Backwash Method Research Articles

Classification of Suspensions by Means of Rotating Filter Discs and Autodynamic High‐Frequency Backwashing

AbstractA new method for the classification of suspensions by means of rotating filter discs is presented. The classification without a filter cake buildup by means of a single shaft disc filter is possible using the high‐frequency autodynamic backwashing method. High‐frequency autodynamic backwashing results from an overpressure fluctuation between the filtrate and concentrate sides, resulting in different flow directions of the filtrate volume flow. The main parameters are the centrifugal force acting on the fluid inside the discs in combination with the fact that the discs are slightly inclined. It is demonstrated that the separation of coarse particles is entirely possible.

The substitution of sand filtration by immersed-UF for surface water treatment: pilot-scale studies

The newly issued National Drinking Water Standard required that turbidity should be lower than 1 NTU, and the substitution of sand filtration by immersed ultrafiltration (immersed-UF) is feasible to achieve the standard. This study aimed to optimise the operational processes (i.e. aeration, backwashing) through pilot scale studies, to control membrane fouling while treating the sedimentation effluent. Results indicated that the immersed-UF was promising to treat the sedimentation effluent. The turbidity was below 0.10 NTU, bacteria and E. coli were not detected in the permeate water. The intermittent filtration with aeration is beneficial to inhibit membrane fouling. The critical aeration intensity is observed to be 60.0 m(3) m(-2) h(-1). At this aeration intensity, the decline rate of permeate flux in one period of backwashing was 1.94% and 7.03% for intermittent filtration and sustained filtration respectively. The different membrane backwashing methods (i.e. aeration 1.5 min, synchronous aeration and water backwashing 2 min, water backwashing 1.5 min; synchronous aeration and water backwashing 3 min, water backwashing 2 min; aeration 3 min, single water backwashing 2 min; synchronous aeration and water backwashing 5 min; single water backwashing 5 min) on the recovery of permeate flux were compared, indicating that the synchronous aeration and water backwashing exhibited best potential for permeate flux recovery. The optimal intensity of water backwashing is shown to be 90.0 L m(-2) h(-1). When the actual water intensity was below or exceeded the value, the recovery rate of permeate flux would be reduced. Additionally, the average operating cost for the immersed UF membrane, including the power, the chemical cleaning reagents, and membrane modules replacement, was about 0.31 RMB/m(3).

Development of novel backwash cleaning technique for reverse osmosis in reclamation of secondary effluent

The objective of the study was to further develop a novel cleaning technique for reverse osmosis in reclamation of municipal secondary effluent. This technique is a new backwash method via direct osmosis (DO) by intermittent injection of the high salinity (HS) solution without stopping of high pressure pump and it is environment and membrane friendly technique. In the study, DO-HS trials were carried out with a UF-RO pilot system which was operated on site with the secondary treated effluent as the raw feed. Different operating conditions for DO-HS treatment in the actual process were investigated. It was found that the operation for implementation of the DO-HS cleaning technique developed was easy. For the first time, the actual profiles of HS concentration, DO backwash flow rate, brine flow rate and permeate pressure during DO-HS treatment have been demonstrated. It was observed that turbidity of the brine stream during DO-HS treatment at 3 NTU was 5 times higher than that before DO-HS treatment. The results from this study have confirmed the previous hypothesis with DO-HS treatment that there would be a strong driving force for DO backwash to lift and sweep the foulants from the membrane surface which would be carried over to the brine. The optimal plant operating conditions in terms of RO feed flow rate, HS concentration and HS injection time are ready for the DO-HS method to be adopted and validated in a long-term continuous plant operation.

Boiler feed water deoxygenation using hollow fiber membrane contactor

A pilot plant scale hollow fiber membrane system was developed for the removal of dissolved oxygen from boiler feed water via vacuum degassing process. Feed water was introduced to the shell side; a vacuum was applied to the lumen side of the hollow fiber. The effects of water flow rate, vacuum level, and water temperature on removal efficiency of dissolved oxygen and mass transfer coefficient were investigated. The membrane fouling issue was further addressed on the membrane used on the full-scale system. The foulants were identified by SEM, ATR/FTIR, EDX and water analysis to be the organic matter with the combination of aluminum silicate. Mass transfer resistances of the fouled membrane were also theoretically calcualted. Finally, two membrane cleaning methods were investigated and the air backwash method was found to be effective to clean the fouled membrane and was recommended as the regular cleaning method.

