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Digestate produced from the anaerobic digestion of food and farm waste is primarily returned to land as a biofertiliser for crops, with its potential to generate value through alternative processing methods at present under explored. In this work, valorisation of a digestate resulting from the treatment of kitchen and food waste was investigated, using dilution, settlement and membrane processing technology. Processed digestate was subsequently tested as a nutrient source for the cultivation of Chlorella vulgaris, up to pilot-scale (800L). Dilution of digestate down to 2.5% increased settlement rate and induced release of valuable compounds for fertiliser usage such as nitrogen and phosphorus. Settlement, as a partial processing of digestate offered a physical separation of liquid and solid fractions at a low cost. Membrane filtration demonstrated efficient segregation of nutrients, with micro-filtration recovering 92.38% of phosphorus and the combination of micro-filtration, ultra-filtration, and nano-filtration recovering a total of 94.35% of nitrogen from digestate. Nano-filtered and micro-filtered digestates at low concentrations were suitable substrates to support growth of Chlorella vulgaris. At pilot-scale, the microalgae grew successfully for 28 days with a maximum growth rate of 0.62 day−1 and dry weight of 0.86 g⋅L−1. Decline in culture growth beyond 28 days was presumably linked to ammonium and heavy metal accumulation in the cultivation medium. Processed digestate provided a suitable nutrient source for successful microalgal cultivation at pilot-scale, evidencing potential to convert excess nutrients into biomass, generating value from excess digestate and providing additional markets to the anaerobic digestion sector.

Reverse osmosis (RO) membrane biofouling is a critical issue in seawater desalination. However, biofouling characteristics are not fully understood owing to the complex structure of the fouling layer. Therefore, the objective of this study is to investigate how the biofouling characteristics of RO membranes are associated with bacterial and archaeal communities and their physiological (surface structure, elemental composition, and thickness) and metabolic characteristics in different locations of the RO membrane element. Raw seawater, feedwater, first- and last-located RO membrane elements, and brine were collected from a full-scale (50 m3 per day) intermittently operated seawater reverse osmosis (SWRO) desalination plant. Bacteria were found to be the most dominant biofouling microorganism on the RO membrane surface rather than archaea or diatoms. This study highlights that the very first element of the RO membrane receiving inflow had fouled biofilm with more heterogeneous morphologies and chemical composition compared with the very last element of the RO membrane where the outflow is discharged. In contrast, the microbial communities in both biofilms were similar to each other during the period of desalination operation. The most dominant bacterial species in the biofilm of RO membranes were Pelagibius, Parvibaculum, Legionella, Hyphomicrobium, and Sphingomonas. Moreover, their physiological and metabolic characteristics, such as salt tolerance, high pressure tolerance, and/or oligotrophic properties may provide advantages for their adaptation and dominance in RO membrane biofilms. A substantial difference in microbial diversity was observed between the feedwater and RO membranes, suggesting that more attention should be given to the biofilm, rather than the feedwater, when investigating how biofouling is developed and eventually controlled.

A waste based biorefinery approach has been tested. This has been investigated by culturing in a 800 L photobioreactor two autotrophic microalgae namely Nannochloropsis oceanica and Scenedesmus quadricauda utilising filtered spent anaerobic digestate fluids of N:P ratio 14.22 as substrate. Significant rates of bioremediation simultaneously with biomass and associated end product formation were achieved. Nitrogen and phosphorus of waste based media was decreased up to 90%. The biomass biochemical analysis of the microalgae when grown on the waste based formulated media demonstrated the comparable content of lipids and proteins with the species grown on f/2 media. Theoretical biomethane potential generation, should the algal cultures be placed in an anaerobic digester, was calculated at 0.58 L CH4 g−1 VS for N. oceanica and 0.48 L CH4 g−1 VS for S. quadricauda showing comparable results with other studies of different source of biomass.

A two-phase outdoor cultivation bioprocess for Arthrospira maxima LJGR1 combined with phycocyanin induction in concentrated cultures under controlled conditions was evaluated using a modified low-cost Zarrouk medium. Growth was monitored during 4 cycles in 2018 and 4 cycles in 2019. Biomass was harvested and concentrated using membrane technology at the end of each cycle for further phycocyanin induction using blue LED light (controlled conditions, 24 h). The highest biomass productivity was observed during spring and summer cycles (13.63–18.97 gDWm−2 d−1); during mid-fall and mid-end fall, a decrease was observed (9.93–7.76 gDWm−2 d−1). Under favorable growth conditions, phycocyanin induction was successful. However, during cycles with unfavorable growth condition, phycocyanin induction was not observed. Reactive-grade phycocyanin (3.72 ± 0.14) was recovered and purified using microfiltration and ultrafiltration technologies.

The effect of specific narrow light-emitting diode (LED) wavelengths (red, green, blue) and a combination of LED wavelengths (red, green and blue - RGB) on biomass composition produced by Porphyridium purpureum is studied. Phycobiliprotein, fatty acids, exopolysaccharides, pigment content, and the main macromolecules composition were analysed to determine the effect of wavelength on multiple compounds of commercial interest. The results demonstrate that green light plays a significant role in the growth of rhodophyta, due to phycobiliproteins being able to harvest green wavelengths where chlorophyll pigments absorb poorly. However, under multi-chromatic LED wavelengths, P. purpureum biomass accumulated the highest yield of valuable products such as eicosapentaenoic acid (∼2.9% DW), zeaxanthin (∼586μgg-1DW), β-carotene (397μgg-1DW), exopolysaccharides (2.05g/L-1), and phycobiliproteins (∼4.8% DW). This increased accumulation is likely to be the combination of both photo-adaption and photo-protection, under the combined specific wavelengths employed.

