Biochar-based functional materials for the abatement of emerging pollutants from aquatic matrices.

Biochar has emerged as a versatile and efficient multi-functional material, serving as both an adsorbent and catalyst in removing emerging pollutants (EPs) from aquatic matrices. However, pristine biochar's catalytic and adsorption capabilities are hindered by its poor surface functionality and small pore size. Addressing these limitations involves the development of functionalized biochar, a strategic approach aimed at enhancing its physicochemical properties and improving adsorption and catalytic efficiencies. Despite a growing interest in this field, there is a notable gap in existing literature, with no review explicitly concentrating on the efficacy of biochar-based functional materials (BCFMs) for removing EPs in aquatic environments. This comprehensive review aims to fill this void by delving into the engineering considerations essential for designing BCFMs with enhanced physiochemical properties. The focus extends to understanding the treatment efficiency of EPs through mechanisms such as adsorption or catalytic degradation. The review systematically outlines the underlying mechanisms involved in the adsorption and catalytic degradation of EPs by BCFMs. By shedding light on the prospects of BCFMs as a promising multi-functional material, the review underscores the imperative for sustained research efforts. It emphasizes the need for continued exploration into the practical implications of BCFMs, especially under environmentally relevant pollutant concentrations. This holistic approach seeks to contribute to advancing knowledge and applying biochar-based solutions in addressing the challenges posed by emerging pollutants in aquatic ecosystems.

Comparative study of the removal of sulfate by UASB in light and dark environment.

At present, the application of sewage treatment technologies is restricted by high sulfate concentrations. In the present work, the sulfate removal was biologically treated using an upflow anaerobic sludge blanket (UASB) in the absence/presence of light. First, the start-up of UASB for the sulfate removal was studied in terms of COD degradation, sulfate removal, and effluent pH. Second, the impacts of different operation parameters (i.e., COD/SO42- ratio, temperature and illumination time) on the UASB performance were explored. Third, the properties of sludge derived from the UASB at different time were analyzed. Results show that after 28 days of start-up, the COD removal efficiencies in both the photoreactor and non-photoreactor could reach a range of 85-90% while such reactors could achieve > 90% of sulfate being removed. Besides, higher illumination time could facilitate the removal of pollutants in the photoreactor. To sum up, the present study can provide technical support for the clean removal of sulfate from wastewater using photoreactors.

Biofuel production for circular bioeconomy: Present scenario and future scope.

In recent years, biofuel production has attracted considerable attention, especially given the increasing worldwide demand for energy and emissions of greenhouse gases that threaten this planet. In this case, one possible solution is to convert biomass into green and sustainable biofuel, which can enhance the bioeconomy and contribute to sustainable economic development goals. Due to being in large quantities and containing high organic content, various biomass sources such as food waste, textile waste, microalgal waste, agricultural waste and sewage sludge have gained significant attention for biofuel production. Also, biofuel production technologies, including thermochemical processing, anaerobic digestion, fermentation and bioelectrochemical systems, have been extensively reported, which can achieve waste valorization through producing biofuels and re-utilizing wastes. Nevertheless, the commercial feasibility of biofuel production is still being determined, and it is unclear whether biofuel can compete equally with other existing fuels in the market. The concept of a circular economy in biofuel production can promote the environmentally friendly and sustainable valorization of biomass waste. This review comprehensively discusses the state-of-the-art production of biofuel from various biomass sources and the bioeconomy perspectives associated with it. Biofuel production is evaluated within the framework of the bioeconomy. Further perspectives on possible integration approaches to maximizing waste utilization for biofuel production are discussed, and what this could mean for the circular economy. More research related to pretreatment and machine learning of biofuel production should be conducted to optimize the biofuel production process, increase the biofuel yield and make the biofuel prices competitive.

Review on ultrasonic technology enhanced biological treatment of wastewater.

