Energy-neutral municipal wastewater treatment based on partial denitrification-anammox driven by side-stream sulphide

Electrochemical nitrite sensing using mass transfer signal with a catalyst-free small-sized rotating disk electrode for wastewater monitoring

Electrochemical nitrite sensing (ENS) is a competitive method for online monitoring in the intelligent control of biological nitrogen removal process. However, its popularity is extremely low due to complex wastewater interference and low sensor durability. Here, we developed a novel ENS method that utilizes the mass transfer signal (MTS) of the nitrite oxidation reaction (NOR), making detection accuracy dependent solely on mass transfer process. These features enabled us to design a catalyst-free, small-sized glassy carbon rotating disk electrode for accurate MTS determination with exceptional durability. The linearity of MTS versus nitrite concentration surpasses that of conventional differential pulse voltammetry and amperometry. The method has a wide linear range of 100 μM-100 mM, a detection limit of 28 μM, and a high sensitivity of 1638 μA mM-1 cm-2. Importantly, solution pH and coexisting buffers show no significant effect on MTS determinations as long as pH does not exceed 10. Excellent immunity to interference from ionic strength, temperature, COD, inert salts, metal ions, dissolved oxygen, and hydrogen peroxide was observed. While reducing substances capable of oxidation reactions do cause interference, they are not common in environmental samples. Finally, a self-designed detection system requiring a sample volume of 4 mL was used for wastewater testing. The results demonstrate good capability for nitrite detection during practical wastewater treatment processes, although relative error increases with the complexity and content of organic pollutants in the wastewater. Overall, this ENS method holds great potential for achieving rapid, stable, and low-cost nitrite sensing in environmental applications.

Start-up of pilot-scale ANAMMOX reactor for low-carbon nitrogen removal from anaerobic digestion effluent of kitchen waste

The pilot-scale simultaneous denitrification and methanation (SDM)-partial nitrification (PN)-anaerobic ammonia oxidation (Anammox) system was designed to treat anaerobic digestion effluent of kitchen waste (ADE-KW). The SDM-PN was first started to avoid the inhibition of high-concentration pollutants. Subsequently, Anammox was coupled to realize autotrophic nitrogen removal. Shortcut nitrification-denitrification achieved by the SDM-PN. The NO2--N accumulation (92 %) and NH4+-N conversion (60 %) were achieved by PN, and the removal of TN and COD from the SDM-PN was 70 % and 73 %, respectively. After coupling Anammox, the TN (95 %) was removed with a TN removal rate of 0.51 kg·m-3·d-1. Microbiological analyses showed a shift from dominance by Methanothermobacter to co-dominance by Methanothermobacter, Thermomonas, and Flavobacterium in SDM during the SDM-PN. While after coupling Anammox, Candidatus kuenenia was enriched in the Anammox zone, the SDM zone shifted back to being dominated by Methanothermobacter. Overall, this study provides new ideas for the treatment of ADE-KW.

Insight into microbial adaptability in continuous flow anaerobic ammonium oxidation process for low-strength sewage treatment

Organic matter concentration is a critical factor influencing the adaptability of anaerobic ammonium oxidation (anammox) bacteria to low-strength sewage treatment. To address this challenge and achieve stable anammox activity, a micro-aeration partial nitrification-anammox process was developed for continuous-flow municipal sewage treatment. Under limited ammonium conditions, the effective utilization of organics in denitrification promoted the stable accumulation of nitrite and enhanced anammox activity. This, in turn, led to enhanced nitrogen removal efficiency, reaching approximately 87.7%. During the start-up phase, the protein content of extracellular polymeric substances (EPS) increased. This enhanced EPS intensified the inhibitory effect of denitrifying bacteria (DNB) on nitrite-oxidizing bacteria through competition for nitrite, thereby facilitating the proliferation of anammox bacteria (AnAOB). Additionally, several types of DNB capable of utilizing slowly biodegradable organics contributed to the adaptability of AnAOB. These findings provide valuable insights for ensuring efficient anammox performance and robust nitrogen removal in the treatment of low-strength sewage.