Solids Loading Rate (SLR) is how we measure the solids loading to a clarifier. It’s calculated by dividing mass of solids (TSS) sent to the clarifier by the clarifier surface area. Typical values are 20-30 lbs/ft²·d.  Higher flow rates and higher MLSS concentrations in the aeration basin result in higher SLRs and stress the clarifiers more.  Tracking SLR can help in troubleshooting clarifier performance.