engleski

SEWAGE SLUDGE DISPOSAL – CASE STUDY SPLIT-DALMATIA COUNTY

Sewage sludge is generated in all technological processes of wastewater treatment, as a by- product of accumulation of solids, primarily through separation from the primary and secondary settling tanks. The construction of wastewater treatment plants (WWTP) in Croatia has intensified due to the commitments towards EU. Sewage sludge disposal is expensive and environmentally and socially highly sensitive process and it is therefore clear why it had become a significant burden to almost all utility companies, as well as to certain aspects of the operation of local governments. Sewage sludge disposal is not only technical issue, but is a result of different approaches that depend on the natural and social givens of each state (region). Therefore, there is no single approach nor guidelines for the disposal of sludge at the global level. It is not only important in terms of meeting the regulations, but also in terms of selecting the optimal treatment concepts, including the sewage sludge treatment procedures. The possibilities of use and recycling of sewage sludge and by-products of its processing as raw materials within the framework of circular economy have become especially attractive solutions recently. The paper presents critical overview of current practices and technical solutions of sewage sludge treatment and disposal with special emphasis on EU countries. On a case study given for the Split-Dalmatia County in Croatia technical and financial aspects of different disposal routes are analysed. Usual procedures of sludge treatment generate stabilized and dehydrated sludge that requires additional treatment. Many of the following sludge treatment processes also generate sludge, compost or ash that should be further disposed. Different options for final disposal stand out: disposal of treated sludge in landfills (restricted or totally banned), disposal of sludge or ash on agricultural or non- agricultural areas, disposal of ash in specially regulated non-hazardous landfills, use and recycling of sludge or ash in the construction industry, co-incineration of sludge with the municipal solid waste or its co-incineration in cement and power plants (with further disposal of ashes). There is also possibility of exporting dehydrated or dried sludge or ashes resulting in its thermal treatment procedures outside the state borders. So far, the disposal of sludge in Croatia can be classified as individual, where utilities for each WWTP perceive their own needs and capabilities in more or less accordance with the relevant legislations. As a case study Split-Dalmatia County is selected and all agglomerations of more than 10.000 PE are taken into consideration (excluding islands). Four variants of final sludge disposal were analyzed: mono-incineration on the location nearby Split, co-incineration in existing cement plants (also near Split), disposal on agricultural land (with included transportation outside the borders of the karst area according to the requirements of the legislation) and export outside the Croatian borders (in particular in Hungary due to the positive experience of other regions). Based on the conducted technical-economical analysis of the sludge disposal in the Split- Dalmatia County, it is evident that co- incineration in cement plants represents the most economical solution. Therefore, there is the need for an integrated consideration of this issue at the regional and national levels, with a review of conclusions of some previously issued study analyzes that promote mono- incineration of sewage sludge as the optimal solution for the whole Croatian territory. The results also indicate the need for a critical consideration of the statutory newly adopted regulations that favor the disposal of sludge on agricultural and non- agricultural land. Before making final conclusions, complete analysis should definitely cover other factors, such as environmental impact, for example by conducting life cycle analysis for each of selected solutions.

sewage sludge disposal ; agriculture ; incineration ; cement plant ; landfilling

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