Enhanced bioelectrochemical treatment of petroleum refinery wastewater with Labaneh whey as co-substrate

Petroleum refinery wastewater (PRW) that contains recalcitrant components as the major portion of constituents is difficult to treat by conventional biological processes. Microbial fuel cells (MFCs) which also produce renewable energy were found to be promising for the treatment of PRW. However, due to the high total dissolved solids and low organic matter content, the efficiency of the process is limited. Labaneh whey (LW) wastewater, having higher biodegradability and high organic matter was evaluated as co-substrate along with PRW in standard dual chambered MFC to achieve improved power generation and treatment efficiency. Among several concentrations of LW as co-substrate in the range of 5–30% (v/v) with PRW, 85:15 (PRW:LW) showed to have the highest power generation (power density (PD), 832 mW/m2), which is two times higher than the control with PRW as sole substrate (PD, 420 mW/m2). On the contrary, a maximum substrate degradation rate of 0.420 kg COD/m3-day (ξCOD, 63.10%), was registered with 80:20 feed. Higher LW ratios in PRW lead to the production of VFA which in turn gradually decreased the anolyte pH to below 4.5 (70:30 feed). This resulted in a drop in the performance of MFC with respect to power generation (274 mW/m2, 70:30 feed) and substrate degradation (ξCOD, 17.84%). 2020, The Author(s)

Integrating electrochemical and bioelectrochemical systems for energetically sustainable treatment of produced water

Pollutants present in produced water (PW) are recalcitrant in nature and difficult to treat with simple processes. Energetically sustainable and novel approach was developed by integrating electrochemical cell (EC, Primary process) and microbial fuel cell (MFC, secondary process) to treat PW. Five different current densities (26, 36, 48, 59 and 71 mA/cm2) were applied in independent EC experiments (4 h). The effluents from each EC operation was further treated by MFC (10 h), to harness bioelectricity. Operational variations were maintained only in EC phase and kept MFC phase similar. This integration revealed that the extent of bioelectricity generation depends on the electrochemical oxidation of EC process. Overall, maximum power generation of 2.74 mW was registered with EC-effluent from 48 mA/cm2. The integration also showed highest TPH removal efficiency of 89% (EC, 305 mg/L; MFC, 317 mg/L) and COD removal efficiency of 89.6% (EC, 2160 mg/L; MFC, 1960 mg/L) at 71 mA/cm2. Other pollutants of PW, such as sulfates and TDS also removed efficiently (sulfates, 42.6%; TDS, 34.3%). Cyclic voltammetric (CV) and derivative analysis of the anodic biofilm were correlated well with MFC performance during different EC-effluents as substrate, indicating NADH involvement in bioanodic electron transfer. The balance between energy utilization in EC and bioelectricity generation by MFC was depicted that the integration of EC and MFC results in net positive energy. Maximum net power generation of 565 mWh (350 mL of anode volume) was resulted by integration. This integration depicts its potential to generate 1615 Whm−3 from the treatment of 1KL PW

Sewage enhanced bioelectrochemical degradation of petroleum hydrocarbons in soil environment through bioelectro-stimulation

The impact of readily biodegradable substrates (sewage and acetate) in bioelectroremediation of hydrocarbons (PW) was evaluated in a bench-scale soil-based hybrid bioelectrochemical system. Addition of bioelectro-stimulants evidenced efficient degradation than control operation. Acetate and sewage were exhibited power density of 1126 mW/m2 and 1145 mW/m2, respectively, which is almost 15 % higher than control (without stimulant, 974 mW/m2). Increased electrochemical activity was correlated well with total petroleum hydrocarbons (TPH) degradation through addition of acetate (TPHR, 525 mg/L, 67.4 %) and sewage (TPHR, 560 mg/L,71.8 %) compared to the control operation (TPHR, 503 mg/L, 64.5 %). Similarly, chemical oxygen demand (COD) reduction was also enhanced from 69.0 % (control) to 72.1 % and 74.6 % with acetate and sewage, respectively. Sewage and acetate also showed a positive role in sulfates removal, which enhanced from 56.0 % (control) to 62.9 % (acetate) and 72.6 % (sewage). This study signifies the superior function of sewage as biostimulant compared to acetate for the bioelectroremediation of hydrocarbons in contaminated soils

