Enhanced animal waste management through application of surfactants to soil material: laboratory feasibility testing

Laboratory testing was conducted to determine the feasibility of using surfactants to enhance soil performance with regard to animal waste management at feedlot and dairy sites. Three surfactants, one anionic (sodium dodecyl benzene sulfonate) and two cationic (polyoxypropylene methyl diethyl ammonium chloride and tetradecyl trimethyl ammonium bromide), were tested on a sandy loam. The best surfactants are those capable of substantially reducing the amount of leaching under saturated and unsaturated flow conditions. Maintaining acceptable mechanical compaction characteristics, and if possible, limiting nitrate mobility are also important. The experimental program therefore focused on three areas: (1) Surfactant influence on leaching as indicated by effects on soil hydraulic properties (saturated hydraulic conductivity, soil moisture diffusivity, and unsaturated soil wetting front penetration); (2) Surfactant effects on mechanical compaction; and (3) Nitrate transport in surfactant-modified soil. Saturated hydraulic conductivity was measured using falling-head permeability tests. Transient unsaturated horizontal column experiments provided information concerning surfactant influence on soil moisture diffusivity and wetting front penetration. Standard Proctor methods were applied in the study of surfactant effects on mechanical compaction. Adsorption batch tests gauged nitrate mobility in surfactant-treated soil The anionic surfactant (sodium dodecyl benzene sulfonate) and one of the two cationic surfactants (polyoxypropylene methyl diethyl ammonium chloride) produced considerable reductions in saturated hydraulic conductivity, soil moisture diffusivity, and unsaturated soil wetting front penetration. With regard to mechanical compaction, the anionic surfactant and the other cationic surfactant (tetradecyl trimethyl ammonium bromide) affected decreases in the optimum moisture content corresponding to maximum dry bulk density. The moisture content range between optimum and the wet value corresponding to 90% or 95% maximum dry bulk density is also much narrower for these two surfactants, thereby increasing the difficulty of field compaction. Interestingly, the cationic surfactant having the greatest influence on soil hydraulic properties was not the same one having the most substantial effect on mechanical compaction. Adsorption batch tests indicate nitrate mobility in the sandy loam is not significantly altered by soil treatment with any of the three surfactants. The polyoxypropylene methyl diethyl ammonium chloride test results (no adverse effects on mechanical compaction and reduced hydraulic conductivity, diffusivity, and wetting front penetration) are alone enough to suggest the feasibility of using surfactants to enhance soil performance for animal waste management. However, more investigation is needed with a greater variety of surfactants on a number of different soils, particularly with regard to hydraulic property testing using leachate typically generated at animal feedlot and dairy facilities.