Strawberry Extrudate Research Articles

Optimization of anaerobic soil disinfestation against Verticillium wilt in strawberry cultivation using local agrowastes as amendments.

The study explores anaerobic soil disinfection as an alternative to soil fumigants for controlling Verticillium wilt in strawberry crops. For this purpose, two agrowastes close to the strawberry-growing areas of Huelva province were tested as potential amendments for the control of Verticillium wilt: rice bran and residual strawberry extrudate. Furthermore, two application rates were evaluated: 13.50 and 20.00 t/ha for the rice bran and 16.89 and 25.02 t/ha for residual strawberry extrudate. Amended and anaerobically disinfested soils were compared with a non-amended soil under anaerobic conditions, a soil treated with the chemical fungicide metam sodium and an untreated soil. One week before the start of disinfection treatment, these soils were artificially inoculated with 250 microsclerotia/g dry soil of Verticillium dahliae. After disinfestation treatments, pathogens were quantified, and strawberry plants were cropped in a growth chamber to further evaluate Verticillium wilt severity, which was measured with a symptom scale in the same potting soils. Measurements of the anaerobic condition, pH and microbial population densities were performed, and the results showed significant differences between the different amendments. In addition, the treatment with rice bran at 20 t/ha recorded the lowest population density of V. dahliae. Likewise, it was possible to achieve a reduction in foliar disease severity in all amended treatments in similar percentage to those obtained by chemical treatment. These results suggest potential application of this technique for the control of Verticillium wilt in the strawberry-growing area of Huelva, reducing the use of chemical fumigants.

Optimization of the Use of Industrial Wastes in Anaerobic Soil Disinfestation for the Control of Fusarium Wilt in Strawberry.

Anaerobic soil disinfestation (ASD) is proposed as an alternative to the use of chemical fumigants against Fusarium wilt in strawberry crops. Different residual wastes (rice bran, fishmeal, and residual strawberry extrudate) were assessed as amendments for ASD. Two different concentrations and two incubation durations were tested in growth chamber trials. The abundance of several microbial groups was noted before and after the treatments. Strawberry plants were grown in the treated soils to record Fusarium wilt disease severity. The population density of F. oxysporum increased after ASD in most amendments with rice bran and residual strawberry extrudate. Changes in Trichoderma spp., copiotrophic bacteria, and Streptomyces spp. populations were observed after anaerobiosis treatments and plant trials. A reduction in the disease severity was achieved in ASD-treated soils with 20 t/ha of rice bran at both 25 and 60 days of incubation, but not when using a 13.5 t/ha dose. Similarly, treatments using 19.3 t/ha of fishmeal for both incubation durations were able to reduce disease severity. In contrast, a severity reduction was only obtained in soils treated with 25.02 t/ha of the residual strawberry extrudate and incubated for 60 days in anaerobic conditions. Two of the three by-products tested were able to reduce Fusarium wilt symptoms in strawberry plants after an ASD-treatment period of only 25 days. Accordingly, the technique seems promising for strawberry growers in Huelva, Spain, and highly sustainable by giving value to residues produced in surrounding areas.

Valorization of strawberry extrudate waste: Recovery of phenolic compounds by direct-hydrothermal treatment and subsequent methane production by mesophilic semi-continuous anaerobic digestion

Strawberry extrudate (SE) is an underused by-product from strawberry industry. Recovery of the phenolic compounds present in SE would represent a very interesting valorisation option. Two main challenges need to be solved, firstly, the solubilisation and recovery of the phenolic compounds contained in SE, and, after that, the stabilisation of the resulted de-phenolized SE. The present research evaluates the potential of a biorefinery process combining a hydrothermal pre-treatment, followed by a phenolic extraction process and, finally, the anaerobic digestion of the remaining SE for producing energy that will contribute to compensate the energy requirements of the whole system. Following the hydrothermal pre-treatment at 170 °C for 60 min, an extraction of 0.6 ± 0.1 g of gallic acid per kilogram of SE was achieved using an adsorbent resin, representing a recovery rate of 64 %. Long-term semi-continuous anaerobic digestion of de-phenolized SE was evaluated at different organic loading rates to evaluate the stability of the process. The anaerobic digestion of pre-treated SE achieved a stable methane production value of 243 ± 34 mL CH4·g volatile solids−1·d−1 at an organic loading rate (ORL) of 1.25 g volatile solids·L−1·d−1. During the operation at this ORL, the control parameters including pH, alkalinity, soluble chemical organic demand (sCOD), and volatile fatty acid (VFA) remained stable and consistently constant. Specifically, the VFA in the reactor during this stable period achieved a value of 102 ± 128 mg O2/L. Also, an economic balance showed that the minimal price of the generated phenolic extract for having benefited from the proposed biorefinery system was 0.812 €·(g of gallic acid equivalents)−1, a price within the range of phenolic compounds used in the food industry.

