What is the effect of oil on sand bed filtration?

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The filtration step forms part of effluent treatment and is designed to remove Magnesium hydroxide Mg(OH)2 colloids from a high pH effluent stream. The worry is that small amount of free oil entering the effluents upstream (eg due to leak from equipment) will affect filtration. Is anyone aware of industrial practice with similar issues? Is there threshold oil concentration?

 

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12 Answers

  1. Following Disadvantage of oil in sand filtration

    1. The porosity of sand filters will be reduced.
    2. Clogging Problem.
    3. Back wash frequency will be increased.
    4. Running cost will be increased

    Following are remedies

    1. The oil should be separated before feed sand filters.For this purpose oil remove with gravity separation or Disc oil seperators.
    2. If not possible above then it is sugestet for increasing of bed depth specially final bed.(about 18-22”)
    3. The sand should be periodically wetted, allowed to consolidate, and then extra sand added. Repeat this procedure until the bed depth has stabilized at 18-22 inches.
    4. Regularly maintenance of the sand i.e. replacement of sand regular interval.

  2. I am in charge of the waste water treatment unit in a refinery so you could say that I am no stranger to oil making its way into my sand filters. If the oil is presenting itself as a sheen on the surface it will be taken away with each backwash provided you don't drain the filter low enough to let it enter the sand. Dissolved or emulsified O&G in ppm quantities (

  3. Identification of threshold quantity of Oil in the feed of sand filter is depends on the various parameters like quality and quantity of sand, pH, temperature, backwash frequency, etc. Considering the feed conditions, in my knowledge, the effect of oil in the feed does not have major change on the filtration of suspended solids, however, the bed life reduces with requirement of quick backwash frequency, as the adsorbed oil degrades the soil quality.

  5. Thanks very much for the response and comments. These seem to reinforce our view that oil should be avoided. At the moment we are not considering to implement a new process step for active oil removal, rather prevention of oil entering the effluent stream. The question was aimed to assess whether we are being overly cautious and also to gain an understanding of the wider industry practice. The question of a "threshold" concentration is an interesting one. The number of 10ppm (or 20ppm) has been mentioned - although I understand that these at most are guidelines and will depend on the specifics of the effluents chemistry and the treatment system in question. We are likely to recommend further laboratory studies to establish the actual influence of oil on our filters as the concerns over its effect seems to be substantial enough to warrant this. A related but difficult issue is the fate of the oil in the treatment train – this will of course have a direct relevance to the question of how it will affect the sand bed filters. The effluent in our case is high pH, which I think could potentially cause additional problems (frothing?). Andras Paksy

  7. Oil water filtration

    The effect of oil on filtration by sand beds will be disastraous. The oil will form a solid film with individual sand particles and will not allow filtration. But, you are concerned about oil leakage from equipment. If you mean the mechanical equipment as per the WTP design, I don't think you have to worry. That is too small to be of any consequence. I am considering normal oil leakage from lubrication chamber of equipment.

    Where in the line do you anticipate oil contamination from equipment? The machinery may be

    1. Pump: Here there is no scope for any oil contamination

    2. Clarifier : Possible of course but the central pillar is usually guarded by a circular closed enclosure. The mechanism will be grease lubricated (the worm gear and the pinion).

    There are ways of cleaning oil from water but you need not be concerned about them as you won't be needing them.
    If you feel that you should do something, I propose a oil skimmer. However, I have seen many RG filter beds and there isn't any oil. Perhaps you need to check if the machines upstream are leaking excessive oil.

    The Oil & Gas Industry faces problems of this type. The pneumatic automation industry also faces this problem. There is a empirical threshold concentration value but I will have to look it up.

    Regards

    Arindom Borah

  8. Oil is very bad for sand filters. What is the oil concentration you expect? If it is high (20-500 ppm), I recommend using a process including flotation and filtration. If it is low (

  10. You shall remove oil before filtration, specially if you are using sand filter that works based in superficial filtration, otherwise you have to backwash your filter more frequently. free oil as you refer to is easy to be removed. In case you can not do it you can try to use a double media filter (anthracite and sand) .

  11. Not sure about a threshold oil concentration, but treating oily water at refineries has a similar issue. I know of a flowsheet that uses oil plate interceptor, pH adjustment, induced air flotation, activated sludge, and then sand filtration. The gradual acuumulation of oil on the sand filter results in frequent backwashes and a treated water that is much closer to the consent values than would be wanted from a filtered effluent.

  12. Dear Andras, We can control oil by placing oil and grease trap which is operated automatically or manually. This will be available based on the flow volume and needs to be replaced once in a while.