DESIGN OF TWO PERMEABLE BARRIERS FOR NITRATE REMOVAL IN GROUNDWATER

The main issue with nitrate relies in the mobile nature of the compound, which in groundwater, is not adsorbed, allowing it to be dissolved in great amounts. Additionally, ingestion above 50 mg/L, NO3- by infants under three months old could cause methemoglobinemia. The aim of the present investigation was to select a microbial consortium to grow on size 2-6 mm tezontle for the biologic denitrification, and the chemical conditioning of size 2-4 mm zeolite, to form permeable barriers for nitrate removal in groundwater. The experimental phase consisted of several activities for the development of a biological barrier and a zeolite anionic exchange barrier. In this investigation, four possible sources of microbial consortia were evaluated for the development of the definite microbial consortium for biological denitritication: i). Uptlow Anaerobic Sludge Blanket (UASB), ii). Anaerobic-Anoxic-Aerobic sludge (A-A-A), and two depths of soil samples from the Xochimilco chinampas iii). From 20 to 30 cm, and iv). From 30 to 40 cm. The zeolite was physically and chemically conditioned in order to obtain a particle size of 4-6 mm, and an anion exchange capacity of 094 meq/g. From the performance in growth curves of the consortia and the nitrate removal, the UASB sludge was selected as the best of the four evaluated. This consortium was multiplied and fixed as a biofilm in a porous material locally knowns as "tezontle", from volcanic origin. Considering a retention time of 20.5 h, the size of the barrier for biological denitrification was dimensioned 0.20 m high and 10.2 cm diameter. As for the design of the zeolite barrier, it was considered a removal in groundwater of 100 mg/L NO3-, dimensions of the barrier were 0.1 m high and 10.2 cm diameter.