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OIL CLEANING BIO-PRODUCTS LTD.
GUIDANCE ON THE USE OF "HEG" PRODUCTS
It is difficult both to stipulate a standard strategy for the bioremediation of contaminated land by Hegrem, and to make precise predictions of how long this will take to achieve. In the performance trial results for Hegrem (see attachment) the periods over which bioremediation of contaminated land was measured in different cases varied from one to three months (in one case longer).
The bioremediation of contaminated land is affected by a large number of variables, some of which can be easily measured, while others are harder to measure. These key factors include:
- Type of contamination (gasoline, diesel, heavy crude, chlorinated hydrocarbons etc.)
- Depth of contamination
- Intensity of contamination
- Temperature
- Soil type
- Hydrogeochemistry of site
- Availability of moisture and air
- pH level
- Presence of bactericides, such as some heavy metals, bacterial predators etc.
In view of these many variables it is clear that even with a good site diagnosis it is not easy to make an exact prediction of the time necessary to achieve any given degree of bioremediation, and users should be cautious in doing so. However, if site conditions are acceptable (pH between 4.5 and 9; temperature between 4°C. and 50°C.; absence of bacterial predators; adequate moisture; absence of persistent chlorinated hydrocarbons; use of correct procedures etc.) it would be reasonable to expect (but not to guarantee) biodegradation of 40% of the original hydrocarbon contamination every 30 days. Naturally, the very last elements of contamination are the hardest to remove - but the significance of this depends on the clean-up standard which is required, and that in turn depends on the local regulatory requirement and on the nature of the intended use of the site.
THE PROCESS
The first objective is to bring the Hegrem into contact with the contamination. The Hegrem will then absorb oil from the earth, in prefernce to water. The oil will not subsequently leach out. It is thus immobilised and will not then migrate to threaten adjacent ground or surface water. The result of the process of absorption, by which the oil is drawn in to the very fine fibres of Hegrem, is that the oil is broken down into very small particles. This vastly increases the surface area of the encapsulated oil and makes it readily available to the natural oil-degrading bacteria which have always resided within the fibres. The bacteria will be activated by the presence of water and the available hydrocarbon substrate. Biodegradation of contaminants by bacterial metabolism will then begin.
The bacterial species in Hegrem are those which naturally occur in the delinted waste cotton husk from which Hegrem is made. They are more robust than many artificial cultures which are sometimes used for the purpose of bioremediation because at all times they remain in their natural environment - the cotton husk fibre. Because of this natural origin, different bacterial species will be found in different batches of Hegrem, according to the type of cotton used and the location of the crop etc. In all tested samples of Hegrem, six species are most commonly found, and these consist of a some aerobes and some anaerobes. No bacteria are added to Hegrem. No pathogenic bacteria have ever been found in any batch of Hegrem. Hegrem has been approved by the Phytotoxicity Division of the US Department of Agriculture as posing no threat to plant life
APPLICATION METHODS
1) The volume of Hegrem needed depends on the level of contamination. For levels of contamination below 50,000 ppm, 1 bag of Hegrem is needed per cubic metre of contaminated soil. (To ensure adequate contact between the oil and the Hegrem, the amount of Hegrem should not be reduced pro-rata for levels of contamination below 50,000 ppm.) Thereafter, the dosage increases as follows:
Level of contamination No. bags of Hegrem required per cubic metre
(1 bag is 1.5 cu. ft./0.04 cu. m., or 30 lbs./13.6 kilos)< 50,000 ppm 1 100,000 ppm 2 200,000 ppm 4 400,000 ppm 8
2) When the Hegrem has been applied by tilling into the soil or by excavation and backfilling, the soil must be kept wet with about 30% moisture content. Retilling from time to time (to improve aeration) is helpful but not essential .
3) If in situ treatment by tilling is not possible on account of the depth of contamination, the affected soil should be excavated, mixed with Hegrem and backfilled. It should not be necessary to go to the trouble of excavating the contaminated soil and forming a treatment heap on an impermeable liner. When backfilling, it would be helpful if the most contaminated layers could be replaced nearest the surface. With backfilling, the quantities of Hegrem in relation to the degree of contamination are the same as for superficial tilling in 1) above. The moisture content should also be kept at about 30%.
