Enhanced sludge settlement of two stage PN/Anammox for reject water treatment with respective diatomite addition

Stoichiometric analysis and control strategy of partial nitrification for treating dewatering liquid from food-waste methane fermentation

Methane fermentation is critical for food-waste management; however, effective treatment of its high-ammonium dewatering liquid remains a major challenge. Anammox, a promising candidate for liquid treatment, requires effective pretreatment, such as partial nitrification (PN), to reduce ammonium and generate sufficient nitrite to optimize efficiency. In this study, an airlift reactor was employed to process the dewatering liquid from food-waste methane fermentation. Stable operation for over 360 days demonstrated its feasibility under high-load conditions. By implementing precise aeration control strategy to stabilize the ammonium removal efficiency (ARE = 50.2-57.1 %), a detailed summary of the optimal operational parameter ranges (consumed inorganic carbon [ΔIC] 1000-1160 mg C/L, effluent [Eff.] IC 282-378 mg C/L, pH 8.05-8.17, Eff. Alkalinity 1000-1350 mg CaCO3/L, free ammonia 61.9-82.5 mg/L, and free nitrous acid 47.6-71.1 μg/L) were provided under the ideal NO2⁻/NH4⁺ ratio of 1.1-1.3. Additionally, variations in ammonium oxidizing bacteria activity with temperature and pH were analyzed by the Arrhenius, cardinal temperature model with inflection, and Haldane models, with R2 values of 0.998, 0.975, and 0.999, respectively. Results suggest that the optimal conditions for partial nitrification were identified as a temperature range of 20-40 °C and a pH range of 7.5-8.5. Microbial sequencing reveals Nitrosomonas markedly enriched during operation, with its abundance rising from 3.67 % to 9.76 % as the NLR increased. Notably, NOB was nearly undetectable throughout the entire process. Additionally, an advanced aeration-based control mechanism with a positive feedback loop were proposed, which allows the airlift PN reactor to effectively treat high-ammonia dewatering liquid, thereby providing a suitable influent for subsequent anammox and offering crucial theoretical insights for future controlling pilot-scale system operation.

A novel process based on powder carriers demonstrates robustness in nitrogen and phosphorus removal from real municipal wastewater

The development of efficient and low-consumption wastewater upgrading process is currently at the forefront of the wastewater treatment field. In this study, a novel wastewater treatment process based on powder carriers was proposed. Three systems, namely the activated sludge (AS) system, powder carrier (PC) system, and moving bed biofilm reactor (MBBR) system, were established and operated for over 140 days to treat real municipal wastewater. The characteristics and differences between the three systems were comprehensively investigated. The results suggested that the PC system exhibited notable advantages in nitrogen and phosphorus removal, especially under high influent load and low aeration conditions. The PC system, characterized by a higher nitrification rate compared to the MBBR system and a higher denitrification rate compared to the AS system, contributed to the stable nitrogen removal performance. The particle size of the zoogloea increased under the linkage of the powder carriers, and the mean size of micro-granules reached 170.88 μm. Large number of hydrophobic functional groups on sludge surface, coupled with increased protein content in EPS, further promoted sludge aggregation. Micro-granules formation improved settling performance and enhanced the abundance and activity of functional microbes. A significant enrichment in denitrifying bacteria and denitrifying phosphorus accumulating bacteria was observed in PC system. Up-regulation of the napA, narG, and nosZ genes was responsible for efficient nitrogen removal of the PC system. Moreover, a higher abundance in polyphosphate phosphotransferase (2.11 %) was found in PC system compared with AS and MBBR systems. The increase in the enzymes associated with poly-β-hydroxybutyrate (PHB) synthesis metabolism in PC system provided the energy for denitrification and phosphorus removal processes.

Feasibility of anaerobic ammonium oxidation process for treatment of pretreated printed circuit board wastewater

The treatment of pretreated printed circuit board (PCB) wastewater by anaerobic ammonium oxidation (anammox) process has been rarely reported. This study sought to investigate the performance of the anammox process during various phases of pretreated PCB wastewater treatment. The nitrogen removal efficiency (NRE) reached 90 ± 10% at a Cu2+ concentration of 2.5 mg·L-1, but declined to 22 ± 11% as the Cu2+ level increased to 10.3  mg·L-1. During phase III, there was a 38% increase in the relative abundance of Candidatus Kuenenia compared to phase I. By adjusting the substrate concentration and introducing synthetic wastewater into the reactor, the anammox performance was nearly restored to that of phase I. These findings underscore the potential of the anammox process for treating pretreated PCB wastewater and expanding its practical applications to industrial wastewater treatment.

Effective enrichment of anaerobic ammonia oxidation sludge with feast-starvation strategy: activity, sedimentation, growth kinetics, and microbial community

To address the issue of floating and loss of floc sludge caused by gas production in anaerobic ammonia oxidation (anammox) reactors, this study proposes a limited nitrite supply strategy to regulate gas production during the settling and enhance sludge retention. Results indicate that the effluent suspended solids in the anammox reactor can be reduced to as low as 0.11 g/L under specific feast-starvation conditions. Even under long-term intermittent nitrite-starvation stress, the maximum growth rate of Candidatus_Kuenenia can still reach 0.085d-1, with its abundance increasing from 0.47% to 8.83% within 69 days. Although the combined effects of starvation and sedimentation would lead to a temporary decrease in anammox activity, this reversible inhibition can be fully restored through substrate intervention. The limited nitrite supply strategy promotes the sedimentation of anammox sludge without significantly affecting its growth rate, and effective sludge retention is crucial for enriching anammox sludge during initial cultivation.