Several factors have the potential to influence microalgae growth. In the present study, nitrogen concentration and light intensity were evaluated in order to obtain high biomass production and high phycoerythrin accumulation from Porphyridium purpureum. The range of nitrogen concentrations evaluated in the culture medium was 0.075&ndash, 0.450 g L&minus, 1 and light intensities ranged between 30 and 100 &mu, mol m&minus, 2 s&minus, 1. Surprisingly, low nitrogen concentration and high light intensity resulted in high biomass yield and phycoerythrin accumulation. Thus, the best biomass productivity (0.386 g L&minus, 1 d&minus, 1) and biomass yield (5.403 g L&minus, 1) were achieved with NaNO3 at 0.075 g L&minus, 1 and 100 &mu, 1. In addition, phycoerythrin production was improved to obtain a concentration of 14.66 mg L&minus, 1 (2.71 mg g&minus, 1 of phycoerythrin over dry weight). The results of the present study indicate that it is possible to significantly improve biomass and pigment production in Porphyridium purpureum by limiting nitrogen concentration and light intensity.

This chapter focuses on the challenges associated with achieving economic value from metabolites derived from cyanobacteria. Significant advances have been made in cyanobacterial biotechnology in the last few years. However, the field is still immature, and many challenges remain. We start with a critical overview of the main technologies associated with cultivation, cell disruption and metabolite extraction. Then, we provide an overview of current significant metabolite groups from cyanobacteria relevant to industry covering phycobilins, carotenoids, polysaccharides, peptides, lipids, mycosporine-like amino acids, polyhydroxyalkanoates, cyanotoxins and platform chemicals, and the potential for stable isotopes production. We cover metabolites that are already in the market and those with future potential with a focus on spirulina (Arthrospira) the most commercially developed species of cyanobacteria. As large-scale cultivation and down-stream processing techniques continue to develop further, combining this with a systems biology and biorefinery approach will ensure that the best economic and environmental sustainability value can be achieved.

Managing organic waste streams is a major challenge for the agricultural industry. Anaerobic digestion (AD) of organic wastes is a preferred option in the waste management hierarchy, as this process can generate renewable energy, reduce emissions from waste storage, and produce fertiliser material. However, Nitrate Vulnerable Zone legislation and seasonal restrictions can limit the use of digestate on agricultural land. In this paper we demonstrate the potential of cultivating microalgae on digestate as a feedstock, either directly after dilution, or indirectly from effluent remaining after biofertiliser extraction. Resultant microalgal biomass can then be used to produce livestock feed, biofuel or for higher value bio-products. The approach could mitigate for possible regional excesses, and substitute conventional high-impact products with bio-resources, enhancing sustainability within a circular economy. Recycling nutrients from digestate with algal technology is at an early stage. We present and discuss challenges and opportunities associated with developing this new technology.

Synthetic solutions of varying concentrations of carboxylic acids, namely acetic and butyric acids (50 mM, 100 mM) and treated digested agricultural wastewater with a carboxylic acids concentration of 21.08 mM of acetic acid and 15.81 mM of butyric acid were processed with a range of nanofiltration membranes and enrichment schemes to concentrate carboxylic acids. The study was conducted with the scope of platform chemicals recovery from complex effluents, investigating the feasibility of nanofiltration as a method of choice. Membrane filtration is easily scalable into various arrangements, allowing versatility in operation and enrichment treatments, which other recovery practices such as liquid extraction do not allow. Among the five nanofiltration membranes used (NF270 (Dow Chemicals, USA), HL, DL, DK (Osmonics, USA), LF10 (Nitto Denko, Japan)) the DK, DL and NF270 were identified as the best candidates for carboxylic acids separation and concentration from these complex effluents, both in terms of retention and permeate flux. These membranes achieved retention ratios, up to 75% giving retentates up to 53.94 mM acetate and 28.38 mM butyrate for the agricultural wastewater. Effluents were modified by the addition of alkali and salts (sodium chloride and sodium bicarbonate), and it was found that highest productivity, retention and flux was achieved at pH 7 but at higher pH there was a significant reduction in flux.

Microalgae biomass is seen as a sustainable and socially more responsible feedstock for the production of biofuels and other fine chemical products. Dewatering algae using membrane filtration is a leading technology, however the associated costs are typically not determined. This work investigates the filtration of Chlorella minutissima using a pilot-scale cross-flow microfiltration unit. A filtration model was developed and validated based on permeate flux as a function of biomass concentration (0.6–19.0 dry cell weight/L) and transmembrane pressure (Δ P , 1.80–2.10 bar). Processing times for harvesting C. minutissima were determined by iteration of the model and costs were related to energy consumption. For the experimental conditions of 1.95 bar, 1.0 g DCW/L initial biomass concentration, 0.70 kWh, 25 °C and 3.8 m 2 membrane area, harvesting costs were determined as 2.86 kWh/kg biomass. Subsequent investigation of the influence of the operating parameters and scale-up effects demonstrated that significant cost reduction to 1.27 kWh/kg biomass was possible at 1.95 bar, 2.0 g DCW/L initial biomass concentration, 0.46 kWh, 20 °C and 7.6 m 2 membrane area. Further, biomass concentration was demonstrated to be one of the major drivers to reduce the cost of harvesting microalgae. Membrane filtration was demonstrated to be a feasible harvesting process allowing biomass concentrations up to 150 g DCW/L without using chemicals which complicate the downstream processing stages.

Spent digester streams were reformulated into nutrient rich effluents, capable of supporting biotechnological production of platform chemicals. This was achieved, using a set of physical pre-treatments including, sedimentation, dilution and sieving, followed by cross-flow microfiltration processing to give particle and cell free nutrient streams with a C:N:P molar ratio of 1:1.35:0.03. These streams were inoculated on bench scale, with Clostridium butyricum NCIMB 7432, a well-known acids producer, giving good growth rates (μmax 0.24 h−1) and acids concentrations of 110 mM acetic acid and 18 mM per litre butyric acid. When the treated effluent was fortified with 2% w/v glucose there was a significant improvement with a 0.38 h−1 μmax and platform chemicals concentration of 279 mM acetic acid and 32 mM butyric acid per litre. These media gave comparable performance with the synthetic media, therefore demonstrating a valid alternative solution to commercial media preparations. The cost of treating the excess digestate by microfiltration within the scope of formulation to nutrient media has been calculated at 0.0033 $USD/kg, 3 times lower than the cost of production of nutrient media.

