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Hazardous airborne pollutants are frequently emitted to the atmosphere in the form of a gaseous mixture. Air biofilters as the primary biotechnological choice for waste gas treatment (low inlet concentration and high gas flow rate) should run properly when the feed contains multiple pollutants. Simultaneous removal of pollutants in biofilters has been extensively studied over the last 10 years. In this review, the results and findings of the mentioned studies including different groups of pollutants, such as methane (CH

Persistent organic pollutants (POPs) and emerging pollutants (EP) are characterized by their difficulty to be removed through biological oxidation processes (BOPs); they persist in the environment and could have adverse effects on the aquatic ecosystem and human health. The electro-oxidation (EO) process has been successfully used as an alternative technique to oxidize many kinds of the aforementioned pollutants in wastewater. However, the EO process has been criticized for its high energy consumption cost and its potential generation of by-products. In order to decrease these drawbacks, its combination with biological oxidation processes has been reported as a solution to reduce costs and to reach high rates of recalcitrant pollutants removal from wastewaters. Thus, the location of EO in the treatment line is an important decision to make, since this decision affects the formation of by-products and biodegradability enhancement. This paper reviews the advantages and disadvantages of EO as a pre and post-treatment in combination with BOPs. A perspective of the EO scale-up is also presented, where hydrodynamics and the relationship of A/V (area of the electrode/working volume of the electrochemical cell) experiments are examined and discussed.

Sewage from residents and industries is collected and transported to wastewater treatment plants (WWTPs) with sewer networks. The operation of WWTPs results in emissions of greenhouse gases, such as methane (CH4), mostly due to sludge anaerobic digestion. Amounts of emissions depend on the source of influent, i.e. municipal and industrial wastewater as well as sewer systems (gravity and rising). Wastewater is the fifth-largest source of anthropogenic CH4 emissions in the world and represents 7-9% of total global CH4 emissions into the atmosphere. Global wastewater CH4 emission grew by approximately 20% from 2005 to 2020 and is expected to grow by 8% between 2020 and 2030, which makes wastewater an important CH4 emitter worldwide. This review initially considers the emission of CH4 from WWTPs and sewer networks. In the second part, biotechniques available for biodegradation of low CH4 concentrations (

The biodiesel industry produces around 10% w/w crude glycerol. This product has great potential to be valorized to obtain more valuable chemicals. Among all upgrading techniques of no-valuable crude glycerol, the electrochemical conversion is a promising technology. In this study, the green electrochemical conversion of glycerol into value-added products was investigated and optimized in a batch electro-catalytic reactor with a 450 ml working volume using platinum-based electrodes. The redox of glycerol in different solutions was studied by cyclic voltammetric study, the electrode behaviour was explored under chronopotentiometry/chronoamperometry conditions, the kinetics of glycerol consumption was investigated, and the electrode passivation/deactivation was studied by SEM (Scanning Electron Microscope), EDS (energy-dispersive X-ray spectroscopy), and regression models. The maximum non-acidic (dihydroxyacetone/hydroxyacetone or acetol/glycidol) and organic acids (acetic acid, lactic acid, formic acid) formations were optimized using response surface methodology (RSM). The effects of the treatment time, current intensity, type of anode electrode, pH and glycerol concentration were examined. Products concentrations and distributions, reaction mechanism and pathway were also investigated. The results showed that under strong acidic conditions (HCl; pH = 1.4), the highest solvent production (yield of 55%) was achieved using Pt electrode, at a current intensity of 0.31 A (5 mA/cm2).

The study was conducted to investigate the effect of sludge retention on bacterial community composition of membrane bioreactor (MBR) treating synthetic hospital wastewater. The removal of four pharmaceuticals, namely carbamazepine, estradiol, venlafaxine, and ibuprofen in MBR, was studied at varying sludge retention time (SRT) duration of 100, 45, and 15 days and hydraulic retention time (HRT) of 18 h. The removal of ibuprofen and estradiol was constant at varying SRT; however, a negligible removal of carbamazepine and low removal of venlafaxine was observed (

Arsenic presence in the water has become one of the most concerning environmental problems. Electrocoagulation is a technology that offers several advantages over conventional treatments such as chemical coagulation. In the present work, an electrocoagulation system was optimized for arsenic removal at initial concentrations of 100 µg/L using response surface methodology. The effects of studied parameters were determined by a 2

Two biofilters B1 and B2 packed with non-porous inorganic materials were operated for 283 days to eliminate methane (CH4), an important greenhouse gas. The biofilters ran under a constant empty bed residence time of 6 min at CH4 inlet loads of 7–63 g m−3.h−1. B1 was fed with a fresh nutrient solution every day (2 L d−1, flow rate of 1 L min−1) whereas B2 was supplied by a recycled nutrient solution from a 10 L tank. The flexibility of both biofilters were evaluated and compared in absence of nutrient solution for 35 days. Also, the performance of both biofilters under a different nutrient solution addition frequency (0.5 L every 6 h, flow rate of 1 L min−1) was investigated. B2 performed appropriately with an average removal efficiency of 62 ± 3% for an inlet load of 13 g m−3.h−1. B1 showed an average removal efficiency of 66 ± 4% for the same inlet load as B2. Analysis of nutrient solution in the recycle tank showed that the highest nutrient consumption over the time was at an inlet load of 63 g m−3.h−1. B1 and B2 were tolerant to nutrient solution deprivation for 25 and 21 days, respectively. Frequent addition of nutrient solution (0.5 L every 6 h, flow rate of 1 L min−1) improved the performance with corresponding average removal efficiency of 64 ± 4% for B1, compared to 57 ± 4% with nutrient solution addition of 2 L every 24 h with a flow rate of 1 L min−1, while no significant change was observed in B2.

