Treatment of waste activated sludge and the enhancement mechanism for electron transfer in an osmotic microbial fuel cell.

An innovative application of osmotic microbial fuel cell (OsMFC) for enhanced activated sludge thickening and stabilization with bioelectricity generation.

In-situ alkaline pretreatment of waste activated sludge in microbial fuel cell enhanced power production

Performance investigation of osmotic microbial fuel cell under different operational conditions: Effect of aeration mode, external resistance, and substrate concentrations

The overall objective of this thesis was to investigate ways to improve the extent and rate of waste activated sludge (WAS) hydrolysis by researching the WAS degrading activities and mechanisms of the aquatic worm Tubifex tubifex (T. tubifex) as a starting point. The WAS degrading aquatic worms were taken as a model “biochemical reactor” of which its conversion processes still need to be unravelled. Because the worms are known for their excellent performance in WAS-solids reduction, i.e., up to 45% volatile solids (VS) reduction in 4 – 5 days, the focus was on worm-based enzymatic processes for improving WAS hydrolysis. Generally, T. tubifex predation shows significantly higher WAS conversion rates compared to anaerobic and aerobic digestion processes. However, information on the effect of WAS predation on the overall WAS biodegradability was lacking. Hereto, experiments were conducted to assess the ultimate WAS biodegradability potential, after which results were used as a reference to compare the biodegradability potential of different combinations of worm predation and anaerobic digestion. Interestingly, worm predation combinations showed superior solids removal rates and superior overall conversion rates, compared to solely conventional anaerobic digestion. However, the overall WAS biodegradability potential was similar in both experimental set-ups, reaching 58% and 49% removal for chemical oxygen demand (COD) and VS respectively. The improved WAS conversion rates during worm predation were related to the efficient removal of protein-like and, to a smaller extent, polysaccharide-like substances from the sludge matrix. Additionally, alginate-like exopolysaccharides (ALE), were partly consumed during worm treatment of WAS. The removal of protein, polysaccharide and ALE-like substances resulted in the disintegration of sludge flocs and the release of fulvic and humic substances as well as the cations Mg2+, Al3+ and Fe3+ from the sludge matrix. The cations and the humic and fulvic substances have a known structural function in the extracellular polymeric substances (EPS) of sludge flocs and are therefore, most likely tightly associated with the removed protein-like fraction. Corroborating with the removal of a protein-like fraction, an increased protease activity was observed in the predated WAS. The improved protease activity was likely related to T. tubifex based enzymes and/or the excretion of intestinal proteolytic bacteria. More specifically, a maximum of 73% of the proteolytic activity, related to the conversion of the model substrate casein, was due to the activity of the worms, while the remaining activity could be linked to the intestinal proteolytic bacteria. The synergy between bacteria and worms was further investigated using microbial community analysis. We showed that the worm faeces produced through WAS predation shared more similarities in microbial structure with predated protein rich substrates as compared to the WAS itself. The microbial change towards a microbiome, which was apparently related to protein degradation, was probably due to favourable conditions in the worm gut that facilitated a protein-degrading microbial community. It was further found that the genera Burkholderiales, Chryseobacterium and Flavobacterium were associated with predation by T. tubifex and are likely related to protein degradation. Overall, the research demonstrated that the key aspects of efficient WAS hydrolysis are related to the removal and conversion of protein- and alginate-like substances as well as elevated protease activity. The type of proteases and possibly other mechanisms such as the lytic capabilities of the aquatic worms are yet to be investigated.

A novel osmotic microbial fuel cell (OsMFC) was developed by using a forward osmosis (FO) membrane as a separator. The performance of the OsMFC was examined with either NaCl solution or artificial seawater as a catholyte (draw solution). A conventional MFC with a cation exchange membrane was also operated in parallel for comparison. It was found that the OsMFC produced more electricity than the MFC in both batch operation (NaCl solution) and continuous operation (seawater), likely due to better proton transport with water flux through the FO membrane. Water flux from the anode into the cathode was clearly observed with the OsMFC but not in the MFC. The solute concentration of the catholyte affected both electricity generation and water flux. These results provide a proof of concept that an OsMFC can simultaneously accomplish wastewater treatment, water extraction (from the wastewater), and electricity generation. The potential applications of the OsMFC are proposed for either water reuse (linking to reverse osmosis for reconcentration of draw solution) or seawater desalination (connecting with microbial desalination cells for further wastewater treatment and desalination).

