Challenges, solutions and prospects of mainstream anammox-based process for municipal wastewater treatment.

Anaerobic ammonia oxidation (anammox) process has a promising application prospect for the mainstream deammonification of municipal wastewater due to its high efficiency and low energy consumption. In this paper, challenges and solutions of mainstream anammox-based process are summarized by analyzing the literature of recent ten years. Slow growth rate of anammox bacteria is a main challenge for mainstream anammox-based process, and enhancement of bacteria retention has been recognized to be necessary. Compared with directly increasing sludge retention time (SRT) with membrane bioreactors or sequencing batch reactors, culturing anammox bacteria in the form of biofilm or granule sludge is more promising for its feasibility of eliminating nitrite oxidizing bacteria (NOB). Besides, adding external electron donors or conductive materials and enriching the concentration of ammonia with absorption materials have also been proved helpful to improve the activity of anammox bacteria. Other challenges include the elimination of NOB and achieving ideal ratio of NH4+ and NO2-. To solve these problems and achieve stable partial nitrification, composite control strategies based on low SRT and limited aeration are needed based on the special characteristics of ammonia oxidizing bacteria (AOB) and NOB. When treating actual wastewater, interference of low temperature and components in the influent is another problem. Relatively high activity of anammox bacteria has been realized after artificial acclimation at low temperature and the mechanism was also preliminary explored. Different pre-treatment sections have been designed to reduce the concentration of COD and S2- from the influent. As for the nitrate produced by the anammox reaction, coupling processes are useful to reduce the concentration of nitrate in the effluent. In brief, suitable reactor and coupling process should be selected according to the temperature, influent quality and discharge targets of different regions. The future prospects of the mainstream anammox-based process are also put forward.

Anammox bacteria enrichment and denitrification in moving bed biofilm reactors packed with different buoyant carriers: Performances and mechanisms.

Anaerobic ammonium oxidation (anammox) is recognized as the most cost-effective process for nitrogen removal from wastewater. In this study, effects of polyethylene plastics, nonwoven fabric, granular activated carbon (GAC) and polyurethane sponge as buoyant carriers were evaluated in lab-scale moving bed biofilm reactors (MBBRs). The overall performance of MBBRs with four types of carriers from priority to inferiority was noticed as, GAC, nonwoven fabrics, polyurethane sponge and polyethylene plastics under the same packing ratio of 20 v% and an average carrier size of 4 × 4 × 4 mm. The hydrophobic surface of GAC could selectively adsorb hydrophobic protein and favor anammox bacteria attachment, which contributed to achieving a total nitrogen removal rate of 0.40 kg-N/(m3·d) in 60 days. In conclusion, our results provide compelling evidence for achieving effective anammox process in an MBBR with GAC carriers and would benefit towards accomplishing a stable partial nitritation-anammox process in the future.

Ni-Induced C-Al2O3-Framework (NiCAF) Supported Core-Multishell Catalysts for Efficient Catalytic Ozonation: A Structure-to-Performance Study.

During catalytic ozonation, Al2O3-supported catalysts usually have stable structures but relatively low surface activity, while carbon-supported catalysts are opposite. To encourage their synergisms, we designed a Ni-induced C-Al2O3-framework (NiCAF) and reinforced it with a Cu-Co bimetal to create an efficient catalyst (CuCo/NiCAF) with a core-multishell structure. The partial graphitization of carbon adjacent to Ni crystals formed a strong out-shell on the catalyst surface. The rate constant for total organic carbon removal of CuCo/NiCAF (0.172 ± 0.018 min-1) was 67% and 310% higher than that of Al2O3-supported catalysts and Al2O3 alone, respectively. The metals on CuCo/NiCAF contributed to surface-mediated reactions during catalytic ozonation, while the embedded carbon enhanced reactions within the solid-liquid boundary layer and in the bulk solution. Moreover, carbon embedment provided a 76% increase in ·OH-production efficiency and an 86% increase in organic-adsorption capacity compared to Al2O3-supported catalysts. During the long-term treatment of coal-gasification wastewater (∼5 m3 day-1), the pilot-scale demonstration of CuCo/NiCAF-catalyzed ozonation revealed a 120% increase in ozone-utilization efficiency (ΔCOD/ΔO3 = 2.12) compared to that of pure ozonation (0.96). These findings highlight catalysts supported on NiCAF as a facile and efficient approach to achieve both high catalytic activity and excellent structural stability, demonstrating that they are highly viable for practical applications.

Boron accumulation by Lemna minor L. under salt stress.

Excess boron (B) is toxic to aquatic organisms and humans. Boron is often present in water with high salinity. To evaluate the potential of duckweed (Lemna minor L.) for removing B from water under salt stress, we cultured duckweed in water with 2 mg/L of B and sodium chloride (NaCl) concentrations ranging from 0 to 200 mM for 4 days. The results show that with increasing salinity, the capacity of L. minor to accumulate B initially decreased and then increased. L. minor used different mechanisms to accumulate boron at lower and higher levels of salt stress. The growth and chlorophyll synthesis of L. minor were significantly inhibited when the concentration of NaCl reached 100 mM. Our results suggest that L. minor is suitable for the accumulation of B when NaCl salinity is below 100 mM.