Integrated simultaneous nitrification/denitrification and comammox consortia as efficient biocatalysts enhance treatment of domestic wastewater in different up-flow bioelectrochemical reactors

Advances in bioelectrochemical systems for bio-products recovery

Bioelectrochemical systems (BES) have emerged as a sustainable and highly promising technology that has garnered significant attention from researchers worldwide. These systems provide an efficient platform for the removal and recovery of valuable products from wastewater, with minimal or no net energy loss. Among the various types of BES, microbial fuel cells (MFCs) are a notable example, utilizing microbial biocatalytic activities to generate electrical energy through the degradation of organic matter. Other BES variants include microbial desalination cells (MDCs), microbial electrolysis cells (MECs), microbial electrosynthesis cells (MXCs), microbial solar cells (MSCs), and more. BESs have demonstrated remarkable potential in the recovery of diverse products such as hydrogen, methane, volatile fatty acids, precious nutrients, and metals. Recent advancements in scaling up BESs have facilitated a more realistic assessment of their net energy recovery and resource yield in real-world applications. This comprehensive review focuses on the practical applications of BESs, from laboratory-scale developments to their potential for industrial commercialization. Specifically, it highlights successful examples of value-added product recovery achieved through various BES configurations. Additionally, this review critically evaluates the limitations of BESs and provides suggestions to enhance their performance at a larger scale, enabling effective implementation in real-world scenarios. By providing a thorough analysis of the current state of BES technology, this review aims to emphasize the tremendous potential of these systems for sustainable wastewater treatment and resource recovery. It underscores the significance of bridging the gap between laboratory-scale achievements and industrial implementation, paving the way for a more sustainable and resource-efficient future.

Microbial nutrient recovery cell as an efficient and sustainable nutrient recovery option in sewage treatment

Globally, nutrient pollution is a serious and challenging concern. Wastewater treatment plants (WWTPs) are designed to prevent the discharge of contaminants resulting from anthropogenic sources to the receiving water bodies. In this study, seasonal nutrient pollution load, and biological nutrient removal efficiency of an anoxic aerobic unit based WWTP were investigated. Seasonal assessment revealed that the average total nitrogen removal efficiency and total phosphorus removal efficiency of the WWTP do not meet the discharge standard of 10 mg/L and 1 mg/L, respectively. Furthermore, the WWTP does not utilize the energy contained in the wastewater. In this regard, dual chamber MFC (D-MFC) has emerged as a promising solution that can not only treat wastewater but can also convert chemical energy present in the wastewater into electrical energy. However, higher N O3- (57 ± 4 mg/L) and P-P O43- (6 ± 0.52 mg/L) concentration in cathodic effluent is a major drawback in D-MFC. Therefore, to solve this issue, D-MFC was transformed into a microbial nutrient recovery cell (MNRC) which demonstrated a final N H4+-N and P-P O43- concentration of nearly 1 mg/L with N H4+-N and P-P O43- recovery up to 74 % and 69 %, respectively in the recovery chamber. Besides, MNRC attained a maximum power density of 307 mW/m3 and a current density of 1614 mA/m3, thus indicating MNRC is an eco-friendly, energy-neutral, and promising technology for electricity generation and recovering nutrients.

A novel simultaneous short-course nitrification, denitrification and fermentation process: bio-enhanced phenol degradation and denitrification in a single reactor

The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2--N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement.

