MICROWAVE ENHANCED CHROMIUM EXTRACTION FROM SEWAGE SLUDGE AND SOIL-SLUDGE MIXTURES USING BIODEGRADABLE CHELANTS

Abstract

Microwave enhanced chromium extraction from sewage sludge and soil-sludge mixtures was carried out using ethylenediaminetetraacetic acid (EDTA) and more biodegradable chelating agents: methyleneglycinediacetic acid (MGDA), S, S’-ethylenediaminedisuccinic acid (EDDS) and S-carboxyl-L-cysteine (SCLC). Raising the temperature using microwave energy had particularly strong effect on Cr extraction efficiency with MGDA from all the investigated biosolids. The higher was the temperature, the larger amount of metal was extracted – maximum removal efficiency with MGDA at 150^oC was 38 times higher than that at 20^oC. The effect of microwave-assisted extraction duration was also significant – extraction effectiveness increased by 40-60 % at 150^oC while increasing duration from 15 min up to 60 min, depending upon the type of biosolid tested. MW-enhanced chromium extraction efficiency from sludge mixture with clay soil was in all cases significantly lower than that from the raw sludge samples as well as sludge mixture with sandy soil. Extraction study showed that such readily degradable agents as EDDS and MGDA can be successfully used to wash biosolids in the presence of chromium contamination instead of persistent EDTA when microwave energy is applied, while SCLC was less efficient. According to the complexation efficiency, the investigated chelants can be ranked in the following order:   EDTA≈MGDA>EDDS>SCLC, while the overall chromium removal capacity of MGDA was better than that of EDDS.