Study of the effects of binding agents on the properties of compost pellets

Abstract

Composting of the organic Municipal Waste (MW) is one of the sustainable answers for the management of MW. The bulky nature of the loose compost is one of the main drawbacks in promoting the use of compost in agriculture governed by various practical and economic reasons. Pelletization of compost seems to be the solution to offset the drawbacks caused by loose compost. The pelletizing process with a die and roller pelletizer is comparatively less complex compared to other common pelletizing methods. This research identified the optimum conditions to form a pellet with the desirable properties of high density, compressive strength, ideal pellet length and disintegration ability with three mesh sizes (2.5 mm, 3.5 mm, and 5 mm sieves), five moisture contents (25%, 30%, 35%, 40%, and 45%), three binding agents (Rice Flour (RF), Lime, Eppawala Rock Phosphate (ERP)) and three different binding agents’ percentages (1%, 2%, and 3%) by weight basis. The pelletizing process increases the bulk density of compost by about 30%. Pellets made with ≤ 5mm particles are longer and show higher strength (50% more) than those prepared with the other two particle sizes (≤ 2.5 mm & ≤ 3.5 mm). It was evidenced that 25% moisture content produces the highest strength pellets than higher moisture contents. Pellets with binding agents at ≤ 5mm particle size and 25% moisture content were tested for bulk density, strength, percentage of long pellets and disintegration ability. It was observed that the tested properties have varied compare to pellets without binding agents. Lime and ERP showed promising results that enhancing pellets’ bulk density and compressive strength and percentage of long pellets than RF. However, the disintegration ability nearly 100% in RF added pellets, which was less than 30% and 10% in ERP and Lime respectively and 0% in non-binding agent added pellets over one month of time in immersed water. With the increasing weight percentages of the binding agents, pellets strength increased in Lime and ERP and the same decreased with RF. Disintegration ability improved in RF and increased with the increased weight percentages. Same decreased in Lime and ERP and when increase the binding agents’ weight percentages, longer the time to disintegration the pellets.