Efficient nitrate removal by Pseudomonas mendocina GL6 immobilized on biochar

Effect of hydraulic residence time on nitrogen removal from a synthetic mariculture wastewater using a bench-scale recirculating bioreactor embedded with aerobic denitrifying bacteria Marinobacter alkaliphilus strain JY28

Beads loaded with tea dregs powder and immobilized aerobic denitrifying bacteria (Marinobacter alkaliphilus strain JY28) were prepared by cross-linking sodium alginate and polyvinyl alcohol. The beads were subsequently utilized for nitrogen removal in treatment of wastewater from a marine recirculating aquaculture system (MRAS). The effects of hydraulic residence time (HRT) on nitrogen removal efficiency, microbial community succession, and the physicochemical properties and kinetic behaviors of the immobilized bacterial beads were investigated. The results indicated that the highest NO3--N removal rate was 99.4 ± 0.6 % at an HRT of 10 h, while the cumulative NO2--N concentration remained at its lowest level (0.04 ± 0.05 mg L-1). Furthermore, the peak maximum specific nitrogen removal rates (μmax) for NO3--N and NO2--N were found to be 16.12 mg L-1·h-1 and 8.61 mg L-1·h-1, respectively. The surface of the immobilized bacterial beads was rough and effectively bound Marinobacter alkaliphilus strain JY28. The interior of the beads possessed an irregular honeycomb-like and porous structure, favorable for the immobilization and proliferation of Marinobacter alkaliphilus strain JY28. The presence of the ring structure in the functional bonds enhanced both the mechanical strength and the immobilized bacterial beads stability. Marinobacter alkaliphilus strain JY28 was retained in the bacterial beads and consistently maintained its dominance during the whole experimental process. The results lay a theoretical foundation for application of immobilized bacterial beads for highly efficient nitrogen removal in MRAS wastewater treatment.

Advancements in Biochar as a Sustainable Adsorbent for Water Pollution Mitigation

Biochar, a carbon-rich material produced from the partial combustion of biomass wastes is often termed "black gold" for its potential in water pollution mitigation and carbon sequestration. By customizing biomass feedstock and optimizing preparation strategies, biochar can be engineered with specific physicochemical properties to enhance its effectiveness in removing contaminants from wastewater. Recent studies demonstrate that biochar can achieve > 90% removal efficiency for heavy metals such as lead and cadmium, > 85% adsorption capacity for organic pollutants such as dyes and phenols, and > 80% reduction in microplastics and nanoplastics. This review explores recent advancements in biochar preparation technologies, such as pyrolysis, carbonization, gasification, torrefaction, and rectification, along with physical, chemical, and biological modifications that are crucial for efficient pollutant removal. The core of this review focuses on biochar's applications in removing a wide range of pollutants from wastewater, detailing mechanisms for organic pollutants, inorganic salts, pharmaceutical contaminants, microplastics, nanoplastics, and volatile organic compounds. In addition, the review introduces machine learning as a key technique for optimizing biochar production and functionality, showcasing its potential in advancing biochar technology. The conclusion provides a comprehensive outlook on biochar's future, emphasizing ongoing research and its role in sustainable environmental management.

Aerobic denitrifying bacterial community with low C/N ratio remove nitrate from micro-polluted water: Metagenomics unravels denitrification pathways

The efficient nitrogen removal from micro-polluted source water is an international challenge to be solved urgently. However, the inner denitrification mechanism of native aerobic denitrifying bacterial communities in response to carbon scarcity remains relatively unclear. Here, the bacterial community XT6, screened from an oligotrophic reservoir, exhibited aerobic denitrifying capacity under low-carbon environments. Up to 76.79-81.64 % of total organic carbon (TOC) and 51.48-67.60 % of NO3--N were removed by XT6 within 48 h at C/N ratios of 2.0-3.0. Additionally, the nitrogen balance experiments further manifested that 26.27-38.13 % of NO3--N was lost in gaseous form. As the C/N ratio decreased, XT6 tended to generate more extracellular polymeric substances (EPS), with the tightly bound EPS showing the largest increase. Pseudomonas and Variovorax were quite abundant in XT6, constituting 59.69 % and 28.65 % of the total sequences, respectively. Furthermore, metagenomics analysis evidenced that XT6 removed TOC and nitrate mainly through the tricarboxylic acid cycle and aerobic denitrification. Overall, the abovementioned results provide a deeper understanding of the nitrogen metabolic pathways of indigenous aerobic denitrifying bacterial communities with low C/N ratios and offer useful guidance for controlling nitrogen pollution in oligotrophic ecosystems.

