An integrated process scheme is developed for valorizing filtered liquid digestates (FLD) from an industrial anaerobic digestion (AD) plant treating dairy-processing effluents with relatively low nutrient concentrations. The process scheme involves FLD treatment by nanofiltration (NF) membranes, followed by struvite recovery from the NF-retentate. An NF pilot unit (designed for this purpose) is combined with a state-of-the-art NF/RO process simulator. Validation of simulator results with pilot data enables reliable predictions required for scaling up NF systems. The NF permeate meets the standards for restricted irrigation and/or reuse. Considering the significant nutrient concentrations in the NF retentate (i.e., ~500 mg/L NH4-N, ~230 mg/L PO4-P), struvite recovery/precipitation is investigated, including determination of near-optimal processing conditions. Maximum removal of nutrients, through production of struvite-rich precipitate, is obtained at a molar ratio of NH4:Mg:PO4 = 1:1.5:1.5 and pH = 10 in the treated stream, attained through the addition of Κ2HPO4, ΜgCl2·6H2O, and NaOH. Furthermore, almost complete struvite precipitation is achieved within ~30 min, whereas precipitate/solid drying at modest/ambient temperature is appropriate to avoid struvite degradation. Under the aforementioned conditions, a significant amount of dry precipitate is obtained, i.e., ~12 g dry mass per L of treated retentate, including crystalline struvite. The approach taken and the obtained positive results provide a firm basis for further development of this integrated process scheme towards sustainable large-scale applications.

Batch fermentations of the wild type Yarrowia lipolytica MUCL 28849 were performed in a bench-top bioreactor to assess crucial operating conditions. A setup of carbon to nitrogen (mol/mol) ratio equal to 34, pH = 6.0 and 52 g/L of crude glycerol showed increased lipid production and complete glycerol consumption at t = 24 h, thus, selected for further process improvement. & Acy; semi-continuous process was implemented, where a pH drop to 4.0 at 24 h, interrupted citric acid secretion without affecting lipid production. An in-situ membrane module was employed for membrane bioreactor fermentations, where yeast cells were successfully retained with minimum fouling. The membrane bioreactor fed-batch process, resulted in a high-cell-density culture reaching 49.8 g/L of dry biomass and 4.9 g/L of lipids. An unstructured model was developed and successfully simulated operation under all fermentation modes, distinguishing diverse physiological shifts.

There is a need to develop facile methods for the determination of UV light extinction characteristics of photocatalysts. For this task, a novel technique is proposed, applicable to dispersed photocatalyst processes of practical interest. The technique is demonstrated by obtaining fairly extensive data sets of transmittance and extinction coefficients, using TiO2 particle suspensions at various concentrations and pH values ~3, ~5, and ~8, with light lamps of different irradiation types (i.e., UVC and UVA), immersed in the medium. To estimate the light absorption coefficient, under various tested conditions, the simplified Kubelka–Munk model is employed. The results obtained, regarding both the total light extinction and absorption coefficient, are in accord with similar literature data. The demonstrated technique is considered useful for process development studies and the design of photocatalytic reactors.

Excessive albumin losses during HC (haemocatharsis) are considered a potential cause of hypoalbuminemia—a key risk factor for mortality. This review on total albumin losses considers albumin “leaking” into the dialysate and losses due to protein/membrane interactions (i.e. adsorption, “secondary membrane formation” and denaturation). The former are fairly easy to determine, usually varying at the level of ~ 2 g to ~ 7 g albumin loss per session. Such values, commonly accepted as representative of the total albumin losses, are often quoted as limits/standards of permissible albumin loss per session. On albumin mass lost due to adsorption/deposition, which is the result of complicated interactions and rather difficult to determine, scant in vivo data exist and there is great uncertainty and confusion regarding their magnitude; this is possibly responsible for neglecting their contribution to the total losses at present. Yet, many relevant in vitro studies suggest that losses of albumin due to protein/membrane interactions are likely comparable to (or even greater than) those due to leaking, particularly in the currently favoured high-convection HDF (haemodiafiltration) treatment. Therefore, it is emphasised that top research priority should be given to resolve these issues, primarily by developing appropriate/facile in vivo test-methods and related analytical techniques.