Microbial electrochemical Cr(VI) reduction in a soil continuous flow system

Microbial electrochemical technologies represent innovative approaches to contaminated soil and groundwater remediation and provide a flexible framework for removing organic and inorganic contaminants by integrating electrochemical and biological techniques. To simulate in situ microbial electrochemical treatment of groundwater plumes, this study investigates Cr(VI) reduction within a bioelectrochemical continuous flow (BECF) system equipped with soil-buried electrodes, comparing it to abiotic and open-circuit controls. Continuous-flow systems were tested with two chromium-contaminated solutions (20-50 mg Cr(VI)/L). Additional nutrients, buffers, or organic substrates were introduced during the tests in the systems. With an initial Cr(VI) concentration of 20 mg/L, 1.00 mg Cr(VI)/(L day) bioelectrochemical removal rate in the BECF system was observed, corresponding to 99.5% removal within nine days. At the end of the test with 50 mg Cr(VI)/L (156 days), the residual Cr(VI) dissolved concentration was two orders of magnitude lower than that in the open circuit control, achieving 99.9% bioelectrochemical removal in the BECF. Bacteria belonging to the orders Solirubrobacteriales, Gaiellales, Bacillales, Gemmatimonadales, and Propionibacteriales characterized the bacterial communities identified in soil samples; differently, Burkholderiales, Mycobacteriales, Cytophagales, Rhizobiales, and Caulobacterales characterized the planktonic bacterial communities. The complexity of the microbial community structure suggests the involvement of different microorganisms and strategies in the bioelectrochemical removal of chromium. In the absence of organic carbon, microbial electrochemical removal of hexavalent chromium was found to be the most efficient way to remove Cr(VI), and it may represent an innovative and sustainable approach for soil and groundwater remediation. Integr Environ Assess Manag 2024;00:1-17. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Construction of a Synthetic Microbial Community for Enzymatic Pretreatment of Wheat Straw for Biogas Production via Anaerobic Digestion

Biological pretreatment is a viable method for enhancing biogas production from straw crops, with the improvement in lignocellulose degradation efficiency being a crucial factor in this process. Herein, a metagenomic approach was used to screen core microorganisms (Bacillus subtilis, Acinetobacter johnsonii, Trichoderma viride, and Aspergillus niger) possessing lignocellulose-degrading abilities among samples from three environments: pile retting wheat straw (WS), WS returned to soil, and forest soil. Subsequently, synthetic microbial communities were constructed for fermentation-enzyme production. The crude enzyme solution obtained was used to pretreat WS and was compared with two commercial enzymes. The synthetic microbial community enzyme-producing pretreatment (SMCEP) yielded the highest enzymatic digestion efficacy for WS, yielding cellulose, hemicellulose, and lignin degradation rates of 39.85, 36.99, and 19.21%, respectively. Furthermore, pretreatment of WS with an enzyme solution, followed by anaerobic digestion achieved satisfactory results. SMCEP displayed the highest cumulative biogas production at 801.16 mL/g TS, which was 38.79% higher than that observed for WS, 22.15% higher than that of solid-state commercial enzyme pretreatment and 25.41% higher than that of liquid commercial enzyme pretreatment. These results indicate that enzyme-pretreated WS can significantly enhance biogas production. This study represents a solution to the environmental burden and energy use of crop residues.

Enhancement of nitrate reduction in microbial fuel cells by acclimating biocathode potential: Performance, microbial community, and mechanism

The enhancement of nitrate reduction in microbial fuel cells (MFCs) by acclimating biocathode potential was studied. An MFC system was started up, and measured by cyclic voltammetry to determine a suitable potential region for acclimating biocathode. The experimental results revealed that potential acclimation could efficiently improve denitrification performance by relieving the phenomenon of nitrite accumulation, and optimum performance was obtained at -0.4 V with a total nitrogen removal efficiency of 87.4 %. Subsequently, the characteristics of electron transfer behaviors were measured, suggesting that a positive correlation between nitrate reduction and the contribution of direct electron transfer emerged. Furthermore, a denitrification mechanism was proposed. The results indicated that potential acclimation was conducive to enhancing denitrifying enzyme activity and that the electron transport system activity could be increased by 5.8 times. This study provides insight into the electron transfer characteristics and denitrification mechanisms in MFCs for nitrate reduction at specific acclimatization potentials.