Biochar coupled with multiple technologies for the removal of nitrogen and phosphorus from water: A review

Water eutrophication caused by nitrogen (N) and phosphorus (P) has become a global environmental issue. Biochar is a competent adsorbent for removing N and P from wastewater. However, compared with commercial activated carbon, biochar has relatively limited adsorption capacity. To broaden the field scale application of biochar, biochar coupled with multiple technologies (BC-MTs) (such as microorganisms, electrochemistry, biofilm, phytoremediation, etc.) have been extensively developed for environmental remediation. Nevertheless, due to the fluctuations and differences in biochar types, coupling methods, and wastewater types, various techniques show different removal mechanisms and performance, hindering the promotion and application of BC-MTs. A systematic review of the research progress of BC-MTs is highly necessary to gain a better understanding of the current research status and progress, as well as to promote the application of these techniques. In this paper, the application of pristine and modified biochar in adsorbing N and P in wastewater is critically reviewed. Then the removal performance, influencing factors, mechanisms, and the environmental applications of BC-MTs in wastewater are systematically summarized. In addition, the cost analysis and risk assessment of BC-MTs in environmental applications are conducted. Finally, suggestions and prospects for future research and practical application are put forward.

Potential effects of Cu2+ stress on nitrogen removal performance, microbial characteristics, and metabolism pathways of biofilm reactor

Sequencing batch biofilm reactors (SBBR) were utilized to investigate the impact of Cu2+ on nitrogen (N) removal and microbial characteristics. The result indicated that the low concentration of Cu2+ (0.5 mg L-1) facilitated the removal of ammonia nitrogen (NH4+-N), total nitrogen (TN), nitrate nitrogen (NO3--N), and chemical oxygen demand (COD). In comparison to the average effluent concentration of the control group, the average effluent concentrations of NH4+-N, NO3--N, COD, and TN were found to decrease by 40.53%, 17.02%, 10.73%, and 15.86%, respectively. Conversely, the high concentration of Cu2+ (5 mg L-1) resulted in an increase of 94.27%, 55.47%, 22.22%, and 14.23% in the aforementioned parameters, compared to the control group. Low concentrations of Cu2+ increased the abundance of nitrifying bacteria (Rhodanobacter, unclassified-o-Sacharimonadales), denitrifying bacteria (Thermomonas, Comamonas), denitrification-associated genes (hao, nosZ, norC, nffA, nirB, nick, and nifD), and heavy-metal-resistant genes related to Cu2+ (pcoB, cutM, cutC, pcoA, copZ) to promote nitrification and denitrification. Conversely, high concentration Cu2+ hindered the interspecies relationship among denitrifying bacteria genera, nitrifying bacteria genera, and other genera, reducing denitrification and nitrification efficiency. Cu2+ involved in the N and tricarboxylic acid (TCA) cycles, as evidenced by changes in the abundance of key enzymes, such as (EC:1.7.99.1), (EC:1.7.2.4), and (EC:1.1.1.42), which initially increased and then decreased with varying concentrations of Cu2+. Conversely, the abundance of EC1.7.2.1, associated with the accumulation of nitrite nitrogen (NO2--N), gradually declined. These findings provided insights into the impact of Cu2+ on biological N removal.

Enhanced nitrate reduction in hypotrophic waters with integrated photocatalysis and biodegradation

Addressing nitrate contamination in water bodies is a critical environmental challenge, and Intimately Coupling Photocatalysis and Biodegradation (ICPB) presents a promising solution. However, there is still debate about the effectiveness of ICPB in reducing nitrate under hypotrophic conditions. Further research is needed to understand its microbial metabolic mechanism and the functional changes in bacterial structure. Here we explored microbial metabolic mechanisms and changes in bacterial structure in ICPB reactors integrating a meticulously screened TiO2/g-C3N4 photocatalyst with biofilm. We achieved a 26.3% increase in nitrate reduction using 12.2% less organic carbon compared to traditional biodegradation methods. Metagenomic analysis of the microbial communities in ICPB reactors revealed evolving metabolic pathways conducive to nitrate reduction. This research not only elucidates the photocatalytic mechanism behind nitrate reduction in hypotrophic conditions but also provides genomic insights that pave the way for alternative approaches in water remediation technologies.

