Summary:

Sewage treatment aims mainly at protection of the natural environment and primarily protection of surface water purity. Sewage treatment process is always accompanied by sewage sludge, which is defined an organo-mineral solid phase of sewage. Chemical composition of the sludge my be different depending on the kind of treated sewage and applied processing technologies. Sewage sludge constitutes about 2% of the total volume inflowing to sewage treatment plants.
Construction of new sewage treatment plants and intensification of treatment process cause an increase in the amount of produced sewage sludge and raises its storage costs, which may be very high, reaching even 50% of total costs generated by a sewage treatment plant. An alternative for storing large amounts of sewage sludge may prove its natural utilization, which would also contribute to reduce costs born by sewage treatment plants. Some previous research has already demonstrated sewage sludge usability for the following purposes: reclamation of devastated lands, plant consolidation of ground surface or composting sewage sludge. However, agricultural utilization of sewage sludge still raises numerous controversies. It is due mainly to insufficient information about sewage sludge.
However, research results convince that the problem of sewage sludge is worth interest. Sewage sludge may prove a valuable raw material and not a troublesome waste material formed in the process of sludge treatment which it has been so far.