Heavy-metal contamination removal by bacterial activity in seeping depositories

Abstract Heavy-metal removal from a toxic waste depository in East Germany occurs through the action of bacterial scavenging, as contaminant-laden waters transit a bounding dam. Measurements inside and outside the toxic domain indicate that this removal can amount to more than 90% of particular heavy metals from the exiting waters. This paper examines the steady-state behavior of interconnected bacterial number density dependence on the heavy-metal concentration, removal of the bacteria by heavy-metal poisoning, and simultaneous removal of the heavy metals by bacterial scavenging. Adjustment of the birth and death rates of bacteria, together with a propensity for the bacteria to seek out and scavenge the richest zones of heavy-metal contamination in the waters seeping through the dam, are the main intertwined components that allow heavy-metal removal. There is also a critical concentration such that bacteria cannot scavenge in waters with heavy metals above the critical concentration; the closeness of the input concentration to the critical value at the toxic side of the bounding dam plays a significant role in the spatial distribution of heavy-metal removal and also in bacterial number density concentration. Measurements both inside and outside the toxic depository allow one to bracket combinations of some of the biological parameters to account for the observations, but there are no uniquely determined values; such would require measurements in the dam materials. For a variety of health-risk reasons, such dam probes are not likely to be allowed in the near future, so that the determinations are limited.