Process for the treatment of a flow of waste water by low-pressure filtration

A method of treating water containing suspended solids and metal ions comprising:

• pre-treating the water;
• after pre-treating the water, directing the water to and through one or more microfiltration or ultrafiltration membranes and producing a first permeate and a first concentrate;
• flowing the water tangentially to the microfiltration or ultrafiltration membranes at a velocity of at least 0.1 m/s;
• mixing an organic sequestering agent with the water at or upstream of the microfiltration or ultrafiltration membranes and wherein the sequestering agent comprises organic phosphonates;
• mixing a sufficient amount of organic phosphonates with the water to achieve a concentration that is effective for sequestering metal ions contained in the water and minimizing the formation of calcium carbonate;
• after sequestering the metal ions and minimizing the formation of calcium carbonate, adsorbing the organic phosphonates onto the suspended solids in the water;
• and
• maintaining a differential pressure across the microfiltration or ultrafiltration membranes that is less than or equal to 5 bar.

A method of treating water containing suspended solids and metal ions comprising:

• filtering the water in one or more microfiltration or ultrafiltration membranes while maintaining the differential pressure on either side of the membrane less than or equal to 5 bar to generate a first permeate and a first concentrate;
• flowing the water tangentially to the microfiltration or ultrafiltration membranes at a velocity of at least 0.1 m/s during said filtering;
• mixing an organic sequestering agent comprising organic phosphonates with the water at or upstream of the microfiltration or ultrafiltration membranes at a concentration effective for sequestering metal ions contained in the water and minimizing the formation of calcium carbonate;
• and
• filtering at least a portion of the first permeate in one or more nanofiltration or reverse osmosis membranes to produce a second permeate and a second concentrate.