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The recovery efficiency of waste valorization processes depends on an interplay of different conditions that are sometimes overlooked. Process optimization by the means of establishing mathematical relations between the process parameters and outputs is a strong tool to identify optimal operating conditions based on experimental data. In this study, the extraction of anthocyanins from chokeberry (Aronia melancocarpa) juice pomace using homogenization in acidified water was selected as a case study for process optimization using response surface methodology. The parameters studied were the citric acid content in the water, the temperature and the liquid–solid ratio. The optimal conditions to maximize both anthocyanin concentration and total anthocyanin content extracted were 1.5 wt% citric acid, 45 °C and 34 g solvent/g fresh pomace. Furthermore, the model developed predicted satisfactorily the overall anthocyanin content and anthocyanin concentration in the extract, as well as the final pH and total dissolved solids. The process optimization performed in this study sets the ground for further process design targeting the production of high-value products from byproducts or biowaste to be used in food ingredients or supplements. Graphic Abstract Electronic supplementary material The online version of this article (10.1007/s12649-020-01127-w) contains supplementary material, which is available to authorized users.

[EN] Forward osmosis is a low-energy water treatment emerging technology, which has demonstrated improved solute rejection and low fouling propensity. In this study, the applicability of aquaporin-based forward osmosis membranes during separation of biogas digestate liquid fractions was investigated. The results showed that Total Ammonia-Nitrogen rejection was higher than 95.5% in all experiments, independently of the type of draw solution (NaCl and hide preservation effluents), experimental period and the use of feed acidification. The results also confirmed that high draw osmotic pressures (i.e. 3.5¿M sodium chloride and hide preservation wastewater) combined with feed acidification had a negative effect on the membrane water permeability. Membrane rinsing after fouling was also successful in recovering the membrane initial water flux as well as removing the remaining foulants on the membrane surface. The membrane inspection results from Scanning-Electron Microscope, Energy-Dispersive X-Ray analysis and Fourier Transform Infrared¿Attenuated Total Reflectance showed that fouling in this application was mild and reversible after membrane rinsing. The applicability of aquaporin-based forward osmosis membranes during separation of biogas digestate liquid fractions has been demonstrated. The results showed the potential of this technology to achieve enhanced ammonia-nitrogen rejections and low-fouling propensity., The authors thank the tannery factory in the region of Murcia (Spain) for providing the wastewater samples as well as Depuración de Aguas del Mediterráneo (DAM, Spain) for funding the forward osmosis project. Thanks to August Bonmatí from IRTA GIRO Joint Research Unit IRTA-UPC, for providing the digestate liquid fractions, to Rebeca Vidal-Pérez as student assistant during the chemical analysis and to the Electron Microscopy Service from the Polytechnic University of Valencia (UPV, Spain). The authors further acknowledge funding from People Programme (Marie Curie Actions) of the European Union Seventh Framework Programme FP7/2007-2013/under REA grant agreement n° [289887].

Manure and digestate liquid fractions are nutrient-rich effluents that can be fractionated and concentrated using membranes. However, these membranes tend to foul due to organic matter, solids, colloids, and inorganic compounds including calcium, ammonium, sodium, sulfur, potassium, phosphorus, and magnesium contained in the feed. This review paper is intended as a theoretical and practical tool for the decision-making process during design of membrane-based systems aiming at processing manure liquid fractions. Firstly, this review paper gives an overview of the main physico-chemical characteristics of manure and digestates. Furthermore, solid-liquid separation technologies are described and the complexity of the physico-chemical variables affecting the separation process is discussed. The main factors influencing membrane fouling mechanisms, morphology and characteristics are described, as well as techniques covering membrane inspection and foulant analysis. Secondly, the effects of the feed characteristics, membrane operating conditions (pressure, cross-flow velocity, temperature), pH, flocculation-coagulation and membrane cleaning on fouling and membrane performance are presented. Finally, a summary of techniques for specific recovery of ammonia-nitrogen, phosphorus and removal of heavy metals for farm effluents is also presented.

