Effects Of Reclainmed Water And Gray Water Irrigation On City Greens And Sodium Removal Using Zeolite

Urban greens planting and maintenance consumes a lot of water, with the accelerating process of urbanization, water shortages become increasingly prominent, and reclaimed water and gray water irrigation is an important measure to alleviate the water crisis. The study on effects of recycled water and gray water irrigation on landscape plants and soil properties has important theoretical and practical value for the implementation of recycled water and gray water irrigation. Soil samples were collected and tested at different depth and periods to study changes that may occur in the soils after recycled wastewater is used for five years. Taken tap water irrigation as blank, long-term effects of Landscape irrigation using household gray water on landscape plants and mineral contents of plant tissue were studied taking tap water irrigation as control, relationship between landscape plant's salinity tolerance and response to graywater irrigation was also compared. To ensure sustainable and affordable water supplies, it is necessary to find ways to combat sodium damage to plants if reclaimed water is to be used for long-term landscape irrigation. Zeolite column was set up to remove sodium from recycled waterf as one way to combat salinity and sodium problems associated with long-term use of recycled wastewater. The main results are as follows:1. A total of 27 soil sample sites at seven Colorado city parks were selected to study effects of five years'recycled water irrigation on soil properties, parameters of each soil sample tested included pH, Na, EC, SAR, Ca, Mg, NO3-N, P, K, OM, Zn, Fe, Mn, Cu, Cl and B. Results showed that soil Na, K, pH, SAR and EC were increased significantly after recycled water is used for five years, and Mn was decreased significantly, while OM,Ca,Mg,NO3-N,P,Zn,Fe,Mn,Cu,Cl and B didn't change significantly. Along the depth of soil after recycled water is used for five years, variance of Na, K and SAR changed significantly, Na and SAR variance at deeper soil increased more than at above depth soil, However, the opposite trend was observed in soil K, other variance of soil parameters didn't change significantly.2. Evaluations of existing household landscapes that have used graywater for irrigation for more than 5 years suggested that:(1) Juniper(Juniper spp), Himalayan Border Jewel (Polygonum affine), Euonymus (Euonymus spp.), Rose of Sharon (Hisbiscus syriacus), Chrysanthemum (Chrysanthemum spp.), St. Augustine grass(Stenotaphrum secundatum) and California Valeriana (Valeriana californica) to be resistant to graywater irrigation. The following plants are moderately sensitive to gray water irrigation, plum tree(Pnunus spp.), Mugo Pine(Pinus mugho) and Bearded Iris (Iris germanica); Landscape plants that are sensitive to graywater irrigation included:Scotch pine (Pinus sylvestris), Hass Avocado (Persea Americana 'Hass'), Lemon tree(Citrus limonium), and Yellow Bush Daisy (Euryops pectinatus). (2)The correlation between gray water tolerance and salinity tolerance was statistically significant (P< 0.01). The regression coefficient value (R2=0.65) suggested that approximately 65% of the variance of landscape plants'response to graywater is associated with their response to salinity, in this case, salinity tolerance. (3)Analysis of variance indicated significant plant species effect for all minerals, but no water treatment effect for all minerals except Mn and K/Na ratio. The interactions between plant species and water treatment were only significant for Cu, S and K/Na.3. Long-term reclaimed water irrigation causes sodium problems, zeolite column was usd for sodium removal from reclaimed water. The results showed that ion exchange of zeolite Na ions and SAR increases with the increase of treated water; and with the increasing content of Na ions, Ca ion content decreases; Zeolite showed pretty week selectivity for K and Mg in the raw water, K and Mg remained almost constant during the entire exchange process, Ion exchange process of reclaimed water in the zeolite column is essentially equivalent exchange between Ca and Na ions.Results of this paper showed that recycled water and gray water irrigation of city greens will have impacts on both plant itself and soil properties which should pay enough attion during the pactice of recycled water and gray water irrigation of city greens.