Natural diatomite mediated continuous anaerobic sludge digestion: Performance, modelling and mechanisms

Anaerobic digestion is generally restricted by the low degradability of waste activated sludge (WAS) and slow hydrolysis rate. This work provided an innovative technique to promote continuous anaerobic digestion performance mediated by natural diatomite. In continuous tests over 125 days, 2 g/g-Total solids (TS) of natural diatomite addition increased daily methane production and volatile solids (VS) destruction by 23.3% and 23.5%, respectively, leading to a 5.6% decrease in digestate volume for disposal. Microbial community in the natural diatomite mediated digester changed toward a favorable direction for anaerobic sludge digestion. Process modelling indicated that the increased natural diatomite presence increased hydrolysis rate, biomethane potential and degradation extent of the rapidly biodegradable substrates in WAS, with the highest enhancement being approximately 78.9%, 44.5% and 45.0%, respectively, achieved at 2 g/g- TS diatomite. However, the slowly biodegradable substrates in WAS stayed relatively stable. The mechanism studies revealed that natural diatomite mitigated ammonia inhibition and enhanced electron transfer for WAS-to-methane conversion mediated by its strong adsorption capacity and conductivity. The versatility of the technology proposed is also verified by the diatomite mediated experiments using different natural diatomite from different sources. Compared to the most natural minerals, diatomite exhibited either a greater anaerobic digestion performance or a lower dosage, bringing strong benefits in economy, environment and technology.