Preliminary assessment of phosphorus mobility in sewage sludge for their potential leaching from soil

Abstract

Sewage sludge is rich in organic matter, nitrogen, phosphorus and other macro and micronutrients, making it a useful raw material for agricultural use. The natural management of sewage sludge, including the use of its fertilizing properties, is characterized by low costs, but it cannot be used without restrictions. It is important that sludge is produced throughout the year, while the possibility of its application occurs during a specific time of the growing season. Poor fertilizer management could result in the release of excess nitrogen and phosphorus from fertilizers and eutrophication of aquatic ecosystems. The study attempted to assess the mobility of phosphorus in various sewage sludges in terms of their potential leaching when used in nature for fertilizer purposes. The method of special analysis according to Golterman, which is originally applied to soils, was used for this purpose. This method makes it possible to determine the content of various forms of phosphorus. This is a novel attempt to assess the potential leaching of mobile forms of phosphorus from sewage sludge, as such analyses are not usually used in the case of potential use of sludge for natural purposes. The study attempted to evaluate the mobility of phosphorus in various sewage sludge in terms of its potential leaching when used in nature for fertilizer purposes. Comparing pre-sludge, activated sludge and surplus sludge and considering its potential use for natural purposes, it seems that surplus sludge containing the most mobile forms of phosphorus (63%) at this time is the most valuable sewage sludge of those analyzed. Obviously, the necessary treatment to meet sanitary requirements when using the sludge for natural purposes is hygienization, which caused an 18% reduction in biodegradable (mobile) forms of phosphorus. The most readily available form of phosphorus is the Ca-EDTA fraction, the proportion of which has been reduced sequentially in the sludge generated at the wastewater treatment plant (preliminary, activated and surplus). This fraction is the most labile and is identified with phosphorus readily released into the soil solution. The low amount of analysis makes it necessary to continue research with a special focus on the analysis of sludge after it has been applied to the soil.