Accumulation of Volatile Fatty Acids from Hydrothermally Treated Strawberry Extrudate through Anaerobic Fermentation at Different pH Values

The accumulation of volatile fatty acids (VFAs) through the anaerobic fermentation of organic waste, such as strawberry extrudate, is proposed for this work. A hydrothermal treatment was carried out, and it was proposed to break the complex matrix of the strawberry extrudate to favour the hydrolysis stage of the anaerobic digestion process. The production of volatile fatty acids from treated and untreated strawberry was evaluated by adjusting the pH to 5 and 9. After the hydrothermal treatment of the strawberry extrudate, an increase in the solubilisation of organic matter, such as sugars and phenols, was observed. In the production of VFAs by means of anaerobic digestion of the pretreated strawberry extrudate, a significant increase in the accumulation of volatile fatty acids was demonstrated at a pH of 9 with respect to the untreated strawberry extrudate. In addition, the operational pH also had a strong effect on the individual VFA profile. A stream enriched in acetic acid was obtained at a pH of 9 (around 65% of the VFAs), whereas the operation at a pH of 5 resulted in a more complex composition with a high percentage of propionic acid (29% of the VFAs).

Effect of metals on mesophilic anaerobic digestion of strawberry extrudate in batch mode

According to recent studies, the anaerobic digestion of strawberry extrudate is a promising option with potential in the berry industry biorefinery. However, the lack and/or unbalance of concentrations of metals in some agro-industrial residues could hamper methane production during the anaerobic digestion of these kinds of wastes. In this study, a fractional factorial design was applied to screen the supplementation requirements regarding six metals (Co, Ni, Fe, Cu, Mn, and Zn) for methane production from strawberry extrudate (SE). The logistic model was used to fit the experimental data of methane production-time. It allowed identifying two different stages in the anaerobic process and obtaining the kinetic parameters for each step. Maximum methane production obtained in the first (Bmax) kinetic stage, the methane production in the second stage (P), and the maximum methane production rates (Rmax) concluded a statistically significant effect for Ni and Zn. The second set of experiments was carried out with Ni and Zn through a central composite design to study the concentration effect in the anaerobic digestion process of the strawberry extrudate. The parameters P and Rmax demonstrated a positive interaction between Ni and Zn. Although, Bmax did not prove a statistically significant effect between Ni and Zn.

Enhancing the recovery of volatile fatty acids from strawberry extrudate through anaerobic fermentation at different pH values

Strawberry extrudate (SE) is a by-product derived from the elaboration of strawberry-tasted products. Adequate management of this substrate would entail a new source of benefit for the berry sector, instead of a costly waste to be treated. The aim of this work is to assess the potential use of SE as a carbon soured for volatile fatty acids (VFA) production through anaerobic fermentation at controlled pH (5, and 9) and without pH control (operational pH around 7). Anaerobic digestion at pH 7 resulted in a negligible accumulation of VFA, being mainly degraded to methane. The operation at the other pHs resulted in a marked drop in methane production and, thus, the accumulation of VFA. At pH 9, around 50% of the fed COD tot (total chemical oxygen demand) was accumulated as VFA. Acetic acid represented 61% of these total VFA. The operation at pH 5 resulted in a lower VFA accumulation, i.e. 15% fed COD tot , although the VFA profile was more complex than at pH 9. Propionic and butyric acids represented 43% and 32%, respectively, of the total VFA accumulated at pH 5. • Operation at pH 5 and 9 effectively limited the methanogenesis activity. • pH 9 was the most effective pH to produce volatile fatty acids, mainly acetic acid. • Accumulation of propionic and butyric acids was favoured at pH 5. • pH 7 favoured the production of biogas instead of the accumulation of acids.

