Impact of rheological properties of substrate on anaerobic digestion and digestate dewaterability: New insights through rheological and physico-chemical interaction.

Mesophilic batch anaerobic digesters fed by different substrates were set up to identify the role of substrate rheology in anaerobic digestion performance while operating below the toxic level. Five substrates of different rheological behaviour but at the same amount of organic matters were prepared by addition of different amount of an inert material (0, 0.03, 0.07, 0.11, and 0.20 g) per g of waste activated sludge (WAS). To gain a comprehensive insight, the interactive relationship between substrate rheology, physico-chemical properties and biogas production as well as digestate dewaterability was investigated. The results proved that better access of microorganisms to organic matters improved the digester performance and led to 19.29% and 12.5% increase in biogas yield and VS removal efficiency, respectively. Moreover, the statistical analysis showed that consistency index and loss modulus of sludge could be employed as promising indications for biogas yield while yield stress could predict dewaterability of digestate as far as the other physico-chemical properties remained unchanged. During digestion measurement of consistency index and loss modulus of digestate could be performed as a reliable tool to monitor biogas production.