As a clean, sustainable and efficient technology of wastewater treatment, ultrasonic irradiation has gained special attention in wastewater treatment. It has been widely studied for degrading pollutants and enhancing biological treatment processes for wastewater treatment. This review focuses on the mechanism and updated information of ultrasonic technology to enhance biological treatment of wastewater. The mechanism involved in improving biological treatment by ultrasonic includes: 1) degradation of refractory substances and release carbon from sludges, 2) promotion of mass transfer and change of cell permeability, 3) facilitation of enzyme-catalyzed reactions and 4) influence of cell growth. Based on the above discussion, the effects of ultrasound on the enhancement of wastewater biological treatment processes can be categorized into indirect and direct ways. The indirect effect of ultrasonic waves in enhancing biological treatment is mainly achieved through the use of high-intensity ultrasonic waves. These waves can be used as a pretreatment to improve biodegradability of the wastewater. Moreover, the ultrasonic-treated sludge or its supernatant can serve as a carbon source for the treatment system. Low-intensity ultrasound is often employed to directly enhance the biological treatment of wastewater. The propose of this process is to improve activated sludge, domesticate polyphosphate-accumulating organisms, ammonia-oxidizing bacteria, and anammox bacteria, and achieve speedy start-up of partial nitrification and anammox. It has shown remarkable effects on maintaining stable operation, tolerating adverse conditions (i.e., low temperature, low C/N, etc.), resisting shock load (i.e., organic load, toxic load, etc.), and collapse recovery. These results indicate a promising future for biological wastewater treatment. Furthermore, virous ultrasonic reactor designs were presented, and their potential for engineering application was discussed.

Persistent free radicals on biochar for its catalytic capability: A review.

Biochar is an economical carbon material for water pollution control, which shows great promise to be applied in the up-scale wastewater remediation processes. Previous studies demonstrate that persistent free radicals (PFRs) on biochar are critical to its reactivity for wastewater remediation. A series of studies have revealed the important roles of PFRs when biochar was applied for organic pollutants degradation as well as the removal of Cr (VI) and As (III) from wastewater. Therefore, this review comprehensively concludes the significance of PFRs for the catalytic capabilities of biochar in advanced oxidation processes (AOPs)-driven organic pollutant removal, and applied in redox processes for Cr (VI) and As (III) remediation. In addition, the mechanisms for PFRs formation during biochar synthesis are discussed. The detection methods are reviewed for the quantification of PFRs on biochar. Future research directions were also proposed on underpinning the knowledge base to forward the applications of biochar in practical real wastewater treatment.

Acclimation of electroactive biofilms under different operating conditions: comprehensive analysis from architecture, composition, and metabolic activity.

Electroactive biofilms (EABs) have aroused wide concern in waste treatment due to their unique capability of extracellular electron transfer with solid materials. The combined effect of different operating conditions on the formation, microbial architecture, composition, and metabolic activity of EABs is still unknown. In this study, the impact of three different factors (anode electrode, substrate concentration, and resistance) on the acclimation and performance of EABs was investigated. The results showed that the shortest start-up time of 127.3 h and highest power density of 0.84 W m-2 were obtained with carbon brush as electrode, low concentration of substrate (1.0 g L-1), and 1000 Ω external resistance (denoted as N1). The EABs under N1 condition also represented strongest redox capacity, lowest internal resistance, and close arrangement of bacteria. Moreover, the EABs cultured under different conditions both showed similar results, with direct electron transfer (DET) dominated from EABs to anode. Microbial community compositions indicated that EABs under N1 condition have lowest diversity and highest abundance of electroactive bacteria (46.68%). Higher substrate concentration (3.0 g L-1) promoted the proliferation of some other bacteria without electroactivity, which was adverse to EABs. The metabolic analysis showed the difference of genes related to electron transfer (cytochrome C and pili) and biofilm formation (xap) of EABs under different conditions, which further demonstrated the higher electroactivity of EABs under N1. These results provided a comprehensive understanding of the effect of different operating conditions on EABs including biofilm formation and electrochemical activity.

Insights into the effects of operating parameters on sulfate reduction performance and microbial pathways in the anaerobic sequencing batch reactor.

Sulfate-reducing bacteria (SRB)-based anaerobic process has aroused wide concern in the treatment of sulfate-containing wastewater. Chemical oxygen demand-to-sulfate ratio (COD/SO42-) and HRT are two key factors that affect not only the anaerobic treatment performance but also the activity of SRB. In this study, an anaerobic sequencing batch reactor was constructed, and the effects of different operating parameters (COD/SO42-, HRT) on the relationship of sulfate (SO42-) reduction performance, microbial communities, and metabolic pathways were comprehensively investigated. The results indicated that the SO42- removal rates could achieve above 95% under different operating parameters. Bioinformatics analysis revealed that microbial community changed with reactor operation. At the genus level, the enrichment of Propionicclava and Peptoclostridium contributed to the establishment of a homotrophic relationship with Desulfobulbus, the dominant SRB in the reactor, which indicated that they took vital part in maintaining the structural and functional stability of the bacterial community under different operating parameters. In particular, an increasing trend of the relative abundance of functional genes encoding dissimilatory sulfate reduction was detected with the increase of COD/SO42-, which indicated high SO42- reduction potentials. This knowledge will help to reveal the mechanism of the effect of operating parameters on the anaerobic sulfate removal process, thus providing effective guidance for the targeted regulation of anaerobic sequencing batch bioreactors treating SO42--containing wastewater.