This work aimed to investigate the optimum conditions of pressure, temperature, ultrasound intensity, solvent concentration and solvent flowrate of ultrasound-assisted pressurized liquid extraction of anthocyanins from Aronia melanocarpa pomace. The novel setup operates with an aqueous solution of citric acid as extraction solvent. The optimization was performed in order to maximize the total anthocyanins content extracted from the pomace. The optimized conditions of 70 °C, 180 bar, a solvent concentration of 1.5 % wt. citric acid, in a 200 W ultrasound bath were obtained. These conditions resulted in 88.0 % wt. extraction of anthocyanins in 45 min. A kinetic study was performed to study the influence of the temperature on the total anthocyanin yield obtained at the optimal extraction conditions. Moreover, the component stability was assessed to prove that the system could successfully operate at 80 °C. Compared to classical batch extraction using the same solvent concentration and feedstock, the total anthocyanin content of the extract was increased by 19%.

The present study investigates the influence of the solid-liquid pretreatment of anaerobically digested slurry on the subsequent ultrafiltration of the obtained liquid fractions in a semi-commercial ultrafiltration pilot plant. The first pretreatment considered is based on centrifugation alone, the second one, is based on a combined flocculation-coagulation and centrifugation step. It was found that during ultrafiltration of the liquid fractions from both pretreatments, the cross-flow velocity had a larger influence on permeate flux than the applied pressure, suggesting the predominance of a gel-like fouling layer. Chemical rejections during ultrafiltration of the liquid fractions were higher than 96.9% for Cu, Zn, Fe, Ca, Mg and Al, without significant differences between the pretreatments. Finally, membrane inspection using SEM showed that the membrane fouling morphology was closely related to the feed pretreatment. Additionally, elemental membrane surface analysis with EDX revealed that alkaline and acidic cleaning was effective in removing most of the inorganic foulants accumulated on the membrane surfaces. However, after chemical cleaning, ultrafiltration membranes processing liquid fractions from centrifugation assisted with flocculation-coagulation restored the membrane pristine surface characteristics to a higher extend. This suggests that obtaining digestate liquid fractions by centrifugation assisted with flocculation-coagulation could have a positive impact on the long-term stability of the subsequent ultrafiltration step.

Ammonia can be recovered from liquid biogas digestate as ammonium sulfate by air stripping. A full-scale plant treating 30,000 kg h−1 of digestate was simulated in Aspen Plus.The classical sequence stripper–absorber was modified by introducing a flash drum to reduce the buffer capacity. The stripped digestate was mixed with NaOH up to a pH value of 9 and fed to the stripping column using air at 90 °C. The air flow rate was optimized considering the possible recycle from the absorption column. The complete process was modeled using the process simulator Aspen Plus considering a recovery of ammonia equal to 95%. The total capital investment was evaluated by means of Aspen Plus Process Economic Analyzer in about 5.5 million US$, and the costs of energy and chemicals were quantified in less than 1 million US$ year−1. A benefit of 1.6 US$ for m3 of digestate was obtained considering an ammonium sulfate price of 522 US$ ton−1.

Biogas plant digestate liquid fractions can be concentrated by microfiltration and ultrafiltration. Two types of microfiltration membranes (polysulphone (PS) and surface-modified polyvinylidene fluoride (PVDF)) were used to process digestate liquid fractions, and to assess their applicability in the recovery of particulate phosphorus, compared to an ultrafiltration membrane (polyethersulphone (PES)). Results show that membrane material, operational conditions, and pore diameter influenced the permeate flux pattern during microfiltration. The PS membranes initially had a higher tendency to foul than PVDF membranes. However, during the filtration process, as fouling built up, the permeate flux behavior of the two membranes became very similar. During the concentration of digestate liquidfractions, the microfiltration PS membrane and the ultrafiltration PES membrane achieved the highest phosphorus rejection (80% w/w), suggesting that there was a correlation between the membrane material and both the fouling trend and phosphorus rejection. A two-step basic-acidic cleaning was unable to recover the initial water flux for the fouled microfiltration membranes. In conclusion, the PS microfiltration membranes might be a good strategy for recovering phosphorus from digestate liquid fractions. Further research leading to adequate cleaning procedures, for microfiltration PS and PVDF membranes treating digestate liquid fractions though, are needed.

