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Bioelectrochemical systems were proposed as a promising approach for the efficient valorization of biomass into 6–8 carbon atom medium-chain fatty acids (MCFAs), the precursors for high value-added chemicals or renewable energy, via acetyl-CoA-mediated chain elongation (CE). To achieve CE processes, exogenous electron donors (EDs), e.g., ethanol or lactic acid, were normally prerequisites. This research built a microbial electrolysis cell (MEC) for MCFAs biosynthesis from acetate without exogenous EDs addition. A wide range of applied voltages (0.6–1.2 V) was first employed to investigate the bioelectrocatalyzing response. The results show that caproate and butyrate were the main products formed from acetate under different applied voltages. Maximum caproate concentration (501 ± 12 mg COD/L) was reached at 0.8 V on day 3. Under this applied voltage, hydrogen partial pressure stabilized at about 0.1 bar, beneficial for MCFA production. Electron and carbon balances revealed that the electron-accepting capacity achieved 32% at 0.8 V, showing the highest interspecies electron transfer efficiency. Most of the carbon was recovered in the form of caproate (carbon loss was 9%). MiSeq sequencing revealed Rhodobacter and Clostridium_sensu_stricto playing the crucial role in the biosynthesis of caproate, while Acetobacterium, Acetoanaerobium, and Acetobacter represented the main ED contributors. Four available flora, i.e., homo-acetogen, anaerobic fermentation bacteria, electrode active bacteria, and nitrate-reducing bacteria, interacted and promoted caproate synthesis by molecular ecological network analysis.

An economically viable production of second-generation bioethanol by recombinant xylose-fermenting Saccharomyces cerevisiae requires higher xylose fermentation rates and improved glucose–xylose co-consumption. Moreover, xylose-fermenting S. cerevisiae recognises xylose as a non-fermentable rather than a fermentable carbon source, which might partly explain why xylose is not fermented into ethanol as efficiently as glucose. This study proposes propagating S. cerevisiae on non-fermentable carbon sources to enhance xylose metabolism during fermentation. When compared to yeast grown on sucrose, cells propagated on a mix of ethanol and glycerol in shake flasks showed up to 50% higher xylose utilisation rate (in a defined xylose medium) and a double maximum fermentation rate, together with an improved C5/C6 co-consumption (on an industrial softwood hydrolysate). Based on these results, an automated propagation protocol was developed, using a fed-batch approach and the respiratory quotient to guide the ethanol and glycerol-containing feed. This successfully produced 71.29 ± 0.91 g/L yeast with an average productivity of 1.03 ± 0.05 g/L/h. These empirical findings provide the basis for the design of a simple, yet effective yeast production strategy to be used in the second-generation bioethanol industry for increased fermentation efficiency.

It is widely accepted that plastic waste is one of our most urgent environmental concerns the world is currently facing. Plastic has contributed greatly to innovation in all fields, but the raw material for its production (fossil fuels), as well as the linear economy in which it is currently produced and used, makes the material problematic from a sustainability and human health perspectives. The emergence of bio-based plastics provides an opportunity to reduce dependency on fossil fuels and transition to a more circular plastics economy. For polyethylene terephthalate (PET), one of the most prevalent plastics in packaging and textiles, there exist two bio-based alternatives that are similar or superior in material property and recyclability. These are polyethylene furanoate (PEF) and polytrimethylene terephthalate (PTT). The overarching aim of this study was to examine the transition from fossil-based to renewable plastics, through the lens of PET upcycling into PEF and PTT. The process for the production of PEF and PTT from three feed streams (post-consumer PET waste, lignocellulosic biomass-derived cellulose and biodiesel-derived crude glycerol) was developed in the software SuperPro Designer and the economic viability assessed via a discounted cumulative cash flow (DCCF) analysis. This study represents a conceptual case study of the valorisation of existing plastic waste into new, recyclable bio-based plastics, for a more sustainable plastics production. A techno-economic analysis of the designed process revealed that the minimum selling price (MSP) of second generation-derived PEF and PTT is 3.13 USD/kg, and that utilities and the feedstock used for the production of 2,5-furandicarboxylic acid (FDCA) needed in PEF synthesis contributed the most to the process operating costs. The effect of recycling PEF and PTT through the process at three recycling rates (42%, 50% and 55%) was investigated and revealed that increased recycling could reduce the MSP of the 2G bio-plastics (by 48.5%) to 1.61 USD/kg. This demonstrates that increasing recycling rates would have a beneficial effect on the economic viability of the plastic biorefinery.

Wastewater and sewage sludge contain organic matter that can be valorized through conversion into energy and/or green chemicals. Moreover, resource recovery from these wastes has become the new focus of wastewater management, to develop more sustainable processes in a circular economy approach. The aim of this review was to analyze current sewage sludge management systems in Scandinavia with respect to resource recovery, in combination with other organic wastes. As anaerobic digestion (AD) was found to be the common sludge treatment approach in Scandinavia, different available organic municipal and industrial wastes were identified and compared, to evaluate the potential for expanding the resource recovery by anaerobic co-digestion. Additionally, a full-scale case study of co-digestion, as strategy for optimization of the anaerobic digestion treatment, was presented for each country, together with advanced biorefinery approaches to wastewater treatment and resource recovery.

