Phosphorus Adsorbent Derived from Concrete Sludge (PAdeCS) and its Phosphorus Recovery Performance

Solid adsorbents for phosphorus recovery (PAdeCS) were prepared from real concrete sludge sampled from an industrial site that produces concrete poles and piles. The concrete sludge was diluted with water at dilution ratios from 1 to 15 to prevent hardening of the cement components. The diluted concrete sludge was then filtered, dried, and used as a solid adsorbent. Two drying methods were examined: natural drying under atmospheric conditions and forced drying in an oven at 105 °C. The phosphorus recovery performances of prepared adsorbents were examined using a potassium dihydrogen phosphate (KH2PO4) solution containing 100 mg-P/L (close to the effluent produced by the sewage sludge dewatering process) as a synthetic for wastewater. All the prepared adsorbents were able to recover phosphorus. Using the forced drying treatment during adsorbent preparation greatly improved the rate of phosphorus recovery from solution. The adsorbent prepared with dilution ratio 10 and forced drying exhibited the highest phosphorus recovery performance. The final phosphorus concentration in solution was 0.83 mg/L, 4 h after addition of the optimized adsorbent, which is extremely promising for application in inexpensive phosphorus recovery processes.