Tower bio-vermifilter system for rural wastewater treatment: bench-scale, pilot-scale, and engineering applications

Abstract

This paper presents a systematic study of a novel tower bio-vermifilter system for rural wastewater treatment at three scales: bench-scale, pilot-scale, and engineering applications. First, three types of bioreactors were tested in the bench-scale experiments: earthworm bioreactor, soil filter, and one-stage bio-vermifilter. Experiments with the earthworm bioreactor and soil filter determined the optimum earthworm density and soil layer depth to be 12.5 g/L and 40 cm, respectively. The one-stage bio-vermifilter’s poor performance in removing nitrogen and phosphorous led to several improvements in the design of the pilot tower bio-vermifilter system including the addition of one anaerobic biofilter for pretreatment, the use of two stages of bio-vermifilters, and the replacement of gravel with ceramsite in the media. Second, a pilot tower bio-vermifilter system built in Yixing City of Jiangsu province showed a good performance in the removal of chemical oxygen demand, ammonium nitrogen, and phosphorous. However, the system’s removal of total nitrogen showed considerable fluctuations, possibly due to the low ratio of carbon to nitrogen in its stage two bio-vermifilter. Finally, four operating tower bio-vermifilter systems in three basins of China were evaluated and compared with two other rural sewage treatment technologies in terms of economic costs and pollutant removal performance. Comparison results show that the tower bio-vermifilter system is a versatile system that can work effectively under a variety of natural and socioeconomic conditions at a reasonable cost.