Wastewater, despite being a serious environmental constraint, has been identified as a source of valuable commodities including phosphate, ammonia, metal ions and volatile fatty acids. Using low-cost physical pre-treatments, filtration technology gives the opportunity of recovering materials in purified concentrated liquid form and purified water. Filtration also allows manipulation of the nutrient content in the effluents enabling the formulation of a series of streams enriched with important chemical components, enabling their reformulation into balanced nutrient media for microbial growth and the production of biofuels, acids and other chemicals such as lipids and enzymes. This approach benefits industry through the use of a relatively abundant inexpensive feedstock able to be recycled to produce high value chemicals while reducing the carbon footprint of the fermentation and reducing waste disposal. Examples of potential schemes of nutrient formulation and their application are presented.

Microbial conversion of syngas to energy-dense biofuels and valuable chemicals is a potential technology for the efficient utilization of fossils (e.g., coal) and renewable resources (e.g., lignocellulosic biomass) in an environmentally friendly manner. However, gas-liquid mass transfer and kinetic limitations are still major constraints that limit the widespread adoption and successful commercialization of the technology. This review paper provides rationales for syngas bioconversion and summarizes the reaction limited conditions along with the possible strategies to overcome these challenges. Mass transfer and economic performances of various reactor configurations are compared, and an ideal case for optimum bioreactor operation is presented. Overall, the challenges with the bioprocessing steps are highlighted, and potential solutions are suggested. Future research directions are provided and a conceptual design for a membrane-based syngas biorefinery is proposed.

Anaerobic Digester (AD) waste, known as digestate (spent anaerobically digested effluents) of agricultural origin, was collected for a feasibility study on the use of membrane filtration to fractionate phosphate and ammonia from digestate into nutrient streams. The digestate was pre-treated to remove bulk solids and then filtered using diafiltration (DF) with ultrafiltration (UF) (5.65 psi TMP) and then nanofiltration (NF) (operating pressure 253.82 psi). Having set the pre-treated effluents at pH 4.0, retention of phosphate reached 6.78 mmols L−1 during UF with lower values being achieved with repeated DF steps. In contrast, nitrogen retention was lower at 8.21 mmols L-1 and was continuously dropping at each DF step. During NF phosphorus was shown to be strongly retained by the membrane at 31.8 mmols L−1, while retention of ammonium was low at 13.4 mmols L-1 demonstrating the potential for this combination of membrane types for fractionating high value components from AD waste.

Waste effluents from anaerobic digesters of agricultural waste were treated with a range of membranes, including microfiltration and nanofiltration (NF), to concentrate volatile fatty acids (VFA). Microfiltration was applied successfully to produce sterile, particle-free solutions with a VFA concentration of 21.08 mM of acetic acid and 15.81 mM of butyric acid. These were further treated using a variety of NF membranes: NF270 (Dow Chemicals, USA), HL, DL, DK (Osmonics, USA) and LF10 (Nitto Denko, Japan), achieving retention ratios of up to 75%, and giving retentates of up to 53.94 mM of acetate and 28.38 mM of butyrate. DK and NF270 membranes were identified as the best candidates for VFA separation and concentration from these multicomponent effluents, both in terms of retention and permeate flux. When the effluents are adjusted to alkali conditions, the highest productivity, retention and flux were achieved at pH 7. At higher pH there was a significant reduction in flux.

Current separation, isolation and purification techniques to obtain highly potent purified lactobacilli and lactococci bacteriocins include chemical precipitation, separation employing solvents and chromatographic techniques. These methods are arduous, costly, with limited scalability, offering low bacteriocin yields ( To facilitate separation, the microorganisms were grown on specially developed low molecular weight medium (LMWM) mainly containing nutritive sources up to 4 kDa molecular weight. Bacterial cells were removed by centrifugation. The clarified broths were filtered using 4 and 1 kDa MWCO. Bacteriocin activity was determined by an antimicrobial activity test using nisin, which has an inhibitory effect on the growth of susceptible microorganisms. Recovery yields using filtration were found to range between 53 and 68%, a high recovery performance. The bacteriocin activity of crude extracts of all the three lactobacilli were between 95 and 105 IU ml−1. When the substances were separated using ultrafiltration membrane (4 kDa MWCO) their activity was enhanced to 145–150 IU ml−1, achieving a total potency yield of 44–53%. Further enhancement of yields up to 36% was attained employing nanofiltration (1 kDa MWCO) membranes with an activity increased up to 200 IU ml−1. Bacteriocin isolation from crude extracts using filtration was found to be effective, offering high recovery yields, optimising their activity as well as presenting a realistic option towards the formulation of these as commercially available antibacterial agents.

A mathematical model of microbial kinetics was introduced to predict the overall volumetric gas–liquid mass transfer coefficient (kLa) of carbon monoxide (CO) in a batch cultivation system. The cell concentration (X), acetate concentration (Cace), headspace gas (Nco and N co 2 ), dissolved CO concentration in the fermentation medium (Cco), and mass transfer rate (R) were simulated using a variety of kLa values. The simulated results showed excellent agreement with the experimental data for a kLa of 13/hr. The Cco values decreased with increase in cultivation times, whereas the maximum mass transfer rate was achieved at the mid-log phase due to vigorous microbial CO consumption rate higher than R. The model suggested in this study may be applied to a variety of microbial systems involving gaseous substrates.

