EFFECT OF LAKE OKEECHOBEE HYDROPHOBIC ORGANIC ACIDS on BACTERIAL ATTACHMENT IN KARST LIMESTONE FROM THE UPPER FLORIDIAN AQUIFER

Aquifer storage and recovery (ASR) is currently being explored in Florida as a way to store excess water during rainy seasons in order to resupply surface waters during dry seasons. Because recovered water from ASR sites must meet state and federal drinking water requirements it is important to determine the most cost-effective approaches for the treatment of recharge and/or recovered water. An important consideration for ASR sites is what water quality characteristics may enhance pathogen attachment within the Upper Floridian aquifer. Because groundwater within the Upper Floridian aquifer in the Miami-Dade area is 15,000 – 20,000 years old there has not been a terrestrial influx of carbon in over a millennium. It is unknown how the addition of surface water carbon would alter bacterial attachment in the Upper Floridian aquifer so the effect of introducing hydrophobic organic acids (HPOA) derived from Lake Okeechobee was investigated. The presence of HPOA had no effect on the surface charge of Escherichia coli across a range of ionic strengths (0.1 mM -1M NaCl). However, the addition of 40 mg/L HPOA to artificial lake water significantly enhanced E. coli transport by 2.37 fold ((p = 0.03) when using static columns with karst fragments made from Upper Floridian cores. It was hypothesized that the addition of HPOA may adsorb to the karst thereby masking potential binding sites for E. coli attachment and/or the addition of HPOA may remove positively charged iron oxides which are important in the removal of bacteria based on charge. However, initial investigations showed that the addition of HPOA did not adsorb to or remove iron oxides from the karst limestone.