Bioelectrochemical systems (BESs) are emerging technologies that are based on catalyzing (bio-)anode and (bio-)cathode reactions from waste biomass by exoelectrogenic microorganisms. Microbial electrolysis cell (MEC), which is one of the BESs’ technologies, is typically used to degrade organic wastes or wastewater for bioenergy recovery and biosynthesis. As one of the promising biotechnologies for resource recovery, value-added products have been obtained by MEC- or ME-integrated systems, such as hydrogen, methane, ethanol, etc. The fundamental reactions of (bio-)electron transport through anodic oxidation are well understood and allow us to increase reactor performance and efficiency. More attentions have been recently paid to cathode reactions on proton/electron transport and recovery, with or without microbial activities. Biogas upgrading systems have also been promoted in integrated systems, by combining bioelectrochemistry with various anaerobic processes. This chapter will focus on energy gas generation from waste organics involved in bioelectrochemical pathways and give an overview of bottlenecks and challenges related to this technology.

The aim of this work was to recover a mixture of carboxylates ranging from 2 to 7 carbon atoms using a strong anion exchange resin, followed by desorption with CO2-expanded methanol. Medium chain carboxylates hexanoate and heptanoate adsorbed better than acetate, and the corresponding medium chain carboxylic acids desorbed easier than acetic acid. Consequently, hexanoate and heptanoate were concentrated up to 14.6 and 20.7 times, respectively. These findings will enable effective separation and purification of the produced carboxylic acids. Notably, the presence of inorganic ions in the sample, such as chloride, decreased the adsorption affinity compared to a synthetic mixture only of carboxylates.

Electro-fermentation (EF) is an attractive way to implement the chain elongation (CE) process, by controlling the fermentation environment and reducing the dosage of external electron donors (EDs). However, besides the coexistence performance of external EDs and electrode, applications of EF technology on the fermentation broth containing both EDs and electron acceptors during CE process, are all still limited. The current study investigated the contribution of EF to caproate production, under different acetate: ethanol ratios (RA/E). The effect of multiple EDs, both from ethanol and the bio-cathode, on caproate production, was also assessed. A proof-of-concept, based on experimental data, was presented for the EF-mediated ethanol-driven CE process. Experimental results showed that ethanol, together with the additional electron donors from the bio-cathode, was beneficial for the stable caproate production. The caproate concentration increased with the decrease of RA/E, while the bio-cathode further contributed to 10.7%–26.1 % increase of caproate concentration. Meanwhile, the hydrogen partial pressure tended to 0.10 ± 0.01 bar in all controlled EF reactors, thus favoring caproate production. This was attributed to the increased availability EDs, i.e., hydrogen and ethanol, generated by the electrode and electrochemically active bacteria (EAB), which might create multiple additional pathways to achieve caproate production. Molecular ecological networks analysis of the key microbiomes further revealed underlying cooperative relationships, beneficial to the chain elongation process. The genus Clostridium_sensu_stricto, as the dominant microbial community, was positively related to acetogens, EAB and fermenters.

Plastic and plastic recycling/degradation has been in the spotlight during last decade, due to its increasing waste accumulation in all world’s ecosystems and the huge challenge deriving from micro-plastic pollution. Therefore, different strategies are under investigation, trying to cope with this problem. Although depolymerisation of plastics by chemico-physical methods seems to represent a promising technology, biodegradation by microorganisms has been raising interest in recent years. In fact, new studies regarding the possibility of engineering specific plastic-degrading enzymes have obtained much attention by the media, due to the hope of overcoming one of the main bottlenecks of this technology: the extremely slow conversion rates. In the following chapter, we will be discussing two important strategies, which are expected to help overcoming these bottlenecks: genetic engineering to improve the catalytic activity of plastic-degrading enzymes and the development of syntrophism and cross-feeding mechanisms in enriched microbial communities. Finally, the potential of ongoing studies and future trends will also be discussed.

The increasingly rapid growth of both, population- and food demands has driven a research race in food production efficiency through the last century, which has made the pesticide use seemingly unavoidable. However, many pesticides are very persistent and tend to accumulate in the ecosystem, often threatening biodiversity and public health. Although abiotic degradation of these compounds plays a role in many cases, the biodegradation of pesticides by microorganisms is usually the most important and dominant process. This natural degradation varies from site to site, depending on several factors, but it can be favourably improved by applying techniques such as bioaugmentation and biostimulation, which can lead to the cleaning-up of pesticide-contaminated soils. The present chapter introduces the most recent findings in the field of bioremediation of pesticides, critically discussing the main bottlenecks and how to overcome them. Factors affecting biodegradation of pesticide-polluted soils are presented, with a clear focus on the enrichment and selection strategies for relevant microbial strains. Case studies on bioaugmentation of contaminated soils and future trends are also described, including the microbial degradation of pesticide mixtures through mixed culture technology.

