CONTENT OF MAGNESIUM AND OTHER FERTILIZER COMPOUNDS IN STABILIZED AND DEWATERED SEWAGE SLUDGE FROM THE MUNICIPAL SEWAGE TREATMENT PLANT IN RECZ

The aim of this study was to determine the content of magnesium and other fertilizer compounds (Ca, K, Na, P, N and S) in stabilized and dewatered sewage sludge stored on dewatered sites at the Municipal Treatment Plant in Recz in 1994-2003. Discharge of post galvanic sewage to the municipal sewer system was evaluated at approximately 10% processed sewage at this treatment plant The fertilizer value and possible utilization of the sludge was evaluated. When evaluating possible use of the sewage sludge for fertilization purposes in agriculture, it was found that the concentration of magnesium in sludge samples was in the range of 0.2-0.5, on average 0.33%, and was substantially lower than the level of this compound given in literature. The content of this compound in sewage sludge is found in the range 0.02 do 7.6% and depends on the type of a treatment plant, treatment process, and also on the share of industrial sewage. Sewage sludge applied in agriculture should be characterized by a high content of magnesium (approximately 0.6%). Some physical and chemical properties of the examined sewage sludge were very good (loose soil consistency, lack of odor, humidity from 40 to 80%, suitable pH and high concentration of Ca, K, Na, P, N and S). The reaction was in the pH range from 5.6 to 7.0 (from slightly acid to neutral), which is typical of sewage sludge obtained during the biological processing of municipal sewage. The mean content of main nutrient compounds in the sludge, which was N - 2.7%, P - 4.7 and K - 0.18%, enables classification of this material as suitable for use in agriculture. Taking under consideration the content of all macronutrients and physical properties of the sludge produced at the Municipal Treatment Plant in Recz, it can be concluded that this sewage sludge may be applied on agricultural land and used for reclamation of degraded soils. But every batch of sewage sludge should be analyzed and evaluated individually because it may contain excessive amounts of heavy metals due to periodical discharge of post galvanic sewage to municipal sewerage.