Rapid start-up strategy and microbial population evolution of anaerobic ammonia oxidation biofilm process for low-strength wastewater treatment

The implementation of the anaerobic ammonium oxidation (anammox) process in treating low-strength wastewater is limited by the difficulty in enriching anammox bacteria (AnAOB). Here, the first enrichment of AnAOB at a high nitrogen (N) loading rate (NLR) as a strategy was proposed to achieve the rapid start-up of the anammox biofilm process treating low-strength wastewater. The long-term stability of the anammox biofilm process after start-up operating at a low NLR of 0.2-0.4 kg N/(m3⋅d) was evaluated. Results showed that the N removal efficiency was up to 75 % under a low NLR of 0.2 kg N/(m3⋅d) condition. Low-strength organic matter promoted the metabolic coupling between partial denitrifying bacteria (PDB) and AnAOB. The genus Candidatus Brocadia as AnAOB (18 %-27 %) can coexist with Limnobacter (PDB, 9 %-12 %) for efficient N removal. This study offers a rapid start-up strategy of anammox biofilm process in treating low-strength wastewater.

Construction of a synthetic microbial community based on multiomics linkage technology and analysis of the mechanism of lignocellulose degradation

The efficient degradation of lignocellulose is a bottleneck for its integrated utilization. This research performed species analysis and made functional predictions in various ecosystems using multiomics coupling to construct a core synthetic microbial community with efficient lignocellulose degradation function. The synthetic microbial community was employed to degrade corn straw via solid-state fermentation. The degradation mechanisms were resolved using proteomics. The optimum culture conditions included 10% inoculum level (w/v), 4% nitrogen source ratio and a fermentation time of 23 d. Under these conditions, the degradation rates of cellulose, hemicellulose, and lignin were 34.91%, 45.94%, and 23.34%, respectively. Proteomic analysis revealed that lignin 1,4-β-xylanase, β-xylosidase and endo-1,4-β-xylanase were closely related to lignocellulose degradation. The metabolic pathways involved in lignocellulose degradation and the functional roles of eight strains were obtained. The synthesis of a microbial community via multiomics linkage technology can effectively decompose lignocellulose, which is useful for their further utilization.

An overview of recent advances and future prospects of three-dimensional biofilm electrode reactors (3D-BERs)

Three-dimensional biofilm electrode reactors (3D-BERs) have attracted extensive attention in recent years due to their wide application range, high efficiency and energy saving. On the basis of traditional bio-electrochemical reactor, 3D-BERs are filled with particle electrodes, also known as the third electrodes, which can not only be used as a carrier for microbial growth, but also improve the electron transfer rate of the whole system. This paper reviews the constitution, advantages and basic principles of 3D-BERs as well as current research status and progress of 3D-BERs in recent years. The selection of electrode materials, including cathode, anode and particle electrode are listed and analyzed. Different constructions of reactors, like 3D-unipolar extended reactor and coupled 3D-BERs are introduced and discussed. Various contaminants degraded by 3D-BERs including nitrogen, azo dyes, antibiotics and the others are calculated and the corresponding degradation effects are described. The influencing factors and mechanisms are also introduced. At the same time, according to the research advances of 3D-BERs, the shortcomings and weakness of this technology in the current research process are analyzed, and the future research direction of this technology is prospected. This review aims to summarize recent studies of 3D-BERs in bio-electrochemical reaction and open a bright window to this booming research theme.

Deciphering three-dimensional bioanode configuration for augmenting power generation and nitrogen removal in air-cathode microbial fuel cells

