RESEARCH WATCH
BIODEGRADATION Soil transport On the basis of field studies in which pesticides infiltrate groundwater earlier than predicted, B. E. Pivetz and colleagues studied the effect of preferential flow paths in soil on the biodegradation of pesticides. They added p-nitrophenol to soil columns containing either an artificial macropore or a channel of coarser textured soil, then calculated biodegradation rates as a function of breakthrough times. Breakthrough occurred earlier in the macropore and channel areas of the columns, but biodegradation rates were enhanced in these areas. {Soil Sci. Soc. Am. J. 1996, 60, 381-88)
DRINKING WATER
Membrane efficiency Membrane technologies that remove significant amounts of natural organic matter (NOM) are being used more frequently in drinking water treatment processes, primarily because of more stringent water quality regulations limiting disinfection by-products (DBP). Elevated DBP in treated water is often caused by NOM in raw water reacting with chlorine. J. A. Nilson and F. A. DiGiano investigated the influence of NOM composition on the efficiency of a nanofiltration membrane system for treating raw water. Results demonstrated a nearly 80% decline in membrane flux because of NOM in the membrane system. Further investigation indicated that the hydrophobic NOM fraction was responsible for almost all of the flux decline. Results suggest that a pretreatment system, such as powdered activated carbon, may remove enough hydrophobic NOM to make nanofiltration more feasible and cost effective. (J. AWWA 1996, 88(5), 53-66)
Assessing the bioavailability of sedimentary contaminants Many aquatic contaminants are adsorbed onto sediments, leading to the assumption that this reduces dispersion and bioavailability. However, exposure may be enhanced by deposit-feeding organisms. L M. Mayer and co-workers measured the solubilization of sedimentary contaminants by digestive fluids from two marine invertebrates. Though the animals were from unpolluted sources, their fluids had high preexisting concentrations of copper, lead, arsenic, and cadmium. Nevertheless, the researchers observed increased solubilization of contaminants relative to seawater, which they ascribed to amino acids and surfactants in the fluids. As much as 10% of the total contaminant sediment loading was considered bioavailable to the deposit-feeders, with observed variations between species. Depositfeeder digestive systems are important in the environmental cycling of contaminants, and the authors propose that this approach be used in routine environmental impact assessments. [Environ. Sci. Techno!., this issue, 2641-45)
Nitrate, pesticide removal Membrane processes can be used to remove contaminants that are not effectively treated by conventional processes. V Urbain and colleagues evaluated a new membrane bioreactor process in a pilot-scale study to determine its effectiveness in denitrification, disinfection, and pesticide and natural organic matter (NOM) removal. Denitrification occurred in a completely mixed bioreactor that used ethanol as the carbon source, and powdered activated carbon was added to remove NOM and pesticides. They passed the effluent through an ultrafilter to remove suspended solids and particulates. Results indicated that the process was highly effective in removing nitrates, NOM, pesticides, and other compounds. This was the first successful demonstration of nitrate and pesticide removal by a membrane bioreactor. (/. AWWA 1996, 88(5), 75-86)
Ozone and coagulation The character and concentration of chemical compounds in raw water can affect particle destabilization and coagulation. Typically, oxidation is used to enhance coagulation in raw water. Few studies exist that evaluate ozone as an oxidant in the oxidation of extracellular organic matter (EOM) produced by algae. A.
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Paralkar and J. K. Edzwald investigated the effects of ozone on EOM oxidation and the subsequent effects on coagulation. Results indicate that EOM impact on coagulation depends on the type of algae and the EOM concentration. At low doses, ozone caused the release of EOM from algae and enhanced coagulation. At higher ozone doses, EOM was oxidized more completely and had little effect on coagulation. (/. AWWA 1996, 88(4), 143-54)
MEASUREMENTS Colloid composition Because of their large surface-tomass ratio, colloids play an important role in contaminant transport and immobilization. However, methods to reliably characterize their composition are scarce. Y. E. Freedman and co-workers used solid sampling graphite furnace atomic absorption spectrometry to determine copper and cadmium content in groundwater colloids. They collected colloids from a groundwater aquifer by passive filtration onto a dialysis cell in the field. Results of subsequent analysis by solid sampling agreed with those obtained by total digestion. The copper and cadmium content of the colloids varied with depth below the water table and also
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