This study describes the enzymatic production of second-generation biodiesel using low-quality acid oil as a substrate. Biolipasa-R, a commercially available and low-cost lipase, was employed for enzymatic transesterification. Response surface methodology was applied to optimize the enzymatic transesterification process. The optimal conditions for biodiesel production, which comprised 42% lipase concentration (per weight of oil), 32% water content (per weight of oil), a methanol to oil molar ratio of 3:1, pH 7.0 and reaction temperature 30°C, resulted in the highest fatty acid methyl ester (FAME) content (71.3%). Subsequently, the synergistic effect of two lipases with different regioselectivities under the optimum transesterification conditions was studied, aiming at the enhancement of process efficiency. The transesterification efficiency of immobilized Biolipasa-R was determined and compared to that of Biolipasa-R in its free form. The results revealed a good performance on FAME content (66.5%), while the recycling of immobilized lipase resulted in a decrease in transesterification efficiency after three consecutive uses.

Background A potential alternative to lactic acid production through sugar fermentation is its recovery from grass silage leachate. The separation and purification of lactic acid from fermentation broths remain a key issue, as it amounts to up to 80% of its industrial production cost. In this study, a genetically engineered E. coli strain (A1:ldhA), that cannot catabolize lactic acid, has been used to selectively remove impurities from a synthetic medium comprising typical components (i.e., glucose and acetic acid) of green grass silage leachate. A systematic approach has been followed to provide a proof-of-concept for a bio-purification process of lactic acid solutions in a membrane bioreactor operating in semi-continuous mode. Results The synthetic medium composition was initially optimized in shake-flasks experiments, followed by scale-up in bench-scale bioreactor. Complete (i.e., 100%) and 60.4% removal for glucose and acetic acid, respectively, has been achieved in batch bioreactor experiments with a synthetic medium comprising 0.5 g/L glucose and 0.5 g/L acetic acid as carbon sources, and 10 g/L lactic acid; no lactic acid catabolism was observed in all batch fermentation tests. Afterwards, a hybrid biotechnological process combining semi-continuous bioreactor fermentation and ultrafiltration membrane separation (membrane bioreactor) was applied to in-situ separate purified medium from the active cells. The process was assessed under different semi-continuous operating conditions, resulting in a bacteria-free effluent and 100% glucose and acetic acid depletion, with no lactic acid catabolism, thus increasing the purity of the synthetic lactic acid solution. Conclusions The study clearly demonstrated that a bio-purification process for lactic acid employing the engineered E. coli strain cultivated in a membrane bioreactor is a technically feasible concept, paving the way for further technological advancement.

BACKGROUND: The present study investigates the in situ electrogeneration of H2O2 by the 2e(-) oxygen reduction reaction in an electrochemical flow cell using three commercially available cathodic electrode materials with different interfacial properties; that is, activated carbon felt (ACF), non-activated carbon felt (NACF) and gas diffusion electrode (GDE). RESULTS: Experiments were first performed to optimize the operating parameters and to determine the yield of H2O2 electrosynthesis. The estimated maximum yield of similar to 40% was achieved with the NACF electrode after 30 min of operation. Furthermore, the performance of the electrodes was investigated in two scenarios, namely (i) under conditions with O-2-saturated electrolyte and (ii) under continuous air supply, to study the differences in O-2 distribution within the electrode material as a function of its interfacial properties. The maximum H2O2 concentration for the first scenario was 3.86 mg L-1 after 60 min of operation, which was obtained with the NACF electrode. In contrast, in the second scenario, H2O2 electrogeneration was significantly increased for all three electrodes, with the GDE exhibiting the best performance, at 43.3 mg L-1 after 60 min of operation. CONCLUSIONS: The properties of the electrode material play a decisive role in H2O2 electrogeneration. The hydrophilicity of the electrode is very important when O-2 is dissolved in the electrolyte. Hydrophobicity is preferable when gaseous O-2 is applied to the electrode as a three-phase interface is formed, which favors the transfer/penetration of O-2. The pore size of the electrode is of crucial importance, as mesoporous materials facilitate the distribution of gaseous O-2 in the electrode body. (c) 2024 Society of Chemical Industry (SCI).

