THE SITE

A former Gasworks which contained a tardistillery and six distilleries, was used for the production of town gas for over a century. Manufactured Gasworks Plants (MGP) sites generally contain contamination including free tars, tar slurry and ammoniacal liquors with high concentrations of polycyclic aromatic hydrocarbons (PAH), monocyclic aromatic hydrocarbons (MAH, BTEX), cyanide, phenolic and heavy metal contamination.

THE ISSUE

Traditionally the tarry material was disposed of to landfill (dig and dump). This is no longer considered the best remediation technique partly due to the European Union Landfill Directive implementation and the increased landfill disposal charges. Numerous alternative remediation techniques have been considered and trialled however, the difficulty has been to deliver remediation of the tarry material on time, on budget and to a concentration that allows reuse of the material onsite a specified time period.

THE SOLUTION

Our technique, Dynamic Biopiles® which is an enhanced bioremediation method, provided a scientific based solution to breakdown total petroleum hydrocarbons (TPH), PAH, BTEX and phenol compounds. The project was undertaken as a large commercial operation with tarry material, which was unable to be treated by the Principal Contractor (using traditional bioremediation methods), given to us for treatment by the use of Dynamic Biopiles®. All tarry wastes from the site, including the sludges from the tank bottom and tar distillery (being ~50,000m3 ex-situ), were treated and reused on-site with the only exception being material containing cyanide (blue billy), which was disposed off-site as hazardous waste. All treated material was validated by a third party and classified as meeting site criteria which allowed 50,000m3 of soil to be reused on site.

THE BENEFIT

Our remediation technique for tarry material delivered the best and most effective outcome for this site. The technology considered the site specific constraints and delivered a solution on cost, on time and in comparison to other techniques it provided a solution with low carbon emissions, low intergenerational transfer, minimal remaining liability and minimal infrastructural impacts (Cartwright et al., 2008).

Our Dynamic Biopile® technology was significantly more cost effective than techniques such as Dig and Dump. Working through a snowy winter and record spring/summer floods caused delays and variations in the treatment methodology, however these variations were undertaken within the existing timeline and budget which clearly demonstrates the project was durable to externalities throughout the period of operation.

ENVIRONMENTAL IMPACT

Traditionally bioremediation of tarry material has been restricted to the 2, 3 and 4 ring PAH compounds.  EESI Contracting has developed a method, Dynamic Biopiles®, which includes the use of solvents and surfactants to allow microbial metabolisation of the previously untreatable bio-available large ring PAH compounds.  EESI Contracting treated all organic waste from the site, including the sludges from the tank bottom, with the only exception being material containing cyanide, which was disposed off-site as hazardous waste.  All treated material was validated by a third party and classified as meeting the site criteria, which allowed all 50,000 m3 of soil to be re-used on-site.

SOCIAL IMPACT

The treatment of material onsite prevented the movement of 3,000 wagons from site or 500,000 miles of road haulage to landfill.  The wagons would most likely have traveled via the seventh most dangerous road in the UK (EuroRAP) as such, the on-site treatment of material reduced the traffic on this already dangerous road.

COST EFFECTIVENESS

Our patented process for enhanced bioremediation known as Dynamic Biopiles® was significantly more cost effective than other techniques such as dig and dump.  The 2007 England floods caused delays and variations in the treatment methodology however these variations were undertaken within the existing timeline and budget, which clearly demonstrates the project was durable to externalities throughout the period of operation.

SIGNIFICANT REDUCTION OF THE POLLUTION

Bioremediation is a well recognised process in which micro-organisms are promoted to break-down hydrocarbon based compounds.

A rapid degradation of 2, 3 and 4 ring compounds occurred in the soil.  The 5 and 6 rings compounds associated with primary gas condensates were also remediated (~50% of the total) however, those associated with Pyrogenic Residues are not bioavailable and as such can not be remediated (eg Nakles et al, 2008; Mulvey, 2008). 

Normalisation fingerprinting (Mulvey and McKay, 2005) of the PAH chemical data over time from all the stockpiles showed a change from correlation with coal tar in soil to good correlations with black carbon at the end of remediation once all tar material (Primary Gas Condensates) had been removed.

The degradation of PAH compounds by the treatment process for Total PAH ranged from 71 to 87 %.  The highest mean percentage reductions were observed for 2 and 3 ring compounds such as Naphthalene (94%), Acenaphthene (92%) and Fluorene (92%).

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