Table 5.
Upper limits of dry density for microbial activity/survival in different bentonites.
| Microbial group | Bentonite type | Microbial inoculum (+/-) | Dry density* limit(kg m−3) | Details | Reference |
|---|---|---|---|---|---|
| Sulphate reducers (survival) | Wyoming | (-) | 1171–1406 | Survival below detection limit at 1406 and 1562 kg m−3 | Bengtsson et al. (2017a,b) |
| Wyoming | (+) | >1562 | Low levels of survival observed at highest tested dry density. | ||
| Asha | (-/+) | >1529 | Survival in uninoculated tests lower than inoculated tests. | ||
| Calcigel | (-) | 1333–1490 | Survival low at 1333 kg m−3 but below detection limit at 1490 kg m−3. | ||
| Calcigel | (+) | >1490 | Low survival rates observed. | ||
| Gaomiaozi | (-/+) | >1469 | Survival was 100 times lower at 1469 kg m−3 than at 1315 kg m−3. | ||
| Rockle | (-/+) | >1408 | No clear decrease in survival with increasing dry density. | ||
| Sulphate reducers (activity) | Wyoming | (-) | 1406–1562 | Activity was very low at 1406 kg m−3 and below detection limit at 1562 kg m−3. | Bengtsson et al. (2017a,b) |
| Wyoming | (+) | >1562 | Low levels of activity observed at highest tested dry density. | ||
| Asha | (-) | 1300–1529 | Activity was very low at 1300 kg m−3 and below detection limit at 1529 kg m−3. | ||
| Asha | (+) | >1529 | One of two tests at 1453 kg m−3 was below the detection limit, however, very low activity was detected in both highest dry density tests. | ||
| Calcigel | (-/+) | >1490 | Activity was detected but 4000 times lower than the next lowest tested dry density (1333 kg m−3) for uninoculated samples. | ||
| Gaomiaozi | (-/+) | >1469 | Activity remained high up to the highest tested dry density. | ||
| Rockle | (-/+) | >1408 | Low activity detected at highest tested dry density. | ||
| Denitrifying bacteria (survival) | Wyoming | (-) | 1850 | Microorganisms capable of reducing nitrate to di-nitrogen did not survive while those caple of reduction to nitrite survived at the single tested density. | Jalique et al. (2016) |
| Heterotrophic bacteria (survival) | Wyoming | (-) | 1850 | Aerobes and anaerobes survived at the single tested density. | Jalique et al. (2016) |
| Acetogens (activity) | Gaomiaozi | (-/+) | >1469 | High activity (acetate production) observed at all tested densities. | Bengtsson et al. (2017b) |
| Rockle | (-/+) | >1408 |
Dry densities provided were the planned dry densities tested. Actual dry densities may have been calculated after test end, differing from planned dry densities in some tests. For the microbial inoculum column, (+) indicates the experiments were inoculated, and (-) indicates they were uninoculated (-). Limiting dry density is reported as a range; the lower value represents the dry density where microbial survival/activity was not impacted, and the upper value represents the dry density at which impacts could be detected. If information on survival or activity above this range is available, this is noted in the ‘details’ column. In some cases, conversions from wet to dry densities have been carried out using information within the original papers.