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A multi-step physicochemical-biotechnological approach for the valorization of olive mill wastewaters
No full textWaste valorization processes carried out through integrated multi-step biorefinery approaches can allow a massive exploitation of the waste organic matter. Olive mill wastewaters (OMWs) are agro-industrial wastes of a high environmental concern. A relevant part of their high COD is typically due to polyphenolic compounds, which are known to be toxic if concentrated to such extents. On the other hands, polyphenols are natural antioxidants of special relevance for several industrial sectors. Therefore, their recovery from OMWs provides the double opportunity to obtain high-added value biomolecules and to reduce the phytotoxicity of the effluent. To such an aim, an effective solid phase extraction process was recently developed [1]. The first aim of the present work was to define a protocol for the recovery and reuse of both the adsorbent (Amberlite XAD16 non-polar resin) and extraction solvent (ethanol), in order to verify the feasibility of a possible process scale-up. Very encouraging results were obtained: ethanol was recovered by means of a rotary evaporator, thus obtaining a concentrated phenolic mixture, whose antioxidant properties were demonstrated via ORAC and DPPH assays; furthermore, after its employment, the resin was washed with a sulphuric acid solution and regenerated: no significant losses of the resin adsorption capabilities were observed after 10 operation cycles. The exploitation of the OMW organic matter was further addressed toward the biotechnological production of biobased chemicals, such as H2 and volatile fatty acids (VFAs), which represent a feasible substrate for aerobic bacteria able to produce and store biopolymers such as polyhydroxyalkanoates (PHAs) [3]. A non conventional anaerobic digestion process carried out under acidogenic conditions for the obtainment of VFAs from dephenolized OMWs was recently developed [4]. The second aim of the present study was a further assessment of that process, with the aim of minimizing the process HRT. At a HRT = 5 days, a stable process capable of an effective bioconversion of the OMW organic matter into VFAs was obtained, with a VFA final concentration of about 19.7 gCOD/L, representing about 83% of the overall effluent COD.
References
[1] Bertin, L., Ferri, F., Scoma, A., Marchetti, L., Fava, F.: Recovery of high added value natural polyphenols from actual olive mill wastewater through solid phase extraction. Chem. Eng. J. 171, 1287-1293 (2011)
[2] Beccari, M., Bertin, L., Dionisi, D., Fava, F., Lampis, S., Majone, M., Valentino, F., Vallini, G., Villano, M.,: Exploiting olive oil mill effluents as a renewable resource for production of biodegradable polymers through a combined anaerobiceaerobic process. J. Chem. Technol. Biotechnol. 84, 901-908 (2009)
[3] Scoma, A., Bertin, L., Zanaroli, G., Fraraccio, S., Fava, F.: A physicochemical–biotechnological approach for an integrated valorization of olive mill wastewater. Biores. Technol. 102, 10273-10279 (2011
Biorefineries: the case study of olive mill wastewaters (OMWs)
No full textAgroindustrial wastes handling represents a serious economical and environmental concern. In some cases, large volumes of a toxic waste, such as olive mill wastewaters (OMWs), are produced within a short time in a limited area. In literature, a number of successful biotechnological approaches were attempted to reduce their toxic content while producing secondary metabolites of a certain industrial interest or biogas (CH4). However, to date the development of several biotechnological integrated processes aimed to fully recover or bioconvert the organic components naturally present in such wastes is a feasible option, and would allow their complete low-cost exploitation as renewable feedstocks in biorefineries.
In the present communication, a case study related to the exploitation of OMWs is presented. Firstly, solid phase extraction of the polyphenolic fraction occurring in OMWs was conducted. Phenols (PHEs) are natural antioxidant compounds of high commercial value. Selective removal almost completely abated PHEs concentration in OMWs, their subsequent recovery being carried out with biocompatible solvents (i.e., ethanol). Thereafter, dephenolized OMWs were fed to a packed-bed-biofilm reactor (PBBR) for the acidogenic digestion of its organic content by means of microbial consortia. The removal of antimicrobial compounds such as PHEs was found to significantly enhance volatile fatty acids (VFAs) production respect to non-pretreated OMWs. In the following step, electrodyalisis of the VFA enriched effluent was performed in order to further increase VFAs concentration. This process also produces a secondary effluent with a reduced VFA content, which was yet sufficient to allow (1) CH4 production in PBBRs loaded with microbial consortia, (2) biohydrogen production with photosynthetic bacteria or algae, or (3) photoheterotrophic growth of algal biomass.
