Wastewater treatment system

Abstract

A system for treating a wastewater stream produces an effluent having an acceptable level of turbidity. A PID controller is operatively coupled to at least one turbidity meter for monitoring turbidity of the effluent stream. A plurality of chemical treatment additive pumps are provided for adding a plurality of treatment chemicals to the wastewater stream in real time under supervision of the controller, and responsive to monitored turbidity.

1 . A system for treating a wastewater stream to produce an effluent stream, comprising:
 a plurality of pumps for supplying a plurality of chemical additives at variable flow rates to said wastewater stream at a plurality of points;   at least one total suspended solids sensor disposed in said wastewater stream downstream of said chemical additives for monitoring the clarity of said wastewater stream; and   a proportional-integral-derivative (PID) for monitoring said flow rate of said wastewater and varying the flow rates of said chemical additives proportionally based upon an algorithm employing each of a proportional term, a derivative term, wherein the PID is configured to set the derivative term for a rapid response dosing scheme, achieved with a predetermined gain in a derivative loop, without over dosing due to an over-shoot; and an integral term, wherein the PID is configured to set the integral term to achieve a desired effluent quality, the value of which is pre-set, in the fastest time possible;   wherein, based upon turbidity measurements made by said at least one sensor, said controller continually and in real time makes chemical adjustments to the system to keep the effluent in a predetermined and set range.   
     
     
         2 . The system of  claim 1 , comprising:
 at least one coagulant pump having a variable flow rate for delivering a coagulant to said wastewater stream; and   at least one polymer pump having a variable flow rate for delivering a polymer to said wastewater stream.   
     
     
         3 . The system of  claim 1 , comprising:
 a second total suspended solids sensor disposed in said effluent stream for monitoring the clarity of said effluent.   
     
     
         4 . The system of  claim 3 , comprising:
 an output from said second total suspended solids sensor representative of effluent clarity operatively coupled to an input of said controller, wherein an output exceeding a predetermined threshold causes said controller to change the chemical dosing.   
     
     
         5 . The system of  claim 1 , comprising:
 a plurality of points of chemical injection through which said wastewater stream is passed, wherein said chemical additives are supplied to said system through said points of chemical injection.   
     
     
         6 . The system of  claim 5 , wherein said first total suspended solids sensor is disposed downstream of a plurality of flocculent tubes. 
     
     
         7 . The system of  claim 1 , comprising:
 at least one pH meter in fluid communication with said wastewater stream having an output representative of the pH of said wastewater stream operatively coupled to said controller; and   at least one pH additive delivery pump for supplying an acidic or alkaline solution to said wastewater stream responsive to said pH meter.   
     
     
         8 . The system of  claim 1 , comprising:
 an automatic cleaning system for said sensor, comprising a clean water source, and a chemical addition system on a timer that interfaces with said PID.   
     
     
         9 . The system of  claim 1 , wherein said PID is set to meet a performance, costing, or a combination of performance and costing objectives;
 wherein said PID controller is set with a high gain for said proportional and integral terms to insure a quick and thorough response to an elevation in contamination in an effluent, providing an acceptable level of chemical over-shooting where compliance is required; and   wherein said PID is set with lower values for the proportional and integral terms and a higher gain for the derivative terms, providing a less responsive system that minimizes chemical over-shooting where maximum cost efficiency is required.   
     
     
         10 . The system of  claim 1 , wherein gain for said integral term is set at a highest value possible for quickest system recovery to return water quality to an acceptable level for discharge in a shortest time possible;
 wherein a large amount of variation in contaminant loading requires a higher gain in the integral term to accommodate loading swings; and   wherein a low amount of variation in contaminant loading requires a lower gain in the integral term.   
     
     
         11 . The system of  claim 1 , wherein gain for the derivative term is set at a highest value possible to ensure a lowest chemical over-shoot;
 wherein a small amount of variation in contaminant levels requires a higher gain value in the derivative term to provide small changes in chemical necessary dosages with a minimal amount of over-shooting; and   wherein a large amount of variation in levels of contamination requires a smaller gain in the derivative term to provide a quick recovery back to a desired set point;   wherein said set point is that which provides a desired water quality for a concentration of contaminants being treated.