Strategy of nitrate removal in anaerobic ammonia oxidation-dependent processes

A novel coupling process to replace the traditional multi-stage anammox process-sulfur autotrophic denitrification coupled anammox system

A novel coupling process to replace the traditional multi-stage anammox process-sulfur autotrophic denitrification (SAD) coupled anaerobic ammonium oxidation (anammox) system was designed, which solved problems of nitrate produced in anammox process and low nitrate conversion rate caused by nitrite accumulation in SAD process. Different filter structures (SAD filter and anammox granular sludge) were investigated to further explore the excellent performance of the novel integrated reactor. The results of sequential batch experiments indicated that nitrite accumulation occurred during SAD, which inhibited the conversion of nitrate to dinitrogen gas. When SAD filter and anammox granular sludge were added to packed bed reactor simultaneously, the nitrate removal rate increased by 37.21% and effluent nitrite concentration decreased by 100% compared to that achieved using SAD. The stratified filter structure solved groove flow. Different proportion influence of SAD filter and anammox granular sludge on the stratified filter structure was evaluated. More suitable ratio of SAD filter to anammox granular sludge was 2:1. Proteobacteria (57.26%), Bacteroidetes (20.12%) and Chloroflexi (9.95%) were the main phyla. The dominant genera of denitrification functional bacteria were Thiobacillus (39.80%), Chlorobaculum (3.99%), norank_f_PHOs-HE36 (2.90%) and Ignavibacterium (2.64%). The dominant genus of anammox bacterium was Candidatus_Kuenenia (3.05%).

Calculation of carbon emissions in wastewater treatment and its neutralization measures: A review

As the pursuit of "carbon neutrality" gains momentum, the emphasis on low-carbon solutions, emphasizing energy conservation and resource reuse, has introduced fresh challenges to conventional wastewater treatment approaches. Precisely evaluating carbon emissions in urban water supply and drainage systems, wastewater treatment plants, and establishing carbon-neutral operating models has become a pivotal concern in the future of wastewater treatment. Regrettably, limited research has been devoted to carbon accounting and the development of carbon-neutral strategies for wastewater treatment. In this review, to facilitate comprehensive carbon accounting, we initially recognizes direct and indirect carbon emission sources in the wastewater treatment process. We then provide an overview of several major carbon accounting methods and propose a carbon accounting framework. Furthermore, we advocate for a systemic perspective, highlighting that achieving carbon neutrality in wastewater treatment extends beyond the boundaries of wastewater treatment plants. We assess current technical measures both within and outside the plants that contribute to achieving carbon-neutral operations. Encouraging the application of intelligent algorithms for the multifaceted monitoring and control of wastewater treatment processes is paramount. Supporting resource and energy recycling is also essential, as is recognizing the benefits of synergistic wastewater treatment technologies. We advocate a systematic, multi-level planning approach that takes into account a wide range of factors. Our goal is to offer valuable insights and support for the practical implementation of water environment management within the framework of carbon neutrality, and to advance sustainable socio-economic development and contribute to a more environmentally responsible future.

Denitrification effect and strengthening mechanism of SAD/A system at low temperature by gel-immobilization technology

Sulfur autotrophic denitrification coupled anaerobic ammonia oxidation (SAD/A) has several advantages over other denitrification processes; for example, it does not consume the organic carbon source, has low operation costs, and produces less excess sludge; however, it has certain disadvantages as well, such as a long start-up time, easy loss of bacteria, and low microbial activity at low temperature. The use of microbial immobilization technology to embed functional bacteria provides a feasible method of resolving the above problems. In this study polyvinyl alcohol‑sodium alginate was used to prepare a composite carrier for fixing anaerobic ammonia oxidizing bacteria (AAOB) and sulfur oxidizing bacteria (SOB), and the structure and morphology of the encapsulated bodies were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Subsequently, the nitrogen removal performance of the immobilized microbial carriers in the gradient cooling process (30 °C to 10 °C) was determined, and the corresponding mechanism was discussed. The results showed that the nitrate-removal efficiencies observed with granular sludge and gel embedding were at 10 °C 21.44 % and 14.31 % lower, than those at 30 °C, respectively, whereas the ammonia-removal efficiency decreased by up to approximately three-fold. The main mechanism was the 'insulation' provided by the external gel composed of PVA and SA for the internal sludge and subsequent improvement of its low temperature resistance, while protecting AAOB and SOB from oxygen inhibition, which is conducive to enriching denitrifying bacteria. In addition, the gel does not change the internal sludge species, it can shift the dominance of specific microorganisms and improve the removal efficiency of nitrogen. In summary, the immobilization of AAOB and SOB by the gel can achieve effectively mitigate nitrogen pollution in low temperature environments, thus indicating that the SAD/A process has broad engineering application prospects.