Bioventing systems

The main requirements for the design of a bioventing system are the following9 ... 

Rathfelder, K.M., Lang, J.R. and Abriola, L.M., A numerical model (MISER) for the simulation of coupled physical, chemical and biological processes in soil vapor extraction and bioventing systems, J. Contam. Hydrol., 43, 239-270, 2000. 

Figure 3. Common bioventing system for treatment of vadose-zone contaminants using oxygen as a terminal electron acceptor. Reprinted from In Situ Bioremediation When Does It Work Copyright 1993 by the National Academy of Sciences. Courtesy of the National Academy Press, Washington, DC.

Bioventing System Installed Alter Tank s Removal... 

An 02 flow must be maintained through the contaminated zone at a level sufficient for the aerobic biodegradation of contaminants. Note that during bioventing the main aim is the maximum utilization of 02 by the microbial cultures. For this reason, air flow rate is usually an order of magnitude lower than that applied in simple SVE systems. A simple empirical rule is that the mean residence time of air in the contaminated soil pore volume should be between 1 and 2 days. 

As previously mentioned, a minimum level of soil moisture is necessary for successful biodegradation. The continuous circulation of air during bioventing results in the evaporation of soil moisture. For this reason, the design of these systems must include an appropriate installation for adding water to the contaminated zone. Care must be taken to avoid the addition of excess water. If soil moisture is significantly increased, e.g., above the limit of 85%, air circulation is no longer effective due to the decrease in free soil porosity. 

A schematic of a bioventing installation, including a system for the addition of water and nutrients, is depicted in Figure 14.4. When the contaminated zone is near the surface and the soil is sufficiently permeable, the addition of water, together with dissolved nutrients, can be carried out using a simple surface irrigation system. When the contamination is located at lower horizons, an underground infiltration system or a network of wells may be more appropriate. 

T0123 BioTrol, Inc., Biological Aqueous Treatment System T0126 Bioventing—General... 

Downey et al., of Parsons Engineering Science, Inc., reported costs for bioventing at a diesel-fuel-contaminated site in Nebraska as 112,000, or less than 10/m of soil treated. This cost included pilot testing, full-scale installation, and 2 years of operation and maintenance but did not include the cost of electricity (estimated at 280 per month) or labor costs for system checks. It is noted that bioventing provides significant economy of scale and that costs for sites smaller than 11,000 m are typically in the range of 10 to 30/m (D151508, p. 124). 

In September 1994, the NMSHTD retained a second consultant, Daniel B. Stephens Associates, Inc. (DBS A) to design and implement a corrective action system at the Artesia Patrol Yard. Sections 3.1 and 3.2 outline DBS A s rationale for and design of the high-vacuum SVE system for the Artesia Yard. The techniques used to enhance the recovery of petroleum vapors from the vadose zone are described in Sections 3.3 and 3.4. These techniques extended the operation of the high-vacuum SVE system and allowed a more effective cleanup of the vadose zone in preparation for the current phase of bioventing. 

Except for a temporary shutdown (due to a lapse in the NMSHTD contract) between July and December 1998, the AS system has operated separately since the end of January 1998. The AS system provides air flow to sweep volatile contaminants from the groundwater and promotes bioventing in the vadose zone. 

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