2014 Volume 27 Issue 3 Pages 105-115
Total phosphorus in water from an adjustment reservoir in Isahaya reclaimed land has regularly exceeded environmental standards. However, sludge from purification plants is known to have the capacity to absorb phosphate. In this study, to promote recycling of sludge and to develop a method for total phosphorus reduction, evaluation of phosphate removal by sludge from a purification plant was performed, in addition to simulation of concentration changes in an adjustment reservoir to which sludge was added. Absorption experiments were conducted using a mixture of phosphate solution and sludge. The coefficient of absorption isotherm and the mass transfer capacity coefficient were measured in relation to the absorption rate. During mixing, water in the reservoir is pumped into the water treatment plant. Phosphate is removed from it by complete mixing with sludge of about1,400-2,000 t/y of sludge. When using the immersion method, sludge is added to the reservoir. Approximately 3,000t/y of sludge is required. However, both methods have shortcomings: a huge absorption tank (e.g. the order of 105m3) must be used for mixing; in the immersion method, sludge remains in the adjustment reservoir and phosphate is not removed from the reservoir. Because the required amount of sludge and scale of treatment plant are large, further investigation is necessary.
