The effect of turning frequency on compost yield and quality in an open windrow municipal solid waste composting plant

Abstract

Inadequate treatment of the municipal solid waste (MSW) and inappropriate disposal are major environmental concerns in several developing countries. In low-income countries, over 90% of waste is often disposed in unregulated dumps or openly burned, creating serious health, safety and environmental consequences.

This study investigated the effect of turning frequency on compost yield and quality in an Open Windrow Composting Plant. MSW received at the composting plant, its composition was determined according to American Standard Test Methods. The development of the composting process for both sorted and unsorted MSW at varying turning frequencies (after 0, 3, 7 and 14 days) was monitored by temperature, moisture content, pH, nutrient content and microorganism levels over a six-month period, from February to July, 2015.

Results show that the bulk MSW of 81.1-85.5% received at the plant was organic. The composting material in all the windrow setups had adequate nutrient levels for composting with C/N ratio between 25:1 and 35:1 and attained sanitizing temperatures of 50oC and beyond. From the experimental setups, the highest yield of compost of 18.3% was achieved in MSW windrow setups that had sorted MSW with 100% organic by composition being organic while for the composting windrow with 81.1% organic fraction that had unsorted MSW, the compost yield was 12.7%. The lowest compost yield from the experiments was 11.4% which occurred in the windrow where no turning was undertaken while the highest yield (18.3%) was obtained in the windrow with a turning frequency of 7 days followed by the windrow set with a turning frequency of 14day with 17.2%. Both windrow setups with a turning frequency of 7 and 14 days attained sanitizing conditions. However, the cost of forming a kilo of compost for windrow setup turned after 14day was lower at UGX 131,034.50 as compared to the setup turned after every 7days at UGX 203,278.70.

In order to improve the compost yield and quality in an Open Windrow MSW Composting Plant, it is recommended that MSW should be sorted and the organic fraction fed into the windrows for composting and turned after every 14days.