Method of and apparatus for filtering

A contaminated liquid filter apparatus comprising, a primary inlet and primary outlet, a first bed of granular filter medium interposed between said primary inlet and primary outlet, a secondary inlet and secondary outlet, a second bed of granular media interposed between said secondary inlet and secondary outlet, a tertiary inlet and tertiary outlet, a third bed of granular filter media interposed between said tertiary inlet and tertiary outlet, liquid transporting means connecting said primary outlet to said secondary inlet, liquid transporting means connecting said secondary outlet to said tertiary inlet, said first bed including at least one distinct layer of granular filter medium, said second bed and third bed each including at least two distinct layers of granular filter media, the layers in said second and third bed being intermixed along an interface, means for supplying contaminated liquid to said primary inlet, said tertiary bed having a filtration cross-sectional area at least approximately three times greater than that of the first bed, and said secondary bed having a filtration cross-sectional area at least approximately twice as large as that of the first bed such that a greater flow rate is established through said first bed to cause larger contaminants to penetrate yet be retained by said first bed, and such that a reduced filtration flow rate is established through the successive beds to enable such beds to more efficiently entrap and retain smaller contaminants, and the average size of granules of filter media of each distinct layer being larger than the average size granules of filter media of a successive layer in the direction of filtration flow.

In a method of filtering, comprising the steps of:

• flowing a contaminated liquid at a first flow rate through a first filter layer of substantially uniform graular medium size to obtain a partially filtered liquid flow, said first flow rate being sufficient to cause substantially all the particulate contaminants in said contaminated liquid to penetrate the inlet surface of said first filter layer to thereby minimize blinding off of the first layer by accumulation of contaminants at said inlet surface;
• flowing the partially filtered liquid at said first flow rate successively through a first interface layer and a second medium layer, said second medium layer comprised of a substantially uniform granular medium size finer than that of said first filter layer, said interface layer comprised of a mixture of granules from both said first and second layers, said interface layer being in intimate contact with and between said first and second layers thereby reducing the accumulation of contaminants at the inlet surface of said second layer during filtration flow;
• flowing the liquid from said second layer and through a third filter layer at a second flow rate less than said first flow rate, said first flow rate being at least approximately twice as great as said second flow rate, and said third filter layer being separated from said second layer and comprised of a substantially uniform size granular medium finer than said second layer granular medium;
• flowing the liquid from said third layer successively through a second interface layer and a fourth filter medium layer at said second flow rate to generate a clarified liquid flow, said fourth medium layer comprised of a substantially uniform granular medium size finer than said third granular medium size, said second interface layer comprised of a mixture of granules from both said third and fourth medium layers and being between and in intimate contact with said third and fourth layer thereby reducing the accumulation of contaminants at the inlet surface of said second layer during filtration flow.

In a method of filtering a contaminated liquid, the steps of:

• 1. flowing the contaminated liquid at a first flow rate through a first filter vessel containing at least two distinct, vertically superimposed layers of granular filter medium, said first flow rate being sufficient to cause substantially all of the contaminants to penetrate the first layer in a direction of filtration flow, said layers being intermixed along an interface to enhance particulate contaminant penetration into the second layer in the direction of filtration flow, and the granules of said first layer having an average size larger than the average size of the granules in said second layer;
• 2. subsequently flowing the liquid from said first vessel through at least two additional distinct, vertically superimposed layers of granular filter medium in a second filter vessel at a flow rate which is approximately only about one-half the flow rate through the first vessel to cause substantially all of the non-filtered contaminants to penetrate the first layer in the direction of filtration flow in the second vessel yet be entrapped within either said first or second additional layers, said additional layers being intermixed along an interface to enhance particulate contaminant penetration into the second additional bed in the direction of filtration flow, and the granules of said first additional layer having an average size smaller than the average particle size of the granules comprising the second layer in said first vessel but larger than the second layer in the second vessel;
• 3. rejuvenating the filter layers by introducing backwash liquid into each of said vessels in the opposite direction of filtration flow at a rate to expand said layers and remove a substantial portion of accumulated contaminants;
• and
• 4. reforming the distinct superimposed layers and intermixed interface regions in each vessel after backwashing.