A critical review on utilization of sewage sludge as environmental functional materials.

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

Insight of the bio-cathode biofilm construction in microbial electrolysis cell dealing with sulfate-containing wastewater.

Signaling molecules are useful in biofilm formation, but the mechanism for biofilm construction still needs to be explored. In this study, a signaling molecule, N-butyryl-l-Homoserine lactone (C4-HSL), was supplied to enhance the construction of the sulfate-reducing bacteria (SRB) bio-cathode biofilm in microbial electrolysis cell (MEC). The sulfate reduction efficiency was more than 90% in less time under the system with C4-HSL addition. The analysis of SRB bio-cathode biofilms indicated that the activity, distribution, microbial population, and secretion of extracellular polymers prompted by C4-HSL, which accelerate the sulfate reduction, in particular for the assimilatory sulfate reduction pathway. Specifically, the relative abundance of acidogenic fermentation bacteria increased, and Desulfovibrio was co-metabolized with acidogenic fermentation bacteria. This knowledge will help to reveal the potential of signaling molecules to enhance the SRB bio-cathode biofilm MEC construction and improve the performance of treating sulfate-containing wastewater.

Enhanced photo-fermentative biohydrogen production from biowastes: An overview.

Clean energy like hydrogen can be a promising strategy to solve problems of global warming. Photo-fermentation (PF) is an attractive technology for producing biohydrogen from various biowastes cost-effectively and environmentally friendly. However, challenges of low light conversion efficiency and small yields of biohydrogen production still limit its application. Thus, advanced strategies have been investigated to enhance photo-fermentative biohydrogen production. This review discusses advanced technologies that show positive outcomes in improving biohydrogen production by PF, including the following. Firstly, genetic engineering enhances light transfer efficiency, change the activity of enzymes, and improves the content of ATP, ammonium and antibiotic tolerance of photosynthetic bacteria. Secondly, immobilization technology is refined. Thirdly, nanotechnology makes great strides as a scientific technique and fourthly, integration of dark and photo-fermentation technology is possible. Some suggestions for further studies to achieve high levels of efficiency of photo-fermentative biohydrogen production are mentioned in this paper.

Advanced strategies for enhancing dark fermentative biohydrogen production from biowaste towards sustainable environment.

As a clean energy carrier, hydrogen is a promising alternative to fossil fuel so as the global growing energy demand can be met. Currently, producing hydrogen from biowastes through fermentation has attracted much attention due to its multiple advantages of biowastes management and valuable energy generation. Nevertheless, conventional dark fermentation (DF) processes are still hindered by the low biohydrogen yields and challenges of biohydrogen purification, which limit their commercialization. In recent years, researchers have focused on various advanced strategies for enhancing biohydrogen yields, such as screening of super hydrogen-producing bacteria, genetic engineering, cell immobilization, nanomaterials utilization, bioreactors modification, and combination of different processes. This paper critically reviews by discussing the above stated technologies employed in DF, respectively, to improve biohydrogen generation and stating challenges and future perspectives on biowaste-based biohydrogen production.

Impact factors and novel strategies for improving biohydrogen production in microbial electrolysis cells.

Microbial electrolysis cell (MEC) system is an environmentally friendly method for clean biohydrogen production from a wide range of biowastes owing to low greenhouse gas emissions. This approach has relatively higher yields and lower energy costs for biohydrogen production compared to conventional biological technologies and direct water electrolysis, respectively. However, biohydrogen production efficiency and operating costs of MEC still need further optimization to realize its large-scale application.This paper provides a unique review of impact factors influencing biohydrogen production in MECs, such as microorganisms and electrodes. Novel strategies, including inhibition of methanogens, development of novel cathode catalyst, advanced reactor design and integrated systems, to enhance low-cost biohydrogen production, are discussed based on recent publications in terms of their opportunities, bottlenecks and future directions. In addition, the current challenges, and effective future perspectives towards the practical application of MECs are described in this review.

Recent advances in attached growth membrane bioreactor systems for wastewater treatment.