Recent advances in osmotic microbial fuel cell technology: A review

Effects of current generation and electrolyte pH on reverse salt flux across thin film composite membrane in osmotic microbial fuel cells

Thermal/alkaline pretreatment of waste activated sludge combined with a microbial fuel cell operated at alkaline pH for efficient energy recovery

Osmotic microbial fuel cells (OsMFCs) with the abilities to simultaneously treat wastewater, produce clean water, and electricity provided a novel approach for the application of microbial fuel cell (MFC) and forward osmosis (FO). This synergistic merging of functions significantly improved the performances of OsMFCs. Nonetheless, despite their promising potential, OsMFCs currently receive inadequate attention in wastewater treatment, water reclamation, and energy recovery. In this review, we delved into the cooperation mechanisms between the MFC and the FO. MFC facilitates the FO process by promoting water flux, reducing reverse solute flux (RSF), and degrading contaminants in the feed solution (FS). Moreover, the water flux based on the FO principle contributed to MFC's electricity generation capability. Furthermore, we summarized the potential roles of OsMFCs in resource recovery, including nutrient, energy, and water recovery, and identified the key factors, such as configurations, FO membranes, and draw solutions (DS). We prospected the practical applications of OsMFCs in the future, including their capabilities to remove emerging pollutants. Finally, we also highlighted the existing challenges in membrane fouling, system expansion, and RSF. We hope this review serves as a useful guide for the practical implementation of OsMFCs.

PURPOSE: An osmotic microbial fuel cell (OsMFC) is derived from the integration of a forward osmosis (FO) membrane into a conventional microbial fuel cell (MFC), with enhanced performance in bioelectricity generation from organic matter and recovery of high-quality water. The environmental impacts of this newly developed technology, however, have not been studied. To understand and potentially reduce the environmental impacts of the OsMFC technology, the environmental impacts have been assessed. METHODS: An attributional life cycle assessment (LCA) model has been developed to evaluate the cradle-to-grave environmental impacts of the OsMFC based on a lab-scale prototype. The International Life Cycle Data System (ILCD) method has been applied to calculate and characterize the environmental impacts of treating 1 L of water by using the OsMFC technology in GaBi 8.7. Sensitivity and scenario analyses have been employed to assess the environmental impact variations based on changing power densities and different disposal methods, respectively. RESULTS AND DISCUSSION: The results indicate that several factors including raw material extraction, system operation, and end-of-life (EoL) stages have relatively large impacts in certain categories. The raw material extraction and system operation take up 50.04% and 32.06% of global warming potential (GWP), respectively. The EoL expends 98.02% of ecotoxicity potential (ETP), 54.31% of eutrophication potential (EP), and 52.24% of human toxicity potential (HTP). A comparison of the OsMFC with other bioelectrochemical systems (BESs) reveals that it has higher GWP due to the polymethylmethacrylate (PMMA) sheeting used to construct the cell and the stainless steel used to build the cathode electrode, but comparable acidification potential (AP), eutrophication potential (EP), ozone depletion potential (ODP), and respiratory inorganics (RI). The greenhouse gas (GHG) emissions of the OsMFC are also benchmarked with those of the conventional wastewater treatment methods, and it shows that the OsMFC has higher GHG emissions than the conventional wastewater treatment methods at the current power density. However, the results may change dramatically with the change of materials and cell configurations. CONCLUSIONS: According to the analysis, cell materials, cell configuration, electricity usage during the operation stage, and disposal methods are major problems to solve in the development of the OsMFC technology. Enhancement of power density and alternation of cell materials and configuration may turn out to be effective methods to alleviate the environmental impacts and increase market competitiveness of the OsMFC technology in the future.

The effects of mixed feeding of boiled potato and waste activated sludge (WAS) on the performance of a microbial fuel cell (MFC) in treating solid potato waste were investigated. The coulombic efficiency (CE) of four MFCs fed with potato cubes containing 0, 48.7, 67.3 and 85.6% of boiled potato was 53.5, 70.5, 92.7 and 71.1%, respectively, indicating enhanced electricity generation and the existence of an optimum mixing ratio. The hydrolysis rate estimated using a first-order sequential hydrolysis model increased from 0.061 to 0.191 day-1, leading to shortening of the startup time for current density reaching its maximum from 25 to 5 days. The final chemical oxygen demand (COD) removal reached 85%. The CE of seven MFCs, fed with raw potato alone, sterilized/unsterilized WAS alone, and four mixed samples of raw potato with sterilized WAS at ratios of 2:1 and 4:1 and unsterilized WAS at 2:1 and 4:1, was found to be 6.1, 43.6, 0.3, 31.0, 16.5, 0.9 and 31.1%, respectively. The hydrolysis rate increased from 0.056 to 0.089 day-1, and the final COD removal changed from 39.5 to 89.6% following the order: potato alone > mixture of potato & WAS > sterilized WAS alone > unsterilized WAS alone.

