Hydrolytic effects of acid and enzymatic pre-treatment on the anaerobic biodegradability of <i>Ascophyllum nodosum</i> and <i>Laminaria digitata</i> species of brown seaweed

Abundant marine biomass in coastal regions has continued to attract increasing attention in recent times as a possible source of renewable energy. This study aimed to evaluate the effects of hydrolytic pre-treatment for the purpose of enhancing biogas yield of Laminaria digitata and Ascophyllum nodosum species found on the west coast of Scotland. Results show that L. digitata, in its natural and untreated form, appears to be more readily hydrolysable than A. nodosum. Two treatments were assessed: acid only and acid followed by enzyme. Both treatments enhanced the hydrolysis of both seaweed species, with acid-enzyme treatment providing a better performance

Ethanol production from brown seaweed using non-conventional yeasts

The use of macroalgae (seaweed) as a potential source of biofuels has attracted considerable worldwide interest. Since brown algae, especially the giant kelp, grow very rapidly and contain considerable amounts of polysaccharides, coupled with low lignin content, they represent attractive candidates for bioconversion to ethanol through yeast fermentation processes. In the current study, powdered dried seaweeds (Ascophylum nodosum and Laminaria digitata) were pre-treated with dilute sulphuric acid and hydrolysed with commercially available enzymes to liberate fermentable sugars. Higher sugar concentrations were obtained from L. digitata compared with A. nodosum with glucose and rhamnose being the predominant sugars, respectively, liberated from these seaweeds. Fermentation of the resultant seaweed sugars was performed using two non-conventional yeast strains: Scheffersomyces (Pichia) stipitis and Kluyveromyces marxianus based on their abilities to utilise a wide range of sugars. Although the yields of ethanol were quite low (at around 6 g/L), macroalgal ethanol production was slightly higher using K. marxianus compared with S. stipitis. The results obtained demonstrate the feasibility of obtaining ethanol from brown algae using relatively straightforward bioprocess technology, together with non-conventional yeasts. Conversion efficiency of these non-conventional yeasts could be maximised by operating the fermentation process based on the physiological requirements of the yeasts

Fate of three bioluminescent pathogenic bacteria fed through a cascade of urine microbial fuel cells

Microbial fuel cell (MFC) technology is currently gaining recognition as one of the most promising bioenergy technologies of the future. One aspect of this technology that has received little attention is the disinfection of effluents and the fate of pathogenic organisms that find their way into the waste stream. In this study, three independent trials were carried out to evaluate the fate of three bioluminescent pathogenic bacteria (Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa and Staphylococcus aureus) introduced into the anodic chamber of a urine-fed cascade of 9 MFCs with matured, electroactive biofilms. These are common examples of enteric human pathogens, which could contaminate urine or waste streams. The results showed that the average power generation in the closed circuit cascade reached 754 ± 16 µW, with an average pathogen log-fold reduction of 6.24 ± 0.63 compared to 2.01 ± 0.26 for the open circuit cascade for all three pathogens. The results suggest that the bio-electrochemical reactions associated with electricity generation were the primary driving force for the inactivation of the introduced pathogens. These findings show that pathogenic organisms introduced into waste streams could be inactivated by the power-generating process within the MFC cascade system, thereby preventing propagation and thus rendering the effluent safer for possible reuse

Investigating the impact of inoculum source on anaerobic digestion of various species of marine macroalgae

