Performance evaluation and microbial community structure of a modified trickling filter and conventional activated sludge process in treating urban sewage

Developments of electrospinning technology in membrane bioreactor: A review

The necessity for effective wastewater treatment and purification has grown as a result of the increasing pollution issues brought on by industrial and municipal wastewater. Membrane bioreactor (MBR) technology stands out when compared to other treatment methods because of its high efficiency, environmental friendliness, small footprint, and ease of maintenance. However, the development and application of membrane bioreactors has been severely constrained by the higher cost and shorter service life of these devices brought on by membrane biofouling issues resulting from contaminants and bacteria in the water. The nanoscale size of the electrospinning products provides unique microstructure, and the technology facilitates the production of structurally different membranes, or the modification and functionalization of membranes, which makes it possible to solve the membrane fouling problem. Therefore, many current studies have attempted to use electrospinning in MBRs to address membrane fouling and ultimately improve treatment efficacy. Meanwhile, in addition to solving the problem of membrane fouling, the fabrication technology of electrospinning also shows great advantages in constructing thin porous fiber membrane materials with controllable surface wettability and layered structure, which is helpful for the performance enhancement of MBR and expanding innovation. This paper systematically reviews the application and research progress of electrospinning in MBRs. Firstly, the current status of the application of electrospinning technology in various MBRs is introduced, and the relevant measures to solve the membrane fouling based on electrospinning technology are analyzed. Subsequently, some new types of MBRs and new application areas developed with the help of electrospinning technology are introduced. Finally, the limitations and challenges of merging the two technologies are presented, and pertinent recommendations are provided for future research on the use of electrospinning technology in membrane bioreactors.

Enhancement of bio-promoters on hexavalent chromium inhibited sulfur-driven denitrification: repairing damage, accelerating electron transfer, and reshaping microbial collaboration

Proposing recovery strategies to recover heavy-metal-inhibited sulfur-driven denitrification, as well as disclosing recovery mechanisms, can provide technical support for the stable operation of bio-systems. This study proposed an effective bio-promoter (mediator-promoter composed of L-cysteine, biotin, cytokinin, and anthraquinone-2,6-disulfonate) to recover Cr(VI) inhibited sulfur-driven denitrification, which effectively reduced the recovery time of NO3--N reduction (18-21 cycles) and NO2--N reduction (27-42 cycles) compared with self-recovery. The mediator-promoter repaired microbial damage by promoting intracellular chromium efflux. Moreover, the mediator-promoter reduced the accumulated reactive oxygen species by stimulating the secretion of antioxidant enzymes, reaching equilibrium in the oxidative-antioxidant system. To improve electron transmission, the mediator-promoter restored S2O32- oxidation to provide adequate electron donors and increased electron transfer rate by increasing cytochrome c levels. Mediator-promoter boosted the abundance of Thiobacillus (sulfur-oxidizing bacterium) and Simplicispira (denitrifying bacterium), which were positively correlated, facilitating the rapid denitrification recovery and the long-term stable operation of recovered systems.

From soil to health hazards: Heavy metals contamination in northern India and health risk assessment

Heavy metals contamination in soil is a global concern affecting the environment with far-reaching consequences for ecosystems and the health of human beings. Heavy metals contamination of soil entails a significant threat to the environment and human health. This research paper focuses on the quantification of heavy metals contamination in soil in Kanpur district, a highly industrialized and densely populated region in India. The study was aimed to identify the sources of heavy metals, map their spatial distribution, and evaluate the potential implications on the environment and human well-being. The prime intent of the current study was quantification of heavy metals in the soil as well as the comparison of risk on the health of human being using two different methods i.e., US EPA methodology for risk assessment and epidemiological study-based risk assessment. Heavy metals like Fe, Ni, Co, Cu, Mn, Cr, and Cd were analyzed in agricultural samples of soil with the help of inductively coupled plasma optical emission spectroscopy. On the basis of epidemiological data, the attributable and relative risk came out to be 0.001 and 1.060, respectively. On the basis of the calculation of Cr alone, the values of carcinogenic risk for adults came out to be 3.87 × 10-7 and for children it was 3.01 × 10- 6. In conclusion, this research paper highlights the alarming levels of heavy metals contamination in the soil of Kanpur district, emphasizing the urgent need for remediation and mitigation efforts, thereby guiding policy makers and stakeholders in developing targeted strategies for soil protection and safeguarding human health.