In this study, the engineering-oriented three-dimensional (3D) bioanode concept was applied, demonstrating that spiral-stairs-like/rolled carbon felt (SCF/RCF) configurations achieved good performances in air-cathode microbial fuel cells (ACMFCs). With the 3D anodes, ACMFCs generated significantly higher power densities of 1535 mW/m3 (SCF) and 1800 mW/m3 (RCF), compared with that of a traditional flat carbon felt anode (FCF, 315 mW/m3). The coulombic efficiency of 15.39 % at SCF anode and 14.34 % at RCF anode also is higher than the 7.93 % at FCF anode. The 3D anode ACMFCs exhibited favorable removal of chemical oxygen demand (96 % of SCF and RCF) and total nitrogen (97 % of SCF, 99 % of RCF). Further results show that three-dimensional anode structures could enrich more electrode surface biomass and diversify the biofilm microbial communities for promoting bioelectroactivity, denitrification, and nitrification. These results demonstrate that three-dimensional anodes with active biofilm is a promising strategy for creating scalable MFCs-based wastewater treatment system.

Exploring the mechanism of Self-Consistent balance between microbiota and high efficiency in wastewater treatment

Sewage treatment mediated by microbial organisms is a promising green trend. However, the complex balance between microbiota stability and highly efficient wastewater treatment requires investigation. This study successfully improved the effectiveness of sewage treatment by resetting the microbial community structure in the activated sludge. Truepera, Methylophaga, unclassified_Fodinicurvataceae, and unclassified_Actinomanarales were the dominant genera, while salinity and NH₃-N content were identified as the key environmental factors governing the microbial structure. By optimizing the microflora structure driven by environmental factors, the key minor genera were activated and coordinated with the aforementioned genera, thereby promoting wastewater treatment. Finally, the chemical oxygen demand, NH₃-N, and total phosphorus removal rates were improved to 86.8 ± 1.9%, 82.4 ± 4.1%, and 94.8 ± 3.8%, respectively. It provides a new insight to improve the wastewater treatment through setting microbiota by environmental factor driven.

Positive Effects of Organic Substitution in Reduced-Fertilizer Regimes on Bacterial Diversity and N-Cycling Functionality in Greenhouse Ecosystem

Conventional fertilization in the greenhouses of North China used excessive amounts of chemical and organic fertilizer, resulting in soil degradation and severe agricultural non-point source pollution. A nine-year study was conducted on a loamy clay soil in Shijiazhuang, Hebei province, to investigate the effects of reduced-fertilizer input regimes on soil property, bacterial diversity, nitrogen (N) cycling and their interactions. There were four treatments, including high organic + chemical fertilizer application rate and three reduced-fertilizer treatments with swine manure, maize straw or no substitution of 50% chemical N. Treatments with reduced-fertilizer input prevented soil salinization and acidification as in local conventional fertilization after being treated for nine years. In comparison to chemical fertilizer only, swine manure or maize straw substitution maintained higher nutrient availability and soil organic C contents. Fertilizer input reduction significantly increased bacterial richness and shifted bacterial community after nine years, with decisive factors of EC, Olsen P and C/N ratio of applied fertilizer. Soil chemical characteristics (EC, pH and nutrients), aggregation and C/N ratio of applied fertilizer selected certain bacterial groups, as well as N-cycling functions. Reduced-fertilizer input decreased the potential nitrification and denitrification functioning of bacterial community, but only in organic substitution treatments. The results of this study suggested that fertilizer input reduction combined with organic C input has potential in reducing non-point source pollution and increasing N-use efficiency in greenhouse vegetable production in North China.

Mixotrophic denitrification processes in basalt fiber bio-carriers drive effective treatment of low carbon/nitrogen lithium slurry wastewater

Lithium battery slurry wastewater was successfully treatedby using basalt fiber (BF) bio-carriers in a biological contact oxidation reactor. This resulted in a significant reduction of COD (93.3 ± 0.5 %) and total nitrogen (77.4 ± 1.0 %) at 12 h of HRT and dissolved oxygen (DO) of 0-1 mg/L. The modified Stover-Kincannon model indicated that the total nitrogen removal rate was 4.462 kg/m3/d in R-BF while the substrate maximum specific reaction rate (qmax) in the Monod model was 0.323 mg-N/mgVSS/d. A stable internal environment was established within the bio-nest. Metataxonomic analysis revealed the presence of denitrification and decarbonization bacteria, combined heterotrophic nitrification-aerobic denitrification bacteria, nitrite-oxidizing bacteria, and ammonia-oxidizing bacteria. Functional analysis displayed changes related to (aerobic)chemoheterotrophy, nitrogen respiration, nitrate reduction, respiration/denitrification of nitrite, and nitrate in R-BF. The study proposes a novel approach to achieve denitrification for the treatment of lithium slurry wastewater at low C/N conditions.

