Organic waste management by a small-scale innovative automated system of anaerobic digestion
ORION was funded by the Research for SME associations fund within the context of the 7th Framework Programme. It consists of an anaerobic digestion machine at the SME scale (1 m3 to 50 m3) combining effectiveness for a large range of organic wastes and reduced capital and operating costs. This system aims to allow a vast majority of HOREC and Agro-food SMEs to manage their organic waste by themselves in order to decrease their treatment costs (storage, transport, landfill or incineration) and increase on-site hygiene conditions. Wastes are also valorised as biomass to produce energy and increase SME autonomy and profitability.
The Orion system includes a grinder, a digester, an energy management unit and a sensor and automation module.
The only end-user interface is with a convenient waste grinder. The grinder reduces the organic matter to be digested to small particle and mix it. A Programmable Logic Controller controls the moment to pump it to the digestion module. An automatic periodic self-cleaning cycle is provided to pump the ground organic matter from the grinding to the digestion module.
The digester is composed by a “head” and a “body”. The head collects the produced biogas in a gasholder and it contains operation and measurement equipment. The body includes a mixing chamber called jabot and a methanation tank. The jabot receives the organic matter from the grinding and it feeds the methanation tank at regular intervals. The anaerobic digestion occurring in the methanation tank can thus be assimilated to an infinitely stirred process with suspended biomass. The intelligent selection of surface materials further contributes to optimise the conditions of the microrganisms which are responsible for the biogas production. The digester is heated and continuously kept at a constant temperature through an hot water bath, surrounding the methanation tank. The digestion module includes all the connecting to the devices necessary to its functioning, apart from some peripheral devices (grinding unit, combustion module, buffer tanks).
The energy management unit includes a small, certified biogas boiler running only on steady state biogas stream and a heat exchanger for the hot water bath. The system is provided with a natural gas boiler working during start-up or transient digester operation. In addition a small natural gas assisted flare deals with poor quality or intermittent biogas for environmental and health and safety reasons. The system is equipped with a simple PLC, relays and switches allowing the automatic functioning of the gas and water circuits. Detectors for CO, HC and temperature are linked to warning/cut off systems. An hazard and operability study has been undertaken to maximise the boiler safety.
A sensor module has been developed in order to autonomously gather essential information on the dynamics of the digestion process. Three different sets of sensor arrays have been integrated in the sensor module. A first set of commercial Ion selective electrodes monitors pH, ORP and ionic concentration of the effluent resulting from the digestion. A second set of commercial electrochemical and infrared sensors measures the composition of the produced biogas. A third set of custom developed conductive polymer sensors responds to the acetic and propionic acid contained in the effluent. The system is completely automatic and does not require any operation from the end user. An automation module (client side) is responsible for controlling the digester, taking decisions on the inputs received from the sensors. The server side of the automation module monitors and centralises the data from all the clients.
|Find more information in the project website: http://www.project-orion.eu/cms/|