Lactococcus lactis species have been and still are extensively investigated due to their significant commercial importance. Current scientific research focuses on strains utilized in food industry, due to their multiple uses in food and beverages fabrication. Biomass of Lactococcus lactis is of great interest as well as the end products of its metabolism such as lactic acid and nisin. However their production is constantly challenged due to end product inhibition occurring during intensive propagation of the coccus in reactor systems. To successfully predict the behavior of the culture, the approach of combining mathematics with biology, ergo the development of an unstructured mathematical model, was taken. Although Luedeking and Piret is the model that has been extensively used to demonstrate growth in end-product inhibition cultures, its applicability is limited due to its dependance on the specific growth and product coefficients, particularly related to the culturing conditions used. To overcome these hurdles, a combination of the non competitive single product end inhibition Taylor and Hinselwood models was used, with the significance of this model laying in the fact that it offers a feasible alternative to the commonly used model of Luedeking and Piret for describing fermentation kinetics governed by end-product inhibitions. The fitting with the experimental values, in batch mode, was tested in terms of the coefficient of determination (R2), having values 0.97 ∼ 0.99 and suggesting a very good fitting with the experimental data. The model was further developed to achieve theoretical predictions of volumetric cell productivity in continuous and fed-batch mode of substrate feed in different culturring systems.

BACKGROUND Contemporary purification techniques of Lactobacilli bacteriocins include chemical precipitation and separation through solvents to obtain highly potent semi-purified bacteriocins. These methods are laborious and bacteriocin yields are low. To address this problem a set of new, efficient, cost effective media, was created, containing low molecular weight nutrient sources (LMWM). Using these media future separation and concentration of the desired metabolic products, using ultra- and nano-filtration from the cultured broth was possible. RESULTS The LMWM were made through serial filtration (filters varying in pore size 30 kDa, 4 kDa and 1 kDa MWCO) of a modified optimum liquid medium for Lactobacilli growth. The developed media were tested for bacteriocin production and biomass growth, using three known bacteriocin-producing Lactobacilli strains, Lactobacillus casei NCIMB 11970, Lactobacillus plantarum NCIMB 8014, Lactobacillus lactis NCIMB 8586. All were successfully grown (µmax 0.16 to 0.18 h−1) on the LMWM and produced a significant amount of bacteriocins in the range 110 to 130 IU mL−1. CONCLUSIONS LMWM do support Lactobacilli growth and bacteriocin production, establishing an alternative to the current production nutrient media. The uptake of the nutrient sources is facilitated as nitrogen sources, which were primarily responsible for growth, were supported in less complex forms. Copyright © 2012 Society of Chemical Industry

Three Lactobacilli strains, Lactobacillus casei NCIMB 11970, Lactobacillus plantarum NCIMB 8014, Lactobacillus lactis NCIMB 8586 have been used for the production of bacteriocins. Though, their production phase, their biochemical nature, their mode of activity even their genetic structure have been widely investigated, there are hardly any studies investigating their potency and activity in depth of time, in other words their shelf life under several physicochemical conditions that may occur during their production in large scale. As such, the effect of several factors influencing the activity and the potency of bacteriocins when produced in large scale was examined as due to bacteriocins peptide nature degradation or denaturation might occur, under extreme physicochemical conditions. During scale-up process, differences between the output data may occur, such as concerning biomass, metabolic by-products and limiting substrate concentrations. These may affect negatively the activity and the potency of the bacteriocins. For investigating these effects and minimizing them, numerous studies were conducted, which were related to the exact phase of the production of these substances, the effect of dilution and temperature changes. These studies could be used in order to minimize the scaling-up effect when decided to produce these peptides in large scale.

A great number of Gram (+) and Gram negative (-) bacteria produce during their growth, substances of protein structure (either proteins or polypeptides) possessing antimicrobial activities, called bacteriocins. Although bacteriocins could be categorized as antibiotics, they are not. The major difference between bacteriocins and antibiotics is that bacteriocins restrict their activity to strains of species related to the producing species and particularly to strains of the same species, antibiotics on the other hand have a wider activity spectrum and even if their activity is restricted this does not show any preferential effect on closely related strains. In addition, bacteriocins are ribosomally synthesized and produced during the primary phase of growth, though antibiotics are usually secondary metabolites. Among the Gram (+) bacteria, lactic acid bacteria (LAB) especially, Lactobacilli have gained particular attention nowadays, due to the production of bacteriocins. These substances can be applied in the food industry as natural preservatives. The use of LAB and of their metabolic products is generally considered as safe (GRAS, Grade One). The application of the produced antimicrobial compounds as a natural barrier against pathogens and food spoilage caused by bacterial agents has been proven to be efficient. Nisin is the only bacteriocin that has been officially employed in the food industry and its use has been approved worldwide. Bacteriocins can be applied on a purified or on a crude form or through the use of a product previously fermented with a bacteriocin producing strain as an ingredient in food processing or incorporated through a bacteriocin producing strain (starter culture).

A fish farm sludge high in P (2–6% w/w as dry matter), Fe (5–7%), C (40–50%) and N (0.8–4%) was subjected to a series of acid leaching treatments using HCl, organic acids, and biologically mediated acid production. Additions of biodegradable organic acid solubilized heavy metals better than HCl, while additions of 1.5% w/v glucose followed by 7 day incubation stabilized the sludge releasing 92% P, 100% Fe. The use of homo-lactic Lactobacillus plantarum starter cultures were more effective than hetero-lactic Lactobacillus buchneri, solubilizing 81.9% P, 92.2% Fe, 93.0% Zn and 96.4% Ca in the sludge. The anaerobic sludge-glucose fermentation using L. plantarum produced a leached sludge that has low heavy metal and nutrient content while affording the recovery of nutrients. The potential of these methods for practical application are briefly discussed.