A Study on the Optimum Backwashing Method applied to Activated Carbon Process in Waterworks

For applying the optimum backwash method to activated carbon absorption process, this study had performed an efficiency test of backwash method and a test for determination of backwash period at the M water purification plant in Daegu metropolitan city. The minimum fluidization velocity was different according to kinds of carbon like spent carbon and reactivated carbon. Changing water position before backwashing was more efficient in backwashing than controlling backwash time. In the case of water position LL(a height of 60cm over the outer layer of activated carbon) before backwashing, the most efficient backwash method has turned out to be 10 min. of air wash and 18 min. of water wash. The turbidity of activated carbon filter outflow water and organic matter change have no big difference according to the days of seasonal operation after backwashing. As backwash period is very related to microbiological growth and is influenced by outflow water change, the study has found that it's desirable to operate in consideration of HPC(Heterotrophic plate counter) distribution of filtered outflow water, water quality, the condition of a filter basin and the years of activated carbon use.

Novel method for enhancing permeate flux of submerged membrane system in two-phase anaerobic reactor

A two-phase anaerobic reactor system with a submerged membrane in the acidogenic reactor was designed for the enhancement of organic acid conversion and methane recovery. A submerged membrane system in a two-phase anaerobic reactor was tested to increase the sludge retention time (SRT) of acidogen and to enhance the solid separation. The pilot plant experiment was performed for piggery wastewater treatment for a year. The membrane material used was mixed esters of cellulose of 0.5 μm pore size. COD removal efficiency was 80% and the methane production showed 0.32 m 3/kg COD removed for the submerged membrane system in the anaerobic digester. As the cake resistance of the membrane caused a serious problem, a stainless-steel prefilter and air backwashing methods were applied to minimize the cake resistance effectively. Among the tested prefilters, the 63 μm pore prefilter showed the best performance for reducing cake resistance and a successful long-term operation. By cleaning with alkali first and acidic solutions later, the permeate flux decreased by long-term operation was recovered to 89% of that with a new membrane.

Process optimisation of a combined system of floating medium and sand filter in prawn farm effluent treatment

A treatment technology known as “a combined system of floating medium and sand filter (FMSF)” was developed and tested successfully with prawn farm effluent. This system has a remarkable techno-economical advantages. Laboratory and semi pilot-scale studies were carried out to optimise the filter bed depth, backwash method and other operating conditions. The dewatering characteristics of sludge from filter backwash was also analysed. The filter was operated at a high rate. The experimental results indicated that: (i) in case of no in-line chemical addition, the smaller ratio between floating medium and sand filter depth gave rise better filter performance. At the filtration rate of 7.5–20 m3/m2.h and with an in-line chemical addition, the suitable depth of floating medium varied from 400–1000 mm for a sand filter depth of 400 mm; (ii) frequent (once in every 90–120 minutes) but short duration of backwash (not more than 60 seconds) was found to be suitable. During the backwash, the water and air were sent for 30 seconds in upward direction and then followed with upflow of water for another 30 seconds. Backwash water amount comprised only 1.2–1.8% of the filtered water production. A mechanical backwash system using rotating paddles is a promising alternative for floating medium filter; and (iii) the filterability of the sludge from filter backwash was low in case of no in-line chemical addition (specific resistance, r = 9.34 × 1010 m/kg) but improved with in-line flocculant addition (r = 3.07 × 109 − 1.29 × 1010 m/kg).