Use Optimization of Organic Wastes in Anaerobic Soil Disinfestation against Strawberry Charcoal Rot Root

The imminent removal of agrochemicals in Europe is directly affecting the strawberry sector in Spain, specifically in the Huelva province. Huelva is currently the main producer in the country. The lack of efficient fumigants has led to the rise of soilborne diseases. Macrophomina phaseolina (the causal agent of charcoal rot in strawberries) is generating serious problems with strawberry farmers. This work proposes to optimize the process of anaerobic soil disinfestation (ASD) against M. phaseolina in strawberry crops as a more sustainable alternative than chemical fumigation. Two trials with different inoculum doses were conducted, amending the soil with rice bran and residual strawberry extrudate as the carbon source for the ASD to evaluate the propagule reduction. After the ASD, these soils were used to crop strawberries in a growth chamber under controlled conditions to assay the disease reduction. Strawberry extrudate and rice bran favored disease reduction over the control, equaling the efficacy of Metam Sodium or even improving it in some cases. Trichoderma spp. and microbial activity could influence the suppressive effect of the ASD. All amended ASD treatments reduced the M. phaseolina propagules and charcoal rot severity. Rice bran and residual strawberry extrudate are suitable amendments to be used in ASD against the pathogen. The resulting soil disinfestation against M. phaseolina with residual strawberry extrudate at 16.89 t/ha and 25 days was similar to the most effective treatment with rice bran (20 t/ha and 40 days) based on the disease foliar severity. Additionally, both treatments were equivalent in efficacy to the Metam Sodium treatment.

Mesophilic Semi-Continuous Anaerobic Digestion of Strawberry Extrudate Pretreated with Steam Explosion.

The production of strawberry concentrate produces a side stream after extrusion that is commonly landfilled. This strawberry extrudate (SE), of lignocellulosic character, contains valuable bioactive compounds such as sugars and phenols. Thermal treatments, such as steam explosion, are currently used for the valorisation of agricultural lignocellulosic wastes due to their ability to impact the structure of the lignocellulose and hemicellulose present in these wastes, favouring the disruption of fibrous material. Steam explosion has already been shown as a promising technology for phenol recovery from SE. Biogas is an additional valuable resource that might be produced from thermally pretreated and de-phenolised SE. This study assessed the influence of a steam-explosion pretreatment and the subsequent recovery of phenolic compounds from the long-term operation of a semi-continuous anaerobic digester of pretreated SE. The anaerobic digestion of SE steam exploded at 220 °C for 5 min and de-phenolised was stable at an OLR of 0.5 g of volatile solids (VS)/(L·d), which permitted a specific production rate of 135 ± 11 mL of CH4/(g of VS d). The system was not able to operate at an OLR of 1 g of VS/(L·d), which resulted in a failure of the process. Despite the inhibition threshold of phenolic compounds not being achieved, the inhibition of the anaerobic digestion process at an OLR of 1 g of VS/(L·d) was most likely due to the overloading of the system. This was indicated by the accumulation of soluble organic matter and volatile fatty acids. The increase in the propionic acid concentration up to 1300 mg/L when operating at OLRs higher than 0.5 g of VS/(L·d) could be the main factor responsible for the inhibition. An economic evaluation showed that the proposed approach (steam explosion, phenol recovery, and anaerobic digestion) would offer positive benefits, taking into account the high phenolic recovery (0.90 g of gallic acid equivalents/kg of extrudate) and the low sales price of the phenol extract, i.e., EUR 0.610/g of gallic acid equivalents, needed to reach zero net profit.

High-Value-Added Compound Recovery with High-Temperature Hydrothermal Treatment and Steam Explosion, and Subsequent Biomethanization of Residual Strawberry Extrudate.

This study was on the comparison of hydrothermal treatments at 170 °C (steam injection) and 220 °C (steam explosion) to solubilize the organic matter contained in residual strawberry extrudate, focusing on phenolic compounds that were susceptible to be extracted and on sugars. After the extraction step, the remaining strawberry extrudate phases were subjected to anaerobic digestion to generate biogas that would compensate the energy requirements of the suggested hydrothermal treatments and to stabilize the remaining waste. Hydrothermal treatment at 220 °C allowed the recovery of 2053 mg of gallic acid eq. per kg of residual strawberry extrudate. By contrast, after hydrothermal treatment at 170 °C, only 394 mg of gallic acid eq. per kg of residual strawberry extrudate was recovered. Anaerobic digestion processes were applied to the de-phenolized liquid phase and the solid phase together, which generated similar methane productions, i.e., around 430 mL CH4/g volatile solids, after both 170 °C and 220 °C hydrothermal treatments. Considering the latest observation, hydrothermal treatment at 220 °C is a preferable option for the valorization of residual strawberry extrudate (RSE) due to the high solubilization of valuable phenolic compounds that can be recovered.

