Improving Anaerobic Digestion of Sewage Sludge Using Free Ammonia Pretreatment

A massive amount of sewage sludge is produced in the primary sedimentation (primary sludge) and wastewater treatment process (secondary sludge) in wastewater treatment plants (WWTPs) adding a heavy economic burden for WWTPs for their disposals. Anaerobic digestion (AD) for sewage sludge treatment is adopted WWTPs globally for sludge reduction and energy recovery through biogas. However, the AD efficiencies for sludge reduction and biogas production are generally limited. Hydrolysis is considered a rate-limiting factor and the low degradation extent of sludge is also the limiting factor. Free ammonia (FA) pretreatment has been recently revealed as a promising approach to improve the biochemical methane potential and hydrolysis rate of sewage sludge through small-scale batch studies. However, a comprehensive understanding of the impact of FA pretreatment on semi-continuous AD is largely unknown, hindering its future real-world application. This thesis investigated the impact of FA pretreatment on the anaerobic digestion of primary and secondary sludge in a semi-continuous AD system with a comprehensive evaluation of the volatile solids (VS) destruction, dewaterability, pathogen removal, and its implications. In comparison to the control (without FA pretreatment), FA pretreatment (560 mg NH3-N/L, 24h) enhanced the VS destruction of primary sludge by 12%, which is related to the 31% of enhancement in hydrolysis rate. FA pretreatment also improved VS destruction of secondary sludge by 26% and improved methane production by 29%, with 9% and 41% improvement in dewaterability and pathogen removal, respectively. FA pretreatment (560 mg NH3-N/L, 24h) on the AD of secondary sludge further allowed an extended treatment capacity of the digester by up to 50% in the semi-continuous operation. This potentially provides an effective strategy for the upgrading of capacity-limited anaerobic sludge digesters, saving capital cost and operational interruptions. In addition, although FA generally can be obtained in situ from the digestion liquor, in some cases, the digestion liquor does not contain an adequate concentration of FA for the treatment, which thereby requires alkali additions. This thesis further proposed to use separately collected human urine as an alternative source for FA since urine contains a high level of ammonium and alkalinity. Urine pretreatment at levels of 5-30% (Vurine/Vurine+WAS) substantially enhanced methane production by 5-35% in biochemical methane potential (BMP) tests, with the highest methane production of 179.6 ± 3.3 mL/g VS achieved under the highest level of urine (i.e. 30 % urine addition). This offers a feasible and economical alternative source of FA for WWTPs.

Author dc:creator

• Liu, Huan

Statement dc:rights

• info:eu-repo/semantics/openAccess
• The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
• © 2023 Huan Liu
• au.edu.uts.lib/cph

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10453/172688

OAI identifier oai:identifier

oai:opus.lib.uts.edu.au:10453/172688