Controlling Metal Mobilization From Waste Organic Carbon Land Application.

Metals naturally present in soil may leach into groundwater from the land application of waste organic carbon.  Excess organic input will result in microbial oxygen consumption greater than that which is in the applied water or can diffuse into the soil from the atmosphere.  High soil moisture levels further limit the amount of organic carbon that can be aerobically biodegraded because of the lack of soil porosity available for oxygen.  The resulting low oxidation/reduction soil environment causes metal reducing microbial populations to predominate, resulting in the mobilization of metals, such as manganese, iron, sulfate, and arsenic that serve as electron acceptors.  Reports of metals leaching into groundwater from soil application systems have resulted from food processing wastewater irrigation, manure application to farmland, farm runoff spread on vegetative filter strips, milking facility wastewater discharged through a filter mound, biosolids stacked for storage, hazardous waste remediation using bioremediation, landfill leachate treatment, and domestic wastewater infiltration basins.  Only minimum scientific and engineering justifications for hydraulic and organic loadings of wastewater and soil monitoring strategies were found.  This research focused on food processing wastewater.  Field studies demonstrated the utility of using soil moisture and oxygen sensors to detect conditions that are conducive for metal mobilization.  With such data, the development of strategic, field-specific irrigation strategies is possible.  Laboratory research qualitatively demonstrated the importance of hydraulic and organic loadings, soil types, and dosing schedules to determine acceptable loading and identify the occurrence of a moving water front that resulted in a sequencing high and low porosity oxygen environment.  The length of time and drop in oxygen resulting from each dosing is theorized as a critical determinant of the aerobic or anaerobic environment that will predominate.