Utilization of strawberry and raspberry waste for the extraction of bioactive compounds by deep eutectic solvents

Deep eutectic solvents were used for the recovery of bioactive compounds from strawberry and raspberry by-products. The best performing eutectic solvent (DES-7) was compared to one organic solvent. Total and individual phenolics, sugars, uronic acid, anthocyanins and the antioxidant activity in vitro were measured. The highest yield and purity of phenolic compounds in the extracts were obtained from strawberry extrudate with acetone (11.5%) and from raspberry extrudate (36.7%) with DES-7. The greatest yields of total sugars and acid sugars were achieved from raspberry extrudate using acetone and from strawberry extrudate using DES-7, 82.23 and 1.88 mg/g of extract, respectively. DES-7 was the solvent that extracted the most anthocyanins (1.28 mg/100 mg of extract). In addition, the extracts obtained with acetone presented the best values of antioxidant activity in vitro (DPPH value of 5.33 mmol TE/kg fresh weight and ORAC value of 37.89 μmol TE/g fresh weight) the extracts obtained with DES-7 also presented an interesting antioxidant activity, and a promising solvent for the extraction of bioactive compounds.

Extraction of phenolic compounds and production of biomethane from strawberry and raspberry extrudates

This study proposes a biorefinery approach system to treat two berry extrudates generated by the berry-tasted products industry. The berry extrudates studied were strawberry extrudate (SE1 and SE2) and raspberry extrudate (RE), both of them processed in the same industrial plant. The proposed biorefinery approach consists in the extraction of bioactive compounds after hydrothermal pre-treatment followed by anaerobic digestion of the remaining biomass after extraction. A high concentration of valuable phenolic compounds was extracted from each extrudate through the absorption-desorption processes, i.e. 876, 392 and 2402 mg of gallic acid equivalents/kg extrudate in SE1, SE2 and RE, respectively. Anaerobic digestion of the remaining biomass after extraction led to high methane production, between 371 and 503 mL CH4/g VS. The economical evaluation showed that the proposed biorefinery approach would offer higher benefits than just anaerobic digestion of the untreated extrudate, although this last option would be economically feasible as well.

Thermally-treated strawberry extrudate: A rich source of antioxidant phenols and sugars

Strawberries have antioxidant, cardiovascular, and antiproliferative properties. The agroindustrial production of strawberry concentrate generates a food waste after extrudation that is usually landfilled. This strawberry extrudate is a rich source of valuable bioactive compounds such as phenols and sugars. In the present study, industrial thermal treatments currently in use for the valorization of other agricultural wastes were determined to be suitable for the treatment of strawberry extrudate. Thermal treatment conditions in the range of 90 degrees C to 200 degrees C were studied. Thermal treatment at 150 degrees C for 60 min without acid addition was the most efficient process based on the solubilization of sugars and phenols as well as the antioxidant capacity of the liquid phase produced. Instead of sending this residual fraction to landfill, such treatment would permit the use of strawberry extrudate as a source for the recovery of valuable bioactive compounds.

Optimizing the selection of organic waste for biomethanization

ABSTRACTThis study evaluates the feasibility of using simultaneous mass balances of different nutrients as a tool for optimizing feeding composition in anaerobic digestion. Different ratios, among them total chemical oxygen demand/total Kjeldahl nitrogen (TCOD/TKN) and soluble chemical oxygen demand/TCOD (SCOD/TCOD), were assessed. The TCOD/total volatile solids (TVS) ratio was 1.73 kg O2/kg TVS, while, with the exception of the sewage sludge, pig slurry and animal wastes, a linear relationship was established between phosphorus and nitrogen (0.06 kg P/kg TKN (R2 = 0.9045)). The study was applied to different mixtures of waste (cucumber, quince, tomato, strawberry waste, vinasse, glycerol, tomato plant, pig slurry, sewage sludge, fish waste, landfill leachate and viscera). The mass balance was performed for 50 mixtures chosen at random, containing three different wastes. After evaluating the theoretical optimal values determined by the mass balances, the most promising data were compared with the experimental results of the anaerobic co-digestion of one of the three waste mixtures. As predicted by the mass balances, the codigestion of glycerol, strawberry extrudate and fish waste (41:54:4 in VS) improved methane production to a maximum value of 0.308 m3 CH4/kg TVSadded for an organic loading rate of 0.62–4.26 kg TVS/m3·d.