The effluent further enriched in VFAs was fed to a second aerobic reactor loaded with microbial consortia for sustaining polyhydroxyalkanoates (PHAs) production and storage. PHAs are biodegradable and biocompatible microbial polymers which represent a renewable alternative to actual oil-derived plastics. Preliminary experiments showed that PHAs can be succesfully loaded with specific drugs, e.g., chlorexidine, which was then released leading to bacterial growth inhibition when in vitro tests with 3 strains of Streptococcus were carried out. This feature could be exploited in medical applications to deliver selected drugs in particular regions. Furthermore, it was observed that changes of the VFAs mixture fed for PHAs storage led to the synthesis of polymers with different chemico-physical properties. Therefore, culture conditions during acidogenic digestion could be adjusted in order to address the synthesis of desired biopolymers for following applications
Chemical-biotechnological integrated process for the dephenolization of olive mill wastewater and its acidogenic fermentation in a packed bed biofilm reactor
No full textPolyhydroxyalkanoates (PHAs) are biopolymers whose costs are not competitive with those of fossil fuel-based plastics. The exploitation of organic waste in PHA biotechnological production is of great interest in the perspective of reducing their costs. To this aim, a three-stage integrated anaerobic-aerobic process fed with olive mill wastewaters (OMWs) was proposed (Dionisi et al., 2005). In its first step, the waste is digested under acidogenic conditions in order to obtain a volatile fatty acids (VFAs) enriched effluent to be fed to the following PAH producing aerobic steps.
OMW polyphenols, which contribute to the waste phytotoxicity, are natural antioxidants whose exploitation can concern several industrial fields.
Thus, an integrated chemical-biotechnological process for the recovery of OMW polyphenols by liquid-solid extraction and for the continuous acidogenic fermentation of the dephenolized waste was developed.
The employed OMW (pH = 4.5) had a total phenol content (on Folin-Ciocalteu method basis) of 4.6 g/L, while COD and VFA concentrations were 55 and 8.4 gCOD /L, respectively. As a result of the adsorption pre-treatment, carried out with resin Amberlite XAD16 as the solid phase (0.7 g/L, contact time = 2 hours), the 90% of OMW polyphenols were removed together with the 25% of the COD, while VFA concentration and pH did not vary appreciably. Almost all the adsorbed phenolic fraction was desorbed by using ethanol as the solvent. The resulting wastewater was processed in a biofilm reactor packed with ceramic filters developed in a recent study (Beccari et al., 2009). On the basis of the results obtained from a preliminary batch experiment, the pH of the influent flow was correct to 7.0 and the reactor was thermostated at 25°C and fed with an OLR of about 6 gCOD/L/day. The process effluent, whose pH was 6.2, had a total VFA and COD concentrations of 19.02 and 25.94 gCOD/L, respectively. A significant enhancement in terms of VFA production yield with respect to the former experience (Beccari et al., 2009) was achieved. In particular, butyric and acetic acids were the main detected VFAs in the obtained effluent where they represented the 28 and 27%, respectively, of the whole VFA mixture.
Beccari M. et al. (2009) J Chem Technol Biotechnol 84:901-908.
