Enhancing start-up strategies for anammox granular sludge systems: A review

Recovery strategies and mechanisms of anammox reaction following inhibition by environmental factors: A review

Anaerobic ammonium oxidation (anammox) is a promising biological method for treating nitrogen-rich, low-carbon wastewater. However, the application of anammox technology in actual engineering is easily limited by environmental factors. Considerable progress has been investigated in recent years in anammox restoration strategies, significantly addressing the challenge of poor reaction performance following inhibition. This review systematically outlines the strategies employed to recover anammox performance following inhibition by conventional environmental factors and emerging pollutants. Additionally, comprehensive summaries of strategies aimed at promoting anammox activity and enhancing nitrogen removal performance provide valuable insights into the current research landscape in this field. The review contributes to a comprehensive understanding of restoration strategies of anammox-based technologies.

Self-cultivating anammox granules for enhancing wastewater nitrogen removal in nitrification-denitrification flocculent sludge system

The feasibility of self-cultivating anammox granules for enhancing wastewater nitrogen removal was investigated in a nitrification-denitrification flocculent sludge system. Desirable nitrogen removal efficiency of 84 ± 4 % was obtained for the influent carbon to nitrogen ratio of 1-1.3 (NH4+-N: 150-200 mg N/L) via alternate anaerobic/oxic/anoxic mode. Meanwhile, some red granular sludge was formed in the system. The abundance and activity of anaerobic ammonia oxidation bacteria (AnAOB) increased from 'not detected' in seed sludge to 0.57 % and 29.4 ± 0.7 mg N/(g mixed liquor volatile suspended solids·h) in granules, respectively, suggesting successful cultivation of anammox granules. Furthermore, some denitrifying bacteria with capability of partial denitrification were enriched, such as Candidatus Competibacter (2.45 %) and Thauera (5.75 %), which could cooperate with AnAOB, facilitating AnAOB enrichment. Anammox was dominant in nitrogen removal with the contribution to nitrogen removed above 68.8 ± 0.3 %. The strategy of self-cultivating anammox granules could promote the application of anammox.

Simultaneous ammonia and nitrate removal by novel integrated partial denitrification-anaerobic ammonium oxidation-bioelectrochemical system

The current study explored the performance of an integrated partial denitrification-anaerobic ammonium oxidation (anammox)-bioelectrochemical system on simultaneous removal of ammonia nitrogen and nitrate nitrogen. Different operational conditions were selected to optimize critical parameters of the process for improving nitrogen removal. The results indicated that more than 90 % of total inorganic nitrogen removal efficiency was achieved under the optimal conditions: ammonia nitrogen/nitrate nitrogen ratio of 1:2, external resistance of 200 Ω and inoculation volume ratio of anammox bacteria/denitrifying at 2:1. Improved nitrogen removal under the optimal conditions were confirmed by microbial community changes (Candidatus Brocadia and Thiobacillus) and enhanced of nitrogen metabolism-related genes (hao, hzsA/C and hdh). Increases of Limnobacter indicated an enhanced electron transfer efficiency. Overall, high-efficiency and stable nitrogen removal efficiency without nitrite nitrogen accumulation could be achieved by the integrated system under the optimal conditions, providing novel insights for simultaneous treatment of domestic wastewater and groundwater.

Reactivation performance and sludge transformation after long-term storage of Partial denitrification/Anammox (PD/A) process

This study explores the startup of innovative Partial denitrification/Anammox (PD/A) process using long-term stored sludge (>2 years at 4 °C). Results indicate a swift recovery performance, characterized by a progressive increase in the activity of functional microorganisms with improved nitrogen volumetric loading rate during operation. Stable nitrogen removal efficiency of 99.6 % was attained at 14.2 °C under influent nitrate and ammonium of 120 and 100 mg/L, respectively. A distinctive transformation was observed as the initially black seeding sludge transitioned to brownish-red, accompanied by rapid sludge granulation with size notably increased from 263.1 μm (day 4) to 1255.0 μm (day 128), significantly contributing to the rapid PD/A performance recovery. Microbial community analysis revealed substantial increases in functional bacteria, Thauera (0.09 %-10.4 %) and Candidatus Brocadia (0.003 %-1.98 %), coinciding with enhanced nitrogen removal performance. Overall, this study underscores the viability of long-term stored PD/A sludge as a seed for rapid reactor startup, offering useful technical support to advance practical PD/A process implementation.

Temporal and spatial variations in the physical and chemical properties of anaerobic granular sludge within a Pilot Spiral Symmetry Stream Anaerobic Bioreactor

Anaerobic granular sludge (AGS) determines the high performance of the bioreactor. To study the regionalization of granular sludge in the bioreactor, a Pilot Spiral Symmetry Stream Anaerobic Bioreactor (P-SSSAB) was established over 216 days, divided into three zones (I, II, and III) from bottom to top. AGS at the bottom of P-SSSAB had a higher porosity (60.35 %-83.27 %) and more suitable settling velocity (60 m/h) when the particle size range was 1.0-2.0 mm. This proved the better metabolic activity and superior settling performance in zone I than in zones II and III. In addition, the elemental composition of AGS in various zones was analyzed. The relative content of iron (5.66 %, 3.36 %, and 1.38 %, respectively) and sulfur (2.47 %, 2.19 %, and 1.49 %, respectively) in zone I, II, and III tended to decrease with the height of P-SSSAB. This also verified the better mass transfer performance and operational stability in lower zone than in upper zone. However, the monitoring of bed temperature in various zones revealed that the microbial activity in zone I was 6.7×10-12~3.5×10-2 times and 1.8×10-15~1.4×10-3 times that in zones II and III, respectively, which indicated that the unit activity of AGS in zone I was the worst. It indicated that AGS in lower zone had poor unit activity but had the highest unit capacity due to the high sludge concentration. Besides, the unit capacity of the upper zone was too weak to produce enough alkalinity to neutralize acid produced by excessive hydrolysis and acidification in lower zone, resulting in the worst treatment efficiency of the upper zone. Therefore, temperature and concentration ratios under various spatial distributions in bioreactors are vital to the overall sewage treatment stability and efficiency of bioreactors in actual engineering applications.