Recycling of Sewage Effluent by Sugarcane Irrigation: A Dilution Study, October 1976 to October 1978, Phase II-A

摘要

An extension of the project, 'Recycling of Sewage Effluent by Irrigation: A Field Study on Oahu.' This portion's objective was to determine the dilution with Waiahole Ditch water necessary for optimal sugar yield when chlorinated, secondarily treated sewage was used for irrigation of cane. Hawaiian sugarcane variety 59-3775 was planted to a random-block design of treatments with 6 replicates in central Oahu near the Mililani Sewage Treatment Plant. The 5 irrigation treatments for the two-cane cycle were: (1) ditch water; (2)12.5%; (3) 25%; (4) 50% effluent diluted with ditch water; and (5) effluent the first year and ditch water the second. The ripener 'Polaris' was applied prior to harvesting. Crop logs monitored the cane growth and test plots hand harvested for assessment of cane and sugar yield. Soil water percolate and sewage effluent were chemically analyzed to check for human enteric viruses. Sugar yields for effluent concentrations up 25%, or for effluent the first year and ditch water the second, were equal to those from conventional ditch-water irrigation. There was a significant loss in juice quality and sugar yield for the 50% effluent concentrations. Immediately after each application of fertilizer and with effluent concentrations of 50 to 100%, the nitrate nitrogen concentrations in the percolate exceeded the critical level of 10 ppm for potable water. Total applications exceeded the sugarcane's ability to take up nitrogen; however, an apparent nitrogen deficit was assigned to gaseous nitrogen loss. No virus was recovered but 40% of the effluent reservoir samples were positive. At least 96% of the virus was inactivated after 1 day of storage.