Effective recovery of the nitritation process through hydrogen peroxide.

This study successfully achieved stable nitritation by adding hydrogen peroxide (H2O2) to the nitrification sludge whose nitritation stability had been destroyed. The batch experiment demonstrated that, the activity of ammonia-oxidizing bacteria (AOB) was restored more rapidly than that of nitrite oxidizing bacteria (NOB) after the addition of H2O2, thereby selectively promoting AOB enrichment and NOB washout. When the H2O2 concentration was 6.25 mg/L, the NOB activity was significantly reduced and the nitrite accumulation rate (NAR) was more than 95% after 18 cycles of nitrifying sludge restoration. As a result, H2O2 treatment enabled a nitrifying reactor to recover stable nitritation performance via H2O2 treatment, with the NAR and ammonia removal efficiency (ARE) both exceeding 90%. High-throughput sequencing analysis revealed that H2O2 treatment was successful in restoring nitritation, as the relative abundance of Nitrosomonas in the nitrifying reactor increased from 6.43% to 41.97%, and that of Nitrolancea decreased from 17.34% to 2.37%. Recovering nitritation by H2O2 inhibition is a low operational cost, high efficiency, and non-secondary pollution nitritation performance stabilization method. By leveraging the varying inhibition degrees of H2O2 on AOB and NOB, stable nitrification can be efficiently restored at a low cost and without causing secondary pollution.

Response of partial nitritation and denitrification processes to high levels of free ammonia in a pilot mature landfill leachate treatment system: Stability and microbial community dynamics.

The high levels of free ammonia (FA) challenge the application of partial nitritation (PN) and denitrification (DN) in the treatment of ammonia-rich wastewater. This study explored the impact of high levels of FA on the PN and DN stability and microbial community dynamics. By reducing reflux and increasing influent load, the concentrations of FA in PN and DN reactors increased from 28.9 mg/L and 140.0 mg/L to 1099.8 mg/L and 868.4 mg/L, respectively. During this process, the performance of PN and DN remained stable. The microbial analysis revealed that the Nitrosomonas exhibited strong tolerance to high levels of FA, and its relative abundance was positively correlated with amoABC (R2 0.984) and hao (R2 0.999) genes. The increase in microbial diversity could enhance the resistance ability of PN against the FA impact. In contrast, high levels of FA had scant influence on the microbial community and performance of DN.

Elucidating nitrogen removal performance and response mechanisms of anammox under heavy metal stress using big data analysis and machine learning.

In this study, machine learning algorithms and big data analysis were used to decipher the nitrogen removal rate (NRR) and response mechanisms of anammox process under heavy metal stresses. Spearman algorithm and Statistical analysis revealed that Cr6+ had the strongest inhibitory effect on NRR compared to other heavy metals. The established machine learning model (extreme gradient boost) accurately predicted NRR with an accuracy>99%, and the prediction error for new data points was mostly less than 20%. Additionally, the findings of feature analysis demonstrated that Cu2+ and Fe3+ had the strongest effect on the anammox process, respectively. According to the new insights from this study, Cr6+ and Cu2+ should be removed preferentially in anammox processes under heavy metal stress. This study revealed the feasible application of machine learning and big data analysis for NRR prediction of anammox process under heavy metal stress.

Improving stability and nitrogen removal performance of pilot-scale autotrophic process for mature landfill leachate treatment utilizing in-situ organics.

This study established a stable and efficient pilot-scale denitrification (DN) and partial nitritation (PN) combined with autotrophic nitrogen removal process for mature landfill leachate treatment. A total inorganic nitrogen removal efficiency (TINRE) of 95.3% was achieved without any external carbon source input, including 17.1%, 1.0% and 77.2% of nitrogen removal contributed by the DN, PN and autotrophic processes, respectively. ANAMMOX genus, Ca_Anammoxoglobus (19.4%) was dominant in autotrophic reactor. Moreover, denitrifying bacteria could utilize in-situ organics, including poorly degradable organics, to enhance the nitrogen removal performance of autotrophic process, contributing 3.4% of TINRE. This study provides new insights for the economical, low-carbon, and efficient treatment of mature landfill leachate.

Large-scale (500 kg N/day) two-stage partial nitritation/anammox (PN/A) process for liquid-ammonia mercerization wastewater treatment: Rapid start-up and long-term operational performance.