Biorefinery perspectives of microbial electrolysis cells (MECs) for hydrogen and valuable chemicals production through wastewater treatment

The degradation of waste organics through microbial electrolysis cell (MEC) generates hydrogen (H2) gas in an economically efficient way. MEC is known as the advanced concept of the microbial fuel cell (MFC) but requires a minor amount of supplementary electrical energy to produce H2 in the cathode microenvironment. Different bio/processes could be integrated to generate additional energy from the substrate used in MECs, which would make the whole process more sustainable. On the other hand, the energy required to drive the MEC mechanism could be harvested from renewable energy sources. These integrations could advance the efficiency and economic feasibility of the whole process. The present review critically discusses all the integrations investigated to date with MECs such as MFCs, anaerobic digestion, microbial desalination cells, membrane bioreactors, solar energy harvesting systems, etc. Energy generating non-biological and eco-friendly processes (such as dye-sensitized solar cells and thermoelectric microconverters) which could also be integrated with MECs, are also presented and reviewed. Achieving a comprehensive understanding about MEC integration could help with developing advanced biorefineries towards more sustainable energy management. Finally, the challenges related to the scaling up of these processes are also scrutinized with the aim to identify the practical hurdles faced in the MEC processes

Sustainable bioelectrochemical systems for bioenergy generation via waste treatment from petroleum industries

Petroleum industries are large water consumers and generate a lot of wastewater at various stages of industrial operations. Wastewater from the petroleum industries contain recalcitrant pollutants such as hydrocarbons that are present in high concentrations, dissolved solids and sulfur compounds that can pose potential environmental threat. Bioelectrochemical systems (BESs) are known to be sustainable processes to treat the various kinds of wastewaters such as petroleum wastewater, while simultaneously generating the bioelectricity and value-added chemicals. This review focuses on various applications of BESs such as microbial fuel cells (MFC), microbial electrolysis cells (MEC), and microbial desalination cells (MDC) using diverse types of wastewaters (petroleum sludge, produced water, formation water, and petroleum refinery wastewater) from the petroleum industries. Overall, a hybrid type BES with hydrocarbon wastewater achieved a 98% of columbic efficiency, 96.5% of chemical oxygen demand (COD), 99% of phenanthrene, 94% of pyrene and 80% of TDS removal which are superior to single and dual chamber BES performances. The review also compares the existing biological processes with BESs in terms of the treatment of hydrocarbons and process sustainability. Treatment efficiency of petroleum wastes via the BES can be further improved by integrating the biological and electrochemical processes to develop a sustainable approach to bio-refinery route

Impact of dissolved carbon dioxide concentration on the process parameters during its conversion to acetate through microbial electrosynthesis

© 2018 The Royal Society of Chemistry. The reduction of carbon dioxide (CO2) released from industry can help to reduce the emissions of greenhouse gases (GHGs) to the atmosphere while at the same time producing value-added chemicals and contributing to carbon fixation. Microbial electrosynthesis (MES) is a recently developed process which accomplishes this idea by using cathodic bacteria at the expense of only minimum energy. In this study, enriched mixed homoacetogenic bacteria as cathodic biocatalysts for the reduction of CO2 with five different concentrations were evaluated to produce acetate at a constant potential. Increasing the carbon concentration showed an improved acetate production rate and carbon conversion efficiency. A maximum acetate production rate of 142.2 mg L per day and a maximum carbon conversion efficiency of 84% were achieved, respectively, at 4.0 and 2.5 g HCO3- L-1. The changes in pH due to interactive reactions between the bicarbonate (substrate) and acetate (products) were able to create a buffering nature in the catholyte controlling the operating parameters of the MES process, such as pH and substrate specificity. A higher acetate production shifted the catholyte pH toward acidic conditions, which further triggered favorable conditions for the bioelectrochemical reduction of acetate to ethanol.G. Mohanakrishna gratefully acknowledges the Marie-Curie Intra-European Fellowship (IEF) supported project BIO-ELECTRO-ETHYLENE (Grant No: 626959) from the European Commission