[Wine Studies 2012; 2:e2] [page 3] Potential of bio-drying applied to exhausted grape marc Elena Cristina Rada, Marco Ragazzi Department of Civil and Environmental Engineering, University of Trento, Italy Abstract In the present work, experimentation was carried out to study the behavior of exhausted grape marc during the bio-drying process. This process was chosen as an alternative to the typical grape marc thermal drying approach. The aim was to reduce the moisture level thanks to the biological exothermal reactions, and to increase the energy content in the bio- dried grape marc. The target was the genera- tion of a product interesting for energy options. For the development of the research, a biological pilot reactor and a respirometric apparatus were used. Results demonstrated that bio-drying can decrease the water content saving the original energy content. The final material could be assumed like a solid recov- ered fuel, class 5:1:1 with a very low potential rate of microbial self-heating. Introduction The wine industry produces every years in the world about 270 millions of hectoliters of wine, of which about the half in European Union (EU), and in particular in Spain, Italy and France; Italy and France compete each year for being the main world wine producer. The central wine regulations in the EU is entitled Council Regulation on the common organization of the market in wine, of 29 April 2008 and was supplemented by Council Regulation (EC) No 491/2009 of 25 May 2009 amending Regulation (EC) No 1234/2007 that establish a common organization of agricultur- al markets and specific provisions for certain agricultural products. From the regulatory point of view the wastewater generated from the sector must be treated according to the principals available for the management of this kind of discharge. The Province of Trento, Italy, where the present research was performed, generates about 800,000 hectoliters of wine per year. To produce one liter of wine about 1.3 kg of grape are utilized, and about the 20% of this grape represents a waste of the wine industry. 1 The exhausted grape marc (GM) or spent GM, is the material that results after fermentation and distillation of the grapes in the wine com- panies and has a high organic content. 2 This exhausted grape marc contains generally about 72% skins, 20-22% seeds and 7-8% stalks. 3 The exhausted GM used for the exper- imentation is presented in Figure 1. Grape marc has traditionally been used to produce pomace brandy (such as grappa), grape-seed oil, polymers and seldom as supple- ment in animal feed. 4-6 Today, it is mostly used as fertilizer or for producing renewable energy. However, in 2011, Devesa-Rey presented a study regarding the possibility of valorization of winery waste vs. the costs of not recycling. 2 The valorization scenarios didn’t take into account the potential role of GM bio-drying. This lack confirms the originality of the con- tents of the present paper, where an alterna- tive technique to treat exhausted grape marc is presented for energy purposes. The chosen process is an aerobic biological-mechanical treatment: the bio-drying one. The aim of this process is the exploitation of the exothermic reactions for the evaporation of the highest part of the water present in the treated materi- al with the lowest conversion of organic car- bon. The experimental results of a pilot scale bio-drying process applied to exhausted grape marc are presented and discussed in this paper. An important advantage of the use of bio-drying is that the final product, like solid recovered fuel (SRF), is considered biomass opening to the incentives market for renew- able energy. An important parameter for the SRF characterization is the potential rate of microbial self heating. This rate can be deter- mined by the real dynamic respiration index (RDRI=average value of the respiration index- es representing 24 h showing the highest aer- obic microactivity). Until 2010 in Italy this parameter has been requested only for the sta- bilized organic fraction and not for fuels. 7 With the transposition of the technical norm CEN/TR 15590 in the decree 205/2010, this RDRI parameter became a key parameter for SRF. 8 Bio-drying of exhausted grape marc can be an alternative to thermal drying generally per- formed in the sector by an integrated plant of thermal-pre-treatment and combustion. This integration has the disadvantage of requiring a centralization of the pre-treatment. Grape marc bio-drying could open to a decentralized pre-treatment of this organic substrate before a centralized combustion. Materials and Methods In order to develop the bio-drying process, a bioreactor of 1 m 3 was used at University of Trento. 9,10 When performing a run, the adopted reactor (Figure 2) was placed on an electronic balance for monitoring the mass loss during the bio-drying process. The process air was sent into the reactor through a steel diffuser, placed at the bottom. The air crossed upward the matter from the lower part, activating the biological reactions and went out of the biolog- ical reactor from the upper part, extracting a part of the water content of the material. The leachate was discharged continuously in order to avoid alterations of the dynamics of weight loss. For monitoring the temperature during the bio-drying process, four temperature probes were placed inside the reactor, one at the air outlet/inlet and two at intermediate lev- els. All these equipments were connected to a data acquisition system developed for a good management of the process. A bio-chemical model based on an energy and mass balance was used for a correct inter- pretation of the experimental data reported in this paper. 9 In particular the model recon- structs the composition of the bio-dried mate- rial through a process balance taking into account the mass, the biochemical reactions stoichiometry and the available energy, result- ing at the end a determined mathematical sys- tem that has as input the quantity of water, carbon, hydrogen, oxygen and nitrogen con- tained in the initial mass of exhausted GM and as output the amount of water, carbon, hydro- gen, oxygen and nitrogen consumed/removed during the bio-drying process. The model also describes the dynamics of the calorific value during the bio-drying process. Additionally the model gives the dynamics of the following parameters of interest: i. internal energy con- sumption (overall available lower heating value, LHV); ii. volatile solids reduction (assessed from an energy balance); iii. net moisture extraction (taking into account the role of hydrogen); iv. highest theoretical NH 3 emission factor (supposing that 100% of nitro- Wine Studies 2012; volume 2:e2 Correspondence: Elena Cristina Rada, Department of Civil and Environmental Engineering, University of Trento, via Mesiano 77, I-38050 Trento, Italy. Fax: +39.0461.282613 - +39.0461.282672. E-mail: elena.rada@ing.unitn.it Key words: bio-drying, exhausted grape marc, solid recovered fuel. Contributions: the authors contributed equally. Received for publication: 11 March 2012. Accepted for publication: 20 June 2012. This work is licensed under a Creative Commons Attribution 3.0 License (by-nc 3.0). ©Copyright E.C. Rada and M. Ragazzi, 2012 Licensee PAGEPress, Italy Wine Studies 2012; 2:e2 doi:10.4081/ws.2012.e2 Non-commercial use only