Energetic and biochemical valorization of cork boiling wastewater by anaerobic digestion

Abstract

BackgroundIn addition to energy benefits, anaerobic digestion offers other interesting advantages. The cork industry is of great environmental, economic and social significance in the western Mediterranean region, with Portugal being the world-leading producer and exporter. Cork boiling wastewater (CBW) is a toxic and recalcitrant organic effluent produced by this sector, which constitutes a serious environmental hazard. However, there is no documented research on anaerobic treatment/valorization performed with this effluent. The work presented here was developed with the aim to use the anaerobic digestion process to convert the CBW polluting organic load into an energy carrier gas and valuable molecules for industry.ResultsNo lag phases were observed and a methane yield of 0.126 to 0.142 m3 kg-1 chemical oxygen demand (COD)added was registered in the mesophilic consortium experiments carried out in batch flasks at 37 ± 1°C. Anaerobic digestion can be advantageously connected to ultrafiltration or electrochemical processes, due to the following: 1) reduction of ellagic acid content and consequent decrease of CBW viscosity; and 2) increase in conductivity after the anaerobic process, avoiding the electrolyte application of the electrochemical process. The improvement of several CBW biochemical features shows that anaerobic digestion may provide additionally useful molecules. The rise in concentration of some of these compounds, belonging to the benzoic acid family (gallic, protocatechuic, vanillic and syringic acids), is responsible for the increase of antiradical activity of the phenolic fraction. Additionally, some enzymatic activity was also observed and while the laccase activity increased in the digested effluent by anaerobiosis, xylanase was formed in the process.ConclusionsThe multidisciplinary approach adopted allowed the valorization of CBW in terms of energy and valuable biomolecules. By exploiting the anaerobic digestion process potential, a novel methodology to toxic and recalcitrant cork processing wastewater was developed.

Cork Boiling Wastewater Treatment in Pilot Constructed Wetlands

“…Hitherto, most studies published on the topic of cork boiling wastewater (CBW) treatment or valorization used physico-chemical treatment options rather than biological processes. However, the related costs are high and above those of the biological treatment alternative for wastewaters with similar organic loads but from different sources [11,12]. Thus, constructed wetland systems (CWs) can be an alternative to conventional biological treatment systems, namely to activated sludge systems, with the prominent virtues of low construction and operation costs [13][14][15].…”

“…The quantification of these pollutants was made through the total phenols (TPh) analysis and less frequently includes tannin determination by the gravimetric method described by Makkar et al (1993) [20]. The methodologies reported for TPh quantification involve several variations on the original procedure published by Folin and Ciocaulteu (1927), namely employ the Folin-Ciocalteau reagent solution, absorbance measurements at 765 nm, use of different compounds for calibration and then to express the overall concentration, namely gallic, caffeic and tannic acids [11,[21][22][23][24][25]. The major drawbacks of these methods are the low selectivity of the reagent solution, which reacts with any reducing substances in addition to phenols [25].…”

“…Hitherto, the quantification of the organic pollutants in CBW includes more than 50 compounds with concentration ranging from 0.22-2.00 mg/L for the syringic acid up to 238.7 mg/L for the ellagic acid. However, research results published for CBW treatment (in mg/L) were limited to phenolic acids, namely gallic (2.46-103.70), protocatechuic (0.38-71.10), caffeic (2.14), vanillic (2.00-8.00), p-cumaric (4.10), ferulic (6.00-7.70) and ellagic (2.92-238.70) [11,21,31,32]. Some of these compounds are also present in other agro-industrial wastewaters, namely from olive mills (OMW), wine-distillery, wood debarking and coffee processing [11,33].…”

“…However, research results published for CBW treatment (in mg/L) were limited to phenolic acids, namely gallic (2.46-103.70), protocatechuic (0.38-71.10), caffeic (2.14), vanillic (2.00-8.00), p-cumaric (4.10), ferulic (6.00-7.70) and ellagic (2.92-238.70) [11,21,31,32]. Some of these compounds are also present in other agro-industrial wastewaters, namely from olive mills (OMW), wine-distillery, wood debarking and coffee processing [11,33]. The potential for recovery and valorization of these by-products as promising sources of renewable chemicals is high due to their bioactive properties and extended range of potential uses, namely as antioxidants, anti-inflammatories, anti-carcinogenics and inhibitors of enzymes with activity related to several diseases, but this has not yet been explored [25,34].…”

Influence of Molecular Size on the Electrochemical Oxidation of Fractioned Cork Boiling Wastewater

“…Additionally, the high molecular size, the recalcitrant and the toxic nature of the organics extracted from the corkwood, namely tannins, phenolic acids and polyphenols, are also contributing factors for the economic and technical constrains concerning effluents treatment. COD removals reported for conventional activated sludge systems, anaerobic digestion, and more recently through constructed wetland treatment system at horizontal subsurface configuration, were restrained to 37 %, 40 % and 75 % at hydraulic retention times of 4 days, 44 days and 6 days, respectively. In addition, treatment processes based on biological oxidation only achieved very limited results for decolorization that are scarce to allow the direct discharge of the treated wastewater.…”