Chemometric analysis and NIR spectroscopy to evaluate odorous impact during the composting of different raw materials

This study evaluated odor generated during the first stage of the composting process in a dynamic respirometer using different raw materials such as the organic fraction of municipal solid waste (OFMSW), a mixture of this organic fraction with orange peel waste (OFMSW-OPW), sewage sludge with bulking agent (SL) and a mixture of strawberry extrudate, fish waste, sewage sludge and bulking agent (SFWSL). The combination of near infrared reflectance (NIR) spectroscopy and chemometric analysis is proposed to correlate the chemical composition and the operational variables of each raw material to odor generated during the composting process. The operational variables temperature, dynamic respirometric index (DRI), airflow (Q), odor concentration (OC) and odor emission rate (OER) were monitored. Adequate linear correlations were obtained between temperature and DRI for each compostable substrate within a confidence interval of 10% and 30%. Operational variables were statistically analyzed by principal component analysis with 87% of total variance explained and from which the substrates were clearly grouped. Near infrared reflectance spectroscopy provided the chemical composition of each raw material, and was found to be an advantageous technique to predict the relationship between odor emissions and absorption bands. Odor emissions were also predicted from the operational variables by multivariate regression, with temperature and DRI being the most influential variables.

Centralized management of sewage sludge and agro-industrial waste through co-composting

In this research study, the co-composting process of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent (SEFW, 190:1:22:90 ratio) was carried out in a dynamic-solid respirometer at pilot scale. The aerobic biodegradability of the mixture was previously ensured in a static-liquid respirometer. The advantages and drawbacks of the SEFW co-composting process were subsequently identified through the determination of respirometric activity and the physical-chemical characterization of the waste, as well as the monitoring of odor emissions. The evolution of the physical-chemical variables showed that pH increased slightly and that the organic matter concentration, expressed as volatile solids (VS, %) or oxidable organic carbon (COXC, %), decreased by around 15% in both cases and by approximately 56% in its biodegradable form (total organic carbon, TOC, %). The low odor emission rate (OER) in the least favorable scenario (the maximum odor generation) during SEFW composting was 1.59 ouE/s, whereas this figure reached 3.52 ouE/s when only the organic fraction of municipal solid waste (OFMSW) was composted. Consequently, the co-composting of SEFW is more favorable in terms of odor emission and permits the simultaneous treatment of different types of waste.

Improvement of the biomethanization of sewage sludge by thermal pre-treatment and co-digestion with strawberry extrudate

Abstract The management of sewage sludge is an important issue in developed countries due to the highly polluting character of this waste. Biomethanization is a widely employed technology for this purpose, although it has several disadvantages such as low methane yield, poor biodegradability, and high sensitivity to nutrient imbalance. In this paper, a thermal pre-treatment (120 °C, 2 atm) is proposed to improve the biomethanization yield of sewage sludge and strawberry extrudate by solubilizing organic matter from the residual raw materials. Additionally, the co-digestion of sewage sludge with strawberry extrudate is evaluated as this combined treatment allows enhancing the nutrient balance and diluting inhibitors from sewage sludge. Therefore, the main aim of this study is the joint evaluation of the pre-treatment and co-digestion of this waste, which has never been described before in literature. The individual thermal pre-treatment of sewage sludge for 15 min was found to increase the soluble carbon concentration (mainly as volatile fatty acids), nitrogen, and phosphorus by 165%, 16%, and 24%, respectively. In contrast, the variation in the concentration of soluble carbon, nitrogen, and phosphorus for strawberry extrudate was as low as 10%, 32%, and 43%, respectively. Subsequent individual biomethanization tests showed a positive relationship between substrate solubilization and methane yield enhancement, with an increase of around 29% and 16% for sewage sludge and strawberry extrudate, respectively. Moreover, the co-digestion of sewage sludge and strawberry extrudate, both without pre-treatment, enhanced the stability and diluted the nitrogen concentration inside the digesters, although the methane yield was slightly lower than expected. In contrast, the most suitable combination was found to be the co-digestion of pre-treated sewage sludge and raw strawberry extrudate as it was also stable, but showed a synergy in methane production (237 ± 29 mLSTP/g VS; STP: 0 °C, 1 atm). This combined treatment might be considered an interesting alternative for the combined treatment of both polluting wastes.

