BIOPILE OPTIMIZATION PRIMER

BIOPILE BIOREMEDIATION DESIGN OPTIMIZATION PRIMER WITH HC-2000

Mark D. Ryckman, P.E., D.E.E.

1. BIOPILE BIOREMEDIATION BACKGROUND

Biopiles are especially effective for degrading petroleum-contaminated soils in an aerobic environment. Biopiles relieves the burden on landfills that are already overloaded with leachate and vapor intrusion. The primary mechanisms of petroleum hydrocarbons concentration reduction in biopiles are by native aerobic degradation and evaporation. Bioremediation is conducted by employing biostimulation (like bioventing and composting, except exsitu rather than insitu), supplying electron acceptors, water, catalysts (nutrients, in the form of organic nitrogen, phosphorus, trace elements, vitamins, excess carbon when needed) and surfactants. Surfactants have been demonstrated to be a significant factor in desorbing bound contaminates and may increase degradation rates by up to 20%.

Remtech has developed a bioremediation catalyst with biosurfactants that optimizes biopile biodegradation in aerobic, methogenic, and anaerobic environments for petroleum and chlorinated compounds in soil and groundwater. This treatise is focused on aerobic environments that are preferred in biopile applications.

Soil normally contains large populations of diverse native microorganisms, bacteria, algae, fungi, protozoa, and actinomycetes that rapidly acclimate and degrade petroleum hydrocarbons. Less than 1% to 10% of petroleum recommended that total heterotrophic microbial plate counts (10 exp 4 to 10 exp 7 CFU/gm) be used to measure potential degrader populations. A minimum of 1,000 CFM/gm is generally required to identify contaminated soils that are capable of degrading petroleum contaminated soils in non-toxic environments.

Bacteria require carbon, nitrogen, and phosphorus for cell growth and an energy source to sustain metabolic functions required for growth. Petroleum hydrocarbons become the desired target carbon source for degradation but frequently require additional carbon supplements. Note that native heterotrophic bacterial degrader populations may frequently dominate over fungi.

Biopiles may be placed on an impermeable base to collect leachates and prevent migration into soil and groundwater. Leachate collection systems collect excess moisture and liquid biochemical catalysts for recirculation and/or treatment.

Refined petroleum products are generally more easily degraded than crude oil. Diesel contaminated soils generally do not require vapor emission treatment for volatile organic compound (VOC) reduction while gasoline contaminated soils may require activated carbon filtration or reinjection into the biopile for further degradation.

Piles may be covered with membranes, seeded with vegetation, or placed in a pole barn to protect from wind and rain. Total petroleum hydrocarbon concentrations may be limited to <50,000 ppm (ideal concentration <10,000 ppm), heavy metals concentrations <2,500 ppm, and trace concentrations of chlorinated compounds. Biopiles typically reduce petroleum hydrocarbon contaminated soils to 250 to 1,000 ppm with treatment times ranging from 3 to 6 months. Concentrations can be further reduced during shorter periods using more aggressive mass transfer mechanisms for mixing, aeration, and biochemical catalyst delivery.

2. SOIL BIOPILE APPLICABILITY

Figure 1 depicts an algorithm to determine the viability and decision tree to optimize the selection and implementation of biopile technology. To determine the suitability for biopile degradation, representative samples of contaminated soil are collected and tested for total petroleum hydrocarbons, PAHs, heavy metals, priority pollutants, PCBs, and other potentially toxic materials.Total heterotrophic plate counts in soil should exceed 1,000 CFU/gm indicating that bacterial activity is present.

The suitability of soil biodegradation is a function of particle size, organic sorption, and permeability. As soil particle size is reduced from small gravel, sand, silt, and clay, biodegradation can become more difficult. Soil with clay or high-molecular-weight humic materials reduces permeability and reduces mass transport of air and additives. Clay and humic materials can absorb up to 60% of petroleum hydrocarbons restricting bioavailability to degraders. Bulking agents may be required to increase airflow, retain water, and overcome mass transfer limitations. Surfactants can be utilized to desorb contaminates to degraders.