For more than 30 years polyimides (PA) have been one of the main polymers for the fabrication of thin film composite membranes. Several researchers have assessed the main fabrication variables that influence the final structure of the polyamide layers including monomer concentration, solvents, additives in aqueous and organic phases and type of support to mention a few [1,2]. However, few studies have reported the influence of the fabrication tools used in the preparation of the PA layer. Each research group report their own recipe and fabrication method according to the general criteria of avoiding bubble formation during fabrication as that would later compromise the function of the membrane, but each process step must be well controlled to obtain reliable and consistent membrane performance. In general, the fabrication of the polyamide membrane layer is carried out in two steps. A polymeric support is initially brought in contact with the aqueous phase containing m-phenylene diamine (MPD) monomer and then with the organic phase containing the trimesoly chloride (TMC) monomer in order to promote PA formation through interfacial polymerization. The critical step occurs immediately after the support has been in contact with the aqueous phase, because formation of irregular drops could be initiation points for defects during the second step. Several tools have been used to eliminate the drop formation including air-knifes, rubber wipers, rubber rollers, glass rollers, or for that matter the absence of any tool using only water evaporation. In this work different methods of avoiding drop formation during the membrane preparation are tested to evaluate how the preparation methods influence the membrane structure and the final membrane properties. Understanding the membrane formation and consequently the defect formation will help to control and reproduce membrane preparation both in laboratory and industrial scale [3]. Specifically this work focuses on the preparation of a polyamide membrane layer supported by a polysulfone support after immersion in MPD/aqueous solution followed by immersion in TMC/heptane solution. The polysulfone support is in contact with the MPD/aqueous phase using immersion or pipetting. Further the use of a rubber wiper or absence of any tool to eliminate the aqueous solution droplets is evaluated. Both NaCl rejection and water and NaCl fluxes are evaluated, in order to relate them with the structural characteristics of the membranes using SEM, contact angle and streaming potential.

Swine manure is a valuable source of nitrogen, phosphorus and potassium. After solid-liquid separation, the resulting swine wastewater can be concentrated by reverse osmosis (RO) to produce a nitrogen-potassium rich fertilizer. However, swine wastewater has a high fouling potential and an efficient cleaning strategy is required. In this study, a semi-commercial farm scale RO spiral-wound membrane unit was fouled while processing larger volumes of swine wastewater during realistic cyclic operations over a 9-week period. Membrane cleaning was performed daily. Three different cleaning solutions, containing SDS, SDS+EDTA and NaOH were compared. About 99% of the fouling resistance could be removed by rinsing the membrane with water. Flux recoveries (FRs) above 98% were achieved for all the three cleaning solutions after cleaning. No significant differences in FR were found between the cleaning solutions. The NaOH solution thus is a good economical option for cleaning RO spiral-wound membranes fouled with swine wastewater. Soaking the membrane for 3 days in permeate water at the end of each week further improved the FR. Furthermore, a fouling resistance model for predicting the fouling rate, permeate flux decay and cleaning cycle periods based on processing time and swine wastewater conductivity was developed.

A conceptual process design with the use of integrated membrane processes is prepared for blackcurrant juice concentrate (BCJC) production to replace traditional multiple step evaporators and aroma recovery. The combination of membrane processes includes aroma recovery with vacuum membrane distillation and water removal by reverse osmosis, nanofiltration and direct contact membrane distillation. It has been combined with optimization of membrane performance and juice quality in mind. The annual production scale is 17,283 ton of 66 degrees Brix out of single strength juice. The operation cost is 0.40 (sic)/kg BCJC, which is lower than the price of a traditional operation by about 43%. Therefore, the economical potential of the process is very promising and could supersede conventional evaporators. (C) 2012 Elsevier B.V. All rights reserved.