Effective permeability KP, the ultrafiltration coefficient (KUF), the sieving coefficient (SC), and the loss/permeation of proteins (primarily albumin) are key parameters/specifications characterizing hemofilter (HF) performance. However, there are uncertainties regarding their determination. This work aims (a) to demonstrate that the co-current flow (of blood and dialysate) can lead to beneficial unidirectional filtration (from blood/plasma to dialysate) under a fairly uniform local trans-membrane pressure (TMP), unlike the presently employed counter-current flow; (b) to study the temporal evolution of key HF performance parameters under co-current flow, particularly during the important early stage of hemocatharsis (HC). Experiments with human plasma and BSA solutions in co-current flow mode (for which a fluid mechanical model is developed) show a fairly uniform local/axial TMP, which also improves the local/axial uniformity of protein membrane fouling, particularly under (currently favored) high convective flux operation. Due to incipient membrane fouling, a significant temporal variability/decline in the effective KP is observed, and, in turn, of other parameters (i.e., the Kuf, SC, and permeation/mass flux Mm for albumin and total proteins). A satisfactory correlation of the albumin/protein mass flux Mm with permeability KP is obtained, indicating strong inter-dependence. In conclusion, co-current flow, allowing for a fair local TMP axial uniformity, enables the acquisition of accurate/representative data on the evolution of HF parameters, facilitating their interpretation and correlation. The new results provide a basis for exploring the clinical application of the co-current flow.

This study aims to integrate a novel bio-purification process employing an engineered E. coli strain in the downstream processing of lactic acid (LA) fermentation broths from low-cost renewable biological feedstocks. Fermentation broth of candy waste and digestate mixture was used as a real biological feedstock. An engineered E. coli strain that selectively catabolize impurities without catabolizing LA was initially adapted on the biological feedstock, followed by shake flask experiments to prove the bio-purification concept. Scale-up and validation in a bench-scale bioreactor followed, before developing a semi-continuous membrane bioreactor (MBR) bio-purification process. The MBR bio-purification was assessed with biological feedstocks which simulated ultrafiltration or nanofiltration permeates. Incomplete removal of impurities and increased fouling was observed in the case of the ultrafiltration permeate. Contrarily, the nanofiltration permeate was successfully treated with MBR bio-purification, since low membrane fouling, 100% maltose and acetic acid removal, and no LA catabolism was achieved. MBR bio-purification as a post-treatment step in the downstream processing of LA was demonstrated as a promising technology for increasing the purity of LA solutions.

Complete valorization of various wastes and effluents, with significant organic content, remains a great challenge in the pursuit of a circular economy. The approach based on anaerobic fermentation, leading to valuable biogas production, has been broadly accepted and employed as an attractive processing scheme. However, despite notable research efforts, complete valorization of the digestates (involving recovery of nutrients/by-products and full recycling/reuse of treated water) requires additional work for sustainable process development. This study aims to make a contribution in this direction by demonstrating a systematic methodology for valorizing the liquid digestate. The proposed membrane-based processing scheme involves UF-membrane pretreatment of the liquid digestate (for sludge separation) and subsequent NF/RO membrane treatment for reuse/recycling of the permeate; the concentrate, enriched in “nutrients” (phosphate and ammonium compounds), can be utilized for soil fertilization, with further conditioning/processing. By performing targeted laboratory experiments and advanced simulations, the membrane-based process was developed to a relatively high technology-readiness level, including a pilot unit design/construction and preliminary testing with satisfactory results. Through pilot testing in industrial environment, further process development and optimization will be pursued, towards practical applications. The demonstrated methodology is also considered appropriate for systematic development of membrane-based processes to valorize/treat a variety of similar effluents.

