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Clean water shortages require the reuse of wastewater. The presence of organic substances such as humic acids in wastewater makes the water treatment process more difficult. Humic acids can significantly affect the removal of heavy metals and other such toxins. Humic acids is formed by the decomposition and transformation of animal and plant remains by microorganisms, and naturally exists in soil and water. It is necessary to degrade and remove humic acids from wastewater. As it seriously human health, effective technologies for removing humic acids from wastewater have attracted great interest over the past decades. This study compared existing techniques for removing humic acids from wastewater, as well as their limitations. Physicochemical treatments including filtration and oxidation are basic and key approaches to removing humic acids. Biological treatments including enzyme and fungi-mediated humic acids degradation are economically feasible but require some scalability. In conclusion, the integrated treatment processes are more significant options for the effective removal of humic acids from wastewater. In addition, humic acids have rich utilization values. It can improve the soil, increase crop yields, and promote the removal of pollutants.

Energy crisis and increasing rigorous management standards pose significant challenges for solid waste management worldwide. Several emerging diseases such as COVID-19 aggravated the already complex solid waste management crisis, especially sewage sludge and food waste streams, because of the increasingly large production year by year. As mature waste disposal technologies, landfills, incineration, composting, and some other methods are widespread for solid wastes management. This paper reviews recent advances in key sewage sludge disposal technologies. These include incineration, anaerobic digestion, and valuable products oriented-conversion. Food waste disposal technologies comprised of thermal treatment, fermentation, value-added product conversion, and composting have also been described. The hot topic and dominant research foci of each area are summarized, simultaneously compared with conventional technologies in terms of organic matter degradation or conversion performance, energy generation, and renewable resources production. Future perspectives of each technology that include issues not well understood and predicted challenges are discussed with a positive effect on the full-scale implementation of the discussed disposal methods.

Thermophilic solid-state anaerobic digestion (SS-AD) of agricultural wastes, i.e., corn straw, cattle manure, and vegetable waste, was carried out in this study. The effects of temperature (40-60°C), initial solid content (ISC, 17.5-32.5%), and C/N ratio (15-32 : 1) on biogas production were evaluated using a Box-Behnken experimental design (BBD) combined with response surface methodology (RSM). The results showed that optimization of process parameters is important to promote the SS-AD performance. All the factors, including interactive terms (except the ISC), were significant in the quadratic model for biogas production with SS-AD. Among the three operation parameters, the C/N ratio had the largest effect on biogas production, followed by temperature, and a maximum biogas yield of 241.4 mL gVS-1 could be achieved at 47.3°C, ISC = 24.81 % , and C / N = 22.35 . After 20 d of SS-AD, the microbial community structure under different conditions was characterized by high-throughput sequencing, showing that Firmicutes, Bacteroidetes, Chloroflexi, Synergistetes, and Proteobacteria dominated the bacterial community, and that Firmicutes had a competitive advantage over Bacteroidetes at elevated temperatures. The biogas production values and relative abundance of OPB54 and Bacteroidia after 20 d of SS-AD can be fitted well using a quadratic model, implying that OPB54 and Bacteroidia play important roles in the methanogenic metabolism for agricultural waste thermophilic SS-AD.

Sludge management represents a critical challenge because of complex compositions and poor dewaterability. Fe

CO2 bioelectromethanosynthesis represents a promising strategy for the capture and utilization of CO2. In such process, the continuous generation of electron (e-) and proton (H+) in anodic oxidation are of prime importance for the efficient cathodic CO2 electroreduction and process stability. Proton transfer, however, is very easy to be hindered due to the fouling of proton exchange membrane (PEM). In this study, an artificial channel in microbial electrolysis cell (MEC) was proposed to strengthen the transport of protons from anodic to cathodic compartment, and H+-rich anolyte was semi-continuously circulated to the cathodic chamber to provide protons for CO2 electroreduction. The results indicated that the daily CH4 yield in cathode with anolyte circulation (18.5 mL/d·L-reactor) was 5.4-fold higher than that without circulation (2.9 mL/d·L-reactor). Meanwhile, efficient anodic biodegradation of organic components was observed with COD, proteins and polysaccharides removal of up to 95.6 ± 1.9%, 96.3 ± 3.7% and 99.1 ± 0.2% respectively, which supplied a continuous e-/H+ donor for CO2 electroconversion. 16S rRNA gene pyrosequencing analysis identified a large number of proteins-utilizing Bacteroidetes (14.11%) and polysaccharides-consuming Thermotogae (18.49%) in anodic biofilm, conductive to the biodegradation of organic components. Moreover, a high abundance of Methanobacterium (81.07%) was detected to prevail in cathodic biofilm, demonstrating the occurrence of highly enhanced CH4 bioelectrosysthesis. The syntrophic and symbiotic relationship was established in the dual-bioelectrode system, creating a beneficial environment and an energy-efficient approach for biowaste refinery and CO2 electromethanosynthesis.

