Energy and Water Savings during Backwashing of Rapid Filter Plants

Abstract

This paper describes an analysis of the effects of adjusting the intensity of filter backwash to the water temperature. The consequences of the lack of such adjustment for the life of filter beds, the amount of water used for backwashing, the amount of energy used for backwashing and the quality of the first filtrate are presented. In order to determine the losses and profits resulting from controlling the intensity of backwash water depending on its temperature, an analysis was carried out at a water treatment plant in southern Poland. Laboratory measurements were used to determine the granulation and specific gravity of sand grains filling the filtration beds. On the basis of measurements on a semi-technical scale, the magnitudes of filter bed expansion were determined for average monthly wash water temperatures. They were first calculated from the Richardson–Zaki equation, using different formulae for the value of the exponent of the power in this equation. Due to significant differences in the density and shape of grains covered with a permanent deposit after several years of filter operation, a satisfactory match between the formulae known from the literature and the results of expansion measurements was not obtained. Therefore, an new formula for the bed expansion was developed based on the Richardson–Zaki equation. A good fit of this formula to the experimental results was obtained. Monthly average values of water temperature were compiled, and on this basis the required amount of backwash water and energy was computed. The computations were made for 25% of fluidized bed expansion. Possible energy and water savings were estimated, as well as further gains from keeping the required expansion of the porous bed constant regardless of the wash water temperature.

Analysis of design criteria for biological post-treatment of ozonated wastewater treatment plant effluent

“…H fluid is independent of backwash velocity and can be calculated with eqn (5),where H 0 is the height of the unexpanded filter bed (2 m), ε 0 is the porosity of the unexpanded filter bed, and ρ g is the density of the filter media grains. 89,90 Since ε 0 and ρ g of different filter media differ significantly, H fluid is determined separately for sand ( ε 0 ≈ 0.4; ρ g ≈ 2600 kg m −3 ), anthracite ( ε 0 ≈ 0.5; ρ g ≈ 1400 kg m −3 ), 90 and GAC ( ε 0 ≈ 0.6; ρ g ≈ 1000 kg m −3 ). 91 The resulting values of H fluid are 1.9 m, 0.4 m and 0.002 m, respectively.…”

Reasoning of the Efficiency of Consistent Filtration on Rapid Filters

“…Скорочення кількості промивної води можливе двома шляхами: удосконалення процесу регенерації та подовження тривалості роботи швидкого фільтру в режимі фільтрування, тобто збільшення часу між промивками. Безпосереднє зменшення об'єму води при промивці можливо в результаті застосування повітряно-водяної [5] пульсуючої або дискретної [5,6] промивки, врахування мінливості фізичних властивостей води та завантаження [7]. Важливою задачею при регенерації є також запобігання розшарування зерен фільтруючої засипки [5,8].…”

The Use of Microfiltration for the Pretreatment of Backwash Water from Sand Filters

“…This means there is a need to search for new sources of water and reduce water losses by introducing a circular economy and the sustainable management of water resources [ 2 ]. Roughly 12% of the world’s water is consumed in households, with rapid filtration processes resulting in backwash water that accounts for between 2% and 10% of the plant’s capacity [ 3 ]. Therefore, the wastewater stream is the subject of research on the possibility of its reuse.…”