- Suspended solids in lagoon water (also do volatile solids if inorganic particles are high)
- Effluent suspended solids
The missing part is the amount of solids accumulating in the bottom of the ponds. Also we are not sure of the amount of cell lysis (digestion). With good record keeping, and knowledge of the cell lysis rates, it is possible to get a true estimate of cell yield and pond sludge accumulation.
A solids mass balance is much more important in activated sludge treatment systems. All the data is usually collected on a frequent basis, but sometimes it is not put into a spreadsheet model for use in monitoring/auditing the system. We need solids concentration and flow for the following:
- Influent Volatile TSS (assume all in BOD20 or BOD ultimate)
- BOD5 or soluble organics inlet (can also use COD/TOC as a proxy – just be consistent)
- Aeration Basin (MLSS/MLVSS)
- Clarifier volumes
- Effluent TSS
- Recycle (MLSS/MLVSS)
While we often calculate sludge age or food/microorganism (F/M) ratios from this data, we can also get an idea for cell yield and amount of in basin endogenous respiration. This can be later evaluated when doing aeration cost evaluations.