Performance evaluation of hybrid constructed wetlands for the treatment of municipal wastewater in developing countries

In developing countries, high cost of conventional wastewater treatment is a major hindrance in its application. Constructed wetlands (CWs) offer low-cost and effective solution to this issue. The current study aimed to evaluate an innovative maneuver of CWs i.e. hybrid flow constructed wetlands (HCWs) for municipal wastewater (MWW). The HCWs included two lab scale CWs; one horizontal and one vertical, in series. Local plant species were used. HCWs were operated in both, batch and continuous mode. Batch mode was used to (1) optimize detention time and (2) find pollutants removal efficiency. Continuous operation (at batch optimized retention time) was carried out for the evaluation of mass removal rate, r (g·m^-2·d^-1), volumetric rate constant, K_v (per day) and areal rate constant, K_a (m·d^-1). Among two local plants tested, Pistia stratiotes gave better removal efficiency than Typha. Optimum detention time in HCWs was found to be 8 days (4 + 4 each). The optimum COD, BOD, TSS, TKN and P removal observed for Pistia stratiotes planted HCWs was 80%, 84%, 82%, 71% and 88% respectively. Effluent standards for COD, BOD and TSS were met at optimum conditions. The values of K_a and K_v demonstrated that more removal occurred in vertical flow as compared to horizontal flow CW.     

Immobilization of trophic anaerobic acetogen for semi-continuous syngas fermentation

The massive consumption of fossil energy forces people to find new sources of energy. Syngas fermentation has become a hot research field as its high potential in renewable energy production and sustainable development. In this study, trophic anaerobic acetogen Morella thermoacetica was successfully immobilized by calcium alginate embedding method. The ability of the immobilized cells on production of acetic acid through syngas fermentation was compared in both airlift and bubble column bioreactors. The bubble column bioreactor was selected as the better type of bioreactor. The production of acetic acid reached 32.3 g·L^-1 in bubble column bioreactor with a space-time yield of 2.13 g·L^-1·d^-1. The immobilized acetogen could be efficiently reused without significant lag period, even if exposed to air for a short time. A semi-continuous syngas fermentation was performed using immobilized cells, with an average space-time acetic acid yield of 3.20 g·L^-1·d^-1. After 30 days of fermentation, no significant decrease of the acetic acid production rate was observed.     

Regulatable pervaporation performance of Zn-MOFs/polydimethylsiloxane mixed matrix pervaporation membranes

Pervaporation (PV) is an emerging separation technique for liquid mixture. Mixed matrix membranes (MMMs) often demonstrate trade-off relationship between separation factor and flux. In this study, by changing the organic linkers (2-methyl imidazolate, imidazole-2-carboxaldehyde, 2-ethyl imidazolate), ZIF-8, ZIF-90 and MAF-6 were prepared and filled in polydimethylsiloxane (PDMS) membranes for dealcoholization of 5% (mass) n-butanol solution, and the membranes properties and pervaporation performances were adjusted. Compared with the pure PDMS membrane, the addition of ZIF-8 resulted in a 9% increase in flux (1136 g·m^-2·h^-1) and a 22.5% increase in separation factor (28.3), displaying anti-trade-off effect. For the MAF-6/PDMS MMMs (2.0% mass loading), the pervaporation separation index (PSI) and separation factor were 32347 g·m^-2·h^-1 and 58.6 respectively (increased by 34% and 154% in contrast with that of the pure PDMS membrane), and the corresponding permeation flux was 552 g·m^-2·h^-1, presenting great potential in the removal butanol from water. It was deduced that the large aperture size combined with moderate hydrophobicity of metal-organic frameworks (MOFs) favor the concurrent increase in permeability and selectivity.     