Isothermal calorimetry (ITC) was used to investigate solvent-free enzymatic biodiesel production. The transesterification of rapeseed oil with methanol and ethanol was catalyzed by immobilized lipase Novozym 435 at 40 °C. The aim of the study was to determine reaction enthalpy for the enzymatic transesterification and to elucidate the mass transfer and energetic processes taking place. Based on the measured enthalpy and composition change in the system, the heat of reaction at 40 °C for the two systems was determined as −9.8 ± 0.9 kJ/mole biodiesel formed from rapeseed oil and methanol, and −9.3 ± 0.7 kJ/mole when rapeseed oil and ethanol was used. Simple Michaelis–Menten kinetics was not an appropriate choice for describing the kinetics of this heterogeneous system. The experiments demonstrated the possibility of investigating complex reaction mixtures using ITC. Although it is possible to determine thermodynamic properties such as reaction enthalpy and reaction rate, the difficulty in actually measuring the true non-mass-transfer-limited reaction kinetics is exposed by the high time resolution of ITC.

Over time fouling leads to membrane wetting. This is the biggest obstacle to widespread use of membrane distillation (MD) for ammonia removal from animal slurry. Feed pretreatment and cleaning strategies of membrane surfaces are the most common methods to prevent or diminish fouling phenomena. This study investigates preliminary fouling of polypropylene (PP) and polytetrafluoroethylene (PTFE) membranes. A model manure solution was used as feed. In addition cleaning efficiencies with deionized water, NaOH/citric acid, and Novadan agents were studied. Further microfiltration and ultrafiltration were examined as manure pretreatment to diminish fouling. To this end polyvinylidene fluoride membranes (PVDF 0.2 µm and 150 kDa respectively) were used. Organic fouling was shown to be dominant. For the model manure solution the fouling comprised lipids, carbohydrates and proteins. For pig slurry the fouling additionally contained carboxylates, free fatty acids and lignin. Among the tested cleaning strategies, Novadan agents were the most successful in removing proteins and carbohydrates from the PTFE membrane while it only removed proteins from the PP membrane. Using microfiltration or ultrafiltration as a pretreatment prior to MD doubled the ammonia mass transfer coefficient for the PTFE membrane, while for the PP membrane, the ammonia mass transfer coefficient was increased 4-fold.

Excessive livestock production in small areas poses a risk of nitrogen release to the environment and thus air and water contamination. Recovery of ammonia is necessary to avoid overfertilization, but manure management of untreated slurry is costly and complex. The authors discuss ammonium fertilizer recovery from manure using membrane processes and physicochemical methods including technology and energy assessments. Currently, nanofiltration, reverse osmosis, membrane distillation combined with ultrafiltration, and air stripping are the best choices. The processes rely highly on selection of appropriate pretreatment, as residual particulates will lead to fouling of membranes and stripping towers hence affect the performance greatly.

Whey protein has passed from being a cheese manufacturing waste product to a valuable food additive in a variety of foods from baby food to health drinks. Traditionally whey protein concentrates are produced by concentrating the whey content in the cheese runoff from 6.5% (w/w) dissolved solids (DS) to 20% DS by ultrafiltration followed by diafiltration to remove dissolved salts and sugars. This is followed by evaporation to 40% DS and spray drying, producing an 80% DS whey protein product [1]. As evaporation takes place at 70°C some valuable whey protein denature giving a lower nutrition value of the product. The evaporation at the same time is a relatively costly process. Both problems could be avoided if the evaporation step could be removed. This is not possible using ultrafiltration, as the osmotic pressure limits this operation to between 25% and 28% DS and this at an uneconomical price [2]. This paper describes the use of direct contact membrane distillation (DCMD) as a method for concentrating whey protein up to a concentration of at least 34% (DS) based on preliminary laboratory scale experiments using a commercially available microfiltration membrane and compares the measured flux with the flux predicted from simple a priori model based on the dusty gas model (DGM).

Prior investigations show that microfiltration (MF) and ultrafiltration (UF) can be used for post treatment of biogas plant digestate. The objective of this research is to evaluate the nutrient (i.e. nitrogen, phosphorus, potassium) recovery potential of MF and UF. MF and UF membranes were tested on biogas plant digestates. The obtained concentrates can be used as concentrated liquid fertilizers in agriculture, the resulting permeate for irrigation.