Enhanced degradation of phthalate esters (PAEs) by biochar-sodium alginate immobilised Rhodococcus sp. KLW-1

In this study, a new strain of bacteria, named Rhodococcus sp. KLW-1, was isolated from farmland soil contaminated by plastic mulch for more than 30 years. To improve the application performance of free bacteria and find more ways to use waste biochar, KLW-1 was immobilised on waste biochar by sodium alginate embedding method to prepare immobilised pellet. Response Surface Method (RSM) predicted that under optimal conditions (3% sodium alginate, 2% biochar and 4% CaCl2), di (2-ethylhexyl) phthalate (DEHP) degradation efficiency of 90.48% can be achieved. Under the adverse environmental conditions of pH 5 and 9, immobilisation increased the degradation efficiency of 100 mg/L DEHP by 16.42% and 11.48% respectively, and under the high-stress condition of 500 mg/L DEHP concentration, immobilisation increased the degradation efficiency from 71.52% to 91.56%, making the immobilised pellets have strong stability and impact load resistance to environmental stress. In addition, immobilisation also enhanced the degradation efficiency of several phthalate esters (PAEs) widely existing in the environment. After four cycles of utilisation, the immobilised particles maintained stable degradation efficiency for different PAEs. Therefore, immobilised pellets have great application potential for the remediation of the actual environment.

Preparation and Immobilization Mechanism on a Novel Composite Carrier PDA-CF/PUF to Improve Cells Immobilization and Xylitol Production

The preparation of a novel composite carrier of polydopamine-modified carbon fiber/polyurethane foam (PDA-CF/PUF) was proposed to improve cell immobilization and the fermentation of xylitol, which is an important food sweetener and multifunctional food additive. Candida tropicalis was immobilized on the composite carrier by adsorption and covalent binding. The properties and immobilization mechanism of the composite carrier and its effect on immobilized cells were investigated. It showed that the modification of PDA enhanced the loading of CF on the PUF surface and the adhesion of cells on the composite carrier surface. Also, the biocompatibility of carriers to cells was improved. In addition, the introduction of PDA increased the active groups on the surface of the carrier, enhanced the hydrophilicity, promoted the cells immobilization, and increased the xylitol yield. It was also found that expression of the related gene XYL1 in cells was significantly increased after the immobilization of the PDA-CF/PUF composite carrier during the fermentation. The PDA-CF/PUF was an immobilized carrier with the excellent biocompatibility and immobilization performance, which has great development potential in the industrial production of xylitol.

Enhancing nitrogen removal performance using immobilized aerobic denitrifying bacteria by modified polyvinyl alcohol/sodium alginate (PVA/SA)

Aerobic denitrification has emerged as a promising and efficient method for nitrogen removal from wastewater. However, the direct application of aerobic denitrifying bacteria has faced challenges such as low nitrogen removal efficiency, bacterial loss, and poor stability. To address these issues, this study developed a novel microbial particle carrier using NaHCO3-modified polyvinyl alcohol (PVA)/sodium alginate (SA) gel (NaHCO3-PVA/SA). This carrier exhibits several advantageous properties, including excellent mass transfer efficiency, favorable biocompatibility, convenient film formation, abundant biomass, and exceptional pollutant treatment capacity. The carrier was modified with 0.3% NaHCO3, 8.0% PVA, and 1.0% SA, resulting in a remarkable 3.4-fold increase in the average pore diameter and a 12.8% improvement in mass transfer efficiency. This carrier was utilized to immobilize the aerobic denitrifying bacterium Stutzerimonas stutzeri W-2 to enhance nitrogen removal (NaHCO3-PVA/SA@W-2), resulting in a NO3--N removal efficiency of 99.06%, which was 21.39% higher than that without modification. Compared with the non-immobilized W-2, the degradation efficiency was improved by 43.70%. After five reuses, the NO3--N and TN removal rates remained at 99% and 93.01%, respectively. These results provide a solid foundation for the industrial application of the modified carrier as an effective tool for nitrogen removal in large-scale wastewater treatment processes.