Current studies have employed various chemicals for disintegrating and hydrolyzing microbial cells in waste activated sludge (WAS). However, a comprehensive process assessment over the whole anaerobic digestion process has seldom been proposed. Besides, the characterization of microbial community responses to these chemicals is not well understood. In this study, the effects of five typical chemicals: solubilizer (β-cyclodextrin, CD), alkaline (NaOH), peroxide (peracetic-acid, PA), biological (rhamnolipid, RL) and chemical (sodium dodecylsulphate, SDS) surfactants on WAS digestion were examined. Higher efficiencies of WAS solubilization, hydrolysis and acidification were achieved by CD treatment, followed by RL and SDS. Methanogenesis was also strongly chemicals-dependent. Shifts in microbial community structure were observed in all chemical-pretreated WAS. The community in RL, CD and PA was dominated by microorganisms that anaerobically hydrolyze organics to acids, while that in NaOH and SDS was mainly associated to biogas production. This study proved that the overall performance of WAS digestion was substantially depended on the initial chemical pretreatments, which in turn influenced and was related to the microbial community structures. Although the economic advantage might not be clear yet, the findings obtained in this work may provide a scientific basis for the potential implementation of chemicals for WAS treatment.

Nowadays, fermentation of organic wastes for the production of carboxylic acids as precursors of higher-value products has attracted significant attention. In this paper, sewage sludge and food waste were co-fermented to produce carboxylic acids and study the subsequent chain elongation process. The Copenhagen waste stream scenario was taken as a case study. Firstly, design of experiments was used to investigate the overall carboxylic acids and hexanoic acid production in batch, as a function of the co-fermentation ratio, substrate to co-culture ratio and initial pH. Optimal operating conditions for hexanoic acid were obtained with SS/FW 6.61, S/Xo 6.73 and initial pH 6.83. Statistical optimization increased the overall carboxylic acid titer by 41%, while co-fermentation allowed to increase hexanoate annual production up to 77%. Furthermore, a continuous fermentation experiment was performed to study the effect of reactor operating conditions. The overall carboxylates titer was 2 times higher, which also favored chain elongation compared to batch mode. An increasing loading rate did not affect the overall carboxylate titer, however the hexanoic acid titer increased by 44%. A maximum titer of 4.9 g/l of hexanoic acid was produced, achieving a productivity of 2.46 g/l/d of hexanoic acid with a retention time of 2 d and no external electron donor addition. This would correspond to 610 t/y of hexanoic acid and 350 t/y of other carboxylic acids that could be produced, based on the waste availability in Copenhagen.

Acetate (HAc) production via acetogenesis is a promising biorefinery approachfor waste activated sludge (WAS); however, it is hampered by the thermodynamicconstraints of the bioconversion of 3-5 carbon atom short-chain fatty acids (SCFAs). Sulfate radical (SO4∙‾)-based advanced oxidation is regarded as an appropriatecandidate for accelerating WAS fermentation. In this study, we enriched anincomplete-oxidative sulfate reducing bacteria (io-SRB), combined with SO4∙‾oxidation (generated by potassium ferrate (PF) and sodium sulfite (Na2SO3)), to boost WAS acetogenesis. Generated sulfate during SO4∙‾ oxidation served as the necessary substrates for io-SRB metabolism. A proof-of-concept based on experimental data for the whole process is presented. Results confirmed that the PF+Na2SO3+SRB test achieved the maximum SCFAs generation (4261 ± 210 mg COD/L with 60.9 ± 0.5% HAc) over the PF+Na2SO3 test without io-SRB mediation (2521 ± 109 mg COD/L with 50.6 ± 0.3% HAc). Particle size analysis and fluorescence spectroscopy indicated that PF+Na2SO3 oxidation had positive effects on accelerating soluble organics release. SO4∙‾ was the key radical, playing the most important role, as indicated by electron paramagnetic resonance and radical scavenging analysis. X-ray photoelectron spectroscopy revealed that io-SRB mediation further promoted the transformation of polysaccharides and proteins into carboxylic acids, based on SO4∙‾ oxidation. Moreover, 79% Fe(VI) was reduced to Fe(III), and most S(IV) was converted to SO42-, approximately 40% of which was metabolized by io-SRB consortium. Clearly, SO4∙‾ oxidation and io-SRB stimulation significantly altered the composition of the key microbiome, with fermentative acidogenic bacteria predominating. The possible synergistic relationships among io-SRB, hydrolyzing bacteria and acidogens were revealed by molecular ecological network analysis. This study provides new insights 3 into the improvement of value-added bio-metabolite recovery from SO4∙−-based WAS fermentation.

