Keywords: bacteria, biodegradation, filters, groundwater, microorganisms, organic compounds, phenols, pollutants, sand, water treatment, water supply, water quality, water pollution, environmental pollution, chlorophenolic contaminants
Secondary removal of chlorophenolic contaminants in water
In this study, several factors important for the design of a water supply treatment system for the removal of trace amounts of organic contaminants by microorganisms in a fixed-film were assessed. This entailed evaluating the effect of seeding with adapted microorganisms on the acclimation time, determining what depth of support material was required for removal of contaminants and observing the effect of hydraulic loading rate on the contaminant removal efficiency by the microorganisms. The study was conducted in the laboratory using sand columns as fixed-film biological reactors. Pentachlorophenol (PCP), 2,4,6 trichlorophenol and 2,4 dichlorophenol were used as the test contaminants. Dechlorinated Philadelphia tap water, which contained concentrations of dissolved organic matter (DOC) in the range of 1 to 4 mg/l, was used as the source water. The DOC of the source water served as a primary substrate for microbial growth in the sand columns. The total concentration of the contaminants added to the source water ranged between 200 and 800 μg/l, making them available as secondary carbon sources for the attached microorganisms. The columns were operated in a downflow mode and the hydraulic loading rates through the columns were varied from 0.5 gpm/ft² to 3 gpm/ft² (1.2 m/hr to 7.3 m/hr). It was observed that each cycle of operation of the treatment system could be divided into three different stages: acclimation; equilibrium removal; and clogging. Acclimation is the period of time between initial startup and equilibrium removal of the contaminants. Equilibrium removal was defined as the consistent removal of the contaminants for at least four days. Clogging of the sand with biological growth was found to occur after long term operation in shallow depths of sand. The acclimation time and the establishment of an adapted population were not shortened by seeding the sand columns with laboratory acclimated cultures. During the second stage, equilibrium removal, the removal of DOC decreased with depth as a first order relationship. However, the removal of the contaminants was observed to be zero order. Removal of the contaminants decreased with increasing hydraulic loading rate. Reductions of 80% or more of μg/l amounts of the chlorophenolic contaminants was achieved in a one inch depth of sand.