A review of microbial fuel cell and its diversification in the development of green energy technology.

The advancement of microbial fuel cell technology is rapidly growing, with extensive research and well-established methodologies for enhancing structural performance. This terminology attracts researchers to compare the MFC devices on a technological basis. The architectural and scientific successes of MFCs are only possible with the knowledge of engineering and technical fields. This involves the structure of MFCs, using substrates and architectural backbones regarding electrode advancement, separators and system parameter measures. Knowing about the MFCs facilitates the systematic knowledge of engineering and scientific principles. The current situation of rapid urbanization and industrial growth is demanding the augmented engineering goods and production which results in unsolicited burden on traditional wastewater treatment plants. Consequently, posing health hazards and disturbing aquatic veracity due to partial and untreated wastewater. Therefore, it's sensible to evaluate the performance of MFCs as an unconventional treatment method over conventional one to treat the wastewater. However, MFCs some benefits like power generation, stumpy carbon emission and wastewater treatment are the main reasons behind the implementation. Nonetheless, few challenges like low power generation, scaling up are still the major areas needs to be focused so as to make MFCs sustainable one. We have focused on few archetypes which majorities have been laboratory scale in operations. To ensure the efficiency MFCs are needed to integrate and compatible with conventional wastewater treatment schemes. This review intended to explore the diversification in architecture of MFCs, exploration of MFCs ingredients and to provide the foreseen platform for the researchers in one source, so as to establish the channel for scaling up the technology. Further, the present review show that the MFC with different polymer membranes and cathode and anode modification presents significant role for potential commercial applications after change the system form prototype to pilot scale.

Performance improvement of the osmotic microbial fuel cell by the pre-treatment of anaerobic sewage sludge using solenoid magnetic field.

This study explored the effect of a solenoid magnetic field (SOMF) as a pre-treatment on anaerobic sewage sludge (ASS) before using it in an osmotic microbial fuel cell (OMFC) as an inoculant. The ASS efficiency in terms of colony-forming unit (CFU) was improved ten times by applying SOMF compared to the control conditions. The obtained highest power density, current density, and water flux in the OMFC were 32.70 ± 5 mW·m-2, 135.13 ± 15 mA·m-2, and 4.24 ± 0.11 L·m-2h-1 respectively, for 72 h at 1 mT magnetic field. The coulombic efficiency (CE) and chemical oxygen demand (COD) removal efficiency were increased to 40-45% and 4-5% respectively, compared to un-treated ASS. Also, the start-up time of the ASS-OMFC system was almost reduced to 1-2 days based on open circuit voltage data. On the other hand, increasing the pre-treatment intensity of SOMF with time, it decreased the performance of OMFC. Also, the low intensity with increased pre-treatment time up to a specific limit enhanced the performance of OMFC.

Hydrothermal carbonization of cow dung with human urine as a solvent for hydrochar: An experimental and kinetic study.

Hydrothermal carbonization (HTC) is the most cost-effective, environmentally friendly, and efficient physicochemical and biochemical process for converting biomass to products with added value. The objective and novelty of this work is to produce and investigate the qualities of hydrochar fuel (as a solid fuel) from cow manure using human urine as a solvent in order to find a suitable replacement for conventional fuel (i.e., coal). HTC based studies were conducted in batch, at three different reaction temperatures (180 °C, 200 °C, and 220 °C) and two different reaction periods (2 and 4 h). For kinetic analysis and reaction mechanism of the combustion behavior of the produced hydrochar, the model free kinetic methods and the z-master plot were used. From the model free kinetics methods, it was observed that the resultant optimum average activation energy and pre-exponential factor for the produced hydrochar at 180 °C and 2 h reaction period (HTC_180_2) were ∼120 kJ/mol and ∼5.59 × 1025 sec-1, respectively. In addition, the little variation between ΔEα and ΔHα (∼10 kJ/mol) suggests that the combustion of produced hydrochar (HTC_180_2) occurred with minimal energy use. Furthermore, the hydrochar exhibited its highest heating value at 200 °C for 4 h (HTC_200_4) which was 1.44 times higher than the raw dung (13.4 MJ/kg) due to the HTC process. The produced hydrochar demonstrated a significant improvement compared to the conventional solvent, i.e. water.