The binding and retention of single metal ions and mixtures of metal ions with polyethylenimine (PEI) was studied using polymer enhanced ultrafiltration (PEUF). Using a highly branched chain form of PEI (Sigma Aldrich 181979) with an average molecular weight 750,000 and approximately 60,000, ultrafiltration experiments were carried out in the stirred dead-end ultrafiltration mode. The results of the binding studies show that the Langmuir isotherm offers a good description of the binding process. At pH 5.5, the maximum polymer binding (Q max) and binding affinity constant (K L) were determined according to Langmuir isotherms. It was observed that the maximum amount of metal ions bound to the polymer for Cu2+, Zn2+, Ni2+ and Cd2+ decreased substantially in solutions containing mixtures of metal ions when compared to the values obtained for single metal ion solutions. For Cr6+ and Co2+ no significant decrease was seen. These data indicate that the binding capacity of Cr6+ and Co2+ remain constant in competit...

Schizochytrium limacinum SR21 was used to remove waste nutrients from a marine recirculating aquaculture wastewater while simultaneously producing a valuable biomass containing PUFA enriched with long chain fatty acids which may have potential as an aquafeed additive. Clean seawater and marine aquaculture wastewater supplemented with yeast extract (1.0–10 g L−1) and glycerol (10–90 g L−1) were used for a comparative study of growth and PUFA production using S. limacinum in batch, continuous and in a packed bed reactor (pall rings, surface area 340 m2/m3) that allow surface growth and cell recycling for a high cell density culture. Good growth rates (μ = 0.013 h−1) were obtained in batch and continuous culture modes. Biomass of S. limacinum was increased from 4.0 g L−1 as DCW in batch culture to 57.9 g L−1 in retention culture (D = 0.062 h−1). Retention culture of S. limacinum in a packed bed reactor also produced total lipids of 36.5 g L−1 (53–65%, w/w as DCW) and long chain fatty acids (>C22) of 12.6 g L−1 (21.8%, w/w as DCW) in 350 h. Long chain fatty acids of C22, C18 and C16, as the main fatty acids, were produced and production was enhanced when supplemented wastewater was used in growth medium. Changes to the relative concentrations of glycerol and yeast extract (C:N ratio) alter the amounts of oil produced and types of fatty acid produced. S. limacinum in continuous culture mode (D = 0.013 h−1) enabled significant reductions (

International audience; A mechanistic model of microalgae is used to explore the implications of modifying microalgal chlorophyll content and photosynthetic efficiency with an aim to optimizing commercial biomass production. The models show the potential for a ten-fold increase in microalgae productivity in genetically modified versus unmodified configurations, while also enabling the use of bioreactors of greater optical depth operating at lower dilution rates. Analysis suggests that natural selection of a trait benefiting the individual (high Chl:C; i.e. high antennae size) conflicts with artificial selection of a trait (low Chl:C) of most benefit to production at the population level. The implication is that GM strains rather than strains selected from nature will be most beneficial for commercial algal biofuels production. Further, escaped GM algae populations may, depending on the specific nature of the modification, be quickly out-competed by the natural forms because individually a high Chl:C is beneficial in low light environments. However, it remains possible that changes in biochemical composition associated with genetic modification of photosystem competence, or with other selection processes to enhance commercial gain, may adversely affect the value of such organisms as prey for zooplankton, leading to the unwanted generation of future harmful algae.

Lactobacilli belong to the group of lactic acid bacteria (LAB), widely used in the food industry nowadays. These microorganisms have several distinguishing abilities such as the production of lactic acid, enzymes such as β- galactosidase and natural antimicrobial substances called bacteriocins. They are mainly used as a natural acidifier for the inoculation of bulk quantities of milk and vegetables in order to produce a variety of fermented products. As such, large quantities of their biomass and the end products of their metabolism are necessary. The possibility of producing these substances in mass quantities will be investigated through several techniques. The selected Lactobacilli, L.plantarum NCIMB 8014, L.casei NCIMB 11970, L.lactis NCIMB 8586 were grown into simple batch cultures without pH control where their physicochemical needs were determined. Through the determination of the optimum nutritional conditions for the propagation of the Lactobacilli, an optimised medium for growth occurred. The optimum pH conditions for the growth of the bacilli were determined as well as parameters such as cellular yield coefficient, substrate and starter inoculum concentration and lactic acid rate and production. The metabolism of the Lactobacilli was determined as homofermentative, mainly producing lactic acid. The efficiency of the medium combining al the optimised parameters, enhancing the productivity biomass and therefore bacteriocins production from the strains, was tested on a 2L STR reactor operated batchwise with continuous pH control. A simple liquid turbidometric method was developed to test the bacteriocin productivity of the selected bacteria. The activity and potency of the bacteriocin produced was tested against L.delbruckii subsp.lactis NCIMB 8117. Index Terms-Doubling time, Growth rate, Lactic acid, Nisin

Micro-organisms were isolated from intake seawater and reverse osmosis (RO) membrane biofilms collected from a full-scale membrane-based desalination process. The results from a culture-dependent approach using 12 media were combined with the microbial community structure on fouled RO membranes as analyzed by a 16S rRNA clone library construction in our previous study. This was followed by selection of 11 target bacteria for further analysis, which were suspected to be responsible for biofilm formation on membrane surfaces. The adhesion of potential biofoulants differing in surface hydrophobicity and charge was examined. Cell wall hydrophobicity was measured as the contact angle of a lawn of bacteria, and by adhesion to hexadecane. The cell surface charge was investigated by measuring electrophoretic mobility. The data obtained from these methodologies were compared. According to the cell surface charge measurements, Pseudomonas aeruginosa, Acinetobacter venetianus, Cellvibrio mixtus subsp. Mixtus, Bacillus sp. Eur1 9.5, and Escherichia coli K12 could mediate initial adhesion to negatively charged RO membranes through electrostatic attraction. Limnobacter sp. KNF002, A. venetianus, and Simiduia agarivorans showed higher affinity to hexadecane than other bacterial strains tested, and Bacillus sp. Eur1 9.5, C. mixtus subsp. Mixtus, and P. aeruginosa were determined to have greater hydrophobic interactions with hydrophobic RO membranes. Refereed/Peer-reviewed

