Aeration strategy based on numerical modelling and the response mechanism of microbial communities under various operating conditions

A green process for total nitrogen removal without extra energy consumption: Synergistic actions for wastewater treatment

Total nitrogen (TN) removal is one of the key issues in improving water quality, while the traditional nitrification-denitrification process with its high energy consumption is unsustainable, due to greenhouse gas (GHG) emission. A method using organic-inorganic pellets and selected microalgae that can operate without electricity consumption was designed for TN removal in actual wastewater treatment. The results showed that the TN removal efficiencies with different pellets were 88.2 % ± 2.2 %, 86.6 % ± 3.0 %, 85.4 % ± 4.3 %, and 82.3 % ± 6.5 %, respectively. Microalgae assimilated inorganic nitrogen within cells, resulting in a significant positive relationship with TN (P < 0.05), and effectively removed TN through sedimentation. The pellets adsorbed nitrogen and microorganisms, released organic substances to regulate the ratio of water chemical oxygen demand (COD) to TN, and correspondingly influenced microbial growth. Microalgae and bacteria such as Romboutsia, Proteiniclasticum, and Rhodopseudomonas cooperated to form a mixed aerobic (water) -anaerobic (pellets) environment in the devices, and acted synergistically to remove TN. This study verifies the feasibility of TN removal with only solar energy in a low flow application in large spaces, benefiting carbon neutrality in wastewater treatment.

Bacillus subtilis grown in a "breathing" vessel without sparger aeration

Here we present a "breathing" vessel consisting of expanded polytetrafluoroethylene, which allows gas exchange but no liquid permeation. The bacterial culture inside needs only agitation to promote air supply. Using this setup, a Bacillus subtilis cell factory for scyllo-inositol production grew to produce scyllo-inositol efficiently. The results indicate that our approach represents a sustainable "greener" approach for the cell factory.

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.

Sustainable removal of nutrients (n and p) in a wastewater treatment plant, with eggshell (biocalcium)

Biological treatments have become insufficient to treat municipal wastewater with greater toxicity and excess nitrogen and phosphate species, thus affecting the organisms that consume the water. In this work, a process was implemented for the removal of nutrients through three stages: stage A, complete aeration (24 h, 43 months); stage B, decreased aeration (12 h, 17 months); and stage C, decreased aeration with biocalcium (12 h, 19 months). The addition of biocalcium from eggshell promoted the formation of flocks, which resulted in the removal of nitrites (61 %), nitrates (84 %), total nitrogen (57 %), total phosphorus (8.3 %), sedimentable solids (50 %), total suspended solids (69 %), BOD5 (76 %), helminth eggs (50 %) and fecal coliforms (54 %). The statistical analyses in the three stages indicated that there is a strong correlation between the concentration of fats and oils and the removal of sedimentable solids and total suspended solids, since these parameters were correlated by 97 and 89 %, respectively. Sedimentable solids were correlated with total suspended solids by 94 %, while nitrates and total nitrogen were correlated 92 %, which favors the removal of nutrients in wastewater. The increase in the concentration of nitrogen in the sludge in stage C generated a C:N ratio of 7.98. This ratio shows that the sludge is feasible for use as a mediator of soils and a biofertilizer because of the high contents of calcium, phosphorus and nitrogen. In addition, biocalcium promoted the precipitation of hydroxyapatite, struvite, calcite and quartz. In general, the three stages of the treatment contributed to the stabilization of the wastewater treatment plant (WWTP) in an efficient, economical, and safe way.