Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges.

Forward osmosis (FO) is a low energy-intensive process since the driving force for water transport is the osmotic pressure difference, Δπ, between the feed and draw solutions, separated by the FO membrane, where πdraw > πfeed. The potential of FO in wastewater treatment and desalination have been extensively studied; however, regeneration of the draw solution (thereby generating clean water) requires application of an energy-intensive process step like reverse osmosis (RO). In this study, the potential of applying FO for direct water recirculation from diluted fermentation effluent to concentrated feedstock, without the need for an energy-intensive regeneration step (e.g. RO), has been investigated. Butanol production during crude glycerol fermentation by Clostridium pasteurianum, has been selected as a model process and the effect of cross-flow velocity and the dilution of draw solution on the water flux during short-term experiments (200 min), were investigated. Statistical analysis revealed that the dilution of the draw solution is the most influential factor for the water flux. Subsequent modelling of an integrated FO-fermentation process, showed that water recoveries could lead to substantial financial benefits, although the integrated FO-fermentation process demonstrated lower water flux than expected. FTIR analyses of the membrane surface implied that the decrease in water flux was due to the presence of proteins, polysaccharides and other extracellular polymeric substances on the membrane active layer, indicating the presence of a fouling layer. Based on these findings, possible fouling alleviation strategies and future research directions are discussed and proposed.

Energy balance and cost-benefit analysis of biogas production from perennial energy crops pretreated by wet oxidation.

Perennial crops need far less energy to plant, require less fertilizer and pesticides, and show a lower negative environmental impact compared with annual crops like for example corn. This makes the cultivation of perennial crops as energy crops more sustainable than the use of annual crops. The conversion into biogas in anaerobic digestion plants shows however much lower specific methane yields for the raw perennial crops like miscanthus and willow due to their lignocellulosic structure. Without pretreatment the net energy gain is therefore lower for the perennials than for corn. When applying wet oxidation to the perennial crops, however, the specific methane yield increases significantly and the ratio of energy output to input and of costs to benefit for the whole chain of biomass supply and conversion into biogas becomes higher than for corn. This will make the use of perennial crops as energy crops competitive to the use of corn and this combination will make the production of biogas from energy crops more sustainable.

Corrigendum to "Comparison of Different Strategies for Selection/Adaptation of Mixed Microbial Cultures Able to Ferment Crude Glycerol Derived from Second-Generation Biodiesel".

[This corrects the article DOI: 10.1155/2015/932934.].

Thermophilic anaerobic fermentation of olive pulp for hydrogen and methane production: modelling of the anaerobic digestion process.

The present study investigates the thermophilic biohydrogen and methane production from olive pulp, which is the semi-solid residue coming from the two-phase processing of olives. It focussed on: a) production of methane from the raw olive pulp; b) anaerobic bio-production of hydrogen from the olive pulp; c) subsequent anaerobic treatment of the hydrogen-effluent with the simultaneous production of methane; and d) development of a mathematical model able to describe the anaerobic digestion of the olive pulp and the effluent of hydrogen producing process. Both continuous and batch experiments were performed. The hydrogen potential of the olive pulp amounted to 1.6 mmole H2 per g TS. The methane potential of the raw olive pulp and hydrogen-effluent was as high as 19 mmole CH4 per g TS suggesting that: a) olive pulp is a suitable substrate for methane production; and b) biohydrogen production can be very efficiently coupled with a subsequent step for methane production.

Application of ADM1 for the simulation of anaerobic digestion of olive pulp under mesophilic and thermophilic conditions.

The management of the wastewater originating from olive oil producing industries poses a serious environmental problem. Recently, two-phase production of olive oil has been developed, leading to almost complete elimination of the bulk of the generated wastewater and, is thus regarded as an environmentally friendly technology. However, the main waste stream (olive pulp) is a slurry material characterized by high solids concentration (approximately 30%), requiring stabilisation before its final disposal. The anaerobic digestion of olive pulp is studied in this work under mesophilic and thermophilic conditions in CSTR-type digesters. The digesters were fed with water-diluted (1:4) olive pulp at an HRT of 20 days and an OLR of 3.94 kg COD m(-3) d(-1). In order to study the process kinetics, the digesters were subjected to impulse disturbances of different substrates. The IWA anaerobic digestion model was used to simulate the reactors' response. Some key process parameters, such as the specific maximum uptake rate constants and the saturation constants for the volatile fatty acids degradation were estimated and compared with the standard values suggested by the ADM1.