Understanding electricity generation in osmotic microbial fuel cells through integrated experimental investigation and mathematical modeling

Combination of microbial fuel cell (MFC) and forward osmosis (FO) is called an osmotic microbial fuel cell (OMFC). Because of the high cost of FO membranes, for the first time laboratory made FO membrane has been used in OMFC. This study investigates the performance of FO membrane in OMFC treating glucose as substrate and 2M NaCl as draw solution. The FO membrane was able to achieve 18.43 lm−2 h−1 (LMH) and for fouled FO membrane it was 15.26 lm−2 h−1. The OMFC constantly produced bioelectricity and achieved maximum current density 139.52 A/m3 and power density 27.38 W/m3. The energy production of OMFC was 0.438 kWh/m3.

Osmotic microbial fuel cells (OsMFCs) can integrate forward osmosis into microbial fuel cells (MFCs), which are able to perform organic elimination, bioenergy production, and high-class water abstraction from wastewater. However, it is not well understood how the unique feature of OsMFCs, i.e., water flux, helps improve current generation. Based on experimental studies and the Springer model theory, a new method for representing water transmission in OsMFC membranes is put forward that considers water transmission by electro-osmosis resulting from proton flux through the membrane and by osmosis resulting from osmotic pressure grades of water. In this research, osmotic water transmission is associated with the permeable differential pressure resulting from the ionic differential concentration in the membrane, and electro-osmotic water transmission is found to be proportional to the current density employed but irrelevant to the composition gradients. The net water transmission in OsMFC depends on the operation time and increases accordingly with higher current density and composition gradients. Furthermore, the membrane’s proton conductibility and water-transmission capabilities are significantly affected by the moisture content, which decreases from the negative electrode to the positive electrode in the OsMFC system. Increasing water flux with higher osmotic pressure and current density is therefore able to diminish the resistance of the membrane.

Activated sludge processes are key technologies to treat wastewater. These biological processes produce huge amounts of waste activated sludge (WAS), now commonly called biosolids. Mechanical, thermal, and/or chemical WAS conditioning techniques have been proposed to reduce the sludge burden. The ultrasonic treatment of WAS is quite novel.The present paper reports on extensive investigations using an ultrasonic treatment of WAS, to study its potential to meet one or all of four objectives: (1) reduce WAS quantities; (2) achieve a better dewaterability; (3) provoke a release of soluble chemical oxygen demand (COD) from the biosolids, preferably transformed into biodegradable organics; and (4) possibly destroy the filamentous microorganisms responsible for sludge bulking. Although meeting these objectives would help to solve the problems cited, the energy consumption could be a considerable drawback: the paper will thus assess whether all or some objectives are met, and at what operational cost.A literature survey defines the occurring phenomena (cavitation) and the important operation parameters [such as frequency, duration, specific energy input (SE)].The experiments are carried out in a batch reactor of volume up to 2.3 L. The ultrasonic equipment consisted of a generator, a converter, and a sonotrode, supplied by Alpha Ultrasonics under the brand name of Telsonic. Three different kinds of sludge were tested, with different concentrations of dry solids (DS) between approximately 3.5 and 14 g DS/L WAS. Ultrasonic energy was introduced in a continuous manner (against possible pulsed operation). The major operational parameters studied include duration of the ultrasonic treatment and specific energy input. The applied frequency was set at 20 kHz.The release of COD from the WAS phase into the filtrate phase is a function of the specific energy input with yields of nearly 30% achievable at SE values of 30,000 kJ/kg DS. A major fraction of the COD is transformed into biodegradable organics (BOD). The reduction in DS fraction of the sludge is proportional to the COD release rates.Although the DS content is reduced, the dewaterability of the sludge is not improved. This reflects itself in increased filtration times during vacuum filtration and in increased values of the capillary suction time (CST). This more difficult dewaterability is the result of considerably reduced floc sizes, offering an extended surface area: more surface water is bound (CST increases) and the filterability decreases as a result of clogging of the cake. To reach the same dryness as for the untreated cake, the required dosage of polyelectrolyte is nearly doubled when the SE of the ultrasound treatment is increased from 7500 to 20,000 kJ/kg DS.The ultrasonic reduction of filamentous WAS organisms is not conclusive and very little effect is seen at low intensities and short treatment durations. Microscopic analysis of the WAS identified the dominant presence of Actynomyces.The release of soluble COD and BOD certainly merit further research. © 2006 American Institute of Chemical Engineers Environ Prog, 2006