Section 45 - Chemical Delivery System

45.01 General Overview

The chemical delivery system is intended to accurately deliver necessary quantities of two chemicals, sodium hypochlorite and sodium hydroxide (NaOCl and NaOH), to various points throughout the treatment plant. The system has four independent subsystems, each serving one or more application points.

1. Shock Application System (secondary clarifier launder, primary clarifier launder, grit chamber effluent, wet well, RAS line)
   
   The shock application system supplies NaOCl to the secondary clarifier launder, primary clarifier launder, grit chamber effluent, wet well, RAS line in an effort to control the growth of undesirable organisms. Initially one metering pump will deliver NaOCl to a header common to the five application points listed above. Dilution water will also be supplied to the header. NaOCl solution will then be split to any of the five points via rotameters. The initial metering pump has been sized to supply only one of the five points at any one time. At the first expansion, the existing metering pump will become dedicated to the primary clarifiers. A new metering pump will be installed at the first expansion to supply the header common to the grit chamber effluent channel, wet well, and RAS line. This system will operate similarly to the original system, but without primary clarifier service. The new metering pump will be replaced with a larger one at the third expansion.
   
   
2. Sludge Transport System (primary sludge pumps, WAS pumps)
   
   NaOCl will be applied to the primary sludge and waste activated sludge (WAS) to inhibit biological activity and control odors to acceptable levels while the sludge is being transported to the solids treatment facility at the Westside Treatment Plant.
   
   Metering pump P-17024 will supply NaOCl to the discharge header of the primary sludge pumps while metering pump P-17027 will supply NaOCl to the discharge header of the WAS pumps.
   
   
3. Plant Water Supply (W3 pump station wet well)
   
   NaOCl will be added to the wet well at the W3 pump station to offer some disinfection to the water that will be used for outdoor hose bibbs and pump seal water. Two metering pumps will be provided for this service to provide redundancy. Dilution water will be added to the pump discharge.
   
   
4. Air Treatment (odor control scrubber)
   
   Both NaOCl and NaOH are required for the odor control scrubber. Two metering pumps will supply NaOCl to the odor control scrubber. Independently, two metering pumps will supply NaOH to the odor control scrubber. Dilution water will be added.

45.02 Design Criteria

The design criteria for the Screenings/Headworks Buildings Air Treatment System is presented below.

       METERING PUMPS

45.03 Computer Assisted Control Strategies

45.03.a. General Overview

At the MPWRF, the operator has the ability to apply Sodium Hypochlorite (NaOCl) to various points throughout the treatment plant. The operator has the ability to start and stop the chemical feed pumps and adjust the stroke through the SCS CRT. The PLC monitors pump operation and will sound an alarm in case of pump failure. Chemical storage tank levels are also monitored by the PLC and an alarm will sound at high and low tank levels.

45.03.b. Control Strategies

Operation:

1. Pump P-17021 is controlled through LP-17020 located in the Chemical Building. In REMOTE mode, the operator can start and stop the chemical feed pump and manually adjust the stroke through the SCS CRT. A manual loading station faceplate at the SCS CRT allows the operator to make the pump stroke adjustments.
   
   
2. If P-17021 fails, a pump fail signal is sent to the PLC which generates FAIL alarm QA-17021. The alarm is displayed on the SCS located in the Operator Laboratory and in the Administration Building. Place the HOR handswitch in OFF to reset the PLC/SCS.

45.03.b.2. Sludge Transport System

Operation:

1. Pumps P-17024 and P-17027 are controlled through LP-17020 located in the Chemical Building. P-17024 supplies NaOCl to the discharge header of the Primary Sludge pumps while P-17027 supplies NaOCl to the discharge header of the WAS pumps. In REMOTE mode, there are two methods for controlling the chemical feed pump sequencing and stroke; AUTO and MANUAL. In MANUAL, the operator can start and stop the chemical feed pump and manually adjust the stroke through the SCS CRT. A manual loading station faceplate at the SCS CRT allows the operator to make the pump stroke adjustments.
   
   In AUTO mode, P-17024 starts whenever a Primary Sludge Pump or Primary Scum Transfer Pump is on. P-17027 starts whenever the WAS or Secondary Scum Transfer Pump is on. The operator is responsible for setting the pump stroke setpoint at the SCS CRT manual loading station.
   
