Backwashing permeate

Liquid Bacbpulse Solid membranes are backwashed by forcing permeate backward through the membrane. Frequent pulsing seems to be the key. 

Air Bacfiflush A configuration unique to microfiltration feeds the process stream on the shell side of a capillary module with the permeate exiting the tube side. The device is run as an intermittent deadend filter. Every few minutes, the permeate side is pressurized with air. First displacing the liquid permeate, a blast of air pushed backward through the membrane pushes off the layer of accumulated solids. The membrane skin contacts the process stream, and while being backwashed, the air simultaneously expands the capillary and membrane pores slightly. This momentary expansion facilitates the removal of imbedded particles. 

There are advantages to hard piping most of the RO system, but some piping needs to remain open so that flows can be observed and measured. In particular, waste flows to drain, such as filter backwash waste, RO reject, and RO permeate divert streams, should be accessible before they enter the drain so that they can be easily observed and sampled if needed waste-flow piping should end 6 to 10 inches above the drain. 

The oscillated backflushing mechanism accounts for the effect of the pressure waveform on TMP. When the minimum pressure of the pulsatile pressure waveform results in a negative TMP, a reverse permeate flow may occur that acts as a backwash flow that drives particles deposited on or near the membrane surface back to the bulk flow. In this way, concentration polarization and cake formation caused by the filtration operation could be limited, depending on the properties of the particles and the magnitude of the reverse pressure. 

A number of operating parameters need to be studied to optimize the overall filtration performance. Critical among these are the cross-flow velocity, transmembrane pressure, pore diameter, or MWCO and concentration of the retained species at the end of a batch operation or steady state concentration in continuous filtration. This latter parameter can be related to the recovery of product in the permeate or retentate. Other important operating variables are temperature (and hence viscosity), pH, backpulse or backwash, and pretreatment. 

Use crossflow batch with 100% retentate recycle, continuous bleed with recycle ratio 15 to 30/1 and multistage when a concentrated retentate is desired or when particle diameter <0.1 pm. Criterion to backwash/or clean when 90% reduction in retentate volume is achieved given quality or volume of permeate the permeate flux <15% of initial flux or when the viscosity of the retentate is 100 to 300 mPa s. This corresponds to concentrations for pigments of 30 to 70% for microorganisms of 1 to 10%. 

Cycle time clean by backwashing with permeate every 6, 24,170, 360, 1000 h (depending on the criteria, the membrane, operating conditions, and the amount of pretreatment) example, 8 h on and 1 to 2 h off to clean or short pulses every 150 to 300 s so that steady-state flux operation is never achieved. 

Of the process options considered, microfiltration (TVIF) is the membrane process with the largest pores. It is generaLl) used for waters of high turbidity, and low colour or organics content. MF can remove bacteria and turbidity . MF is also a common pretreatment process for NF and RO. The fact that MF pores are relatively large allows cleaning methods, such as air backflush or permeate backwash, which remove deposits from pores and surface. 

The relatively large pores of MF allow the removal of the deposit using air backflush or permeate backwash. Crossflow, rather than dead-end filtration mode, can be used to control the thickness of the... 

Permeate backwash is a possible means to remove cake deposit in UF. The choice of a more hy drophilic membrane can decrease adsorption significantly and changes in the solution chemistry can impact on the deposit structure and porosity. 

The MF unit was operated at 0.6 bar with the feed tank continuously fed with surface water direcdy from the bottom of the dam. Concentrate and excess permeate, were both recycled to the feed tank, generating a continuous overflow. Filtration cycles were of 4 to 10 minutes and samples were taken immediately after backwash in order to have a comparable water quality with lowest losses of organic material due to filter cake buildup. 

Smith et al. [80] studies the effect of backwash in maintaining the flow in membrane systems and concluded that the performance of this procedure, during the process of membrane filtration, can effectively remove most of the compounds responsible for the reversible fouling of the membrane, reducing the pressure of work and increasing the permeate flux. 

Use crossflow batch with 100% recycle continuous with recycle ratio 15-30/1 or multistage (often three stages). Criterion to backwash and clean operate until a given concentration or volume reduction is reached in the retentate or a given purity or volume is achieved in the permeate. 

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