Biological oxidation methods for the removal of organic and inorganic contaminants from wastewater: A comprehensive review

Enzyme-based bioremediation is a simple, cost-effective, and environmentally friendly method for isolating and removing a wide range of environmental pollutants. This study is a comprehensive review of recent studies on the oxidation of pollutants by biological oxidation methods, performed individually or in combination with other methods. The main bio-oxidants capable of removing all types of pollutants, such as organic and inorganic molecules, from fungi, bacteria, algae, and plants, and different types of enzymes, as well as the removal mechanisms, were investigated. The use of mediators and modification methods to improve the performance of microorganisms and their resistance under harsh real wastewater conditions was discussed, and numerous case studies were presented and compared. The advantages and disadvantages of conventional and novel immobilization methods, and the development of enzyme engineering to adjust the content and properties of the desired enzymes, were also explained. The optimal operating parameters such as temperature and pH, which usually lead to the best performance, were presented. A detailed overview of the different combination processes was also given, including bio-oxidation in coincident or consecutive combination with adsorption, advanced oxidation processes, and membrane separation. One of the most important issues that this study has addressed is the removal of both organic and inorganic contaminants, taking into account the actual wastewaters and the economic aspect.

Establishment and optimization of partial nitrification/anammox/partial nitrification/anammox (PN/A/PN/A) process based on multi-stage ammonia oxidation: Using response surface method as a tool

The presence of nitrite-oxidizing bacteria (NOB) when treating low-strength ammonia wastewater was a challenge in the application of the PN/A process. The partial nitrification/ANAMMOX/partial nitrification/ANAMMOX (PN/A/PN/A) process based on multiple oxidations of ammonia was proposed to solve this problem. The influence of independent variables such as nitrite concentration was analyzed based on the response surface method (RSM). The model showed that nitrite concentration has an adverse impact on ammonia removal efficiency and nitrite accumulation rate. The model provided optimal parameters for the PN/A/PN/A process: the dissolved oxygen concentration was 0.60 mg/L, and the cycle duration was 90 min. Advanced nitrogen removal was achieved by maintaining the nitrite concentration below 10.0 mg/L. The nitrogen removal efficiency was 81.44 ± 4.15 %, and the nitrogen removal rate was 0.18 ± 0.02 kg N/(m³⋅d). Potential functions of microorganisms were analyzed by functional annotation of prokaryotic taxa (FAPROTAX) and the correlation network analysis was performed.

Three-dimensional biofilm electrode reactors (3D-BERs) for wastewater treatment

Three-dimensional biofilm electrode reactors (3D-BERs) are highly efficient in refractory wastewater treatment. In comparison to conventional bio-electrochemical systems, the filled particle electrodes act as both electrodes and microbial carriers in 3D-BERs. This article reviews the conception and basic mechanisms of 3D-BERs, as well as their current development. The advantages of 3D-BERs are illustrated with an emphasis on the synergy of electricity and microorganisms. Electrode materials utilized in 3D-BERs are systematically summarized, especially the critical particle electrodes. The configurations of 3D-BERs and their integration with wastewater treatment reactors are introduced. Operational parameters and the adaptation of 3D-BERs to varieties of wastewater are discussed. The prospects and challenges of 3D-BERs for wastewater treatment are then presented, and the future research directions are proposed. We believe that this timely review will help to attract more attentions on 3D-BERs investigation, thus promoting the potential application of 3D-BERs in wastewater treatment.