Acid Extraction of Heavy Metals from Bio-Waste and Bio-Solids

Abstract

The opportunity to market secondary fertilizers such as bio-wastes and sewage sludges, for example, depends significantly on the pollution load of the final products (e.g. composts, soils) and on the acceptance of people to reuse these products. To ensure a high quality, different kinds of regulations and seals of approval (e.g. Bio-Waste Ordinance) have been passed or introduced in Germany and elsewhere. At present about 90% of the waste treatment operators in Germany can meet these standards, but an increasing amount of separately collected bio-waste will lead to a reduction in raw substrate quality. To support a high recycling rate, payable technologies have to be developed to reduce the pollutant load, especially for highly loaded fractions or charges. Regardless, all efforts have to be undertaken to reduce the amount of pollutants in order to minimise the necessary treatment.

This paper focuses on the possibilities for reducing the heavy metal loads of bio-waste, primary, and excess sludge. The leaching experiments were performed in lab scale reactors, varying the dosage of chemicals or acids. The internally-produced and externally-dosed acids and chemicals were citric acid, acetic acid, hydrochloric acid and a CaCl solution.