The first step to improving wastewater treatment plant performance is to give operators greater visibility through accurate solids measurement.

The next step is to automate the operation of the key process variables. There are many possible controls for process variables and Tecumseth can provide guidance and implementation services that will ensure success.

SOLIDS BASED PUMPING

The settled solids in each hopper of Primary Clarifiers are typically pumped to subsequent operations on a time or duration basis that is programmed into the monitoring SCADA system. This frequently results in very low density sludge being moved through the operation, and that reduces overall capacity and efficiency of the entire treatment process. With the addition of total solids measurement and the integration of Solids Based Pumping control into the SCADA system, Tecumseth allows operators to choose between Time Based Pumping or Solids Based Pumping to achieve the best performance and throughput possible.

Solids Based Pumping uses the measured total solids value of the sludge to determine the length of pumping time for each hopper. A lower solids limit is set and pumping is instructed to stop when the sludge reaches that degree of dilution. The system will then either instruct the operation to begin pumping from the next hopper immediately or to do so at the next time interval. The benefits of this approach are evident in the more stable and higher solids loading of the remaining operations through the digesters, thickener and compaction to cake.

WASTING RATE CONTROL
Wasting Rate Control for secondary treatment clarifiers uses the total solids measurement together with flow and volume to calculate the retention time of solids. When the retention time is determined, a pumping flow rate can be set to optimize the secondary clarifier operation. This capability maximizes the capacity of the secondary treatment operation and ensures effective treatment is being achieved.
GAS COLLECTION OPTIMIZATION

Digester Gas Collection Optimization occurs after Solids Based Pumping has been implemented at the primary clarifiers. As the sludge solids feed to the digester reaches higher levels and is held there, increased amounts of gas are generated.

Learn how reliable online solids measurements can be used to optimize and improve plant operations and process by reducing costs through chemical and energy savings, and improving even further the environmental and public health benefits of wastewater treatment.

Over-use of polymer is a constant issue in most plant operations. Regulating its usage is a multivariable problem that can be optimized through advanced control. Tecumseth has a solution waiting for implementation in processes where the Fournier Rotary Press is installed.

Rotary Press optimization is also a final critical step to cost control and dewatering sludge. However, compared to centrifuge operation, rotary press control is not nearly as critical for generating value because of the stability of this equipment.

The key component to minimizing polymer usage is to have effective measurement of certain process parameters and the ability to regulate their operation.

Operation of the rotary press will remain stable through changing inlet solids but the amount of polymer required is determined by the flow and solids of the inlet sludge.

Process Measurement:

• Inlet solids – metsoTS microwave solids transmitter
• Inlet pressure – pressure transmitter and control
• Polymer flow – flow meter
• Filtrate solids/turbidity – metsoLS

Control Parameters:

• Rotary Press speed – through the VFD
• Inlet flow – control throughput a valve or pump
• Polymer rate of addition – to maximize filtrate clarity, cake solids

The more uniform the solids feed into the centrifuge, the more stable is the centrifuge operation and higher throughput can be obtained at a consistently high cake solids.
Polymer addition is required to get good water removal from the feed sludge but polymer addition has a point of diminishing returns where the more that is added, the less effective it is at flocculating the solids and enabling the centrifuge to produce the desired solids in the cake.

Centrifuge operations are often easily upset by factors that affect its operation. Unfortunately the operating variables are interactive and could upset each other as well as the centrifuge. Fortunately, the interactions can be captured and included in a multivariable control strategy that will stabilize operations, provide optimal throughput and maintain minimal cost of polymer addition.  

Optimization of centrifuge operations is a final critical step to cost control and dewatering sludge.
The key components to ensuring stable operation, maximizing cake solids and minimizing polymer usage are to have effective measurement of process parameters and the ability to regulate the operation.

Process Measurement:

• Inlet solids – metsoTS microwave solids transmitter
• Inlet flow – appropriate flow meter
• Polymer flow – appropriate flow meter
• Filtrate solids/turbidity – metsoLS
• Centrifuge Load (amps)

Control Parameters:

• Centrifuge speed – if variable
• Inlet flow – control throughput with a valve or pump
• Polymer rate of addition – to maximize filtrate clarity, cake solids

The more uniform the solids feed into the centrifuge, the more stable is the centrifuge operation and higher throughput can be obtained at a consistently high cake solids.
Polymer addition is required to get good water removal from the feed sludge but polymer addition has a point of diminishing returns where the more that is added, the less effective it is at flocculating the solids and enabling the centrifuge to produce the desired solids in the cake.

Valmet SDO applies inputs from solids and centrifuge measurements to optimize the dewatering process. Valmet Total Solids Measurement (Valmet TS) offers measurements for feed solids and dry cake percent solids and Valmet Low Solids Measurement (Valmet LS) gives accurate centrate suspended solids measurements. While, the Valmet Dry Solids Measurement (Valmet DS) provides continuous reliable measurements of dry solids. With key data, Valmet SDO utilizes a multi-variable model predictive control (MPC) to control polymer dosing and centrifuge torque. The multi-variable MPC is unique to Valmet SDO and is an essential component for centrifuge optimization, as centrifuge control is a non-linear process.

The Tecumseth team will work with plant personnel to identify variability issues that are affecting performance issues such as product quality, throughput and cost. Our extensive experience in capturing and identifying process variability through our hands-on approach has huge implications for performance.

Tecumseth and our associates provide process optimization services to remove variability and improve operation stability.  Automation can provide the best overall performance when all elements work as intended and operate in coordinated fashion.  Instruments sometimes decline in measurement accuracy or regulation performance, loops often need to be re-tuned or tuned to operate in concert with each other.

Our assessments include an evaluation of process design and placement of instruments.  Software is used to determine the process dynamics that determine how each loop needs to perform relative to others for best overall stability and throughput.  Recommendations that will lead to performance improvement through instrument and valve upgrade or placement are provided. Implementation of optimal tuning performance will provide immediate results.