Biochar mediated high-rate anaerobic bioreactors: A critical review on high-strength wastewater treatment and management

Treatment of high-strength wastewater is critical for the aquatic environment and receiving water bodies around the globe. Untreated or partially treated high-strength wastewater may cause severe damage to the existing water bodies. Various high-rate anaerobic bioreactors have been developed in the last decades for treating high-strength wastewater. High-rate anaerobic bioreactors are effective in treating industrial wastewater and provide energy in the form of methane as well. However, the physical or chemical properties of high-strength industrial wastewater, sometimes, disrupt the functioning of a high-rate anaerobic bioreactor. For example, the disintegration of granular sludge in up flow anaerobic sludge blanket reactor or membrane blocking in an anaerobic membrane bioreactor are the results of a high-strength wastewater treatment which hamper the proper functioning and may harm the wastewater treatment plant economically. Biochar, if added to these bioreactors, may help to alleviate the ill-functioning of high-rate anaerobic bioreactors. The primary mechanisms by biochar work in these bioreactors are direct interspecies electron transfer, microbial immobilization, or gene level alternations in microbial structure. The present article explores and reviews the recent application of biochar in a high-rate anaerobic bioreactor treating high-strength industrial wastewater.

Enhanced nitrate removal efficiency and microbial response of immobilized mixed aerobic denitrifying bacteria through biochar coupled with inorganic electron donors in oligotrophic water

The nitrogen removal characteristics and microbial response of biochar-immobilized mixed aerobic denitrifying bacteria (BIADB) were investigated at 25 °C and 10 °C. BIADB removed 53.51 ± 1.72 % (25 °C) and 39.90 ± 4.28 % (10 °C) nitrate in synthetic oligotrophic water. Even with practical oligotrophic water, BIADB still effectively removed 47.66-53.21 % (25 °C), and 39.26-45.63 % (10 °C) nitrate. The addition of inorganic electron donors increased nitrate removal by approximately 20 % for synthetic and practical water. Bacterial and functional communities exhibited significant temperature and stage differences (P < 0.05), with temperature and total dissolved nitrogen being the main environmental factors. The dominant genera and keystone taxa exhibited significant differences at the two temperatures. Structural equation model analysis showed that dissolved organic matter had the highest direct and indirect effects on diversity and function, respectively. This study provides an innovative pathway for utilizing biochar and inorganic electron donors for nitrate removal from oligotrophic waters.

Weathered Coal-Immobilized Microbial Materials as a Highly Efficient Adsorbent for the Removal of Lead

Most research on immobilized microorganisms employs biomass charcoal as a carrier, but limited studies explore coal-based resources for microbial immobilization. Herein, lead-resistant functional strains were immobilized using weathered coal as a carrier, resulting in the development of a weathered coal-immobilized microbial material (JK-BW) exhibiting high efficiency in lead removal from solutions. A quadratic polynomial model for the adsorption capacity and adsorption rate of JK-BW on Pb2+ was developed using the Box-Behnken method to determine the optimal adsorption conditions. The Pb2+ adsorption mechanism of JK-BW was studied through batch adsorption and desorption experiments along with SEM-EDS, BET, FT-IR, and XPS analyses. Findings indicated that optimal conditions were identified at 306 K temperature, 0.36 g/L adsorbent dosage, and 300 mg/L initial solution concentration, achieving a peak adsorption performance of 338.9 mg/g (308 K) for the immobilized material, surpassing free cell adsorption by 3.8 times. Even after four cycles of repeated use, the material maintained its high adsorption capacity. Pb2+ adsorption by JK-BW involved monolayer chemisorption with ion exchange, complexation, precipitation, physical adsorption, and microbial intracellular phagocytosis. Ion exchange accounted for 22-42% and complexation accounted for 39-57% of the total adsorption mechanisms, notably involving exchanges with K, Ca, Na, and Mg ions as well as complexation with -OH, -COOH, CO-OH, -COOH, CO-, NH2, and the β-ring of pyridine for Pb2+ adsorption.