This study investigated the intrinsic biodegradation potential of marine organic sediment for effective biogas production from various species of marine macroalgae and non-marine biomass. Biogas production potential tests were carried out on three species of seaweed harvested from the west coasts of Scotland, Laminaria digitata, Fucus serratus, and Saccharina latissima, and on a non-marine cellulose biomass seeded with uncultivated and unadapted anoxic marine sediments. As a comparison, the same experiments were repeated using the same substrates but seeded with active mesophilic anaerobically digested sewage sludge. For the cultures seeded with anoxic marine sediments, the highest methane yield was observed in both L. digitata and S. latissima cultures while F. serratus and cellulose, cultures performed relatively poorly. For those seeded with digested sludge, all cultures performed relatively well, except F. serratus. These results show that marine sediments can be effective inoculum for seaweeds digestion. Phylogenetic analyses of the methanogenic community in both sources of inoculum showed that the methanogen community within the sediment and sludge seeded cultures were different. Each culture was dominated by methanogenic populations suitable for the utilisation of the specific biomass derivatives and environmental conditions. For instance, members of the genus Methanosaeta which, dominated sludge seeded cultures were not detected in the sediment seeded cultures. A similar occurrence was observed for the genus Methanofollis which was only detected in the sediment seeded cultures. Hence, in areas where seaweed forms part of a co-digestion with non-marine biomass, start-up using a mixture of anoxic marine sediments and digested wastewater sludge has the potential to provide greater process stability and robustness than using either as sole inoculum

Resilience and limitations of MFC anodic community when exposed to antibacterial agents

This study evaluates the fate of certain bactericidal agents introduced into microbial fuel cell (MFC) cascades and the response of the microbial community. We tested the response of functioning urine fed MFC cascades using two very different bactericidal agents: a common antibiotic (Ampicillin, 5 g/L) and a disinfectant (Chloroxylenol 4.8 g/L) in concentrations of up to 100 times higher than the usual dose. Results of power generation showed that the established bacteria community was able to withstand high concentrations of ampicillin with good recovery after 24 h of minor decline. However, power generation was adversely affected by the introduction of chloroxylenol, resulting in a 99% loss of power generation. Ampicillin was completely degraded within the MFC cascade (>99.99%), while chloroxylenol remained largely unaffected. Analysis of the microbial community before the addition of the bactericidal agents showed a significant bacterial diversity with at least 35 genera detected within the cascade. Microbial community analysis after ampicillin treatment showed the loss of a small number of bacterial communities and proportional fluctuations of specific strains within the individual MFCs community. On the other hand, there was a significant shift in the bacterial community after chloroxylenol treatment coupled with the loss of at least 13 bacterial genera across the cascade

Development of efficient electroactive biofilm in urine-fed microbial fuel cell cascades for bioelectricity generation

The Microbial fuel cell (MFC) technology harnesses the potential of some naturally occurring bacteria for electricity generation. Digested sludge is commonly used as the inoculum to initiate the process. There are, however, health hazards and practical issues associated with the use of digested sludge depending on its origin as well as the location for system deployment. This work reports the development of an efficient electroactive bacterial community within ceramic-based MFCs fed with human urine in the absence of sludge inoculum. The results show the development of a uniform bacterial community with power output levels equal to or higher than those generated from MFCs inoculated with sludge. In this case, the power generation begins within 2 days of the experimental set-up, compared to about 5 days in some sludge-inoculated MFCs, thus significantly reducing the start-up time. The metagenomics analysis of the successfully formed electroactive biofilm (EAB) shows significant shifts between the microbial ecology of the feeding material (fresh urine) and the developed anodic biofilm. A total of 21 bacteria genera were detected in the urine feedstock whilst up to 35 different genera were recorded in the developed biofilm. Members of Pseudomonas (18%) and Anaerolineaceae (17%) dominate the bacterial community of the fresh urine feed while members of Burkholderiaceae (up to 50%) and Tissierella (up to 29%) dominate the anodic EAB. These results highlight a significant shift in the bacterial community of the feedstock towards a selection and adaptation required for the various electrochemical reactions essential for survival through power generation

Urine in bioelectrochemical systems: An overall review

In recent years, human urine has been successfully used as an electrolyte and organic substrate in bioelectrochemical systems (BESs) mainly due of its unique properties. Urine contains organic compounds that can be utilised as a fuel for energy recovery in microbial fuel cells (MFCs) and it has high nutrient concentrations including nitrogen and phosphorous that can be concentrated and recovered in microbial electrosynthesis cells and microbial concentration cells. Moreover, human urine has high solution conductivity, which reduces the ohmic losses of these systems, improving BES output. This review describes the most recent advances in BESs utilising urine. Properties of neat human urine used in state‐of‐the‐art MFCs are described from basic to pilot‐scale and real implementation. Utilisation of urine in other bioelectrochemical systems for nutrient recovery is also discussed including proofs of concept to scale up systems