Performance evaluation of deep eutectic solvent as a draw solute and vertical up-flow forward osmosis module for desalination of seawater.

Forward osmosis (FO) has gained prominence in recent years particularly in desalination due to its ability to operate at low or no hydraulic pressure, with relatively limited membrane fouling and high-water recovery. However, pre-treatment of seawater is required to reduce membrane fouling caused by the presence of suspended solid particles. Also, a significant area of research in forward osmosis is still finding a suitable draw solute (DS) with the ideal characteristics. In this study, a novel deep eutectic solvent (DES) draw solute was used and able to extract water after the 500% dilution of DS. This signifies it as the potential candidate for the ideal DS. A comparative study of plate and frame and vertical up-flow forward osmosis (VUF) FO modules has been evaluated to eliminate the drawbacks associated with FO in terms of membrane fouling and draw solute. In addition, the performance of a novel DES as reline (choline chloride-urea) has been tested in both the modules. In VUF module, significantly less fouling was observed than in the plate and frame module. The initial water flux in plate and frame module was 2.30 LMH with seawater (without pre-treatment) as feed. However, it dropped to 1 LMH after 26 h of run. However, initial water flux in VUF was 1.90 LMH, and it was maintained to 1.50 LMH after 89 h of run. Regeneration of draw solute was carried out using a phase separation method and it was observed that phase separation was only observed for 10% dilution of DES.

A foam column system harvesting freshwater algae for biodiesel production: An experiment and process model evaluations.

The purpose of this study was to examine the application of the mathematical model of drift flux to the experimental results of the effect of cationic trimethyl-ammonium bromide (CTAB)-aided continuous foam flotation harvesting on the lipid content in Chlorella vulgaris microalgae. An experiment was conducted to determine the effect of the operating conditions on the enrichment factor (EF) and percentage recovery efficiency (%RE), where the flow rates at the inlet and bottom outlet remained constant. Data for the binary system (without algae) and ternary system (with algae) in an equal-area foam column show that the EF decreases linearly with increasing initial CTAB concentrations ranging from 30 to 75 mg/L for three levels of the studied air volumetric flow rate range (1-3) L/min. The percentage harvesting efficiency increased with increasing initial CTAB concentration and air volumetric flow rate to 96 % in the binary systems and 94 % in the ternary systems. However, in the foam column with the riser used in the three systems, a lower volume of liquid foam in the upward outlet stream resulted in a lower RE% than that of the column without the riser. The objective function of EF for the system with algae increased when the initial CTAB concentration was increased from 30 to 45 mg/L in the foam column with a riser for all air flow rates, and after 45 mg/L, a sudden drop in the microalgae EF was observed. In the comparison between the foam column with and without the riser for the system with algae, the optimum EF was 145 for the design of the column with the riser and 139 for the column without the riser.

Enhancement of electrode properties using carbon dots functionalized magnetite nanoparticles for azo dye decolorization in microbial fuel cell.

Technology integration of nanomaterials with microbial fuel cell (MFC) have led to simultaneous degradation of recalcitrant dyes and energy extraction from textile wastewater. Limited electron transfer capacity and hydrophobicity of electrode are the bottlenecks for enhancing the performance of MFC. Nanomaterials can provide surface functionalities for electron transfers and serve as catalyst for pollutant degradation. In this paper, magnetite nanoparticles functionalized with carbon dots (Fe3O4@CDs) were used to enhance the electron transfer capacity of the electrodes due to numerous surface-active functional groups of CDs and the reversible redox reaction of Fe2+/Fe3+. Polydopamine (PDA) was used as binder to coat Fe3O4@CDs onto the surface of carbon felt (CF) electrodes in a sono-chemical reaction, favoring to form biocompatible electrodes. Charge transfer resistance of Fe3O4@CDs@PDA-CF was 5.02Ω as compared to 293.34Ω of unmodified CF. Fe3O4@CDs@PDA-CF installed MFC could achieve almost 98% dye degradation efficiency within 48 h and 18.30 mW m-2 power output as compared to 77% dye degradation and 0.34 mW m-2 power output by unmodified CF electrode MFC. Moreover, metagenomic analysis of microbial consortia developed in Fe3O4@CDs@PDA-CF MFC showed enrichment of electrogenic and dye degrading microbial communities of Achromobacter. Delftia, Geobacter and Pseudomonas.