Techniques and mechanisms of bacteria immobilization on biochar for further environmental and agricultural applications

Bacteria immobilization on biochar is a promising approach to achieve high concentration and stability of microbial cells for several applications. The present review addressed the techniques utilized for bacteria immobilization on biochar, discussing the mechanisms involved in this process, as well as the further utilization in bioremediation and agriculture. This article presents three immobilization techniques, which vary according to their procedures and conditions, including cell growth, adsorption, and adaptation. The mechanisms for cell immobilization are primarily adsorption and biofilm formation on biochar. The favorable characteristics of biochar immobilization depend on the pyrolysis methods, raw materials, and properties of biochar, such as surface area, pore size, pH, zeta potential, hydrophobicity, functional groups, and nutrients. Scanning electron microscope (SEM) and colony forming unit (CFU) are the analyses commonly carried out to verify the efficiency of bacteria immobilization. The benefits of applying biochar-immobilized bacteria include soil decontamination and quality improvement, which can improve plant growth and crop yield. Therefore, this emerging technology represents a promising solution for environmental and agricultural purposes. However, it is important to evaluate the potential adverse impacts on native microbiota by introducing exogenous microorganisms.

Discovery of a heterotrophic aerobic denitrification Pseudomonas sp. G16 and its unconventional nitrogen metabolic pathway

From the aerobic pond of the farm, the Pseudomonas sp. G16 was screened and isolated, which was confirmed to exhibit heterotrophic nitrification and aerobic denitrification. The removal rates of Ammonia (100 mg/L), nitrate (120 mg/L), and nitrite (100 mg/L) by the strain were 94.13%, 92.62%, and 85.67%, and the nitrogen metabolism pathway of strain G16 was analyzed by whole genome sequencing combined with its nitrification-denitrification intermediate products, it was found that the strain had independent nitrification-denitrification ability and no nitrite accumulation. Under the conditions of carbon source of sodium succinate hexahydrate, C/N ratio of 15, pH of 7.5, temperature of 15 °C, and DO of 210 rpm, strain G16 showed excellent denitrification performance. Strain G16 was prepared into biochar-based immobilized bacterial particles, which successfully improved its nitrogen removal efficiency and stability. Therefore, the application of strain G16 in the field of real wastewater treatment has very necessary research value.

Degradation of p-cresol in the presence of UV light driven in an integrated system containing photocatalytic and packed bed biofilm reactor

Integratingphotocatalysisand biodegradation has shown great potential in wastewater treatment technology. In this study, the degradation of p-cresol in water has been investigated through an integrated system comprising of photocatalytic and packed bed biofilm reactor (PBBR). In the photocatalytic reactor, the biodegradability index (BOD5/COD, BOD5/TOC) of the p-cresol solution was first shown to increase (from 0.098±0.023 to 0.59±0.089 for BOD5/COD and from 0.27±0.030 to 1.74±0.03 for BOD5/TOC). The pseudo-first-order rate constant (kap) was found to be 0.011 min-1. The % removal of the integrated system was found to be 98.43±1.31% at an initial concentration of 700 mg L-1 and residence time of 120 h, which was significantly higher than the PBBR operated alone (34.82±2.62%) under optimized conditions (pH 7.0 and T = 32±2 °C). Using an integrated approach, the efficient removal of p-cresol opens novel future perspectives for catalytic degradation using chemical oxidation.

Microorganisms and Biochar Improve the Remediation Efficiency of Paspalum vaginatum and Pennisetum alopecuroides on Cadmium-Contaminated Soil

Phytoremediation can help remediate potential toxic elements (PTE) in soil. Microorganisms and soil amendments are effective means to improve the efficiency of phytoremediation. This study selected three microorganisms that may promote phytoremediation, including bacteria (Ceratobasidium), fungi (Pseudomonas mendocina), and arbuscular-mycorrhizal fungi (AMF, Funneliformis caledonium). The effects of single or mixed inoculation of three microorganisms on the phytoremediation efficiency of Paspalum vaginatum and Pennisetum alopecuroides were tested under three different degrees of cadmium-contaminated soil (low 10 mg/kg, medium 50 mg/kg, and high 100 mg/kg). The results showed that single inoculation of AMF or Pseudomonas mendocina could significantly increase the biomass of two plants under three different degrees of cadmium-contaminated soil, and the growth-promoting effect of AMF was better than Pseudomonas mendocina. However, simultaneous inoculation of these two microorganisms did not show a better effect than the inoculation of one. Inoculation of Ceratobasidium reduced the biomass of the two plants under high concentrations of cadmium-contaminated soil. Among all treatments, the remediation ability of the two plants was the strongest when inoculated with AMF alone. On this basis, this study explored the effect of AMF combined with corn-straw-biochar on the phytoremediation efficiency of Paspalum vaginatum and Pennisetum alopecuroides. The results showed that biochar could affect plant biomass and Cd concentration in plants by reducing Cd concentration in soil. The combined use of biochar and AMF increased the biomass of Paspalum vaginatum by 8.9-48.6% and the biomass of Pennisetum alopecuroides by 8.04-32.92%. Compared with the single use of AMF or biochar, the combination of the two is better, which greatly improves the efficiency of phytoremediation.