Stable and efficient performance of biological treatment plants requires optimization of treatment system operating parameters. Among the various operating parameters, temperature is an imp...

This study was performed to understand the dynamics of the microbial community of submerged membrane bioreactor during the acclimatization process to treat the hospital wastewater. In this regard, three acclimatization phases were examined using a mixture of synthetic wastewater (SWW) and real hospital wastewater (HWW) in the following proportions; In Phase 1: 75:25 v/v (SWW: HWW); Phase 2: 50:50 v/v (SWW: HWW); and Phase 3: 25:75 v/v (SWW: HWW) of wastewater. The microbial community was analyzed using Illumina high throughput sequencing to identify the bacterial and micro-eukaryotes community in SMBR. The acclimatization study clearly demonstrated that shift in microbial community composition with time. The dominance of pathogenic and degrading bacterial communities such as Mycobacterium, Pseudomonas, and Zoogloea was observed at the phase 3 of acclimatization. This study witnessed the major shift in the micro-eukaryotes community, and the proliferation of fungi Basidiomycota was observed in phase 3 of acclimatization.

International audience; Landfill gases (LFGs) are gaseous emissions containing several harmful compounds such as volatile organic compounds (VOCs), volatile inorganic compounds (VICs) along with methane (CH4) which is a powerful greenhouse gas. In the case of small or older landfills, disposal of LFG can be economically challenging, and a possible solution is biofiltration. Biofiltration of CH4 in the presence of two VOCs was studied, ethylbenzene (EB) for biofilter 1 (BF1) and xylene (X) for biofilter 2 (BF2). Both biofilters were packed with inorganic packing materials and operated with an empty bed residence time (EBRT) of 4.5 min. Methane concentrations varied from 2000 to 10,000 ppmv along with 2 concentrations for both VOCs i.e., 200 and 500 ppmv. In the case of individual VOC's removal, the acclimation period of the microorganisms to EB and X were close to 30 days, indicating a similar adaptation period for X and EB. The addition of CH4 under low inlet concentration of 2000 ppmv had minor effect on VOCs biodegradation such that the average VOC removal efficiencies (REs) remained above 85% for VOC inlet concentrations of 200 ppmv while the average CH4-RE were around 56% in both biofilters. When CH4 inlet concentration increased up to 10,000 ppmv, inhibition became an issue for all VOC concentrations and dropped VOC and CH4-REs down to 80% of their original values. The type and concentration of the VOC played a key role in the intensity of the inhibition. In general, mass transfer was controlling the elimination of the three substrates.

Chemical Coagulation (CC) and Electrocoagulation (EC) processes using iron as coagulating agent were compared while treating aquifer water contaminated by a relatively high concentration of total chromium (CrT = 19.0 mg L−1). A continuous semi-pilot comprising of EC (or CC), followed by flocculation, sedimentation and sand-filtration steps was used to remove CrT from water in order to get drinking water. A ratio of Fe/CrT ≥ 3 was required to reach the best efficiency of treatment using EC and CC. More than 99% of CrT was removed and residual CrT concentration below 0.05 mg L−1 (the limiting value recommended by WHO) could be obtained using the both configurations. However, CC increased the concentration of dissolved solids above the guideline recommended for drinking water.

A combination of processes was required for the proper treatment of old landfill leachate, as it contained a high concentration of pollutants. Humic substances comprised half of the total organic carbon in the raw leachate. Mobility of di(2-ethylhexyl) phthalate (DEHP) and metals could depend on the fate of these substances. Characterization of carbon in raw leachate and effluent of the membrane bioreactor, biofiltration, electro-oxidation, electro-coagulation, and nanofiltration showed complete removal of suspended solids and colloids. Physical processes could not remove the hydrophilic fraction due to its lower molecular weight. However, high removal of the hydrophilic fraction with a molecular weight500 Da was expected in the biological process. In comparison with fulvic acid, larger sized humic acid resulted in complete removal by physicochemical processes. Because of DEHP partitioning on dissolved organic matter, especially on humic substances, its removal could be correlated with total organic carbon removal. Metals such as iron, aluminum, magnesium, and lead showed removal efficiency80% in biological processes. Electro-deposition on the surface of an electrode and precipitation by hydroxide resulted in removal efficiencies90 and50% in electro-coagulation and electro-oxidation, respectively. Rejection of metals by nanofiltration was80% and depended on the size and charge of cation. All in all, a combination of membrane bioreactor and nanofiltration seems to be the optimal process configuration for efficient treatment of old landfill leachate.

