Treatment of landfill leachate using microbial fuel cells: alternative anodes and semi-continuous operation

Application of a membrane-less air cathode microbial fuel cell to treat municipal waste composting leachate

The adverse effects of high strength wastewaters on the microbial activities have created a challenge to biological treatments. Microbial fuel cell has been considered as a promising process because the electrical potential generation can stimulate microorganisms and overcome the inhibitory effect. However, several issues (e.g., scalability, high costs and maintenance) have prevented the process from the industrial applications. Elimination of the proton exchange membrane has been suggested as a remedy to the mentioned problems. In this work, a membrane-less microbial fuel cell was modified by putting the cathode within a thin sand layer (instead of the proton exchange membrane) to treat a high strength wastewater sample. The influences of the feed organic load and time of treatment in the modified system were studied in batch and continuous operations. It was revealed that the batch operation efficiency was higher for the lower feed loadings as a 5-day batch treatment removed 66 ± 4% of the 15,000 ± 500 mg/L initial chemical oxygen demand while the continuous process efficiency with 9-day hydraulic residence time was slightly more than 50%. However, the efficiency of the continuous operation for treatment of higher initial loading values was better than the batch mode with the removal efficiency of 41 ± 2% versus 12 ± 2% for a more concentrated leachate feed (45,000 ± 1000 mg/L). Finally, it was disclosed that the modified membrane-less MFC employed in this work can be effective in treatment of high strength wastewaters in larger scales with lower costs.

Concentrations of perfluoroalkyl and polyfluoroalkyl substances before and after full-scale landfill leachate treatment

Many consumer and industrial products, industrial wastes and dewatered sludge from municipal wastewater treatment plants containing per- and polyfluoroalkyl substances (PFAS) are disposed of in landfills at the end of their usage, with PFAS in these products leached into landfill leachates. On-site leachate treatment is one possible method to reduce PFAS in leachates. Many landfills are equipped with on-site leachate treatment systems, but few full-scale facilities have been systematically evaluated for PFAS concentration changes. The objective of this study was to evaluate a cross-section of full-scale on-site landfill treatment systems to measure changes in PFAS concentrations. Leachate samples were collected before and after treatment from 15 facilities and were evaluated for 26 PFAS, including 11 perfluoroalkyl carboxylic acids (PFCAs), 7 perfluoroalkyl sulfonic acids (PFSAs), and 8 perfluoroalkyl acid precursors (PFAA-precursors). Transformation of precursors was evaluated by the total oxidizable precursor (TOP) assay. Results showed no obvious reductions in total measured PFAS (∑26PFAS) for on-site treatment systems including ponds, aeration tanks, powdered activated carbon (PAC), and sand filtration. Among evaluated on-site treatment systems, only systems fitted with reverse osmosis (RO) showed significant reductions (98-99 %) of ∑26PFAS in the permeate. Results from the TOP assay showed that untargeted PFAA-precursors converted into targeted short-chain PFCAs increasing ∑26PFAS in oxidized samples by 30 %, on average. Overall, results of this study confirm the efficacy of RO systems and suggest the presence of additional precursors beyond those measured in this study.

Effects of carbon source on electricity generation and PAH removal in aquaculture sediment microbial fuel cells

Sediment microbial fuel cells (SMFCs) have been used for treating pollutants in sediment or overlying water. This study investigated the feasibility of constructing SMFCs under aquaculture conditions by employing indigenous carbohydrates as substrates to enhance the removal efficiency of polycyclic aromatic hydrocarbons (PAHs) in sediment, as well as the correlation between PAHs removal and electricity generation in SMFCs. The results showed that adding glucose could allow SMFCs to generate more electrical power and increase the removal efficiency of PAHs (by 57.2% for naphthalene, 41.3% for acenaphthene, and 36.5% for pyrene). In addition, starch enhanced PAHs removal by 49.9%, 35.8%, and 31.2%, respectively, whereas cellulose enhanced removal by 44.3%, 29.3%, and 26.9%, respectively. Pearson correlation coefficients between the level of electrical power generated and the removal masses of the three PAHs were 0.485, 0.830**, and 0.851**. Thus, the use of SMFCs could be an effective approach for PAH treatment in aquaculture, and the electrical power generated could be used as an in-situ indicator for the biodegradation rate of SMFCs.