Significant advances in the design of bioelectrochemical systems (BES) have promoted these applications to be seen as contemporary biotechnological platforms. However, notable issues in system architecture are still to be addressed and overcome, in particular concerning the membrane separators, which rely widely on polymers. These architectural components play a key-role in facilitating the transport of ions (i.e. protons) between the (compartments containing the) electrodes and therefore, their properties substantially influence the overall BES performance. This article aims presenting an up-to-date survey on the important accomplishments and promising outlooks with polymer-based membranes (both porous/non-porous, charged/uncharged) applied in BES (first and foremost microbial fuel cells, MFCs) that could drive this technology towards enhanced efficiency. Because of the interdisciplinary concept of BES, it attracts attention from scientists and engineers involved in environmental biotechnology, microbial electrochemistry and applied material sciences and as a result, this review paper would target the audience of these fields with particular interest on the progress with membrane separators fabricated with various polymeric materials.

Sludge management represents a critical challenge because of complex compositions and poor dewaterability. Fe2+-activated persulfate oxidation (Fe2+/S2O82−) is an effective, and widely investigated method for enhancing sludge dewatering. However, the potential effects of Fe2+/S2O82− on sludge drying efficiency, anaerobic biodegradation behaviors and potential recycling of sludge residua are not yet well-known. In this study, a new sludge disposal route (step i: enhanced dewatering via Fe2+/S2O82−, and step ii: drying-incineration or anaerobic digestion) was proposed and appraised comprehensively. Results showed that Fe2+/S2O82− oxidation destroyed extracellular polymeric substances, lysed sludge cells and enhanced the dewaterability greatly. Capillary suction time and mechanical filtration time at 2.0/1.6 mmol-Fe2+/S2O82−/g-VS decreased by 88.0% and 79.6%, respectively. Moreover, 89.8% of micro-pollutants (e.g., methylbenzene, ethylbenzene, p-m-xylene and o-xylene) in sludge were removed. Besides, the pretreatment was able to alter sludge drying behaviors and methane-producing potential. Pretreated sludge exhibited faster drying rate and shorter lag-time for methane production. Incineration residua of dewatered sludge could be re-coupled with S2O82− as the conditioner to enhance sludge dewaterability, thereby reducing the chemical input and disposal cost. This study provides a novel, self-sustainable strategy for sludge management, reutilization and final safe disposal.

Underlying mechanism of continuous nano zero-valent iron (nZVI) supply in functional microbes enrichment and methane bioconversion of waste activated sludge were investigated in a lab-scale continuous stirred tank reactor (CSTR). Results indicated that methane productivity strongly relied on nZVI dosage (R = 0.998, p (0.05)

This study investigated the potential and possibility of three mixed microalgae consortia collected from various ecological niches towards bioenergy production of H 2 and CH 4 in batch experiments under mesophilic conditions. Three different consortia collected from wastewater treatment plant, in an open pond system and in the lake bed possess different compositions and characteristics during their growth under a light intensity of 8000 lux and are referred as OP1, OP2 and LB. After 40 days of cultivation, collected wet biomass is directly used for H 2 and CH 4 fermentation and the results indicated that, consortia OP1 is good for H 2 production whereas consortia OP2 and LB showed nearly the similar CH 4 production performances. Peak hydrogen production rate (HPR) and methane production rate (MPR) were achieved as 289 mL/L-d and 97 mL/L-d, respectively from consortia OP1 and OP2. The energy production from this process could significantly contribute towards CO 2 emission reduction. Besides, this approach could be helpful in choosing the consortia towards which kind of biofuel (either H 2 or CH 4 ) production.