木质框架土壤渗滤系统处理养猪废水厌氧消化液的效能

为处理高氨氮、低C/N比的养猪废水厌氧消化液, 构建了具有缓释碳源特性的木质框架土壤渗滤系统(WFSI), 并通过运行测试了进水浓度和表面水力负荷(SHL)对系统处理效能的影响。在SHL为0.2 m³·m^-2·d^-1条件下, 当进水COD和NH₄⁺-N平均浓度分别从152和175.5 mg·L^-1提高到421和788.7 mg·L^-1时, 系统对COD的去除率从52.3%提高到61.2%, NH₄⁺-N去除率从84.2%下降到61.5%, TN去除率从28.6%提高到了33.5%, NH₄⁺-N和TN去除负荷分别达到了75.5和41.7 g·m^-3·d^-1。当SHL提高为0.32 m³·m^-2·d^-1时, 系统仍能维持运行, 但处理效能受到显著影响。在进水COD 和NH₄⁺-N分别为265和465 mg·L^-1左右时, COD、NH₄⁺-N及TN的去除率分别平均为56.5%、53.3%和20.9%。木质填料及其附着层形成的NH₄⁺-N浓度梯度, 可使系统承受较高的SHL的同时获得缓释碳源, 并保护氨氧化细菌免受自由氨毒性。     

AD-MFC中甲醇与硝酸盐的偶合过程与作用机制

在双室微生物燃料电池(MFC)阳极内接种反硝化细菌富集培养物,同时加入硝酸盐和甲醇,构建了阳极反硝化微生物燃料电池(AD-MFC),并以批式操作研究了AD-MFC的反硝化产电性能。试验结果表明,在初始硝氮浓度为(100.22±0.62)mg·L^-1,COD浓度为(500.40±1.67)mg·L^-1的条件下,AD-MFC的最大容积NO₃^--N和COD去除速率分别达到0.31 kg N·m^-3·d^-1和1.06 kg COD·m^-3·d^-1,最大电压达到(602.80±5.42)mV,相应最大功率密度为(908.42±0.07)mW·m^-3。AD-MFC的产电过程是甲醇氧化与硝酸盐还原的偶合过程,电压变化与反硝化作用密切相关,可用于指示反硝化进程。AD-MFC的电压曲线呈现降低-升高-再降低的三阶段特性,其原因是反硝化作用、甲醇降解作用和细胞水解发酵作用依次成为阳极液中的主导反应。     

Simultaneous recovery of phosphorus and nitrogen from liquid digestate by vacuum membrane distillation with permeate fractional condensation

A vacuum membrane distillation(VMD) process with permeate fractional condensation on membrane downstream has been developed for simultaneous recovery of phosphorus and nitrogen from liquid digestate. The polytetrafluoroethylene(PTFE) membrane flux could reach 6000 g·m~(-2)·h~(-1) with the rejection efficiency of total phosphorus(TP) over 0.99, under the condition of flowrate being 120 L·h~(-1) and temperature being 40°C. Membrane fouling occurred with a film of organics and microorganism deposited on the surface of the membrane. Membrane flux could be reversed after the membrane was rinsed by water. Higher feed temperature and flowrate could improve the membrane flux, while hardly affect the rejection efficiency of total phosphorus. The concentration of TP could reach 1600 mg·L~(-1) after membrane distillation, which is about 5 times of that in initial liquid digestate. On the downstream of the membrane, some of the permeate vapor was condensed under the vacuum condition and most of water was collected here. The remaining vapor enriched with total nitrogen(TN) was compressed and pumped to the atmospheric condition to condense. The TN concentration in atmospheric condensate was as high as 7000 mg·L~(-1) with the process separation factor for ammonia being enhanced to 114.     