Synchronous bio-degradation and bio-electricity generation in a Microbial Fuel Cell with aged and fresh leachate from the identical subtropical area

Seasonal leachate from both sealed and operating landfill in the identical district were employed as the sole substrate in the Microbial Fuel Cell (MFC) to evaluate the power output performance and aqueous organic waste disposal. The electrical performance was characterized to study the power generation, while the Chemical Oxygen Demand (COD) removal ratio and Coulombic Efficiency (CE) were calculated to illustrate the substrate disposal effect. In addition, Scanning Electron Microscope (SEM) on the operated anode was conducted to preliminarily explain the microbial community difference, and the phylogenetic tree constructed on the cultivated microorganism was an insight into the dominant bacteria suitable for leachate degradation. It was found that the MFCs inoculated with seasonal leachate from both sealed and operating landfill could generate electricity successfully. Although the fresh leachate-inoculated MFCs had better electrical output performance (22.7-25.6 W/m³ versus 6.61-7.48 W/m³) and COD removal efficiency (55.8%∼61.7% versus 47.7%∼51.4%), the CEs were only 4.3%∼7.6%, which were lower than the aged leachate inoculated group (5.9%∼11.3%). Based on the SEM images and the phylogenetic tree of the operated anode, the composition impacts on the microbial community and power output performance were verified, which was instructive for the leachate disposal in the MFC.

Extractive membrane bioreactor to detoxify industrial/hazardous landfill leachate and facilitate resource recovery

Landfill leachate is a highly polluted and toxic waste stream harmful to the environment and human health, its biological treatment, even if challenging, offers the opportunity of recovering valuable resources. In this study, we propose the application of an extractive membrane bioreactor equipped with a polymeric tubing, made of Hytrel, as an innovative device able to remove specific organic toxic compounds of the leachate and, at the same time, to produce an effluent rich in valuable chemicals suitable for recovery. The leachate treatment consists in a two-step process: the extraction of specific toxic compounds through the polymeric tubing based on the affinity with the polymer, and their subsequent biodegradation in controlled conditions in the bulk phase of the extractive membrane bioreactor, thus avoiding the direct contact of the microbial consortium with the toxic leachate. Three synthetic streams simulating leachates produced by landfills of typical industrial/hazardous waste, mixed municipal and industrial solid waste, and oil shale industry waste, whose toxic fraction is mainly constituted by phenolic compounds, have been tested. Successful performance was achieved in all the tested conditions, with high removal (≥98%) and biodegradation efficiencies (89-95%) of the toxic compounds. No mass transfer limitations across the tubing occurred during the operation and a marginal accumulation (in the range of 4-7%) into the polymer has been observed. Furthermore, volatile fatty acids and inorganic compounds contained in the leachates were fully recovered in the treated effluent. Feasibility study confirmed the applicability of the proposed bioreactor as a powerful technology able to achieve high toxic removal efficiency in leachate treatment and facilitate resource recovery.

Use of Biochar-Based Cathodes and Increase in the Electron Flow by Pseudomonas aeruginosa to Improve Waste Treatment in Microbial Fuel Cells

