In the worldwide practice, cleaning of ground from oil products is being conducted with use of the whole range of methods and means for liquidation of oil contaminations.
Therefore, a range of criteria exists of assessment of effectiveness of the processing technologies of oil sludge and remediation of contaminated grounds for determination the most effective method for every concrete case:
- Conformance with principles of the best available technologies ;
- Economical effectiveness, including based on an opportunity of sale of the products of processing of waste in the form of secondary raw material;
- Attraction of the investors (profitableness, payback);
- Conformance with ecological requirements;
- Industrial safety.
Specific features and advantages to the technologies based on mechanical and physical-chemical methods of affect:
- High effectiveness (up to 90% for the one vegetation period) at comparatively low operational costs.
- Large scale. 50-75 Ha? of oil contaminated soils can be processed per the one vegetation period (150 000 – 220 000 m³) and to reach reduction of contamination more than by 90%. Universality of the method. Effectiveness of bioremediation is not limited by water cut of wastes, aggregative state, mechanical composition of grounds, contents of paraffins and asphaltens, use of chemical reagents, oil chilling temperature and other factors limiting use of majority physical-chemical methods. Balanced microbial community of the bioproduct works effectively in any conditions in wide intervals of its adaptive mechanism.
- Isolation. Bioremediation does not need in the energy sources (gas, electrical energy) and may be accomplished at any distance from communications.
- Safety for environment and small invasiveness for all its facilities. In the process of conduction of bioremediation, there is no harmful influence on other facilities (atmospheric air, soil cover, water resources).
- Absence of purified soil to the balance of the ecosystem.
- Absence of any secondary wastes.
- Comparatively cheap cost (up to 15 000 tenge per 1 ton of the purifying ground) at higher effectiveness and ecological safety.
Thermal methods: suppose high temperature burning of the ground in the furnaces with receiving of the construction material. Negative quality of this method is secondary formation of emission into environment in the form of emissions to the atmosphere pollution agents being formed at burning, including toxic combustion of oil hydrocarbons and greenhouse gases. The product of thermal processing is burnt cake holds no value for agriculture and may be used only in construction needs. Provided that, for observance of condition of established of direction of reclamation, removal of the contaminated grounds with its next burning in furnace will lead to necessary of delivery and distribution of soil layer in this territory that will cause to essential appreciation of the reclamation project. In the world practice, this method of processing is outmoded and recognized as hazardous for environment.
Mechanical method: this method concludes in multi-stage centrifuging with physical separation in oil, ground and process solution. As the studies showed, separation of sludge on the centrifuges for some kind of sludge is ineffectively.
Physical-chemical method: this method concludes in washing of oil contaminated soil on the plants with variable geometry, nozzles with addition of chemical reagents for coagulation and flocculation of oil hydrocarbons and stage centrifuging. As the result of cleaning, heavy hydrocarbon fraction, mechanical mixtures (ground, sand) purified to maximal permissible concentration and clear water are being formed in output.
Disadvantages of the method are high specificity to the ground being fed for cleaning, where the limiting factors are:
- Content of oil hydrocarbons – no more 20%;
- Fractional composition of the cleaning ground;
- Moreover, it is noted high need in energy (it is required of supply of gas and electric energy with power no less than 500 kW) and formation of secondary wastes in the form of wasted chemical reagents.
The higher cost of cleaning connected with the costs for energy supply of the processing complex is also disadvantage.
Biological method: this method is based on soil cultivation adapted by the microorganisms-decomposers of oil hydrocarbons with use of the range of the land capability actions. The advantages are biological safety, an opportunity of degradation of oil hydrocarbons to the values of maximum permissible concentration at completely keeping structure of soil with reclamation of the original level of fertility. The process occurs without additional secondary contamination of environment without any formation of secondary wastes. Use of this technology is limited by a degree of oil contamination of the ground (no more than 60%), process time and dependence of natural-climatic factors.
ACCOMPLISHMENT OF BIOREMEDIATION CAN BE CONVENTIONALLY SEPARATED INTO TWO STAGES: TECHNICAL AND BIOLOGICAL.
The technical stage connected with mechanical affect on the cleaning ground and the biological stage in which the main factor is influence of microbial community.
Technical stage includes the following operations:
- Choice of the area for placement of oil contaminated soil;
- Dugout of contaminated soil and distribution of it in the area;
- Creation of the even layer in 0,3-0,4 m. and a slope for drainage (if necessary);
- Soil loosening;
- If necessary, in the case with acidic soils, liming is being accomplished for normalization of hydrogen index or gypsuming for reduction of salinity.
- Primary soil moistening up to 25-40% field water capacity with the next support of this level depending on meteorological conditions;
- After microbiological remediation of contaminated soils, planning and compaction of soil are being foreseen.
- Preparation of working suspension of the bioproduct;
- Introduction of the first batch of the bioproduct;
- Moistening and loosening;
- Introduction of the mineral and organic fertilizers;
- Control over number of the active microflora, content of the microelements in soil, dynamic of hydrocarbons consumption.
The second and third introduction of the bioproduct with cyclical moistening and agronomic processing is being accomplished, if necessary.
Introduction of the complex of the mineral fertilizers in the form of granules of solution in strictly approved concentrations is being accomplished simultaneously with introduction of the cell mass of the bioproduct. Potassium nitrate, ammonium nitrate phosphate fertilizer, ammonium nitrate, superphosphate, urea etc. are being used as the nitrogen-phosphate fertilizers.