One of the main obstacles impeding implementation of membrane distillation for the recovery and concentration of ammonia from swine manure is wetting caused by fouling. Due to the different types of fouling which can occur in a membrane system, foulants characterization is a complex problem. To elucidate the fouling mechanism, deposit morphology and composition of foulants have been determined using Scanning Electron Microscopy, X-ray Energy Dispersive Spectrometry, Attenuated Total Reflectance Infrared Spectrometry, Ion chromatography and Inductively coupled plasma-optical emission spectroscopy. Based on the analysis of fouled membranes, it is concluded that membrane fouling is dominated by organic fouling in combination with deposits of inorganic elements and microorganisms. After a week of running the membrane process without cleaning, the average fouling layer thickness was estimated to 10-15μm. The fouling layer further results in a loss of membrane hydrophobicity. This indicates that fouling could be a severe problem for membrane distillation performance.

Anaerobic digestion and solid-liquid separation of animal wastes are a viable technology for waste management to reduce transport cost and environmental hazards in areas with increased livestock production. However, post processing of manure is necessary due to significant amount of nitrogen and phosphorus, which even though they are essential nutrients also pose potential risk of over fertilizing fields leading to contamination of water streams and air. Liquid-liquid membrane contactors (MC) present a possible technology for ammonia recovery. In general one of the main obstacles though impeding the implementation of membrane contactors is membrane fouling. This must also be expected to be the case for the recovery and concentration of ammonia from swine manure. The presence of organic matter and multivalent ions in pig slurry may greatly influence the membrane fouling due to surface adsorption and pore plugging. The aim of this work is to add knowledge on how the overall mass transfer coefficient of ammonia (km) is affected by different solid-liquid separation techniques of pig slurry at different temperatures (30ºC, and 50ºC) and feed flow velocity (0.9 m/s and 1.8 m/s). Further a comparison on how digestion of manure influences membrane fouling at 40ºC and a feed velocity of 0.9 m/s is conducted. Ammonia stripping of the liquid fraction of both digested and undigested manure was performed using tubular polypropylene (PP) membranes. Intensity, morphology and composition of fouling layers have been determined using Scanning Electron Microscopy and Fourier Transform Infrared Spectrometry (ATR-FTIR). Based on the experimental results, it can be concluded that mass transfer of ammonia from the liquid fraction is neither influenced by solid-liquid separation nor by anaerobic digestion. For digested manure the overall mass transfer coefficient km was equal to 19±1∙10-3 m/h and for undigested km was found to be 18.9±0.9∙10-3 m/h at 40ºC, and flow velocity of 0.9 m/s. Further, investigations show that increasing the temperature from 30ºC to 50ºC doubled the overall mass transfer coefficient of ammonia, while increasing feed flow velocity had negligible effect on the overall mass transfer coefficient of ammonia. No significant difference was found between undigested manure effluents with different dry matter content but similar particle size distribution, meaning that pre-processing of manure has little influence on the mass transfer coefficient of ammonia as long as the particle size is unchanged. Membrane fouling in case of digested and undigested pig slurry was a combination of organic fouling, biofouling and colloidal fouling. SEM observations revealed presence of bacteria suggesting biofouling, while the obtained ATR-FTIR spectra are characteristic for proteins and carbohydrates deposit.

The process of separating sugars from anthocyanins in black currant juice has been investigated. Diafiltration on a laboratory scale flat sheet module (Labstk M20, Alfa Laval Nakskov A/S, Denmark) loaded with an ultrafiltration membrane (ETNA01-PP, MWCO = 1,000 Da, Alfa Laval Nakskov A/S, Denmark) with a total installed area of 0.25 squaremeters distributed on 14 sheets showed good retention of anthocyanins as compared to fructose and glucose. In order to investigate whether the different flow pattern in a commercial size module would affect separation experiments were conducted with the same membrane in a 4'' spiral wound module. As the retention were mainained for anthocyanins, fructose and glucose the process have been demonstrated to be viable for scale up.

Hydrolysed whey (lactose 4% w/vol) was fermented in laboratory reactors for production of lactic acid. By using a non0sterile unsupplemented continuous process with a hydraulic retention time of 10 hours, lactic acid was produced in a concentration of approx. 2.5 w/vol % with less than 0.1% volatile fatty acids and less than 0.2% lactose/galactose present in the effluent.