In this paper, we tested the combined use of a biochar-based material at the cathode and of Pseudomonas aeruginosa strain in a single chamber, air cathode microbial fuel cells (MFCs) fed with a mix of shredded vegetable and phosphate buffer solution (PBS) in a 30% solid/liquid ratio. As a control system, we set up and tested MFCs provided with a composite cathode made up of a nickel mesh current collector, activated carbon and a single porous poly tetra fluoro ethylene (PTFE) diffusion layer. At the end of the experiments, we compared the performance of the two systems, in the presence and absence of P. aeruginosa, in terms of electric outputs. We also explored the potential reutilization of cathodes. Unlike composite material, biochar showed a life span of up to 3 cycles of 15 days each, with a pH of the feedstock kept in a range of neutrality. In order to relate the electric performance to the amount of solid substrates used as source of carbon and energy, besides of cathode surface, we referred power density (PD) and current density (CD) to kg of biomass used. The maximum outputs obtained when using the sole microflora were, on average, respectively 0.19 Wm−2kg−1 and 2.67 Wm−2kg−1, with peaks of 0.32 Wm−2kg−1 and 4.87 Wm−2kg−1 of cathode surface and mass of treated biomass in MFCs with biochar and PTFE cathodes respectively. As to current outputs, the maximum values were 7.5 Am−2 kg−1 and 35.6 Am−2kg−1 in MFCs with biochar-based material and a composite cathode. If compared to the utilization of the sole acidogenic/acetogenic microflora in vegetable residues, we observed an increment of the power outputs of about 16.5 folds in both systems when we added P. aeruginosa to the shredded vegetables. Even though the MFCs with PTFE-cathode achieved the highest performance in terms of PD and CD, they underwent a fouling episode after about 10 days of operation, with a dramatic decrease in pH and both PD and CD. Our results confirm the potentialities of the utilization of biochar-based materials in waste treatment and bioenergy production.

Review on upgrading organic waste to value-added carbon materials for energy and environmental applications

Value-added materials such as biochar and activated carbon that are produced using thermo-chemical conversion of organic waste have gained an emerging interest for the application in the fields of energy and environment because of their low cost and unique physico-chemical properties. Organic waste-derived materials have multifunctional abilities in the field of environment for capturing greenhouse gases and remediation of contaminated soil and water as well as in the field of energy storage and conversion. This review critically evaluates and discusses the current thermo-chemical approaches for upgrading organic waste to value-added carbon materials, performance enhancement of these materials via activation and/or surface modification, and recent research findings related to energy and environmental applications. Moreover, this review provides detailed guidelines for preparing high-performance organic waste-derived materials and insights for their potential applications. Key challenges associated with the sustainable management of organic waste for ecological and socio-economic benefits and potential solutions are also discussed.

Simultaneous energy harvest and nitrogen removal using a supercapacitor microbial fuel cell

The insufficient removal of pollutants and bioelectricity production have become a bottleneck for high-concentration saline wastewater treatment through microbial fuel cell (MFC) technology. Herein, a novel supercapacitor MFC (SC-MFC) was constructed with carbon nanofibers composite electrodes to investigate pollutant removal ability, power generation, and electrochemical properties using real landfill leachate. The possible extracellular electron transfer and nitrogen element conversion pathways in the bioanode were also analyzed. Results showed that the SC-MFC had higher pollutant removal rates (COD: 59.4 ± 1.2%; NH₄⁺-N: 78.2 ± 1.6%; and TN: 77.8 ± 1.2%), smaller internal impedance R_t (∼6 Ω), higher exchange current density i₀ (2.1 × 10^-4 A cm^-2), and a larger catalytic current j₀ (704 μA cm^-2) with 60% leachate than those with 10% and 20% leachate, resulting in a power output of 298 ± 22 mW m^-2. Ammonium could be incorporated by chemoautotrophic bacteria to produce organic compounds that could be further utilized by heterotrophs to generate power when biodegradable organic matters are depleted. Three conversion pathways of nitrogen might be involved, including NH₄⁺ diffusion from anode to cathode chamber, nitrification, and the denitrification process. Additionally, cyclic voltammetry tests showed that both the direct electron transfer (DET) and the mediator electron transfer in bioanode were involved and dominated by DET. The microbial analysis revealed that the bioanode was dominated by salt-tolerant denitrifying bacteria (38.5%), which was deduced to be the key functional microorganism. The electrochemically active bacteria decreased significantly from 61.7% to 4% over three stages of leachate treatment. Overall, the SC-MFC has demonstrated the potential for wastewater treatment along with energy harvesting and provides a new avenue toward sustainable leachate management.