The effect of gap thickness reduction 2h (i.e., the reduction h at each membrane surface) is studied on the flow field and mass transfer, in membrane channels filled with novel spacers, under conditions representative of those prevailing in RO desalination modules. The patented novel net-type spacers are comprised of regularly-spaced spherical nodes (in contact with the membranes) and interconnecting cylindrical filaments at the midplane of the channel. Advanced 3D flow simulations, performed at “unit cell” level, show the strong effect of a modest gap reduction on the flow field. Analysis of the computational results leads to new insights regarding flow development as well as to useful correlations of key process parameters (i.e., for friction losses, mass-transfer rates, wall shear stresses) accounting for the effect of gap reduction. Contrary to conventional spacers, the novel spacer geometry, under conditions of usual/modest channel-gap reduction, exhibits no stagnant flow zones and relatively high shear stresses on both the membranes and the filaments, which leads to desirable mitigation of fouling and a reduction in concentration polarization. The developed correlations can be adapted to existing advanced simulators of RO module performance for improved process design and optimization.

Vacuum Membrane Distillation (VMD) is systematically investigated herein, for recovering ammonia after phosphates precipitation, towards development of a sustainable process to valorize anaerobic-fermentation liquid-digestates (separated from the sludge). Initially, batch tests were performed, with representative synthetic solutions, to identify a narrow range of conditions favoring optimal ammonia (i.e. total ammonia nitrogen-TAN) separation, mainly regarding selectivity and recovery in H2SO4 scrubbing-solution. Next, guided by the preceding test-results, targeted batch experiments with digestate samples from an industrial plant, led to determination of near-optimum conditions for ammonia recovery. Specifically, for the small TAN concentration (<200 mg/L) encountered in the digestate feeds, VMD at modest temperature (T< similar to 45 degrees C) and driving force Delta p (<20 mbar) allowed high ammonia removal fraction r (greater than 0.85) with fair selectivity. Under such conditions, the (ammonia-water) distillate flux J exhibited linear dependence on Delta p; moreover, J and pH of feed solution remained practically constant for a significant distillate removal-fraction R (under constant Delta p and T). Based on theoretically supported correlation of ammonia removal-fraction r with distillate removal-fraction R, and other results, an approach is proposed for realistic preliminary design of a continuous VMD-based process, thus facilitating further steps towards large-scale process development.

Extraction of intracellular lipids of the oleaginous yeast Yarrowia lipolytica has been systematically studied aiming towards a sustainable extraction process for lipid recovery. Selection of suitable industrial (bulk) solvents and extraction parameters that lead to maximization of lipid recovery are significant issues to be addressed, with industrial applications motivating this study. Biomass from fermentation of Yarrowia lipolytica (MUCL 28849) was used in small laboratory tests to assess different solvent mixtures (i.e., methanol/hexane, isopropanol/hexane, and methanol/ethyl acetate), implementing a systematic design of experiments methodology to identify near-optimum values of key extraction variables (i.e., polar/non-polar ratio, vortex time, dry biomass/solvent ratio) in regard to lipid yield (g lipids/g dry biomass). The methanol/hexane mixture exhibited the highest extraction yield in a wide range of experimental conditions, resulting in the following optimum parameters: polar/non-polar ratio 3/5, vortex time 0.75 h, and dry biomass/solvent ratio 40. Extraction tests on a fifty-times-larger scale (in a Soxhlet apparatus employing the optimal extraction parameters) confirmed the optimization outcome by obtaining up to 27.6% lipids per dry biomass (L/DB), compared to 12.1% L/DB with the reference lipid extraction method employing chloroform/methanol. Assessment of lipid composition showed that unsaturated fatty acid recovery was favored by the methanol/hexane solvent. Fatty acid composition was not affected by the increase in Soxhlet reflux cycles, whilst the lipid yield was notably favored.

