Biological treatment of water and waste by means of aerobic and anaerobic processes
Energy recovery module in Water2REturn project is based on the anaerobic digestion process of the organic matter contained in the slaughterhouse wastewaters. The organic matter is transformed into a biofuel as CH4 by the action of a specific microbial consortium. Firstly hydrolytic-acidogenic bacteria transform the most complex organic matter, such as carbohydrates, fat and proteins, in simple structures like organic acids, CO2 and H2. Subsequently, the acetogenic and homo-acetogenic bacteria transform the volatile fatty acids into H2 and CO2 and acetate. In the last stage, the methanogenic Archaea transform the previous products obtained into CH4. This CH4 is stored and can be used in 2 ways.
On the one hand, the generated CH4 is burnt in a co-generation unit, producing gases that are used to generate electrical power that can be used in the plant. On the other hand, CH4 is converted into H2 – hydrogen gas, a clean combustible gas – in an autothermal methane reforming unit (ATR), through the reaction of CH4 with water vapourcogeneration unit. This hydrogen gas is converted in energy with a fuel cell. Thus, the complete anaerobic digestion process requires the sequential perform of different operating units: the homogenization tank, the anaerobic reactor, the biogas holder, the cogeneration unit and the ATR unit.
Water2Return project proposes the codigestion of both the unused fermented waste sludge for biofertilizer products and the raw slaughterhouse wastewater using an Anaerobic Sequencial Batch Reactor (AnSBR) to generate energy that can be used ecologically and economically in the slaughterhouse wastewater prototype itself.
Different laboratory tests were carried out by the University of Cádiz in order to determine the best operating conditions, including the co-substrate ratio, the operating cycle time and the hydraulic retention time (HTR), that optimize the biomethane generation potential from the substrates. Furthemore, the optimal conditions were used by Adventech company to design and to implement the Anaerobic AnSBR technology and the complete energy line for the treatment of the slaughterhouse waste generated in Matadero del Sur S.A., a company at industrial scale.
Currently, all the necessary equipment is installed and ready for the start-up of the energy line of the prototype Water2Return,. After the start-up and commissioning period, optimization of the process will be carried out on an industrial scale.