Acid precipitation coupled electrodialysis to improve separation of chloride and organics in pulping crystallization mother liquor

Inefficient separation of inorganic salts and organic matters in crystallization mother liquor is still a problem to industrial wastewater treatment since the high salinity significantly impedes organic pollutant degradation by oxidation or incineration. In the study, acidification combined electrodialysis (ED) was attempted to effectively separate Cl^- ions from organics in concentrate pulping wastewater. Membrane's rejection rate to total organic carbon (TOC) was 85% at wastewater intrinsic pH=9.8 and enhanced to 93% by acidifying it to pH=2 in ED process. Negative-charged alkaline organic compounds (mainly lignin) could be liberated from their sodium salt forms and coagulated in acidification pretreatment. Neutralization of the organic substances also made their electro-migration less effective under electric driving force and in particular improved separation efficiency of chloride and organics. After acid-ED coupled treatment (pH=2 and J=40 mA·cm^-2)[TOC] remarkably reduced from 1.315 g·L^-1 to 0.048 g·L^-1 and[Cl^-] accumulated to 130 g·L^-1 in concentrate solution. Recovery rate of NaCl was 89% and the power consumption was 0.38 kW·h·kg^-1 NaCl. Irreversible fouling was not caused as electric resistance of membrane pile maintained stably. In conclusion, acidic-ED is a practical option to treat salinity organic wastewater when current techniques including thermal evaporation and pressure-driven membrane separation present limitations.     

Plant-inspired biomimetic hybrid PVDF membrane co-deposited by tea polyphenols and 3-amino-propyl-triethoxysilane for high-efficiency oil-in-water emulsion separation

Membrane pollution caused by separating oily wastewater is a big challenge for membrane separation technology. Recently, plant-/mussel-inspired interface chemistry has received more and more attention. Herein, a high antifouling poly (vinylidene fluoride) (PVDF) membrane, coated with tea polyphenols (TP, extracted from green tea) and 3-amino-propyl-triethoxysilane (APTES), was developed to purify oil-in-water emulsions. ATR-FTIR, XPS and SEM were used to demonstrate the evolution of surface biomimetic hybrid coatings. The performances of the developed membranes were investigated by pure water permeability and oil rejection for various surfactant-stabilized oil-in-water emulsions. The experimental results revealed that the membrane deposited with a mass ratio of 0.1/0.2 exhibited ultrahigh pure water permeability (14570 L·m^-2·h^-1·bar^-1, 1 bar=0.1 MPa) and isooctane-in-water emulsion permeability (5391 L·m^-2·h^-1·bar^-1) with high separation efficiency (>98.9%). Even treated in harsh environment (acidic, alkaline and saline) for seven days, the membrane still maintained considerable underwater oleophobic property (148°–153°). The fabricated plant-inspired biomimetic hybrid membranes with excellent performances light a broad application prospect in the field of oily wastewater treatment.     

Influence of coke rate on thermal treatment of waste selective catalytic reduction (SCR) catalyst during iron ore sintering

Waste selective catalytic reduction (SCR) catalyst as a hazardous waste has a significant impact on the environment and human health. In present study, a novel technology for thermal treatment of waste SCR catalyst was proposed by adding it to sinter mix for iron ore sintering. The influences of coke rate on the flame front propagation, sinter microstructure, and sinter quality during sintering co-processing the waste SCR catalyst process were studied. In situ tests results indicated the maximum sintering bed temperature increased at higher coke rate, indicating more liquid phase generated and higher airflow resistance. The sintering time was longer and the calculated flame front speed dropped at higher coke rate. Sinter microstructure results found the coalescence and reshaping of bubbles were more fully with increasing coke rate. The porosity dropped from 35.28% to 25.66%, the pore average diameter of large pores decreased from 383.76 μm to 311.43 μm. With increasing coke rate, the sinter indexes of tumbler index, productivity, and yield, increased from 33.2%, 9.2 t·m^-2·d^-1, 28.9% to 58.0%, 36.0 t·m^-2·d^-1, 68.9%, respectively. Finally, a comprehensive index was introduced to systematically assess the influence of coke rate on sinter quality, which rose from 100 to 200 when coke rate was increased from 3.5% (mass) to 5.5% (mass).     