In Situ Development of Efficient Electrogenic Bacterial Community in Urine Fed Microbial Fuel Cell Cascades

Microbial fuel cell technology harnesses the potential of some naturally occurring bacteria for electricity generation. To initiate the operation of microbial fuel cells, inoculation with different types of bacterial community, including those found in activated sludge, are employed. There are however, health hazards associated with the use of digested activated sludge and this of course depends on where the sample has been sourced from. Organisms such as Mycobacterium tuberculosis, Pseudomonas aeruginosa and enteric viruses have been reported in activated sludge, which can have practical difficulties when working with such samples. Therefore, the development of an efficient electroactive bacterial community, capable of producing optimum power output without the need for sludge inoculation, would eliminate any potential risks. In the current study, we developed an efficient electroactive bacterial community within a ceramic based MFC system, using only fresh urine as the inoculum. Efficient biofilm development was achieved by stepwise adjustment of the external resistance, following 48 hours of open circuit operation. This resulted in a uniform bacterial community with power output levels &gt;50% higher than those inoculated (as per standard practice) with activated sludge. The results showed that power generation begins within 2 days of experimental set-up, compared to at least 5 days in sludge inoculated systems, thus significantly reducing start up time. Incidentally, the development of the bacterial community occurs irrespective of the freshness or age of the urine feed. Given the difficulty in moving suitable activated sludge across countries/borders and that practical application of MFCs technology is more likely to occur in remote rural locations, it is possible that suitable activated sludge might not be available for inoculation locally. Therefore, deployment of MFC systems capable of producing optimum power without the need for sludge-inoculation would be beneficial to their widespread global application. This is the first report of an in situ development of an electroactive bacterial community in urine-fed MFC systems that outperform those initially inoculated with activated sludge

Long-term bio-power of ceramic microbial fuel cells in individual and stacked configurations

© 2020 The Authors In order to improve the potential of Microbial Fuel Cells (MFCs) as an applicable technology, the main challenge is to engineer practical systems for bioenergy production at larger scales and to test how the prototypes withstand the challenges occurring during the prolonged operation under constant feeding regime with real waste stream. This work presents the performance assessment of low-cost ceramic MFCs in the individual, stacked (modular) and modular cascade (3 modules) configurations during long term operation up to 19 months, utilising neat human urine as feedstock. During 1 year, the performance of the individual MFC units reached up to 1.56 mW (22.3 W/m3), exhibiting only 20% power loss on day 350 which was significantly smaller in comparison to conventional proton or cation exchange membranes. The stack module comprising 22 MFCs reached up to 21.4 mW (11.9 W/m3) showing power recovery to the initial output levels after 580 days, whereas the 3-module cascade reached up to 75 mW (13.9 W/m3) of power, showing 20% power loss on day 446. In terms of chemical oxygen demand (COD) removal, the 3-module cascade configuration achieved a cumulative reduction of >92%, which is higher than that observed in the single module (56%)

Impact of inoculum type on the microbial community and power performance of urine-fed microbial fuel cells

Bacteria are the driving force of the microbial fuel cell (MFC) technology, which benefits from their natural ability to degrade organic matter and generate electricity. The development of an efficient anodic biofilm has a significant impact on the power performance of this technology so it is essential to understand the effects of the inoculum nature on the anodic bacterial diversity and establish its relationship with the power performance of the system. Thus, this work aims at analysing the impact of 3 different types of inoculum: (i) stored urine, (ii) sludge and (iii) effluent from a working MFC, on the microbial community of the anodic biofilm and therefore on the power performance of urine-fed ceramic MFCs. The results showed that MFCs inoculated with sludge outperformed the rest and reached a maximum power output of 40.38 mW·m−2anode (1.21 mW). The power performance of these systems increased over time whereas the power output by MFCs inoculated either with stored urine or effluent decreased after day 30. These results are directly related to the establishment and adaptation of the microbial community on the anode during the assay. Results showed the direct relationship between the bacterial community composition, originating from the different inocula, and power generation within the MFCs.</p