Conceptual design of zero discharge and safe discharge biological wastewater treatment systems using fast-growing wetland trees

Abstract

Conceptual designs of two wastewater treatment systems using trees adapted to wetlands (e.g. poplars) are developed for southern Arizona's desert environment. The "zero discharge" system uses the large difference between potential evapotranspiration and precipitation to fully consume the applied wastewater. The "safe discharge" system processes more water and uses tree and soil microbial bioremediation to reduce pollutants in wastewater to tertiary treatment levels. Nutrients in the wastewater enhance the growth of the poplars and produce valuable biomass in systems more cost-effective than conventional treatment facilities. Zero discharge systems for a design population of 1000 people will require about 8.5 ha (21.4 ac) to process 1600 mm (63 in.) of wastewater annually. Safe discharge systems can handle higher hydraulic loading rates of about 2500 mm (98 in.) per year and require only 5.5 ha (13.8 ac) for 1000 people.. Both systems require a storage pond approximately 3m (10 ft.) deep and 1.5 ha (3.75 ac) surface area when irrigation is curtailed during the winter dormancy period.