Co-Authors:
Acher, A.J., Institute of Soils and Water, ARO, The Volcani Center, Bet Dagan, 52250, Israel
Fischer, E., Institute of Soils and Water, ARO, The Volcani Center, Bet Dagan, 52250, Israel
Manor, Y., Sheba Medical Center, Central Virology Laboratory, Ramat Gan, Israel
Abstract:
The photochemical method of disinfecting domestic effluents planned for use as irrigation water for edible crops was developed further, reaching a stage at which it can be used on an industrial scale. This disinfection method uses sunlight as the activation energy source; the oxygen dissolved in water (DO) as the oxidizing agent; and a dye-sensitizer (methylene blue) as an intermediary for the absorption and transfer of the sunlight energy to activate DO and/or to destabilize the organic matter molecules and the microorganisms as the oxidation target. The study was carried out in an experimental pilot-scale plant, capable of treating up to 50 m3/h of effluent supplied by an activated sludge sewage treatment plant located in the Tel-Aviv area. The plant consists of a series of 10 identical photoreactors (6 × 2 × 0.3 m3), installed in series on an unpaved road with a 2% slope which ensures free overflow of the treated effluent through the pilot plant. Preceding the photoreactors there is a mixing reactor (2 × 2 × 1 m3) which supplies the effluent with DO (> 6 g O2/m3), MB (0.7 ± 0.1 g/m3) and calcium hydroxide (33 ± 3 g/m3) for pH correction (8.7-8.9). Operating the pilot plant at an effluent flow rate of 33 ± 3 m3/h (effluent detention time: 35 ± 2 min), sunlight intensities 700-2600 μEm-2 s-1, the following decreases in microbial counts were observed (log counts): coliforms -3.2 ± 0.3; fecal coli -3.12 ± 0.2; fecal streptococci -3.9 ± 0.3; poliovirus -1.9 ± 0.25. The treated effluents did not show regrowth of these microorganisms during 7 days storage in photoreactors, and did not form an impermeable crust when infiltrated into sandy soils. The effluent disinfection cost in a "sunlight disinfection plant" producing 200 m3 disinfected effluent per hour is estimated to be U.S.$ 3.95 per 100 m3. © 1994.