In the membrane process industries, membrane cleaning is one of the most important concerns from both economical and scientific points of view. The characterisation of membrane surface by using zeta potential technique provides a more appropriate tool to study the cleaning performance and membrane integrity. The use of zeta potential technique to characterize the cleaning effect on membrane surfaces has very little precedence in literature. In this study the cleaning performance has been studied with membrane zeta potential and hydraulic permeability measurement. Virgin nanofiltration (NF) membranes provided by GE Osmonics (DK, HL and DL), as well as fouled DK membranes were used in this study. Several cleaning agents were investigated, some of them were analytical grade, such as HCl, NaOH and others were commercial grade agents that are already in use in commercial plants. Zeta potential of virgin and fouled NF membranes before and after chemical cleaning were measured and compared. The results of the zeta potential measurements with and without chemical cleaning of virgin and fouled membrane indicated that zeta potential may be used to characterise the membrane surface cleanliness and permeability. The effects of temperature, pH and the cleaning agents on membrane zeta potential were also investigated. The temperature was not found to have any significant effect on membrane zeta potential; however, the effect of pH and cleaning agents had pronounced effects on the surface charge and zeta potential. At high pH values mixed cleaning agents of mixture of trisodium phosphate, sodium tripolyphosphate and EDTA (recommended by membrane manufacturer) had a marked effect on zeta potential of HL and DL membranes compared to other cleaning agents. A DK fouled membrane was found to be almost negatively charged with no isoelectric point compared to a virgin DK membrane. At low pH, the zeta potential values of a fouled DK membrane were in close agreement with those obtained with an untreated virgin membrane after cleaning by NaOH followed by HCl. The zeta potential of all virgin membranes cleaned with SDS changed to more negative for the entire pH range compared to untreated virgin membranes. The study revealed that the SDS cleaning agent had the highest effect on surface charge for both virgin and fouled NF membranes.

This study investigated the performance of bio-filters immobilized nitrifying bacteria, ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB). In particular, it was to assess the consumption of ammonia-nitrogen (NH 3 -N) by the AOB. The experiment was conducted in a one litre reactor.The reactor consisted of bio-filters with NH 3 -N as the substrate for the nitrifying bacteria. Low concentration of NH 3 -N (between 5 and 25 mg/L) and high concentrations (between 35 and 100 mg/L) were used in this batch culture experiment.Simultaneously, the production of nitrate-nitrogen was also evaluated by the consumption of nitrite-nitrogen by the NOB.The results showed that the nitrifying bacteria in the bio-filters were able to reduce the NH 3 -N rapidly between 5 and 15 mg/L of NH also found that the highest removal rate of NH 3 -N was in 100 mg/L. Keywords : ammonia-nitrogen; immobilized; biobio-filter; batch culture.

Membrane filtration of wastewater sludge is a feasible technology for the recovery of sustainable nutrients in bacteria and particle-free solutions. Diafiltration and acidification strategies were investigated for the recovery of phosphorus (P) from trout farm sludge. Extraction costs were determined using a pilot-scale unit. pH of 2.7 was found to maximize the extraction of P (and metals) and highest concentrations were achieved by acidic leaching of the sludge sediment. Levels of P, Ca, Fe, Mg, and K recovered in soluble fractions were 418 mg/L, 6730 mg/L, 66.8 mg/L, 29 mg/L, and 34.1 mg/L, respectively. Operational costs associated with acidification and power consumption were estimated to be 0.018 kWh/L permeate or 0.037 kWh/g P obtained. The extraction of P by membrane filtration was mainly dependent on pH and cost was considerably lower than that for P-based fertilizers. Owing to the high concentration of Ca and P in the permeate fractions, 99% of the soluble P was precipitated from solution at pH 8. Elemental analysis and FTIR of the precipitate obtained indicated to be carbonated calcium-deficient hydroxyapatite.

The fractionation of nitrogen (as ammonia/ammonium) and phosphorus (as phosphate ions) present in the dairy manure digestate was investigated using a nanofiltration membrane NF270. The filtration and separation efficiencies were correlated to pH across the range 3 < pH < 11. Filtration at pH 11 enabled higher permeate flux of 125–150 LMH at 20 bar, however rejection of ammonia was high at 30–36% and phosphate was 96.4–97.2%. At pH 3 and pH 7, electrostatic charge effects led to higher permeation of ammonium and thus more efficient separation of nitrogen. The rejection of phosphorus was relatively constant at any given pH and determined as 83% at pH 3, 97% at pH 7 and 95% at pH 11. The fractionation of nitrogen and phosphorus from complex aqueous solutions was demonstrated to be highly dependent on the charge of the membrane and ionic speciation. Solutions rich in nitrogen (as ammonia/ammonium) were obtained with almost no phosphorus present (

Spent digester effluents were formulated into nutrient media , suitable for microbial growth of industrially important microorganisms, using filtration and diafiltration. The waste effluents were pretreated by dilution, sedimentation and sieving for the removal of large particulate material. The scheme used allowed the successful formulation particle, free sterile effluents, with an N:P ratio 36.6 The prepared microfiltered effluents were then physicochemically characterized before being assessed for their utilization as growth substrates of microorganism associated with chemical and fuels production. Microfiltered treated digested propagated with Escherichia coli NCIMB 8277, agricultural sludge based media were compared with in vitro media when supplied with or without addition carbohydrate sources. in bench scale batch aerobic. Good growth was achieved compared to synthetic growth media with the microorganism using filtrates. When the treated effluents were supplied with 2% w/v glucose solution a significant improvement in the growth rates and growth yields was achieved giving comparable performance with the synthetic media.