Performance evaluation of microbial fuel cell for landfill leachate treatment: Research updates and synergistic effects of hybrid systems

Over half of century, sanitary landfill was and is still the most economical treatment strategy for solid waste disposal, but the environmental risks associated with the leachate have brought attention of scientists for its proper treatment to avoid surface and ground water deterioration. Most of the treatment technologies are energy-negative and cost intensive processes, which are unable to meet current environmental regulations. There are continuous demands of alternatives concomitant with positive energy and high effluent quality. Microbial fuel cells (MFCs) were launched in the last two decades as a potential treatment technology with bioelectricity generation accompanied with simultaneous carbon and nutrient removal. This study reviews capability and mechanisms of carbon, nitrogen and phosphorous removal from landfill leachate through MFC technology, as well as summarizes and discusses the recent advances of standalone and hybrid MFCs performances in landfill leachate (LFL) treatment. Recent improvements and synergetic effect of hybrid MFC technology upon the increasing of power densities, organic and nutrient removal, and future challenges were discussed in details.

Effects of char from biomass gasification on carbon retention and nitrogen conversion in landfill simulation bioreactors

The application of char from biomass gasification as a filling material in landfill simulation reactors was investigated to evaluate the effect of char on carbon retention and nitrogen leaching, nitrogen denitrification, and waste stabilization. Landfill simulation columns filled with fine fraction of aged refuse (AR) and solid fraction of digestate (SFD) were used, with two char application methods: embedding a char layer between AR and SFD layers and mixing char with the SFD. The experimental results show that char application increased the biodegradable organic matter content as the respiration index (RI₄) of the mixture char-SFD increased up to 37.7%, which could enhance the heterotrophic denitrification. Moreover, 12.3% of ammonia leaching was avoid by applying the SFD mixed with char. These results indicate that char from biomass gasification poses a significant enhancement on nitrogen and carbon retention which might increase the denitrification capacity of the SFD in the long run. Although high nitrogen removal rates were achieved (up to 23.1 mg N/kg-TS day), the addition of char from biomass gasification has little effect on the nitrate removal.

Real-Time Monitoring of Micro-Electricity Generation Through the Voltage Across a Storage Capacitor Charged by a Simple Microbial Fuel Cell Reactor with Fast Fourier Transform

The pattern of micro-electricity production of simple two-chamber microbial fuel cells (MFC) was monitored in this study. Piggery wastewater and anaerobic sludge served as fuel and inocula for the MFC, respectively. The output power, including voltage and current generation, of triplicate MFCs was measured using an on-line monitoring system. The maximum voltage obtained among the triplicates was 0.663 V. We also found that removal efficiency of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the piggery wastewater was 94.99 and 98.63%, respectively. Moreover, analytical results of Fast Fourier Transform (FFT) demonstrated that the output current comprised alternating current (AC) and direct current (DC) components, ranging from mA to μA.

A bio-electro-Fenton system with a facile anti-biofouling air cathode for efficient degradation of landfill leachate

Bio-electro-Fenton (BEF) system holds great potential for sustainable degradation of refractory organics. Activated carbon (AC) air cathode was modified by co-pyrolyzing of AC with glucose and doping with nano-zero-valent iron (denoted as nZVI@MAC) in order to promote two-electron oxygen reduction reaction (2e^- ORR) for enhanced oxidizing performance. Single chamber microbial fuel cells (SCMFCs) with nZVI@MAC cathode was examined to degrade landfill leachate. It was revealed that nZVI@MAC cathode SCMFC showed higher degradation efficiency towards landfill leachate. Six landfill leachate treatment cycles indicated that nZVI@MAC cathode SCMFC exhibited higher COD removal efficiencies over AC and nZVI@AC and greatly enhanced columbic efficiency compared to AC and nZVI@AC cathode. Anti-biofouling effect was found on nZVI@MAC cathode because of the high Fenton oxidation effects at the vicinity of the cathode. Electrochemical characterizations indicated that MAC cathode had superior 2e^- ORR capability than AC and nZVI@AC cathode, which was further evidenced by higher H₂O₂ production from nZVI@MAC cathode in SCMFC. Graphitic structure of MAC was evidenced by High Resolution Transmission Electron Microscopy, and glucose pyrolysis also resulted in nano carbon spheres on the activated carbon skeletons. Raman spectra indicated more defects were generated on MAC during its co-pyrolyzation with glucose.