Dionisi D. et al. (2005) Wat Res 39:2076-2084
A chemical-biological integrated approach for the valorization of olive mill wastewaters
No full textAn integrated chemical-biological process for the recovery of natural phenolic compounds from an olive mill wastewater (OMW) and for the anaerobic production of volatile fatty acids (VFAs) from the pre-treated OMW was developed in this work. The recovery of OMW polyphenols was carried out through solid phase extraction (SPE) by
using Amberlite XAD16 resin as the adsorbent and ethanol as the biocompatible desorbing phase. Thereafter, the acidogenic digestion of the dephenolized OMW was performed in a mesophilic packed-bed biofilm reactor filled with ceramic cubes, who was operated at an OLR of about 5.9 g L-1 day-1. As a result of the integrated process, more than 60% of polyphenols were recovered and 19 gCOD L-1 of VFAs were obtained, representing more than 70% of the anaerobic effluent COD
Effect of hydraulic retention time on biohydrogen and volatile fatty acids production during acidogenic digestion of dephenolized olive mill wastewaters
No full textThe influence of Hydraulic Retention Time (HRT) on the performances of a recently developed biotechnological anaerobic acidogenic process fed with dephenolized Olive Mill Wastewater (OMW) was investigated. The study was carried out under mesophilic conditions in Packed Bed Biofilm Reactors (PBBRs), filled with ceramic cubes and inoculated with
a characterized and acclimated acidogenic microbial consortium. The PBBRs were fed with a HRT of 7, 5, 3 or 1 day, which corresponded to Organic Loading Rates (OLRs) of about 5.5, 7.8, 12.9 and 38.8 g L-1 d-1, respectively. A significant production of a H2-rich biogas was observed when shorter HRTs were applied: in particular, H2 relative amount and productivity increased from 3% to 32% and from 0.20 to 6.10 dm3 m3 h1, respectively, by decreasing the HRT from 7 to 1 day. On the contrary, shorter HRTs turned into a lower accumulation of Volatile Fatty Acids (VFAs), whose highest amounts were found with HRTs of 7 and 5 days (about 18.4 and 19.7 g L-1 COD equivalents, respectively). The highest conversion yield of COD into VFAs (36%) was obtained with a HRT of 5 days, when VFAs represented about 78% of the effluent COD. HRT also influenced the composition of the VFA
mixture: acetic, propionic and butyric acid were the most prominent VFAs, being their relative amounts higher when PBBRs were operated with shorter HRTs (up to 19, 12 and 42% of the whole mixture, respectively, when HRT was 1 day)
Polyphenols from olive mill wastewaters: large scale sustainability of their recovery, and selective extraction by means of molecularly imprinted polymers
No full textThe use of agroindustrial wastes as potential renewable resources for the production of high added-value compounds, biomolecules or bioenergy has been largely investigated in recent years. To date, integrated multi-step physicochemical biotechnological processes are allowing the extensive valorization of an increasing number of biowastes. In this respect, the design of a biorefinery for the case study of olive mill wastewaters (OMWs) has been recently proposed [1]. Particular attention was given to polyphenols and their recovery through a solid phase extraction procedure. Several commercial adsorbing agents were tested (namely, Amberlite XAD resins, as well as IRA96 and Isolute ENV+). First investigations on their adsorption and desorption capacities were carried out with synthetic solutions made of 10 polyphenols among those commonly found in OMWs, using ethanol as desorbing solvent [2]. Performances of such adsorbing agents were then tested with actual site OMWs [3], showing that Amberlite XAD16 was the most effective, particularly when valuable polyphenols such as hydroxytyrosol and tyrosol were considered. Notwithstanding the fact that solid phase extraction procedure may be very practical, yet proofs of the feasibility of its scale-up have to be shown once the process economy is considered. As a matter of fact, fully activated Amberlite resins may cost some 600 euro per kg, and solvent price may be too high for industrial scale. To this aim, sustained recycling of both the resin and the solvent (i.e., ethanol) was tested [4]. The same amount of Amberlite XAD16 was used in 10 consecutive cycles for polyphenols recovery from actual site OMWs. At the end of each cycle, resin was re-activated using fully biocompatible solutions (i.e., ethanol and water). Sustained reuse of the resin had no negative effects on adsorption capacity, while desorption one was only slightly reduced. Ethanol regeneration was carried out using a rotary evaporator. As a result, Folin Ciocalteu's and HPLC analyses showed no trace of polyphenols in the regenerated ethanol while, notably, the HPLC profile of the concentrated polyphenolic mixture, its anti-radical and antioxidant capacity remained constant. This approach would significantly reduce overall operational costs, and determine a theoretically infinite reuse of the solvent employed. However, if on the one hand intensive recovery of polyphenolic mixtures appears feasible, on the other hand recovery of target molecules from complex substrates appears very difficult yet. In this respect, molecularly imprinted polymers (MIPs) are known to represent a promising solution. First attempts to selective extract and purify a single phenol (i.e., gallic acid, GA) were conducted [5]. Imprinting efficiency was evaluated in different water/ethanol solutions by using pyrogallic acid as the template analogue. When actual site OMWs were employed, recovery values were between 85 and 97%. However, provided that the highest recognition with MIPs usually occurs with pure ethanol, selective recovery of target polyphenols using the concentrated alcoholic mixture as obtained after rotary evaporator is underway
Production of biohydrogen and volatile fatty acids from dephenolized olive mill wastewaters in a sequential two-step anaerobic process
No full textAnaerobic acidogenic digestion of a dephenolized olive mill wastewater in a biofilm reactor packed with ceramic filters
No full textAcclimation to hypoxia in Chlamydomonas reinhardtii: Can biophotolysis be the major trigger for long-term H2 production?
