Solids Capture Efficiency

Solids capture efficiency is the percentage of incoming suspended solids removed by a filtration device, expressed as 100 x (influent TSS minus effluent TSS) divided by influent TSS. It is the core specification for comparing mechanical filters in RAS. Values depend strongly on particle size: a well-run drum filter captures 40–80% of the >40 micron fraction but may pass most fines below 20 microns, so a single number without a particle-size distribution is misleading. Practical RAS design targets overall mechanical removal of 60–80% of total solids production per pass, because uneaten feed and fecal particles left in the water decay into fine colloids that foul the biofilter, raise oxygen demand, and fuel off-flavor compounds. Capture efficiency declines as filter screens blind or flow exceeds rated velocity, so it must be verified in operation with TSS measurements rather than taken from brochures. High capture efficiency upstream directly reduces degasser load, biofilter maintenance, and the volume of sludge that reaches dewatering, cutting total treatment cost per kg of fish produced.