APPLICATION OF SERIAL SELF-TURNING REACTOR SYSTEM (STR) TO SEWAGE SLUDGE COMPOSTING

Abstract

 This research is an action research following on from a joint-research project on composting technology. The objective of the study is to apply a new composting technology called a serial self-turning reactor system (STR) which was originally developed for municipal solid waste treatment to be used for sewage sludge composting from a wastewater treatment plant. A series of lab-scale and plant-scale STR experiments was performed at Thammasat University’s Rang sit campus. All experiments were comprised of sewage sludge (as a substrate), woodchip, and recycled compost (as an amendment). The lab-scale experiment was separated into 12 ratios of sewage sludge, wood chip, and recycled compost, i.e. 1:0.25:0, 1:0.25:0.25, 1:0.25:0.5, 1:0.25:1, 1:0.5:0, 1:0.5:0.25, 1:0.5:0.5, 1:0.5:1, 1:1:0, 1:1:0.25, 1:1:0.5, and 1:1:1 with an aeration rate of 0.25 L/min/kg. The results of the lab-scale experiment indicated that the ratios of 1:1:0.25 and 1:1:0.5 were the optimal mixing conditions for STR composting because these ratios can improve the reheating potential more than the other ratios that met the Thai organic fertilizer criteria. The result of the final study has found that the ratio of 1:1:0.25 is the most suitable mixing ratio for sewage sludge composting using the STR technology because the amount of sewage sludge that can be treated in 1 cycle is more than for the ratio of 1:1:0.5 (being more economical) and the composting performance is better as well. The final products of the STR are compatible with the Thai organic fertilizer standard. The major nutrients of the 1:1:0.25 ratio for planting, namely total nitrogen, available phosphorus, and total potassium had average contents of 2.17, 2.08, and 0.71, respectively. The results for the chemical properties of both the lab-scale and STR experiments are not much different. From this study, the STR has been shown to be an effective system that can be applied with other substrates beyond wood waste (which the STR was originally designed for) without requiring any minor or major modifications. Moreover, the composting cycle can be completed within 2 weeks which was considered as a quick enough composting cycle time.