Effect of a Gravel Bed Flocculator on the Efficiency of a Low Cost Water Treatment Plants

Authors: Alaa Hussein Wadi

Abstract:

The principal objective of a water treatment plant is to produce water that satisfies a set of drinking water quality standards at a reasonable price to the consumers. The gravel-bed flocculator provide a simple and inexpensive design for flocculation in small water treatment plants (less than 5000 m3/day capacity). The packed bed of gravel provides ideal conditions for the formation of compact settleable flocs because of continuous recontact provided by the sinuous flow of water through the interstices formed by the gravel. The field data which were obtained from the operation of the water supply treatment unit cover the physical, chemical and biological water qualities of the raw and settled water as obtained by the operation of the treatment unit. The experiments were carried out with the aim of assessing the efficiency of the gravel filter in removing the turbidity, pathogenic bacteria, from the raw water. The water treatment plant, which was constructed for the treatment of river water, was in principle a rapid sand filter. The results show that the average value of the turbidity level of the settled water was 4.83 NTU with a standard deviation of turbidity 2.893 NTU. This indicated that the removal efficiency of the sedimentation tank (gravel filter) was about 67.8 %. for pH values fluctuated between 7.75 and 8.15, indicating the alkaline nature of the raw water of the river Shatt Al-Hilla, as expected. Raw water pH is depressed slightly following alum coagulation. The pH of the settled water ranged from 7.75 to a maximum of 8.05. The bacteriological tests which were carried out on the water samples were: total coliform test, E-coli test, and the plate count test. In each test the procedure used was as outlined in the Standard Methods for the Examination of Water and Wastewater (APHA, AWWA, and WPCF, 1985). The gravel filter exhibit a low performance in removing bacterial load. The percentage bacterial removal, which is maximum for total plate count (19%) and minimum for total coliform (16.82%).

Keywords: Gravel bed flocculator, turbidity, total coliform.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1057899

References:

[1] Fair, G.M., J.G. Geyer, and D.A. Okun, 1971, "Element of Water Supply and Wastewater Disposal," Wiley, New York.
[2] Kardile, J.N., 1972, "Crushed Coconut Shell as a New Filter Media for Dual and Multi-Layer Filters," Jour. Indian water works assoc., vol. 1, no. 1.
[3] Wagner, G., 1982, "The Latin America Approach to Improving Water Supply," Jour. AWWA, Vol. 74, No. 4.
[4] Bhole, A.G., 1981, "Design and Fabrication of a Low Cost Package Water Treatment Plant for Rural Areas in India," AQUA, No. 5.
[5] Wagner, G., 1982, "The Latin America Approach to Improving Water Supply," Jour. AWWA, Vol. 74, No. 4.
[6] CEPIS 1982, "Modular Plants for Water Treatment," Vol. 1 and Vol. 2, Technical Document No. 8, Pan American Health Organization, Lima, Peru.
[7] Richards, P.A., 1996, "Unit Operations and Processes in Environmental Engineering," 2nd ed., PWS Publishing Co., Boston, MA.
[8] Salvato, J.A., 1982, "Environmental Engineering And Sanitation", 3rd Ed., ," John Wiley & Sons Inc., New York.
[9] AWWA, 1999, "Water Quality and Treatment," 5th ed., McGraw-Hill Book Co., New York.
[10] AWWA, 1990, "Water Quality and Treatment: A Handbook of Public Water Supply," 4th ed., McGraw-Hill, Inc., New York.
[11] Tchobanoglous, D. and Schroeder, E., 1985, "Water Quality", Addison Wesley Publishing Co., Reading, Mass.
[12] Al-Samawi, Adnan, 1979, "Time Series Analysis of Rectangular Sedimentation Tank", Ph.D thesis, University of Strathclyde, U.K.
[13] APHA, AWWA and WPCF, 1985, "Standard Methods for the Examination of Water and Wastewater", 16th ed., American Public Health Association, Washington, U.S.A.