Technical Report No. 79
WATER RECYCLING OF SEWAGE EFFLUENT BY IRRIGATION: A FIELD STUDY ON OAHU
Second Progress Report for July 1972 to July 1973
Project Principal Investigator
L. Stephen Lau
Co-Investigators
Paul C. Ekern Soil and Irrigation Studies
Philip C.S. Loh Virology Studies
Reginald H.F. Young Water Quality Analysis
Nathan C. Burbank,Jr. Public Health Aspects
Gordon L. Dugan Data Management and Report Preparation
November 1974
ABSTRACT
An investigation of recycling sewage effluent by irrigation under Hawaiian conditions is being conducted in pilot field studies near Mililani Town in central Oahu under the sponsorship of the Board of Water Supply and the Division of Sewers, City and County of Honolulu. The primary objective of the project is to determine the feasibility of waste water application to the soil and its probable effects on the quality of groundwater in terms of dissolved materials and viruses. Corollary objectives are to ascertain its effects on sugarcane yield and grasslands.
The studies began in September 1971 with the construction of a five-foot (1.52 m) deep hydraulic lysimeter in a grassed area on the grounds of the Mililani Sewage Treatment Plant. The upper surface of the lysimeter was at ground level. Soil within the lysimeter was repacked to the approximate original density. In an adjacent site, a number of two-foot square pans were placed at various depths down to five ft (1.52 m) in undisturbed soil adjacent to an access pit. The lysimeter and pan areas were sprinkler-irrigated with secondary sewage effluent from the Mililani Sewage Treatment Plant on a regular schedule. Five furrows of maturing sugarcane in the nearby Oahu Sugar Company (OSC) sugarcane Field No. 240 were also irrigated with the secondary effluent while the adjoining furrows continued to receive regular irrigation water. Numerous point water samplers were positioned in both furrows and ridges of the sugarcane field at depths to 33 in. (84 cm). Thirty test plots with uniform areas of approximately 0.1 acre (0.041 ha) each were established in a newly planted (February 1973) OSC sugarcane Field No. 246. The test plots were divided into three basic irrigation schemes of ten plots each–A, B, and C. Plots “A” will receive ditch water only for the nearly 24 month culture cycle; “B” plots are scheduled to receive secondary effluent for the first half of the growth cycle and ditch water thereafter; and “C” plots will receive effluent only for the full growth cycle. Fifty ceramic plant samplers were installed in representative “A”, “B”, and “C” plots at depths of 9 to 12 in. (23 to 30 cm) and 18 to 21 in. (46 to 53 cm). Two five-foot (1.52 m) deep field lysimeters were also installed in a furrow row adjacent to the test plot. The sugarcane growing on one lysimeter is irrigated with ditch water while the other receives secondary effluent. Sugarcane growth parameters are being monitored periodically throughout the culture cycle. The soil within the test sites of both the grass and sugarcane areas is of the Oxisol Lahaina series, the , general soils type on which approximately 90 percent of Hawaii’s irrigated sugarcane is grown.
Raw sewage, secondary effluent, and leachate from the soils were assayed for various physical, chemical, sanitary, and microbiological quality parameters. Analyses for pesticides and heavy metals were also performed occasionally. A virus laboratory, the first of its kind in Hawaii, was established at the University of Hawaii at the initiation of the project to serve the project and to assist in training the personnel of the Board of Water Supply. Consumptive use of water was determined by use of the hydraulic lysimeter.