It looks like the MBR effluent turbidity is very low (200 mg/L at this turbidity. Can you take a picture of a beaker of MBR effluent for us? It is possible that the TSS sample is not being rinsed well enough. Given the high TDS of this wastewater, try rinsing more thoroughly with at least 300 mL of deionized water. If this will not go through the filter, try diluting the TSS sample by 10X.