Review of sewage sludge management: standards, regulations and analytical methods

Abstract

This article presents the most popular methods of sewage sludge management and associated unit operations and processes referring to them. The most popular methods are: Reclamation and adaptation of lands to specific needs; plant cultivation not intended for consumption or for production of food; usage in agriculture; usage in building; recovery of phosphorus, rare earth metals or fats and usage in industry; producing combustible pellets, granulates or other usable materials such as absorbents; and storage on territory of treatment plant and landfills. Processing connected with stabilization leads to generation of materials which might be contaminated with variety of organic compounds. Since this type of management generally assumes introduction of processed sludge to the ground, it can cause soil contamination with unknown compounds of organic origin. However, thermal processing of raw sewage sludge essentially excludes such possibility. Majority of organic matter is transformed into simple, mineralized form. In this case the most problematic issue is sewage sludge ash contamination with heavy metals. Although, determination of heavy metals in ashes is much simpler than determination of organic compounds. Chemical analysis can be very useful to asses environmental safety of processed and managed sewage sludge. That is why there is a significant quantity of used analytical techniques which are likely to support the processes of designing and implementing new economically and environmentally reasonable ways of re-using sewage sludge. Further, the process of technological utilization of sewage sludge conducted in Wastewater Treatment Plant “Wschod” in Gdansk is described. Recently technological line was upgraded. Now excessive sewage sludge is anaerobic digested with biogas recovery. Fermentation residues are incinerated in fluidized bed furnace. Ashes are cemented and land filled. Gdanska Infrastruktura Wodociągowo-Kanalizacyjna, which is owner of the treatment plant “Wschod“ is planning development strategy for the implementation of a pro-ecological management method connected with production of light construction materials and phosphorus recovery. Management of thermal treated sewage sludge is simpler and cheaper than non-thermal management, especially in case of large amounts of treated sewage sludge like in Wastewater Treatment Plant “Wschod”. Management in smaller installations of treatment plants collecting sewage sludge from less industrialized agglomerations is also less complicated. Sewage sludge management process should be developed separately for each treatment plant. Only then all management methods will be ecologically and economically justified.