Effects of External Resistance on Microbial Fuel Cell’s Performance

Biodegradation of human faecal sludge for photosynthetic bioelectricity generation and seawater desalination in a microbial desalination cell

ABSTRACTInaccessibility and expensiveness of vital infrastructures are the main problems in some urban and rural areas to supply fresh water, sustainable energy, and wastewater treatment. An effective solution is the integration of several systems in an environmentally friendly technology of the photosynthetic microbial desalination cell (PMDC). The aim of this study is to assess the process characterisation of an algae-based PMDC, which was loaded with a high-strength mixture of human feces and urine (HFS). The PMDC was also able to efficiently remove COD and total nitrogen of HFS by 50% and 94%, respectively. The maximum power density, voltage, and desalination efficiency of 362.5 mW/m², 175.2 mV, and 60% were accomplished. Adequate parameter adjustment led to a remarkable maximum of 2.25 g/L.d in the ion removal rate. In addition, an energy balance was governed showing that zero or positive net energy in PMDC is feasible by replacing the main energy consumers. Based on the results, this type of MDC had a high efficiency for simultaneous saline water desalination and HFS treatment, which makes it attractive for further studies of upscaling and its application in remote areas.

Bioelectrochemical system as an innovative technology for treatment of produced water from oil and gas industry: A review

Disposal of the high volume of produced water (PW) is a big challenge to the oil and gas industry. High cost of conventional treatment facilities, increasing energy prices and environmental concern had focused governments and the industry itself on more efficient treatment methods. Bioelectrochemical system (BES) has attracted the attention of researchers because it represents a sustainable way to treat wastewater. This is the first review that summarizes the progress done in PW-fed BESs with a critical analysis of the parameters that influence their performances. Inoculum, temperature, hydraulic retention time, external resistance, and the use of real or synthetic produced water were found to be deeply related to the performance of BES. Microbial fuel cells are the most analyzed BES in this field followed by different types of microbial desalination cells. High concentration of sulfates in PW suggests that most of hydrocarbons are removed mainly by using sulfates as terminal electron acceptor (TEA), but other TEAs such as nitrate or metals can also be employed. The use of real PW as feed in experiments is highly recommended because biofilms when using synthetic PW are not the same. This review is believed to be helpful in guiding the research directions on the use of BES for PW treatment, and to speed up the practical application of BES technology in oil and gas industry.

Interrelation between sulphur and conductive materials and its impact on ammonium and organic pollutants removal in electroactive wetlands

This investigation is the first of its kind to evaluate the interrelation of sulphate (SO₄^2-) with conductive materials as well as their individual and synergetic effects on the removal of ammonium and organic pollutants in electroactive wetlands, also known as constructed wetland (CW) - microbial fuel cell (MFC). The role of MFC components in CW was investigated to treat the sulphate containing wastewater under a long-term operation without any toxicity build-up in the system. A comparative study was also performed between CW-MFC and CW, where sulphate containing wastewater (S-replete) and without sulphate wastewater (S-deplete) was assessed. The S-replete showed high NH₄⁺ removal than the S-deplete, and the requesnce of removal was: CW-MFC-replete>CW-MFC-deplete>CW-replete>CW-deplete. The chemical oxygen demand (COD) removal was high in the case of CW-MFC-replete, and the sequence of removal was CW-MFC-replete>CW-MFC-deplete>CW-deplete>CW-replete. X-ray photon spectroscopic study indicates 0.84% sulphur accumulation in CW-MFC-replete and 2.49% in CW-replete, indicating high sulphur precipitation in CW without the MFC component. The high relative abundance of class Deltaproteobacteria (7.3%) in CW-MFC-replete along with increased microbial diversity (Shannon index=3.5) rationalise the symbiosis of sulphate reducing/oxidising microbes and its impact on the treatment performance and electrochemical activity.

Performance of air-cathode stacked microbial fuel cells systems for wastewater treatment and electricity production

Two different air-cathode stacked microbial fuel cell (MFC) configurations were evaluated under continuous flow during the treatment of municipal wastewater and electricity production at a hydraulic retention time (HRT) of 3, 1, and 0.5 d. Stacked MFC 1 was formed by 20 individual air-cathode MFC units. The second stacked MFC (stacked MFC 2) consisted of 40 air-cathode MFC units placed in a shared reactor. The maximum voltages produced at closed circuit (1,000 Ω) were 170 mV for stacked MFC 1 and 94 mV for stacked MFC 2. Different power densities in each MFC unit were obtained due to a potential drop phenomenon and to a change in chemical oxygen demand (COD) concentrations inside reactors. The maximum power densities from individual MFC units were up to 1,107 mW/m² for stacked MFC 1 and up to 472 mW/m² for stacked MFC 2. The maximum power densities in stacked MFC 1 and MFC 2 connected in series were 79 mW/m² and 4 mW/m², respectively. Electricity generation and COD removal efficiencies were reduced when the HRT was decreased. High removal efficiencies of 84% of COD, 47% of total nitrogen, and 30% of total phosphorus were obtained during municipal wastewater treatment.