Biological nitrogen removal from low carbon wastewater

Influence of high-load shocks on achieving mainstream partial nitrification: Microbial community succession

Driving microbial community succession through the regulation of operational strategies is crucial for achieving partial nitrification (PN) in municipal wastewater. However, at present, there is a decoupling between the strategic regulation of PN systems and the succession characteristics of the microbial community. This study examined the correlation between microbial community succession and PN performance under two high-load shocks (HLS1 and HLS2) treating actual sewage. During HLS1, the influent organic loading rate (OLR) and nitrogen loading rate (NLR) increased from 116.7 ± 37.7 to 219.7 ± 24.7 mg COD/(g VSS·d) and 0.21±0.02 to 0.33±0.02 kg N/m3/d respectively, with the nitrite concentration and nitrite accumulation ratio only reaching 11.7 ± 2.7 mg/L and 49.3 ± 13.9 %, respectively. During HLS2, the influent OLR and NLR increased from 123.5 ± 17.2 to 300.3 ± 49.2 mg COD/(g VSS·d) and 0.19±0.03 to 0.32±0.03 kg N/m3/d respectively, resulting in a nitrite accumulation ratio of 89.4 ± 10.7 %. The system achieved efficient PN performance and sustained for 124 days. High-throughput sequencing results showed that community diversity remained consistently high, and the community composition returned to its initial state following a minor succession during HLS1. During HLS2, the high-load shock reduced the richness and evenness of the microbial community. The community underwent succession in a new direction, leading to community composition and function changes. The results indicate that the realization, stabilization, and disruption of PN are influenced not only by operational parameters but also by microbial community structure.

Nanotechnology in action: silver nanoparticles for improved eco-friendly remediation

Nanotechnology is an exciting area with great potential for use in biotechnology due to the far-reaching effects of nanoscale materials and their size-dependent characteristics. Silver and other metal nanoparticles have attracted a lot of attention lately because of the exceptional optical, electrical, and antimicrobial characteristics they possess. Silver nanoparticles (AgNPs) stand out due to their cost-effectiveness and abundant presence in the earth's crust, making them a compelling subject for further exploration. The vital efficacy of silver nanoparticles in addressing environmental concerns is emphasized in this thorough overview that dives into their significance in environmental remediation. Leveraging the distinctive properties of AgNPs, such as their antibacterial and catalytic characteristics, innovative solutions for efficient treatment of pollutants are being developed. The review critically examines the transformative potential of silver nanoparticles, exploring their various applications and promising achievements in enhancing environmental remediation techniques. As environmental defenders, this study advocates for intensified investigation and application of silver nanoparticles. Furthermore, this review aims to assist future investigators in developing more cost-effective and efficient innovations involving AgNPs carrying nanoprobes. These nanoprobes have the potential to detect numerous groups of contaminants simultaneously, with a low limit of detection (LOD) and reliable reproducibility. The goal is to utilize these innovations for environmental remediation purposes.

Wastewater Treatment with Bacterial Representatives of the Thiothrix Morphotype

Bacteria of the Thiothrix morphotype, comprising the genera Thiothrix, Thiolinea and Thiofilum, are frequently encountered in domestic and industrial wastewater treatment systems, but they are usually not clearly differentiated due to the marked similarity in their morphologies. Methods ranging from light microscopy, FISH and PCR to modern high-throughput sequencing are used to identify them. The development of these bacteria in wastewater treatment systems has both advantages and disadvantages. On the one hand, the explosive growth of these bacteria can lead to activated sludge bulking or clogging of the treatment system's membranes, with a consequent decrease in the water treatment efficiency. On the other hand, members of the Thiothrix morphotype can improve the quality of granular sludge and increase the water treatment efficiency. This may be due to their capacity for sulfide oxidation, denitrification combined with the oxidation of reduced sulfur compounds, enhanced biological phosphate removal and possibly denitrifying phosphate removal. The recently obtained pangenome of the genus Thiothrix allows the explanation, at the genomic level, of the experimental results of various studies. Moreover, this review summarizes the data on the factors affecting the proliferation of representatives of the Thiothrix morphotype.

Highly selective electrochemical reduction of nitrate via CoO/Ir-nickel foam cathode to treat wastewater with a low C/N ratio

