In addition to its focus on horticulture, education, and research, the San Luis Obispo Botanical Garden strongly emphasizes sustainability. So it’s no surprise that the Garden’s education and administration building earned LEED Gold certification. Large windows on south-facing walls let in sunlight for winter heating. Shelving, counters, and cabinets all contain recycled materials. And effluent from the garden’s wastewater treatment facility is used for subsurface drip irrigation.


Designed as a training opportunity for Cal Poly engineering students, the treatment facility has a 15,000-gallon (56.8-m3) septic/equalization tank, followed by three types of secondary treatment: a 980-ft2 (91-m2) subsurface wetland, a 500-ft2 (46-m2) sand filter, and an AdvanTex® Treatment System. With by far the smallest footprint, the AdvanTex system consists of two AX20 units – each occupying just 20 ft2 (1.8 m2) – and a 2,000-gallon (7.8-m3) recirculation tank. The system can treat up to 1,600 gpd (6.1 m3/day), compared to the sand filter’s maximum of 1,250 gpd (4.7 m3/day) and the wetland’s maximum of 1,000 gpd (3.8 m3/day).