The dispersion of granules in upflow anaerobic sludge blanket (UASB) reactor represents a critical technical issue in methanolic wastewater treatment. In this study, the potentials of coupling a microbial electrolysis cell (MEC) into an UASB reactor for improving methanolic wastewater biodegradation, long-term process stability and biomethane recovery were evaluated. The results indicated that coupling a MEC system was capable of improving the overall performance of UASB reactor for methanolic wastewater treatment. The combined system maintained the comparatively higher methane yield and COD removal efficiency over the single UASB process through the entire process, with the methane production at the steady-state conditions approaching 1504.7 ± 92.2 mL-CH4 L−1-reactor d−1, around 10.1% higher than the control UASB (i.e. 1366.4 ± 71.0 mL-CH4 L−1-reactor d−1). The further characterizations verified that the input of external power source could stimulate the metabolic activity of microbes and reinforced the EPS secretion. The produced EPS interacted with Fe2+/3+ liberated during anodic corrosion of iron electrode to create a gel-like three-dimensional [-Fe-EPS-]n matrix, which promoted cell-cell cohesion and maintained the structural integrity of granules. Further observations via SEM and FISH analysis demonstrated that the use of bioelectrochemical stimulation promoted the growth and proliferation of microorganisms, which diversified the degradation routes of methanol, convert the wasted CO2 into methane and accordingly increased the process stability and methane productivity.

Microbial fuel cells (MFCs) are biocatalyzed systems which can drive electrical energy by directly converting chemical energy using microbial biocatalyst and are considered as one of the important propitious technologies for sustainable energy production. Much research on MFCs experiments is under way with great potential to become an alternative to produce clean energy from renewable waste. MFCs have been one of the most promising technologies for generating clean energy industry in the future. This article summarizes the important findings in electro-active biofilm formation and the role of exo-electrogens in electron transfer in MFCs. This study provides and brings special attention on the effects of various operating and biological parameters on the biofilm formation in MFCs. In addition, it also highlights the significance of different molecular techniques used in the microbial community analysis of electro-active biofilm. It reviews the challenges as well as the emerging opportunities required to develop MFCs at commercial level, electro-active biofilms and to understand potential application of microbiological niches are also depicted. Thus, this review is believed to widen the efforts towards the development of electro-active biofilm and will provide the research directions to overcome energy and environmental challenges.

Excess consumption of energy by humans is compounded by environmental pollution, the greenhouse effect and climate change impacts. Current developments in the use of algae for bioenergy production offer several advantages. Algal biomass is hence considered a new bio-material which holds the promise to fulfil the rising demand for energy. Microalgae are used in effluents treatment, bioenergy production, high value added products synthesis and CO2 capture. This review summarizes the potential applications of algae in bioelectrochemically mediated oxidation reactions in fully biotic microbial fuel cells for power generation and removal of unwanted nutrients. In addition, this review highlights the recent developments directed towards developing different types of microalgae MFCs. The different process factors affecting the performance of microalgae MFC system and some technological bottlenecks are also addressed.

The start-up of microbial electrohydrogenesis cells (MECs) is a key-step to realize efficient biohydrogen generation and adequate, long-term operation. This review paper deals with the lessons and experiences reported on the most important aspects of H 2 producing MEC start-up. The comprehensive survey covers the assessment and discussion of the main influencing factors and methods (e.g. inocula selection, enrichment, acclimation, operating conditions and cell architecture) that assist the design of MECs. This work intends to be a helpful guide for the interested readers about the strategies employed to successfully establish microbial electrochemical cells for sustainable biohydrogen production.

Microbial fuel cells (MFCs) the most extensively described bioelectrochemical systems (BES), have been made remarkable progress in the past few decades. Although the energy and environment benefits of MFCs have been recognized in bioconversion process, there are still several challenges for practical applications on large-scale, particularly for relatively low power output by high ohmic resistance and long period of start-up time. Anodes serving as an attachment carrier of microorganisms plays a vital role on bioelectricity production and extracellular electron transfer (EET) between the electroactive bacteria (EAB) and solid electrode surface in MFCs. Therefore, there has been a surge of interest in developing advanced anodes to enhance electrode electrical properties of MFCs. In this review, different properties of advanced materials for decorating anode have been comprehensively elucidated regarding to the principle of well-designed electrode, power output and electrochemical properties. In particular, the mechanism of these materials to enhance bioelectricity generation and the synergistic action between the EAB and solid electrode were clarified in detail. Furthermore, development of next generation anode materials and the potential modification methods were also prospected.

The stabilization and disposal of the large amounts of sewage sludge pose a worldwide challenging problem. To solve this problem, the technical feasibility of coupled alkali-microwave–H2O2–oxidation pretreatment with in-situ bioelectrochemical regulation was used for enhancing sludge biodegradability and methane productivity. The optimum condition of the combined pretreatment was pH 10.0 ± 0.1, microwave 700 W and H2O2 0.4 g/g TS. In this case, soluble chemical oxygen demand (SCOD) of pretreated sludge was increased from initial 330.9 ± 10.0 to 3328.8 ± 49.6 mg/L. The highest accumulative methane yield of 234.3 mL CH4/g VS was obtained for pretreated sludge at the cathodic potential of −0.8 V vs. Ag/AgCl, increasing by 4.3-, and 1.9-fold compared with the raw and pretreated sludge, respectively. The microbial community analysis further provided a compelling evidence that bioelectrochemical regulation stimulated the growth of the functional microorganisms, especially in protein-degrading (Firmicutes), polysaccharides-utilizing (Chloroflexi), electroactive (Geobacter, and Desulfomicrobium) and methane-producing (Methanobacterium) microorganisms. In addition, pH adjustment of pretreated sludge by addition of H2SO4 could further enrich the abundance of microbial community and build a strong syntrophic interaction, accordingly provoking the hydrolysis and subsequent methane production. The result of this study will contribute to the establishment of an efficient sludge stabilization and bioenergy recovery strategy.

