Bench-scale evaluation of sand-only and sand-activated carbon filtration for treating handwashing greywater from basic schools in Oforikrom Municipality, Kumasi, Ghana

Handwashing greywater from basic schools represents a potentially important non-potable water resource in water-stressed low- and middle-income settings, yet evidence on low-cost treatment options for institutional reuse remains limited. This study evaluated the bench-scale performance of sand-only and sand–granular activated carbon (GAC) filtration for treating handwashing greywater collected from five basic schools in Oforikrom Municipality, Kumasi, Ghana. Three downflow filter configurations were operated in parallel over 28 days: a sand-only Control, Setup A (sand + 50 mm GAC), and Setup B (sand + 85 mm GAC). School-level characterisation revealed substantial variability in greywater quality, with turbidity ranging from 40 to 265 NTU, BOD₅ from 118 to 226 mg/L, COD from 203 to 445 mg/L, and total coliforms from 2.6 × 10⁴ to 1.8 × 10⁵ CFU/100 mL. Composite greywater was moderate- to high-strength, with mean turbidity of 278.9 NTU, TSS of 277.3 mg/L, BOD₅ of 202.3 mg/L, COD of 999.9 mg/L, Salmonella of 12,572 CFU/100 mL, and total coliforms of 219,875 CFU/100 mL. All configurations achieved substantial reductions in pollutants, with Setup B consistently producing the best overall performance, including removals of turbidity (89.0%), TSS (91.2%), BOD₅ (81.9%), COD (85.7%), Salmonella (90.1%), and total coliforms (98.3%). Pairwise post-hoc analysis showed significantly lower effluent turbidity, TSS, Salmonella, and total coliforms in Setup B relative to the sand-only Control (p ≤ 0.041). Despite these improvements, residual microbial concentrations exceeded WHO unrestricted-reuse thresholds, confirming that sand–GAC filtration alone is insufficient for safe unrestricted reuse. The findings demonstrate the potential of low-cost sand–GAC systems as decentralised greywater treatment options for schools in Ghana and similar resource-constrained settings when integrated with downstream disinfection.