Udgivelsesdato: April 1st Enzymatic biodiesel production has been investigated intensively, but is presently employed industrially only in a 20,000 tons/year pilot plant in China (Du et al. [2008] Appl Microbiol Technol 79(3):331–337). This review presents a critical analysis of the current status of research in this area and accentuates the main obstacles to the widespread use of enzymes for commercial biodiesel transesterification. Improved results for enzymatic catalysis are seen with respect to increased yield, reaction time and stability, but the performance and price of the enzymes need further advances for them to become attractive industrially for biodiesel production. Critical aspects such as mass transfer limitations, use of solvents and water activity are discussed together with process considerations and evaluation of possible reactor configurations, if industrial production with enzymes is to be carried out. Results of published studies on the productivity of enzymes are also presented and compared to the use of chemical catalysts

A unit performing a simple and effective way to extract active phytochemicals from the plant specimens has been developed. The unit is mobile enabling operation near the place of collection of plant specimens reducing waste of potential valuable phytochemicals. The design is based on counter current liquid extraction following a pretreatment, where the plant material is harvested and macerated to an extent increasing the extraction of relevant components. The pretreated plant material is fed to an inclined conveyor, counter currently with the extracting solution. The technology, known as solid/liquid extraction is developed on the basis similar to sugar extraction from sugar beets, albeit in a much more compact form. The equipment has been tested on extraction of ethereal oils from dried, stored oregano and extraction of natural compounds from freshly harvested Artemesia with 96% EtOH as the solvent. Preliminary results from a continuous oregano extraction show efficiency between 55% and 85% of a more ideal laboratory batch extraction of a marker compound like carvacrol, which is most abundant in the ethereal oil. The operation can be repeated with another liquid in order to extract compounds not soluble in the previous liquid and thus enabling optimal extractions of all compounds. Practically all known extracting liquids can be used by this equipment. Extracts from the extraction operation can subsequently be concentrated using a membrane distillation unit operating with hydrophobic microporous membranes for polar solvents and pervaporation membranes for unpolar solutes, where solutes with a low vapour pressure are retained, while components with higher vapour pressures permeate the membrane including water and most other solvents. The operation is performed at relatively low temperature enabling concentration of extracted solutes without deterioration due to influence of high temperatures.

Membrane technology is a promising candidate for producing mineral fertilizers from animal slurry. This paper presents a combination of membrane technologies for processing digested slurry, lists retentions of nitrogen (N), phosphorus (P) and potassium (K) and evaluates the economic and technological potential of the processes presented. To increase the content of plant nutrients in mineral concentrates substantially, improved RO (reverse osmosis) or additional technology is required.

A techno-economic comparison of membrane technologies (microfiltration (MF), nanofiltration (NF)and reverse osmosis (RO)) and physico-chemical operations (struvite precipitation and ammoniastripping) for obtaining nutrient-rich fractions from biogas digestates, has been carried out. Fourdifferent treatments for the digestate including solid-liquid separation using a decanter centrifuge or ascrew press are compared. A screw press followed by membrane technologies (treatment B) shows thebest economical potential with a total potential of 4.9€/t feed.Keywords: Digested manure, nutrient recovery, membrane technology, techno-economics

The recovery of nutrients and minerals for application outside the agricultural sector or for improving crop nutrients management efficiency has become a necessity in regions of concentrated confined animal production. Problems associated with surplus nutrients, could be partly solved by the use of membrane technology to perform a separation of the liquid swine manure into small concentrated fractions with high fertilizer value that could be exported to other agricultural regions. Many conventional ways to remove ammonia by lime treatment and aeration or stripping are generally costly and inefficient. Membrane contactors offer attractive advantages compared to the traditional techniques. One major advantage being the larger interfacial area per unit volume facilitating fast separation of ammonia from pig slurry with a lower energy input per mole ammonia removed. One of the major challenges though is to develop proper scale-up procedures from laboratory to full scale equipment. The aim of this work was to alleviate some of those problems.

Udgivelsesdato: 1. Marts