Save on sludge disposal costs

Typically, anaerobic digestion reduces the organic content (volatile solids) of primary sludge by 55-60% and for waste activated sludge (WAS) by only about 20-30%. Biological hydrolysis is the limiting factor for the digestion of WAS because the cell material is more difficult to lysis. A thermal hydrolysis process, such as LYSOTHERM®, helps to overcome this limitation by improving the digestion process, which increases the volatile solids reduction (VSR) and gas yield, reduces the residual organic content in the digested sludge, and the quantity of solids that go to dewatering. With an increase of up to 5%-points in dewaterability by implementing thermal hydrolysis, savings of more than 30% of disposal costs can be achieved with LYSOTHERM®.

The precipitation and binding of the phosphate in the digested sludge with ELOVAC® improves the dewaterability of the digested sludge by 5%. This can result in significant cost savings for a treatment plant. For example, for a 200,000 P.E. with disposal costs of 85 €/tonne, the solution can reduce the disposal quantity from 42 tonnes/day to 33 tonnes/day with a 5% improvement in dewaterability, resulting in 260,000 € of annual savings.

Furthermore, phosphate removal is the ideal add-on to an advanced digestion process such as thermal hydrolysis. In Lingen, Germany , we achieved an increase in dewaterability of 10%-points and, with that, a 40% total reduction in the disposal costs by combining thermal hydrolysis with phosphate removal.

With a low temperature sludge belt drying process such as ELODRY®, more than 90% dry solids can be achieved, which is equivalent to a 75% mass reduction and 40% volume reduction of the total sludge quantity. In a plant with 200,000 P.E. with 85€/tonne disposal costs, this results in approximately 700,000 € savings in disposal costs per year. Adding a PYREG® unit can further increase the mass reduction to more than 90% resulting in further savings in the disposal costs. Combining a drying step with upstream processes to increase the dewaterability, such as THP and phosphate precipitation, minimises the heat demand to an optimum, so it can even be operated solely from the waste heat from a CHP.