Design Blueprint: Household-Cluster Greywater Treatment Wetland — Build Specification Derived from the Subsurface-Flow Constructed Wetland Paper

DESIGN BLUEPRINT — SIMULATED, NOT MEASURED — NOT BUILT. A complete build specification for a horizontal subsurface-flow constructed wetland treating 600 L/day of greywater from a 10-person household cluster. Derived from the source paper: https://doi.org/10.5281/zenodo.24109216. The bed is 12.92 m2 in plan (6.23 m by 2.08 m, derived), 0.60 m deep, with 7.75 m3 of gravel media, sized by areal first-order kinetics (k20 = 0.10 m/day, temperature factor 1.06) to reach 30 mg/L BOD at 15 C. It delivers a 1.68 log E. coli reduction to 20,717 per 100 mL: sufficient for RESTRICTED irrigation only, 20.72 times the unrestricted limit of 1,000 per 100 mL, and barred from unrestricted reuse independently by a virus ceiling of at most 2.0 log against a 4.0 log requirement. In the arid case it recovers 522.46 L/day at a salinity concentration factor of 1.148 (1.00 to 1.15 dS/m), with leaching requirements of 2.96% for tolerant crops and 10.12% for moderately sensitive crops, but 29.82% for sensitive crops, for which the loop does not close. The blueprint gives dimensions and layout, a bill of materials in generic specification classes, a construction sequence, the operating envelope, tolerances tied to the source figures, failure modes, a maintenance schedule, and the measurements a first build must make. Nothing has been built or measured; every derived quantity is reproducible from the accompanying compute.py.