Municipal sewage sludge is a problematic waste that needs to be managed. Modern wastewater treatment plants (WWTPs) generate stabilized sewage sludge with good chemical and biological parameters. Plenty of WWTPs digest sewage sludge in fermentation chambers for two purposes – the use of biogas and thermal sludge stabilization. The fermented sewage sludge can be utilized for organic or organo-mineral fertilizer production. The Central Mining Institute (CMI) in Katowice (Poland) has developed a proprietary technology for production of a granulated organo-mineral fertilizer from the stabilized sewage sludge.
The innovative fertilizer developed by CMI (patent PL 233754), fully complying with the Polish law requirements, is a mixture of municipal dewatered sewage sludge collected from municipal WWTPs, dolomite (50% CaCO3, 40% MgCO3), lime (96% CaO), gypsum, ammonium carbonate and microcrystalline cellulose. Sewage sludge for fertilizer production contained heavy metals at levels lower than: Cr, 100 mg; Cd, 5 mg; Ni, 60 mg; Pb, 140 mg; Hg, 2 mg.
Sewage sludge-based fertilizer made with the CMI technology was free from live eggs of intestinal parasites Ascaria sp., Trichuris sp., and Toxacara sp. as well as from bacteria of the genus Salmonella. The fertilizer was verified to fulfill the environmental safety rules and to have a stimulatory impact on plant growth.
Micro-field tests were conducted at WWTP in Żory (Poland) and carried out on five fields (5m2 each). To evaluate the effectiveness of plant growth, drone photos were made to show field coverage upon vegetation, and the plant dry mass was determined after harvest. Dry mass analyses showed significant changes in biomass chemical composition: the N concentration was 289,6% of the control and 98,2% of commercial fertilizer, whereas the respective P content was 145,1% and 300%. The results prove that the fertilizer produced from municipal sewage sludge is highly competitive with other available commercial products.