Thermal pre-treatment of primary and secondary sludge at 70 degrees C prior to anaerobic digestion.

In general, mesophilic anaerobic digestion of sewage sludge is more widely used compared to thermophilic digestion, mainly because of the lower energy requirements and higher stability of the process. However, the thermophilic anaerobic digestion process is usually characterised by accelerated biochemical reactions and higher growth rate of microorganisms resulting in an increased methanogenic potential at lower hydraulic retention times. Furthermore, thermal pre-treatment is suitable for the improvement of stabilization and could be realized at relatively low cost especially at low temperatures. The present study investigates the effect of the pre-treatment at 70 degrees C on thermophilic (55 degrees C) anaerobic digestion of primary and secondary sludge in continuously operated digesters. Thermal pre-treatment of primary and secondary sludge at 70 degrees C enhanced the removal of organic matter and the methane production during the subsequent anaerobic digestion step at 55 degrees C. It also greatly contributed to the destruction of pathogens present in primary sludge. Finally it results in enhanced microbial activities of the subsequent anaerobic step suggesting that the same efficiencies in organic matter removal and methane recovery could be obtained at lower HRTs.

Potential for biohydrogen and methane production from olive pulp.

The present study investigates the potential for thermophilic biohydrogen and methane production from olive pulp, which is the semi-solid residue coming from the two-phase processing of olives. It focussed on: a) production of methane from the raw olive pulp, b) anaerobic bio-production of hydrogen from the olive pulp, and c) subsequent anaerobic treatment of the hydrogen-effluent with the simultaneous production of methane. Both continuous and batch experiments were performed. The hydrogen potential of the olive pulp amounted to 1.6 mmole H2 per g TS. The methane potential of the raw olive pulp and hydrogen-effluent was as high as 19 mmole CH4 per g TS. This suggests that olive pulp is an ideal substrate for methane production and it shows that biohydrogen production can be very efficiently coupled with a subsequent step for methane production.

Continuous Fermentation of Wheat Straw Hydrolysate by Clostridium tyrobutyricum with In-Situ Acids Removal.

The present study focused on fermentative butyric acid production by Clostridium tyrobutyricum from pre-treated and hydrolysed wheat straw (PHWS) based on continuous operation mode and in situ acids extraction by reverse electro enhanced dialysis (REED). Different dilutions of PHWS in a synthetic medium (60-100 % v/v) were tested. It was found that continuous fermentation of PHWS greatly enhanced the sugar consumption rates and butyric acid productivity compared to batch tests, while application of REED enhanced them even further. Specifically, applying combined continuous operation mode and REED system for the fermentation of 70 % PHWS resulted in 19- and 53-fold higher glucose (1.37 g L-1 h-1) and xylose (0.80 g L-1 h-1) consumption rates, respectively, compared to those obtained by batch processing. Fermentation of 100 % PHWS continued unhindered with just urea and K2HPO4 added with butyric acid production rate, yield and selectivity being 1.30 g L-1 h-1, 0.45 g g-1 sugars and 0.88 g g-1 acids, respectively. These results were also confirmed in a 20 L pilot plant bioreactor system.

Butyric acid fermentation from pretreated and hydrolysed wheat straw by an adapted Clostridium tyrobutyricum strain.

