Water Reuse Case Study

secondary treatment, low dose coagulant/polymer addition, filtration, and disinfection), although both treatment trains reliably removed or inactivated more than 5 logs of virus during seeding experiments. Naturally occurring viruses were not detected in the product water of either tertiary treatment pilot plant.

Irrigation Water Quality: Both types of reclaimed water had higher levels of most chemicals, including metals, than the native local groundwater. Electrical conductivity, total dissolved solids (TDS), boron, chloride, and sodium in the reclaimed waters were similar to each other but higher than levels in well water. The TDS levels in all three types of water were below the severe problem range for irrigation water, and the sodium adsorption ratio in all three waters was in the favorable range for irrigation water.

Virus Removal/Inactivation: Measurable levels of viruses were detected in 53 of 67 samples (80 percent) of secondary effluent. No naturally occurring viruses were detected in disinfected tertiary effluent from either pilot treatment train throughout the study, and no viruses were detected in any of the crop or soil samples. An environmental chamber was constructed in a laboratory to determine virus survival under field conditions. The laboratory study indicated that the time required for 99 percent inactivation of seeded viruses ranged from 7.8 to 15.1 days, depending on the type of crop. Subsequent field studies produced similar results, and no seeded viruses were detected in any soil samples after 12 to 14 days of exposure.

Bacteria and Parasites: Coliform organisms were occasionally found in all three types of irrigation water. None of the samples taken from the three water sources or the soil indicated the presence of Salmonella, Shigella, Ascaris lumbricoides, Entamoeba histolytica, or other parasites. Parasites were detected in plant tissues during the first year of the study, but there were no differences between the levels in reclaimed and well water.

Aerosols: Aerosol tests were conducted during both daytime and nighttime irrigation. Microorganism transport via aerosols generated during spray irrigation of tertiary effluent was not significantly different from transport via aerosols generated during spray irrigation with well water, thus indicating that aerosol transmission of bacteria originating in the reclaimed water was unlikely.

Heavy Metals: There was no significant difference in any of the nine heavy metals studied (cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, and zinc) among plots irrigated with the different water types. Except for copper, the concentration of the metals did not show an increase in the soil during the five-year study period. Copper did increase gradually for all water types but remained below the average for California soils during the course of the study. Heavy metal input from commercial fertilizer impurities was far greater than from irrigation waters and accounted for the differences observed in soil samples throughout the five-year study period. Analyses of edible plant tissues indicated no consistent significant differences in heavy metal concentrations

The wastewater reuse system of Limassol, the second largest urban area of Cyprus, with about 200,000 inhabitants, is in operation since 1995. The high quality effluent with an annual flow of about 3.5 million m3 is fully recycled and used for many purposes such as groundwater recharge, restricted irrigation such as public amenity areas, golf courses, etc., but excluding vegetable and similar irrigation. Wastewater reuse has the main advantage of environmental protection and upgrading whilst at the same time it offers an alternative water resource, with a marginal cost much lower than the cost of desalinated water. The marginal cost for tertiary treatment is also much less than the cost paid for dam water or desalinated water. As a result, recycled water provides the potential for the utilization of the national water resources in the most economical and efficient way, providing to the national economy great savings in real terms. In conclusion the Limassol reclaimed water reuse scheme has demonstrated in practice that domestic wastewater is a valuable resource which can and should be used in order not only to combat the water shortage in our country in an economical way, but also to upgrade and maintain the environment which is constantly under tremendous pressure and violation.

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