winery waste recycling through anaerobic co-digestion with waste activated sludge
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Waste Management 34 (2014) 20282035Contents lists available at ScienceDirect
journal homepage: www.elsevier .com/ locate/wasmanWinery waste recycling through anaerobic co-digestion with wasteactivated sludgehttp://dx.doi.org/10.1016/j.wasman.2014.07.0170956-053X/ 2014 Elsevier Ltd. All rights reserved.
Corresponding author. Address: Via Cesare Pavese 18, 31100 Treviso, Italy.Tel.: +39 0422 321037; fax: +39 0422 326498.
E-mail addresses: email@example.com (C. Da Ros), firstname.lastname@example.org(C. Cavinato), email@example.com (P. Pavan), firstname.lastname@example.org (D. Bolzonella).C. Da Ros a,, C. Cavinato a, P. Pavan a, D. Bolzonella b,caDepartment of Environmental Sciences, Informatics and Statistics, University Ca Foscari of Venice, Calle Larga Santa Marta, 30123 Venice, ItalybDepartment of Biotechnology, University of Verona, Strada le Grazie 15, 37134 Verona, Italyc Interuniversity National Consortium Chemistry for the Environment, Via delle Industrie, 21/8, 30175 Venice, Italy
a r t i c l e i n f oArticle history:Received 27 February 2014Accepted 22 July 2014Available online 20 August 2014
Keywords:Anaerobic co-digestionHeavy metalsOrganic pollutantsPathogensDewaterabilitya b s t r a c t
In this study biogas and high quality digestate were recovered from winery waste (wine lees) throughanaerobic co-digestion with waste activated sludge both in mesophilic and thermophilic conditions.The two conditions studied showed similar yields (0.40 m3/kgCODfed) but different biological processstability: in fact the mesophilic process was clearly more stable than the thermophilic one in terms ofbioprocess parameters.The resulting digestates showed good characteristics for both the tested conditions: heavy metals,
dioxins (PCDD/F), and dioxin like bi-phenyls (PCBs) were concentred in the effluent if compared withthe influent because of the important reduction of the solid dry matter, but remained at levels acceptablefor agricultural reuse. Pathogens in digestate decreased. Best reductions were observed in thermophiliccondition, while at 37 C the concentration of Escherichia coli was at concentrations level as high as1000 UFC/g. Dewatering properties of digestates were evaluated by means of the capillary suction time(CST) and specific resistance to filtration (SRF) tests and it was found that a good dewatering level wasachievable only when high doses of polymer (more than 25 g per kg dry solids) were added to sludge.
2014 Elsevier Ltd. All rights reserved.1. Introduction
Wine production is one of the leading sector in food processingindustry. The world production accounted for 281 million tons in2013: Italy, France and Spain generated 46% of the worldwideproduction (OIV, 2013). Winery process generates different kindof waste as grape stalks, grape marc, exhausted yeast, wine leeand high loaded wastewater (Bustamante et al., 2008). The winerywastes, although prevalent during the vintage period, are distrib-uted along the year and could be considered hazardous materialsif they are not properly disposed of (Devesa-Rey et al., 2011). Thesewastes are typically characterized by exceptionally high levels ofCOD, both particulate and soluble, and high biodegradability.Semi-solid wastes like lees and vinasses are often treated inanaerobic stirred reactors (Moletta, 2005) to recovery renewableenergy: applied organic loading rates (OLRs) are between 3 and8 kgCOD/m3 d and the corresponding hydraulic retention time(HRT) is higher than 20 d. The COD removal yields are in the range6595% and the corresponding biogas production is between 0.4and 0.6 m3/kgCODremoved, with a methane content around 60%(Moletta, 2005). If fed substrates contain considerable levels oflignin, like the grape marc and stalks, then, biogas production islower than 0.3 m3/kgVS (Dinuccio et al., 2010). The most commonobserved problems when digesting winery wastes are relatedto process instability due to missing nutrients and to the presenceof recalcitrant compounds like polyphenols and copper (Melamaneet al., 2007).
The anaerobic co-digestion with another substrate has someadvantages in process management, environmental impact andeconomic sustainability. The effluents of anaerobic digestion canbe used as amendment, in this way organic matter and the nutri-ents were recycled, while pollutants emissions are reduced. Thetreatment of winery waste in the digesters of wastewater treat-ment plants (WWTPs) together with waste activated sludge(WAS) represents an interesting disposal option for at least partof these materials at a local level.