The nitrogen pollution control of liquid-ammonia mercerization wastewater (LMWW) is one of the typical obstacle restricting the sustainability of textile industry. In this study, a 500 kg N/day two-stage partial nitritation/anammox (PN/A) process containing PN reactor filled with zeolite and biofilm anammox reactors was successfully started up in 45 days and operated stably with high shock resistance over one year for LMWW treatment. The large-scale process achieved an average ammonium removal efficiency (94.3 ± 2.3%), total nitrogen removal efficiency (89.4 ± 2.7%) and nitrogen removal rate (1.003 ± 0.386 kg N/m3/day) during one year engineering operation. Simultaneous denitrification was revealed by the contribution of 5.2% total nitrogen removed. High-throughput sequencing results showed that Nitrosomonas was the most dominant genus in PN reactor, and Ca. Anammoxoglobus and Ca. Kuenenia were the functional bacteria for nitrogen removal in anammox reactors. Compared to traditional nitrification-denitrification process, the large-scale process reduced a total operational cost of 46.03 CNY/kg N for LMWW. This study revealed the proposed process was quite reliable with fast start-up and high impact resistance to overcome the obstacle of nitrogen pollution control for LMWW economically and conducive to the sustainable development for textile industry.

[Nitrogen Removal from Mature Landfill Leachate via Denitrification-Partial Nitritation-ANAMMOX Based on a Zeolite Biological Aerated Filter].

A combined process of denitrification-partial nitritation-ANAMMOX based on a zeolite biological aerated filter (ZBAF) was applied to treat mature landfill leachate. We investigate the partial nitritation characteristics of the ZBAF and the nitrogen removal performance as well as the carbon removal performance of the combined process. Results showed that, based on the selective inhibition of nitrite oxidizing bacteria (NOB) by free ammonia (FA), the ZBAF could successfully achieve stable and efficient partial nitrification of mature landfill leachate, with an average nitrite accumulation rate (NAR) of 93.8% and a maximum nitrite production rate (NPR) of 1.659 kg·(m3·d)-1. After adding 700 mg·L-1 glucose to the influent, due to the synergistic effect of denitrification and anammoxidation, the combined process achieved its best nitrogen removal performance at a reflux ratio of 2.0 and hydraulic retention time (HRT) of 2.2 days. The average ammonia removal efficiency (ARE), total nitrogen removal efficiency (NRE), total nitrogen removal loading rate (NRR), and average chemical oxygen demand (COD) removal efficiency were 97.2%, 90.0%, 0.585 kg·(m3·d)-1, and 45.3%, respectively. Furthermore, the NRR of the anaerobic ammonium oxidation (ANAMMOX) process (NRRANA) reached 1.268 kg·(m3·d)-1. High-throughput sequencing technology was used to analyze the microbial community structure in each device. Results showed that denitrifiers (Paracoccus and Comamonas), ammonia-oxidizing bacteria (AOB) (Nitrosomonas), and ANAMMOX bacteria (Candidatus Kuenenia and Candidatus Anammoxoglobus) were the dominant bacteria in the UASB, ZBAF, and ANAMMOX reactor, respectively, which corresponded to the stable nitrogen removal performance of the combined process.

Effect of alkalinity on bio-zeolite regeneration in treating cold low-strength ammonium wastewater via adsorption and enhanced regeneration.

Low temperature severely inhibits microbial activity, making biological method inefficient for ammonium removal from wastewater. A zeolite biological fixed-bed (ZBFB) was successfully established for 6.0-8.0 °C low-strength ammonium wastewater treatment via adsorption-regeneration. Ion exchange was a remarkable alternative and zeolite was mostly applied. Nevertheless, insufficient zeolite bio-regeneration rate was the key obstacle for economically sustainable utilization. By adsorption, effluent NH4+-N was around 1.5-2.5 mg/L. About 26% regeneration rate was obtained. With a ceramsite biological aerobic filter (CBAF) operated with ZBFB in series at the regeneration stage, the regeneration rate reached 95%, 3.5 times higher. Studies of alkalinity effects on bio-zeolite regeneration process indicated that Na2CO3 worked better than NaHCO3. Greater amount and one dose mode of alkalinity addition, higher regeneration rate could be obtained. The bio-zeolite regeneration process followed pseudo first-order kinetics with K = 0.0629 h-1. High-throughput sequencing analysis indicated the enriched nitrifying microorganisms in CBAF fully oxidized NH4+-N in regeneration solution, which accelerated desorption and conversion of NH4+-N by the circulation of regeneration solution between ZBFB and CBAF. The dynamic adsorption experiment proved that ZBFB-CBAF was feasible for cold low-strength ammonium wastewater treatment.