Eubacterium limosum KIST612 was cultivated on carbon monoxide using a cell-recycled continuous fermentation system to produce organic acids. A bubble column reactor system (kLa=72 h−1) was used with a membrane to allow on-line products removal with cell recycle. When cell concentration reached 5.25 g l−1 in the reactor, the cell concentration did not increase at carbon monoxide (CO) partial pressures lower than 74 kPa though CO was consumed with the acidic products formation. At this stage, the overall CO mass transfer rate (kLa[C*−CL]) was lower than required for the maximum cell growth (qCOmaxX), but higher than that to meet the maintenance requirement (msX). When the CO mass transfer rate was maintained higher than maintenance requirement by increasing CO partial pressure, the cell concentration increased to 9.5 g l−1.

An atomic force microscope has been used to image four commercial stainless steel samples of widely differing surface finishes. Analysis of the images allowed quantification of surface roughness over different area scales, 50 × 50 μm, 10 × 10 μm and 1 × 1 μm. The atomic force microscope was also used to measure directly the adhesion of a single polymer latex particle (radius ∼5 μm) to the surface in solution using the colloid probe technique. It was found that the adhesion increased with decreasing roughness, except for the smoothest surface which exhibited very regular surface features on the area scale most relevant to adhesion of the particle (1 × 1 μm). There was a good correlation between the variability of adhesion over each surface and the corresponding variability in surface roughness. Measurements of this type should prove useful in the technical/economic choice of surface finish for a particular purpose. As the colloid probe has dimensions comparable to those of bacteria and yeast cells, such measurements should especially be of value in the selection of surface finish likely to minimise bioadhesion.

An atomic force microscope (AFM) has been used to quantify directly the adhesion between single Aspergillus niger spores and freshly cleaved mica surfaces in air, a system that is relevant to the removal of spores by filtration. The measurements used ‘spore probes’ constructed by immobilising a single spore at the end of a tipless AFM cantilever. It was found that adhesion was reproducible at a relative humidity of 64%, but that it showed substantial variability at a relative humidity of 33%, findings that are consistent with capillary forces playing a dominant role in the adhesion process. The technique should prove useful both in the evaluation of different types of filter materials and in assessing the effect of environmental conditions on spore removal efficiency.

Atomic force microscopy (AFM) has been used to study the micromechanical properties of biological systems. Its unique ability to function both as an imaging device and force sensor with nanometer resolution in both gaseous and liquid environments has meant that AFM has provided unique insights into the mechanical behaviour of tissues, cells and single molecules. As a surface scanning device, AFM can map properties such as adhesion and the Young's modulus of surfaces. As a force sensor and nanoindentor AFM can directly measure properties such as the Young's modulus of surfaces or the binding forces of cells. As a stress-strain gauge AFM can study the stretching of single molecules or fibres and as a nanomanipulator it can dissect biological particles such as viruses or DNA strands. The present paper reviews key research that has demonstrated the versatility of AFM and how it can be exploited to study the micromechanical behaviour of biological materials.

An atomic force microscope (AFM) has been used to quantify directly the adhesive interactions between a silica sphere and a planar silica surface. Electrostatic double-layer interactions have also been quantified through analysis of approach curves. The surfaces of the sphere and planar surface were treated prior to measurements either by ethanol washing or by plasma treatment. Adhesion forces were then measured in 0.01 M NaCl solutions at pH 3 and 8. The adhesion force did not vary greatly with pH for a given cleaning procedure. However, the magnitudes of the adhesion forces were substantially less for the plasma treated surfaces. The adhesion forces did not vary systematically with the loading force. Agreement of the adhesion measurements with theory (DLVO, using a non-retarded Hamaker constant based on the latest interpretation of spectroscopic data for water) was good for the ethanol treated surface at pH 3 — conditions where double layer interactions are negligible. However, the plasma treated surface at pH 3 showed adhesion an order of magnitude lower than calculated. In contrast, adhesion at pH 8 was in both cases greater than theoretical expectations, though the lower adhesion for the plasma treated surface was in quantitative agreement with the increased electrostatic double–layer interactions induced by plasma treatment. The results show that the adhesion of such surfaces is a complex phenomenon and that non-DLVO interactions probably play a substantial overall role.

The pressure driven membrane processes of microfiltration and ultrafiltration are usually classified in terms of the size of solutes (colloids) separated. However, theoretical calculations have shown that electrostatic double-layer interactions can have a strong influence on rejection at the pores of such membranes. The present paper provides experimental evidence to support these findings. Firstly, atomic force microscopy in conjunction with the colloid probe technique is used to measure directly the repulsive electrostatic force experienced when a single colloidal particle approaches a microfiltration membrane. Scanning of such a membrane with the colloid probe provides a direct visualisation of the membrane surface as would be experienced by a colloidal particle during filtration. Secondly, filtration flux/time data is presented for the case of filtration of particles of size very close to the pore size in an ultrafiltration membrane. For such a case, theoretical calculations allow definition of a critical pressure at which the hydrodynamic force transporting the colloid toward the membrane pore is exactly balanced by the opposing electrostatic force. The experiments show that operating above this pressure results in a rapid loss in filtration flux, but operation below this pressure allows continuing filtration with only a minor decrease in flux, in agreement with the calculations.

An Atomic Force Microscope (AFM) has been used to quantify directly the adhesive force between a colloid probe and two polymeric ultrafiltration membranes of similar MWCO (4000 Da) but different materials (ES 404 and XP 117, PCI Membrane Systems (UK)). The colloid probe was made from a polystyrene sphere (diameter 11 μm) glued to a V shaped AFM cantilever. Measurements were made in 10 −2 M NaCl solution at pH 8. It was found that the adhesive force at the ES 404 membrane was more than five times greater than that at the XP 117 membrane. As it allows direct quantification of particle/membrane interactions, this technique should be invaluable in the development of new membrane materials and in the elucidation of process behaviour.

