Use of organic acids in the composting of municipal solid waste: a pilot-scale study

Abstract

Compost made from municipal solid waste (MSW) contains heavy metals that can interfere with the use of organic amendment in soil. In order to find effective ways to reduce the potential risk of heavy metals, we have investigated a novel approach by use of organic acid during MSW composting. Citric and oxalic acid dissolutions (0.25 mol·l⁻¹) were used at determined ratios (kg dried MSW: cm³ acid). Cr and Ni concentrations were similar in compost, independent of acid contribution. By contrast, Cu concentrations decreased by 63% (at citric acid ratio 1:15), 65% (at citric acid ratios 1:20 and 1:40) and 83% (at oxalic acid ratio 1:40); furthermore, Pb concentrations reduced by 71% (at citric acid ratios 1:20 and 1:40 and at oxalic acid ratio 1:40) and Zn concentrations reduced by 67% (at citric acid ratios 1:10 and 1:20) and 70% (at oxalic acid ratio 1:40). The total metal mass decreased by an average of 12% in the compost fraction, whereas the total percentage of the residual fraction increased by an average of 20%. The acid addition in the studied ratios improved compost quality without negatively influencing biostabilization.

Keywords:

• composting
• heavy metals
• speciation
• citric acid
• oxalic acid

Acknowledgements

The authors would like to acknowledge the Ministry of Education and Science (Project: REN 2002-02602 and CTM 2005-01293) and the Junta of Andalucia (Counselling of Innovation, Science and Enterprise) for funding this research.