Effect of hydraulic retention time on effluent pH in anammox bioreactors: Characteristics of effluent pH and pH as an indicator of reactor performance.

In order to assess the performance of anaerobic ammonium oxidation (anammox) bioreactors, it is necessary to study the stoichiometry of the anammox reaction and pH. This study focused on the effect of the hydraulic retention time (HRT) on the effluent pH in anammox-upflow anaerobic sludge blanket (UASB) bioreactors. Anammox-UASB bioreactors with and without a recirculation system were used to investigate the effluent pH and bioreactor performance. It was concluded that under varying HRT conditions, the decrease in effluent pH did not indicate the deterioration of nitrogen removal, but did indicate that the nitrogen removal efficiency was reduced owing to a sudden increase in the nitrogen loading rate resulting from the decrease in HRT. Moreover, the results showed that the HRT directly affected the concentration of OH-, which affected the increase/decrease in effluent pH. This study demonstrated that effluent pH is a more powerful tool than previous techniques used to assess bioreactor performance. We suggest that the effluent pH could be used for preliminary assessment.

[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.

[Effects of Alkalinity on Partial Nitrification in a Zeolite Sequencing Batch Reactor].

Stable partial nitrification was successfully achieved in a zeolite sequencing batch reactor (ZSBR) with an excellent nitrite accumulation ratio of over 90.0%, and the effects of four alkalinity concentrations (calculated by CaCO3) on the nitritation in the ZSBR were investigated at an influent ammonia nitrogen concentration of 500 mg·L-1. The results showed that the key for the partial nitrification achieved in ZSBR was that the inhibitory effect of free ammonia (FA) on nitrite oxidizing bacteria (NOB) was much greater than that on ammonia oxidizing bacteria (AOB). Additionally, the wastewater containing ammonia nitrogen converted by this process can be used as the influent for anaerobic ammonium oxidation to further remove ammonia nitrogen and total nitrogen in wastewater. When the dosage of alkalinity was 2500 mg·L-1 in the ZSBR, the best nitritation efficiency was obtained with an average ammonia nitrogen conversion efficiency of 66.7%, nitrite accumulation ratio of 98.1%, and nitrite production rate of 0.74 kg·(m3·d)-1. It was demonstrated by high-throughput sequencing analysis that significant microbial community variations occurred after a long period of operation, and these changes involved an enrichment of AOB and inhibition of NOB in the ZSBR.