C respect to 25.2°C); and inlet water pH higher than the outlet one (11.28 respect to 10.67)
The temperature profile along the tower was determined by the cooling action of the stripping air coming from the ammonia absorption towers, while pH profile was influenced by the acid character of the air recirculated to the stripping towers
Summary
Scientific literature documents many cases of groundwater pollution due to the leachate generated by landfills of municipal solid waste (MSW) and similar waste (Raboni et al, 2015; Rada et al, 2014b; Regadío et al, 2012; Torretta et al, 2014). The quality of the leachate is mainly characterized by the relevant presence of ammonia, organic compounds and heavy metals. Leachate treatment can be performed with various biological and physical-chemical processes and a combination of different techniques is required due to the complex quality of the wastewater. Biological processes are widely used in the treatment of wastewaters with medium-low ammonia concentrations. Great interest is currently directed to biological processes for the treatment of waste air streams contaminated by ammonia and other volatile compounds (Copelli et al, 2012; Rada et al, 2014a; Torretta et al, 2013a)
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