Abstract
The long process of sludge stabilization (7–15 years) remarkably reduces the organic matter content and causes the process of sludge humifaction. This paper presents the results of using low-cost methods of sludge treatment in the wastewater treatment plant located in Zambrow, Podlaskie Province. The results of studies on the organic matter and heavy metals content in sewage sludge after treatment in a reed bed system are presented. The aim of the research was to evaluate and model organic matter and heavy metals concentrations during sewage stabilization in reed bed lagoons. The lowest concentration, below 1.3 mg/kg DM of the examined seven heavy metals was mercury (Hg). The highest concentration, exceeding 1300 mg/kg DM was zinc (Zn). The obtained results for the heavy metals in sewage sludge from the reed bed lagoons in Zambrow show that the average content of the analyzed heavy metals is approximately 1620 mg/kg DM. The results of the study demonstrate a high efficiency of low-cost methods used in Zambrow WWTP in terms of the quality of the processed sludge. Sewage sludge from the lowest layer of the reed lagoon (12–14 years of dewatering and transformation) is characterized by the lowest organic matter and heavy metals content. The higher a sediment layer lies, i.e. the shorter the time of processing, the higher is the heavy metals content. This indicates a great role of reeds in the accumulation of these compounds.
Highlights
Low-input methods of processing sewage sludge are characterized, first of all, by their simple design, technology and ease of operation
The lowest dry matter content was recorded in the top layer of the vertical profile at 12.6%
From the study results obtained from the long-term stabilization and dehydration of sewage sludge in the reed lagoon, the following conclusions can be drawn: 1. An increase in dry matter and decline of organic matter occurred in the stabilized sewage sludge
Summary
Low-input methods of processing sewage sludge are characterized, first of all, by their simple design, technology and ease of operation. These methods allow using only a limited number of process equipment due to which the consumption of electrical energy is low. Reed lagoons are successfully used for long-term stabilization and dehydration of sludge from wastewater treatment. They are easy to construct and operate and consume small amounts of energy [2, 3]. The content of heavy metals in stabilized sewage sludge is often crucial for the possibility of its use in agriculture. Their excessive content in sewage sludge may be toxic and dangerous to the environment
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