Anaerobic membrane bioreactor (AnMBR) has been applied as a promising technology for treating a variety of industrial wastewaters. Nevertheless, the potential of AnMBR for methanolic wastewater treatment is still not well recognized. In this study, a lab-scale AnMBR fed with low-strength methanolic wastewater was operated for 166 days with stepwise decreased HRT, and the roles of colloidal particles and soluble biopolymers in membrane fouling behaviors were elucidated comprehensively. The results showed that AnMBR showed the desirable performance and process stability with total chemical oxygen demand removal of 89.8 ± 1.1% and the highest methane production rate of 5.49 L/L-reactor/d at organic loading rate of 20.00 g-COD/L-reactor/d and hydraulic retention time of 18 h. The serious membrane fouling was observed after a period of operation at low HRT or high OLR due to the production of colloidal particles and the liberation of soluble biopolymers. Decreased particle size, and increased adhesion forces of gel-like flocs caused by the secretion of hydrophobic protein-bearing biopolymers accelerated the deposition of foulants and the formation of cake layer, inducing the easily mitigated membrane fouling. Further observations proved that the main bioconversion pathway of methanolic wastewater to biomethane was methylotrophic methanogenesis, followed by acetotrophic/hydrogenotrophic processes. Collectively, although the membrane fouling cannot be eliminated, this research confirmed the technical feasibility of AnMBR for methanolic wastewater treatment in real-world applications.

Nowadays there is a huge demand for new and sustainable technologies aiming the reduction of the greenhouse gas, in particular carbon dioxide emission. In this work, enzymatically-boosted supported ionic liquid membrane (EB-SILM) was developed to permeate carbon dioxide with improved efficiency. Firstly, the selected biocatalyst, carbonic anhydrase (CA) was prepared and purified from spinach, a cheap plant biomass containing the enzyme of our interest. Afterwards, the CA enzyme preparation was used for SILM fabrication in order to test the properties towards enhanced carbon dioxide permeation over CH 4 , H 2 and N 2 . The results indicate basically that EB-SILMs possess an increased ability to permeate CO 2 in comparison with enzymeless controls and therefore, may be viewed as a promising approach e.g. towards enhanced CO 2 -capture bioprocesses.

The use of liquid fraction of pressed municipal solid waste (LPW) for hydrogen production was evaluated via electrohydrogenesis in a single-chamber microbial electrolysis cell (MEC). The highest hydrogen production (0.38 ± 0.09 m3 m−3 d−1 and 30.94 ± 7.03 mmol g−1 CODadded) was achieved at an applied voltage of 3.0 V and pH 5.5, increasing by 2.17-fold than those done at the same voltage without pH adjustment (pH 7.0). Electrohydrogenesis was accomplished by anodic oxidation of fermentative end-products (i.e. acetate, as well as propionate and butyrate after their acetification), with overall hydrogen recovery of 49.5 ± 11.3% of CODadded. These results affirm for the first time that electrohydrogenesis can be a noteworthy alternative for hydrogen recovery from LPW and simultaneous organics removal. Electrohydrogenesis efficiency of this system has potential to improve provided that electron recycling, electromethanogenesis and deposition of non-conductive aggregates on cathode surface, etc. are effectively controlled.

