5 october 2017

Anaerobic digestion

Innovation serving green energy.

With anaerobic digestion, innovation is at the heart of the production of green energy.
What is anaerobic digestion?
Anaerobic digestion uses bacteria to transform organic waste into energy in the complete absence of oxygen. This transformation occurs in nature, in marshes, for example. In order to be useable on a larger scale, the process has been tamed and optimized in closed tanks called digesters. The micro-organisms digest the organic fraction of the waste and convert it into biogas, a source of renewable energy. The residual organic matter (fraction not degraded during the process) forms the digestate that is dewatered, composted and used as fertilizer by farmers.
Anaerobic digestion: why and for whom?
Anaerobic digestion delivers two types of recovery from organic waste in a virtuous carbon circle: agronomic with the production of compost, and energy in the form of biogas, electricity or heat. This technology is widely used across Europe and is gaining momentum all around the world.
It provides an answer to one of the current challenges facing the farming sector: design new models of production taking into account environmental constraints and improve competitiveness. Anaerobic digestion is not just used by the agricultural sector. It targets all types of organic waste, whether it is derived from farming, food and beverage industries or municipalities, such as green waste from parks and gardens and the byproducts from wastewater treatment plants.
What does anaerobic digestion mean for Veolia?
With anaerobic digestion, Veolia is stepping away from the linear production and consumption approach and moving towards the circular economy, an economy in which the waste discarded by some systematically becomes valuable resources for others.
Artois Anaerobic Digestion Plant is a perfect illustration of the convergence between environmental services and energy efficiency from anaerobic digestion at Veolia.

Veolia's process at Artois Anaerobic Digestion Plant

Since April 2012, on a 9,000 m2 site in Graincourt-lès- Havrincourt (northern France), the Artois anaerobic digestion plant recovers all types of organic waste from farming (agricultural biomass, endive roots, etc.), industry (biological sludge, flotation grease, production waste, meat waste and restaurant grease), municipalities (grass clippings, municipal canteen waste and treatment plant waste) and the mass retail sector.
Each year , this anaerobic digestion plant recovers 25,000 metric tons of waste and generates 8,000 MWh, the equivalent electricity consumption of 6,500 people. The 7,000 metric tons of digestate, or organic material, not degraded by the process, is composted and used to fertilize the surrounding farmland.
Artois plant
Waste delivery.
The waste is delivered in bulk and liquids are stored in storage tanks. Pasty and solid waste is directly transferred to the preparation pits. Packaged waste is first unpackaged to extract the organic matter.
Anaerobic digestion with Biomet™ process.
All this waste forms the energy mix which is fed into the hydrolysis tank. For 3 days, hydrolytic bacteria degrade the waste. After hydrolysis, the energy mix is fed into a digester. For 30 days, methanogen bacteria produce methane from the energy mix. The digestate, or residue from this fermentation, is delivered to a post-digester to complete the degassing process. The biogas storage tank above this post-digester is used to control supply to the cogeneration motor.
Energy recovery.
The biogas, 60% methane and 40% CO2, is treated prior to its use in a cogeneration motor. Each year, this process produces several million cubic meters of biogas. The biogas is used as a fuel to produce electricity that is then fed into the French national grid.
Agricultural recycling.
The digestate undergoes stabilization heat treatment at 70°C for one hour prior to being dewatered in a centrifuge. At the exit from the centrifuge, the solid fraction of the digestate is composted and ready for recovery as a fertilizer that can replace the chemical fertilizers used by farmers.