Method of maintaining the steady grain-size composition of rapid filter media

Summary

During the operation of rapid filters the grains of the filter media inevitably wear off and disintegrate which affects adversely the output of the filtration plants. To restore the design grain-size composition of the filter media the upper reduced in size layer is usually removed. This process is fairly labor-intensive and economically unjustified. The consistency of the grain-size composition of rapid filter media can be maintained eliminating labor-intensive processes of manual removal of fine grains and media unloading and rescreening. A method of maintaining the steady grain-size composition directly in the filter by intermittent washing with preestimated stabilization rate is suggested. The formulae for calculating the rate and process stages of stabilization wash are presented.

Key words

rapid filter , filter bed , filtration plant , grainsize composition , intermittent wash , filter media fineness stabilization

Review of the trends of rapid filtration improvement:
designs, technologies, calculation methods

Summary

The results of the works carried out at Rostov Research Institute of Public Utilities for the period of 1980–2016 on improving the design, calculation methods and technologies of rapid filtration are presented. The works were mainly relevant to two basic elements of rapid filters: drainage-distribution systems and filtering media as well as improvement of water coagulation processes. The obtained results were published elsewhere during 1983–2016 and found practical use at many filtration plants in Russia. More than 120 years of practice of using rapid filters in municipal water supply as well as the results of numerous studies show that from the reliability and durability standpoint quartz sand filter media is the most stable in relation to the basic indicators (including wear capacity and grindability). Using this media in combination with advanced coagulants and flocculants provides for stable high quality filtrate. Another very important element of a rapid filter is the drainage-distribution system designed for reliable regeneration of the filtering media. One of the advanced types is porous drainage developed by the experts of Rostov NII AKKH: porous polymer concrete drainage on the basis of epoxy bonding agents and tubular-porous drainage with fixed porous layer. The reliability of these drainages has been proved by 20-year practice of field work. The core results of the described work are presented to help using them by the employees of engineering companies, water providers and students studying municipal drinking water supply.

Key words

filter bed , filtration plant , rapid filters of big and small surface area , drainage design , washing process , head loss curves