Continuous primary energy consumption has motivated the scientists of the world to search for renewable energy sources that could substitute fossil fuels. Microalgae can be an alternative substrate for renewable energy recovery. In this study, biochemical methane potential (BMP) assays were used as a tool to examine the technical potential of methane production from microalgae (MA) through co-digesting with food waste (FW) at different MA: FW ratios on volatile solids (VS). Three mathematical models (i.e. first-order kinetic, modified Gompertz, and Cone models) were also utilized to fit the experimental data, with the purpose of elucidating the biological degradation and principle kinetics of the co-digestion. The results showed that supplementing food waste significantly improved microalgae digestion performance, with the highest methane yield of 639.8 ± 1.3 mL/g VSadded obtained at a MA:FW ratio of 0.2:0.8, which was 4.99-fold increase with respect to that (106.9 ± 3.2 mL/g VSadded) of the microalgae alone. Cone model had the best fitness and reliability to the experimental results and could describe the co-digestion kinetics more reasonably. Parameter analysis and synergistic impact evaluation together revealed that the improvement in methanogenesis potential (fd) caused by the synergy of co-digestion might be the fundamental cause for the upgraded methane production. These results validated the superiority of co-digestion as a step towards maximizing methane production from microalgae, aiding the development of multi-biomass co-disposal and ultimately bioenergy recovery techniques.

Hydrogen production from mixed microalgae biomass, predominantly containing Scendesmus and chlorella species, was investigated with a focus on enhancement strategies, in particular (i) pH control (at 5.5) and (ii) methanogenic inhibitor (BESA) addition along with pH control at 5.5. The results obtained showed that the later condition remarkably increased the performances. This was mainly ascribed to the occurrence of a suitable environment for the hydrogen producers to perform actively. Hydrogen production under these conditions (i.e., both pH 5.5 and pH5.5+BESA) was significantly higher than that of the control experiment. Using the pH control at 5.5 and BESA addition, peak hydrogen production rate (HPR) and hydrogen yield (HY) were attained as 210 mL/L/d and 29.5 mL/g VSadded, respectively. This improvement was nearly 3-folds higher compared with the control experiment with an HPR of 62 mL/L/d and an HY of 9.5 mL/g VSadded.

Sulfate radicals are well-known for their strong oxidation potential (2.60 V), their high reaction rate (106–109 M/s) and longer life span (t1/2 = 30–40 μs). Owing to the revealed impact it is accomplished by oxidizing, many pesticides, dye, and heavy organic substances such as waste activated sludge (WAS) in a very short time duration. In this review, current research exploration, novel encounters, long pathway of sulfate radicals travelling in environmental management and commercial implementation prominence to persulfate oxidation process are abridged and revealed. A broad evaluation analysis intended in this review established its mesmerizing ascendancies over the conventional persulfate oxidation process with respect to rapid, more efficient, broad pH range and outstanding reaction. Regardless of the abundant improvement attained earlier, there are still several challenges for persulfate activation through transition metals such as heavy metal deposit, metal leaching, removal of sulfate, reusability, etc. To tackle the overhead complications, a novel scenario catalyst with a non-radical pathway, i.e. carbon-grounded catalyst (activated carbon, graphene oxide, biochar, etc.) is under extensive trials. The challenge and practical problems faced in the course of sulfate radical usage are deliberated and the upcoming need for a study to promote full-scale implementations of those approaches are proposed.

Thermal hydrolysis (TH) was integrated into an anaerobic membrane bioreactor (AnMBR) to stimulate sludge bioconversion and methane production. Sludge solubilization degree and methane productivity increased with TH temperature. The optimal performance was observed at 125 °C, with a 2.56-time increase in soluble chemical oxygen demand (1116.2 ± 62 mg/L). Methane production rate approached 73.2 ± 7.5 mL/Lreactor/d, rising by 2.96 times. Integration of TH effectively mediated membrane fouling, inducing a stable membrane flux of 10.8 ± 0.5 L/m2/h and low transmembrane pressure (TMP, ≤4.7 kPa). Cake layer deposited on the membrane surface accounted for 66.1 ± 1.0% of total resistance, with proteins and polysaccharides as the main contributors to membrane fouling (or increased TMP) (protein: Rp = 0.89, p0.05 = 0.04; polysaccharide: Rp = 0.99, p0.05 = 0.01). 16s rRNA gene analysis demonstrated that utilization of TH could regulate microbial diversity and enhance the proliferation of organics-degrading bacteria (i.e. Bacteroidetes, Firmicutes, etc.) and methane-producing methanogens (i.e. Methanosaeta, Methanobacterium, etc.), which accelerated the biodegradation of organics while alleviating membrane fouling and upgrading methane production. This study demonstrated the great potential of the combined TH-AnMBR system as a new strategy in promoting sludge solubilization, methane bioconversion and membrane fouling mitigation.

