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Delectric heating pretreatment of organic slurries Nkansah-Boadu, Frank


This study reports on the research findings from the investigations of three studies conducted on dielectric heating treatments of separated dairy manure and sewage sludge for the purpose of solids disintegration and nutrients release were carried out under batch operation. The treatment processes investigated included; radiofrequency/hydrogen peroxide advanced oxidation process (RF/H2O2-AOP), microwave/hydrogen peroxide advanced oxidation process (MW/H2O2-AOP) and combination of conventional heating (CH) and MW/H2O2-AOP. The broad objectives were to investigate the effects and factors affecting these processes. Significant factors affecting the RF/H2O2-AOP process; hydrogen peroxide dosage, heating time and input power were optimized using surface response methodology. The optimized operating conditions were determined to be an input power of 63%, holding time 60 min and H2O2 dose of 1.1% for orthophosphate release, and an input power of 71%, holding time 5 min and H2O2 dose of 2.4% for soluble chemical oxygen demand. The second study was to examine the effects of organic acids (acetic, oxalic and citric) and mineral acids (sulfuric and hydrochloric acid) as acidifying reagents in MW/H2O2-AOP. The results showed that organic acids were good acidifying reagents comparable to mineral acids. The MW/H2O2-AOP and oxalic acid treatment could be combined into a single-stage process which could release phosphates, solubilize solids and remove calcium from dairy manure at the same time. A mixture of oxalic and mineral acids could produce the maximum volume of clear supernatant. A combination of CH and MW/H2O2-AOP was applied for the treatment of aerobic sewage sludge and dairy manure in the final study. The substrates were preheated by CH method (40oC, 50oC and 60oC) followed by MW/H2O2-AOP (100oC and 120oC). The maximum SCOD/TCOD ratio obtained for sewage sludge and dairy manure were 60% and 22%, respectively. The best treatment conditions for COD solubilization for both sewage sludge and dairy manure was obtained for the treatment set conducted at CH temperature of 60ºC followed by MW temperature 120ºC with hydrogen peroxide. A maximum ortho-P/TP ratio of 50% and 98% was obtained for sludge and dairy manure, respectively. The overall results suggest that dielectric heating was effective in the treatment of dairy manure and sewage.

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