This paper presents the energy potential of biogas obtained from the anaerobic digestion (AD) of sewage sludge (SS) preceded by thermal hydrolysis (THP) using Cambi THP® technology. The presented data are for the Tarnów (Poland) wastewater treatment plant for the year 2020. A detailed energy balance of biogas and its use in the cogeneration process and in the production of heat in the water boiler and the steam boiler is presented. The article contains data on the amount of processed SS and the content of dry matter and dry organic matter at different stages of the technological process. The annual plant operation resulted in the production of 3,276,497 Nm3 of biogas as a result of processing 8684 tonnes of dry solids (tDS) of municipal SS from the Tarnów wastewater treatment plant (WWTP) and regional WWTPs. The energy potential of the produced biogas was 75,347.06 GJ. The average calorific value of biogas was 23,021 kJ/Nm3.. The obtained biogas production allowed us to cover the thermal energy demand of the THP 100%. The annual average specific biogas conversion rate during the study period was 0.761 Nm3/kg of dry organic matter reduced and the average organic matter content reduction in the sludge was 64.60%.
Purpose -To determine the influence of alkali components (especially Ca compounds) on the hematite phase formation during thermal processing of sewage sludge and the observation of transformations proceeding at different ratios of Ca to FePO 4 . Design/methodology/approach -The model compositions were heated to temperatures of 6008C and 9508C, then calcined within 3 hours without mixing. Cooled products were subjected chemical analysis regarding the content of phosphorus that was soluble in cold water, 0.4 per cent HCl, 2 percent citric acid and aqua regia as well as crystallographic identification. Findings -On calcining at 6008C, CaO reacts with FePO 4 , forming hydroxylapatite. The hematite phase which is insoluble in mineral acids crystallizes above 6008C. Further increasing the calcining temperature leads to transformations resulting in Ca 9 Fe(PO 4 ) 7 and hematite formation. Molar ratios of CaO to FePO 4 • 2H 2 O of 1.0 and 2.0 lead to hematite phase formation and increase the availability of phosphorus compounds (characterized by phosphate solubility in 0.4 percent HCl and 2 percent citric acid) in compositions after calcining. Practical implications -The addition of CaO to sewage sludge before the combustion process should be beneficial from the point of view of further extraction of phosphorus compounds from the ash obtained. Suitable CaO addition favours iron binding into the hematite phase and raises the solubility of the phosphorus compounds in the ashes formed. Originality/value -This paper is a new source of information which complements existing knowledge about phosphorus recovery from sewage sludge.
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