| The potential applications of magnesium hydroxide for municipal wastewater treatment have, for the first time, been intensively investigated in this study. The experiments were carried out at lab scale, pilot scale and field scale. The primary objective of this project was to determine the efficacy of using magnesium hydroxide recovered from a coal-fired power plant as a chemical agent in the treatment of municipal wastewaters and/or sludges. The result is a conversion of a waste material into a usable product, a reduction in waste disposal costs to both the power utility and the wastewater treatment plant, and a potential new source of income to the utility.; After extensive and intensive research, exciting results have been obtained. Comparison studies between magnesium hydroxide and other commonly used chemicals revealed that magnesium hydroxide was a more effective neutralization agent than other chemicals. Evaluation of the effect of magnesium hydroxide on the microorganisms' physical and biological properties demonstrated that magnesium hydroxide could effectively improve the settleability of the mixed liquor in aeration tanks and the dewaterability of the anaerobically digested sludge in the sludge dewatering facilities, respectively. Investigation of magnesium hydroxide application in anaerobic sludge digesters proved that magnesium hydroxide enhanced the overall process, in terms of organic matter destruction percentage and biogas production rate. Furthermore, with the amendment of magnesium hydroxide in a sludge anaerobic digester, the anaerobic supernatant has a lower level of nutrients, implying that the biosolids thus generated have a higher agricultural value. Experiments on nutrient removal revealed that removal of phosphate and ammonium using magnesium hydroxide from centrate/filtrate generated in the sludge dewatering facilities will not only reduce the nutrient load to the head works of treatment plant, but also generate a very good plant fertilizer—struvite. It is more effective than other commonly used chemicals, e.g., ferric chloride and aluminum sulfate. Studies on struvite precipitation/crystallization demonstrated that different magnesium containing chemicals and seeding materials had different effects; aeration (for mixing) plus magnesium chloride (supplement of Mg2+) plus struvite (seeding material) proved to be the best combination. |