Acid precipitation coupled membrane-dispersion advanced oxidation process (MAOP) to treat crystallization mother liquor of pulp wastewater

Treatment to crystallization mother liquor containing high concentration of organic and inorganic substances is a challenge in zero liquid discharge of industrial wastewater. Acid precipitation coupled membrane-dispersion advanced oxidation process(MAOP) was proposed for organics degradation before salt crystallization by evaporation. With acid–MAOP treatment CODCrin mother liquor of pulping wastewater was eliminated by 55.2% from ultrahigh initial concentration up to 12,500 mg·L~(-1). The decolorization rate was 96.5%. Recovered salt was mainly NaCl(83.3 wt%) having whiteness 50 brighter than industrial baysalt of whiteness 45. The oxidation conditions were optimized as CO_3= 0.11 g·L~(-1) and C_(H_2O_2)= 2.0 g·L~(-1) with dispersing rate 0.53 ml·min~(-1) for 100 min reaction toward acidified liquor of p H = 2. Acidification has notably improved evaporation efficiency during crystallization. Addition of H_2O_2 made through membrane dispersion has eliminated hydroxyl radical "quench effect" and enhanced the degradation capacity, in particular, the breakage of carbon–chloride bonds(of both aliphatic and aromatic). As a result, the proposed coupling method has improved organic pollutant reduction so as the purity of salt from the wastewater mixture which can facilitate water and salt recycling in industry.     

Conversion of Malaysian low-rank coal to mesoporous activated carbon: Structure characterization and adsorption properties

Malaysian Selantik low-rank coal (SC) was used as a precursor to prepare a form of mesoporous activated carbon (SC-AC) with greater surface area (SA) via a microwave induced KOH-activation method. The characteristics of the SC and SC-AC were evaluated by the iodine number, ash content, bulk density, and moisture content. The structure and surface characterization was carried out using pore structure analysis (BET), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), elemental analysis (CHNS), thermogravimetric analysis (TGA), and determination of the point of zero charge (pH_PZC). These results signify a mesoporous structure of SC-AC with an increase of ca. 1160 times (BET SA=1094.3 m²·g^-1) as compared with raw SC without activation (BET SA=1.23 m²·g^-1). The adsorptive properties of the SC-AC with methylene blue (MB) was carried out at variable adsorbent dose (0.2-1.6 g·L^-1), solution pH (2-12), initial MB concentrations (25-400 mg·L^-1), and contact time (0-290 min) using batch mode operation. The kinetic profiles follow pseudo-second order kinetics and the equilibrium uptake of MB conforms to the Langmuir model with a maximum monolayer adsorption capacity of 491.7 mg·g^-1 at 303 K. Thermodynamic functions revealed a spontaneous endothermic adsorption process. The mechanism of adsorption included mainly electrostatic attractions, hydrogen bonding interaction, and π-π stacking interaction. This work shows that Malaysian Selantik low-rank coal is a promising precursor for the production of low-cost and efficient mesoporous activated carbon with substantive surface area.     

基于神经网络与遗传算法结合的硝化细菌发酵培养基优化(英文)

Two artificial intelligence techniques, artificial neural network and genetic algorithm, were applied to optimize the fermentation medium for improving the nitrite oxidization rate of nitrite oxidizing bacteria. Experiments were conducted with the composition of medium components obtained by genetic algorithm, and the experimental data were used to build a BP (back propagation) neural network model. The concentrations of six medium components were used as input vectors, and the nitrite oxidization rate was used as output vector of the model. The BP neural network model was used as the objective function of genetic algorithm to find the optimum medium composition for the maximum nitrite oxidization rate. The maximum nitrite oxidization rate was 0.952 g 2 NO-2-N·(g MLSS)-1·d-1 , obtained at the genetic algorithm optimized concentration of medium components (g·L-1 ): NaCl 0.58, MgSO 4 ·7H 2 O 0.14, FeSO 4 ·7H 2 O 0.141, KH 2 PO 4 0.8485, NaNO 2 2.52, and NaHCO 3 3.613. Validation experiments suggest that the experimental results are consistent with the best result predicted by the model. A scale-up experiment shows that the nitrite degraded completely after 34 h when cultured in the optimum medium, which is 10 h less than that cultured in the initial medium.     

