BIOREMEDIATION

Lessons learnt in implementing

To briefly summarise the concept of enhanced in situ bioremediation (EISB) discussed in this series, the strategy is to stimulate the existing microbial population in an aquifer, by adding substrate or other microbes. The aim of this is to enhance the ability of that microbial system to degrade chlorinated hydrocarbons or other chemicals of concern.

By Michelle Roux and

Sathisha Barath*

his article considers some of the

Tkey practical elements in applying bioremediation technology, which turns an aquifer – a matrix of water, rock and soil – into what is essentially a giant, underground bioreactor. A primary step in the design of an effective intervention is the accurate characterisation of the aquifer’s microbiology, geochemistry and geology. This lays the groundwork for the task of physically reaching the microbes with the substrate.

Understanding conditions

Characterisation will describe conditions such as the depth at which the contaminant mass is located, the size of the mass, and what type of contamination exists. In the case of dense nonaqueous phase liquids (DNAPLs), for example, there may be chlorinated ethanes or ethenes present – and there may exist a co-mingled plume with more than one chemical. This will determine which microbes are to be targeted for enhancement.

General groupings such as the Dehalobacter species are considered effective in degrading chlorinated ethanes, for instance, while the genus Dehalococcoides is more commonly used in addressing chlorinated ethenes. However, for some sites, there may not be a specific group of microbes associated with the degradation required – which will need intensive research and trials. Microbes can also give each other the ability to adapt – rather like a flu virus.

Holistic approach

In addition to the gene sequencing of the groundwater to establish which microbe groups are present, characterisation of the site demands data generated within a range of specialist fields. This holistic approach highlights the need for integrated and multidisciplinary teams in these projects, with each discipline bringing its own crucial insights. The expertise required ideally includes microbiology, molecular biology, geology, environmental science, toxicology, isotopic chemistry, geochemistry, and several aspects of engineering.

This makes for robust teams, where knowledge is reinforced while members can trade their strengths and weaknesses. Such a team is also better able to develop and apply a detailed understanding of exactly what processes are under way in the system. This is much more productive and rewarding than the simplistic use of a checklist to drive this intricate process.

Independent experts

Involving a range of specialised skills, bioremediation projects can often struggle to find the right levels of experience. Such expertise, however, is a vital ingredient to success. Creating and managing these living ‘bioreactors’ needs constant review and data assessment by experts, even outside of the project team. Bear in mind that the performance of the system can only be monitored indirectly – as it cannot be physically observed; the accuracy and interpretation of data is therefore paramount.

Not only must the project team be open to modifying and adapting its strategies based on expert advice – but the client must also be prepared to regularly rethink the project’s direction. No two projects will be identical, and each will need its own iterative strategy. Even between boreholes on the same project, the consortium of microbial populations may vary. Constant evaluation is key, followed by the necessary adaptations of strategy.

Cultures – source or grow?

A range of microbes that can be purchased to stimulate the microbial mass in a contaminated aquifer are specially cultivated in mainly American and European laboratories. There is no guarantee, however, that they will function effectively in any specific local environment. Our experience has been that existing microbes, which have already adapted to the local aquifer conditions, tend to be more robust and adapted to the in situ environment – even if this might take longer. Again, the key is detailed monitoring and regular adaptation wherever necessary.

SRK has achieved considerable success, for instance, in distributing existing microbes from stronger to weaker sections of a biobarrier. This ‘inoculation’ of the lagging parts of the biobarrier helps to create greater homogeneity across the aquifer.

