Impact Low-Cost Processing Methods on the Contents of Polycyclic Aromatic Hydrocarbons in Sewage Sludge

Abstract

In Poland, more and more often to the processing of sewage sludge are used low-input methods: composting, vermicomposting, reed bed, willow energy and solar driers. Also in the north-eastern part of Poland for many years successfully operate objects using these methods. The paper presents the experience of the use of low-cost methods of sludge treatment in wastewater treatment plant located in Zambrow, Podlaskie Province. The results of studies of sewage sludge on the PAHs content after treatment in reed bed system were presented. In 2012, samples of sediment were taken from the middle part of the oldest red bed (still in service) in the 3-meter profile of the sediment fill. Sampling was performed using a special probe to enable the extraction of sewage sludge from the full depth of the lagoon. Samples were averaged and sediment samples from each 0.5 m section were tested. The obtained results for the PAHs in sediments from the lagoon of sludge from reed sewage treatment plant in Zambrow show that the average content of PAHs studied is approximately 5552.8 g kg d.m. At the same time, there are clear differences in the content of these compounds in each of the processed layers of sludge in the lagoon. An average contents of PAHs tested in individual layers of the sludge were as follows: 5852.2 g PAHs kg d.m. in the upper sludge layer (0–1 m), 6636.8 g PAHs kg d.m. in the middle sludge layer (1–2 m) and 4169.5 g PAHs kg d.m. in the oldest, bottom sludge layer (2–3 m). A significant decrease in the total PAHs content with increasing the time period of the processing of sludge lagoons at the lowest bottom layer was observed after 10–12 years. Sewage sludge processed by California earthworms for vermicompost was characterized by the lowest total content of studied PAHs, which amounted 2550.2 g kg d.m.