Heavy metal and proximate composition associated with the composting of cassava (Manihot esculenta) peels used in the cultivation of mushrooms in Ghana

Abstract

Changes in the heavy metal content and proximate composition during the 28 day composting of cassava peels used in the cultivation of the oyster mushrooms Pleurotus ostreatus strain EM-1 was studied. Significant dry weight variations of cellulose, hemicellulose and fat contents were observed from day 0 to 12. Decreases from day 12 to 28 had the values of 15.4, 57.6 and 56.12%, respectively, while lignin, protein and crude fibre values showed a gradual increase from day 0 to 28, with maximum values of 23.73, 49 and 73%, respectively. Cyanide content however showed a reduction from the initial 3.89 to 2.01 mg/L by day 12 and a marginal increase of 16 by day 28. This was however not detected in the mushroom harvested. The levels of heavy metal content in composted cassava peels in decreasing order was iron (Fe), manganese (Mn), zinc (Zn), lead (Pb) and copper (Cu) while that for uncomposted cassava was Fe, Zn, Pb, Mn and Cu. Levels of Cu, Mn, Pd and Zn in mushroom samples analysed were in agreement with reported values in literature. Of all the heavy metals examined, iron accumulated excessively, indicating that P. ostreatus strain EM-1 is a good bio-accumulator of Fe