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.

厌氧消化是减少和稳定废水处理厂中产生的废活性污泥的常用方法。然而，厌氧消化污泥由于其体积大且质量通常较差而仍是有问题的废物流。在这项研究中，建立了两个好氧消化池来处理厌氧消化的污泥，其中一个在自生酸性条件下运行的消化池作为实验反应器，一个在中性pH下的消化池作为对照反应器。在实验反应器中的酸性条件是通过一个特殊的接种氨氧化细菌，“驱动暂定Nitrosoglobus”，这可以容忍的低pH。由于铵被Ca氧化。亚硝基球体，pH降至4.8±0.2，亚硝酸盐累积并保持在200.0±17.2 mg NL ^-1，由此原位形成8.5±1.8 mg HNO ₂ N L ^-1的游离亚硝酸（FNA）。由于低pH和高浓度FNA的共同作用，实验反应器将AD污泥中的总固体（TS），挥发性固体（VS）和非挥发性固体（NVS）降低了25.2±7.0％，29.8±4.3 ％和22.6±5.5％。相反，对照反应器没有Ca。接种硝化球菌（在6.8±0.3的近中性pH值下操作且无FNA形成）仅将AD污泥中的VS降低了10.4±4.3％，同时NVS的降低可忽略不计。另外，实验反应器中的酸性需氧消化可显着稳定AD污泥，将比氧吸收率（SOUR）降低至0.5±0.1 mg O ₂ g ^-1 VS h ^-1，而粪便大肠菌群的最大可能数（MPN）降低至2.4±0.1 log（MPN g ^-1 TS），均符合USEPA A类生物固体标准。相比之下，对照反应器仅产生B级生物固体，其SOUR为1.8±0.2 mg O ₂ g ^-1 VS h ^-1和粪大肠菌群的MPN为3.6±0.1 log（MPN g ^-1 TS）。通过减少AD污泥的体积并提高其质量，Ca可实现AD污泥的酸性好氧消化。亚硝基球菌有潜力显着节省废水处理中的污泥处置成本。