Abstract
The formation of disinfection by-products (DBPs) during chlorination of drinking water is an issue which has drawn significant scientific attention due to the possible adverse effects that these compounds have on human health and the formation of another DBPs. Factors that affect the formation of DBPs include: chlorine dose and residue, contact time, temperature, pH and natural organic matter (NOM). The most frequently detected DBPs in drinking water are trihalomethanes (THMs) and haloacetic acids (HAAs). The MCLs are standards established by the United States Environmental Protection Agency (USEPA) for drinking water quality established in Stage 1, Disinfectants and Disinfection Byproducts Rule (DBPR), and they limit the amount of potentially hazardous substances that are allowed in drinking water. The water quality data for THMs were evaluated in the Puerto Rico Aqueduct and Sewer Authority (PRASA). During this evaluation, the THMs exceeded the maximum contamination limit (MCLs) for the Comerio Water Treatment Plant (CWTP). USEPA classified the THMs as Group B2 carcinogens (shown to cause cancer in laboratory animals). This research evaluated the THMs concentrations in the following sampling sites: CWTP, Río Hondo and Pinas Abajo schools, Comerio Health Center (CDT), and the Vázquez Ortiz family, in the municipality of Comerio Puerto Rcio. The results show that the factors affecting the formation of THMs occur in different concentrations across the distribution line. There are not specific ranges to determine the formation of THMs in drinking water when the chemical and physical parameters were evaluated. Three different nanostructured materials (graphene, mordenite (MOR) and multiwalled carbon nanotubes (MWCNTs)) were used in this research, to reduce the THMs formation by adsorption in specific contact times. The results showed that graphene is the best nanomaterial to reduce THMs in drinking water. Graphene can reduce 80 parts per billion (ppb) of THMs in about 2 hours. In addition mordenite can reduce approximately 80 ppb of THMs and MWCNTs adsorbs 71 ppb of THMs in the same period of time respectively. In order to complement the adsorption results previously obtained, total organic carbon (TOC) analyses were measured, after different contact times with the nanomaterials. During the first 30 minutes, graphene C/Co was reduced to c.a. 0.9, in presence of each THMs solution. MWCNTs and MOR show similar adsorptions trends in comparison with graphene.
Highlights
In Puerto Rico the water treatment plants are administrated by the Puerto Rico Aqueduct and Sewer Authority (PRASA)
natural organic matter (NOM) is composed of an heterogeneous mixture of humic substances (HS), carboxylic acids, proteins, amino acids, polysaccharides, hydroxyl acids and other common components of surface waters and are primarily of concern because it is a precursor to the formation of disinfection by-products (DBPs) in drinking water [6] [7]
THMs concentrations exceeding MCL established by United States Environmental Protection Agency (USEPA) are present in drinking water of Puerto Rico
Summary
In Puerto Rico the water treatment plants are administrated by the Puerto Rico Aqueduct and Sewer Authority (PRASA). The process for treating drinking waters is similar in the majority of drinking water treatment plants (DWTP) in Puerto Rico because they use chlorine as a disinfectant to produce drinking water quality for consumption. These processes begin with pre-chlorination in the water intake, and the water passes to a mixing chamber where Polymer 6803 is added to form sedimentation. The principal municipalities with this problem in Puerto Rico are: Aibonito, Aguas Buenas, Bayamon, Caguas, Canovanas, Cidra, Gurabo, Isabela, San Juan, Toa Baja, and Quebradillas In these municipalities THMs were detectable more than two times in a year
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