Removal of trace-level organics by slow-rate land treatment

A 2 yr study was performed on an outdoor, prototype, slow-rate system to determine the removal efficiency for 16 organic substances in wastewater. The 16 organics were chloroform, benzene, toluene, chlorobenzene, bromoform, m-dichlorobenzene, dibromochloromethane, pentane, hexane, nitrobenzene, m-nitrotoluene, diethylphthalate, PCB 1242, napthalene, phenanthrene and pentachlorophenol. The initial concentration of each of these substances in the wastewater was approx. 50 μg l −1. Initial removal was via volatilization during spray application. The final concentration of substances after spraying correlated well with their calculated liquid-phase transfer coefficients and the substances' initial concentration losses were up to 70% for the most volatile components. Total percent removal for the system, based on the residual concentration in the percolate, was >98% for all substances. Only chloroform, which has a low octanol-water partition coefficient and according to the literature is not degraded aerobically, was continuously detected in the percolate. Breakthrough of several other organics in early spring was also observed, apparently as a result of application in late fall. The two substances that were most persistent in the soil were PCB and diethylphthalate (DEP). PCB was retained near the surface while DEP leached deeper in the soil profile as predicted by their respective octanol-water partition coefficients.