4) This treatment will normally suffice to produce remediation to the required standard. However, in cases where the contamination is markedly persistent and when a high degree of remediation is necessary, it may be necessary after 45 - 60 days to resort to a second stage. This involves the use of the liquid Hegboost, which contains biodegradable surfactant, more bacteria and additional nutrient.
One part water should be added to one part Hegboost concentrate. 5 litres of this 1:1 mixture will treat 1 cubic metre of mixed soil and Hegrem. Therefore, to treat a case of 1 cu. m. of contaminated soil+Hegrem, 5 litres of mixture would be required, made from 2.5 litres of Hegboost. On a larger scale, the dosage is proportionate:
Volume of contaminated soil + Hegrem Volume of Hegboost needed Volume of 1:1 mixture 10 cu. m. 25 litres 50 litres 25 cu. m. 62.5 litres 125 litres 50 cu. m. 125 litres 250 litres
TREATMENT OF OIL SLUDGES
The method of treatment and the likely outcome will depend on the nature of the original oil, the thickness of the sludge (e.g. liquid or solid phase), the presence of chlorinated hydrocarbons or heavy metals, pH etc.
Normally, oil sludges should be treated on a "dry contamination" basis. The sludge should first be thoroughly mixed with and absorbed by loose Hegsorb until dry to the touch. The resulting mixture should then be treated with Hegrem, exactly as if it were contaminated land.
SITE DIAGNOSIS, MEASUREMENT AND MONITORING
The first step is to map the contamination of the site. This will enable the operator a) to devise a remediation strategy based on the use of the correct and most economical amount of Hegrem in different zones and b) to establish benchmarks from which remediation in test and control sites can be measured over the period of the trial. The site should be mapped in the form of a grid with the point of spill at the centre. The size of grid squares will depend on the extent of the site, but should be not less than five metres square and not more than twenty metres square. The grid should extend to the extremity of contamination as judged by eye and nose. Samples should be taken from the point of spill itself and from the centre of each grid square. Every point should be tested at least two depths - the intervals of which will depend on local assessment.
Once the baseline data for each grid square at both depths have been entered (on separate charts) contamination contour lines may be drawn at appropriate contour intervals, depending on the range of contamination to be covered. These contours will reveal the pattern of contamination. It will not necessarily be symmetrical around the point of spill, since there may have been an initial flow in one direction or another. The contamination contour lines will enable an effective and economical treatment strategy to be devised. The grid square readings will enable similar grid squares to be selected for test and control, and make it possible for subsequent readings to monitor performance. It is not necessary to continue to sample and monitor all grid squares throughout the trial, only those which have been selected. Pairs of comparable grid squares should be selected across a range of intensities of contamination. One of each pair should be treated in accordance with guidance, the other of each pair should be untreated and monitored as control.
Sampling should therefore be conducted at both depths (i) before treatment ( to determine dosage and to establish benchmarks), (ii) a week later and then (iii) at intervals of two or three weeks over the whole period, which may last from 60 - 90 days. A series of readings would be established as shown in the attached sheet.
In practice, the characteristics of the site may prevent the taking of samples from grid squares exactly as described here - in which case variations will have to decided on the spot. It is important to log and mark precise locations from which samples were taken. Sampling and testing on this scale are only necessary for trial purposes. Sample bags should be sealed and labelled immediately. Samples should be stored at a temperature between 2 and 6°C. if possible.
The timing of the move to Stage 2 of the treatment (addition of Hegboost) should also be noted, since it should have a discernible effect on the readings in the later stages of remediation.
It is possible to treat some relatively fluid sludges on a "liquid contamination" basis, as shown in the notes on performance results. While appropriate in some cases, it is likely to be more costly and the "dry" technique is normally preferred. "Liquid" treatment is achieved by adding Hegsolv in the ratio of approximately 1 part sludge to 3 parts Hegsolv (plus bacteria) to 12 parts water. The mixture would need constant agitation and aeration by means of a circulating pump. It is possible that over 40% degradation could be achieved in a month - but this should not be guaranteed.
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