world map

World’s Leading supplier in Precision Dissolved Oxygen Measurement and Respirometry

email us at


call us on

icn-phone +44 (0)1698 730400


Strathkelvin Instruments/ASP-SVI (Settlement Volume Index) Automated

ASP-SVI (Settlement Volume Index) Automated

Activated Sludge Plant – Suspended Volume Index

Strathkelvin Instruments Ltd provide ASP-SVI (Settlement Volume Index) – an online device which automatically measures %Settlement and MLSS and calculates the SVI parameter. This is demonstrated in the ASP-Con capability animation Click here

The test frequency can be programmed by the operator. The system is fully compatible with PLC, SCADA and DCS systems, and has local alarm trending and test interrogation capability as standard. Remote access, alarm and I/O capability are also provided as optional extras.

Testing Principle

The ASP-SVI is located in the Activated Sludge Process at the point where the SVI test is required to be carried out. A sample is drawn into the testing chamber. The mixture is then allowed to settle for an adjustable time period (normally 30 minutes). The settled sample is then exhausted from the chamber, past turbidity sensors, which can detect the level at which the activated sludge has settled.

Testing Method

MLSS Settlement

  1. ASP-SVI measures the turbidity and produces results in mg/l.
  2. ASP-Con performs settlement test and measures how much of the sample settles in (x) or 30 minutes.
  3.  Calculation =(100 – %Settlement) x 10/ MLSS/1000)

= SVI in ml/l


ASP–SVI (Activated Sludge Plant – Suspended Volume Index)

Activated Sludge Settlement and the SVI tests are critical parameters in the Activated Sludge Process.

  • This test determines how well the sludge will settle in the Final Clarifier and,
  • is a predictor of TSS in the final effluent.

Most Activated Sludge plants complete this test on a daily basis on each lane or basin. Each manual test can take up to 30-minutes of operator time, including sampling, transfer to lab, setting up the test and recording the results. However, this test frequency cannot give a true measure of settle ability under all conditions and during upset conditions will ideally be completed more frequently at the very time the operator will have many other pressing time demands.

Test Frequency – The Operator can program how often the SVI test is carried out. For a standard 30-minute settlement test the maximum frequency is every 40 minutes. The SVI test frequency can also be controlled locally or by the site PLC system.

– The settlement and MLSS sensors are wiped clean after every test.



As standard;

  •  Hardwired fully programmable digital I/O (additional I/O available on request)
  •  Modbus RTU
  •  Modbus TCP I/P

Optional Extras (On Request)

  • Hardwired fully programmable Analogue & Digital I/O
  • Profibus
  • Profinet
  • Others on request


1.     % Settlement – no calibration is required.

2.     MLSS. The operator can input laboratory results for both MLSS values and TSS to calibrate the Sensor. Recommended frequency – monthly

ASPCON Float System (optional extra)

Our float system tracks the level of the effluent in situations where the level varies to ensure the ASP-Con instrument is always in the optimum position for measurement, sampling and monitoring. Our standard offering is 2m draft system, however this can be extended using our modular design extensions. Ideal for installations where the level fluctuates and particularly suitable to SBR systems. The system consists of our level sensing system which feeds information to our control panel and in turn utilises a multi-turn actuator to raise and lower the instrument as required to the optimum level. Our standard automatic hoist system is controlled via our local control panel however we can also offer various other options including linking the automatic level system directly to the plant PLC level detection. This can be hardwired or via various communication protocols such as Modbus, Profibus etc.

Speak to us today about your specific plant set up and we can offer advice and design the most appropriate system to meet your requirements.

Technical Support- The ASP-SVI is supplied with a router to allow remote access under operator control. By fitting a SIM card we can provide full technical support with full fault- finding and result interpretation capability. This service is provided free of charge for the first 3 months, and on an ongoing basis to customers who take our service contract. (Fair use conditions apply). For local authorised distributors please see check our Distributors page.

– No consumables are required.

Maintenance and Servicing
– The unit performs best with an annual service to replace seals and wipers. A manufacturer’s service contract, which can extend the warranty up to 7 years, and includes all spare requirements, available globally with either a local Distributor, if available, or back to manufacturer basis.

Spares Recommendation

1. Sensor Wiper * 1
2. Sample Seals * 1

Print Friendly

SVI graph

SVI graph

Print Friendly
quick quote icon

  quick enquiry

Please leave this field empty.

blue bird

Strathkelvin Instruments Limited,

Rowantree Avenue,

North Lanarkshire, ML1 5RX,


01698 730400
Fax: 01698 730401
    • visa
    • visa-electron
    • maestro
    • delta
    • m-card
    •   paypal