Community Analysis And Control Technology Of Invertebrates In The Biological Activated Carbon (BAC) Filters

Ozone-biological activated carbon (BAC) technology is one of the popular and advanced processes of drinking water purification in China. Most of organic matter in water bodies can be effectively eliminated by activated carbon absorption and biofilm biodegradation. Water in BAC pool contains high concentrations of dissolved oxygen and biofilms that benefit the growth of invertebrates. In the present study, community structure of invertebrate in the BAC pool from October 2006 to September 2007 was investigated, and countermeasure of invertebrate control was proposed.1) Experiments were performed for one year in two drinking water plants (A, B) with the Ozone-BAC treatment in South China. 28 species of rotifer and 8 species of crustacean were identified during the survey period in water and carbon samples. Other species including oligochaeta, nematode, chironomus and water mites were also recorded. Densities of invertebrates in two water plants were higher in the summer than that in the winter. A large number of species and high densities of invertebrates at A were found when compared with that in B, which may be caused by the difference in food source and water temperature.A marked succession of invertebrate community exists in the modeling carbon cylinder. When the carbon cylinders were run for about three months, densities of invertebrates in carbon-filtered water began to increase. After six months, animal density reached the maximum and then decreased gradually. The sequence of the dominant species succession was cladocera→rotifer→nauplius and cyclopoida→oligochaeta and nematode.The eliminating effect on invertebrate was evident with the normal treat process. Backwashing had important effects on invertebrate in BAC pool. Densities of invertebrates in the carbon cylinders without backwashing were higher than that with backwashing.2) Enclosure experiments showed that net filtering, ultrafiltration membrane, some chemicals such as Cl₂, NH₃, and NaCl, and drying of the BAC pool, had an important role on the elimination of invertebrates. Soaking with saliferous water was the best method in comparison with others including backwashing with the chloric water, drying the filter pool, soaking with ammoniac water, and adding chlorine in thenormal process.3) Measures of invertebrate prevention in BAC pool include 2-days of backwashing, 0.5-1.0mg/L of residual chlorine in the water under the condition of normal process, and backwashing with chloric water. Emergency measure of soaking filters pool for 1-2 days with 10-20g/L of salierous water was proposed.