Crude glycerol, a by-product from the biodiesel industry, can be converted by mixed microbial consortia into 1,3-propanediol (1,3-PDO) and volatile fatty acids. In this study, further conversion of these main products into polyhydroxyalkanoates (PHA) was investigated with the focus on 1,3-PDO. Two different approaches for the enrichment of PHA accumulating microbial consortia using an aerobic dynamic feeding strategy were applied. With the first approach, where nitrogen was present during the whole cycle, no net production of PHA from 1,3-PDO was observed in the fermented effluent, not even in a nitrogen-limited PHA accumulation assay. Nevertheless, experiments in synthetic substrates revealed that the conversion of 1,3-PDO to PHA was possible under nitrogen limiting conditions. Thus, a different enrichment strategy was formulated where nitrogen was limited during the feast phase to stimulate the storage response. Nitrogen was still supplied during the famine phase. With the latter strategy, a net production of PHA from 1,3-PDO was observed at a yield of 0.24 Cmol PHA/Cmol 1,3-PDO. The overall yield from the fermented effluent was 0.42 Cmol PHA/Cmol substrate. Overall, the PHA yield from 1,3-PDO seemed to be limited, similarly to when using glycerol as a substrate, by a decarboxylation step and accumulation of other storage polymers such as glycogen, and possibly, lipid inclusions.

This study investigated the possibility to perform statistical optimization of an enriched mixed microbial consortium, MMC, fed in continuous with a highly inhibiting 2G glycerol, for the joint production of 1,3 propanediol (1,3 PDO) and butyric acid (BuA). Key variables taken into consideration were HRT, pH and feed concentration. The optimized process reached a glycerol consumption rate of 137 g/L/d and a maximum predicted production rate of 82.61 g/L/d and 21.13 g/L/d for 1,3 PDO and BuA, respectively. This corresponded to a 2.2 and 1.9-fold increase compared to the non-optimized process. The model was able to satisfactorily predict the joint maximum production of 1,3 PDO and BuA (22.6 and 8.1 g/L respectively) of the steady state also in non-sterile conditions, implying thus that MMC can be a robust and reliable biological production platform.

Crude glycerol is an important by-product of the biodiesel industry, which can be converted into volatile fatty acids (VFA) and/or 1,3-propanediol (1,3-PDO) by fermentation. In this study, a selective conversion of VFA to polyhydroxyalkanoates (PHA) was attained while leaving 1,3-PDO in the supernatant by means of mixed microbial consortia selection strategies. The process showed highly reproducible results in terms of PHA yield, 0.99 ± 0.07 Cmol PHA/Cmol S (0.84 g COD PHA/g COD S), PHA content (76 ± 3.1 g PHA/100 g TSS) and 1,3-PDO recovery (99 ± 2.1%). The combined process had an ultimate yield from crude glycerol of 0.19 g COD PHA and 0.42 g COD 1,3-PDO per g of input COD. The novel enrichment strategy applied for selectively transforming fermentation by-products into a high value product (PHA) demonstrates the significance of the enrichment process for targeting specific bio-transformations and could potentially prove valuable for other biotechnological applications as well.

Objective of this study was the selection and adaptation of mixed microbial cultures (MMCs), able to ferment crude glycerol generated from animal fat-based biodiesel and produce building-blocks and green chemicals. Various adaptation strategies have been investigated for the enrichment of suitable and stable MMC, trying to overcome inhibition problems and enhance substrate degradation efficiency, as well as generation of soluble fermentation products. Repeated transfers in small batches and fed-batch conditions have been applied, comparing the use of different inoculum, growth media, and Kinetic Control. The adaptation of activated sludge inoculum was performed successfully and continued unhindered for several months. The best results showed a substrate degradation efficiency of almost 100% (about 10 g/L glycerol in 21 h) and different dominant metabolic products were obtained, depending on the selection strategy (mainly 1,3-propanediol, ethanol, or butyrate). On the other hand, anaerobic sludge exhibited inactivation after a few transfers. To circumvent this problem, fed-batch mode was used as an alternative adaptation strategy, which led to effective substrate degradation and high 1,3-propanediol and butyrate production. Changes in microbial composition were monitored by means of Next Generation Sequencing, revealing a dominance of glycerol consuming species, such asClostridium,Klebsiella, andEscherichia.

