| With the developing shortage of water resource, the reuses of reclaimed water has attracted more attentions from government. Exorbitant sodium accumulation in soils could be a risk factor in the process of irrigation with reclaimed water. How to reduce sodium ion concentration in reclaimed water has caused more and more attention.This study analyzed the possibility of soil salinization caused by reclaimed water irrigation for many years and investigated the sodium ion removal efficiency of three typical non-metal clay mineral adsorbents. The effects of 2- or 3-year irrigation with reclaimed water on soil saline accumulation of tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) were studied using plot experiment. The best adsorbent was selected among three typical non-metal clay mineral adsorbents: bentonite, attapulgite, and stilbite and relevant modification method was studied. The removal efficiency of sodium ion of the best adsorbent for reclaimed water was evaluated under both static and dynamic experimental conditions. The conclusions are as the followings:1. The effect of reclaimed water irrigation on soil salinizationThere was no significant effect in soil pH value regardless of different irrigation periods, water sources, soil depth, and grass species. Compared with the fresh water, soil sodium ion content and SAR value were significantly increased in Kentucky bluegrass soil irrigated with reclaimed water in the second and third year and tall fescue in third year. Total salt content in Kentucky bluegrass soil was significantly increased for two consecutive years. In the second year, with the depth of soil increased, the content of total salt, soil sodium ion content and SAR value in the tall fescue soil showed increscent trends, but no significant effect detected in Kentucky bluegrass soil. In the third year, all the above soil parameters showed increscent trends along with the soil depth increasing for two kinds of turf grass soil. Total salt content, sodium ion content, and SAR value in tall fescue soil were less than those in Kentucky bluegrass soil in root distribution soil layers. Salt was accumulated in 30-60 cm layer of tall fescue soil and in 10-30 and 30-60 cm layers of Kentucky bluegrass soil. Compared with the second year, sodium ion contents in two kinds of turf grass soil irrigated with reclaimed water were increased but total salt contests decreased in third year. SAR value showed an increscent trend in both 10-30 cm and 30-60 cm soil layers with an significant increase in 30~60 cm soil layer.2. Selection of clay minerals and the removal efficiency of sodium and potassium ions of reclaimed water.The removal efficiency of sodium ion of three kinds of natural clay minerals, e.g. bentonite, attapulgite and stilbite, for reclaimed water was poor before modification, but relatively good for potassium ion. Four modification methods were respectively applied to the three clay minerals including particle size modification, temperature modification, ammonium chloride modification, and acid modification. By comparing the removal efficiency of sodium ion and modification costs, the best adsorbent and modification methods were obtained. The best adsorbent was bentonite and the best modification methods were room temperature, 0.2~1.0 mm particle size, 0.1 mol/L concentration acid modification. Ion exchange adsorption of bentonite was basically saturated under static experimental conditions with room temperature, 150 r/min shock speed and shock 60 min. Different solid-liquid proportion played a significant role for increased removal of sodium ion. Solid-liquid proportion 1 g/5mL was the best choice when considering the costs. The removal of sodium ion in reclaimed water by bentonite reached 27.5%. The removal effect under dynamic experimental condition was better than it under static condition. The effluent efficiency and effluent rate of three kinds of matrix exchange column were bentonite < bentonite-sand |
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