Scalable architecture of low-cost household microbial fuel cell for domestic wastewater treatment and simultaneous energy recovery.

Researchers are still trying to achieve desirable results while treating actual wastewater at the field size when scaling up a microbial fuel cell (MFC). This pilot-scale project aimed to create a decentralised system for treating domestic wastewater and concurrent energy generation that may be used as a model for the decentralisation process. In this investigation, a cylindrical-shaped earthen membrane was utilized. The arrangement was deployed on-site at a residence for the treatment of domestic wastewater as well as simultaneous generation of power. From August until November 2021, the 36 L pilot-scale setup was operational for a period of 92 days. The setup's performance was affected by seasonal temperature variations during the operation period. The system's performance was measured in terms of COD, nitrate, and NH3-N removal, with the highest results being 93.52 %, 84.93 %, and 74.78 %, respectively. The pilot-scale setup achieved the highest current of 43.7 mA, and the output voltage of the setup was boosted to 4.1 V using a power management system. The sustainable operation of pilot household MFC showed a positive indication for field application with a low-cost solution.

Performance of pilot-scale constructed wetland osmotic microbial fuel cell under different gravel conditions.

This paper explores the performance of pilot-scale constructed wetland osmotic microbial fuel cell (CW-OMFC) in different gravel conditions. The performance was measured in terms of power generation, water flux, chemical oxygen demand (COD) removal, and coulombic efficiency. The CW-OMFC was divided into four sections based on the porosity of the materials. The surface area of materials at Side A, Side B, Side C, and Side D were 2.717 m2.g-1, 0.228 m2.g-1, 0.095 m2.g-1, and 0.072 m2.g-1, respectively. The CW-OMFC achieved maximum water flux, minimum reverse salt flux, high power density, and COD removal efficiency of 6.66 ± 0.5 L.m-2.h-1, 3.33 ± 1.2 g.m-2.h-1, 59.53 ± 10 mW.m-2 and 84.69%, respectively, by using high porous materials. The nutrients (nitrogen, phosphorus, and potassium) uptake by plants from wastewater were 12.17%, 12.01%, and 21.73%, respectively.

Physico-chemical and biological treatment strategies for converting municipal wastewater and its residue to resources.

An increase in urbanization and industrialization has not only contributed to an improvement in the lifestyle of people, but it has also contributed to a surge in the generation of wastewater. To date, conventional physico-chemical and biological treatment methods are widely used for the treatment of wastewater. However, the efficient operation of these systems require substantial operation and maintenance costs, and the application of novel technologies for the treatment and disposal of sludge/residues. This review paper focuses on the application of different treatment options such as chemical, catalyst-based, thermochemical and biological processes for wastewater or sludge treatment and membrane-based technologies (i.e. pressure-driven and non-pressure driven) for the separation of the recovered products from wastewater and its residues. As evident from the literature, a wide variety of treatment and resource recovery options are possible, both from wastewater and its residues; however, the lack of planning and selecting the most appropriate design (treatment train) to scale up from pilot to the field scale has limited its practical application. The economic feasibility of the selected technologies was critically analyzed and the future research prospects of resource recovery from wastewater have been outlined in this review.

Biological treatment of saline domestic wastewater by using a down-flow hanging sponge reactor.

In this study, the effect of salinity on the removal of organic matter and nitrogen concentrations in bioreactor was investigated using a hybrid bench scale down-flow hanging sponge (DHS) system for 145 days of operation. The reactor had three identical sections that were filled to 30% volume with Bio-Bact to serve as attached media. The DHS reactor was fed with domestic wastewater that was mixed with increasing concentration of sodium chloride from 0.5 to 3.0% stepwise. The influent and effluent concentrations of BOD5, CODCr, NH4+-N, and TN were analyzed to evaluate the performance of the DHS reactor during the operational period. Results indicate that when salinity was increased from 0.5 to 3.0%, the removal efficiency gradually decreased from 80.3% to 61.5% for CODCr, 76.4%-65.0% for BOD5, 64.1%-48.4% for NH4+-N, and 50%-36% for TN. Besides, the changes in biofilm characteristics with increasing salinity were observed during the operational period. The results indicate that salinity has a significant influence on the removal of organic matters and nitrogen transformation in the biofilm of the bioreactor. Even so, the DHS reactor revealed a good potential for treating saline wastewater.

