Refine search
Results 1-2 of 2
Interactions on the Soil-Rainfall System of a Lime-Stabilized Sludge as Surface Amendment
2001
Suárez, D. | Rendueles, M. | Díaz, M.
Sludge from a wastewater treatment plant can be applied to soil to make use of its fertilizing properties, neverthelessit is necessary to study all the effects of this deposition to ascertain any possible hazardous properties. Interactions among the soil, the water, and a lime-stabilized waste watersludge were studied, both in batch experiments, and in columnpercolation experiments. Firstly a physico-chemical characterization of the soil and the sludge used for the experiments was carried out. This analysis included pH, organic matter, cation exchange capacity, metals and cations.The kinetics and equilibrium of the sludge-water and leachate-soil systems were studied in batch experiments; thekinetics were fitted to a first order differential equation and distribution coefficients were found for the equilibrium.Experiments in columns (10 cm diameter × 50 cm height) were carried out with a bed of sludge over a bed of soil usingdifferent sludge/soil ratios and then 6 L of water (rainfall)was poured over the beds. Results showed good adsorption of Ca and a complete leaching of the aqueous phase of this ion afterpassing a volume of water equivalent to three volumes of the column. The concentration of heavy metals (Zn, Ni, Hg, Cd, Pb and Cr) in the leachates did not reach the admissible legal limits (Spanish and European regulations) in any case.
Show more [+] Less [-]The Impact of Road De-Icing Salts (NaCl) on Colloid Dispersion and Base Cation Pools in Roadside Soils
2001
Norrström, A.-C. | Bergstedt, E.
The maintenance of safe-drivingconditions in snow and ice-affected areas in thewintertime includes the use of sodium chloride (NaCl)as de-icing salts. In this study, the impact of NaClon soil-colloid mobilisation and exchangeablebase-cation leaching has been evaluated. The chemistryof groundwater samples below an infiltration trenchfor highway runoff and leachate from column studiessuggested that soil-colloid mobilisation had occurred,as the exchangeable sodium (Na) concentration and theelectrical conductivity (EC) in the groundwater/columnleachate reached the threshold values for colloiddispersion. Generally, samples with no dispersionproblems had high Na and calcium (Ca) concentrations,suggesting that the initial effect of the de-icingsalt was to stabilise the colloids. In the columnstudy there was a good agreement between the degree ofcolloid dipersion problems and lead (Pb) concentrationwhen the pH value was above 7.0. Significant negativecorrelations between Na/CEC (cation exchange capacity)and Ca/CEC in roadside soils from three sitesindicated that Na preferentially displaces Ca from theexchange sites. However, the groundwater dataindicated that Na ions also displace potassium (K) andmagnesium (Mg). A positive effect of NaCl seen at onesite was an increase in the K concentration, which ishighly likely an effect of Na ions displacing fixed Kbetween the layers of 2:1 type clay minerals. In soilslacking these types of clay minerals, severe Kshortage may result from a high plant demand combinedwith the low K concentration in the readily availablefractions in the original soil and a highsusceptibility to leaching. The most significantimpact on soil exchange processes was found to occurwithin 6 m from the road.
Show more [+] Less [-]