HYDROTHERMAL CARBONIZATION OF SEWAGE SLUDGE – AN EFFECTIVE APPROACH TO TREAT AND MANAGE SEWAGE SLUDGE IN RURAL AREAS OF GERMANY?

As the result of new regulation from the German Sewage Sludge Ordinance (AbfKlärV 2017) and the future obligation to recover phosphorus, thermal treatment (mono-incineration) has become increasingly popular, whereas land-based utilization has decreased. Germany has produced 1.71 million metric tons (DM) of sewage sludge in the year 2021. Sewage sludge contains important nutrients such as phosphorus but also heavy metals and organic pollutants making the direct utilization of sewage sludge in agriculture controversial. Rural areas in particular have benefited from land-based sewage sludge utilization however the future ban on direct land-based utilization is forcing them to find alternative solutions for sewage sludge treatment and management. Hydrothermal carbonization (HTC) has developed considerably over the last 15 years and offers a viable alternative for the utilization of municipal and industrial organic waste such as sewage sludge. The process takes place in an aqueous environment without the need for pre-drying sewage sludge and thereby facilitating direct processing. HTC is especially suitable in combination with the recovery of nutrients like phosphorus. Technologies to recover this essential resource are important because phosphorus is an element that cannot be substituted and is therefore essential. HTC could make a significant contribution to sewage sludge management in combination with phosphorus recovery. However, the technology has yet to establish itself as a sewage sludge valorization process (2023) and is not yet a recognized state-of-the-art. Nevertheless, the HTC technology could gain greater relevance in the future, especially as an alternative valorization pathway for sewage sludge in rural areas of Germany.