Highlights • Anaerobic co-digestion of grease trap waste and food waste is feasible. • Higher methane yield was achieved in the co-digestion compared with mono-digestion. • Biogas production decreased due to lipid accumulation at high lipid concentrations. • Temperature and mixing frequency play a key role in the lipid distribution. • Lipid concentration under 40% is recommended in the co-digestion., To investigate the influence of lipid concentration (of total solids, w/w) on anaerobic treatment of food waste under thermophilic condition, a siphon-driven self-agitated anaerobic reactor was operated for 220 days. The average lipid concentration was changed from 12.8% to 59.3% (w/w) step by step. The gas production rate increased from 1.97 to 2.31 L/L/d with lipid concentration increased from 12.8% to 19.7% (w/w), whereas decreased sharply to 0.78 L/L/d when the concentration further increased to 59.3% (w/w). The COD recovery from output at different lipid concentration was analyzed in this study. With the concentration increased from 12.8% to 59.3% (w/w), the percentage of COD recovered as methane gas decreased from 80.9% to 35.4%, while the percentage of COD remained in the effluent was also decreased significantly from 15.5% to 2.60%. The lipid concentration under 40% (w/w) was recommended in the co-digestion of food waste and grease trap waste.

Chemical conditioning before mechanical dewatering is an indispensable step to enhance the waste activated sludge (WAS) dewaterability and solid-liquid separation. Feasibility of utilizing Fe(II)/S2O82− oxidation integrated with microwave irradiation (MW) in improving gel-like floc destruction, water seepage and WAS dewaterability was investigated. Comprehensive characterization of the treated WAS was conducted to explore the effects of MW on the catalyzing kinetics of Fe(II)/S2O82− oxidation and reveal the underlying dewatering principle. The results demonstrated that MW-Fe(II)/S2O82–process was more cost-efficient, reagent-saving than single Fe(II)/S2O82− oxidation or MW irradiation in stimulating WAS dewaterability and the optimal conditions were 0.4/0.5 mmol-Fe(II)/S2O82− g−1-TS (total solids) and 500 W with 94.6% capillary suction time (CST) reduction within 120 s of conditioning. Thermal effect of MW reduced the activation energy of S2O82− decomposition and stimulated the generation of more SO4−· while athermal effect could create additional gel-network destruction and cell lysis, which reduced the water-binding energy and induced the seepage of more extracellular polymeric substances (EPS)-bound and cell water. Further analysis via fluorescence excitation-emission matrix combined with parallel factor analysis demonstrated that protein-like, humic- and fulvic-like substances in slime EPS (S-EPS) and loosely bound EPS (LB-EPS) together affected sludge dewaterability. Additionally, the hybrid process could further remove the released COD and ammonia, facilitating the subsequent advanced treatment.

The feasibility of anaerobic co-digestion of waste activated sludge (WAS) and grass Egeria densa ( E.d. ) with four different WAS: E.d. ratios was evaluated for the first time under mesophilic conditions. First-order kinetic, modified Gompertz, and Cone models were employed to reveal the principle kinetics of methane-rich bioenergy production from co-digestion. The results showed that the addition of E.d. could greatly upgrade the sludge methane production, and the highest methane yield averaged 198.32 ± 2.61 mL/g VS added for WAS: E.d. ratio of 0.7: 0.3, 18.72 ± 0.14% higher respective to that of WAS alone (about 176.36 mL/g VS added ). E.d. improved the solubilization of co-substrates and avoided the build-up of volatile fatty acids (VFAs) and free ammonia ([NH 3 ]) and subsequent inhibition, inducing a stable digestion environment. Model simulation indicated Cone model best fitted the actual evolution of methane production, as evidenced by low Root Mean Square Prediction Error (rMSPE) and Akaike’s Information Criterion (AIC), as well as high Pearson’s correlation between the predicated and actual values. Additionally, the parameters analysis highlighted that the co-digestion with E.d . substantially promoted the hydrolysis rate ( k hyd ) and methanogenesis potential ( f d ) of sludge, further explaining the increased solids removal and output of methane. This study demonstrated the sustainability and attractiveness of anaerobic co-digestion of sludge and grass E.d. , providing a sound basis for cost-efficient biomass stabilization and bioenergy recovery.

