Modern landfill leachates – quality and treatment

Abstract: Waste management in Europe has changed, mainly as a result of stricter regulations, most notably the European Landfill Directive 1999/31/EC. In Sweden, landfill tax and a ban on the landfilling of waste with total organic carbon content over 10 % have diverted large amounts of waste from landfills. The biogeochemistry of landfills has changed due to their reduced organic content. The research presented in this thesis aimed at improving understanding of leachate quality in modern landfills. Biodegradation and leaching tests were employed on wastes typical of a waste manage¬ment system shifting away from landfilling. Multivariate data analysis using principal component analysis and canonical correlation analysis was employed to identify processes governing leachate quality and relations between leachate parameters. As heavy metals are expected to be relatively more pronounced in modern landfills, sorption to granular activated carbon, bone meal and iron fines was evaluated as a means of removing heavy metals from leachate. The main difference in two leachates from landfills with less than 10 % organic carbon in the waste in relation to leachates from older landfills containing municipal solid waste was the extremely low ammonium content. Very low dissolved organic carbon content was also observed. Leaching of heavy metals in the same order of magnitude as in MSW landfills was observed in modern landfills. The results further indicate that a certain degradation potential must be expected, even in the carbon poor wastes deposited in modern landfills. Therefore reducing conditions will be likely to occur in the landfills. Although landfill gas formation will be low, degradation is likely to significantly affect the biogeochemical conditions, thus affecting metal leaching and rendering it relatively similar to that in municipal solid waste landfills. However, since the amounts of biodegradable organic matter are smaller they will be depleted sooner than in municipal solid waste landfills. As a result, the long term differences may be greater. The multivariate data analysis identified variation in the concentration of salts as the most important process governing leachate quality. This variation had various causes, including dilution, depletion and varying input materials. Redox potential was also identified as an important process. In the cases where samples were taken before and after treatment, the effect of the treatment strongly influenced the results. All the sorption materials studied had the potential to remove heavy metals, but none was effective against all the metals in the leachate. They also all had the drawback of releasing unwanted substances into the leachate. This illustrates the importance of site-specifically evaluating all treatments and analysing a large number of substances in the leachates, not just those targeted by the treatment. The main pollutants to be expected in modern landfills with only small amounts of organic matter will probably be inorganic, e.g. heavy metals. While the organic matter emitted by older landfills can be changed into more or less inert forms, metals can never be destroyed, just concentrated, diluted or moved to another medium. Enhancing biodegradation and flushing pollutants by allowing water to infiltrate into landfills is advocated as a sustainable management option for municipal solid waste landfills. However, in the case of mainly inorganic landfills, containment aimed at keeping the metals in the landfills for as long as possible rather than dispersing them into the environment might be a better option.