An efficient, rapid, ex-situ two phase partitioning detoxification has been developed to reduce inhibitor concentration in biomass hydrolysate and enhance biobutanol production from brewery liquid waste (BLW) and brewery spent grain (BSG). About 80 ± 2.0% extraction of furan derivatives and more than 95 ± 2.0% extraction of phenolic compounds and almost no extraction of reducing sugar from simulated synthetic media as well as real waste hydrolysate have made this method more interesting. Detoxification of brewery liquid waste and brewery spent grain hydrolysate by over liming and charcoal gave biobutanol production of 4.3 g/L, 6.3 g/L and 4.6 g/L, 5.8 g/L respectively. Ex-situ extraction of microbial inhibitors from brewery liquid waste and brewery spent grain hydrolysates using bis (2-ethylhexyl sebacate) as extractant gave biobutanol production of 8.0 g/L and 7.2 g/L respectively. Lower power consumption (0.081 W/L) and reuse of the extracting solvent made this detoxification technique extremely useful for improving production of biobutanol from agro-industrial waste.

Biofiltration followed by electrocoagulation represents an alternative approach to efficiently treat landfill leachates. However, the drawback related to this combination is the formation of ammonium during electrocoagulation used as tertiary treatment. Nitrate can be transformed into ammonium by electro-reduction at the cathode. To overcome this issue, different cathode materials (Fe, Al, SS, Cu, and (Ti/Pt)) were investigated using voltammetry study. Subsequently, electrocoagulation experiments were conducted using landfill leachate pre-treated by biofiltration. The initial concentration of NH 4 in bio-filtrated landfill leachate (BFLL) was very low ( 3 /L was recorded. During electrocoagulation of BFLL, Ti/Pt was more effective to avoid NH 4 formation (1.2 mg N/L), followed by Cu, Al, SS and Fe (10.5, 13.7, 21.0 and 23.5 mg N/L, respectively). In order to further minimize the residual NH 4 concentration using SS cathode, additional experiments were conducted using different electrode areas (27.5, 55, 82.5 and 110 cm 2 ). For a constant current density of 9.1 mA/cm 2 , the residual NH 4 concentration could be optimally diminished by reaching the limiting value recommended (10 mg N/L) and around 61% of refractory chemical oxygen demand (COD) could be removed when 55 cm 2 of SS surface was imposed.

In a view to uplift the biodiesel industry as a major energy carrier, new approach of minimizing the waste and utilizing generated waste needs to be explored. The spent media generated from the co-culture system is cost effective and can serve as renewable supplement for mixed-culture based hydrogen (H 2 ) production and lipid production. Direct conversion of spent media along with crude glycerol (CG) at 20 g/L using heat-shock pretreated wastewater sludge resulted in 38.12 ± 0.84 mmol/L of H 2 . In another approach, the spent media was used as co-supplement along with fresh media at 3:2 for algal growth, resulting in 0.098 ± 0.007 g/L of lipid. The spent media contained dead biomass, residual media nutrients, biomolecules and unutilized glycerol together acting as supplementary source during H 2 and lipid production. According to the closed system results, the H 2 produced (1.47 × 10 9 L of H 2 ) can be converted into energy (1.87 × 10 4 GJ) for electricity (1.77 × 10 4 GJ) and heat (4.32 × 10 3 GJ). The produced H 2 can be used as in-house energy source and the lipids can be used as third generation feedstock. The study explores the utilization of CG and spent media valorization towards an efficient closed system approach for a competitive biodiesel industry.

The properties of eggshells (EGS) as neutralizing and immobilizing agent were investigated for hydrogen (H2) production using crude glycerol (CG) by co-culture system. Eggshells of different sizes and concentrations were used during batch and repeated-batch fermentation. For batch and repeated-batch fermentation, the maximum H2 production (36.53±0.53 and 41.16±0.95mmol/L, respectively) was obtained with the EGS size of 33μm

Using renewable resources to produce chemicals and fuels is increasing. Organic materials from wastes and carbon dioxide are renewable and serve as alternative sources for the production of biofuels and biochemicals. This review provides a survey of solvents and alcohols production from organic matter by microbial electrosynthesis (MES) as a new emerging technology. Using electricity-assisted system in anaerobic microorganisms metabolism (biocatalysts) showed improvement in solvent production compared to conventional fermentation methods. Electrotrophs, the kind of microbial strains which can accept electron from cathode to reduce organic carbon source materials to valuable biochemicals is of interest nowadays. Glucose, glycerol, and other organic compounds could be converted into high value added bio-solvents, such as ethanol, butanol, acetone, and propanediol. This review addresses electricity-driven microbial synthesis of chemicals especially solvents and alcohols by reduction of multi-carbon substrates considering the characteristics and advantages of MES.

Electrocoagulation (EC) was employed to treat residual organic matter from a landfill leachate pretreated by an aerated bio-filter system. Organic matter (humic acids (HA), fulvic acids (FA) and hydrophilic compounds (Hyl)) was fractionated using DAX-8 resin in order to estimate the efficiency of EC on each fraction. Initial characterization of the bio-filtrated landfill leachate showed that humic substances (HA + FA) represented nearly 90% of TOC. The effects of current densities, type of anode (Aluminum versus iron), and treatment time on the performance of COD removal were investigated. The best COD removal performances were recorded at a current density ranging between 8.0 and 10 mA cm−2 during 20 min of treatment time. Under these conditions, 70% and 65% of COD were removed using aluminum and iron electrodes, respectively. The fractionating of organic matter after EC treatment revealed that HA was completely removed using either aluminum or iron anode. However, FA and Hyl fractions were partially removed, with the percentages varying from 57 to 60% and 37–46%, respectively. FA and Hyl removal were quite similar using either aluminum or iron anode. Likewise, a significant decrease in 254-nm absorbance was recorded (UV254 removal of 79–80%) using either type of anode. These results proved that EC is a suitable and efficient approach for treating the residual refractory organic matter from a landfill leachate previously treated by a biological system.

