Disposing of sewage sludge is expensive. In addition to the energy costs, it generates the largest portion of operating costs. As a result, the goal must be to reduce the amount of sludge to the greatest extend possible. In addition sludge represents a major energy resource. Digestion alone only makes use of this potential to a certain extent. A PYREG® plant mineralises even wet biomass like sewage sludge. This dramatically reduces the amount of sludge to be disposed of. The intelligent integration of the plant into the overall system uses the energy remaining in the digested and dried sewage sludge for the mineralisation process. What remains is mineralised sewage sludge ash. Studies have shown that the phosphorus contained in this end product is to a large extent available to plants. Therefore, the sewage sludge ash can be processed directly into fertiliser. The PYREG® process was developed and patented by PYREG GmbH, and has won multiple awards. ELIQUO STULZ GmbH is partner of PYREG in the implementation of PYREG® systems for the mineralisation of sewage sludge. ELIQUO STULZ is responsible in particular for the drying of the sludge and the integration into the overall system. In September 2015 at the Linz-Unkel wastewater treatment plant we, together with PYREG GmbH, installed and commissioned the first industrial scale PYREG® facility for sewage sludge treatment in Germany.
How the innovative PYREG® process works
The sludge is fed to the PYREG® reactor by means of a rotary wheel sluice. The rotary wheel sluice prevents the entry of air into the reactor and serves as back-burn protection.
In the PYREG® reactor, two inter-meshing augers provide transportation through the reactor and allow the uniform heating of the fuel up to 650°C. The exhaust gases from the connected combustion chamber provide the heat.
During the heating of the fuel, burning gases escape into the combustion chamber with a flameless burner and are cleanly burnt at around 1,250°C. The system operates under negative pressure, which prevents the release of flammable gases and emissions.
The mineralisation product – sewage sludge ash – is discharged via a rotary wheel sluice.
Process for mineralisation of sewage sludge for wastewater treatment plants of approximately 50,000 PE and above.
In the case of optimal implementation into an existing plant the PYREG® plant functions autonomously regarding thermal energy. No external energy is required for drying and mineralisation.
In the PYREG® reactor the phosphorus contained in the sewage sludge is not vitrified – this distinguishes the process from monoincineration. Consequently no complex and energy intensive processing is necessary. The sewage sludge ash can be marketed directly as raw material for the fertilizer industry. It is highly valued because of its purity and the very high plant availability of the recycled phosphorus.
Other biomasses can be converted to high-quality biochar in the PYREG® reactor. In this case the structure of the carbon contained in the mineralised material is similar to charcoal. Bound in the biochar, the carbon is no longer released as climate hazardous and flammable carbon dioxide, and – used as a fertilizer – it remains in the soil and serves as a soil improver and reservoir for micronutrients and water.