A lot of attention has been paid in current literature to sewage sludge due to its increasing amount and problem with its disposal. In the age of expensive energy sources and depletion of natural feedstocks it is necessary to find ways of reusing and recycling waste. Sewage sludge has a high valuable fertilizing potential. It is known as a rich source of nutrients. In addition, it includes a large amount of organic matter, which could facilitate the bioavailability of macro- and micronutrients and improves the soil structure. However, a direct application of sewage sludge to the soil is restricted by heavy metals content. Sewage sludge commonly includes pathogenic microorganisms and toxic compounds. The aim of the study was to determine the state of the art and availability of technology for fertilizers production based on waste, especially on sewage sludge. As sewage sludge from different wastewater treatment plants varies in its chemical composition and physical properties, it is important to find a local solution to the problem of sewage sludge disposal. It has been found that organo-mineral fertilizers (OMFs) derived from sewage sludge and modified by the addition of mineral fertilizers seem to be suitable for application to the soil. Adding acids or alkali agents provide sterilization and binding of the components. Novel OMFs gave a comparable crop yield response as conventional fertilizers. They show a slow release of nutrients, which is the main advantage in relation to mineral fertilizers.

Silver nanoparticles (AgNPs) were prepared by a chemical reduction method in an aqueous solution of silver nitrate and sodium borohydride as a reducing agent in the presence of polyvinylpyrrolidone as a stabiliser. The effect of silver salt concentration on the synthesis and properties of AgNPs was investigated. The nanosized silver colloids have been characterised by using scanning electron microscopy and atomic absorption spectrometry. The optical properties of the silver nanoparticles were studied through UV–vis spectroscopy and Fourier transformed infrared (FTIR) spectroscopy. Dynamic light scattering measurement using Zetasizer nano ZS was applied for the size estimation of AgNPs. The results confirmed that silver nanoparticles were formed in each sample independently of silver salt content; however, silver nitrate concentration had a significant influence on silver nanoparticles morphology and other properties. The absorption intensity, the band of the FTIR spectra intensity increases with an increase of silver nitrate concentration. Also, the shape and size of particles depends on the silver nitrate concentration.