Butyric acid is a valuable building-block for the production of chemicals and materials and nowadays it is produced exclusively from petroleum. The aim of this study was to develop a suitable and robust strain of Clostridium tyrobutyricum that produces butyric acid at a high yield and selectivity from lignocellulosic biomasses. Pretreated (by wet explosion) and enzymatically hydrolysed wheat straw (PHWS), rich in C6 and C5 sugars (71.6 and 55.4 g l(-1) of glucose and xylose respectively), was used as substrate. After one year of serial selections, an adapted strain of C. tyrobutyricum was developed. The adapted strain was able to grow in 80% (v v(-1) ) PHWS without addition of yeast extract compared with an initial tolerance to less than 10% PHWS and was able to ferment both glucose and xylose. It is noticeable that the adapted C. tyrobutyricum strain was characterized by a high yield and selectivity to butyric acid. Specifically, the butyric acid yield at 60-80% PHWS lie between 0.37 and 0.46 g g(-1) of sugar, while the selectivity for butyric acid was as high as 0.9-1.0 g g(-1) of acid. Moreover, the strain exhibited a robust response in regards to growth and product profile at pH 6 and 7.

Comparison of Different Strategies for Selection/Adaptation of Mixed Microbial Cultures Able to Ferment Crude Glycerol Derived from Second-Generation Biodiesel.

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 as Clostridium, Klebsiella, and Escherichia.

Wet explosion of wheat straw and codigestion with swine manure: effect on the methane productivity.

The continuously increasing demand for renewable energy sources renders anaerobic digestion to one of the most promising technologies for renewable energy production. Twenty-two (22) large-scale biogas plants are currently under operation in Denmark. Most of these plants use manure as the primary feedstock but their economical profitable operation relies on the addition of other biomass products with a high biogas yield. Wheat straw is the major crop residue in Europe and the second largest agricultural residue in the world. So far it has been used in several applications, i.e. pulp and paper making, production of regenerated cellulose fibers as an alternative to wood for cellulose-based materials and ethanol production. The advantage of exploiting wheat straw for various applications is that it is available in considerable quantity and at low-cost. In the present study, the codigestion of swine manure with wheat straw in a continuous operated system was investigated, as a method to increase the efficiency of biogas plants that are based on anaerobic digestion of swine manure. Also, the pretreatment of wheat straw with the wet explosion method was studied and the efficiency of the wet explosion process was evaluated based on (a) the sugars release and (b) the methane potential of the pretreated wheat straw compared to that of the raw biomass. It was found that, although a high release of soluble sugars was observed after wet explosion, the methane obtained from the wet-exploded wheat straw was slightly lower compared to that from the raw biomas s. On the other hand, the results from the codigestion of raw (non-pretreated) wheat straw with swine manure were very promising, suggesting that 4.6 kg of straw added to 1t of manure increase the methane production by 10%. Thus, wheat straw can be considered as a promising, low-cost biomass for increasing the methane productivity of biogas plants that are based mainly on swine manure.

Influence of anaerobic culture acclimation on the degradation kinetics of various substrates.

The adaptation of an anaerobic culture (anaerobic sludge) to a specific substrate brings significant changes to its microbial population. These changes can be described by the sludge's ability to treat various substrates such as carbohydrates or proteins or "intermediate" products of anaerobic metabolism such as L-lactic, propionic, and acetic acids. The activity of the sludge with respect to a specific substrate is a critical parameter, because the anaerobic degradability of wastewaters depends strongly on it. This work examines and quantifies the differentiation of two anaerobic sludges of the same origin, following an adaptation period of about 18 months to lactose and gelatin, respectively. The acclimation has a significant effect on the maximum specific utilization rates of various compounds and on their apparent consumption kinetics. It is noticeable, however, that even if the anaerobic cultures were not exposed to a specific substrate for a prolonged period of time (more than a year), they still kept the ability of hydrolyzing or degrading it. In addition, the acclimation has an unquestionable effect on the stoichiometry of the production of volatile fatty acids and L-lactate. Finally, from codigestion experiments it is shown that codigestion of lactose and gelatin appears to have no effect on their hydrolysis kinetics in any of the lactose or gelatin acclimated cultures; specifically, the hydrolysis kinetics remained the same as calculated when lactose or gelatin were the only fed substrates. Similarly, the kinetics of L-lactate and D-glucose biodegradation seemed to be unchanged. On the other hand, codigestion has a significant effect on the production of L-lactic, propionic, and acetic acids, which can be attributed to the increased hydrogen production accompanying gelatin biodegradation.