A review of landfill leachate induced ultraviolet quenching substances: Sources, characteristics, and treatment

Landfill leachate contains extremely diverse mixtures of pollutants and thus requires appropriate treatment before discharge. Co-treatment of landfill leachate with sewage in wastewater treatment plants is a common approach because of low cost and convenience. However, some recalcitrant organic compounds in leachate can escape biological treatment processes, lower the UV transmittance of waste streams due to their UV-quenching properties, and interfere with the associated disinfection efficacy. Thus, the leachate UV quenching substances (UVQS) must be removed or reduced to a level that UV disinfection is not strongly affected. UVQS consist of three major fractions, humic acids, fulvic acids and hydrophilics, each of which has distinct characteristics and behaviors during treatment. The purpose of this review is to provide a synthesis of the state of the science regarding UVQS and possible treatment approaches. In general, chemical, electrochemical, and physical treatments are more effective than biological treatments, but also costlier. Integration of multiple treatment methods to target the removal of different fractions of UVQS can aid in optimizing treatment. The importance of UVQS effects on wastewater treatment should be better recognized and understood with implemented regulations and improved research and treatment practice.

Simultaneous energy generation and UV quencher removal from landfill leachate using a microbial fuel cell

The presence of UV quenching compounds in landfill leachate can negatively affect UV disinfection in a wastewater treatment plant when leachate is co-treated. Herein, a microbial fuel cell (MFC) was investigated to remove UV quenchers from a landfill leachate with simultaneous bioelectricity generation. The key operating parameters including hydraulic retention time (HRT), anolyte recirculation rate, and external resistance were systematically studied to maximize energy recovery and UV absorbance reduction. It was found that nearly 50% UV absorbance was reduced under a condition of HRT 40 days, continuous anolyte recirculation, and 10 Ω external resistance. Further analysis showed a total reduction of organics by 75.3%, including the reduction of humic acids, fulvic acids, and hydrophilic fraction concentration as TOC. The MFC consumed 0.056 kWh m^-3 by its pump system for recirculation and oxygen supply. A reduced HRT of 20 days with periodical anode recirculation (1 hour in every 24 hours) and 39 Ω external resistance (equal to the internal resistance of the MFC) resulted in the highest net energy of 0.123 kWh m^-3. Granular activated carbon (GAC) was used as an effective post-treatment step and could achieve 89.1% UV absorbance reduction with 40 g L^-1. The combined MFC and GAC treatment could reduce 92.9% of the UV absorbance and remove 89.7% of the UV quenchers. The results of this study would encourage further exploration of using MFCs as an energy-efficient method for removing UV quenchers from landfill leachate.

Energy consumption by forward osmosis treatment of landfill leachate for water recovery

Forward osmosis (FO) is an alternative approach for treating landfill leachate with potential advantages of reducing leachate volume and recovering high quality water for direct discharge or reuse. However, energy consumption by FO treatment of leachate has not been examined before. Herein, the operational factors such as recirculation rates and draw concentrations were studied for their effects on the quantified energy consumption by an FO system treating actual leachate collected from two different landfills. It was found that the energy consumption increased with a higher recirculation rate and decreased with a higher draw concentration, and higher water recovery tended to reduce energy consumption. The highest energy consumption was 0.276±0.033kWhm^-3 with the recirculation rate of 110mLmin^-1 and 1-M draw concentration, while the lowest of 0.005±0.000kWhm^-3 was obtained with 30mLmin^-1 recirculation and 3-M draw concentration. The leachate with lower concentrations of the contaminants had a much lower requirement for energy, benefited from its higher water recovery. Osmotic backwashing appeared to be more effective for removing foulants, but precise understanding of membrane fouling and its controlling methods will need a long-term study. The results of this work have implied that FO treatment of leachate could be energy efficient, especially with the use of a suitable draw solute that can be regenerated in an energy efficient way and/or through combination with other treatment technologies that can reduce contaminant concentrations before FO treatment, which warrants further investigation.

