Straw addition improves the stability and efficiency of high-solids anaerobic digestion of dewatered sludge via creating balanced function microbial community

In this study, thermophilic high-solids anaerobic co-digestion of dewatered sludge (DS) and rice straw (RS) was conducted at a constant C/N ratio of 10 (hereafter called C/N ratio-adjusted DS); the long-term reactor performance and microbial community dynamics were compared with DS mono-digestion. The co-digestion allowed stable performance for 952 days, and biogas evolution was 402 ml/g-VTS with methane content of approximate 50 % at a higher VTS loading rate of 8.0 g/kg-sludge/d. In contrast, the performance of DS mono-digestion was negatively influenced by the varied properties in DS even at a low VTS loading rate of 1–2 g/kg-sludge/d. Interestingly, the deteriorated DS mono-digestion performance was recovered and promoted by adding RS. Beta-diversity analyses revealed significant differences in the microbial community between co- and mono-digestion. The stable performance of co-digestion was attributed to more balanced function microbes in protein and cellulosic matter degradation, as a result, leading to alleviation of ammonia inhibition. • Thermophilic anaerobic co-digestion of dewatered sludge (DS) with rice straw (RS). • Variant properties in DS feed negatively affected DS mono-digestion process. • Maintaining C/N ratio at 10 by adding RS resulted in long-term stable performance. • A high VTS loading rate of 8 g/kg/d was achieved with CH 4 yield of 201 ml/g-VTS. • A balanced microbial community in co-digestion was key for stable performance.