Soil homogenising optimises bioremediation decontamination

Land Clean Ltd, which deals with the remediation of contaminated land and groundwater, provides bioremediation as one of its fields of expertise. This involves the use the use of micro-organisms which break down large organic molecules. The technology is becoming increasingly tried and tested in the UK. Land Clean sees this is a financially favourable method of removing the hazard at contaminated sites and hence reducing risks.

Land Clean's large windrow turner

Land Clean's large windrow turner

Ex-situ bioremediation requires equipment able to efficiently process large volumes of soil. Land Clean Ltd has undertaken many successful bioremediation projects with soil homogenising machinery. The aim is to optimise the conditions necessary for micro-organisms to proliferate and maximise the availability of the contaminants to these micro-organisms. There are several varieties of machine that can be used to break up large clumps of soil and screen out large stones etc. This has the effect of greatly increasing the air space and surface area of the material under treatment. At the same time, it also thoroughly mixes and blends the material.

The most convenient method of treating soil is known as windrowing. This involves setting up long triangular piles of soil. When the windrows are turned with the homogenising machines nutrients, moisture and bacteria can be added. Temperature and moisture levels can also be controlled by the use of specially constructed fleeces. All of which optimise the biological activity in the soil and speed up the rate of biodegradation of the contaminant.

For larger volumes of material that require biological treatment, a larger soil turning machine is required. The Allu 38 can work roughly 800m3 per hour. Most of these machines have been designed with compost production in mind and have been specially strengthened to handle soils.

Case study
On a site with Polycyclic Aromatic Hydrocarbon (PAH) contamination resulting from past use as a creosote wood treatment works, approximately 10,000m3 of contaminated soil was bioremediated by Land Clean during the late summer of 1999.

Scenario Turn Rate Date Concentration (mg/kg PAH)
Cool / moist weather Weekly Day 1
Day 31
3659
5
Hot / dry weather Fortnightly Day 1
Day 31
5601
4

As can be seen, if weather conditions are less favourable, a higher work rate is required to achieve the same level of treatment. As with all biological activities, the weather can often prove a key factor in determining the length of time the process takes.



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