To remove seaweed, twigs, colloid etc. that would be suspended particles in the sea water our desalination systems choose to use multi medium filters, which is use of quartz sand, anthracite two filter material removal of suspended matters in the raw water, is a common fast filter equipment.
How Multi-medium Filter Works
The water with suspended particles is sufficiently mixed with the flocculant to form a double layer of colloidal particles in the water. When the colloid particle flows through the filter material layer of the multi medium filter, the gap of the filter material plays the role of screening and filtering to make the suspended matter easy to adsorb on the surface of the filter material.
When a certain amount of dirt is trapped in the surface of the filter, the filter is formed, and the pressure difference between the filter and the filter will be increased. At this time need to use reverse flow backwashing filter, loosen the filter g. and smokeless coal suspension, so that the adhesion on the surface of quartz sand, anthracite interception stripping and is carried by a stream of water, to restore the filtering function. Used in the project of dual media is placed in the upper part of the filter layer of the lighter particle anthracite, lower for the high proportion of small particles of quartz sand. Only in this way can give full play to the filter efficiency, improve the capacity of sewage interception.
How to Maintain Multi Medium Filter
1. Daily operation check:
The operator should regularly inspect the equipment on the spot every hour. Record the results of the inspection, together with the operation records to give a summary, as a regular maintenance of the information.
| Inspection cycle | Inspection items | Check method or check point | Remarks |
| Once per shift | Check whether there is leakage | sealing parts and the auxiliary valve whether is leaking. | If there is vibration, identify the cause, take timely measures to solve
Check flow |
| Check whether there is vibration | When the valve is closed, whether there is abnormal vibration | If there is vibration, identify the cause, take timely measures to solve | |
| Once a month | Check flow | Check the flow meter to verify that the flow is normal. | If the flow display is not normal, timely identify the reasons, troubleshooting |
2. Regular inspection:
Equipment to carry out regular inspections, the purpose is to ensure the safe operation of the system over a long period of time. The equipment is relatively large equipment, inspection operations require a longer time. In order to shorten the time to check the parking time, should try to and the original water treatment equipment and other equipment maintenance at the same time, if found abnormal, should be timely treatment.
| No. | Inspection items | Inspection method |
| 1 | Packing inspection | Check quartz sand anthracite filter material, such as quartz sand anthracite pollution is serious, should all be replaced. |
| 2 | Filter cap inspection | Remove the filler, rinse with water, the filter cap on the porous plate to check, found damaged or loose, timely replacement or fixed. |
| 3 | Rubber lining inspection | If found lining layer has a bubble, crack, peel, micropore to be repaired |
| 4 | Internal fastener inspection | Check the bolts, nuts and other fasteners in the filter, such as loose should be tightened. |
| 5 | Manhole seal check | Replacement of deformation of the manhole gasket, bolt and nut dipped in the cleaning oil, rust cleaning; manhole cover mounting bolt nut butter. |
3. Filter replacement:
| No. | Operation steps | Operation method |
| 1 | drainage | Water accumulation inside the filter |
| 2 | Unloading | Open the filter backwash discharge port, from a small amount of water will fill out the mouth. |
| 3 | clearing | Drain the water filter, open the manhole, into the filter, filter out the remaining filter |
| 4 | cleaning | Clean the inside of the filter with a rag |
| 5 | Filling material | Closed discharge port, according to the provisions of high fill fill filter material, the first loaded quartz sand, after loading and unloading flat, and then loaded with anthracite |
| 6 | Closed filter | Check the loading height of filter material to meet the requirements, closed on manhole |
| 7 | Washing filter | According to the step filter backwash flushing filter, to drainage turbidity less than 1 degrees |
Filter material:
(1) Anthracite (upper layer): particle size: 0.8-1.2mm; thickness: 400mm
(2) Quartz sand (lower layer): particle size: 0.4-0.65mm; thickness: 800mm
