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Applications of microwave technology to wastewater treatment Wong, Wayne Thai

Abstract

A novel microwave process was developed on a laboratory batch scale for the purposes of solubilizing nutrients, such as orthophosphate and ammonia, from sewage sludge. The present research aimed to explore whether microwave technology could be used as a simple and effective means of enhancing nutrient recovery, where struvite (magnesium ammonium phosphate) crystallization technology could be subsequently used to recover the nutrients as a useful fertilizer product. The objectives of this research were to: (1) investigate whether microwave irradiation could solubilize nutrients from sewage sludge, (2) explore the role of chemical treatment on enhancing nutrient solubilization, (3) identify the major factors associated with microwave operation that affect nutrient solubilization, and (4) determine the theoretical optimum microwave operating conditions that maximize nutrient solubilization. Microwave irradiation of various types of sewage sludge resulted in the simultaneous solubilization of both orthophosphate and ammonia. At microwave heating temperatures of 60-170°C and a microwave heating time of 5 minutes, up to 84% of total phosphorus and up to 136% of the total Kjeldahl nitrogen were solubilized as orthophosphate and ammonia, respectively. Nutrient solubilization levels varied with respect to temperature. Exploratory studies using hydrogen peroxide and sulphuric acid treatment were found to have varying effects on nutrient solubilization. Subsequently, microwave heating temperature, heating time, hydrogen peroxide treatment and sulphuric acid treatment were incorporated into a screening design to determine which factor(s) were significant for maximizing nutrient solubilization. Microwave heating time was ultimately eliminated as a significant factor for both orthophosphate and ammonia solubilization. Microwave heating temperature and hydrogen peroxide treatment were the most significant factors affecting orthophosphate and ammonia, respectively. Optimization studies with the remaining factors resulted in prediction models which were in agreement with the general trends determined from the previous findings in this research. The models predicted the optimum orthophosphate yield at 200°C, 2 % (v/v) H₂0₂ and 1% (v/v) H₂SO₄, and optimum ammonia yield at 200°C, 2 % (v/v) H₂0₂ and no H₂SO₄ addition. The results of this research clearly indicated that microwave irradiation could be used as an effective means of solubilizing nutrients from sewage sludge.

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