Research on the development of a passive phosphorus entrapment process characterized by biofilters with active wood-based media impregnated with iron hydroxide has been conducted. Phosphorus removal was done by sorption which includes adsorption, exchange of ions and precipitation. Experiments were performed in order to investigate the effect of nitrate, generally present at the end of secondary treatment, on the phosphorus removal performance. Columns tests were performed with anaerobic activated wood-based media and immersion over a period of 150 days. Columns were fed for 32 days with a synthetic solution of 5 mg P L

Hydrogen is an important source of energy and is considered as the future energy carrier post-petroleum era. Nowadays hydrogen production through various methods is being explored and developed to minimize the production costs. Biological hydrogen production has remained an attractive option, highly economical despite low yields. The mixed-culture systems use undefined microbial consortia unlike pure-cultures that use defined microbial species for hydrogen production. This review summarizes mixed-culture system pretreatments such as heat, chemical (acid, alkali), microwave, ultrasound, aeration, and electric current, amongst others, and their combinations to improve the hydrogen yields. The literature representation of pretreatments in mixed-culture systems is as follows: 45⁻50% heat-treatment, 15⁻20% chemical, 5⁻10% microwave, 10⁻15% combined and 10⁻15% other treatment. In comparison to pure-culture mixed-culture offers several advantages, such as technical feasibility, minimum inoculum steps, minimum media supplements, ease of operation, and the fact it works on a wide spectrum of low-cost easily available organic wastes for valorization in hydrogen production. In comparison to pure-culture, mixed-culture can eliminate media sterilization (4 h), incubation step (18⁻36 h), media supplements cost ($4⁻6 for bioconversion of 1 kg crude glycerol (CG)) and around 10⁻15 Millijoule (MJ) of energy can be decreased for the single run.

A set of experiments have been performed to investigate the production of biobutanol as a novel applicable biofuel in a bioelectrolysis cell (BEC). The objective of this work was to understand the mechanism and production rate of the biobutanol by bioelectrosynthesis (BES) using glucose as a substrate. Four main factors, such as electrode materials, substrate concentration, operating temperature, and poised applied voltage were investigated in batch mode to achieve optimum condition for producing maximum butanol by C. pasteurianum in BEC. Standard modified P2 medium (MP2) and standard minimal medium (SMM) were used as fermentation media in batch operation mode. Numerical optimization using central composite design (CCD) method has been used to maximize the butanol production within the experimental range. The maximum butanol production 13.31 g/L was obtained by applying 1.32 V indicating the suitability of this procedure. The results showed that by applying optimum conditions in SMM, the butanol could be enhanced remarkably by electroactive microorganisms in cathode chamber.

Biological treatment of landfill leachate is challenging due to the presence of complex compounds. Here, we treated an old landfill leachate using a membrane bioreactor under the following conditions: 24 h for hydraulic retention, 65 days of sludge retention and an average organic load rate of 1.71 ± 0.16 g/L/day. We observed a high removal of ammonia, phosphorous and some metals. However, removal of organic carbon was incomplete. Despite a major removal of suspended solids, hydrophobic and volatile hydrophilic compounds, high concentration of fulvic acid and hydrophilic contaminants was found in the effluent. Overally, we demonstrate that the presence of humic substances in the effluent is associated with the detection of arsenic, copper and chromium and di(2-ethylhexyl) phthalate.

The presence of recalcitrant dissolved organic matter (DOM) could have a significant effect on the adsorption mechanism and capacity of the sludge for many trace organic carbons (TrOCs). In this study, adsorption of three TrOCs on the sludge and HA was investigated. The results revealed that neutral hydrophilic compounds had an insignificant interaction with both sludge and HA. Positively charged compounds, such as fluoranthene, had more affinity toward HA than sludge with solid/liquid partitioning of 57 and 3.2 L/g, respectively. The adsorption intensity (Kf) of di-2-ethyl hexyl phthalate was 0.5 and 1.13 for the HA and the sludge, respectively. By introducing the sludge to the solution of HA and TrOCs that already reached equilibrium, the sludge adsorption capacity in the presence of HA was investigated. The finding showed that at the lower concentration, adsorption of HA on the sludge was considered as the main removal pathway for the adsorbed emerging contaminants, as 70 mg of HA was adsorbed ...

Butanol produced from renewable feedstock is defined as an emerging biofuel and biochemical. Research efforts made during the last three decades on biochemical production of butanol via conventional ABE (acetone-ethanol-butanol) fermentation has tried to bring biobutanol close to competition with petrobutanol. However, each new effort of development has been often countered by new challenges, confining biobutanol production mostly to the laboratory scale. This review provides a systematic, comparative analysis of different steps in biochemical production of butanol and identifies the counteractive aspects and challenges to overcome. A special emphasis is given on process inhibitors, applied detoxification techniques, chemical supplements and research & development in industry in order to enhance and update ABE fermentation and make it cost effective. Biobutanol future lies in utilization of inexpensive cellulose enriched lignocellulosic hydrolysates and hyper-butanol producing bacteria, combined with specific detoxification techniques and followed by efficient continuous fermentation technologies together with in situ product recovery.