highlights � Zero valent scrap iron (ZVSI) was used to stimulate the anaerobic digestion of sludge. � The highest methane yield was 174.9 ± 1.5 mL/g VSSfed with ZVSI 1.0 g/g VSS, increasing by 38.3%. � ZVSI enhanced the methanogenesis via acting as electron donors and creating favorable environment. � Responsible mechanisms for enhancing methane formation in the presence of ZVSI were proposed. graphical a bstract abstract The use potential of zero valent scrap iron (ZVSI) for promoting anaerobic production of waste activated sludge (WAS) was assessed. The results indicated that the presence of ZVSI effectively enhanced WAS methane production. Methane yield reached the maximum of 174.9 ± 1.5 mL/g VSSfed with addition of 1.0 g-ZVSI/g VSS, increasing by 38.3%. The corresponding values for sludge hydrolysis (%H), acidogenesis (%A), and methanogenesis rate (%M) increased into 52.6 ± 0.4%, 44.5 ± 2.9% and 40.8 ± 0.3%, respectively, versus 45.2 ± 0.5%, 40.9 ± 2.0% and 29.5 ± 0.2% in the test without ZVSI. Further investigations confirmed that ZVSI could offer electrons (H2/(H)), promote H2 consumption and afford beneficial pH environment for WAS digestion, which stimulated the metabolisms of critical microbes involved in the process and, subsequently accelerated the hydrolysis-acidification-methanation steps of WAS. As a result of this, methane production was upgraded. The superior ability of ZVSI to serve as a source of electron donors will open a new door for WAS treatment. Moreover, ZVSI is less expensive, and convenient to use, providing a cost-efficient alternative for simultaneous energy recovery along with waste iron scrap conservation.

The removal performance of high-concentration H

Pretreatment can be used prior to anaerobic digestion to improve the efficiency of waste activated sludge (WAS) digestion. In this study, electrolysis and a commonly used pretreatment method of alkaline (NaOH) solubilization were integrated as a pretreatment method for promoting WAS anaerobic digestion. Pretreatment effectiveness of combined process were investigated in terms of disintegration degree (DDSCOD), suspended solids (TSS and VSS) removals, the releases of protein (PN) and polysaccharide (PS), and subsequent anaerobic digestion as well as dewaterability after digestion. Electrolysis was able to crack the microbial cells trapped in sludge gels and release the biopolymers (PN and PS) due to the cooperation of alkaline solubilization, enhancing the sludge floc disintegration/solubilization, which was confirmed by scanning electron microscopy (SEM) analysis. Biochemical methane potential (BMP) assays showed the highest methane yield was achieved with 5 V plus pH 9.2 pretreatment with up to 20.3% improvement over the non-pretreated sludge after 42 days of mesophilic operation. In contrast, no discernible improvements on anaerobic degradability were observed for the rest of pretreated sludges, probably due to the overmuch leakage of refractory soluble organics, partial chemical mineralization of solubilized compounds and sodium inhibition. The statistical analysis further indicated that increased solubilization induced by electrical-alkali pretreatment increased the first-order anaerobic hydrolysis rate (khyd), but had no, or very slight enhancement on WAS ultimate methane yield (fd), demonstrating that increased solubilization of WAS from a pretreatment does not always induce an improved anaerobic digestion efficiency.

Potential reuse of dewatered sludge (DS) and municipal solid waste incineration (MSWI) bottom ash as components to develop controlled low-strength material (CLSM) was explored. The effects of DS:MSWI bottom ash:calcium sulfoaluminate (C S ¯ A) cement ratio and thermal treatment of MSWI bottom ash at 900 °C on the mechanical and microstructural properties of CLSM were intensively studied to optimize the process. Results showed DS and MSWI bottom ash could be utilized for making CLSM. The CLSM prepared with milled MSWI bottom ash gave higher unconfined compressive strength (UCS) of 2.0–6.2 MPa following 1 year of curing at 1.0:0.1:0.9 ≤ DS:MSWI bottom ash:C S ¯ A ≤ 1.0:0.8:0.2. However, the corresponding strengths for CLSM containing thermally treated MSWI bottom ash ranged from 0.7 to 4.6 MPa, decreasing 26–65%. The microstructural analysis by X-ray powder diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), as well as scanning electron microscopy (SEM) combined with an energy dispersive X-ray spectroscopy (EDS) revealed that ettringite (C 3 A·3C S ¯ ·H 32 , or AFt) crystals were the most important strength-producing constituents which grew into and filled the CLSM matrix pores. Milled MSWI bottom ash addition favored the formation of highly crystalline AFt phases and accordingly enhanced compressive strengths of CLSM specimens. In contrast, thermal treatment at 900 °C produced new phases such as gehlenite (Ca 2 Al 2 SiO 7 ) and hydroxylapatite (Ca 5 (PO 4 ) 3 (OH)), which deteriorated the pozzolanic activity of bottom ash and caused the strengths to decrease. Leaching tests evidenced that leachable substances from CLSM samples exhibited negligible health and environmental risks. The results of this study suggested that MSWI bottom ash can be effectively recycled together with DS in developing CLSM mixtures with restricted use of C S ¯ A cement.

