EFFECT OF FLOW-RATE AND PATH-LENGTH ON P-NITROPHENOL BIODEGRADATION DURING TRANSPORT IN SOIL

The effect of how rate and path length on the biodegradation of p-nitrophenol (PNP) during its transport through soil was measured in columns of unsaturated soil receiving a continuous application of the compound. The PNP concentration in the effluents increased to a maximum and then decreased. Within 3 to 4 d after the initial addition of PNP, the number of microorganisms capable of degrading PNP reached a density that was sufficient to degrade all of the applied compound. The percentage of PNP entering the effluents from the soil decreased as the flow rate was reduced or the path length was increased, presumably because of the longer period of contact between the microorganisms and the test compound. When PNP was still leaching into the effluent from a TO-cm column of soil, the microorganisms able to degrade PNP grew extensively at the 2.5- but not the 7.0-cm depth. At the time that all of the PNP flowing through the soil was degraded, microorganisms capable of transforming PNP were concentrated in the top one-fourth of the soil column. The reasons for the lack of extensive growth of the PNP-degrading population at lower depths in soil containing PNP are unknown.