There is no Waste in Nature

One of the principles of modern environmental protection is the recycling of products. Recycling should always be preferred to simple disposal and this is also applicable for organic waste. Frederik Véster stated correctly in the 1970s that society would have to take nature as an example because: "Nature is a company which has not gone bankrupt for more than four billion years." However, nature does not have any waste, nor can it afford waste in the long term.

Anaerobic fermentation
Organic waste can be recycled in two ways. On the one hand, there is good old composting, and then there is anaerobic fermentation. This innovative method of biowaste fermentation has already become permanently established in the waste and disposal industry. This technology became established in the mid-1990s as part of active environmental protection and efficient utilisation of resources, as the energy and recycling advantages of the system are particularly evident.

Process of wet fermentation
The biowaste collected, such as garden waste or organic domestic waste, is first separated from foreign substances such as plastic, metal or textiles and is then reduced to a grain size of less than 60 mm by rotating disks. The waste is then mixed with water, and hygienic conditions are created at 70 °C within one hour. After sand has been removed, the solids in the biowaste/water mixture are again broken down. This suspension with a grain size of less than 10mm can now be allowed to ferment under anaerobic conditions in the fermentation tower.

Production of biogas
The fermentation process in the fermenter produces biogas, which consists of methane and carbon dioxide. When the gas is dry and after suspended particles have been removed, the gas is used for generating electricity in gas engines. Biogas is rich in energy because the bacteria in the fermenter are only able to use up a small part of the chemical energy. Between 90 and 95 percent of the energy content of the degraded material can thus be used.

The biogas is sent to combined heat and power units. The generated electrical energy is either fed into the public network and paid for in accordance with the Renewable Energy Sources Act or it is used to cover the fermentation unit's own electricity requirement. The waste heat from the combined heat and power units is used for heating the fermenters. Surplus heat can be transferred to external users or used and paid for in holistic fermentation residue treatment concepts. In view of global warming and the limited availability of fossil fuels, this environmentally friendly method of generating energy is becoming a key factor in future energy systems. This is because energy is extremely important in present-day society.

Decanter: Link between biogas production and secondary fermentation residue treatment

Westfalia Separator decanters are used for dewatering the fermented biomass from the fermenter. The suspension is supplied to the continuously operating scroll-type centrifuge, which has been designed completely in high-alloy stainless steels, and is decanted at between 3,000 to 4,000 times gravity. The machine removes the solid particles that are capable of being separated and dewaters them to a dry consistency. The solids discharged from the decanter are valuable compost as a result of the inorganic constituents, and are suitable for use in gardening or agriculture and forestry. Strict quality controls guarantee that there are no hygiene problems. The clear centrate water is recycled back into the process. The waste has now been used to create valuable materials and energy.

Successful concept
Westfalia Separator has equipped more than thirty fermentation plants with decanters in recent years. These reference installations in Germany, Sweden, Spain and Portugal demonstrate the importance of biowaste recycling for reducing the strain on the environment.

The advantages at a glance

Substitution of fossil fuels

High DS value in the biodegradable solids

• High separation performance and good centrate quality
• Preliminary stage for further treatment processes
• Recirculation to slurrying
• Reduction of logistical and spreading costs
• Closed material flows through fertilizer production, recirculation and the possibility of direct discharge
• No environmental pollution through unpleasant odours