Complex dissolved organic matter (DOM) present in landfill leachate provides reliable media for adsorption of highly hydrophobic contaminants, such as Di 2-ethyl hexyl phthalate (DEHP). In this research, the feasibility of submerged membrane bioreactor (SMBR) for treatment of landfill leachate (LFL) was determined. Later, the operating conditions were optimized for removal of DEHP, COD, NH4(+) and PO4(3-), and finally the effect of bioavailability was examined by introduction of different concentrations of humic acid into the influent. The result revealed that presence of complex agglomerated organic compounds increased the removal efficiency of DEHP and COD, even though DEHP biodegradation rate in sludge dramatically decreased (from 58.8% to 12.8%). MBR retention of different metals in the absence and in the presence of recalcitrant DOM was also studied. Like DEHP, ternary interaction between metals, DOM, and sludge play a pivotal role in their removal efficiency and their concentration in sludge.

This study aims to demonstrate that a combined system of membrane bioreactor (MBR) with electro-oxidation (EO) can be a promising technology to treat compounds such as carbamazepine (CBZ). The MBR showed high capacity to remove the chemical oxygen demand (COD) and low capacity for the degradation (20% of removal), after 120 d of operation; which presumably indicates that CBZ was not toxic for microorganisms, despite its poor degradation. On the other hand, the EO system was capable to completely degrade CBZ (99.99% of removal). In addition, the MBR achieved 83% of conversion efficiency of NH 4 + to NO 3 − or NO 2 − ; and only 20.5% of PO 4 − removal. A toxicity test using Dapnia magna and Vibrio fischeri was carried out. Results indicated that MBR is an efficient method to decrease wastewater toxicity but during electrooxidation treatment higher toxicity was obtained, probably due to the generation of more toxic compounds than the initial pollutants.

A novel upflow microaerobic sludge reactor (UMSR) was constructed to treat manure-free piggery wastewater with high NH4(+)-N concentration and low COD/TN ratio, and the effect and biological mechanism of COD/TN ratio on nitrogen removal were investigated at a constant hydraulic retention time of 8h and 35°C. The results showed that the UMSR could treat the wastewater with a better synchronous removal of COD, NH4(+)-N and TN. The microaerobic UMSR allowed nitrifiers, and heterotrophic and autotrophic denitrifiers to thrive in the flocs, revealing a multiple nitrogen removal mechanism in the reactor. Both the nitrifiers and denitrifiers would be restricted by an influent COD/TN ratio more than 0.82, resulting in a decrease of TN removal in the UMSR. To get a TN removal over 80% with a TN load removal above 0.86kg/(m(3)·d) in the UMSR, the influent COD/TN ratio should be less than 0.70.

Three different inexpensive, abundant agro-industrial wastes: suspended brewery liquid waste (BLW), starch industry wastewater (SIW) and apple pomace ultra-filtration sludge (APUS) have been explored for biobutanol production. Physicochemical analysis of biomass for carbohydrate and nutrient pool, acid hydrolysis, fermentation of raw extracts and hydrolysates by Clostridium beijerinckii NRRL B-466 for ABE production and glucose supplementation to increase butanol production have been studied. The efficiency of the microorganism to produce butanol and other metabolites was explored via carbon balance. Inhibitory effects were minimized by dilution and detoxification method. Pretreated diluted extracts having reducing sugar content of 30 g/L gave optimum butanol production of 4.68 g/L, 1.4 g/L and 1.8 g/L from SIWH, APUSH and BLWH, respectively, as compared to 5.1 g/L obtained from control. Reducing sugar concentration in each diluted extract was increased to 60 g/L by 3% (w/v) glucose supplement and the butanol production was increased to 11.04 g/L (0.27 g/g), 9.3 g/L (0.24 g/g) and 8.06 g/L (0.25), respectively. For SIWH, the maximum yield of butanol (0.27 g/g) and acetone–butanol–ethanol (ABE) (0.46 g/g) was obtained. Thus, production of butanol, with 3% glucose supplement demonstrated that these inexpensive agro-industrial wastes could have important implications in stimulating energy-economics.

Di (2-ethylhexyl) phthalate (DEHP) is the most detected and concentrated plasticizer in environment and wastewaters, worldwide. In this study, different operating parameters such as current intensity, treatment time, type of anodes, and supporting electrolytes were tested to optimized the electro-oxidation process (EOP) for the removal of DEHP in the presence of methanol as a dissolved organic matter. Among the anodes, the Nb/BDD showed the best degradation rate of DEHP, at low current intensity of 0.2 A after 90 min of treatment time with a percentage of degradation recorded of 81 %, compared to 70 % obtained with the Ti/IrO2-RuO2. Furthermore, due to the combination of direct and indirect oxidation, the removal of DEHP in the presence of 1 g/L Na2SO4 was higher than NaBr, even though the oxidant production of NaBr was 11.7 mmol/L against 3.5 mmol/L recorded in the presence of sulfate at 0.5 A and after 60 min of electrolysis time. Under optimal condition (current intensity = 0.5 A, time = 120 min, using Nb/BDD anode and Na2SO4 as supporting electrolyte), the removal of 87.2 % of DEHP was achieved. The total cost of 0.106 US$/m(3) of treated water was achieved based on economical optimization of reactor with current intensity of 0.2 A and 1 g/L Na2SO4.

