Water treatment - multi-media filtration
Water treatment - multi-media filtration
Let's start by saying why does pretreatment require multi-media filtration?
The larger the turbidity, it will cause the pressure difference in the back-end membrane treatment process to become larger, thereby reducing the filtration efficiency of RO membrane and EDI filtration equipment, in order to improve the stability and reliability of the final pharmacopoeia water, the turbidity control of pretreatment is indispensable, and multi-media filtration is an effective way to control turbidity.
The main equipment of the multi-media filtration process is the multi-media filter, which includes two processes: multi-media filtration and backwashing, and today we will share these two processes.
1. Multi-media filtration
Filter Media:
Multi-media filtration refers to the layered filling of sand and gravel, anthracite and other filter materials of different particle sizes in stainless steel containers, as a filter medium anthracite can improve the filtration water production rate, and reduce backwash regeneration, whether from the perspective of deep filtration or water saving, anthracite coal has its advantages.
Packing method:
Usually the larger particle size quartz sand is filled at the bottom end, the smaller particle size quartz sand is filled in the middle, the lighter anthracite coal is usually filled at the top, the original water tank tap water from top to bottom through anthracite and quartz sand gradually fine medium layer to achieve water flow filtration, the main function of the multi-media filter is to filter and remove large particles, suspended solids, colloids and sediment in the raw water, reduce the turbidity of the effluent, so that the turbidity of the effluent is <3, so as to meet the water purification requirements of the subsequent membrane filtration process. Usually, multi-media filters can effectively remove particles in the range of 10~40μm.
According to the different water quality of raw water, flocculant may need to be added to the multi-media inlet pipeline, and the function of flocculant is to turn most of the suspended solids and colloids in the water into microflocculents and improve the interception rate in the multi-media filter layer.
2. Backwashing
When turbidity is removed during the filtration process of multimedia filters, as the pressure drop of the filter media increases, the turbidity level increases, and eventually backwash is required to clean the filter bed. The particles accumulated in the filtration process such as suspended solids, colloids and sediment need to be removed regularly (or based on pressure drop) by backwashing, this kind of right-up flushing or air scouring to achieve the decompression of the filter layer, the multi-media filter bed will be loosened and lifted, so that suspended solids, particles, etc. are discharged from the top of the backwash stream, so as to remove the filtered particle impurities, this process is called backwashing, the backwash flow rate is usually 3~10 times the filtration operation flow. After backwashing, the filter bed settles and re-stratifies, and is put back into use.
3. Maintenance
Over time, the jagged edges of sand and other media can also become rounded, reducing the filtration capacity and requiring timely adjustment of backwash cycles or replacement of filter media based on turbidity data.
