Abstract
The National Pollutant Discharge Elimination System (NPDES) permit for the City of Davis was renewed in 2007with strict effluent quality requirements. These permit requirements prompted a plan to upgrade the city’s existing wastewater system to tertiary treatment. The city government is also working to meet greenhouse gas emission reduction goals. This project is a feasibility study of using treated municipal wastewater to irrigate long- lived trees on a city-owned 770-acre site to incorporate carbon from atmospheric carbon dioxide (CO2) into biomass. The major components of this study are: choosing a crop based on the amount of carbon it can sequester per year and its climate and water quality requirements; determining the degree of wastewater treatment needed under California law for this application; performing a water balance based on the irrigation requirements of the tree crop and potential threats to groundwater such as nitrogen or salinity loading; and determining the mass of carbon that can be sequestered annually by this facility. Based on the preliminary analysis contained herein, up to 569 acres of redwood trees could be irrigated with the city’s wastewater flow. A forest of this size would capture 2236 Metric Tons annually, which would more than offset the city’s CO2 emissions associated with its water and wastewater utilities.