Acidic aerobic digestion of anaerobically-digested sludge enabled by a novel ammonia-oxidizing bacterium

Zhiyao Wang; Min Zheng; Haoran Duan; Gaofeng Ni; Wenbo Yu; Yanchen Liu; Zhiguo Yuan; Shihu Hu

doi:10.1016/j.watres.2021.116962

Acidic aerobic digestion of anaerobically-digested sludge enabled by a novel ammonia-oxidizing bacterium

Water Res. 2021 Apr 15:194:116962. doi: 10.1016/j.watres.2021.116962. Epub 2021 Feb 23.

Authors

Zhiyao Wang¹, Min Zheng², Haoran Duan¹, Gaofeng Ni¹, Wenbo Yu³, Yanchen Liu⁴, Zhiguo Yuan¹, Shihu Hu⁵

Affiliations

¹ Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia.
² Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia. Electronic address: m.zheng@awmc.uq.edu.au.
³ Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia; School of Environmental Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China.
⁴ State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
⁵ Advanced Water Management Centre, The University of Queensland, St Lucia, QLD 4072, Australia. Electronic address: s.hu@awmc.uq.edu.au.

PMID: 33657493
DOI: 10.1016/j.watres.2021.116962

Abstract

Anaerobic digestion is a commonly used process for the reduction and stabilization of wasted activated sludge generated in wastewater treatment plants. However, anaerobically-digested (AD) sludge is still a problematic waste stream due to its large volume and often poor quality. In this study, two aerobic digesters were set up to treat anaerobically-digested sludge, with one digester operated in self-generated acidic condition as the experimental reactor, and one at neutral pH as the control reactor. The acidic condition in the experimental reactor was driven by an inoculated special ammonia-oxidizing bacterium, 'Candidatus Nitrosoglobus', which can tolerate low pH. As a result of ammonium oxidation by Ca. Nitrosoglobus, the pH decreased to 4.8 ± 0.2 and nitrite accumulated to and stayed at 200.0 ± 17.2 mg N L^-1, from which free nitrous acid (FNA) at 8.5 ± 1.8 mg HNO₂N L^-1 formed in-situ. As a combined effect of low pH and high concentration of FNA, the experimental reactor reduced the total solids (TS), volatile solids (VS) and non-volatile solids (NVS) in the AD sludge by 25.2 ± 7.0%, 29.8 ± 4.3%, and 22.6 ± 5.5%, respectively. In contrast, the control reactor without Ca. Nitrosoglobus inoculation (operated at a near-neutral pH of 6.8 ± 0.3 and no FNA formation) only reduced VS in the AD sludge by 10.4 ± 4.3%, along with negligible NVS reduction. Additionally, the acidic aerobic digestion in the experimental reactor significantly stabilized AD sludge, decreasing the specific oxygen uptake rate (SOUR) to 0.5 ± 0.1 mg O₂ g^-1VS h^-1 and the most probable number (MPN) of Faecal Coliforms to 2.4 ± 0.1 log(MPN g^-1TS), both of which meet USEPA standards for Class A biosolids. In comparison, the control reactor produced biosolids at Class B level only, with an SOUR of 1.8 ± 0.2 mg O₂ g^-1VS h^-1 and a Faecal Coliforms MPN of 3.6 ± 0.1 log(MPN g^-1TS). By reducing the volume and improving the quality of the AD sludge, the acidic aerobic digestion of AD sludge enabled by Ca. Nitrosoglobus has the potential to significantly save the sludge disposal costs in wastewater treatment.

Keywords: Acidic aerobic digestion; Anaerobic digestion; Candidatus Nitrosoglobus; Sludge reduction; Stabilization.

MeSH terms

Ammonia*
Anaerobiosis
Bioreactors
Digestion
Oxidation-Reduction
Sewage*
Waste Disposal, Fluid

Substances

Sewage
Ammonia