Simultaneous degradation of refractory organic pesticide and bioelectricity generation in a soil microbial fuel cell with different conditions

In this study, the soil microbial fuel cells (MFCs) were constructed based on sandy soil to remove the refractory organic pesticide hexachlorobenzene (HCB) in topsoil by a simple method. The construction of membraneless single-chamber soil MFCs by setting up the cathode- and the anode-activated carbon, inoculating the sludge and adding the co-substrates can promote HCB removal significantly. The results showed that HCB removal efficiencies in the soils contaminated with 40, 80  and 200 mg/kg were 71.14%, 62.15% and 50.06%, respectively, which were 18.65%, 18.46% and 19.17% higher than the control, respectively. The electricity generation of soil MFCs in different HCB concentrations was analyzed. The highest power density reached was 70.8 mW/m², and an internal resistance of approximately 960 Ω was obtained when an external resistance loading of 1000 Ω was connected. Meanwhile, the influences of temperature, substrate species and substrate concentrations on soil MFCs initial electricity production were investigated. The addition of the anionic surfactant sodium dodecyl sulfate (SDS) into the soil MFCs system contributed to the improvement in HCB removal efficiency.

Removal of ammonia nitrogen from distilled old landfill leachate by adsorption on raw and modified aluminosilicate

This study aimed to evaluate the ammonia-nitrogen removal by aluminosilicates, using both standard solutions as pretreated landfill leachate. Three types of commercial clays and one commercial zeolite were initially tested using standard solution; however, only one clay with the best removability and the zeolite were tested with pretreated leachate. The chosen clay sorption capacity with the standard solution reached 83%, while with the pretreated leachate solution has reached 95% and zeolites have reached, respectively, a removal of 73% and 81%. For this two adsorbents' studies of equilibrium and kinetic of the sorption were also performed. The Langmuir model was more adequate to describe the ion exchange equilibrium and the sorption mechanism fit the pseudo-second-order kinetic model. Moreover, the pretreatment used on leachate proved to be essential not only for ammonium detection in solution, but also to facilitate its sorption in aluminosilicates. This alternative of ammonia-nitrogen removal also generates a product derived from treatment that can be used as agricultural feedstock in the form of fertilizer.

Municipal waste liquor treatment via bioelectrochemical and fermentation (H2 + CH4) processes: Assessment of various technological sequences

In this paper, the anaerobic treatment of a high organic-strength wastewater-type feedstock, referred as the liquid fraction of pressed municipal solid waste (LPW) was studied for energy recovery and organic matter removal. The processes investigated were (i) dark fermentation to produce biohydrogen, (ii) anaerobic digestion for biogas formation and (iii) microbial fuel cells for electrical energy generation. To find a feasible alternative for LPW treatment (meeting the two-fold aims given above), various one- as well as multi-stage processes were tested. The applications were evaluated based on their (i) COD removal efficiencies and (ii) specific energy gain. As a result, considering the former aspect, the single-stage processes could be ranked as: microbial fuel cell (92.4%)> anaerobic digestion (50.2%)> hydrogen fermentation (8.8%). From the latter standpoint, an order of hydrogen fermentation (2277 J g^-1 COD_removed d^-1)> anaerobic digestion (205 J g^-1 COD_removed d^-1)> microbial fuel cell (0.43 J g^-1 COD_removed d^-1) was attained. The assessment showed that combined, multi-step treatment was necessary to simultaneously achieve efficient organic matter removal and energy recovery from LPW. Therefore, a three-stage system (hydrogen fermentation-biomethanation-bioelectrochemical cell in sequence) was suggested. The different approaches were characterized via the estimation of COD balance, as well.

