Analyse des sous-produits de chloration dans une filiere de biodenitrification sur substrat ligno-cellulosique naturel (Analysis of by-products of chlorination in a biodenitrifying line on a natural lignocellulose substrate)

The highest levels of nitrates in wells are generally found in areas where agricultural activities are more intense. Thus, in areas of coastal cultures of Doukkala (Province of El Jadida, Morocco) nitrate concentrations of groundwater intended for human consumption exceeds the permissible level for drinking water and sometimes reach levels of 100 to 400 mg / L. The nitrate removal of this water can be achieved either by biological treatment or by physical-chemical treatment. For this purpose, a heterotrophic biodenitrifying / chlorination line has been developed at the Laboratory. However, this conventional line is insufficient to meet the requirements of the World Health Organization (WHO). The addition of an aeration followed by filtration on granular activated carbon-sand has reduced these recurring problems. Moreover, analyzes carried out previously on the phenolic extracts from the substrate, groundwater and treated water (denitrified, aerated and filtered) revealed the presence of phenolic compounds with high chlorine consumption. Some of them are derivatives of lignin constituent of natural substrate. The others are micro-pollutants from the effluent to be treated or formed in the reactor. The aim of this work is to identify the by-products of interaction between chlorine (used for disinfecting denitrified and filtered water) and the organic matter present in denitrified and filtered water. For this purpose two chlorination tests were conducted in parallel. The first test was conducted on commercial phenolic compounds previously identified in the substrate and / or may be present in treated water: p-cresol, 4-ethylphenol, 4-tert-butylphenol, 2,4-di-tert-butyl phenol ; 3,5-di-tert-butylphenol; 2,6-di-tert-butylphenol and 2,4,6-tri-tert-butylphenol. The second test was conducted on denitrified filtered water after chlorine disinfection. The chlorination by-products were extracted with dichloromethane and analyzed by gas chromatography coupled with mass spectrometry (GC / MS). For commercial phenolic compounds, the by-products of chlorination identified are chlorophenols, oxygenated and / or chlorinated benzene derivatives and aliphatic oxygenated compounds. For treated water, chlorinated aliphatic hydrocarbons such as 1-chloro-hexadecane and 1-chloro-octadecane have been identified.