Helium extraction from natural gas using DD3R zeolite membranes

Helium (He) is commercially produced from natural gas by low-temperature condensation. The process is energy extensive because of the extremely low He concentration (<0.3%) and the operation at cryogenic temperature. Herein we demonstrated DD3R zeolite membrane was efficient to extract He from natural gas at atmosphere temperature. The membrane performance was evaluated in terms of temperature, pressure and molar fractions. The overall membrane performance was dominated by the diffusivity selectivity. The single He permeance and ideal He/CH₄ selectivity were 5.8×10^-9 mol·m^-2·s^-1·Pa^-1 and 79 under a feed pressure of 1.3 MPa. Even though He concentration was as low as 0.22%, the He permeance and He/CH₄ mixture selectivity were 3.0×10^-9 mol·m^-2·s^-1·Pa^-1 and 44 at 0.7 MPa. During the long-term operation (～130 h) the membrane performance was stable even the feed mixture containing 3.6% ethane as contaminations. The results approved the feasibility of DD3R zeolite membranes for He extraction from natural gas.     

短程硝化耦合厌氧氨氧化工艺处理低C/N比生活污水

为快速实现低C/N比生活污水高效低耗稳定脱氮,在常温条件下,对短程硝化-厌氧氨氧化工艺的启动及脱氮性能进行研究,在常温,高DO（2.5 mg·L^-1）条件下,采用实时控制结合神经网络模型预测控制可快速启动短程硝化,亚硝积累率达到95%以上。由于生物膜的独特结构可为厌氧氨氧化（Anammox）菌提供良好的厌氧环境,因此选用生物滤池来实现厌氧氨氧化,启动期间克服了温度变化的影响,第173天后,NH₄⁺-N和NO₂^--N去除率达到90%以上,TN去除率达到80%,Anammox滤池成功启动。后续将短程硝化与厌氧氨氧化耦合,通过逐步提高滤速启动耦合系统,Anammox滤池滤速可提高到0.5 m·h^-1,总氮容积负荷达到0.75 kg·m^-3·d^-1。系统出水TN平均浓度为8 mg·L^-1,实现了短程硝化耦合厌氧氨氧化工艺稳定高效地处理生活污水。     

Fabrication of anti-fouling polyamide nanofiltration membrane by incorporating streptomycin as a novel co-monomer

Polyamide (PA) thin-film composite (TFC) nanofiltration (NF) membrane has extremely broad application prospects in separation of monovalent/divalent inorganic salts mixed solution. However, membrane fouling is the main obstacle to the application of PA, TFC and NF membrane. Streptomycin (SM) is a hydrophilic antibiotic containing a large number of hydroxyl and amino groups. In this work, the NF membrane was prepared via interfacial polymerization (IP) between trimesoyl chloride (TMC) in the organicphaseand SM/piperazine (PIP) mixture in theaqueousphase. The NF membrane structure and performance were characterized in detail. The results showed that SM successfully participated in the IP. The negative charge and hydrophilicity of membrane surface were improved. The prepared membrane exhibited good anti-adhesion and anti-bacterial performance. Additionally, when the SM concentration was 2%, the prepared membrane exhibited the optimal permselectivity. The water permeance was 89.4 L·m^-2·h^-1·MPa^-1. The rejection of NaCl and Na₂SO₄ were 17.17% and 97.84%, respectively. The NaCl/Na₂SO₄ separation factor of the SM2-PIP/TMC membrane in 1000 mg·L^-1 NaCl and 1000 mg·L^-1 Na₂SO₄ mixed solution was 40, which was 3.3 times that of PIP/TMC membrane. It indicated that SM2-PIP/TMC demonstrated excellent monovalent/divalent salts separation performance. This work provided an easy and effective approach to preparing anti-fouling NF membrane while possessing superior monovalent/divalent salts separation performance.     

