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 method for treating a wastewater stream to produce an effluent stream, the method comprising:
 providing a plurality of pumps that supply a plurality of chemical additives at variable flow rates to the wastewater stream;   providing a first sensor that is disposed within the wastewater stream downstream of the plurality of pumps and that continuously samples directly from the wastewater stream to monitor clarity of the wastewater stream;   using a proportional-integral-derivative (PID) controller to monitor flow rate of the wastewater stream, and
 vary the flow rates of the plurality of chemical additives based upon an algorithm employing each of:
 a proportional term, 
 a derivative term set for a rapid response dosing scheme without overdosing due to an over-shoot, and 
 an integral term set to achieve a desired effluent quality in the fastest time possible; and 
 
   continually injecting, by the plurality of pumps based upon measurements made by the first sensor, the plurality of chemical additives into the wastewater stream in real time responsive to adjustments specified by the PID controller to keep the clarity of the effluent stream in a predetermined and set range.   
     
     
         2 . The method of  claim 1 , wherein the first sensor is selected from:
 a biological oxygen demand (BOD) sensor;   a chemical oxygen demand (COD) sensor;   a conductivity sensor;   a potential of hydrogen (pH) sensor;   a total suspended solids (TSS) sensor; and   a turbidity sensor.   
     
     
         3 . The method of  claim 1 , further comprising:
 providing at least one coagulant pump that delivers a coagulant to the wastewater stream at a first variable flow rate; and   providing at least one polymer pump that delivers a polymer to the wastewater stream at a second variable flow rate.   
     
     
         4 . The method of  claim 1 , further comprising:
 providing a second sensor that is disposed within the effluent stream and that continuously samples directly from the effluent stream to monitor the clarity of the effluent stream.   
     
     
         5 . The method of  claim 5 , further comprising:
 providing an output from the second sensor representative of effluent clarity that is operatively coupled to an input of the PID controller,   wherein the PID controller changes the chemical dosing upon determining the output exceeds a predetermined threshold.   
     
     
         6 . The method of  claim 1 , further comprising:
 providing a plurality of points of chemical injection through which the wastewater stream is passed and at which the plurality of chemical additives are injected into the wastewater stream.   
     
     
         7 . The method of  claim 1 , wherein the first sensor is disposed downstream of a plurality of flocculent tubes. 
     
     
         8 . The method of  claim 1 , wherein the first sensor is a pH sensor in fluid communication with the wastewater stream having an output representative of pH of the wastewater stream that is operatively coupled to the PID controller. 
     
     
         9 . The method of  claim 8 , further comprising:
 providing at least one pH additive delivery pump that supplies an acidic solution or an alkaline solution to the wastewater stream based on the output of the pH sensor.   
     
     
         10 . The method of  claim 1 , further comprising:
 providing an automatic cleaning system for the first sensor, wherein the automatic cleaning system includes
 a clean water source, and 
 a chemical addition system on a timer that interfaces with the PID controller. 
   
     
     
         11 . The method of  claim 1 , further comprising:
 setting the PID controller to meet a performance objective, a costing objective, or a combination of performance and costing objectives.   
     
     
         12 . The method of  claim 11 , wherein the PID controller is set with high values for the proportional term and the integral term to ensure an acceptable level of chemical over-shooting where compliance is required. 
     
     
         13 . The method of  claim 11 , wherein the PID controller is set with lower values for the proportional term and the integral term and a higher gain for the derivative term to minimize chemical over-shooting where cost efficiency is required. 
     
     
         14 . The method of  claim 1 , further comprising:
 setting gain for the integral term at a highest value possible for quickest system recovery to return effluent 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. 
   
     
     
         15 . The method of  claim 1 , further comprising:
 setting gain for the derivative term 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, 
 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, and 
 wherein the desired set point is that which provides a desired water quality for a concentration of contaminants being treated. 
   
     
     
         16 . A method for treating a wastewater stream to produce an effluent stream, the method comprising:
 continually measuring, by a flow meter, flow rate of the wastewater stream;   continually measuring, by a sensor, clarity of the wastewater stream by sampling directly from the wastewater stream;   determining, by a proportional-integral-derivative (PID) controller, an appropriate chemical additive flow rate by
 receiving a flow rate value for the wastewater stream from the flow meter, 
 receiving a clarity value for the wastewater stream from the sensor, 
 automatically determining the appropriate chemical additive flow rate needed to achieve a specified effluent quality level based on the flow rate value and the clarity value, 
 output a chemical additive flow rate signal to a pump that specifies an amount of chemical additive to be injected into the wastewater stream, and 
 continually monitor the flow rate value and the clarity value in real time to determine whether an adjustment to the amount of chemical additive is needed to maintain clarity of the effluent stream at a substantially steady level after reaching the specified effluent quality level; and 
   injecting, by the pump, the amount of chemical additive into the wastewater stream responsive to receiving the chemical additive flow rate signal from the PID controller.   
     
     
         17 . The method of  claim 16 , wherein the sensor is selected from:
 a biological oxygen demand (BOD) sensor;   a chemical oxygen demand (COD) sensor;   a conductivity sensor;   a potential of hydrogen (pH) sensor;   a total suspended solids (TSS) sensor; and   a turbidity sensor.   
     
     
         18 . The method of  claim 16 , further comprising:
 measuring, by another sensor, clarity of the effluent stream by continually sampling directly from the effluent stream.   
     
     
         19 . The method of  claim 18 , wherein an output of the other sensor representative of effluent clarity is operatively coupled to an input of the PID controller, and wherein the PID controller adjusts the amount of chemical additive responsive to determining the output exceeds a specified threshold. 
     
     
         20 . A method for treating a wastewater stream to produce an effluent stream, the method comprising:
 providing a flow meter that continually monitors flow rate of the wastewater stream;   providing a pump that continually injects a chemical additive into the wastewater stream responsive to real-time adjustments specified by a proportional-integral-derivative (PID) controller;   providing a sensor that continually monitors clarity of the wastewater stream by sampling directly from the wastewater stream;   using the PID controller to determine an appropriate chemical additive flow rate by
 receiving a flow rate value for the wastewater stream from the flow meter, 
 receiving a clarity value for the wastewater stream from the sensor, 
 automatically determining the appropriate chemical additive flow rate needed to achieve an effluent quality level specified by a user,
 wherein the appropriate chemical additive flow rate is based at least in part on the flow rate value, the clarity value, and a predetermined gain value, 
 
 output a chemical additive flow rate signal to the pump that specifies an amount of chemical additive to be injected into the wastewater stream by the pump, and 
 continually monitor the flow rate value and the clarity value for the wastewater stream in real time to determine whether an adjustment to the amount of chemical additive is needed to maintain clarity of the effluent stream at a substantially steady level after reaching the effluent quality level specified by the user; and 
   causing the pump to inject the amount of chemical additive into the wastewater stream responsive to receiving the chemical additive flow rate signal from the PID controller.   
     
     
         21 . The method of  claim 20 , wherein the predetermined gain value is based on a dosing scheme selected by the user. 
     
     
         22 . The method of  claim 20 , wherein the pump is one of a plurality of pumps that are each operatively coupled to the PID controller, and wherein each of the plurality of pumps is associated with a different chemical additive. 
     
     
         23 . The method of  claim 22 , wherein the PID controller is configured to output a distinct flow rate signal to each of the plurality of pumps, and wherein each distinct flow rate signal is adjusted in real time based on the flow rate value and the clarity value for the wastewater stream.