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Assessing Reclaimed Water Use and Biomass Production on an Irrigated, Short-Rotation Tree Farm in Northeast Florida

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JEA is investigating the viability of using irrigated, short-rotation-intensive culture (SRIC) tree farms toproduce woody biomass for forest products or “green power.” This action is in light of initiatives to reduce wastewater discharges to the river; regulatory requirements for providing reuse capacity associated with permits for its WRFs; and a commitment to evaluate renewable energy sources as part of the Clean and Green Power Program. By applying the correct amount of water and nutrients and controlling pests and weeds, JEA can then harvest trees every 4 to 10 years instead of the normal harvest cycle of 20 to 40 years. To develop appropriate design criteria for such an innovative project, JEA began implementation of a 15-acre demonstration project in mid-1999 to evaluate the growth performance and water use of four fast-growing hardwood trees (eastern cottonwood, hybrid poplar, yellow poplar, sycamore) and loblolly pine. JEA is also testing various drip and microsprinklerirrigation system components for applying reclaimed water to the trees.

The demonstration project provides up to 100,000 gpd of reuse capacity for the District 2 WRF through the irrigation of approximately 11,000 trees on the 15-acre site. The specific objectives of the JEA tree reuse demonstration project include: 1) enhance positive public relations associated with linking an existing JEA community enhancement program to sustainable practices, 2) provide a mechanism to promote public awareness of reuse, 3) provide possible credits for air quality mitigation associated with power plant permits, 4) provide credits towardsmeeting regulatory requirements for reuse capacity, 5) reduce wastewater discharge to the St. Johns River, 6) determine the technical and economic feasibility of using reclaimed water for the irrigation of hardwood and loblolly pine trees used for full-scale SRIC practices, and 7) develop site specific water usage and evapotranspiration rates for each specific tree species. This type of information is currently not readily available in the southeastern U.S.

The tree reuse site was planted during the first 2 weeks of April 2001. All of the trees were irrigated with potable water through the end of June because of delays in getting modifications to the new plant filtration anddisinfection systems completed. Within a month of planting, most of the hybrid poplar cuttings had sprouted and grown approximately 12 inches in height. By the first week in June, many of the hybrid poplar trees ranged in height from 2 to 3 feet. The eastern cottonwood cuttings have grown somewhat slower than the hybrid poplar cuttings over the first few months of growth. Growth rates have been approximately one-half of those observed for the hybrid poplar. Mortality rates have also been higher for the cottonwoods as compared to the hybrid poplar, sycamore, and yellow poplar. The loblolly mortality rate is the highest of all species. Survival percentages for hybrid poplar, eastern cottonwood, sycamore, yellow poplar, and loblolly, based on a tree survey conducted one month after planting, were 87.3, 70.2, 75.2, 84.8, and 60.2 percent, respectively. Also, there appears to be definite growth differences between drip and micro-spray blocks, regardless of species, with the drip blocks having larger and more uniform trees than the microsprinkler blocks. JEA will continue to monitor growth rates in the sampleplots to determine if there is a relationship to the type of system on overall growth performance.

Overall, JEA is pleased with the initial growth rates and performance observed on the tree reuse site and is excited about the potential of this technology to provide added reuse capacity for its WRFs and biomass to meet “green power” goals. JEA intends to collect data from the demonstration site for several growing seasons before making decisions concerning the full-scale viability of this technology.

Document Type: Research Article


Publication date: 2001-01-01

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