Biodiesel production across the globe has resulted in a proportional increase of crude glycerol (CG) as waste by-product. Utilization of CG will increase the economic viability of the biodiesel industry. This study compared the energy balance for CG utilization during dark fermentation for hydrogen production with glycerol purification for glycerol. The energy balance for each of the materials used during inoculum, media preparation steps and electricity consumed across both the methods was calculated. The total energy input for glycerol purification (872.39 MJ) was 2.5-fold higher in comparison to maximum total energy input of vegetable feedstock derived CG (344.25 MJ). The market value of pure glycerol is decreasing in comparison to increasing market value of hydrogen as fuel. For efficient utilization of CG, bioconversion to hydrogen production by dark fermentation can be considered an energy efficient and sustainable fuel generation option. The net energy (MJ) for different feedstocks (vegetable source 158.90, multi-feedstock 113.23 and animal waste 83.14) during hydrogen production varied with glycerol content. Performing dark fermentation at ambient conditions and utilization of electricity generated from biogas capture will surely reduce the total energy input. By doing so, the net energy for different feedstocks will have a positive value.

Valorization of crude glycerol (CG), a waste of biodiesel production process, was investigated for increased hydrogen production by co-culture system using Enterobacter aerogenes NRRL B-407 and Clostridium butyricum NRRL B-41122. The ability of E. aerogenes was evaluated as a replacement of expensive reducing agent to maintain anaerobic conditions for the growth of C. butyricum. The co-culture resulted in increased hydrogen production, reaching a maximum of 19.46 ± 0.95 mmol-H2/L-medium in comparison to monoculture of E. aerogenes (15.64 ± 0.47) and C. butyricum (17.44 ± 0.38) in the presence of reducing agent. The effect of inoculum ratio was investigated and hydrogen yield was 0.95 mmol-H2/mol-glycerol at 1:11 inoculum ratio with more than 85% of substrate utilization was comparable to other mixed and co-culture studies. In addition to hydrogen, value added by-products such as 1,3-propandiol, acetic acid, butyric acid and ethanol have also been produced. Co-culture indicated the possibility of v...

Four upflow 0.018 m3 biofilters (3 beds), B-ME, B-200, B-500 and B-700, all packed with inorganic materials, were operated at a constant air flow rate of 0.18 m3 h−1 to eliminate methane (CH4), a harmful greenhouse gas (GHG), and styrene (C8H8), a carcinogenic volatile organic compound (VOC). The biofilters were irrigated with 0.001 m3 of recycled nutrient solution (NS) every day (flow rate of 60 × 10−3 m3 h−1). Styrene inlet load (IL) was kept constant in each biofilter. Different CH4-ILs varying in the range of 7–60 gCH4 m−3 h−1 were examined in B-ME (IL of 0 gC8H8 m−3 h−1), B-200 (IL of 9 gC8H8 m−3 h−1), B-500 (IL of 22 gC8H8 m−3 h−1) and B-700 (IL of 32 gC8H8 m−3 h−1). Finally, the effect of C8H8 on the macrokinetic parameters of CH4 biofiltration was studied based on the Michaelis-Menten model. Average C8H8 removal efficiencies (RE) varying between 64 and 100% were obtained at CH4-ILs increasing from 7 to 60 gCH4 m−3 h−1 and for C8H8-ILs range of 0–32 gC8H8 m−3 h−1. More than 90% of C8H8 was removed in the bottom and middle beds of the biofilters. By increasing C8H8-IL from 0 to 32 gC8H8 m−3 h−1, maximal EC in Michaelis-Menten model and macrokinetic saturation constant declined from 311 to 39 g m−3 h−1 and from 19 to 2.3 g m−3, respectively, which confirmed that an uncompetitive inhibition occurred during CH4 biofiltration in the presence of C8H8.

Chloramphenicol (CAP) is a broad-spectrum antibiotic widely used in animal farming and aquaculture industries. Despite its ban in many countries around the world, it is still used in several developing countries, with harmful effects on the surrounding aquatic environment. In this study, an electrooxidation process using a Ti/PbO anode was used to investigate the degradation of CAP in both synthetic solution and real aquaculture wastewater. A central composite design was used to determine the optimum conditions for CAP removal. Current intensity and treatment time had the most impact on the CAP removal. These two factors accounted for ∼90% of CAP removal. The optimum conditions found in this study were current intensity of 0.65 A, treatment time of 34 min, and CAP initial concentration of 0.5 mg L. Under these conditions, 98.7% of CAP removal was achieved with an energy consumption of 4.65 kW h m. The antibiotic was not present in the aquaculture wastewater, which received 0.5 mg L of CAP and was treated (by electrooxidation) under the optimum conditions. A complete removal of CAP was obtained after 34 min of treatment. According to these results, electrooxidation presents an option for the removal of antibiotics, secondary compounds, and other organic and inorganic compounds from solution.

Brewery liquid waste (BLW), brewery spent grain (BSG), apple pomace solid wastes (APS), apple pomace ultrafiltration sludge (APUS) and starch industry waste (SIW) were evaluated as alternative feedstocks for levulinic acid (LA) production via microwave-assisted acid-catalyzed thermal hydrolysis. LA production of 204, 160, 66, 49 and 12 g/kg was observed for BLW, BSG, APS, APUS, and SIW, respectively, at 140 °C, 40 g/L substrate concentration (SC), 60 min and 2 N HCl (acid concentration). Based on the screening studies, BLW and BSG were selected for optimization studies using response surface methodology. Maximum LA production of 409 and 341 g/kg for BLW and BSG, respectively were obtained at 160 °C, 4.5 M HCl, 85 g/L SC and 27.5 min. Results demonstrated the possibility of using brewery wastes as promising substrates for economical and higher yield production of LA, a renewable platform chemical and versatile precursor for fuels and chemicals.