Biological modification in air-cathode microbial fuel cell: Effect on oxygen diffusion, current generation and wastewater degradation.

Oxygen diffusion in the anodic chamber is the major limitation of air-cathode microbial fuel cell (MFC) design. To address this drawback, the application of microbial (Escherichia coli EC) patch on cathode was tested. Pseudomonas aeruginosa BR was used as exoelectrogen during the study. The MFC reactor with a patch had a better electron transfer rate, degraded 94.64% of synthetic wastewater (BRSyW) and its current generation was increased by 95.66%. The maximum power density recorded for BRSyW was 259.34 ± 7.28 mW/m2. Application of patch in real wastewater (BR + Sludge) condition registered 63.18% of wastewater degradation, increment in current generation (59.71%) and decreased the charge transfer and ohmic resistances by 97.95% and 97.01% respectively. Apart from hindering oxygen diffusion and better current generation, this simple design also worked as a two-step degradation system. Thus, such MFC reactor is a potential candidate for wastewater management and green energy generation.

A novel concept of Vertical Up-Flow Forward Osmosis reactor: Design, performance and evaluation.

Performance of the forward osmosis (FO) process is limited due to the decline in water flux and increase in reverse salt flux. In this study, a novel Vertical Up-Flow Forward Osmosis (VUF-FO) reactor was designed and evaluated for eight different contacting patterns of feed and draw agent (DA). The best contacting pattern was compared with the basic H-shape reactor. Pulsating inlets were used for the recirculation of the feed and DA which helped in improving the performance by reducing the concentration polarization on membrane. Water flux in FO (active layer facing feed side) and PRO (active layer facing draw side) mode was 12.75 and 16.28 L/m2hr (LMH) respectively for the contacting pattern R3 and R5 after 8 h of the process. While the water flux in the H-shape reactor was 9.12 and 12.54 LMH for FO and PRO mode respectively. Diffusional behavior of water flux and reverse salt flux were also evaluated for both the FO reactors. Water flux in the H-shape reactor was declined to more than 60% from its initial value in both the modes (i.e. FO and PRO) due to the concentration polarization on membrane. Only 10% decline in water flux was observed for the VUF-FO reactor. This showed a better consistency of water flux in the VUF-FO reactor. The reverse salt flux in the VUF-FO reactor was less than 85% compared to the H-shape reactor. Therefore, a novel designed reactor improved the overall performance of FO in terms of water flux and reverse salt flux.

Technologies for the recovery of nutrients, water and energy from human urine: A review.

The global demand for a constant supply of fertilizer is increasing with the booming of the population. Nowadays more focus is given to the recovery and reuse of the nutrients rather than synthesis of the fertilizer from chemicals. Human urine is the best available resource for the primary macronutrients (Nitrogen, Phosphorus and Potassium) for the fertilizer as it contains 10-12 g/L nitrogen, 0.1-0.5 g/L phosphorous and 1.0-2.0 g/L potassium. For the recovery of these nutrients from human urine, various technologies are available which requires source separation and treatment. . In this review, a wide range of the technologies for the treatment of source-separated human urine are covered and discussed in detail. This review has categorized the technologies based on the recovery of nutrients, energy, and water from human urine. Among the various technologies available, Bio-electrochemical technologies are environmental friendly and recovers energy along with the nutrients. Forward Osmosis is the best available technology for the water recovery and for concentrating the nutrients in urine, without or minimal consumption of energy. However, experimental work in this technology is at its prior stage. A single technology is still not sufficient to recover nutrients, water and energy. Therefore, integration of two or more technologies seems essential.

Bioelectrochemical behaviour of a sequentially added biocatalytic coculture in a microbial fuel cell.