Abstract Background Yarrowia lipolytica is a well-studied oleaginous yeast known for its ability to accumulate and store intracellular lipids, while growing on diverse, non-conventional substrates. Amongst them, crude glycerol, a low-cost by-product of the biodiesel industry, appears to be an interesting option for scaling up a sustainable single-cell oil production process. Adaptive laboratory evolution (ALE) is a powerful tool to force metabolic adaptations endowing tolerance to stressful environmental conditions, generating superior phenotypes with industrial relevance. Results Y. lipolytica MUCL 28849 underwent ALE in a synthetic medium with increasing concentration of pure or crude glycerol as a stressing factor (9–20% v/v) for 520 generations. In one case of pure glycerol, chemical mutagenesis with ethyl methanesulfonate (EMS) was applied prior to ALE. Growth profile, biomass production and lipid content of 660 evolved strains (EVS), revealed 5 superior isolates; exhibiting from 1.9 to 3.6-fold increase of dry biomass and from 1.1 to 1.6-fold increase of lipid concentration compared to the parental strain, when grown in 15% v/v crude glycerol. NGS for differential gene expression analysis, showed induced expression in all EVS affecting nucleosomal structure and regulation of transcription. As strains differentiated, further changes accumulated in membrane transport and protein transport processes. Genes involved in glycerol catabolism and triacylglycerol biosynthesis were overexpressed in two EVS. Mismatches and gaps in the expressed sequences identified altered splicing and mutations in the EVS, with most of them, affecting different components of septin ring formation in the budding process. The selected YLE155 EVS, used for scale-up cultivation in a 3L benchtop bioreactor with 20% v/v crude glycerol, achieved extended exponential phase, twofold increase of dry biomass and lipid yields at 48 h, while citric acid secretion and glycerol consumption rates were 40% and 50% lower, respectively, compared to the parental strain, after 24 h of cultivation. Conclusion ALE and EMS-ALE under increasing concentrations of pure or crude glycerol generated novel Y. lipolytica strains with enhanced biomass and lipid content. Differential gene expression analysis and scale-up of YLE155, illustrated the potential of the evolved strains to serve as suitable “chassis” for rational engineering approaches towards both increased lipid accumulation, and production of high-added value compounds, through efficient utilization of crude glycerol.

Treated municipal wastewater is considered a valuable non-conventional water resource. However, a substantial number of wastewater treatment plants installed in the Mediterranean region have proven to be unsuccessful copies of systems operating in technolo-gically advanced countries. In addition to high operating and maintenance cost, these systems are often unsuited to address the local challenges of wastewater treatment. Therefore, treated municipal water is commonly under-exploited throughout the region. To address these challenges, the AQUACYCLE project aims to develop an eco-innovative wastewater treatment process scheme, comprised of anaerobic digestion, constructed wetlands and a solar photocatalytic reactor, for cost-effective treatment of urban wastewater and maximum environ-mental benefits. This paper presents the distinct features of the novel process scheme and the characteristics of three such demonstration units to be installed in Tunisia, Lebanon and Spain to test and validate the efficiency and cost-effectiveness of the hybrid system.

Membrane processes can be integrated with fermentation for the selective separation of the products from the fermentation broth. Sterilization with saturated steam under pressure is the most widely used method; however, data concerning heat sterilization applicability to polymeric ultrafiltration (UF) membranes are scarcely available. In this study, the effect of the sterilization process on the filtration performance of a commercial polyvinylidene difluoride (PVDF) hollow fiber UF membrane was evaluated. Membrane modules were constructed and sterilized several times in an autoclave. Pure water flux tests were performed, to assess the effect of heat sterilization on the membrane’s pure water permeance. Dextran rejection tests were performed for the characterization of membrane typical pore size and its fouling propensity. Filtration performance was also assessed by conducting filtration tests with real fermentation broth. After repeated sterilization cycles, pure water permeance remained quite constant, varying between approx. 830 and 990 L·m−2·h−1·bar−1, while the molecular weight cut-off (MWCO) was estimated to be in the range of 31.5–98.0 kDa. Regarding fouling behavior, the trans-membrane pressure increase rate was stable and quite low (between 0.5 and 7.0 mbar/min). The results suggest that commercial PVDF UF membranes are a viable alternative to high-cost ceramic UF membranes for fermentation processes that require heat sterilization.

