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Cesena anaerobic digestion and composting plant

Via Rio della Busca 1325, in the Tessello area - Cesena (FC)

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Composting plant at Tessello Cesena (FC).

The plant, located at Via Rio della Busca in Tessello, Cesena (FC), is dedicated to the storage and recovery of municipal waste and non-hazardous special waste through a virtuous anaerobic-aerobic type process which, as well as producing high-quality compost, also produces energy from renewable sources.

The plant also houses a plant for the treatment of process wastewater and wastewater from the plant’s road run-off and, partially, from the nearby landfill for non-hazardous waste.

Page updated 2 February 2016

    Treatment capacity

    The maximum total quantity of waste accepted for recovery operations is 55,000 tonnes/year, broken down into the following quantities:

    • 40,000 tonnes/year of organic waste
    • 15,000 tonnes/year of lignocellulosic waste (prunings)
    Types of waste accepted

    The plant treats the following types of organic waste:

    • Slowly decomposable organic waste (primarily green and lignocellulose waste from pruning and the maintenance of gardens and parks, untreated wood waste, etc.)
    • Easily decomposable organic waste (humid organic fraction from separate collection, organic and vegetable waste from fruit and vegetable industries and agro-industrial activities)

    The plant features two main treatment lines:

    • production line for High-quality Compost (or composted mixed soil improver);
    • untreated wood recovery line for the production of wood biomass.

    The High-quality Compost production line consists of the following sections and related processes:

    • section for receiving easily decomposable organic waste in dedicated storage boxes;
    • section for grinding the incoming organic waste;
    • section for mixing the ground, easily decomposable organic fraction with digested material extracted from the fermentation cell (roughly 50%) and any lignocellulosic fraction (builder). In this section, the cell is opened and the mixture (digestate and builder) is formed; roughly 50% of the extracted digestate is then sent to the aerobic bio-oxidation area, while the remaining part is used as inoculum for subsequent loading of the digester;
    • section for anaerobic digestion consisting of 11 fermentation cells (digesters), where the digestion process lasts at least 25 days and produces biogas, which is conveyed to the internal combustion engines generating electricity and heat;
    • oxidation section (intensive bio-oxidation and aerobic stabilisation) in which the oxidation process lasts for a total of approximately 21 days;
    • section for final screening and storage of the compost produced;
    • section for treatment of the exhausted air captured from the waste storage and treatment buildings by means of scrubbers and, thereafter, a biofilter covering an overall surface of approximately 600 m2.

    The proposed technology is based on a batch type, single-stage dry anaerobic degradation process (not continuous). In this type of process, the anaerobic stages of biological biomass degradation and biogas production (hydrolysis and acidification, acetogenesis and methanogenesis) all occur within the same fermenter. The digestion process takes place under controlled mesophilic conditions and is carried out at a temperature of approximately 37 - 45 °C.
    The batch plants are operated via a discontinuous process that consists of cyclically loading the inoculated substrate, activating the process for a given time (≥25 days) and emptying the fermenter. The mixture to be treated is loaded into the digester using a wheel loader.
    During the dry anaerobic digestion process, the constant humidity of the substrate, needed to execute the digestion process, is guaranteed by use of the leachate generated by the process itself, stored in a dedicated tank, and sprayed over the fermenting mass. The proper temperature is guaranteed by using the heat generated by the energy recovery section. Thus are promoted the most favourable conditions for the development and growth of the bacterial strains required for the digestion process. Each single digester consists of a concrete bio-tunnel of appropriate size, closed by a gas-tight hatch. The mixture undergoes the digestion process in a gas-tight environment under anaerobic conditions, with no need for any further mixing.
    The biogas produced by the anaerobic digestion process is conveyed towards two 499 kWe cogeneration units for the combined generation of electricity and heat.
    Even though this is a discontinuous process, by exploiting multiple digesters in series that are loaded and emptied at precise intervals, it ensures the constant production of biogas, and thus of both thermal and electrical energy.

    In the subsequent intensive bio-oxidation stage, the mixture output from the anaerobic digestion section is arranged in piles on aeration tracks, in which an oxidative microbiological process is triggered through the addition of oxygen via a forced ventilation system located under the piles
    During this fundamental stage, characterised by the bio-oxidation of microorganisms such as bacteria, fungi and actinomycetes, degradation of the waste takes place, with simultaneous production of carbon dioxide, water and heat. Due to the poor thermal conductivity of the biomass, the heat accumulated inside it reaches and exceeds a temperature of 55°C, which guarantees that the material is completely hygienised as the microorganisms harmful to humans and plants disappear.

    As the enzymatically oxidisable compounds become depleted, microbial activity and heat generation decrease, and a "humified" fraction is obtained, namely compost.
    Finally, the material taken from the intensive bio-oxidation phase is transferred and arranged in piles for the secondary curing stage, thereby completing the oxidation cycle, which lasts at least 21 days in total.

    Finally, the material is conveyed to the screening and refining section, where the coarse fractions are separated and the composted mixed soil improver (high-quality compost) used in agriculture is produced.
    The product is stored in a dedicated area pending its distribution on the market. Wastes and by-products of refining, such as biostabilised material (non-conforming compost), are transferred to suitable authorised facilities for recycling or disposal.

    The untreated wood recovery line consists of the following sections and related processes:

    • section for receiving, storing and grinding lignocellulosic waste;
    • section for treatment (grinding, deferrisation and possibly screening);
    • untreated wood and associated product storage section.

    The untreated wood recovery production line yields the following products: wood biomass fuel to be transferred to suitable facilities, dry fraction for compost, materials for the production of panels, materials for the production of pellets, materials for mulching, materials for biofilters.

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