Abstract
IntroductionThe influence of the interaction of calcium carbonate (CaCO3) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed.ResultsLaboratory simulations indicate reduced negative influences on cationic SAS nitrification/self-purification processes in the presence of anionic species. This suggests the role of complex ionic formation [anionic SAS * cationic SAS] as a cause of this effect. UV-Vis spectra of lauryl sulfate (LS) and of cetyltrimethylammonium (CTMA), as well as of their mixtures in ratios of 2:1 and 1:1, treated by fine particles of CaCO3, display decreased amounts of SAS in analyzed solutions and their presence on the surface of CaCO3 nanoparticles. UV-Vis spectra reveal the decomposition of the complex [anionic SAS (SAS-An) * cationic SAS (SAS-Ct)] in solutions when CaCO3 is added. CTMA can be bonded by LS through hydrophobic chains, on the surface of CaCO3 particles. Therefore, CaCO3 modifies the nature of LS and CTMA interactions. This leads to an increased degree of toxicity of cationic SAS in aquatic environment. The amounts of CTMA in aqueous solutions are diminished in the presence of ammonium ion NH4+ (2 mg/L). In the presence of two orders higher concentration of ammonium ion, this effect strongly increases, making the association obvious. The structure of cationic SAS does not influence this effect. The obtained results have been confirmed both by timed natural aquatic sample analysis and laboratory simulations using water from Moldovan small rivers (Isnovat, Raut, and Bic).ConclusionsUV-Vis spectra and laboratory simulations demonstrate the change due to the addition of calcium carbonate. Simulations and laboratory tests of water samples from Isnovat, Bic, and Raut Rivers, establish the cationic SAS negative influence on treatment and self-purification processes.
Highlights
The influence of the interaction of calcium carbonate (CaCO3) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed
This paper presents a continuation of our research of the water pollution in the Nistru and Prut Rivers with a series of surface-active substances for small river sections with a different urban influence
Spring samples from the Nistru River and the rivers of the Cunicea village were investigated by means of a model described in Spataru et al 2015, using water samples both in the presence and absence of Calcium carbonate (CaCO3)
Summary
The influence of the interaction of calcium carbonate (CaCO3) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed. The presence of suspended solid particles and naturally occurring dissolved substances decreases the bioavailability of cationic surfactants but not that of anionic and nonionic ones (Lechuga et al 2016; Thomas et al 2009). The presence of cationic detergents (Sandu et al 2007; Sandu et al 2008) can explain the difference between the samples from the Nistru River in Varancau village and the Cunicea village in terms of calcium carbonate impact (Fig. 1). The dynamics of the concentrations of NH4+ and NO2− ions for the river in the Cunicea village, whose waters do not contain synthetic surfactants, and the oxidation of ammonia is similar in both samples (with and without CaCO3)
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