Impact of volatile solids destruction on the shear and solid-liquid separation behaviour of anaerobic digested sludge

• Published in: The Science of the total environment 2023-10, Vol.894, p.164546-164546, Article 164546
• Main Authors: Das, Tanmoy, Usher, Shane P., Batstone, Damien J., Othman, Maazuza, Rees, Catherine A., Stickland, Anthony D., Eshtiaghi, Nicky
• Format: Article
• Language: English
• Subjects: Anaerobic digested sludge; Anaerobiosis; Bioreactors; Filtration; Sewage; Shear rheology; Solid-liquid separation; Viscosity; Volatile solids destruction; Waste Disposal, Fluid
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2023.164546

Systematic and comprehensive characterisation of shear and solid-liquid separation properties of sludge across a wide range of solids concentration and volatile solids destruction (VSD) is critical for design and optimization of the anaerobic digestion process. In addition, there is a need for studies at the psychrophilic temperature range as many unheated anaerobic digestion processes are operated under ambient conditions with minimal self-heating. In this study, two digesters were operated at different combinations of operating temperature (15–25 °C) and hydraulic retention time (16–32 d) to ensure a wide range of VSD in the range of 0.42–0.7 was obtained. For shear rheology, the viscosity increased 1.3 to 3.3 times with the increase of VSD from 43 % to 70 %, while other parameters (temperature, VS fraction) having a negligible impact. Analysis of a hypothetical digester indicated that there is an optimum VSD range 65–80 % where increase in viscosity due to the higher VSD is balanced by the decrease in solids concentration. For solid-liquid separation, a thickener model and a filtration model were used. No significant impact of VSD on the solids flux, underflow solids concentrations or specific solids throughput was observed in the thickener and filtration model. However, there was an increase in average cake solids concentration from 21 % to 31 % with increase of VSD from 55 % to 76 %, indicating better dewatering behaviour. [Display omitted] •Digestate viscosity increases 1.3 to 3.3 times when VSD changes from 43 % to 70 %.•Optimum digestate viscosity is achieved in the VSD range 65 %–80 %.•Dewatering behaviour (final cake solids) improves by increasing VSD.•Final cake solids increases from 21 % to 31 % when VSD changes from 55 % to 76 %.•VSD has no impact on solids flux and throughput of thickener and filter press.