A method for increasing the efficiency of the dewatering of sludge in wastewater treatment, by increasing the mixing efficiency of polymer, sludge, and air, including the steps of
- (a) Providing an in-line mixing apparatus to a sludge flow stream, said in-line mixing apparatus comprising (1) a mixer housing having a closed-liquid flow conduit configuration;
- (2) a housing inlet at one end of said housing and fluid flow passage;
- (3) a housing outlet at opposed axial ends of said housing and fluid flow passage;
- (4) a fluid flow passage for a sludge stream to flow through said mixer housing from the housing inlet to the housing outlet;
- (5) a rotating axis, said rotating axis traversing the opposed internal walls of the mixer housing at pivot points on the internal walls, (6) a flow restriction device internal to mixer housing and mounted to said rotating axis;
- (7) a controller means controllably engaged to flow restriction device, to control positioning of flow restriction device;
- (8) an air plenum, radially connected to said mixer;
- (9) an air inlet;
- (10) a bubble infusion means;
- (11) an air pumping means for introducing the air, through the air inlet, and through said bubble infusion means, into the fluid flow passage;
- (12) said air inlet means fixedly attached to bubble infusion means;
- (13) a plurality of polymer inlets circumferentially placed around said mixer, upstream of said bubble infusion means;
- (14) a polymer conduit axially connected to said polymer inlets;
- (15) a polymer pumping means for introducing polymer through the polymer inlets, and through the said conduit for polymer, into fluid flow passage;
- (16) a zone of intense mixing for mixture of sludge-polymer-air, said zone immediately downstream of interface between the fluid flow passage and the bubble infusion means;
- (17) a throat, said throat comprising an opening for sludge flow travel along the longitudinal axis of said mixer housing immediately downstream of zone of intense mixing, said throat having a cross-sectional area less than cross-sectional area of said housing inlet, said throat having a cross-sectional area less than cross-sectional area of said housing outlet;
- (18) said bubble infusion means provided upstream of said throat section;
- (19) a first conduit means connecting said throat to said housing inlet;
- (20) a second conduit means connecting said throat to said housing outlet, said conduit means having a width that increases in a divergent manner as it moves axially from said throat to said mixer housing outlet;
- (21) pressure gauge means to measure pressure of sludge mixture inside housing;
- (b) Adding polymer to said sludge stream upstream of flow restriction device at said in-line mixing apparatus;
- (c) Adding air to said sludge stream downstream of the polymer addition at said in-line mixing apparatus;
- (d) Adding polymer and air into the sludge stream, independent of mixing energy, over changes in flow rate up to 33%, by adjustably controlling the speed of the sludge flow through the in-line mixer, during changes in the rate of sludge flow through the in-line mixer, by adjustably restricting the sludge flow with said flow restriction device;
- (e) Shearing air bubbles into sludge stream with the force of the perpendicular velocity of the sludge flow stream flowing perpendicular to the introduction of air into the sludge flow stream;
- (f) Creating highly charged air bubbles to aid the charge-driven activity of floc formation in dewatering, through the interaction of bubbles colliding with one another in the sludge flow after shearing.