Phosphorus recovery and biochar production from waste digested sludge

In this study, it was aimed to obtain new usable products from waste by recovering phosphorus and obtaining biochar from two different forms of anaerobically digested sewage sludge (ADSS) collected from the domestic wastewater treatment plant in Yüreğir district of Adana province. In phosphorus recovery studies, 58.7% of the total phosphorus in the sludge was converted into soluble form at pH 2 through the acidification process carried out with H2SO4. Soluble phosphorus was recovered in precipitate form by the alkaline precipitation method using NaOH and Ca(OH)2 solutions. 60% of the total phosphorus in the sludge was recovered at pH 8 with both bases. It has been determined that the obtained precipitates, with their phosphorus content of up to 17%, that can be used as a raw material instead of low-grade carbonic phosphate rocks in the phosphate industry. In the biochar preparation study, dried ADSS samples were pyrolysed at temperatures of 300, 400, 500, 600 and 700oC. As the pyrolysis temperature increases, the volatile solids (UKM) (from 44.9% to 15.1%) and fixed carbon contents (from 2.3% to 0.9%) of the resulting biochars decrease, and the ash contents (from 52.8% to 84%) were found to increase. The yield of biochar by mass was calculated as 72.6% at 300oC pyrolysis temperature and 47% when it increased to 700oC. It was observed that the surfaces of biochars obtained at low pyrolysis temperatures were rougher and more heterogeneous than the surfaces of biochars obtained at higher temperatures. It was determined that the porosity of biochars increased with the increase in pyrolysis temperature. C=C and –OH functional groups were found with the FTIR analyzes performed on the obtained biochars. When the results obtained were examined, it was concluded that biochars have the properties to adsorb phosphate, textile dye and heavy metals on their surfaces and therefore they are a suitable product that can be used in both wastewater treatment and agricultural applications.