Improvement of solar septic tank performance by recovering waste heat from an air conditioner (AC) unit

Abstract

One of the valuable alternative approaches to improving overall energy efficiency is to capture and reuse the “lost or waste heat” from an AC unit. A waste heat recovery (WHR) unit could be integrated to a septic tank unit with high energy efficiency. The combination of waste heat energy with the solar septic tank (SST) is considered a novel technique to improve efficiency of the on-site treatment systems. This study aimed to develop an appropriate design of SST integrating WHR and to evaluate energy efficiency and treatment performance. From the overall results, temperatures of the pilot-scale SST integrated with the WHR could increase up to about 45°C. The system performance resulted in the effluent TCOD, BOD5 and TSS concentrations of 100, 30 and 18 mg/L, respectively. The effluent E. coli and total coliform concentrations were found to be lower than the WHO guideline, which were about 2–3 log. The application of the household scale waste heat recovery unit for the septic tank unit is recommended in this study.