Partial nitritation-anammox (PN-A) process, which significantly reduces energy and chemical input compared to the conventional biological nitrogen removal process, is a game-changing nitrogen-removal alternative. PN-A treating municipal wastewater (mainstream PN-A) may shed light on achieving a more sustainable energy-neutral municipal wastewater treatment, but practical applications are still not available. This review is therefore critically conducted to identify the challenges impeding the application of mainstream PN-A. At temperatures ≥ 25 °C, PN-A process treating mainstream wastewater can achieve comparable nitrogen removal performance to conventional processes, but the effluent quality may need to be improved to meet stringent discharge standards; at temperatures < 20 °C, long-term process instability, low nitrogen removal efficiency, and poor effluent quality are the main operating difficulties. The reasons are attributed to challenges in maintaining sufficient anammox activity and effective NOB suppression. A framework of operable solutions to these difficulties and challenges is suggested, among which the efficient anammox biomass retention should be prioritized. The effectiveness and practical availability of these solutions are also assessed. Ultimately, depending on technological readiness, a roadmap for the PN-A application is proposed to make the best of the benefits of PN-A and promote the implementation of energy-neutral/positive municipal wastewater treatment.
Iron (Fe)-based denitrification is a proven technology for removing nitrate from water, yet challenges such as limited pH preference range and low N2 selectivity (reduction of nitrate to N2) persist. Adding biochar (BC) can improve the pH preference range but not N2 selectivity. This study aimed to improve nitrate reduction and N2 selectivity in iron filling/biochar (Fe/BC) systems with a simplified approach by coupling unacclimated microbes (M) in the system. Factors such as initial pH, Fe/BC ratio, and Fe/BC dosage on nitrate removal efficiency and N2 selectivity were evaluated. Results show that the introduction of microbes significantly enhanced nitrate removal and N2 selectivity, achieving 100 % nitrate removal and 79 % N2 selectivity. The Fe/BC/M system exhibited efficient nitrate reduction at pH of 2–10. Moreover, the Fe/BC/M system demonstrated an improved electrochemical active surface area (ECSA), lower electron transfer resistance and lower corrosion potential, leading to enhanced nitrate reduction. The high i0 value in Fe/BC/M system means more Hads could be generated, thus improving the N2 selectivity. This study provides valuable insights into a novel approach for effective nitrate removal, offering a potential solution to the environmental challenges posed by excessive nitrate in wastewater, surface water and ground water.
This study proposed a novel electrodialysis (ED) system, named anode-ED, which can utilise the anode of ED in situ to electrochemically remove the antibiotics during nutrient (N and P) recovery from animal manure digestate. The oxidation of targeted antibiotics (sulfadiazine, SD; and tetracycline, TC) by the anode of ED was first assessed in a single-compartment reactor containing only one pair of ED electrodes. The results showed that Cl2 generated from the anode played the primary role in SD and TC removal. The anode-ED was then established based on a conventional ED process, in which the wastewater successively flowed into the anode compartment and the dilute compartment of the reactor. There was no observable difference in N and P recovery between the anode-ED and conventional ED, while the targeted antibiotics in the anode-ED were removed much more efficiently, with SD and TC removed in the 30 and 60 min, respectively, in comparison with conventional ED. In addition, in the anode-ED, membrane fouling was mitigated due to gas bubbling and the pathogenic microorganism indicators (E. coli and Enterococcus) were inactivated efficiently. Regarding the formation of disinfection by-products, only 134 μg/L of trihalomethanes and 192 μg/L of haloacetic acids were detected in the effluent due to membrane sorption, far less than those generated during conventional electrochemical oxidation and chlorination of wastewater. This study shows that anode-ED is a promising option to remove the antibiotics in an ED system, simultaneously achieving nutrient recovery, antibiotics removal, membrane fouling mitigation and pathogen inactivation.
This study aims to investigate the effects of the organic loading rate (OLR) and the aeration rate on denitrifying phosphate removal (DPR) from slaughterhouse wastewater treated at a temperature of 11 °C. Three laboratory-scale intermittently aerated sequencing batch reactors (IASBRs) were set up and three OLRs and five aeration rates were employed in the study. The results indicated that efficient removals of nitrogen (N) and phosphorus (P) from DPR were achieved. Furthermore, the intermittent aeration pattern benefitted both the phosphorus-accumulating organisms (PAOs) and the denitrifying phosphorus-accumulating organisms (DPAOs) that accumulated at 11 °C. The ratio of P uptake in the aeration periods/P release in the non-aeration periods was in the range of 0.94–1.10 in the three stages. The relationship between the specific poly-β-hydroxybutyrate (PHB) degradation rate (z), the specific P removal rate (x), and the specific total oxidized nitrogen(TON) reduction rate (y) can be fitted approximately as a plane ( z = 1.3626 x + 0.2882 y − 0.6722 , R2 = 0.83).
Ammonia inhibition is a common issue encountered in anaerobic digestion (AD) when treating nitrogen-rich substrates. This study proposed a novel approach, the electrodialysis-integrated AD (ADED) system, for in-situ recovery of ammonium (NH
MFC centered hybrid technologies have attracted attention during the last few years due to their compatibility and dual advantages of energy recovery and wastewater treatment. In this study, a MFC was integrated into a dewatered alum sludge (DAS)- based vertical upflow constructed wetland (CW). Powder activate carbon (PAC) was used in the anode area in varied percentage with DAS to explore its influences on the performance of the CW-MFC system. The trial has demonstrated that the inclusion of PAC improved the removal efficiencies of COD, TN and RP. More significantly, increasing the proportion of PAC from 2% to 10% can significantly enhance the maximum power densities from 36.58 mW/m(2) to 87.79 mW/m(2). The induced favorable environment for bio-cathode formation might be the main reason for this improvement since the content of total extracellular polymeric substances (TEPS) of the substrate in the cathode area almost doubled (from 44.59 μg/g wet sludge to 87.70 μg/g wet sludge) as the percentage of PAC increased to 10%. This work provides another potential usage of PAC in CW-MFCs with a higher wastewater treatment efficiency and energy recovery.
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