Comparative Analysis of Sludge Utilization in Agriculture in Bulgaria and Selected European Union Countries

The purpose of this study is to illustrate the convergence of sludge utilization in Bulgaria and other selected European Union countries (Hungary, Poland, Czechia, and Romania) and examine by correlation and asymmetric analysis how and to what extent the transaction costs and sludge utilization impact the use of sludge and inorganic fertilizers in agriculture. The usage of sludge from wastewater plants in the agriculture is still a widespread way of sludge utilization, even though the trend in the recent years shows a gradual regress and visible growth in other wastewater outlets. The correlation and asymmetric analyses were carried out to give insights about the role of transaction costs in sludge use and the effect of sludge disposal in agriculture to supplement the mineral fertilizers. It is noted that the agriculture is still a leading outlet of sludge disposal, the eventual transaction costs incurred by farmers to use it are not changing during last years, whereas the prices of mineral fertilizers were not perceived to boost sludge demand in agriculture. In countries such as Hungary and Poland, there is a relatively considerable symmetry between the increase in the use of inorganic fertilizers and the shrink in the sludge use in agriculture, while in Bulgaria the persistent trend of using inorganic fertilizers is supplemented by a temperate growth in sludge agriculture disposal. In turn, in Romania there is a strong asymmetry between the use of inorganic nitrogen and sludge in agriculture, however, it is attributed to lack of sludge application in agriculture in the first half of the period under consideration.