Efficacy of Bioremediation Agents
A standard recipe has been shown to treat soil contaminated with AO (500 ppm) and TCDD 40,000 (ppb).
A Joint Venture between EkoGea and HLAllen3 Environmental
A Standard Recipe has been shown to be effective in bioremediating soil contaminated with Agent Orange at 500 mg/kg and TCDD at 40,000 ng/kg. Two EkoGea Bio-complex (BCx 900 and BCx 900+2) have been proposed to accomplish the same job. These algal extracts purportedly support microbial growth and have ion exchange properties which enable the degradation of complex organics. This Study seeks to demonstrate the performance of these three methods using contaminated soil from the former Da Nang Air Base, Da Nang, Vietnam.
Background
Fourteen years ago, the principal investigator (HLAllen3 Environmental, then with the US EPA) cooperated with the Vietnam Academy of Science and Technology conducted a successful pilot study in Da Nang, VN. The overall removal efficiency of the treatment pilot study was 25.6%, but the treatment efficiency of the Standard Recipe was 60.3% after 6 months.
Over 100 sample jars containing 80-100 grams of soil were recovered from the study and were composited for this project. The average TCDD concentration in the samples was approximately 35,000 ng/kg (PPT) after treatment. These samples were mixed together thoroughly, making a wet mixture of about 15 kg. Using an average dry weight estimated from the samples, the total dry weight should be about 11 kg.
Using a sampling trowel the stockpile was evenly distributed into 12 portions of about 2 kg (4.4 lbs) each, which is the basis for the amendment loading. The entire stockpile was used. The Standard Recipe is based upon EPA studies of bioremediation of Pentachlorophenol-contaminated soil, which has proven very effective. Loading is based on a dry soil weight. The Standard Recipe consists of 50 g/kg sawdust, 10 g/kg CaCO3, 2.4 g/kg NH4NO3 (substituted K2NO3) and a pinch of Bloodmeal (12% organic Nitrogen), 0.3 g/kg of Na2HPO4 *
The phosphorus is needed to metabolize the sawdust and other incidental organics. These soils were treated 14 years ago and should still contain phosphorous, which is a conservative element.
*Note: The phosphorus is needed to metabolize the sawdust and other incidental organics. These soils were treated 14 years ago and should still contain phosphorous, which is a conservative element.
The sawdust was amended dry with KNO4 as a nitrogen source and CaCO3 to moderate pH as the sawdust degrades, because this soil is poorly buffered. The Control plots contained unamended sawdust only.
Fifty (50) grams of sawdust was placed in 3 piles in each of 4 - 10”x18” (0.118 sq.m.) aluminum pans. (The 9”x12” pans are 0.071 sq.m.)
Using a sampling trowel the stockpile was evenly distributed into 12 portions of about 2 kg (4.4 lbs) each, which is the basis for the amendment loading.
The loading factor for the BCx was 250 g/sq.m. Since each portion occupied 0.039 sq.m. I added 10 ml of BCx 900 or BCx 900+2 to the appropriate pile.
Sampling and Analysis
When the soil became less soupy, each plot was mixes thoroughly and relocate the plots. Composites samples were prepared from each of the 3 treatments, with one replicate, and an untreated control. All samples were sent selected lab. The samples were collected after the treatment plots were constructed and again after 13 months.
The team analyzed for the herbicides 2,4-D, 2,4,5-T, and 2,4,5-TP. Dioxin congener analysis by GC/MS can be limited to TCDD and OCDD, because other congeners are almost absent.
Because biodegradation is a linear reaction, rather than first-order, we assert there must be cosubstrates supporting identified microbial growth. In previous studies, the Vietnamese did a comprehensive analysis of probable cosubstrates.
Discussion & Recommendations
A large-scale (3,384 m3) study was conducted in Bien Hoa by the Vietnamese from April 2009 to July 2011. The results from the averages of 12 composite samples at the start and 64 composite samples distributed over the 13 month study showed a 99.5% reduction in TCDD toxic equivalents from 10,865 ppt. to 52 ppt. This translates into a linear degradation rate of about -30 ppt./day (R2= 93.9%) using least squares analysis (MS Excel @linest function). The Mann-Kendall test yielded a significant downward trend (p=0.0002; S=-94; n=114). These results show reduction rates for TCDD similar to those seen at Da Nang, where the VAST aerobic treatments evidenced a linear trend of about -81 ppt./day. Reproducing the results obtained in Da Nang at Bien Hoa proved that the dioxin remediation goal of 1,000 ppt. could be readily achieved by bioremediation.
The results clearly demonstrate the EPA method and both the BCx900 and BCx900+2 effectively treat TCDD in Da Nang soil and even more effectively treat Agent Orange Compounds 2,4-D and 2,4,5-TP. It also appeared that the dioxin-degrading microorganisms were nearly eliminated in the samples. The populations of herbicide degrading bacteria have also seemingly decreased this is likely because the soil samples are ex-situ and several years old. Nonetheless, herbicide degrading bacteria are very likely present, facilitating the loss in concentration in the treatment test. Both the Standard recipe and the EkoGea amendments encouraged the degradation of the AO herbicides, compared to the control.