City water pollution by soot-surface-active agents revealed by FTIR spectroscopy

The aim of the study presented in this paper is to investigate and evaluate the water contamination during different episodes of pollution, with different symptoms that proved to be generated by the same contaminant source, the soot. FTIR investigation on diesel cars muffler-collected compound proved that the soot is a composite structure where agglomerations of granular phases in the experiment are incorporated in matrix of continuous films phase. Experimental investigation and spectra of the separated two phases confirmed this supposition. Similar spectra were obtained for the particles remained on the filter paper from filtering the foaming rain water from the streets of two major Romanian cities in the spring after a dry winter, sulfonic groups R−SO3− being identified in both cases. The surfactant structures have also been identified in the FTIR spectra for the continuous phase prepared from the liquid resulted from the same filtration process of foaming rain waters. Due to its ampholytic character, part of the surface active compound, remained bonded to the insoluble particles from soot through its hydrophobic region, and part of it bonded with water through its hydrophilic region, i.e. sulfonic groups. The same sulfonic groups had been detected before in the air and reported in a study. The source is herein identified as the soot from diesel fuel combustion dispersed in the air and the sink is proved to be the rain that washes it down to the ground. The source of foaming was found within this study as being surfactants added to the diesel fuel for cleaning the engine and those were mixed with the soot during combustion and exhausted in the atmosphere with the combustion gases. Further investigation as to the continuous phase composition resulted from evaporating the water from the liquid of the filtration showed in FTIR spectra that part of the surface active agent bonded with the water and passed through the filter paper. Using FTIR method of investigation, a flocculation process noticed in tap water from domestic city supply in Ploiesti, Romania proved to be caused by sodium aluminate (NaAlO2, Na2O·Al2O3, or Na2Al2O4, and for this specific case as hydrated form NaAl(OH)4). The source could be either excessive use of aluminate for water treatments, i.e. separation of colloids from water, or a hazardous contamination with waters used in constructions. The flakes studied with FTIR spectroscopy, proved to be of the same or similar composition as for the continuous phase of soot composite, and that is the evidence of the transport, and infiltration to the groundwater of soot components. That is the evidence of extended effects of pollution with soot that starts from the air and returns to the ground, harming the safety of human's health in direct and indirect ways.