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Enhancing nutrient solubilization from organic waste using the microwave technology Kenge, Anju A.

Abstract

Organic wastes like sewage sludge and dairy manure were subjected to microwave enhanced advanced oxidation process ( MW/H₂0₂-AOP). The MW/H₂O₂-AOP was developed to release nutrients like phosphorus and nitrogen in the soluble form from the organic waste; these nutrients could be further recovered and reused. In the past, this process has been successfully applied to a series of organic waste for the purpose of solubilizing nutrients. The objectives of this research were to: (1) improve the MW/H₂0₂-AOP in terms of nutrient release by determining the different factors that influence the treatment, (2) define the factors affecting the process in their order of significance and (3) check the efficacy of the process on various waste. In the MW/H₂0₂-AOP, the role of mixing was verified, using municipal sewage sludge (aerobic and anaerobic). It was speculated that mixing the samples during the process would facilitate uniform heating and thus promote more nutrient release. At a microwave temperature of 80 °C, heating time of 5 minutes and hydrogen peroxide dosage of 1 mL per 1% of total solids, the results showed that mixed samples gave a higher nutrient solubilization compared to the unmixed. Subsequently, mixing and solids concentration were incorporated in a screening design with the other proven important factors viz., microwave temperature and hydrogen peroxide dosage. The results showed that microwave temperature and hydrogen peroxide dosage were the most significant factors for the release of orthophosphate, ammonia and soluble chemical oxygen demand. Preliminary experiments treating anaerobic sludge using MW/H₂O₂-AOP showed a decrease in orthophosphate concentration below the initial untreated value while for ammonia and volatile fatty acids the concentrations remained same as the initial. In this case, the set microwave temperature was 80 °C with 5 minutes heating and hydrogen peroxide dosage of 1 mL per 1% total solids at pH 7. To investigate this behavior, anaerobic sludge was treated at two pH conditions (7.8 and 4) at microwave temperatures ranging from 80 to 160 °C with hydrogen peroxide dosage of lmL per 1% total solids for 5 minutes. The results showed that acid addition helped in the destruction of sludge solids and release of nutrients. TheMW/H₂0₂-AOP was used to treat separated solid dairy manure. Solid dairy manure with total solids 1.6% was subjected to microwave temperature of 120 °C for 10 minutes with a hydrogen peroxide dosage of 2 mL per 1% total solids at three pH conditions (3.5, 7.3 and 12). Only at pH 3.5, substantial quantity of orthophosphate, ammonia, soluble chemical oxygen demands and volatile fatty acids could be released. Further, a screening experiment was designed including microwave temperature, hydrogen peroxide dosage and heating time, to determine the factors most affecting nutrient solubilization from solid dairy manure. Hydrogen peroxide dosage and temperature were important factors in orthophosphate release while microwave temperature and heating time were important in the release of ammonia and volatile fatty acids. The results clearly define the efficacy of the MW/H₂0₂-AOP on various organic waste as well as the conditions under which the treatment can be optimized.

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