Abstract
A long-term pilot scale experiment was conducted to verify the phosphate removal ability of a prospective phosphate adsorbent prepared by baking volcanic ash soil mixed with iron (II) sulfate at 500°C. A tank packed with 300l of the adsorbent was placed in a municipal wastewater treatment plant. The adsorbent layer was backwashed for 3.5 minutes with air and water every day in order to prevent the adsorbent from becoming filled with suspended solids. Secondary effluent was supplied to the tank at a rate of 600l·h-1. The average PO4-P concentration in the influent was 1.35mg·l-1, which was decreased in the μg·l-1 order in the effluent after about 50 d. The concentration then started to increase very gradually after about 60 d, increased up to 0.5mg·l-1 after 120 d, and increased about 1.0mg·l-1 after 240 d.
An average of 3.30mg·l-1 of suspended solids in the influent was almost completely removed from the effluent as a result of the daily backwashing. The pH of effluent was maintained at almost the same level as that of the influent throughout the pilot study. The PO4-P removal ability was found to be unaffected by water temperature, indicating that the adsorbent would be useful in cold regions. The overall results of this pilot study show that baked volcanic ash soil is an effective medium for the removal of PO4-P from secondary effluent in municipal wastewater treatment plants.
