In situ Lagoon Treatment
Background
Lagoon treatment is an in situ bioremediation process that degrades a mixture of organic and inorganic hazardous substances in a lagoon. Cleanup usually requires a combined treatment approach. Aerobic and anaerobic biodegradation methods can be applied, depending on contaminant characteristics. For wastes containing volatile chlorinated hydrocarbons, anaerobic metabolism processes are applied, followed by an aerobic phase. Solids distribution and slurry mixing techniques, including air sparging, pumping, mechanical, and dredging, must be used in the lagoon treatment in order to maintain high bioremediation rates [1].
Applicability
Studies indicate that in situ lagoon treatment can remediate galvanizing wastes, phenols, pickling acids, polychlorinated biphenyl (PCB), heavy metals, polycyclic aromatic hydrocarbons (PAHs), and benzene, toluene, ethylbenzene, and xylene (BTEX). This technique has been successfully used to treat hazardous substances discharged into lagoons by industrial or other sources. Sludge lagoons usually contain a broad chemical mixture. Lagoon treatment minimizes soil and sludge handling and has been performed at costs significantly less than alternate technologies [1].
Performance
Various investigations were performed at a waste lagoon formed by a sand mining operation in Texas [2]. The licensed waste disposal facility covered 7.3 acres and was estimated to contain 70,000 cubic yards of sludges and 50,000 to 70,000 cubic yards of contaminated soil. The lagoon and soil were contaminated with industrial waste oils, acidic galvanizing wastes, phenols, pickling acids, PCB, and heavy metals to a depth of 30 ft. Laboratory-scale experiments determined that microbial activity was maximized when phosphates and nitrogen were added at a 3:1 ratio. Pilot-scale studies conducted in 20,000 gallon tanks over a two month period confirmed laboratory results. Results of demonstration-scale treatments indicate that in situ lagoon treatment (aeration and nutrient addition) was an efficient and cost-effective cleanup method [2].Results of in situ lagoon remediation of wastewater-sludge generated by a refinery is summarized in Table 1. Aeration and the addition of nitrogen and phosphorus were employed at the lagoon, which contained 7,000 cubic meters of oil- and grease-rich sludge contaminated with 2,000 mg and 200 mg of PAHs and BTEX, respectively, per kg of sludge [3].
Table 1. Aerated lagoon treatment of oil- and grease-rich sludge [3].
Compound
Concentration, mg/kg
Initial
Attained
Benzene 64.4
1.19
Toluene 19.4
1.14
Ethylbenzene 32.4
0.32
Naphthalene 290
ND
Phenanthrene 150
ND
Pyrene 540
0.03
Anthracene 20
0.02
Benzoanthracene 91
ND
Chrysene 20
ND
Benzopyrene 100
<0.01
ND: not detected
Data from: Vail, R.L., 1991, Refining: Refiner biodegrades separator-type
sludge to BDAT standards, Oil and Gas Journal, 89 (45), pp.53-57.
Data Requirements
Lagoon treatment is designed to optimize biodegradation in a lagoon containing contaminated slurry. The general procedure is as follows: (1) establish the volume of contaminated liquid, sludge, and subsoil, as well as the nature and concentration of contaminants in the lagoon; (2) evaluate the biodegradability and toxicity of the waste mixture; (3) select the microbial metabolism mode for degradation (more than one system may be needed due to the chemical variety in the slurry); (4) monitor the process frequently; and (5) apply mixing and solid distribution systems to increase the bioremediation rate [1]. Monitoring for process control should be performed frequently
Cost
Not available.
Status of Technology
Laboratory- , pilot-, and demonstration-scale studies have been performed. Successful remediation of contaminated wastewater sites have been achieved.
References
1. Cookson, J.T. Jr., 1995, Bioremediation Engineering Design and Application, McGraw-Hill, Inc., New York, NY.2. Baker, K.H. and D.S. Herson, 1994, Bioremediation, McGraw-Hill, New York, NY.
3. Alexander, M., Biodegradation and Bioremediation, Academic Press, San Diego, CA.