The activated sludge process of wastewater leads to the production of a substantial amount of excess activated sludge. The increasing interest of Fe(II)-mediated persulfate ( S 2 O 8 2 - ) oxidation in improving sludge dewatering highlights a need to understand their environmental impacts on subsequent treatment, but the potential effects on sludge anaerobic digestion remains unknown. In this study, the response of waste activated sludge anaerobic digestion to a shock load of Fe ( II ) / S 2 O 8 2 - oxidation were investigated. It was observed that total suspended solids (TSS) and volatile suspended solids (VSS) removals were considerably lowered when Fe(II) and S 2 O 8 2 - dosages were greater than 0.8 and 1.0 mmol/g VSS, respectively, while 34.6–60.5% drop in hydrogen sulfide (H 2 S) took place. Degradation of extracellular polymeric substances (EPS) of sludge induced by Fe ( II ) / S 2 O 8 2 - oxidation resulted in their deteriorating protective role on the microorganisms, which may cause the inhibitory effects on the microbial activity, and subsequently reduce digestion efficiency and H 2 S generation. Then, sludge dewaterability during digestion process was investigated. It was found that dewaterability of sludge, firstly improved by Fe ( II ) S 2 O 8 2 - pretreatment, was gradually worsened during subsequent digestion because of slightly increased EPS. The visualization of EPS with three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy further revealed that the discernable rise in tyrosine and tryptophan protein-like substances together contributed to poorer dewaterability.

Microbial electrochemical systems (MESs) are an attracting technology for the disposal of wastewater treatment and simultaneous energy production. In MESs, at the anode microorganisms through the catalytic activity generates electrons that can be converted into electricity or other valuable chemical compounds. Microorganisms those having ability to donate and accept electrons to and from anode and cathode electrodes, respectively are recognized as 'exoelectrogens'. In the MESs, it renders an important function for its performance. In the present mini-review, we have discussed the role of microbiome including pure culture, enriched culture and mixed culture in different BESs application. The effects of operational and biological factors on microbiome development have been discussed. Further discussion about the molecular techniques for the evaluation of microbial community analysis is addressed. In addition different electrochemical techniques for extracellular electron transfer (EET) mechanism of electroactive biofilms have been discussed. This review highlights the importance of microbiome in the development of MESs, effective operational factors for exo-electrogens activities as well their key challenges and future technological aspects are also briefly discussed.

In this work, the performance of dual-chamber microbial fuel cells (MFCs) constructed either with commonly used Nafion ® proton exchange membrane or supported ionic liquid membranes (SILMs) was assessed. The behavior of MFCs was followed and analyzed by taking the polarization curves and besides, their efficiency was characterized by measuring the electricity generation using various substrates such as acetate and glucose. By using the SILMs containing either [C 6 mim][PF 6 ] or [Bmim][NTf 2 ] ionic liquids, the energy production of these MFCs from glucose was comparable to that obtained with the MFC employing polymeric Nafion ® and the same substrate. Furthermore, the MFC operated with [Bmim][NTf 2 ]-based SILM demonstrated higher energy yield in case of low acetate loading (80.1 J g −1 COD in m −2 h −1 ) than the one with the polymeric Nafion ® N115 (59 J g −1 COD in m −2 h −1 ). Significant difference was observed between the two SILM-MFCs, however, the characteristics of the system was similar based on the cell polarization measurements. The results suggest that membrane-engineering applying ionic liquids can be an interesting subject field for bioelectrochemical system research.

Renewable energy recovery from submerged aquatic plants such as Egeria densa ( E. densa ) via continuous anaerobic digestion (AD) represents a bottleneck because of process instability. Here, a single-chamber membrane-free microbial electrolysis cell (MEC) equipped with a pair of Ti/RuO 2 mesh electrodes (i.e. the combined MEC-AD system) was implemented at different applied voltages (0–1.0 V) to evaluate the potential effects of bioelectrochemical stimulation on methane production and process stability of E. densa fermentation. The application of MEC effectively stabilized E. densa fermentation and upgraded overall process performance, especially solid matters removal. E. densa AD process was operated steadily throughout bioelectrochemical process without any signs of imbalance. The solubilization-removal of solid matters and methane conversion efficiency gradually increased with increasing applied voltage, with an average methane yield of approximately 248.2 ± 21.0 mL L −1 d −1 at 1.0 V. Whereas, the stability of the process became worse immediately once the external power was removed, with weaken solid matters removal along with methane output, evidencing the favorable and indispensable role in maintaining process stability. The stabilizing effect was further quantitatively demonstrated by statistical analysis using standard deviation (SD), coefficient of variance (CV) and box-plots. The syntrophic and win–win interactions between fermenting bacteria and electroactive bacteria might have contributed to the improved process stability and bioenergy recovery.