Successful management of membrane scaling by inorganic, sparingly soluble, salts is a key issue in the design and operation of sustainable reverse osmosis (RO) desalination plants. This problem, particularly acute in the case of brackish-water membrane desalination, imposes a limitation on clean water recovery and necessitates consumption of environment-burdening chemicals and energy (for scaling mitigation and periodic membrane cleaning) to maintain a targeted plant productivity. Failure at the design stage of RO desalination plants to specify effective scale control schemes (and related process parameters) can have serious consequences for the plant operation. Indeed, underpredicting the feed-fluid scaling propensity (and the dosage of scale-inhibiting chemicals/additives) can impair membrane performance and plant productivity, whereas overpredictions (and thus excessive use of such chemicals) can cause undue environmental burden and other complications, including unexpected membrane fouling of a different type (biofouling and organic fouling) due to organic additives.

Reliable mathematical models are important tools for design/optimization of haemo-filtration modules. For a specific module, such a model requires knowledge of fluid- mechanical and mass transfer parameters, which have to be determined through experimental data representative of the usual countercurrent operation. Attempting to determine all these parameters, through measured/external flow-rates and pressures, combined with the inherent inaccuracies of pressure measurements, creates an ill-posed problem (as recently shown). The novel systematic methodology followed herein, demonstrated for Newtonian fluids, involves specially designed experiments, allowing first the independent reliable determination of fluid-mechanical parameters. In this paper, the method is further developed, to determine the complete mass transfer module-characteristics; i.e., the mass transfer problem is modelled/solved, employing the already fully-described flow field. Furthermore, the model is validated using new/detailed experimental data on concentration profiles of a typical solute (urea) in counter-current flow. A single intrinsic-parameter value (i.e., the unknown effective solute-diffusivity in the membrane) satisfactorily fits all data. Significant insights are also obtained regarding the relative contributions of convective and diffusive mass-transfer. This study completes the method for reliable module simulation in Newtonian-liquid flow and provides the basis for extension to plasma/blood haemofiltration, where account should be also taken of oncotic-pressure and membrane-fouling effects.

Results are presented from an ongoing R&D project, aiming at full utilization of dairy-industry effluents. Development of a membrane-based method is pursued, for treatment of digestate (after fermentation yielding bio-gas) to recover nutrients (N-NH4, P-PO4) and water for reuse/recycling or safe disposal. The performance is investigated herein of four commercial nanofiltration/ultra-low-pressure reverse osmosis membranes, employed in dead-end filtration mode, for nutrients recovery from solutions simulating the liquid digestate/effluent of an anaerobic membrane-bioreactor (AnMBR). Best-performing membranes, regarding nutrients’ rejection, were assessed within a sufficiently broad range of all key process parameters, including trans-membrane pressure and feed-composition. Further testing took place in a cross-flow set-up, simulating real operating conditions. For ~80% permeate recovery, the concentrate was significantly enriched in nutrients; i.e. compared to feed-solution, N-NH4 was concentrated twice, whereas P-PO4 was concentrated by 3- to 4-times. Research with real AnMBR effluent is on-going, for process improvements/optimization, mainly focusing on composition of concentrate/nutrients (for use in liquid fertilizers), membrane-fouling mitigation and quality of permeate/water for possible reuse.

The topic of chemical-free spiral wound membrane (SWM) cleaning, dealt with in this paper, is certainly of great interest to both industry and academia. However, in this Letter, the reasons are outlined for the serious limitations, imposed on implementation of the proposed deformation-induced cleaning (DIC) method to SWM modules, which have been apparently disregarded in this paper. These limitations are due to the dominant structural characteristics of SWM module-design; in particular, to the imposed (during fabrication) interlayer pressure on the membrane leaves and to the overall rigidity of the currently employed modules. These issues/imitations, and the implications of neglecting them are outlined herein.