Sustainable sludge treatment: dilemmas in future research and development

Sewage sludge is a serious problem due to the high treatment costs and the risks to environment and human health. Looking to the future the question arises of which sludge research and development issues are most important. Based on a brief evaluation of current sludge treatment systems and research results it can be concluded that land application of sewage sludge remains one of the most attractive options. However, more research into the health risks is necessary to make this method worldwide more acceptable. Recovery of energy from sludge is becoming more and more attractive. High thermal processes are interesting if sludge does not satisfy the guidelines for land application. Integration of these high thermal processes with existing industrial activities or other thermal waste treatment processes can be very attractive. Research into dewatering and drying can make the energy recovery more efficient. Processes for recovery of valuable products from sludge such as aquatic worms and P-compounds are potentially very attractive but their feasibility strongly depends on the marketing and market value of these products. It is expected that supercritical sludge treatment and direct production of electricity require still a long research and development path.