Environmental aspect of using ash from thermal treatment of municipal sewage sludge in hardening slurries

Owing to the increasing popularity of the thermal treatment of municipal sewage sludge (TTMSS) in Poland, constant growth in the quantity of ash generated within this process has been recorded. Due to their properties, it is difficult to utilize this type of ash within the concrete production technology. One of the methods of waste utilization is to add it to hardening slurries, used in, among others, cutoff walls. The slurry operating conditions (contact with groundwater) and elevated heavy metal content in ash raise justified concerns in terms of environmental safety of the aforementioned methods. In the study, the release of heavy metals from a matrix, namely, the hardened slurry has been examined. The so-called “batch test” dynamic leachability testing method was applied for this purpose. A high level of heavy metal immobilization in the slurry was achieved. The obtained results indicate an environmentally safe possibility of using TTMSS ash in hardening slurries in cut-off walls