Bioaugmented fermentation of cellulosic substrates to produce biohydrogen via co-culture of isolated strains was investigated. Two mesophilic anaerobic bacterial strains, known for their ability to hydrolyze cellulosic substrates, were taken in consideration: Shigella flexneri str. G3, which shows high cellulolytic activity but cannot ferment oligosaccharides to bioenergy, and Clostridium acetobutylicum X9, able to convert microcrystalline cellulose into hydrogen. The ability of the selected strains to effectively convert different cellulosic substrates to hydrogen was tested on carboxymethyl cellulose (AVICEL), as well as pretreated lignocellulosic material such as Bermuda grass, corn stover, rice straw, and corn cob. Results showed that co-culture of Shigella flexneri str G3 and Clostridium acetobutylicum X9 efficiently improved cellulose hydrolysis and subsequent hydrogen production from carboxymethyl cellulose. Hydrogen production yield was enhanced from 0.65 mol H 2 (mol glucose) −1 of the X9 single culture to approximately 1.5 mol H 2 (mol glucose) −1 of the co-culture, while the cellulose degradation efficiency increased from 50% to 95%. Co-culture also efficiently improved hydrogen production from natural lignocellulosic materials (which was up to 4-5 times higher than mono-culture with X9), with the highest performance of 24.8 mmol L -1 obtained on Bermuda grass. The results demonstrate that co-culture of S. flexneri G3 and C. acetobutylicum X9 was capable of efficiently enhance cellulose conversion to hydrogen, thus fostering potential biofuel applications under mesophilic conditions.

Microbial electrolysis cells (MECs) use exoelectrogenic microorganisms to convert organic matter into H2, although yields can vary significantly with environmental conditions, likely due to variations in microbial communities. This study was undertaken to better understand how microbial communities affect reactor function. Using wastewater as inoculum, 15 MEC reactors were operated for >50 days and subsequently five reactors were selected for further analysis. Solution (26 mL) was collected every 3–4 days for DNA extraction. DNA was hybridized to GeoChip, a comprehensive functional gene array, to examine differences in the reactor microbial communities. A large variety of microbial functional genes were observed in all reactors. Performances ranged from poor (0.1 ± 0.1 mL) to high (12.2 ± 1.0 mL) H2 production, with a maximum yield of 5.01 ± 0.43 mol H2/molglucose. The best performance was associated with higher cytochrome c genes, considerably higher exoelectrogenic bacteria (such as Shewanella, Geobacter), less methanogens and less hydrogen-utilizing bacteria. The results confirmed the possibility to obtain an effective community for hydrogen production using wastewater as inoculum. Not like fermentation, hydrogen production was significantly controlled by electron transporting process in MECs. GeoChip findings suggested that biofilm formation can be highly stochastic and that presence of dissimilatory metal-reducing bacteria and antagonistic methanogens is critical for efficient hydrogen production in MEC reactors.

A novel strategy for improving volatile fatty acids (VFAs) bioproduction from waste activated sludge (WAS) was developed by coupling pretreatments with conditioning (CPC). Agaricus bisporus substrate (ABS) was used as external carbohydrate additive source of conditioning step. Pretreatment was studied in three ways: alkaline, alkaline-thermal and ultrasonic. WAS hydrolysis and protein degradation was distinctly improved by CPC treatments, resulting in a considerable enhancement of VFAs yield. The maximal VFAs yield was 614 ± 71, 712 ± 49 and 598 ± 19 mg COD/g VSS at pre-optimized alkaline, alkaline-thermal and ultrasonic CPC treatments, respectively, with an increase of 35%, 50% and 38% compared to the yields of pretreated WAS fermentation. Fourier transformed infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy indicated that a synergistic effect occurred in co-digesting WAS and ABS. The conditioning of carbohydrate with feasible pretreatment provided large room for the digestibility improvement and the operation cost reduction in the whole WAS treatment system.

Lignocellulosic biomass can be an ideal feedstock for fermentative hydrogen production if properly pretreated and hydrolyzed. In this research, to enhance hydrogen production from cornstalk, acid and alkali pretreatments were performed. Alkali pretreatment was conducted at 80°C for 60 min and room temperature for 7 days with the addition of 4% NaOH; acid pretreatments at 190°C, and 120°C for 10 min and 120 min, respectively, with the addition of 1.7% H2SO4. All the chemical components change of the substrates was detected. The highest lignin reduction of 75.6%, compared to untreated samples, was found at 80°C with 4% NaOH dosage. Under this pretreatment condition, highest increase in reducing sugar and hydrogen yield (up to 11.8 g/L and 71.8 ml/g-pretreated cornstalk) was obtained. The present results suggested an efficient pretreatment method to increase hydrogen production from lignocellulosic biomass.

Design of Experiments (DoE) was applied to improve the ability of enriched activity sludge to efficiently convert crude glycerol from biodiesel industry into hydrogen and ethanol, using a very simple synthetic medium. Based on Plackett–Burman screening design, glycerol concentration, temperature and initial pH were identified as significant variables. Box–Behnken design and Response Surface Method (RSM) were then used for optimization. The maximum hydrogen yield of 0.96 mol H2/mol glycerol was estimated at the temperature of 37.0 °C, initial pH of 7.9 and glycerol concentration of 15.0 g/L. Maximum hydrogen production rate of 2191 mL/L/d was estimated at the temperature of 37.3 °C, initial pH of 8.0 and glycerol concentration of 15.2 g/L. Finally maximum ethanol production of 7.92 g/L was estimated at an initial pH of 8.0 and glycerol concentration of 15.0 g/L (temperature had no significant effect). These results show that it is possible to obtain both, high yield and production of hydrogen and ethanol together, using a very simple synthetic medium, without trace element- and vitamin solution, tryptone or yeast extract.