Process optimisation of a combined system of floating medium and sand filter in prawn farm effluent treatment

A treatment technology known as “a combined system of floating medium and sand filter (FMSF)” was developed and tested successfully with prawn farm effluent. This system has a remarkable techno-economical advantages. Laboratory and semi pilot-scale studies were carried out to optimise the filter bed depth, backwash method and other operating conditions. The dewatering characteristics of sludge from filter backwash was also analysed. The filter was operated at a high rate. The experimental results indicated that: (i) in case of no in-line chemical addition, the smaller ratio between floating medium and sand filter depth gave rise better filter performance. At the filtration rate of 7.5 – 20 m3/m2.h and with an in-line chemical addition, the suitable depth of floating medium varied from 400-1000 mm for a sand filter depth of 400 mm; (ii) frequent (once in every 90–120 minutes) but short duration of backwash (not more than 60 seconds) was found to be suitable. During the backwash, the water and air were sent for 30 seconds in upward direction and then followed with upflow of water for another 30 seconds. Backwash water amount comprised only 1.2–1.8% of the filtered water production. A mechanical backwash system using rotating paddles is a promising alternative for floating medium filter; and (iii) the filterability of the sludge from filter backwash was low in case of no in-line chemical addition (specific resistance, r = 9.34 × 1010 m/kg) but improved with in-line flocculant addition (r = 3.07 × 109 – 1.29 × 1010 m/kg).

Crossflow filtration of yeast broth cultivated in molasses

A broth of yeast cells cultivated in molasses was crossfiltered with a thin-channel module. The permeation flux gradually decreased at a constant cell concentration. The flux was much lower than that obtained for yeast broth cultivated in yeast extract, polypeptone, and dextrose (YPD) medium during the filtration. The flux did not depend on the membrane pore size (0.45 to 5 mum). The steady-state flux was one-twentieth that calculated for a cake filtration mode from the amount of cake per unit filtration area and the specific resistance of the cake measured in a dead-end filtration apparatus. The lower flux was due to small particles (most of which were less than 1 mum in diameter) in the molasses. The mehanism of crossflow filtration of broths of yeast cells cultivated in molasses was clarified by analysis of the change in flux with time and observations with scanning electron microscopy. At the initial stage of crossflow filtration the yeast cells and particles from the molasses were deposited on the membrane to form the molasses were deposited on the membrane to form a cake in a similar way to dead-end filtration. After the deposition of cells onto the membrane ceased, the fine particles from molasses formed a thin layer, which had higher resistance than the cake formed next to the membrane. The backwashing method was effective to increase the flux. The flux increased low when the pore size was 0.45 to 0.08 mum, but using larger pores of 3 to 5 mum it returned almost to the bases line. (c) 1994 John Wiley & Sons, Inc.

Hollow fiber membrane based on polyacrylonitrile with a high degree of polymerization and its properties

For the first time a hollow fiber membrane has been prepared based on polyacrylonitrile with a high degree of polymerization. From the examination of its microstructure using FE-SEM and UHR-FE-SEM microphotographs it was shown that the outer surface consists of a skin layer with a pore size of 10 to 30 nm and that the interior consists of a sponge-like layer without large voids. The pure water flux was 500 ml/hr-mmHg-m 2 at 25°C. The rejection of polystyrene latex beads of uniform size with an average diameter of 38 nm was > 99% and that of dextran with an average molecular weight of 2 × 10 6 was approximately 70%. Although the differential pressure of the membrane gradually rose caused by the capture of particles on the membrane surface when water containing suspended iron compounds was fed to the hollow fiber, the pressure could be easily returned to its initial value using the backwash method.

4537687 Open gravity backwash filter and method : Louis H Piper assigned to Infilco Degremont Inc

4537687 Open gravity backwash filter and method : Louis H Piper assigned to Infilco Degremont Inc

Fluorimetric method for the determination of long-chain amines in water

A method is presented for the determination of long-chain quaternary ammonium salts, tertiary amines and secondary amines in water or aqueous raffinates, based on their extraction and fluorimetric determination as amine salts with Eosine Yellowish in toluene—hexanol (4:1) as solvent. No interferences were obtained from metal ions, or chloride, nitrate or phosphate ions when a back-washing method was applied to the sample extract. The method allows the determination of long-chain tertiary amines down to 4 ppM.

Public Water Supplies of Queensland, Australia

This article provides a comprehensive discussion of public water supplies of Queensland, Australia. It begins by classifying Queensland's sources of water supplies into six categories, followed by a discussion of the number of supply systems, population served, and per capita consumption. Treatment practices are discussed, along with treatment plant design, filter backwashing methods, and disinfection. The Brisbane River system, the only major river system in Queensland, is described in detail with specific focus on the town of Miles water supply, Bribie Island water supply, and the Helidon water supply.