Reducing riverbed infiltration using mixtures of sodium bentonite and clay

Abstract

Using reclaimed water has become one of the most effective ways to solve the problem of urban water shortage. Using mixtures of sodium bentonite and clay to reduce infiltration is an important safeguard measure to meet the need of groundwater recharge and water quality safety. The microscopic structure of sodium bentonite was studied with environmental scanning electron microscopy. The effect of different mix ratios of sodium bentonite and clay on the performance of reducing infiltration was studied with constant head infiltration experiments and adsorption of ammonium and phosphate with the batch method. The results showed that the dry particles of sodium bentonite had lamellar and compact structure, after absorbing water, and both the number and size of pores gradually reduced to become uniform distributions. With the increase of bentonite mix ratio (10–20 % of the total dry weight), the infiltration coefficient of the mixed materials decreased exponentially (R2 = 0.95). Linear, Freundlich, and Langmuir equations could be used to describe adsorption of N/P on the mixed materials. There were significant correlations between adsorption parameters (Sm and MBC) and bentonite mix ratio. The effect of removing ammonium with mixtures was better than that of phosphate. Considering synthetically the capability of reducing infiltration and decontamination, a mixture of 19 % bentonite and 81 % clay was a suitable model in the Yongding River in Beijing plain segment.