No full textSummary: In anaerobiosis, the microalga Chlamydomonas reinhardtii is able to produce H2 gas. Electrons mainly derive from mobilization of internal reserves or from water through biophotolysis. However, the exact mechanisms triggering this process are still unclear. Our hypothesis was that, once a proper redox state has been achieved, H2 production is eventually observed. To avoid nutrient depletion, which would result in enhanced fermentative pathways, we aimed to induce long-lasting H2 production solely through a photosynthesis : respiration equilibrium. Thus, growing cells were incubated in Tris Acetate Phosphate (TAP) medium under low light and high chlorophyll content. After a 250-h acclimation phase, a 350-h H2 production phase was observed. The light-to-H2 conversion efficiency was comparable to that given in some reports operating under sulphur starvation. Electron sources were found to be water, through biophotolysis, and proteins, particularly through photofermentation. Nonetheless, a substantial contribution from acetate could not be ruled out. In addition, photosystem II (PSII) inhibition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) showed that it actively contributed to maintaining a redox balance during cell acclimation. In appropriate conditions, PSII may represent the major source of reducing power to feed the H2 evolution process, by inducing and maintaining an ideal excess of reducing power
High impact biowastes from South European agro-industries as feedstock for second-generation biorefineries
No full textAvailability of bio-based chemicals, materials and energy at reasonable cost will be one of the forthcoming issues for the EU economy. In particular, the development of technologies making use of alternative resources to fossil fuels is encouraged by the current European research and innovation strategy to face the societal challenge of natural resource scarcity, fossil resource dependence and sustainable economic growth. In this respect, second-generation biorefineries, i.e. biorefineries fed with biowastes, appear to be good candidates to substitute and replace the present downstream processing scheme. Contrary to first-generation biorefineries, which make use of dedicated crops or primary cultivations to achieve such a goal, the former employ agricultural, industrial, zootechnical, fishery and forestry biowastes as the main feedstock. This leaves aside any ethical and social issue generated by first-generation approaches, and concomitantly prevents environmental and economical issues associated with the disposal of the aforementioned leftovers. Unfortunately, to date, a comprehensive and updated mapping of the availability and potential use of bioresources for second-generation biorefineries in Europe is missing. This is a lack that severely limits R&D and industrial applications in the sector. On the other hand, attempts at valorizing the most diverse biowastes dates back to the nineteenth century and plenty of information in the literature on their sustainable exploitation is available. However, the large majority of these investigations have been focused on single fractions of biowastes or single steps of biowaste processing, preventing considerations on an integrated and modular (cascade) approach for the whole valorization of organic leftovers. This review aims at addressing these issues by gathering recent data on (a) some of the main high-impact biowastes located in Europe and in particular in its Southern part, and (b) the bio-based chemicals, materials and fuels that can be produced from such residues. In particular, we focused on those key compounds referred to as "chemical platforms", which have been indicated as fundamental to generate the large majority of the industrially relevant goods to date
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