Secondary effluent filtration

[Lan123]

I would like to hear forum members experience on using single media rapid sand filtration unit (polishing) to filter municipal extended aeration secondary effluent. If a coagulant (Alum)is added, is settling before the filter a must? What is the type, size and the uniformity coefficient of the filter media used?

Thanks is advance

 

[ch81pc]

Absolutely, settlement is a must. At normal RGF flow rates of 10m3/m2 per hour at a MLSS of 3000mg/l thats 30kg of solids loading per m2 per hour. Your filter will last a matter of minutes rather than hours between washes, especially if operating contact filtration through.

 

[bimr]

Secondary effluent is the effluent from the secondary clarifier.

Filters used for secondary effluent are operated at lower flow rates than rapid sand filters, typically 1/3 less gpm/sq ft.

If you add alum, you can add the alum prior to the secondary clarifier.

You would not add an additional clarification step between the secondary clarifier and the tertiary filter.

 

[ch81pc]

Misunderstood in thinking you were going straight from ASP to filter with no settlement in between. Assuming a post FST solids loading of 20mg/l + whatever your hydroxide loading will be, it will work without pre-settlement, but your washing will be increased.

 

[stanier]

Suggest you should consider dual media filters(coal/sand). The coal will hold a larger quantity of solids between backwashes.

Yes you will need a coagulant if you are going to comply with PEA discharge regulations.

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