Anaerobic co-digestion of sewage sludge and strawberry extrudate under mesophilic conditions

The biomethanization of sewage sludge has several disadvantages such as low methane yield, poor biodegradability and nutrient imbalance. In this paper, a sewage sludge and strawberry extrudate mixture in a proportion of 40:60 (wet weight) is proposed to improve the viability of the process. The addition of an easily biodegradable co-substrate enhanced the nutrient balance and diluted the heavy metals and inhibitors from sewage sludge. Two different experimental set-ups at lab and semi-pilot scale were employed in order to ensure the reproducibility and significance of the obtained values. Co-digestion improved the stability of the process by decreasing the alkalinity to a mean value of 3215±190 mg CaCO3/L, while maintaining the pH within the optimal range for anaerobic digestion. The methane yield coefficient and biodegradability were 176 L/kg VS (total volatile solids) (0°C, 1 atm) and 81% (VS), respectively. Kinetic parameters decreased at the highest loads, suggesting the occurrence of a slowing down phenomenon. A quality organic amendment with a heavy metal content lower than the limits established under European legislation for agricultural applications was obtained from the digestate of the proposed treatment.

Optimization of anaerobic co-digestion of strawberry and fish waste.

Anaerobic co-digestion of agri-food waste is a promising management alternative. Its implementation, however, requires evaluating the proportion in which waste should be mixed to optimize their centralized treatment. The combined treatment of strawberry extrudate and fish waste, which are widely generated in Mediterranean areas, was optimized. Strawberry extrudate and fish waste were mixed and treated at different proportions (88:12, 94:6, and 97:3, respectively; wet basis). The proportions selected for the mixture allow the different flows to be absorbed simultaneously. The highest methane production was observed for the ratio 94:6 (0.205m(3) STP CH4/kg volatile solid) (VS) (STP; 0°C, 1atm), with a methane production rate in the range of 5 · 10(-3)-9 · 10(-3)m(3) STP/kg VS · d, while the highest organic loading rate was observed for the mixture at a proportion 88:12 (1.9 ± 0.1kg VS/m(3) · d). Biodegradability was found to be similar for the 88:12 and 94:6 proportions, with values around 90% in VS. Nevertheless, the 97:3 ratio was not viable due to a low methane production. An inhibition phenomenon occurred at increasing loads due to the effect of some compounds contained in the fish waste such as chloride or nitrogen.

Improvement of mesophilic anaerobic co-digestion of agri-food waste by addition of glycerol

Anaerobic co-digestion is a promising alternative to manage agri-food waste rather than landfilling, composting or incineration. But improvement of methane yield and biodegradability is often required to optimize its economic viability. Biomethanization of agri-food solid waste presents the disadvantage of a slow hydrolytic phase, which might be enhanced by adding a readily digestible substrate such as glycerol. In this study, strawberry extrudate, fish waste and crude glycerol derived from biodiesel manufacturing are mixed at a proportion of 54:5:41, in VS (VS, total volatile solids), respectively. The mesophilic anaerobic co-digestion at lab-scale of the mixture was stable at loads lower than 1.85 g VS/L, reaching a methane yield coefficient of 308 L CH4/kg VS (0 °C, 1 atm) and a biodegradability of 96.7%, in VS. Moreover, the treatment capacity of strawberry and fish waste was increased 16% at adding the crude glycerol. An economic assessment was also carried out in order to evaluate the applicability of the proposed process. Even in a pessimistic scenario, the net balance was found to be positive. The glycerol adding implied a net saving in a range from 25.5 to 42.1 €/t if compared to landfill disposal.

Agri-food waste valorization through anaerobic co-digestion: fish and strawberry residues

The generation of fish waste is an environmental problem mainly associated to the canning industry in many Mediterranean countries. The application of anaerobic digestion is not advisable, however, due to the organic matter deficit in the chemical oxygen demand:nitrogen:phosphorus ratio (COD:N:P) of this waste, which entails the destabilization of the process. The co-digestion of fish waste with residual strawberry extrudate was evaluated at laboratory scale under mesophilic conditions. Strawberry waste increased the organic matter concentration in the mixture and diluted the inhibitory compounds contained in the fish waste, such as chloride, nitrogen and phosphorus. Co-digestion improved the stability of the treatment, while biodegradability was found to be 83% in total volatile solids. Moreover, the methane production yield reached a mean value of 120 mL/g total volatile solids (at 1 atm, 0 °C) for an organic loading rate in the range of 22.8–50.6 kg waste mixture/(m3 d), while the digestate was rich in nutrients, which might enable it to be used as an organic amendment in agriculture.