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Each wastewater treatment plant (WWTP), whether it treats sanitary or industrial wastewater, generates certain quantities of sewage sludge, primarily through the settling process in primary and secondary sedimentation tanks. Generated sludge needs to be adequately treated at WWTP and disposed of in the environment in accordance with certain regulations and laws. In most EU countries, the problem of adequate disposal of sewage sludge has not been solved, nor is determined by the rules, instructions or guidelines. Due to the different technological possibilities of wastewater and sludge treatment as well as sludge disposal and possible negative social and environmental impacts, scientific and professional community of each country should achieve a consensus at the national level on which solutions are acceptable and at what level. Among the solutions that seem reasonable recycling of sewage sludge and its by-products reaches the top recommendation. Determining the optimum way of sludge disposal is important not only in terms of meeting the regulations, but the aspect of selecting optimal concept of wastewater treatment, including the selection of optimum technology for sludge treatment. Within the framework of sustainable development, recycling of sludge almost completely closes the cycle of wastewater treatment in which only negligible amounts of waste products that need to be disposed in the environment are generated. In most EU countries, significant amounts of stabilized and dehydrated sludge are incinerated. Current proposal of sewage sludge management strategy in Croatia is also oriented towards the construction of four to five sludge incineration plants. In the process of sewage sludge incineration special form of ash is generated – incinerated sewage sludge ash (ISSA), which is three to five times less in volume compared to stabilized and dehydrated sludge. ISSA also need to be disposed of in accordance with certain legislation. In this paper special emphasis is given on the possibility of recycling the ISSA in concrete industry. Up to date results on a worldwide basis will be described in the paper.