Bioremediation of aniline aerofloat wastewater at extreme conditions using a novel isolate Burkholderia sp. WX-6 immobilized on biochar

Aniline aerofloat (AAF) is a refractory organic pollutant in floatation wastewater. Little information is currently available on its biodegradation. In this study, a novel AAF-degrading strain named Burkholderia sp. WX-6 was isolated from mining sludge. The strain could degrade more than 80% of AAF at different initial concentrations (100-1000 mg/L) within 72 h. AAF degrading curves were fitted well with the four-parameter logistic model (R² >0.97), with the degrading half-life ranging from 16.39 to 35.55 h. This strain harbors metabolic pathway for complete degradation of AAF and is resistant to salt, alkali, and heavy metals. Immobilization of the strain on biochar enhanced both tolerance to extreme conditions and AAF removal, with up to 88% of AAF removal rate in simulated wastewater under alkaline (pH 9.5) or heavy metal pollution condition. In addition, the biochar-immobilized bacteria removed 59.4% of COD in the wastewater containing AAF and mixed metal ions within 144 h, significantly (P < 0.05) higher than those by free bacteria (42.6%) and biochar (48.2%) only. This work is helpful to understand AAF biodegradation mechanism and provides viable references for developing practical biotreatment technique of mining wastewater.

Biochar enhanced the stability and microbial metabolic activity of aerobic denitrification system under long-term oxytetracycline stress

Reactors were established to study the feasibility of the direct addition of modified biochar to alleviate the long-term stress of oxytetracycline (OTC) on aerobic denitrification (AD) and improve the stability of the system. The results showed that OTC stimulated at μg/L, and inhibited at mg/L. The higher the concentration of OTC, the longer the system was affected. The addition of biochar, without immobilization, improved the tolerance of community, alleviated the irreversible inhibition effect of OTC, and maintained a high denitrification efficiency. Overall, the main mechanisms of AD enhancement by biochar under OTC stress were: enhancing the bacteria metabolic activity, strengthening sludge structure and substrate transport, and improving the community stability and diversity. This study confirmed that direct addition of biochar could effectively alleviate the negative effect of antibiotics on the microorganisms, strengthen the AD, which provided a new idea to broaden the application of AD technology in livestock wastewater.

Enhanced Bioremediation of Aged Polycyclic Aromatic Hydrocarbons in Soil Using Immobilized Microbial Consortia Combined with Strengthening Remediation Strategies

Microbial biodegradation is considered as one of the most effective strategies for the remediation of soil contaminated with polycyclic aromatic hydrocarbons (PAHs). To improve the degradation efficiency of PAHs, PAH-degrading consortia combined with strengthening remediation strategies was used in this study. The PAH biodegrading performance of seven bacterial consortia constructed by different ratios of Mycobacterium gilvum MI, Mycobacterium sp. ZL7 and Rhodococcus rhodochrous Q3 was evaluated in an aqueous system containing phenanthrene, pyrene, benzo[a]pyrene and benzo[b]fluoranthene. Bacterial consortium H6 (Q3:ZL7:MI = 1:2:2) performed a high degrading efficiency of 59% in 8 days. The H6 was subsequently screened to explore its potential ability and performance to degrade aged PAHs in soils from a coking plant and the effects of strengthening strategies on the aged PAH degradation, including the addition of glucose or sodium dodecyl benzene sulfonate (SDBS) individually or as a mixture along immobilization of the inoculant on biochar. The highest degradation efficiencies, which were 15% and 60% for low-molecular-weight (LMW) PAHs and high-molecular-weight (HMW) PAHs, respectively, were observed in the treatment using immobilized microbial consortium H6 combined with the addition of glucose and SDBS after 24 days incubation. This study provides new insights and guidance for future remediation of aged PAH contaminated soils.