An atomic force microscope (AFM) in conjunction with the colloid probe technique has been used to measure directly the interaction of adsorbed layers of the protein bovine serum albumin (BSA). The BSA was adsorbed on both a silica colloid probe and a silica surface. Measurements of force-distance curves were made at various salt concentrations and pHs. The measured force-distance curves were in good quantitative agreement with predictions based on the DLVO theory using zeta potentials (outer Helmholtz plane potentials) calculated for BSA from an independently validated site-binding-site-dissociation surface model. The paper hence provides a direct confirmation that the AFM colloid probe technique can provide a useful means of directly quantifying the interaction of biological macromolecules. Copyright 1998 Academic Press. Copyright 1998Academic Press

In the present study, a monolithic alumina coated microfiltration ceramic membrane was used for solid particulate removal and nutrient recovery from anaerobic digester complex effluent streams. The aim was to test the effect of the cake layer developed by the solids, on the surface of the membrane channels, to the filterability of these materials. The solid content ranged between 2.6 g/L to 15.1 g/L. During practical application, two processing techniques targeting the enhanced recovery of the materials of interest including ammonia, phosphate, calcium bicarbonate and volatile fatty acids, namely dewatering and diafiltration, were used. These had an immediate effect on the solid content (PDS 13 μm to 3.97 μm) enhancing the filterability of the effluents. Their processability was evaluated in terms of flux, cross flow velocity, membrane resistance and cake resistance. An important finding of this study is the nonalignment of the flux rates to the cake resistance, explained by the formation of a compressible, permeable cake layer that allowed the continuous operation of the system, under constant low pressure conditions (TMP 15 psi). Permeate flux remained constant to 120 L/m2 h when applying diafiltration, while when dewatering process is used the permeate flux remained constant at 115.4 L/m2 h.

The harvesting of the microalgae Scenedesmus species using a 200 L pilot-scale microfiltration system was investigated and critically assessed. The energy requirement was determined and correlated to the different operating parameters, such as transmembrane pressure (ΔP), membrane area, temperature, and initial biomass concentration. A filtration model was developed and showed a strong correlation with experimental data up to 20.0 g of dry cell weight (DCW)/L. The non-optimized filtration system had an energy requirement of 2.23 kWh/m(3) with an associated cost of $0.282/kg of microalgae. The investigation into the influence of the operating parameters and scale-up effects showed that the energy requirement could be substantially reduced to 0.90 kWh/m(3) and $0.058/kg of microalgae harvested. Maintenance costs associated with cleaning were estimated to be 0.23 kWh or $0.029/batch of microalgae processed. Dependent upon the operating conditions, harvesting may represent 6-45% of the energy embedded in the microalgae with a carbon footprint of 0.74-1.67 kg of CO2/kg of microalgae. Microfiltration was demonstrated to be a feasible microalgae harvesting technology allowing for more than 99% volume reduction. The energy requirement and associated carbon footprint of microalgae harvesting reported here do not forfeit the need for an industrial-scale study; however, the information provided presents a more realistic approximation than the literature reported to date.

The future of microalgae as a sustainable feedstock for biofuel and other products is still uncertain. Although productivity and environmental benefits surpass that of many other types of feedstock, the associated costs with production and downstream processing hinder this type of technology. The microalgae biorefinery approach addresses many of these issues in which upstream and downstream processes are important. Upstream technologies associated to nutrient recovery from waste effluents have been reviewed and discussed. Potentially, waste-derived nutrients will enable the formulation of optimal growth media from wastewater at lower costs. Microalgae dewatering is still seen as a major burden. A thorough review of the associated membrane processes in the literature has highlighted lack of consistency in terms of the influence of pore size and membrane materials. Moreover, only very few pilot-scale cost estimates could be found. The fractionation of microalgae products is perhaps the less developed area in the context of a microalgae biorefinery. Membrane filtration for the recovery of lipids, proteins and carbohydrates from microalgae is still an infant technology and major developments are expected to take place within the next few years. This review highlights the achievements, potential and future challenges of integrating membrane technology into microalgae-based biorefineries.

Biofouling is a crucial issue, and it causes seawater reverse osmosis membrane to deteriorate the performance of desalination. In this study, excitation emission matrix (EEM) fluorescence spectroscopy and parallel factor analysis (PARAFAC) were used to monitor the strength of biofouling on the fouled membrane which was obtained from real plant. Based on EEM and PARAFAC results of raw seawater, feed water, permeate, brine and fouled membrane, three components were identified as the major peaks: (1) microbial product-like materials at Ex/Em = 280/370 nm, (2) humic-like substances at Ex/Em = 330/420 nm, and (3) aromatic proteins at Ex/Em = 240/320 nm. Using the fluorescence intensity changes, the effects of replacing fouled RO membranes were found to be most significant at one of the components (Ex/Em = 270–300/350–380 nm) which could be considered the substances desorbed from fouled RO membrane. Compared to the data for salt rejection, this component monitoring of the brine EEM image is shown to be more sensitive than conductivity monitoring for predicting the biofouling strength during the desalination process.

An atomic force microscope has been used to study the electrical double layer interactions between a silicon tip (with an oxidised surface) and two polymeric membranes, one microfiltration (nominally 0.1 μm) and the other ultrfiltration (25 000 MWCO), in aqueous NaCl solutions. Force-distance curves were measured for the two membranes at four ionic strengths. The membranes were also imaged under the same conditions using electrical double layer repulsive forces of differing magnitudes —; “electrical double layer mode” imaging. Image analysis was used to determine surface pore size distributions. The force-distance curves, together with numerically calculated potential profiles at the entrance to a charged pore, allow an explanation and identification of the optimum imaging conditions. The best images were obtained at high ionic strength with the tip close to the membrane surface.