污泥含炭吸附剂的制备及其吸附模拟烟气中汞蒸汽的应用(英文)

The carbonaceous adsorbent was prepared from mixtures of dewatered sludge and sawdust with enhanced ZnCl2 chemical activation.Characteristics of the adsorbent were studied using scanning electron microscope(SEM) ,Fourier transform infrared spectroscopy(FT-IR) ,and adsorption of nitrogen.The surface analysis showed that the carbonaceous adsorbent had good specific surface and porosity(394 m 2 ·g-1of BET surface,0.12 and 0.10 ml·g-1of microporous and mesoporous volume,respectively) .The oxygen functional groups such as OH,C O and C O were found on the surface by FTIR and XPS(X-ray photoelectron spectroscopy) .The adsorption of elemental mercury(Hg0) on the carbonaceous adsorbent was studied in a fixed bed reactor.The dynamic adsorption capacity of carbonaceous adsorbent increased with influent mercury concentration,from 23.6μg·g-1at 12.58μg·m-3to 87.9μg·g-1at 72.50μg·m-3,and decreased as the adsorption temperature increased,from 246 μg·g-1 at 25°C to 61.3μg·g-1 at 140°C,when dry nitrogen was used as the carrier gas.The carbonaceous adsorbent presented higher dynamic adsorption capacity than activated carbon,which was 81.2μg·g-1and 53.8μg·g-1respectively.The adsorption data were fitted to the Langmuir adsorption model.The physical and chemical adsorption were identified on the adsorbent.     

Hydrophobic modification of SAPO-34 membranes for improvement of stability under wet condition

SAPO-34 zeolite membranes show high efficiency for CO₂/CH₄ separation but suffer from the reduction of separation performance when exposed to humid atmosphere. In this work, n-dodecyltrimethoxysilane (DTMS) was used to modify the hollow fibers supported SAPO-34 membranes to increase the external surface hydrophobicity and thus sustain their performance under moisture environment. The modified membranes were fully characterized. Their separation performance was extensively investigated in both dry and wet gaseous systems and compared with the un-modified ones. The un-modified SAPO-34 membrane exhibited a high separation selectivity of 160 and CO₂ permeance of 1.18×10^-6 mol·m^-2·s^-1·Pa^-1 for separation of dry CO₂/CH₄ at 298 K. However, its separation selectivity declined to 0.9 and the CO₂ permeance was only about 1.7×10^-8 mol·m^-2·s^-1·Pa^-1 for wet CO₂/CH₄ at same temperature. High temperature (e.g. 353 K) could reduce the effect of moisture to improve SAPO-34 separation selectivity, but further increasing temperature (e.g. 373 K) led to decrease in CO₂/CH₄ separation selectivity. A significant decrease of selectivity was observed at higher pressure drop. The modified SAPO-34 membrane showed decreased CO₂ permeance but increased separation selectivity for dry CO₂/CH₄ gas mixture, and super performance for wet CO₂/CH₄ gas mixture due to the improved hydrophobicity of membrane surface. A separation selectivity of 65 and CO₂ permeance of 4.73×10^-8 mol·m^-2·s^-1·Pa^-1 for wet CO₂/CH₄ mixture can be observed at 353 K with a pressure drop of 0.4 MPa. Furthermore, the modified membrane exhibited stable separation performance during the 120-hour test for wet CO₂/CH₄ mixture at 353 K. The hydrophobic modification paves a way for SAPO-34 membranes in real applications.     