In-situ enrichment and application of heterotrophic nitrification-aerobic denitrification bacteria in membrane aerated biofilm reactor

In order to reduce the resource and energy consumption of traditional biological nitrogen removal (BNR) process, heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria was in situ enriched in membrane aerated biofilm reactor (MABR) by inoculating conventional activated sludge. Contaminants removal performance, EPS composition and microbial community were explored. The results indicated that the average removal efficiency of COD and TN under optimal condition reached 84.13% and 91.54%, respectively, which demonstrated that the reactor possessed excellent contaminants removal capacity. EPS analysis suggested that abundant protein especially tryptophan protein-like substance played a vital role in maintaining the microbial stability of biofilms. Multiple HN-AD genera, mainly Paracoccus, were detected with the highest relative abundance of 54.70%, which confirmed the successful enrichment of the HN-AD bacteria. Conventional nitrifiers and denitrifiers also thrived in biofilm, which demonstrated the synergistic nitrogen removal of multiple microorganisms. This study provided important insights into application of HN-AD bacteria and synergistic nitrogen removal in BNR system.

Enhanced biodegradation of oil-contaminated soil oil in shale gas exploitation by biochar immobilization

The enhanced biodegradation of oil-contaminated soil by fixing microorganisms with corn cob biochar was investigated. It was found that the components of oil in the test soil were mainly straight-chain alkanes and branched alkanes. When using corn cob biochar as a carrier to immobilize microorganisms, the best particle size of corn cob biochar as an immobilization carrier was 0.08 mm, and the best immobilization time was 18 h. SEM analysis confirmed that the microorganisms were immobilized on the corn cob biochar. Immobilized microorganisms exhibited high biodegradability under stress to high concentrations of petroleum pollutants, heavy metals, and organic pollutants. Infrared spectroscopy analysis showed that oxygen-containing groups such as hydroxyl, carboxyl, and methoxy on the surface of biochar were involved in the complexation of heavy metals. The mechanism of immobilization promoted microbial degradation of oil contamination was explained by gas chromatography mass. First, alkanes and aromatics were adsorbed by corn cob biochar and passed to immobilized microorganisms to promote their degradation. Their bioavailability increased, especially for aromatics. Second, biochar provided a more suitable environment for microorganisms to degrade. Third, the conversion of ketones to acids was accelerated during the biodegradation of alkanes, and the biodegradation of alkanes was accelerated by immobilization. The biodegradable efficiency of oil by immobilized microorganisms in soil was 70.10% within 60 days, 28.80% higher than that of free microorganisms. The degradation of immobilized microorganisms was highly correlated with the activities of catalase, urease, and polyphenol oxidase.

Efficient nitrate removal of immobilized mixed aerobic denitrifying bacteria and community dynamics response to temperature and low carbon/nitrogen polluted water

The denitrification performance of immobilized mixed aerobic denitrifying bacteria (IMADB) was investigated. IMADB displayed strong temperature adaptability under low Carbon/Nitrogen conditions. At 5, 15, and 25 °C, the nitrate removal efficiencies of volcanic rock and polyester fiber sponge immobilized system reached 83.95%-98.25% and 89.71%-98.14%, respectively. The nitrate content removed by the carrier accounted for 41.18%-82.47% of the nitrate content removed by the immobilized system at different temperature, and played a major role in nitrate removal. The lower the temperature, the greater the role of the carrier. At the same temperature, carrier had a relatively higher richness, diversity, and evenness. Network analysis revealed that carrier species, which were positively correlated with nitrate removal efficiency, had the largest OTUs and abundance. Meanwhile, carrier had the widest niche. The total nitrogen removal efficiency of IMADB reached 56.10%-62.31% in the natural water system, highlighting a promising application prospect.

