The effect of water purification by oyster shell contact bed

The purpose of this study is to utilize wasted oyster shells as the media of the contact bed to purify domestic wastewater on Erchong Floodway, Taipei County. There are three horizontal flow tanks in this system, horizontal flow and aerated oyster shell tank (HAOS), horizontal flow oyster shell tank (HOS), and horizontal flow gravel tank (HG), respectively.In the results of the horizontal flow and aerated oyster shell tank (HAOS), the average mass removal of BOD5, SS, NH4-N, NO3-N, PO4-P, and TP were 18.78, 58.95, 11.74, −1.19, 0.50, and 0.87 g/m2 day. The BOD5 first-order reaction reducing rate constant in 20 °C was 2.20/day. Consequently, using oyster shells as the material of the subsurface flow, constructed wetland had better water purification efficiency than using gravels. In this system, part of the BOD5 was removed because of the removal of SS, and there was better blocking effect when using oyster shells as the materials than gravels. Aeration can effectively remove ammonia nitrogen, but the main purpose was to strengthen the nitrification in the water, so that ammonia nitrogen was converted into nitrate nitrogen. Oyster shells as the material still had better removal effect of nitrogen than gravels.