Water treatment plant and corresponding method

A ballasted flocculation water treatment system for treating water containing suspended solids comprising:

• a line for directing the water into the system;
• a coagulant line configured to direct a coagulant into the water to form a coagulated water;
• a flocculating-settling device configured to receive the coagulated water and comprising:
• (i) an external tank including a first hopper and a treated water outlet;
• (ii) an internal tank disposed in the external tank and including a stirrer and a second hopper;
• (iii) a space defined between the internal tank and the external tank;
• (iv) a flocculant line configured to direct a flocculant into the internal tank;
• (v) a ballast line configured to direct a ballast into the internal tank;
• (vi) wherein the stirrer in the internal tank is configured to mix the flocculant, the ballast and the coagulated water and produce ballasted floc;
• (vii) said second hopper including an aperture that opens into the external tank and the first hopper and which is configured to direct ballasted floc from the second hopper into the external tank;
• (viii) a decantation zone in the external tank and formed at least partially below the internal tank and configured to separate the water from the ballasted floc;
• (ix) wherein the first hopper forms a settling zone where the ballasted floc from the internal tank thickens and settles to form a ballasted sludge;
• (x) said first hopper including an outlet configured to discharge the ballasted sludge from the first hopper;
• and
• (xi) a ballasted sludge discharge line operatively connected to the outlet of the first hopper and configured to discharge the ballasted sludge that exits the outlet of the first hopper.

A method of treating water in a flocculating-settling device comprising:

• mixing a coagulant with the water to form coagulated water;
• directing the coagulated water to the flocculating-settling device which includes an external tank an internal tank contained in the external tank;
• directing the coagulated water into the internal tank;
• directing a flocculant and a ballast into the internal tank;
• with a stirrer contained in the internal tank, flocculating the water by mixing the water, the ballast and the flocculant to form a mixture containing ballasted floc;
• during the course of mixing the water, the ballast and the flocculant, directing the mixture upwardly through a flow guide tube, contained in the internal tank, and directing the mixture from the top of the flow guide tube downwardly through a space defined between the internal tank and the flow guide tube;
• directing the water in the internal tank downwardly through an aperture in a hopper that forms a lower part of the internal tank and into the external tank;
• wherein the water in the external tank then flows upwardly through the external tank and between the external tank and the internal tank to where the water is discharged from a top portion of the external tank;
• directing the ballasted floc through the aperture of the hopper of the internal tank into a hopper that forms a lower part of the external tank;
• settling the ballasted floc in the hopper of the external tank and in the process yielding a ballasted sludge in the hopper of the external tank;
• directing the ballasted sludge from the hopper of the external tank to a ballast separator and separating the ballast from the ballasted sludge to yield separated ballast and separated sludge;
• and
• recycling the separated ballast to the internal tank.