Resource recovery from landfill leachate using bioelectrochemical systems: Opportunities, challenges, and perspectives

Landfill leachate has recently been investigated as a substrate for bioelectrochemical systems (BES) for electricity generation. While BES treatment of leachate is effective, the unique feature of bioelectricity generation in BES creates opportunities for resource recovery from leachate. The organic compounds in leachate can be directly converted to electrical energy through microbial interaction with solid electron acceptors/donors. Nutrient such as ammonia can be recovered via ammonium migration driven by electricity generation and ammonium conversion to ammonia in a high-pH condition that is a result of cathode reduction reaction. Metals in leachate may also be recovered, but the recovery is affected by their concentrations and values. Through integrating membrane process, especially forward osmosis, BES can recover high-quality water from leachate for applications in landscaping, agricultural irrigation or direct discharge. This review paper discusses the opportunities, challenges, and perspectives of resource recovery from landfill leachate by using BES.

Relieving the fermentation inhibition enables high electron recovery from landfill leachate in a microbial electrolysis cell

The energy value of the organic matter in landfill leachate can be captured with a microbial electrolysis cell (MEC), which oxidizes organic compounds at an anode and generates H₂gas at a cathode.

Harvest and utilization of chemical energy in wastes by microbial fuel cells

Energy generated from wastes by using MFC technology could be effectively stored and utilized for real-world applications.

Recovery of nitrogen and water from landfill leachate by a microbial electrolysis cell-forward osmosis system

A microbial electrolysis cell (MEC)-forward osmosis (FO) system was previously reported for recovering ammonium and water from synthetic solutions, and here it has been advanced with treating landfill leachate. In the MEC, 65.7±9.1% of ammonium could be recovered in the presence of cathode aeration. Without aeration, the MEC could remove 54.1±10.9% of ammonium from the leachate, but little ammonia was recovered. With 2M NH4HCO3 as the draw solution, the FO process achieved 51% water recovery from the MEC anode effluent in 3.5-h operation, higher than that from the raw leachate. The recovered ammonia was used as a draw solute in the FO for successful water recovery from the treated leachate. Despite the challenges with treating returning solution from the FO, this MEC-FO system has demonstrated the potential for resource recovery from wastes, and provide a new solution for sustainable leachate management.

Transformation of dissolved organic matters in landfill leachate-bioelectrochemical system

A membraneless bioelectrochemical system (BES) reactor and an anoxic/oxic (A/O) reactor of identical configurations were applied to treat the landfill leachate (20,100 mg l(-1) chemical oxygen demand (COD) and 1330 mg l(-1) NH4(+)-N) at 24-h hydraulic retention time and 3 kg chemical oxygen demand m(-3) d(-1) volume loading. The BES with maximum power density of 2.77±0.26 W m(-3) and internal resistance of 47.5±1.4 Ω removed 84-89% COD and 94-98% NH4(+)-N, 11% and 47%, respectively, higher than the A/O reactor. The dissolved organic matters (DOM) in effluents from the BES and the A/O reactor were for the first time characterized and compared. The MFC preferentially degraded hydrophilic fraction (HPI) of the fed DOM and yielded excess humin with high aromaticity. The electric fields by bioelectrochemical reactions occurred at cathode stimulate the activities of COD degraders and nitrifiers in biofilms to enhance ammonium removals by BES reactor.

