RESEARCH ARTICLE Conductometric measurement of the changes in humic substances caused by ozone oxidation Alejandra Martín-Domínguez 1 & Abigail Lara-Sánchez 2 & Anne M. Hansen-Hansen 1 & M. Teresa Alarcón-Herrera 3 Received: 16 June 2015 /Accepted: 29 February 2016 /Published online: 11 March 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Humic substances (HS), a broad category of or- ganic compounds and a major constituent of soil, are re- sponsible for serious problems during water purification processes. In particular, HS react with chlorine during dis- infection processes to produce a variety of organochlorine compounds such as trihalomethanes (THMs), which are potentially carcinogenic to humans. The use of ozone as a disinfection method represents a potential solution to this problem; however, HS that are not completely oxidized may form by-products more reactive than the original mol- ecules. The structural changes of HS during oxidation with ozone were evaluated through a replicated 2 2 design, where concentrations of 5 and 30 mg/L of two commercial HS (Aldrich and Fluka) were ozonized over different time intervals (0, 10, and 20 min). The ozone-treated HS were titrated with acid and base solutions, and the shifts of the slopes were then analyzed and finally related to the ionic alterations of the HS. The Aldrich HS (AHS) showed only protonated functional groups; the Fluka HS (FHS) showed only ionized groups; and in both cases, the amount of functional groups increased with increasing ozonation. For AHS and FHA, respectively, the maximum ozone ex- posure time (20 min) and the highest concentration of HS (30 mg/L) produced the greatest reductions in total organic carbon (TOC) (39 and 34 %), UV254 (50 and 60.8 %), and color (16.4 and 19.6 %). As for aromaticity, AHS showed removals of 39.6 % (from a starting concentration of 5 mg/ L) and 17.2 % (from a starting concentration of 30 mg/L). FHS showed the opposite effect, with removals of 33.3 % (starting at 5 mg/L) and 40.1 % (starting at 30 mg/L). In this study, the structural changes of HS submitted to ozon- ation were inferred in a relatively quick and easy way by using a conductometric titration, thus demonstrating the applicability of the technique. Keywords Humic substances . Ozone . Conductometric titration Introduction Surface water contains varied concentrations of numerous or- ganic compounds, including natural organic matter and other compounds resulting from the infiltration of water through the soil; from photochemical, chemical, and biological reactions; and from the metabolism and degradation of biota. The main natural organic compounds in environmental systems are polymerized acids and humic substances (HS). The latter are usually amorphous, black or brown, hydrophilic, and of varying molecular weights, and include a wide range of acids that have similar constitutions and common properties (Brechelt 2004). Humic substances can be classified according to their sol- ubility: humic acids (soluble in alkali), humins (insoluble in alkali), and fulvic acids (soluble in both acid and alkali) (Stevenson 1982). Responsible editor: Philippe Garrigues * M. Teresa Alarcón-Herrera teresa.alarcon@cimav.edu.mx 1 Instituto Mexicano de Tecnología del Agua (IMTA), Paseo Cuauhnáhuac 8532, Progreso, CP 62550 Jiutepec, Mor., Mexico 2 Buckman Laboratories S.A. de C.V., Paseo Cuauhnáhuac Km 13.5, Progreso, CP 62550 Jiutepec, Mor., Mexico 3 Centro de Investigación en Materiales Avanzados (CIMAV-Durango), Victoria 147 Nte., CP 34000 Durango, Dgo., Mexico Environ Sci Pollut Res (2016) 23:12085–12094 DOI 10.1007/s11356-016-6391-0