Bacterial isolates Pseudomonas aeruginosa BR, Alcaligenes faecalis SW and Escherichia coli EC from a microbial fuel cell (MFC) were cocultured with each other. The isolates were added in a specific sequence one after the other (two cultures in one reactor). The study helped us conceptualise the synergistic and antagonistic behaviour of bacterial isolates and also emphasised the sequence in which a culture can be introduced in an anode chamber. The coculture conditions were evaluated on the basis of redox activity, electron transfer rate, columbic efficiency, and internal resistances. A good syntropy in terms of power production was found between P. aeruginosa BR and E. coli EC that recorded a power generation of 207.593 ± 1.705 µW/m2 . The addition of any culture in any sequence affected the performance of P. aeruginosa BR. This culture when added as a secondary culture in the reactor enhanced the performance of that reactor. The sequence of addition of a culture in a reactor affected the performance in the combinations of (a) P. aeruginosa BR and A. faecalis SW and (b) A. faecalis SW and E. coli EC.

Occurrence of anionic surfactants in treated sewage: risk assessment to aquatic environment.

A comparative evaluation of occurrence of and risk to aquatic environment due to anionic surfactants (AS) in treated effluents from three main treatment processes, i.e. activated sludge process (ASP), oxidation pond (OP), and upflow anaerobic sludge blanket reactor (UASBR) is presented. UASBR effluents contained substantial concentrations of AS (4.25-5.91mg/L as average AS removal was not found to exceed 18%). Post-treatment of UASBR effluent using 1-1.6 days detention, anaerobic polishing ponds (PP) was also found quite ineffective. In UASBR-PP combine, AS reduced only up to 30%. Effluents from OP based sewage treatment plants (STPs) also contained significant concentrations of AS. On the contrary, effluent AS or linear alkylbenzene sulfonate (LAS) concentrations recorded in ASP effluents were quite low (less than 0.2mg/L). Unlike UASBR, LAS or AS removals greater than 99% are achieved in ASP. Treated effluents from UASBR and OP based STPs when discharged to aquatic ecosystems are likely to cause substantial risk to aquatic environment due to the presence of AS while effluents from ASP are not supposed to pose risk. Need to find an effective aerobic post-treatment unit to UASBR for desired removal of AS is emphasized.

Anionic surfactants in treated sewage and sludges: risk assessment to aquatic and terrestrial environments.

Compared to low concentrations of anionic surfactants (AS) in activated sludge process effluents (ASP) (<0.2 mg/L), upflow anaerobic sludge blanket-polishing pond (UASB-PP) effluents were found to contain very high concentrations of AS (>3.5 mg/L). AS (or linear alkylbenzen sulfonate, LAS) removals >99% have been found for ASP while in case of UASB-PP it was found to be < or = 30%. AS concentrations averaged 7347 and 1452 mg/kg dry wt. in wet UASB and dried sludges, respectively. Treated sewage from UASB based sewage treatment plants (STPs) when discharged to aquatic ecosystems are likely to generate substantial risk. Post-treatment using 1-1.6d detention, anaerobic, non-algal polishing ponds was found ineffective. Need of utilizing an aerobic method of post-treatment of UASB effluent in place of an anaerobic one has been emphasized. Natural drying of UASB sludges on sludge drying beds (SDBs) under aerobic conditions results in reduction of adsorbed AS by around 80%. Application of UASB sludges on SDBs was found simple, economical and effective. While disposal of treated UASB effluent may cause risk to aquatic ecosystems, use of dried UASB sludges is not likely to cause risk to terrestrial ecosystems.

Degradation of anionic surfactants during drying of UASBR sludges on sand drying beds.

Anionic surfactant (AS) concentrations in wet up-flow anaerobic sludge blanket reactor (UASBR) sludges from five sewage treatment plants (STPs) were found to range from 4480 to 9,233 mg kg(-1)dry wt. (average 7,347 mg kg(-1)dry wt.) over a period of 18 months. After drying on sand drying beds (SDBs), AS in dried-stabilized sludges averaged 1,452 mg kg(-1)dry wt., a reduction of around 80%. The kinetics of drying followed simple first-order reduction of moisture with value of drying constant (k(d))=0.051 d(-1). Reduction of AS also followed first-order kinetics. AS degradation rate constant (k(AS)) was found to be 0.034 d(-1) and half-life of AS as 20 days. The order of rates of removal observed was k(d)>k(AS)>k(COD)>k(OM) (drying >AS degradation>COD reduction>organic matter reduction). For the three applications of dried-stabilized sludges (soil, agricultural soil, grassland), values of risk quotient (RQ) were found to be <1, indicating no risk.