Studies were conducted to undertake a physico-chemical analysis and to examine the bioavailability as well as the leachability of potential toxic elements during the rotary drum reactor composting of water fern with rice husk and cattle manure in different combinations. The highest temperature (54.2 degrees C) was measured in trial 3 (water fern, cattle manure and rice husk at a ratio of 6:3:1) during the process. The highest reductions of the moisture content and volatile solids were observed approximately 31.4 and 32.9%, respectively, in trial 3. The soluble biochemical oxygen demand (BOD) and the oxygen uptake rate of the compost in trial 3 indicated that the compost was stable after the process. The total concentrations of potential toxic elements (Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr) were increased in the process of composting. The total concentrations of the macronutrients in the final composts of different trials were increased by 1.4-2.0% for K, 1.1-1.3% for Ca and 0.76-0.82%. The highest reduction in the soluble BOD was found to be 82.4% in trial 3. Composting of water fern biomass with the appropriate ratio of cattle manure decreased the bioavailable and leachable forms of the potential toxic elements greatly. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.