Enhancing nitrogen removal performance through intermittent aeration in continuous plug-flow anaerobic/aerobic/anoxic process treating low-strength municipal sewage

Advanced nitrogen removal cannot be achieved through the conventional biological nitrogen removal process, which requires higher carbon sources and aeration energy. The proposal of intermittent aeration in the aerobic chambers offered an innovative approach to enhance nitrogen removal in low carbon-to-nitrogen ratio (C/N) municipal sewage, using a plug-flow reactor with anaerobic/aerobic/anoxic (AOA) process. Due to the effective utilization of internal carbon sources through the intermittent aeration, the total inorganic nitrogen removal efficiency (NRE) increased to 77.9 ± 3.2 % with the mean aerobic hydraulic retention time of only 3.2 h and a low C/N of 3.3 during the operation of 210 days. Polyhydroxyalkanoates dominated the nitrogen removal in this AOA system, accounting for 48.0 %, primarily occurring in the alternant aerobic/anoxic chambers. Moreover, the microbial community structure remained unchanged while the NRE increased to 77.9 %. This study provided an efficient and economic strategy for the continuous plug-flow AOA process.

Limited dissolved oxygen facilitated nitrogen removal at biocathode during the hydrogenotrophic denitrification process using bioelectrochemical system

Effects of limited dissolved oxygen (DO) on hydrogenotrophic denitrification at biocathode was investigated using bioelectrochemical system. It was found that total nitrogen removal increased by 5.9%, as DO reached about 0.24 mg/L with the cathodic chamber unplugged (group R_Exposure). With the presence of limited DO, not only the nitrogen metabolic pathway was influenced, but the composition of microbial communities of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were enriched accordingly. After metagenomic analysis, enriched genes in R_Exposure were found to be associated with nearly each of nitrogen removal steps as denitrification, nitrification, DNRA, nitrate assimilation and even nitrogen fixation. Moreover, genes encoding both Complexes III and IV constituted the electron transfer chain were significantly enriched, indicating that more electrons would be orientated to the reduction of NO₂^--N, NO-N and oxygen. Therefore, enhanced nitrogen removal could be attained through the co-respiration of nitrate and oxygen by means of NH₄⁺-N oxidation.

Biocides with Controlled Degradation for Environmentally Friendly and Cost-Effective Fecal Sludge Management

Didecyldimethylammonium chloride (DDAC) and polyhexamethylene guanidine (PHMG) exhibit high antimicrobial activity and are widely used as biocidal agents in chemical toilet additives for the management of fecal sludge (FS). Disposal of such biocide-treated FS to a wastewater treatment plant (WWTP) is a major environmental problem. It is possible to reduce environmental damage through the use of biocidal agents, which easily decompose after performing their main biocidal functions. In this work, it is proposed to use the fact of a gradual increase in pH of FS from the initial 7.5 to 9.0-10.0 due to the decomposition of urea. Six biocidal compounds were selected that are capable of rapidly degrading in an alkaline environment and one that naturally degrades upon prolonged incubation. Four of them: bronopol (30 mg/L), DBNPA (500 mg/L), Sharomix (500 mg/L), and sodium percarbonate (6000 mg/L) have shown promise for environmentally friendly management of FS. In selected dosage, they successfully reduced microbial activity under both aerobic and anaerobic conditions and are cost-effective. After 10 days of incubation, degradation of the biocide occurred as measured by biological oxygen demand (BOD₅) in biocide-treated FS. Such FS can be discharged to WWTP without severe damage to the activated sludge process, the need for dilution and additional procedures to neutralize toxicity.