Investing in local labs

Bioremediation projects are not short term; they take years, if not decades, and demand that considerable expertise be developed over the duration. For this reason, it is ideal to invest in the capability and knowledge of local

Without South Africa is seeing valuable innovations in the use of bioremediation to treat industrial sites impacted by chlorinated hydrocarbons. This groundbreaking accurate data work is particularly urgent as the country makes greater use of groundwater resources – a receptor that is vulnerable to contamination from surface from extensive sources of pollution. In this four-part series, SRK Consulting discusses the current advances monitoring over time, it is making locally and how these will benefit efforts to clean up legacy impacts in the subsurface environment. In this, the third article in the a bioremediation series, the authors examine a range of issues related to the practical implementation of enhanced in situ bioremediation (EISB) technology. project is at a high Looking back over the ground covered to date, the first article provided an overview of why EISB is an effective option for degrading chlorinated risk of failure hydrocarbons. In the second article, the focus was on the use of emulsified vegetable oil as substrate for EISB. In the May 2021 edition of ReSource, a fourth and final article will focus on monitoring the EISB system and identifying key indicators to evaluate its success.

Electron micrograph of bacteria present in groundwater at a site impacted by chlorinated hydrocarbons

Bioremediation projects are not short term; they take years, if not decades, and demand that considerable expertise be developed over the duration. For this reason, it is ideal to invest in the capability and knowledge of local laboratories

laboratories – in a way that ensures that their growing internal expertise will constantly add value to the project.

There are many variables in the testing process, for example, and a close working relationship with a laboratory is really the only way to steadily build and maintain the accuracy of test results and trust in the monitoring data. Without accurate data from extensive monitoring over time, a bioremediation project is at a high risk of failure. Service providers and subcontractors, even including the drilling contractors and map makers, are not just tools; they must become integral parts of the project team and buy into the project for the long haul.

The same principle applies to team members; communication and learning are core to the job, as the overall project success relies on attention to detail – which changes constantly. New members must be effectively inducted and be kept informed; regular site visits and training workshops for this purpose are very useful and should, where possible, be included in the project budget.

Fostering practical innovation

Given the complexity and dynamism of bioremediation, everyone involved needs to be innovative. In SRK’s projects, we have even requested ideas from our subcontractors on how to address certain challenges. In one case, an automated injection system was developed by a subcontractor in close collaboration with the SRK team to accommodate the pumping requirements for emulsified vegetable oil on certain sites.

This high-tech system, based on the concept of diesel fuel injectors, allows for the injection of substrate in varying volumes and pressures into boreholes in different sections of the biobarrier. This kind of engagement with partners, along with a willingness to experiment with their concepts, has delivered considerable efficiency in delivering the emulsified vegetable oil into the aquifer, thus resulting in financial and time savings to our projects – while advancing innovation for the sector.

A chemical emulsion has also been developed in collaboration with expert suppliers in the USA, so that only the emulsifier portion of the substrate now is imported from abroad – saving the client substantial logistical costs. There was also a requirement for a fit-forpurpose mixing system on-site, which was locally designed in consultation with chemical and mechanical engineers.

Implementing a bioremediation solution, therefore, is as much about relationships as it is about technology, science and engineering. Building a diverse and resourceful team – one that is close to the project and committed to collaboration – is the foundation for success over the many years that these endeavours usually demand.

About Michelle Roux

Michelle is a principal hydrogeologist and contaminated land scientist in SRK Consulting’s Durban office, with more than 14 years of experience in hydrogeology, microbiology, contaminated land characterisation and management. Her specialisation includes project management, groundwater assessment and remediation, and bioremediation in situ treatment design. Her work includes conducting contaminated site assessments, developing and implementing long-term groundwater monitoring projects, and developing site conceptual models for DNAPL and LNAPL sites. Michelle holds an MSc Geohydrology, and a BSc (Hons) Microbiology.

About Sathisha Barath

As a senior hydrogeologist at SRK Consulting’s Durban office, Sathisha has more than 11 years of experience in land contamination, remediation and groundwater projects. Her specialisations include EISB of chlorinated hydrocarbons, site characterisation of LNAPL and DNAPL sites, and soil and groundwater remediation of contaminated sites. She holds an MSc Hydrogeology and a BSc (Hons) Geology.