A lab-scale anoxic/oxic-bioelectrochemical reactor for leachate treatments

A membraneless, liter-scale bioelectrochemical reactor with both bioanode and biocathode was established for landfill leachate treatment. Anoxic/oxic (A/O) zones at anode compartment and cathode compartment, respectively, were connected with a reflux to facilitate nitrogen removal. With raw landfill leachate of 17,500-22,600 mg L(-1) chemical oxygen demand (COD) and 1170-1490 mg L(-1) NH4(+)-N, the tested reactor removed 89.1±1.6% of chemical oxygen demand and 99.2±0.1% of NH4(+)-N at 3.0 kg COD m(-3) d(-1). The corresponding maximum power density was 2.71±0.09 W m(-3), with internal resistance of 46.7±1.6 Ω and open circuit voltage of 727±7 mV. The species of Pseudomonas, Desulfovibrio, Bacillus, Enterococcus, Pelospora, Dehalobacter dominated the anodic community, while those of methylotrophs, Rhodobacter, Verrucomicrobiaceae, Geobacter, Flavobacterium, Thauera, Desulfovibrio and Aeromonas dominated the cathodic community. The proposed A/O bioelectrochemical reactor is a prototype for practical treatment of landfill leachate at affordable costs.

Towards energy neutral wastewater treatment: methodology and state of the art

Conventional biological wastewater treatment processes are energy-intensive endeavors that yield little or no recovered resources and often require significant external chemical inputs. However, with embedded energy in both organic carbon and nutrients (N, P), wastewater has the potential for substantial energy recovery from a low-value (or no-value) feedstock. A paradigm shift is thus now underway that is transforming our understanding of necessary energy inputs, and potential energy or resource outputs, from wastewater treatment, and energy neutral or even energy positive treatment is increasingly emphasized in practice. As two energy sources in domestic wastewater, we argue that the most suitable way to maximize energy recovery from wastewater treatment is to separate carbon and nutrient (particularly N) removal processes. Innovative anaerobic treatment technologies and bioelectrochemical processes are now being developed as high efficiency methods for energy recovery from waste COD. Recently, energy savings or even generation from N removal has become a hotspot of research and development activity, and nitritation-anammox, the newly developed CANDO process, and microalgae cultivation are considered promising techniques. In this paper, we critically review these five emerging low energy or energy positive bioprocesses for sustainable wastewater treatment, with a particular focus on energy optimization in management of nitrogenous oxygen demand. Taken together, these technologies are now charting a path towards to a new paradigm of resource and energy recovery from wastewater.

Fermentation pre-treatment of landfill leachate for enhanced electron recovery in a microbial electrolysis cell

Pre-fermentation of poorly biodegradable landfill leachate (BOD5/COD ratio of 0.32) was evaluated for enhanced current density (j), Coulombic efficiency (CE), Coulombic recovery (CR), and removal of organics (BOD5 and COD) in a microbial electrolysis cell (MEC). During fermentation, the complex organic matter in the leachate was transformed to simple volatile fatty acids, particularly succinate and acetate in batch tests, but mostly acetate in semi-continuous fermentation. Carbohydrate had the highest degree of fermentation, followed by protein and lipids. j, CE, CR, and BOD5 removal were much greater for an MEC fed with fermented leachate (23 A/m(3) or 16 mA/m(2), 68%, 17.3%, and 83%, respectively) compared to raw leachate (2.5 A/m(3) or 1.7 mA/m(2), 56%, 2.1%, and 5.6%, respectively). All differences support the value of pre-fermentation before an MEC for stabilization of BOD5 and enhanced electron recovery as current when treating a recalcitrant wastewater like landfill leachate.

Treatment of landfill leachate using microbial fuel cells: alternative anodes and semi-continuous operation

Microbial fuel cells were designed and operated to treat landfill leachate while continuously producing power. Two different anodes were tested in batch cycles using landfill leachate as a substrate without inoculation: an activated carbon anode and biochar anode. In addition, a semi-continuous serpentine design was evaluated. No significant difference of the mean was found for the peak voltage, current density or power densities between the batch cell with activated carbon or biochar. Similar COD reduction occurred at both the batch (with biochar) and semi-continuous scale (28% ± 8.8% and 21.7% ± 12.2%, respectively). The batch MFC with activated carbon anode had significantly higher COD removal (74.7% ± 5.5%). BOD was removed by the semi-continuous MFC, but ammonia was not removed in four of the five cycles. The results provide further information on the possibility of using MFCs in landfill leachate treatment systems.