Natural Zeolite Stabilizes Sodium and Boron In Municipal Solid Waste Compost

Composting is a sustainable and beneficial solution for utilizing municipal solid waste (MSW). Salt and heavy metal content are, however, the two main factors affecting quality of MSW compost. This study focuses on stabilization of sodium (Na), boron (B) and potentially toxic heavy metals (i.e. Cd, Zn, Pb, Ni and Cr) by natural zeolite during aerobic composting of municipal solid waste. Zeolite was homogenously incorporated at 0, 1, 3 and 6% (w/w) into raw material before the onset of composting process in small scale reactors containing 100 kg of composting material. Composting process was terminated at the end of the eighth week. The resulting compost product had a substantially high level of total soluble salt content (EC1:5: 9.4 ds m-1) whereas addition of 1, 3 and 6% of zeolite reduced the soluble salt content by 10, 11 and 29% respectively. The compost product obtained was further tested in a greenhouse pot experiment with maize. There was no significant difference in shoot dry matter production when composts with different zeolite amendments were applied to soil at 0 or 4% (w/w). As expected, shoot Na and B concentrations were significantly enhanced with 4 and 8% compost treatments without zeolite amendments. In the case of zeolite application, shoot Na and B concentrations were significantly reduced. Zeolite addition clearly prevented root uptake of Na and B and was effective to stabilize excess Na and B in the compost product. By contrast, there was no effect on the shoot concentrations of heavy metals.