At the same time the implementation of this process intoWWTPs would improve the economical and energetic balance ofthe sludge line and will result in a resolution of final disposal prob-lems for such streams (Bolzonella et al., 2006).
C. Da Ros et al. /Waste Management 34 (2014) 20282035 2029Clearly, the implementation of a co-digestion process shouldconsider the final disposal of digestate: this issue needs to be prop-erly addressed case by case. The beneficial properties of digestateas bio-fertiliser are well known, but the characteristics of digestateproduced by a co-digestion treatment need to be consideredagainst law limits. At the moment European Community rulesgoverning the application of digestate in agriculture do not exist.The sludge application limits are defined by Directive 86/278/EEC, but more stringent limits were proposed by 3rd draft onsludge (EEC, 2000) and from End of Waste criteria (Saveyn andEder, 2014). The aim of legislation is to prevent harmful effectson soil, vegetation, animals and human beings. Heavy metals con-tent typically increases during anaerobic digestion (AD) because ofthe reduction of the organic content of sludge. Recently, moreinterest has been dedicated to organo-chlorine micro-pollutants(poly-chlorinated biphenyls PCBs and dioxin/furans PCDDs/Fs) and some limits are proposed by Saveyn and Eder (2014).These compounds are recalcitrant and accumulate along thetrophic chain but in anaerobic conditions could be partiallydegraded by reductive dehalogenation (Bertin et al., 2007). Thesame regulation defines limits for pathogens contents. In this caseanaerobic treatment depletes pathogens in the WAS with variableefficiency depending on nature of pathogens, moreover processtemperature (especially thermophilic) and hydraulic retentiontimes (HRT) could inactivate pathogens within a few days of treat-ment (Sahlstrm, 2004).
Biosecurity is not the only aspect to influence sludge use: dewa-tering properties have consequences on logistic and managementcosts and should be considered in feasibility studies. Severalfactors affect dewaterability characteristics of sludge and experi-mental tests are necessary for their determination.
According to the above scenario, this study considered theanaerobic co-treatment of waste activated sludge and wine leesboth at mesophilic and thermophilic conditions in pilot scale stir-red reactors. Different organic loading rates were tested and theprocess could be considered stable, for both temperatures, onlywith OLR lower than 3 kgCOD/m3 d (Da Ros et al., 2014). Stabilityparameters and biogas production in these operational conditionswere monitored to determine the real benefits from anaerobic co-treatment. Moreover, digesters effluents characterization in termsof nutrients content, concentration of pollutants and pathogenswas carried out, to evaluate the characteristics of digestates andtheir potential use as fertilisers or amendment for productive soils.
This study is the first one, to authors knowledge, that provides acomprehensive evaluation of this process option: critical aspectsand performances were determined and digestates were fully char-acterized to define their potential use as fertilisers.2. Materials and methods
2.1. Experimental setup
AD tests were carried out at pilot scale, in mesophilic and ther-mophilic conditions. Two identical continuous stirred reactors(CSTRs) of 230 l of working volume each were employed. The oper-ational temperatures (37 C and 55 C) were monitored by PT100probes that controlled hot water recirculation system in the exter-nal jackets of the reactors.
The seed sludge used as inoculum for the reactors was collectedin the wastewater treatment plant located in Treviso (northernItaly) where a 2200 m3 anaerobic digester treats waste activatedsludge produced by wastewater treatment and separately collectedbiowaste at a working temperature of 35 C.
In the thermophilic reactor the temperature was increased inone step, from mesophilic to thermophilic condition as suggestedby Cecchi et al. (1993). Inoculum sludge, maintained without feed-ing, was then acclimatized for one month to the higher operationaltemperature and no instability conditions were observed in thereactors.
The reactor feed was prepared daily, mixing thickenedWAS andwinery waste. The mixture of two substrates was pumped intoreactors once a day to obtain hydraulic retention time of some21 d and an organic loading rate of 2.8 kgCODfed/m3 d: 22% of theload (COD basis) was wine lee. The HRT was chosen to guaranteesufficient time for growth of anaerobic micro-organisms, fororganic matter degradation and for hygienisation of the inputmaterials. Pilot trials lasted one year to evaluate the long-term pro-cess stability.
2.2. Analytical methods
Substrates and effluents were monitored once a week in termsof total and volatile solids content (TS and VS), chemi