Methane production rate (MPR) in waste activated sludge (WAS) digestion processes is typically limitedby the initial steps of complex organic matter degradation, leading to a limited MPR due to sludgefermentation speed of solid particles. In this study, a novel microbial electrolysis AD reactor (ME-AD) wasused to accelerate methane production for energy recovery from WAS. Carbon bioconversion wasaccelerated by ME producing H2 at the cathode. MPR was enhanced to 91.8 gCH4/m3 reactor/d in themicrobial electrolysis ME-AD reactor, thus improving the rate by 3 times compared to control conditions (30.6 gCH4/m3 reactor/d in AD). The methane production yield reached 116.2 mg/g VSS in the ME-ADreactor. According to balance calculation on electron transfer and methane yield, the increasedmethane production was mostly dependent on electron contribution through the ME system. Thus, theuse of the novel ME-AD reactor allowed to significantly enhance carbon degradation and methaneproduction from WAS.

Anaerobic digestion (AD) represents a potential way to achieve energy recovery from waste organics. In this study, a novel bioelectrochemically-assisted anaerobic reactor is assembled by two AD systems separated by anion exchange membrane, with the cathode placing in the inside cylinder (cathodic AD) and the anode on the outside cylinder (anodic AD). In cathodic AD, average methane production rate goes up to 0.070 mL CH4/mL reactor/day, which is 2.59 times higher than AD control reactor (0.027 m(3) CH4/m(3)/d). And COD removal is increased ∼15% over AD control. When changing to sludge fermentation liquid, methane production rate has been further increased to 0.247 mL CH4/mL reactor/day (increased by 51.53% comparing with AD control). Energy recovery efficiency presents profitable gains, and economic revenue from increased methane totally self-cover the cost of input electricity. The study indicates that cathodic AD could cost-effectively enhance methane production rate and degradation of glucose and fermentative liquid.

This work adopted an innovative approach for fermentative H 2 production from common domestic organic waste, at 28 °C, in the absence of pretreatment: the self-fermentation of non-sterile vegetable waste and the bioaugmentation of microbial indigenous fermenting communities. For this purpose, three new H 2 -producing strains, Buttiauxella sp. 4, Rahnella sp. 10 and Raoultella sp. 47, isolated and enriched from vegetable waste, were individually tested on two types of vegetable waste and compared with a bacterial artificial consortium composed of the three strains put together. The three single strains were also characterized for their ability to produce H 2 on different sugars, such as xylose, arabinose and cellobiose, as these are key products of hydrolysis of cellulose and hemicelluloses. H 2 production occurred from self-fermentation with yields ranging from 18.08 to 21.95 ml H 2 /g VS. All bacterial inocula promoted a significant increase of the H 2 yield and the H 2 production rate, compared to the self-fermentation. The inocula of the artificial consortium yielded the maximum H 2 production of 85.65 ml H 2 /g VS with the highest H 2 production rate of 2.56 ml H 2 /h.

Background Bioelectrochemical systems have been considered a promising novel technology that shows an enhanced energy recovery, as well as generation of value-added products. A number of recent studies suggested that an enhancement of carbon conversion and biogas production can be achieved in an integrated system of microbial electrolysis cell (MEC) and anaerobic digestion (AD) for waste activated sludge (WAS). Microbial communities in integrated system would build a thorough energetic and metabolic interaction network regarding fermentation communities and electrode respiring communities. The characterization of integrated community structure and community shifts is not well understood, however, it starts to attract interest of scientists and engineers. Results In the present work, energy recovery and WAS conversion are comprehensively affected by typical pretreated biosolid characteristics. We investigated the interaction of fermentation communities and electrode respiring communities in an integrated system of WAS fermentation and MEC for hydrogen recovery. A high energy recovery was achieved in the MECs feeding WAS fermentation liquid through alkaline pretreatment. Some anaerobes belonging to Firmicutes (Acetoanaerobium, Acetobacterium, and Fusibacter) showed synergistic relationship with exoelectrogens in the degradation of complex organic matter or recycling of MEC products (H2). High protein and polysaccharide but low fatty acid content led to the dominance of Proteiniclasticum and Parabacteroides, which showed a delayed contribution to the extracellular electron transport leading to a slow cascade utilization of WAS. Conclusions Efficient pretreatment could supply more short-chain fatty acids and higher conductivities in the fermentative liquid, which facilitated mass transfer in anodic biofilm. The overall performance of WAS cascade utilization was substantially related to the microbial community structures, which in turn depended on the initial pretreatment to enhance WAS fermentation. It is worth noting that species in AD and MEC communities are able to build complex networks of interaction, which have not been sufficiently studied so far. It is therefore important to understand how choosing operational parameters can influence reactor performances. The current study highlights the interaction of fermentative bacteria and exoelectrogens in the integrated system. Electronic supplementary material The online version of this article (doi:10.1186/s13068-016-0493-2) contains supplementary material, which is available to authorized users.

