For routine S3A checks, start with a defined record that connects the sample, the completed test and the operating conditions. Use the treatment works’ agreed procedure to decide when a result requires follow-up.
Define the comparison before collecting the sample
Give each sampling point a clear name and identify the process stage it represents. Record the sampling time separately from the time the settlement test finishes. If the point or operating phase changes, keep that change visible in the record rather than silently continuing the same series.
Use a safe, representative mixed-liquor sample. The S3A uses 210 ml and provides an MLSS result in approximately 10 seconds, followed by its 30-minute settlement cycle. The compact sample does not remove the need for consistent collection and preparation.
Keep concentration and settlement results together
MLSS describes concentration; SVI relates settled volume to that concentration. Retain settled sludge level, supernatant clarity and floating-sludge observations alongside them. An index alone cannot describe every aspect of how the sample separated.
Identify whether the test was unstirred or used the optional stirrer. SVI and SSVI belong to different methods and should not be combined into one unlabelled trend. Read the SVI versus SSVI guide before comparing the two.
Use a consistent minimum record
Sampling location, collection date and collection time
Process phase and relevant operating observations
MLSS value and units
Settled sludge level, SVI and associated separation results
Stirred or unstirred method and any procedure deviation
Person reviewing the result and any agreed follow-up
Investigate differences without inventing a diagnosis
When a result differs from the established pattern, first check whether the sample and method are comparable. Then review it with the site’s process observations and laboratory information. Do not infer a cause or change operating settings solely from one reading.
The S3A can retain 28 completed results for each of three locations with date and time information. Agree how required records will be retained within the site’s own system; instrument storage is not a substitute for the site’s record-retention policy.
Connect the trend to the measurement definitions
Use the MLSS parameter guide and the SVI guide to keep terminology consistent. The representative sampling article explains the starting point.
Review the S3A specification and limitations, or contact PMA to discuss a routine that fits your treatment works. Required compliance sampling and laboratory analysis remain separate.
