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Abstract
The influence of thermal processing of sewage sludge on the usage properties of the formed ash The influence of sewage sludge incineration temperature on the formed ash constitution was examined. The comparative extraction tests of two differently prepared ashes (laboratory and industrial) were carried out in order to verify if the parameters of sewage sludge incineration influence the extraction selectivity of phosphorus compounds. The laboratory ash (Alab ) were prepared from sewage sludge incinerated at 950°C on a laboratory scale while the industrial ash (Aind ) comes from thermal utilization system of the sewage sludge at the Gdynia Sewage Treatment Plant, which uses fluid-bed furnace incineration at 850 - 900°C. It was found that the temperature and the conditions of the sewage sludge incineration process have an effect on the usage properties of the formed ash. Despite the twofold lower Fe content in the industrial ash than that of the laboratory one, its content in extracts after phosphoric acid leaching is 4.7 times higher. The lower values of PO4 3- leaching degree from the industrial ash than the laboratory ash were observed, as well as a decrease of extraction productivity.
Highlights
The sewage sludge, waste after municipal sewage treatment processes, are the source of mineral and organic elements including a series of valuable fertilizing components, which make them a potential substitute for natural phosphorus ore.The sewage sludge causes significant problems in the global system of waste management because of its complicated composition and properties[1, 2]
In order to get better acquainted with the differences between the conducted experiments the concentration of PO43, Ca2+, Mg2+ and Fe2+ ions in the extracts after ash extraction with phosphoric acid (Figure 3) and nitric acid (Figure 4) were compared
The higher extraction degree of phosphate ions from the laboratory ash results in obtaining the extracts with higher phosphate content, 103.9 g/dm[3], respectively, when nitric acid was used and 91.9 g/dm[3] for the phosphoric acid extraction (347.5 g/dm[3], including phosphate ions introduced with the acid)
Summary
The sewage sludge, waste after municipal sewage treatment processes, are the source of mineral and organic elements including a series of valuable fertilizing components, which make them a potential substitute for natural phosphorus ore. Ltd.[10, 11] developed a fertilizer production technology, melted calcium-magnesium phosphate, on the basis of ash from sewage sludge combustion This method consists in ash melting with an addition of calcium and magnesium at the temperature of 1350 – 1500°C. To the influence of sewage sludge combustion temperature on the obtained ash composition, reveal that ash extraction selectivity depends significantly on the parameters of its thermal processing[13,14,15]. In the instance when the sewage treatment plant uses chemical precipitation for phosphorus removal in the form of iron phosphate, the sewage sludge, as well as the obtained ash, contain unwanted iron ions, which have an unfavorable impact on phosphorus availability in fertilizers or feed products. Tech., Vol 9, No 4, 2007 after sewage sludge combustion on a laboratory scale and from the industrial sewage sludge combustion plant
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