ATTACHMENT DETACHMENT AND TRICHLOROETHYLENE DEGRADATION-LONGEVITY OF A RESTING CELL METHYLOSINUS-TRICHOSPORIUM OR3B FILTER/

We are investigating a methanotrophic filter strategy for the in situ bioremediation of low levels of chlorinated aliphatic, volatile organi c chemicals (VOCs). It is based on the use of pregrown, resting cells, instead of growth-nutrient stimulations. The economic feasibility of such a filter is dependent on its operational longevity at groundwater temperatures. The latter, in turn, is dependent on several key parame ters, such as the bacterial attachment densities reached during the in jection of the microbial suspension and the subsequent detachment-remo val of cells from the filter over time. Scaled attachment/ detachment experiments were carried out using a representative quartzitic sand in glass 1-cm x 10-cm columns to simulate a filter. A rosette-dominated form of Methylosinus trichosporium OB3b was isolated and used in these and the subsequent catalytic longevity experiments. Its initial attac hment, employing Higgins' medium phosphate buffer, pH 7.0 (HPB), was 7 .0 to 8.0 x 10(8) bacteria/g of dry sand. This was elevated to similar to 1.5 x 10(9) cells/g by including 1.0 mM MgCl2, 100 mu M FeSO4, and 0.025% agar in the cell-suspension loading buffer. These loading addi tives also increased the time required to reach 50% cell detachment wi th HPB alone from 5 days to similar to 45 days. The functional longevi ty of a column biofilter, formed with resting-state rosette-enriched c ells in the presence of the aforementioned additives, was determined a t 21 degrees C by challenging it with weekly 12 h, similar to 250 ppb pulses of trichloroethylene (TCE). The column results indicate that fo r our attached-cell filter to biodegrade TCE levels of several hundred ppb sufficiently, to <5 ppb, it will likely need replenishment at sim ilar to 8 week intervals, due to the instability of the endogenous who le-cell soluble methane monooxygenase specific activity beyond that ti me period. This study represents the first time that anyone has shown that a rosette-enriched substrain can be isolated from a well-known me thanotrophic strain and then stably cultured and utilized advantageous ly for a specific application-namely its improved attachment-slowed de tachment characteristics in a microbial filter. (C) 1996 John Wiley & Sons, Inc.