The effects of three widely-used surfactants on waste activated sludge (WAS) fermentation and microbial community structures were investigated. Rhamnolipid bio-surfactants (RL) showed more positive effects on WAS hydrolysis and acidification compared to chemosynthetic surfactants, such as sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS). The highest SCOD and VFAs concentrations obtained with RL were 1.15-fold and 1.16-fold that of SDS, and up to 1.73 and 3.63 times higher than those obtained with SDBS. Pyrosequencing analysis showed that an evident reduction in bacterial diversity in surfactant-treated WAS. Moreover, acid-producing bacteria (such as Megasphaera and Oscillibacter), detected with RL, were (6.8% and 6.4% in proportion) more abundant than with SDS, and were rarely found in SDBS and the control. The results also revealed that RL allowed efficient hydrolysis enhancement and was favorable to functional microorganisms for further acidification during WAS fermentation.

The aim of this study was to investigate functional differences in two Italian coastal lagoons (Caprolace and Fogliano, Tyrrhenian Sea) characterized by the dominance of two different seagrass species: Cymodocea nodosa (Ucria) Ascherson in the Caprolace lagoon and Ruppia cirrhosa (Petagna) Grande in the Fogliano lagoon. 2. A monitoring system was set up in both lagoons in order to (i) map the distribution of macrophytes, (ii) measure spatio-temporal changes in the biological parameters of the seagrasses, and (iii) measure spatio- temporal changes in biological and chemical-physical parameters in the water column and sediments. 3. The results showed that the relationships between macrophytes and aquatic and sediment compartments entail functional differences described by buffering systems that counteract the accumulation of free sulphide. 4. This study also suggests that R. cirrhosa and C. nodosa are indicators of different levels of ecological stability. Copyright # 2008 John Wiley & Sons, Ltd.

To improve anaerobic digestibility of waste activated sludge (WAS), a novel treatment was explored by a plant-derived biosurfactant (saponin biosurfactant (SB)). SB showed positive effects on WAS hydrolysis and acidogenesis with increasing concentration, but was insignificant at dosage >0.20 g SB/g total suspended solids (TSS). Soluble protein and carbohydrate concentrations reached 2029 ± 28 and 343 ± 52 mg chemical oxygen demand (COD)/L (0.20 g SB/g TSS, 48 h), which were 4.77-fold and 5.87-fold higher than that without treatment. Volatile fatty acids (VFAs) bioproduction showed a 3.51-fold increase in 72 h. Moreover, acetic acid increased already after 2 h with SB treatment, but after 8 h in the control, indicating that SB accelerated syntrophic acetogenesis from butyric acid degradation to acetic acid. Additionally, methane production was enhanced at lower dosage ( 0.10 g SB/g TSS), with 63.0 and 20.3 mL/g volatile suspended solids (VSS), respectively, while it was 46.5 mL/g VSS in the control. The results obtained are in good agreement with previous ones obtained with chemosynthetic surfactants. Moreover, SB has advantages of easy production and sustainability of supply, which should promote the implementation for WAS treatment.

Self-fermentation of cellulosic substrates to produce biohydrogen without inoculum addition nor pretreatments was investigated. Dark fermentation of two different substrates made of leaf-shaped vegetable refuses (V) and leaf-shaped vegetable refuses plus potato peels (VP), was taken in consideration. Batch experiments were carried out, under two mesophilic anaerobic conditions (28 and 37 °C), in order to isolate and to identify potential H2-producing bacterial strains contained in the vegetable extracts. The effect of initial glucose concentration (at 1, 5 and 10 g/L) on fermentative H2 production by the isolates was also evaluated. H2 production from self-fermentation of both biomasses was found to be feasible, without methane evolution, showing the highest yield for V biomass at 28 °C (24 L/kg VS). The pH control of the culture medium proved to be a critical parameter. The isolates had sequence similarities ≥98% with already known strains, belonging to the family Enterobacteriaceae (γ-proteobacteria) and Streptococcaceae (Firmicutes). Four genera found in the samples, namely Pectobacterium, Raoultella, Rahnella and Lactococcus have not been previously described for H2 production from glucose. The isolates showed higher yield (1.6–2.2 mol H2/mol glucoseadded) at low glucose concentration (1 g/L), while the maximum H2 production ranged from 410 to 1016 mL/L and was obtained at a substrate concentration of 10 g/L. The results suggested that vegetable waste can be effectively used as both, substrate and source of suitable microflora for bio-hydrogen production.

