A Two-Stage Manual Sorting Line for a Small Materials Recovery Shed: Picker Throughput, Belt Coverage Saturation, and a Sized Design for 20 Tonnes per Day

Small towns often cannot justify a fully automated materials recovery facility, yet sending mixed recyclables to landfill loses material value and incurs disposal cost. This paper models a two-stage manual sorting line for a shed handling 20 tonnes per day of mixed recyclables in a single 8-hour shift, derives the bound at which adding pickers stops paying in recovered yield, prices the recovered fractions, and specifies ergonomic design choices that affect injury and exposure. SIMULATED, NOT MEASURED: all results are from the accompanying computation, not from a built line. At the design point of eight pickers and a belt speed of 0.30 m/s, the model recovers 6.39 tonnes per day, 50.7 percent of the target material mass, for $1,088 per day in material revenue at the stated prices. Marginal recovery per added picker falls from 6.85 percentage points between two and four pickers to 2.13 percentage points between twelve and sixteen pickers. No hard coverage plateau occurs before the physical station limit of the belt: reaching 95 percent of the material recovery ceiling would require about 27 pickers, while a 12 m belt at 1.2 m per station holds at most 20. Material revenue per added picker is below loaded labour cost at every staffing level modelled. The honest conclusion is that a manual line of this size is justified by recovery obligations and avoided disposal, not by material revenue alone.