   
2. If P-17024 or P-17027 fails, a pump fail signal is sent to the PLC which generates FAIL alarms QA-17024 or QA-17027. These alarms are displayed on the SCS located in the Operator Laboratory and in the Administration Building. Place the HOR handswitch in OFF to reset the PLC/SCS.

45.03.b.3. W3 Water Supply

Operation:

1. Pumps P-17022 and P-17023 are controlled through LP-17020 located in the Chemical Building. These pumps supply NaOCl to the W3 Pump Station wet well. In REMOTE mode, there are two methods for controlling the chemical feed pump sequencing and stroke; MANUAL and RATIO. In MANUAL, the operator can start and stop the chemical feed pump and manually adjust the stroke through the SCS CRT. A manual loading station faceplate at the SCS CRT allows the operator to make the pump stroke adjustments.
   
   In RATIO mode, the first pump placed in REMOTE becomes the LEAD pump. The operator can change LEAD pumps by using the SCS CRT handswitch. The chemical pump feed stroke is adjusted by the PLC to maintain a desired ratio of the NaOCl feed to the W3 flow. The operator is responsible for setting the pump stroke setpoint at the SCS CRT manual loading station.
   
   
2. If P-17022 or P-17023 fails, a pump fail signal is sent to the PLC which generates FAIL alarms QA-17022 or QA-17023. These alarms are displayed on the SCS located in the Operator Laboratory and in the Administration Building. Place the HOR handswitch in OFF to reset the PLC/SCS.

45.04 Operating Strategies

45.04.a. General Operating Strategy

In the REMOTE mode, the Shock Application Feed Pump can be started and stopped and its stroke adjusted manually through the SCS CRT. A manual loading station faceplate at the SCS CRT allows operating personnel to make pump stroke adjustments.

When selected to REMOTE there are two modes for operating the Sludge Application Feed Pump control; MANUAL and AUTO. In MANUAL mode, each pump can be started and stopped and its stroke adjusted through the SCS CRT. Manual loading station faceplates allow personnel to make pump stroke adjustments. In AUTO mode P-17024 is started whenever a Primary Sludge Pump or Primary Scum Transfer Pump is on. In AUTO mode P-17027 is started whenever the WAS or Secondary Scum Transfer pump is on. In AUTO the pump stroke is adjusted to the value set by operating personnel at the SCS CRT manual loading station.

The LEAD pump for the Plant Water Supply Feed Pump is selected using a switch at the SCS CRT. When selected to REMOTE there are two modes for pump control; MANUAL and RATIO. The pumps function in MANUAL in a manner similar to the sludge transport NaOCL pumps.

When selected to RATIO mode, the NaOCL pump stroke is adjusted to maintain a desired ratio of NaOCL flow to W3 flow. W3 flow is measured by flow meter FIT-16311. Personnel can enter the desired ratio setpoint using a faceplate at the SCS CRT. When the plant water supply NaOCL pump function is in RATIO mode the NaOCL dose is automatically adjusted as the W3 pumps transition between small and large pumps.

The operation of the odor control NaOCL and NaOH pumps is described in the Air Treatment System narrative.

45.04.b. Normal Operating Conditions

Note: Normal plant operation will use the PLC and the SCS CRT to enter setpoints, select equipment operating modes and monitor equipment status. If a process can be controlled manually through the SCS CRT then this will also be included in this section.

45.04.c. Alternate Operating Conditions

Blank.

45.04.d. Startup/Shutdown Conditions

• Chemical Feed Pumps

45.04.e. Key Control Data and 4 Level Alarm Table

Not used.

45.04.f. Contingency Plans

A contingency Plan is written to handle an unpredictable occurrence that has a reasonable chance of happening. Most Contingency Plans deal with situations where having a written procedure can help prevent loss of a unit process, handle a process upset or respond to a hazardous situation. The following is a list of Contingency Plans developed for the Chemical Delivery System process. The plans are kept in the Contingency Plan Notebook located in the Operator Laboratory and the Shift Supervisor Office.

• [None defined at this time.]

45.04.g. Standard Operating Procedures

A Standard Operating Procedure (SOP) is written to handle operator activities performed on a regular but not necessarily daily basis. Most SOPs deal with potentially hazardous activities making it important that a written, step-by-step procedure be available. The following is a list of SOPs developed for the Chemical Delivery System process. The procedures are kept in the SOP Notebook located in the Operator Laboratory and the Shift Supervisor Office.

• Chemical Feed Pump Calibration

45.05. Troubleshooting

45.07 Records/Sampling

45.07.a. Sampling Schedule

Not used.