Application of biochar immobilized microorganisms for pollutants removal from wastewater: A review

Microbial immobilization technology (MIT) has been rapidly developed and used to remove pollutants from water/wastewater in recent years, owing to its high stability, rapid reaction rate, and high activity. Microbial immobilization carrier with low cost and high removal efficiency is the key of MIT. Biochar is considered to be an efficient carrier for microbial immobilization because of its high porosity and good adsorption effect, which can provide a habitat for microorganisms. The use of biochar immobilized microorganisms to treat different pollutants in wastewater is a promising treatment method. Compared with the other biological treatment technology, biochar immobilized microorganisms can improve microbial abundance, repeated utilization ratio, microbial metabolic capacity, etc. However, current research on this method is still in its infancy. Little attention has been paid to the interaction mechanisms between biochar and microorganisms, and many studies are only carried out in the laboratory. There are still problems such as difficult recovery after use and secondary pollution caused by residual pollutants after biochar adsorption, which need further clarification. To have comprehensive digestion and an in-depth understanding of biochar immobilized microorganisms technology in wastewater treatment, the wastewater treatment methods based on biochar are firstly summarized in this review. Then the mechanisms of immobilized microorganisms were explored, and the applications of biochar immobilized microorganisms in wastewater were systematically reviewed. Finally, suggestions and perspectives for future research and practical application are put forward.

Biochar immobilized bacteria enhances nitrogen removal capability of tidal flow constructed wetlands

To improve the nitrogen removal (NR) capability of tidal flow constructed wetlands (TFCWs) for treatment of saline wastewater, biochar, produced from Cyperus alternifolius, was used to adsorb and immobilize a salt tolerant aerobic denitrifying bacteria (Zobellella sp. A63), and then was added as a substrate into the systems. Under low (2:1) or high (6:1) C/N ratio, the removal of NO₃^--N and total nitrogen (TN) in the biochar immobilized bacteria (BIB) dosing system (TFCW3) was significantly higher (q < 0.05) than that in the untreated system (TFCW1) and the biochar dosing system (TFCW2). At low C/N ratio, the removal rates of NO₃^--N, TN and chemical oxygen demand (COD) of TFCW3 were 68.2%, 72.6% and 82.5%, respectively, 15-20% higher than TFCW1 and 5-10% higher than TFCW2. When C/N ratio was further increased to 6, the pollutant removal rate of each system was greatly improved, but the removal rate of TFCW3 for NO₃^--N/TN was still nearly 10% and 5% higher than TFCW1 and TFCW2, respectively. Microbial community analysis showed that aerobic denitrifying bacteria, sulfate reducing bacteria and sulfur-driven denitrifiers (DNSOB) played the most important role of NR in TFCWs. Moreover, biochar bacterial agent significantly increased the abundances of genes involved in NR. The total copy numbers of bacterial 16S rRNA, nirS, nirK, drsA and drsB genes in the TFCW3 were 1.1- to 3.76-fold higher than those in the TFCW1; Especially at low C/N ratio, the copy number of drsA and drsB in the upper layer of TFCW3 were 85.5 and 455 times that of TFCW1, respectively. Thus, BIB provide a more feasible and effective amendment for constructed wetlands to improve the N removal of the saline wastewater by enhancing the microbial NR capacity mainly via aerobic and sulfur autotrophic denitrification.

Biochar enhanced high-solid mesophilic anaerobic digestion of food waste: Cell viability and methanogenic pathways

The underlying mechanisms of biochar enhance high-solid anaerobic digestion (HSAD) of food waste were investigated with a focus on the cell viability, microbial community, and methanogenic pathways. This study assessed the effects of different dosages of biochar in HSAD. Optimal biochar dosage was found to be 25 g/L, which produced accumulative methane yields of up to 251 mL CH₄/g VS significantly promote volatile fatty acid degradations, especially in butyric acid concentrations. Effects of biochar with a dosage of 25 g/L on the cell viability showed that viable cells based on cell membrane integrity increased from 2.9% to 6.4%. Meanwhile, intact and highly active cells with high DNA content were probably involved in direct interspecies electron transfer (DIET) via membrane-bound electron transport proteins. Further analysis demonstrated that Syntrophomonas and methanogens Methanosarcina &Methanocelleus were selectively enriched by biochar, which resulted in the methanogenic pathways shifting from acetoclastic/hydrogenotrophic methanogenic pathways to more metabolically diverse methanogenic pathways. Accordingly, biochar-mediated DIET was possibly established between Syntrophomonas and Methanosarcina species due to those viable cells. In conclusion, biochar is a feasible additive in enhancing HSAD methanogenic performance.