Off-Grid Greywater: USDA Vertical-Flow Wetland Guide

The USDA ARS team's guide details vertical-flow constructed wetlands for polishing greywater in off-grid homes, based on a 2025 California field trial. Hydraulic loading rates are set at 0.05-0.1 m/day for optimal treatment, using media mixes of 60% gravel (3/4-inch), 30% pea gravel, and 10% peat moss for porosity and nutrient adsorption. E. coli removal hit 99.9% efficiency, with BOD reduction over 95% via aerobic microbial zones. Nitrous oxide emissions stayed below 0.5 kg/ha/year, minimized by precise carbon-to-nitrogen ratios in influent. Design specs: 5-10 m² per bedroom equivalent, with 1m depth divided into primary (sand filter) and secondary (gravel/plant) cells. Plants like cattails (Typha latifolia) and bulrush oxygenate roots, supporting denitrification. In the trial, a 4-bedroom home system treated 1,500 L/day, producing reuse-quality water for subsurface irrigation with zero detectable pathogens post-UV polishing. Construction steps: excavate to frost line, line with geomembrane, layer media precisely, and seed with wetland starter cultures. Monitoring includes piezometers for flow uniformity and monthly grab samples for TSS (<10 mg/L target). Costs: $2,500-$5,000 DIY, scaling linearly. The guide includes AutoCAD templates, pump specs (e.g., 1/3 HP effluent pumps), and troubleshooting for clogging via media refresh every 5 years. This provides concrete, data-backed methods for safe wastewater reuse in regenerative homesteads.