Alternative SVE Vapor Treatment Technologies

Two Stage Biological Reactor – (Envirogen)

The two-stage reactor described below is a system that removes VOCs from the air utilizing two distinct processes. These two stages consist of a fixed-film biofilter followed by a completely mixed, continuously stirred (CSTR), suspended-growth biological reactor.

The fixed film bioreactor, the first stage of the system, was designed to remove VOCs from the process-gas stream. All liquid discharged from the biofilter is pumped to a liquid waste storage container for disposal. The biofilter consists of a bioreactor vessel, support medium for the biofilm, control panel and a vapor feed blower.

The second stage of the biological treatment system consists of a CSTR that was used to degrade any residual contaminants in the gas stream following treatment in the first-stage reactor. The CSTR is composed of a bioreactor vessel with automatic pH control, foam, and temperature control, nutrient feeds and discharge tank. Treated vapor exited the liquid at the top of the water column while the wastewater was discharged from the reactor after passing over an overflow weir.

System monitoring and maintenance is required to maintain the health of the biosystem. In particular, maintaining proper humidity is essential. Once established, biofilter systems can adapt to varying influent concentrations, but they will respond more slowly to changes in influent contaminant composition than physico-chemical systems. Therefore, pilot scale studies are typically required to ensure process effectiveness. In addition, biofilters operate best under mild ambient conditions; therefore, removal efficiency can decrease in cold environments. Generally this type of system is most efficient when the used to remove concentrations less than 1000 ppm_v.

There are some general worker health risks associated with biofilters, but exposure of the general public to these risks is believed to be low. For example, biofilters can be large vessels or tanks that may require entry by personnel for inspection, repair and maintenance. Typical hazards associated with entry into confined spaces include asphyxiation from lack of oxygen, exposure to toxic compounds and/or byproducts and engulfment/entrapment in filtration media. Workers may also be exposed to hazardous chemicals during the application of nutrients and chemicals to the system such as ammonia, nitrate, urea, hydrochloric acid and sodium bicarbonate. Additionally there is a potential for workers to be exposed to pathogenic microbes during entry into the biofilters and during other maintenance or repair activities. However, most aerobic biofilter research has not indicated a propensity to support pathogens, although opportunistic microorganisms are commonly present of the species that would be found in typical soils.

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