升流式微氧生物膜反应器处理高氨氮低C/N比养猪废水的效能

针对高氨氮低C/N比干清粪养猪废水处理面临的脱氮问题,制作并运行了一种升流式微氧生物膜反应器（UMBR）,考察了废水水质和由出水回流比调控的溶解氧（DO）对系统处理效能的影响。结果表明,将系统内DO控制在0.23～0.70 mg·L^-1范围,不会对UMBR的COD去除率造成不良影响,而且能够保证NH₄^--N的氧化效能。但DO为0.70 mg·L^-1的微氧环境,会抑制厌氧氨氧化作用,降低系统的TN去除效能。在HRT 8 h、27℃和DO 0.40 mg·L^-1的条件下,UMBR对NH₄^--N和TN的去除负荷平均可达0.94和0.91 kg·m^-3·d^-1,COD去除负荷也能达到0.60 kg·m^-3·d^-1左右。分析认为,填料的布设及生物膜的着生,不仅保证了UMBR的微生物持有量,而且可为化能自养菌群、氨氮氧化菌群、自养反硝化菌群和异养反硝化菌群等微生物类群创造各自适宜的微环境,是系统保持污染物高效去除的生物学基础。     

Potential use of nanofiltration like-forward osmosis membranes for copper ion removal

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated. In this work, the performance of emerging nanofiltration(NF) like-forward osmosis(FO)membrane was evaluated for its efficiency to remove copper ion from water. Conventionally, copper ion is removed from aqueous solution via adsorption and/or ion-exchange method. The engineered osmosis method as proposed in this work considered four commercial NF membranes(i.e., NF90, DK, NDX and PFO) where their separation performances were accessed using synthetic water sample containing 100 mg·L~(-1) copper ion under FO and pressure retarded osmosis(PRO) orientation. The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force.The high removal rates were in good agreement with the outcomes of the membranes tested under pressuredriven mode at 1 MPa. The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process, achieving a relatively low reverse solute flux. The findings showed that the best performing membrane is PFO membrane in which it achieved N 99.4% copper rejection with very minimum reverse solute flux of 1 g·m~(-2)·h~(-1).     

Simultaneously energy production and dairy wastewater treatment using bioelectrochemical cells: In different environmental and hydrodynamic modes

A successful design, previously adapted for treatment of complex wastewaters in a microbial fuel cell (MFC), was used to fabricate two MFCs, with a few changes for cost reduction and ease of construction. Performance and electrochemical characteristics of MFCs were evaluated in different environmental conditions (in complete darkness and presence of light), and different flow patterns of batch and continuous in four hydraulic retention times from 8 to 30 h. Changes in chemical oxygen demand, and nitrate and phosphate concentrations were evaluated. In contrast to the microbial fuel cell operated in darkness (D-MFC) with a stable open circuit voltage of 700 mV, presence of light led to growth of other species, and consecutively low and unsteady open circuit voltage. Although the performance of theMFC subjected to light (L-MFC)was quite lowand unsteady in dynamic state (internal resistance = 100 Ω, power density = 5.15 W·m^-3), it reached power density of 9.2 W·m^-3 which was close to performance of D-MFC (internal resistance = 50 Ω, power density = 10.3 W·m^-3). Evaluated only for D-MFC, the coulombic efficiency observed in batch mode (30%) was quite higher than the maximum acquired in continuous mode (9.6%) even at the highest hydraulic retention time. In this study, changes in phosphate and different types of nitrogen existing in dairy wastewater were investigated for the first time. At hydraulic retention time of 8 h, the orthophosphate concentration in effluent was 84% higher compared to influent. Total nitrogen and total Kjeldahl nitrogen were reduced 70% and 99% respectively at hydraulic retention time of 30 h, while nitrate and nitrite concentrations increased. The microbial electrolysis cell (MEC), revamped from D-MFC, showed the maximum gas production of 0.2 m³ H₂·m^-3·d^-1 at 700 mV applied voltage.