Enhancing methane production from waste activated sludge using combined free nitrous acid and heat pre-treatment

• Published in: Water research (Oxford) 2014-10, Vol.63, p.71-80
• Main Authors: Wang, Qilin, Jiang, Guangming, Ye, Liu, Yuan, Zhiguo
• Format: Article
• Language: English
• Subjects: Activated sludge; Anaerobic digestion; Applied sciences; Biochemistry; Biological and medical sciences; Biological treatment of sewage sludges and wastes; Biomass; Biotechnology; Byproducts; Economics; Energy; Environment and pollution; Exact sciences and technology; Free nitrous acid; Fundamental and applied biological sciences. Psychology; Heat; Hot Temperature; Hydrolysis; Inactivation; Industrial applications and implications. Economical aspects; Methane; Methane - metabolism; Models, Theoretical; Natural energy; Nitrous Acid - analysis; Other industrial wastes. Sewage sludge; Pathogen; Pollution; Sewage - chemistry; Waste activated sludge; Waste Disposal, Fluid - methods; Wastes
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2014.06.010

Methane production from anaerobic digestion of waste activated sludge (WAS) is often limited by the slow degradation and poor substrate availability of WAS. Our previous study revealed that WAS pre-treatment using free nitrous acid (FNA, i.e. HNO2) is an economically feasible and environmentally friendly method for promoting methane production. In order to further improve methane production from WAS, this study presents a novel strategy based on combined FNA and heat pre-treatment. WAS from a full-scale plant was treated for 24 h with FNA alone (0.52–1.43 mg N/L at 25 °C), heat alone (35, 55 and 70 °C), and FNA (0.52–1.11 mg N/L) combined with heat (35, 55 and 70 °C). The pre-treated WAS was then used for biochemical methane potential tests. Compared to the control (no FNA or heat pre-treatment of WAS), biochemical methane potential of the pre-treated WAS was increased by 12–16%, 0–6%, 17–26%, respectively; hydrolysis rate was improved by 15–25%, 10–25%, 20–25%, respectively, for the three types of pre-treatment. Heat pre-treatment at 55 and 70 °C, independent of the presence or absence of FNA, achieved approximately 4.5 log inactivation of pathogens (in comparison to ∼1 log inactivation with FNA treatment alone), thus capable of producing Class A biosolids. The combined FNA and heat pre-treatment is an economically and environmentally attractive technology for the pre-treatment of WAS prior to anaerobic digestion, particularly considering that both FNA and heat can be produced as by-products of anaerobic sludge digestion. [Display omitted] •FNA + heat pre-treatment is effective in enhancing anaerobic methane production.•FNA + heat pre-treatment improves hydrolysis rate and methane potential of the sludge.•FNA + heat pre-treatment attains higher methane production than FNA or heat alone does.•FNA + heat pre-treatment has the potential to achieve Class A biosolids.•FNA + heat pre-treatment is economically and environmentally attractive.