Thorough nitrate removal from reclaimed water by biological techniques without carbon sources is difficult. Flexible, controllable electrochemical nitrate reduction is widely researched. Herein, ultrathin CoO nanosheets were constructed through amino group induction and orientation. The interfacial electron transfer resistance of two-dimensional CoO was 43.4% lower than that of one-dimensional nanoparticles, resulting in higher current density and improved nitrate reduction efficiency. Nickel foam and IrO2-nickel foam electrodes have almost no effect on nitrate reduction. It is worth noting that iridium loading on CoO (nanosheet) regulated the electronic band structure and generated active atomic H* . The nitrate removal rate increased from 45.1% (CoO (nanoparticle)-nickle foam) and 63.8% (CoO (nanosheet)-nickle foam) to 94.64% (CoO/Ir10 wt%-nickle foam). The proton enhancement effect improved indirect nitrate reduction by atomic H* and increased the NO3--N removal rate to 99.8%. Active chlorine species generated by Cl- in the wastewater selectively converted more than 99% of nitrate to N2, exceeding previous Co-based cathode results. In situ DEMS indicated that electrochemical reduction of nitrate included deoxidation (NO3-→*NO2-→*NO→*N/*N2O→N2) and hydrogenation (*NH2→*NH3→NH4+). The NO3--N removal rate of CoO/Ir10 wt% exceeded 65% during treatment of wastewater treatment plant effluents, verifying the feasibility of electrochemical nitrate reduction with the CoO/Ir10 wt% cathode. A strategy for designing electrochemical nitrate reduction electrocatalysts with excellent potential for full-scale application to treat wastewater treatment plant effluent is provided.

Research progress of novel bio-denitrification technology in deep wastewater treatment

Excessive nitrogen emissions are a major contributor to water pollution, posing a threat not only to the environment but also to human health. Therefore, achieving deep denitrification of wastewater is of significant importance. Traditional biological denitrification methods have some drawbacks, including long processing times, substantial land requirements, high energy consumption, and high investment and operational costs. In contrast, the novel bio-denitrification technology reduces the traditional processing time and lowers operational and maintenance costs while improving denitrification efficiency. This technology falls within the category of environmentally friendly, low-energy deep denitrification methods. This paper introduces several innovative bio-denitrification technologies and their combinations, conducts a comparative analysis of their denitrification efficiency across various wastewater types, and concludes by outlining the future prospects for the development of these novel bio-denitrification technologies.

Bioelectrochemical system for nitrogen removal: Fundamentals, current status, trends, and challenges

Biological nitrogen removal (BNR) is essential for the treatment of nitrogen-containing wastewater. However, the requirement for aeration and the addition of external carbon sources, resulting in greenhouse gas emissions and additional costs, are disadvantages of the traditional BNR process. Alternative technologies have been devised to overcome these drawbacks. Bioelectrochemical nitrogen removal (BENR) has been proposed for efficient nitrogen removal, demonstrating flexibility and versatility. BENR can be performed by combining nitrification, denitrification, anaerobic ammonium oxidation (ANAMMOX), or organic carbon oxidation. Bioelectrochemical-ANAMMOX (BE-ANAMMOX) is the most promising method for nitrogen removal, as it can directly convert NH4+ to N2 and H2 in one step when the electrode is arranged as an electron acceptor. High-value-added hydrogen can potentially be recovered with efficient nitrogen removal using this concept, maximizing the benefits of BENR. Using alternative electron acceptors, such as electrodes and metal ions, for complete total nitrogen removal is a promising technology to substitute NO2- production from NH4+ oxidation by aeration. However, the requirement of electron donors for NO3- reduction, low NH4+ removal efficiency, and low competitiveness of exoelectrogenic bacteria still remain the main obstacles. The future direction for successful BENR should aim to achieve complete anaerobic NH4+ oxidation without any electron acceptor and to maximize selectivity in H2 production. Therefore, the bioelectrochemical pathways and balances between efficient nitrogen removal and high-value-added chemical production should be further studied for carbon and energy neutralities.

Optimizing SCND with carbon-rich hydrolysates from typical organic wastes: Material composition, augmentation performance, microbiome response, and life cycle impact

The rapid growth of production and consumption has led to severe environmental pollution, creating a major challenge to achieving the United Nations' sustainable development goals (SDGs). To address it, recycling of organic wastes into value-added products is a possible solution. In this work, four typical organic wastes including sewage sludge (SS), chicken manure (CM), food waste (FW), and corn straw (CS) were employed to produce hydrolysates augmenting shortcut nitrification-denitrification (SCND) for nitrogen depletion in wastewater. The hydrolysates were carbon-rich, with total COD (TCOD), soluble COD (SCOD), and volatile fatty acids (VFA) concentrations ranging from 32.5 to 102.7, 5.7 to 48.4, and 2.0-16.5 mg/L, respectively. The most effective nitrogen depletion was obtained in units supplemented with CM and FW hydrolysates, which had reduced average NH₃-N concentrations and near-zero TN removal failure rates under legal requirements. The microbial community analysis demonstrated that various functional bacteria from phylum to genus level were detected in all scenarios, which was corroborated by abundant genetic functions involved in nitrogen metabolism. Further, life cycle assessment revealed negative environmental impact on all categories, with an exception of eutrophication potential (EP) with negative values (∼-0.04 kg Phosphate eq.), allowing positive net environmental benefit (NEB). Operational cost analysis revealed that CM and FW are more effective but costlier than SS and CS. Together, these results indicate that, after hydrolysis, organic wastes can be efficient stimulant augmenting SCND performance for nitrogen depletion in wastewater, benefiting the overall environmental impact.