Meeting increased demands on sludge quality – Experience with full scale plant for thermal disintegration

Stricter regulations in terms of lower values for xenobiotic substances in sewage sludge used in Danish agriculture forces sewage treatment plant owners to install processes which reduce these substances or to change the disposal route. By partly aerobically stabilising biosludge and avoiding primary sludge it is possible to reduce the xenobiotic substances in the sludge and to meet the latest regulations. The sludge produced is difficult to digest and difficult to dewater. In the town of Naestved, thermal disintegration was introduced to solve these problems. The degree of digestion for volatile solids was increased from 29% for conventional mesophilic digestion to above 50%. The dry solids content in the sludge cake increased from 18% ds to 30% ds using existing dewatering equipment.