Bioremediation and the Feasibility Study

BIOREMEDIATION 
Bioremediation is the treatment of contaminated material using the capacity of microorganisms to either break down and destroy organic pollutants, or convert them into less harmful biodegradation by-products. The process is particularly suitable for hydrocarbon contaminants, such as petrol and diesel range organics. The efficiency of natural biodegradation is limited, and hydrocarbon contaminant bioremediation may be enhanced greatly by the addition of proprietary inocula – this process is known as bioaugmentation; more information is provided in the section BIOREMEDIATION METHODS below.

BIOREMEDIATION FEASIBILITY STUDY
An important step in helping you decide whether to utilise a bioremediation method or not, is by initiating a Bioremediation Feasibility Study (BFS) before commencement of the site-scale process. Within any contaminated matrix, several possible constituents may be present that are biocidal (lethal to microorganisms). Laboratory identification and quantification of such biocidal compounds is both costly and time consuming. Even so, initiating a bioremediation method without prior knowledge of the method feasibility can result in an even greater waste of time and money.

Fortunately, there is an alternative route you can take.

ECSOL Limited has designed a cost-effective BIOREMEDIATION FEASIBILITY STUDY protocol which identifies whether contaminated materials may be bioremediated successfully. Application of the protocol prior to launching the site-scale process can provide you with much more assurance that the method will be successful.

Advantageous features of the ECSOL BFS protocol:

• Suitable for the majority of contaminated soil, water, waste materials;
• Provides useful organic compound speciation data (type and quantity) of the starting material (see NOTE below);
• Adaptable to suit your preferred system – the BFS may utilise your own, or ECSOL recommended, bioaugmentation and/or nutrient supplement;
• Identifies unsuitable bioremediation methods within 7 days;
• Where suitability of the method is demonstrated, the entire study to final report production typically lasts 4 weeks only;
• Organic compound speciation (type and quantity) of the bioremediated materials at completion of the study are presented (see NOTE below).

(NOTE: the method of organic compound speciation involves GC/MS Analysis which provides both identification and quantification; thus, the data differentiates between true hydrocarbons and biodegraded by-products. This must not be confused with traditional laboratory TPH methods, which can misleadingly include both types of organic compounds in the single figure produced) (see Interpretation).

BIOREMEDIATION METHODS

The Environment Agency has published datasheets recommending various remediation strategies including bioremediation methods (click on PDF icon to view EA datasheets).

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The datasheets detail the prime controlling factors – air (oxygen) availability, moisture content, nutrient levels, matrix pH, and ambient temperature. Nevertheless, above all other factors, the success of a bioremediation project requires a thorough understanding of each individual project, end effective management throughout that project.

Bio-piles – ex-situ method
Biopiles are piles of contaminated soil, sited under covered structures, bunded to manage leachate generation. Biopiles often using various methods to enhance the growth and viability of the microbes; such enhancements include provision of temperature controlled air (supplying optimum temperature and oxygen levels), control of water and nutrient, and adjustment of pH. However, once in place, the physical characteristics of Biopiles are difficult to engineer.

Windrows – ex-situ method
Windrows are piles of contaminated, fashioned to maximise oxygen availability, covered with readily-removable structures, and bunded to manage leachate generation. Windrows are regularly turned which effects enhanced aeration and prevents consolidation of soil material. Moisture content, nutrient levels, pH adjustment, and bioaugmentation is facilitated by recirculation of generated leachate, with any necessary supplements. This method is often preferred since ease of engineering ensures the microorganisms are in direct contact with contaminants.

In-situ bioremediation
Where it is uneconomical or not feasible to remove material, in-situ bioremediation methods exist. These methods manage the prime controlling factors using engineering solutions, such as, boreholes, trenches. One major drawback with in-situ bioremediation is the reduced control of generated leachate; to compensate for this, considerable engineering of the site to incorporate adequate bunding maybe necessary to prevent leached organic compounds from entering the downstream sub-stratum environment.

Site Assessment
Successful bioremediation projects require a thorough initial assessment by researching the site and its contamination. The typical ‘tick list’ employed for an oil contaminated site is as follows:

• Age of contamination
• Average concentration of contamination
• Depth of contamination
• Volume to be treated
• In Situ or Ex Situ preference/suitability
• Type of matrix (clay, sludge, gravel, water, etc)
• Target level for approval
• Matrix pH
• Other contaminants present
• Water table level
• Average day and night temperatures
• Average rainfall at site

The Desk Top Study accumulates data necessary to identify whether mitigating measures need to be established to promote optimum conditions. The data list comprises:

• Identity of hydrocarbon – quantity AND composition;
• Average level of contamination – TPH content of several samples;
• Target level – customer-established, but commonly driven by legislation;
• Depth of contamination – to ensure all soil is removed to biopile/windrow;
• Volume – to provide a guide for space, equipment, materials, and time requirement, and consequent associated financial costs;
• In situ or ex situ – dependent on the facilities offered by the site;pH of soil matrix – a vital factor that affects living organism performance;
• Type of soil – to ensure the adequate porosity for percolation, and to review nutrient / organic matter requirements, etc;
• Review of existing analysis – to establish if any other significant factors may be present in the soil, e.g. biocides, heavy metals;
• Review of site conditions – to identify available space, power, water, organic matter, nutrient, etc;
• Assess risks associated with site and proposed operations – to ensure personnel involved with the process are aware of site operations, and that other personnel can be precluded from the zone.

Bioremediation can offer the following benefits:

• Quantitative reduction of site soil and/or water pollutants to prescribed target levels – effective site remediation;
• Complete removal of pollutants – environmental enhancement;
• Reduction of Hazardous and ‘Orphan’ Waste to lower status (e.g. Inert Waste - WAC classification) – in today’s market, offering substantial cost savings;
• Effective, economic decontamination of a wide range of materials, e.g. soil, water, built environment products, engineering products, railway ballast, etc;
• Simultaneous remediation of soil, leachate, groundwater, surface water, and/or wastewater.

Bioremediation is particularly applicable to the following situations:

• Sub-surface decontamination caused by LUSTs;
• Ground contamination resulting from domestic heating oil spillage;
• Oil Refineries – production waste and/or spillage;
• Decontamination of sites historically used for coal tar distillery, coal gas generation, oil distilleries, and similar processes.

If you are interested in reading more, please download the document “BIOREMEDIATION OF HYDROCARBON CONTAMINATED SOIL” by clicking on the MS Word icon here.

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