In this study, a submerged membrane bioreactor was used to study the effect of low and high bisphenol A (BPA) concentration on the sludge biological activity. The pilot was operated over 540 days with hydraulic retention time and solid retention time of 5.5 hours and 140 days, respectively. As a hydrophobic compound, BPA was highly adsorbed by activated sludge. In lower concentrations, the biodegradation rate remained low, since the BPA concentration in the sludge was lower than 0.5 mg/g TS; yet, at an influent concentration up to 15 mg/L, the biodegradation rate was increasing, resulting in 99% BPA removal efficiency. The result for chemical oxygen demand removal showed that BPA concentration has no effect on the heterotrophic bacteria that were responsible for the organic carbon degradation. In higher concentrations, up to 16 mg of BPA was used for each gram of sludge as a source of carbon. However, the activity of autotrophic bacteria, including nitrifiers, was completely halted in the presence of 20 mg/L of BPA or more. Although nitrification was stopped after day 400, ammonia removal remained higher than 70% due to air stripping. Assimilation by bacteria was the only removal pathway for phosphorus, which resulted in an average 35% of P-PO4 removal efficiency.

Biobutanol has conventionally been generated by fermentation of carbohydrates derived from biomass (starch or sugar-based feedstock, such as corn) using Clostridia strains (mainly C. beijerinckii and C. acetobutylicum) under anaerobic conditions in batch mode. Under these premises, it has been tough for the acetone-butanol-ethanol fermentation to compete with petro-butanol production from an energy efficiency and material consumption standpoint. Challenges for butanol production from biomass comprised high cost of feedstock, scarcity of hyper-butanol producing bacteria and low butanol yield, volumetric productivity and titre, leading to high water usage and separation-purification costs. This article is an up-to-date review on several under explored sections, such as optimization of fermenter feed, microbial culture responsible for solvent production (co-culture techniques and electro-biochemical process), latest recovery techniques and the studies integrating in situ continuous fermentation processes. Biobutanol refinery way forward should build upon the use of low-cost lignocellulosic matter and zero cost organic wastes and by-products from food, agriculture, forestry, fermentation and paper industries as feedstock; optimized fermentation of such diversified feed with appropriate hyper-butanol producing strains in biofilm reactors and integration of fermentation step with hybrid high butanol-selective recovery techniques.

In terms of greenhouse gas emission reduction potential, hydrogen is superior to commercial biofuels and fossil fuels because it has high energy density and it generates only water as major emission. Biohydrogen production has additional environmental benefit as different organic wastes can be valorized during the process; however, because of high process cost, its commercial production is not yet there. During dark fermentation, in addition to hydrogen, around 60% of the feedstock may convert to various industrial chemicals including ethanol, 1, 3 propanediol and butyric acid. If these products are not recovered, the liquid waste generated during the process can be used as the feedstock for production of polyhydroxyalkanoates, lipid, methane, hydrogen and electricity. The liquid waste is also a potential substitute of phosphate solubilizing bio-fertilizers. Thus, in this review, biohydrogen production process is evaluated as a potential biorefinery producing biofuels, fine chemicals and biomaterials. The strategy could be useful to reduce overall cost of the process by generating revenue from multiple sources.

Co-substrate utilization of various wastes with complementary characteristics can provide a complete medium for higher hydrogen production. This study evaluated potential of apple pomace hydrolysate (APH) co-fermented with crude glycerol (CG) for increased H2 production and decreased by-products formation. The central composite design (CCD) along with response surface methodology (RSM) was used as tool for optimization and 15 g/L of CG, 5 g/L of APH and 15% (v/v) inoculum were found to be optimum to produce as high as 26.07 ± 1.57 mmol H2/L of medium. The p-value of 0.0017 indicated that APH at lower concentration had a significant effect on H2 production. By using CG as sole carbon source, reductive pathway of glycerol metabolism was favored with 19.46 mmol H2/L. However, with APH, oxidative pathway was favored with higher H2 production (26.07 ± 1.57 mmol/L) and decrease in reduced by-products (1,3-propanediol and ethanol) formation. APH inclusion enhanced H2 production, and decreased substrate inhibition.

SUMMARY Biological hydrogen production from organic wastes is a less expensive, less energy-demanding, and environmentalfriendly process. Pure monoculture delivers low H2 content and low yield; these limitations are overcome by a defined co-culture system, which outperforms mixed cultures with increased H2 yield. The strategies used in co-culture systems for increasing H2 production have been discussed in this review. The strategies include hydrolysis of a variety of complex substrates, such as cellulose, molasses, crude glycerol, and algal biomass into simple fermentable sugars for increased H2 yield by eliminating the use of exogenous enzymes. The strategies can bring geographically distant isolated microorganisms from different sources to coexist for simultaneous utilization of substrate and end metabolites into H2 production of 99.99% purity without the expenses of reducing agents. In the case of maximum hydrogen production using co-culture strategies, Clostridium, Enterobacter, and photo-fermenting bacteria in a consolidated bioprocess system will result in increased H2 yield. A co-culture system is more feasible to achieve theoretical H2 yield with high conversion efficiency of organic wastes, enhance the economic viability of H2 production, provide better effluent treatment quality, and concurrently address the limitations of H2 production. Copyright © 2015 John Wiley & Sons, Ltd.

