Research articleMesophilic and thermophilic anaerobic co-digestion of winery wastewater sludge and wine lees: An integrated approach for sustainable wine production
Introduction
The winemaking process produces large volumes of waste streams, including solid organic waste, wastewater, greenhouse gases, and packaging waste (Lucas et al., 2010). Winery wastewater is a major waste stream resulting from a number of activities that include tank, floor and equipment washing; barrel cleaning; wine and product losses; bottling facilities; filtration units; and rainwater captured in the wastewater management system (Ioannou et al., 2014). The quantification of the produced wastewater is difficult, and it depends on the cellar dimensions and the technologies applied. In general, wastewater production ranges from 0.7 to 14 L per liter of wine produced (Andreottola et al., 2009), but specific studies conducted in different countries demonstrated that typical values are approximately 2–6 L of wastewater per liter of wine produced (a short review of winery wastewater in the main production countries is available in Supplementary Material).
This effluents generally presents a considerable level of COD, the major part of which is soluble (Beck et al., 2005) and highly biodegradable (Andreottola et al., 2005) due to the presence of ethanol, sugars, and organic acids (Malandra et al., 2003, Mosteo et al., 2008, Petruccioli et al., 2000, Vlyssides et al., 2005).
Because of its characteristics, this stream is generally treated using either aerobic or anaerobic processes (Ioannou et al., 2014). Among biological processes, the activated sludge process is the most commonly employed because of its high efficiency and simplicity. It can remove 98% of COD and cope with large variations in the hydraulic and pollution load (Beck et al., 2005, Fumi et al., 1995, Petruccioli et al., 2000).
The removal of organic material generates considerable quantities of excess sludge, normally in the range 0.21–0.28 kg MLVSS (mixed liquor volatile suspended solids) per kg of COD removed (Brucculeri et al., 2005, Torrijos and Moletta, 1997). Ruggieri et al. (2009) estimated that dewatered wastewater sludge represents 12% of the total organic solid waste produced by wineries and that its management via external companies is expensive and often difficult. An alternative to valorize this waste stream could be the use of an anaerobic digestion process. Anaerobic digestion (AD) is a mature technology and it is applied to treat different types of organic wastes (municipal solid wastes, sewage and waste activated sludge, agro-industrial residues, livestock effluents, etc.) and to reduce their biodegradability while simultaneously recovering bio-energy. The combination of the conventional activated sludge process (CAS) and AD is a common practice in municipal wastewater treatment plants and limits the external management costs for sludge disposal thanks to a reduction in the sludge volume. Biogas is a renewable source of energy that is usable inside the same production process and/or wastewater treatment plant, which reduces the energy requirements (Shen et al., 2015). Moreover, digestate, the effluent from the anaerobic process, can be reused in agricultural fields because of the presence of nutrients such as N, P, and K together with stabilized C and humic substances. AD removes pathogens and polyphenolic compounds with different efficiencies based on the operating conditions used. Pathogen reduction is affected by temperature, retention time and fed substrates (Poudel et al., 2010, Sahlström et al., 2004), whereas the efficiency of polyphenol degradation is mainly determined by the operational temperature (Cavinato et al., 2014, Levén and Schnürer, 2005).
Once AD is implemented for winery wastewater WAS, other winemaking process residues (e.g., wine pomace, pressed cake, or lees) should be co-treated to increase the biogas production, to improve the reactor utilization and to make the anaerobic process more economically advantageous.
Wine lees (WL) in particular are an interesting co-substrate because of their biodegradability and availability throughout the year. Like wastewater, WL contain a high organic content and their disposal requires the appropriate treatment. The composition of WL depends on the winemaking technology, although, according to de Bustamante and Temiño (1994), the main characteristics are an acidic pH (between 3 and 6), a COD greater than 30,000 mg/L, potassium in concentrations greater than 2500 mg/L, and phenolic components in quantities up to 1000 mg/L.
This paper considers the production of winery waste activated sludge and lees and their anaerobic co-digestion under both mesophilic and thermophilic conditions. The study assesses the process feasibility at pilot scale and evaluates the effluent quality in terms of pollutant removal and dewatering capacity. The suggested approach is schematically represented in Fig. 1.
Section snippets
Winery wastewater treatment plant
Waste activated sludge was collected in a cellar where a wastewater treatment plant was operating. The cellar was located in the northeast of Italy and produced approximately 300,000 hL of wine per year. It processed and bottled both self-produced and bought wines; therefore, the working period is not restricted to the grape harvest, but rather, it is distributed throughout the year. Therefore, there is no real seasonal variation in the output. Considering the wine production and winery
Substrates characterization
The substrates fed to the reactors were waste activated sludge from secondary sedimentation tank of plant treating winery wastewater and wine lees, both of which originated from the same cellar.
The solids in the dewatered WAS generally ranged from 129.0 to 193.7 g TS/kg. However, outliers were detected due to technical reasons (conditioner doses and filter press setting, Table 2). The volatile solids to total solids ratio (VS/TS) in the winery was higher (88%) than for typical sludge from
Conclusions
The cellar monitored in this work, which produced approximately 300,000 hL of wine per year, generated 196 L of wastewater, 0.1 kg of WAS (dry matter) and 1.6 kg of lees per hl of wine produced. Anaerobic co-digestion WAS and lees was feasible, both in mesophilic and thermophilic conditions, when operating with an OLR of 3.2 kg COD/(m3d) and an HRT of 23 d. The mesophilic process was stable over a long period in terms of the stability parameters (pH 7.46, 400 mg NNH4+/L and 2248 mg CaCO3/L) and
Acknowledgments
The authors would like to thank Vinicola Serena srl for its collaboration and ATS scarl and the Treviso City Council for their hospitality at Treviso WWTP.
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