US 4,544,489 A · Process and apparatus for controlled addition of conditioning material to sewage sludge

Abstract

The invention provides processes and apparatus for the controlled addition of conditioning (polymer) material to sewage sludge to improve its dewaterability. These materials are expensive and overdosage is to be avoided, while underdosage causes difficulty in sludge handling. The principal problem has been the absence of a system capable of continuous determination of proper dosage. It has been found that shear stress tests with a viscometer result in characteristics that exhibit a unique peak when dosage is adequate or above. A control system controlling the rate of pumping of the polymer to mix with the sludge is operative by measuring the shear stress and increasing the dosage in the absence of a peak. Upon detection of a peak the rate of decrease after the peak is also measured and used to resolve the potential ambiguity of whether dosage should be increased, decreased or remain steady. The viscometer can be of variable shear rate type, but it is found that the control system can also employ a simple fixed rate viscometer, the shear stress then being evaluated for peak and slope over a predetermined time interval. Specific control strategies are disclosed that will reduce the rate of change of dosage as the optimum is approached to avoid overshoot, and also to increase the time interval between tests to avoid unnecessary operation.

Claims20

Dependent claims

A process for the controlled addition of dewatering conditioning polymer material to a sewage sludge to produce a mixture thereof comprising the steps of:

(a) measuring with a viscometer in a quantity of the sludge/material mixture the value of the shear stress in the said quantity of the mixture to determine the existence or not of a predetermined maximum in the value of the measured shear stress representing a measured shear stress yield value;
(b) in the absence of detection of such a predetermined maximum value increasing the rate of addition of conditioning polymer material to the mixture;
(c) upon the detection of such a predetermined maximum value, measuring the rate of subsequent decrease of the measured shear stress immediately following the maximum value;
and
(d) increasing or decreasing or maintaining the rate of addition of conditioning polymer material respectively as the rate of decrease is less than, or more than, or about equal to a predetermined rate of said subsequent decrease.

2 more elements

Apparatus for the controlled addition of dewatering conditioning polymer material to a sewage sludge to produce a mixture thereof including:

(a) pump means including conduit means for supplying a flow of sewage sludge at predetermined rate of flow to a container therefor;
(b) controllable pump means including conduit means for supplying a flow of conditioning polymer material at a controlled rate of flow to said container;
(c) means for mixing the said flows of sewage sludge and conditioning material to produce a sludge/polymer material mixture;
(d) a viscometer insertable into a quantity of the sludge/polymer material mixture for measuring the shear stress of the sludge/material mixture and producing an output electric signal representative thereof;
(e) means operative to examine the viscometer output electric signal for the detection of a predetermined maximum value therein representing a measured shear stress yield value;
(f) control means responsive to the absence of such detection of a predetermined maximum value signal to control the said controllable pump means to increase the supply of conditioning polymer material to the sludge/polymer material mixture;
(g) means operative to examine the viscometer output electric signal upon the detection of said predetermined maximum output value to determine the value of the rate of subsequent decrease of the measured shear stress immediately following the maximum output value;
(h) the control means being responsive to the said value of the rate of subsequent decrease of the measured shear stress to control the controllable pump means to increase the supply of conditioning polymer material to the mixture, or to decrease the supply of conditioning polymer material to the mixture, or to maintain the supply of the conditioning polymer material to the mixture at its previous value as the value of the rate of decrease is less than, or more than, or about equal to a predetermined value of the rate of said decrease.

5 more elements

Dependencies are inferred from the claim text.

Process and apparatus for controlled addition of conditioning material to sewage sludge

Life of this patent

Process and apparatus for controlled addition of conditioning material to sewage sludge

Life of this patent

Abstract

Claims20