In this study, we evaluated the effectiveness of lake sediment as inoculum for hydrogen production through dark fermentation in a repeated batch process. In addition, we investigated the effect of heat treatment, applied to enrich hydrogen-producing bacteria, on the bacterial composition and metabolism. Denaturing gradient gel electrophoresis and molecular cloning, both performed using the 16S rDNA gene as target gene, were used to monitor the structure of the bacterial community. Hydrogen production and bacterial metabolism were analysed via gas chromatography and high-performance liquid chromatography. Both treated and non-treated inocula were able to produce high amounts of hydrogen. However, statistical analysis showed a clear difference in their bacterial composition and metabolism. The heat treatment favoured the growth of different Clostridia sp., in particular of Clostridium bifermentans, allowing the production of a constant amount of hydrogen over prolonged time. These cultures showed both butyrate and ethanol fermentation types. Absence of heat treatment allowed species belonging to the genera Bacillus, Sporolactobacillus and Massilia to outgrow Clostridia sp. with a reduction in hydrogen production and a significant metabolic change. Our data indicate that lake sediment harbours bacteria that can efficiently produce hydrogen over prolonged fermentation time. Moreover, we could show that the heat treatment stabilizes the bacterial community composition and the hydrogen production. © 2013 Springer-Verlag Berlin Heidelberg.

The effects of environmental factors on bacterioplankton distribution along the water column of Lake Averno (Naples, Italy) have been investigated by means of denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments, and multivariate analysis applied to molecular data and physico-chemical parameters. Bacterial richness, estimated from DGGE profiles, remains constant throughout the water column, whereas archaeal richness increases with depth. Moreover, archaeal richness was significantly correlated to most of the measured abiotic variables, whereas bacterial richness did not. Analysis of sequences from DGGE bands revealed that the dominant bacterial populations belong to Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Bacteroidetes and Firmicutes, whereas sequences of the archaeal DGGE bands are affiliated to Methanomicrobiales and Methanosarcinales orders. Moreover, bacterial sequences affiliated to Proteobacteria and Bacteroidetes do not group closely to typical freshwater lineages/clades/tribes within these phyla. Bacterioplankton distribution along the water column was apparently correlated with the vertical gradient of physico-chemical parameters as a statistically significant relationship between most of them with grouping of specific taxonomic units was observed. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

The worldwide energy demand has been continuously increasing, thus requesting more sustainable alternatives to the rapidly depleting fossil fuels. Therefore, biofuels such as hydrogen, bioethanol and biodiesel are gaining more importance as a renewable and pollution-free solution, which might give a significant contribution to the future energy mix. In recent years, the exponential growth of biodiesel production has led to a glycerol glut, however, according to some authors, crude glycerol might represent a suitable, abundant and low-priced feedstock for fermentation technologies. In this study we performed an energetic and economic assessment of an innovative process, which is under development in our lab, for the bioconversion of crude glycerol into ethanol and hydrogen. Ongoing experiments showed the possibility to reach at least 26g/L of ethanol, together with 9L of hydrogen, in non-sterile conditions and without nutrient supplements. Since kinetics and ethanol concentration need to be further improved, we performed this study with a view to evaluate the possibility of reaching economic viability. Results showed that with 26g/L of ethanol and a retention time as high as 120h, the calculated energy cost would be about 0.019€/kWhth and 0.057€/kWhel, considering the contribution of both, hydrogen and bioethanol. Moreover, bioethanol cost would be as low as 0.21€/L, even without taking into account the possible hydrogen revenues. These results are very promising and suggest that the process has reasonable chances to achieve economic viability, thus deserving further attention. The procedure followed in this work provided a realistic and concrete target to pursue in the future lab experiments, in order to bring this technology closer to the market.

Background: Sustainable biohydrogen production can be achieved by dark fermentation of organic wastes, and studies were carried out using a range of substrates and inocula. The bacterial populations involved were mainly identified as facultative anaerobes (Enterobacteriaceae) and strictly anaerobes (Clostridiales), and their dynamics in relation to H2 and metabolite production depends on the physical and environmental conditions of the bioreactor. This study has evaluated the use of length heterogeneity (LH)-PCR fingerprinting to detect changes in the microbial community during continuous hydrogen production under dark fermentation. Methods: A mesophilic continuous dark fermentation was established using coastal lake sediment as an inoculum in a synthetic medium with glucose as a substrate. The LH-PCR profiling associated to the sequencing of 16S rRNA genes was used for the characterization of the bacterial community and identification of species during a continuous production of H2. Results: The resulting dominant units of the communities present at both 24 h (batch) and 210 h (continuous culture) were affiliated to species of the genus Clostridium. Fluctuations based on their relative abundance over time were observed. At 24 h, a higher ratio was detected for the group Clostridium butyricum - Clostridium tertium followed by Clostridium bifermentans and Clostridium perfringens, while at 210 h, the group Clostridium aurantibutyricum - Clostridium acetobutylicum was the most abundant. Conclusions: The LH-PCR profiling has proven to be a sensitive and rapid method for the evaluation of the dynamics of a functional consortium formed by species of the genus Clostridium and has a potential for studies aimed at the optimization of biohydrogen production. © 2013 Di Bonito et al.; licensee Springer.