To tackle membrane fouling and limited removals of pollutants (nutrients and emerging pollutants) that hinder the wide applications of membrane bioreactor (MBR), attached growth MBR (AGMBR) combining MBR and attached growth process has been developed. This review comprehensively presents the up-to-date developments of media used in both aerobic and anaerobic AGMBRs for treating wastewaters containing conventional and emerging pollutants. It also elaborates the properties of different media, characteristics of attached biomass, and their contributions to AGMBR performance. Conventional media, such as biological activated carbon and polymeric carriers, induce formation of aerobic, anoxic and/or anaerobic microenvironment, increase specific surface area or porous space for biomass retention, improve microbial activities, and enrich diverse microorganisms, thereby enhancing pollutants removal. Meanwhile, new media (i.e. biochar, bioaugmented carriers with selected strain/mixed cultures) do not only eliminate conventional pollutants (i.e. high concentration of nitrogen, etc.), but also effectively remove emerging pollutants (i.e. micropollutants, nonylphenol, adsorbable organic halogens, etc.) by forming thick and dense biofilm, creating anoxic/anaerobic microenvironments inside the media, enriching special functional microorganisms and increasing activity of microorganisms. Additionally, media can improve sludge characteristics (i.e. less extracellular polymeric substances and soluble microbial products, larger floc size, better sludge settleability, etc.), alleviating membrane fouling. Future studies need to focus on the development and applications of more new functional media in removing wider spectrum of emerging pollutants and enhancing biogas generation, as well as scale-up of lab-scale AGMBRs to pilot or full-scale AGMBRs.

Optimization and mechanism of oily sludge treatment by a novel combined surfactants with activated-persulfate method.

Recently, the extensive discharge of oily sludge, due to excessive use of fossil oil, has become a serious worldwide concern, as it leads to serious environmental pollution and even threat human health. However, the complex properties and compositions of oily sludge make it difficult for the treatment of oily sludge. This study proposed a novel method of combined degradation of oily sludge by surfactants with activated-persulfate, and analyzed the degradation efficiency and degradation pathway. The organics in oil sludge were eluted by surfactant, and the residual oil difficult to be eluted was further oxidized by activated persulfate. The combined method significantly improved the degradation efficiency of oily sludge, and the removal rate reached 94.6 ± 2.8%, and the oil content of the residual oily sludge was 0.57%, which had reached the discharge standard. The mechanism analysis indicated that surfactant could increase the solubility of oil by reducing the surface tension, and the hydroxyl radical and sulfate radical generated by activated persulfate could degrade the complex organic matters into small molecule matters, achieving efficient degradation of oil sludge. This work demonstrated a new avenue for the efficient and cost-effective treatment of oily sludge, opening an environmentally friendly treatment concept.

Analyses of community structure and role of immobilized bacteria system in the bioremediation process of diesel pollution seawater.

Immobilized bacteria system plays an important role during degradation process in oil contaminated seawater. Although the immobilized bacteria system can be recycled to avoid pollution after remediation, it remains an open question on whether or not the secondary pollution occurs during the degradation process. Additionally, the research on the role of immobilized bacteria system in the process of oil removal is not clear enough. In this study, both the diesel degradation rate of diesel by immobilized bacteria system and changes in marine microbial community structure were determined to explore the role of immobilized bacteria system. The immobilized bacteria system was added to the diesel polluted seawater (1% diesel) for 30 days. The degradation performance was investigated during the process, and the microbial community structure was analyzed simultaneously. The results illustrated that the degradation rate of diesel by immobilized bacteria system reached 78.39% after 30 days, and Alcanivorax (59.09%), Achromobacter (24.34%) and Thalassospira (9.84%) were the dominant genera in the immobilized bacteria system. The addition of immobilized bacteria system increased the content of nitrogen and phosphorus, and then promoted the growth of oil-degrading bacteria. Thus, functional genes related to oil degradation increased. Additionally, there was little difference in the microbial composition between the treated seawater and the unpolluted seawater. Based on all results, it can be inferred that immobilized bacteria system triggered and stimulated diesel degradation process. This study provides a promising way to improve the removal of oil, and provides theoretical support for the wide application of immobilized microorganism technology.

Effect of calcium peroxide pretreatment on the remediation of sulfonamide antibiotics (SMs) by Chlorella sp.

This study investigated the effect of CaO2 pretreatment on sulfonamide antibiotics (SMs) remediation by Chlorella sp. Results showed that a CaO2 dose ranging from 0.05 to 0.1 g/g biomass was the best and led to higher SMs removal efficacy 5-10% higher than the control. The contributions made by cometabolism and CaO2 in SMs remediation were very similar. Bioassimilation could remove 24% of sulfadiazine (SDZ) and sulfamethazine (SMZ), and accounted for 38% of sulfamethoxazole (SMX) remediation. Pretreatment by CaO2 wielded a positive effect on microalgae. The extracellular polymeric substances (EPS) level of the CaO2 pretreatment microalgae was three times higher when subjected to non-pretreatment. For the long-term, pretreatment microalgae removed SMs 10-20% more than the non-pretreatment microalgae. Protein fractions of EPS in continuous operation produced up to 90 mg/L for cometabolism. For bioassimilation, SMX intensity of the pretreatment samples was 160-fold less than the non-treatment one. It indicated the CaO2 pretreatment has enhanced the biochemical function of the intracellular environment of microalgae. Peroxidase enzyme involved positively in the cometabolism and degradation of SMs to several metabolites including ring cleavage, hydroxylation and pterin-related conjugation.

