Total solids (TS)
What does the term mean?
Total solids determination asks how much of a sample remains after an agreed drying procedure. When reported as a mass fraction, TS equals dry residue mass divided by original sample mass, multiplied by 100%. The result must be accompanied by the method used.
Relevance to process measurement
A process sensor does not dry the sample. Its signal is related to laboratory results to track TS during operation. That relationship needs to suit the particular material, such as a specific sludge or substrate.
What matters when comparing laboratory and process results?
In a hypothetical test, an 80 g sample leaves 4.8 g after the agreed drying procedure, giving 6% TS. Different drying conditions may leave a different residue, for example when volatile constituents escape.
Use one documented reference method and collect representative samples matched to the relevant process readings. Settling materials also require attention to solids distribution. Following a change in sludge type or recipe, check the existing relationship with fresh control samples.
Compare TS using a standardised reference method
A TS value describes the residue remaining after the agreed drying method. Results from different methods may therefore not be directly comparable. For comparison with a process sensor, laboratory conditions should remain consistent and be documented. Record which sample was analysed and the corresponding process value at that point in time. Where slurries or substrates vary, the composition of the sample is also important. An identical percentage does not automatically mean that the remaining solid components have the same composition.
The TS content should not be equated with the organic fraction of the dry matter. Further information is required for tasks such as assessing organic load. Nor does a Brix reading generally replace the TS reference. You should therefore determine, prior to calibration, which parameter the process value is intended to represent and according to which method it is to be monitored.
For media that settle, sampling and further sample treatment should take the distribution of solids into account. Initially, check any noticeable deviations by taking repeat samples at appropriate intervals. When making an enquiry, it is helpful to provide details of the medium, TS range, temperature conditions and any existing laboratory findings. This allows the assessment to be tailored to the actual intended product and operating range.