Hydrogen (H 2 ), a possible future clean energy carrier, requires process-based improvement routes for cutting down the production cost. The impact of nitrogen (N 2 ) sparging on H 2 production during co-culture system of Enterobacter aerogenes and Clostridium butyricum from crude glycerol (CG) was studied to reduce the overall process cost. H 2 production using 1% CG under nitrogen sparged medium before autoclaving resulted in 1.2 mmol-H 2 /mol of glycerol in comparison to 1.5 mmol-H 2 /mol of glycerol without sparging. In the presence of air ranging from 5 mL to 75 mL in the headspace volume, H 2 production increased to a maximum of 26.14 mmol/L with 1.4 g/L of ethanol production. The concentration of 1,3-propanediol with N 2 sparging was around 3.0 g/L and decreased to 0.5 g/L due to presence of 75 mL of air in the headspace. This observation can be attributed to a shift from reductive to oxidative metabolism of glycerol. A process-based improvement strategy to optimize H 2 formation resulted in metabolic pathway shift from reductive to oxidative with increase in H 2 production. Synergistic influence of co-culture system in absence of expensive reducing agent and without nitrogen sparging step can offer a better process-based economic strategy for H 2 production, minimize the metabolite production and increase field-scale application of biodiesel plant.

Owing to CO2-free emission, hydrogen is considered as a potential green alternative of fossil fuels. Water is the major emission of hydrogen combustion process and gravimetric energy density of hydrogen is nearly three times more than that of gasoline and diesel fuel. Biological hydrogen production, therefore, has commercial significance; especially, when it is produced from low-cost industrial waste-based feedstock. Light independent anaerobic fermentation is simple and mostly studied method of biohydrogen production. During hydrogen production by this method, a range of organic acid byproducts are produced. Accumulation of these byproducts is inhibitory for hydrogen production as it may result in process termination due to sharp decrease in medium pH or by possible metabolic shift. For the first time, therefore, a two-phase anaerobic bioreactor system has been reported for biohydrogen production which involves in situ extraction of different organic acids. Among different solvents, based on biocompatibility oleyl alcohol has been chosen as the organic phase of the two-phase system. An organic:aqueous phase ratio of 1:50 has been found to be optimum for hydrogen production. The strategy was capable of increasing the hydrogen production from 1.48 to 11.65 mmol/L-medium.

High process costs arising from expensive media components, hydrogen partial pressure buildup in the head-space of the reactor, sharp decrease in medium pH due to accumulation of organic acids, substrate inhibition, as well as loss of biomass due to short hydraulic retention times are the major bottlenecks of fermentative hydrogen production. Therefore, the purpose of the present investigation was to develop a process to deal with all these problems at a time. The proposed approach demonstrates enhanced hydrogen production by a low cost process involving crude glycerol (CG), the waste from the biodiesel production process, as the only feedstock. This semi-continuous type of fermentation carried out in a 7.5 L bioreactor helped to eliminate substrate inhibition with no compromise in cumulative hydrogen production. By controlling product inhibition and the negative effect of by-product accumulation, as well as by preventing the loss of active biomass, a production of 5.18 L-H2 per L-medium has been achieved. This amount is higher than the 2.02 to 2.68 L-H2 per L-medium previously reported for CG bioconversion. Reduction of feed CG concentration from 120 g L−1 to 60 g L−1 was found to improve the glycerol utilization from 65% to 91%.

In coming years, the generation of organic wastes will exceed 250 billion tonnes worldwide. The organic wastes offer plentiful source of readily available and inexpensive substrates for fermentative hydrogen production. A sustainable approach for hydrogen production from various methods, such as photo-, dark fermentation and sequential two-stage has significant advantages to complement traditional process. During hydrogen fermentation, defined, well-characterized and composite microorganisms are studied. Substantial research efforts have been carried out to increase hydrogen production by using co-culture system, which offers advantage of increased H2 yield and production rate in comparison with mono-culture. The concept of co-culture system is a simple step of mixing different microbial strains for improving the individual properties that other strain lacks. Co-culture system is cost-effective, which potentially eliminates pretreatment step and avoids the use of expensive reducing agent. By eliminating t...

Landfill leachates are known for their high and complex composition of organic, inorganic and microbial pollutants. As a result, it is quite challenging to treat these effluents by using only one treatment process. A combining approach is generally required to treat efficiently these wastewaters and comply with the discharge standards. In this present study, electrocoagulation (EC) and biofiltration (BF) processes were sequentially used to treat landfill leachate. EC process has been able to remove 37 ± 2% of the initial total COD. A fractionation of organic compounds showed that EC was particularly efficient to remove insoluble COD and humic acids. In addition, other pollutants such as turbidity, true color, Zn and phosphorus were significantly reduced by EC with 82 ± 2.7%, 60 ± 13%, 95 ± 2.6% and 82 ± 5.5% of removal respectively. The subsequent treatment by BF process led to completely removal of ammonia pollution (>99% of NH4 removal) and a partial removal of dissolved organic compounds (42 ± 7% of COD removal). The hybrid process EC/BF could form the basis of a process capable of removing organic and inorganic pollutants from many refractory wastewaters (mature landfill leachates, industrial and municipal wastewaters).