Roles and applications of enzymes for resistant pollutants removal in wastewater treatment.

Resistant pollutants like oil, grease, pharmaceuticals, pesticides, and plastics in wastewater are difficult to be degraded by traditional activated sludge methods. These pollutants are prevalent, posing a great threat to aquatic environments and organisms since they are toxic, resistant to natural biodegradation, and create other serious problems. As a high-efficiency biocatalyst, enzymes are proposed for the treatment of these resistant pollutants. This review focused on the roles and applications of enzymes in wastewater treatment. It discusses the influence of enzyme types and their sources, enzymatic processes in resistant pollutants remediation, identification and ecotoxicity assay of enzymatic transformation products, and typically employed enzymatic wastewater treatment systems. Perspectives on the major challenges and feasible future research directions of enzyme-based wastewater treatment are also proposed.

Sustainable enzymatic technologies in waste animal fat and protein management.

Waste animal fats and proteins (WAFP) are rich in various animal by-products from food industries. On one hand, increasing production of huge amounts of WAFP brings a great challenge to their appropriate disposal, and raises severe risks to environment and life health. On the other hand, the high fat and protein contents in these animal wastes are valuable resources which can be reutilized in an eco-friendly and renewable way. Sustainable enzymatic technologies are promising methods for WAFP management. This review discussed the application of various enzymes in the conversion of WSFP to value-added biodiesel and bioactivate hydrolysates. New biotechnologies to discover novel enzymes with robust properties were proposed as well. This paper also presented the bio-utilization strategy of animal fat and protein wastes as alternative nutrient media for microorganism growth activities to yield important industrial enzymes cost-effectively.

Improving sulfonamide antibiotics removal from swine wastewater by supplying a new pomelo peel derived biochar in an anaerobic membrane bioreactor.

Sulfonamide antibiotics (SMs), as a class of antibiotics commonly used in swine industries, pose a serious threat to animal and human health. This study aims to evaluate the performance of an anaerobic membrane bioreactor (AnMBR) with and without supplying a new pomelo peel derived biochar to treat swine wastewater containing SMs. Results show that 0.5 g/L biochar addition could increase more than 30% of sulfadiazine (SDZ) and sulfamethazine (SMZ) removal in AnMBR. Approximately 95% of chemical oxygen demand (COD) was removed in the AnMBR at an influent organic loading rate (OLR) of 3.27 kg COD/(m3·d) while an average methane yield was 0.2 L/g CODremoved with slightly change at a small dose 0.5 g/L biochar addition. SMs inhibited the COD removal and methane production and increased membrane fouling. The addition of biochar could reduce the membrane fouling by reducing the concentration of SMP and EPS.

Evaluation of a continuous flow microbial fuel cell for treating synthetic swine wastewater containing antibiotics.

Microbial fuel cell (MFC) systems are promising technologies for wastewater treatment and renewable energy generation simultaneously. Performance of a double-chamber microbial fuel cell (MFC) to treat synthetic swine wastewater containing sulfonamide antibiotics (SMs) was evaluated in this study. The MFC was operated in continuous modes at different conditions. Results indicated that the current was successfully generated during the operation. The performance of MFC under the sequential anode-cathode operating mode is better than that under the single continuous running mode. Specifically, higher removal efficiency of chemical oxygen demand (>90%) was achieved under the sequential anode-cathode operating mode in comparison with that in the single continuous mode (>80%). Nutrients were also be removed in the MFC's cathode chamber with the maximum removal efficiency of 66.6 ± 1.4% for NH4+-N and 32.1 ± 2.8% for PO43--P. Meanwhile, SMs were partly removed in the sequential anode-cathode operating with the value in a range of 49.4%-59.4% for sulfamethoxazole, 16.8%-19.5% for sulfamethazine and 14.0%-16.3% for sulfadiazine, respectively. SMs' inhibition to remove other pollutants in both electrodes of MFC was observed after SMs exposure, suggesting that SMs exert toxic effects on the microorganisms. A positive correlation was found between the higher NH4+-N concentration used in this study and the removal efficiency of SMs in the cathode chamber. In short, although the continuous flow MFC is feasible for treating swine wastewater containing antibiotics, its removal efficiency of antibiotics requires to be further improved.