Environmental Biotechnology - Theory and Application - G. M. Evans & J. C. Furlong

84 Environmental Biotechnology

programmes and thirdly, to identify more pheromones to widen the number of phytophagous stink bug species which can be countered in this way.

As something of an aside, one interesting and somewhat unusual use has been proposed for this technology. The Siberian moth Dendrolimus superans is a vigorous defoliating pest of northern Asian coniferous forests and, though it does not presently occur in North America, its arrival is much feared. In an attempt to provide a first line of defence against this potential threat to native woodlands, it has been suggested that a blend of Z5,E7-dodecadienol and Z5,E7-dodecadienol, which has been shown to act as a powerful sex attractant for male Siberian moths, be deployed at US ports of entry.

However, as illustrated by the case of another pentatomid, Nezara viridula, the southern green stink bug, the use of this approach to biological control is not universally applicable. These insects are major agricultural pests affecting a variety of field crops, vegetables, fruits and nuts. While it has been known for sometime that sexually mature males produce an attractant pheromone, the active ingredients of which have been identified, early attempts to use this knowledge to exclude them from crops have been of only limited effectiveness. As a result, an alternative method of Nezara control has been suggested involving the genetic engineering of its gut symbionts to produce a reduced tolerance of environmental stress. Preliminary work at the Agricultural Research Center, Beltsville, USA has isolated and cultured in vitro a gram-negative bacterium from the mid-gut of the pest insect, which appears to be a specific symbiont and has been putatively identified as a species of Yokenella. This kind of application of transgenic technology may increasingly be the future of biological control for species which do not respond favourably to pheromone trapping.

Not all approaches to biocontrol truly qualify as environmental biotechnologies, at least not within the frame of reference used in this book. However, where the use of biological systems results in reduced insecticide use and thus a corresponding lowering of the attendant pollution potential, the net environmental gains of the application of biotechnology are clear.

Biosubstitutions

The biosubstitution of suitable, less harmful alternatives for many of today’s polluting substances or materials is a major potential avenue for the environmentally beneficial application of biotechnology. The question of biofuels and the major renewable contribution which organised, large-scale biomass utilisation could make to energy demands is examined in some detail in Chapter 10 and will not, therefore be repeated here. The biological production of polymers, likewise, features in the same section on integrated biotechnology and, though clearly distinctly germane to the present discussion, will also not appear in this consideration. However, the other major use of mineral oils, as lubricants, is an excellent case study of the opportunities, and obstacles, surrounding biotech

Pollution and Pollution Control 85

substitutes. Biodegradable alternatives to traditional lubricating oils have existed for some time, but in many ways they exemplify the pressures which work against novel biological products.

Barriers to uptake

Typically, most of the barriers which they must overcome are nontechnical. The pollution of many inland and coastal waters around the world is a wellappreciated environmental problem and wider use of these nontoxic, readily biodegradable alternatives products could make a huge difference. The main obstacles to wider market acceptance of the current generation of alternative lubricants are neither performance based, nor rooted in industrial conservatism. Cost is a major issue, as biolubricants are around twice as expensive as their conventional equivalents, while for some more specialist formulations the difference is significantly greater. Though, inevitably, users need to be convinced of the deliverable commercial benefits, the potential market is enormous. The petrochemical industry has sought to meet the growing demand for more environmentally friendly products by developing biodegradable lubricants based on crude oil. However, with the agricultural sector, particularly throughout Europe, being encouraged to grow nonfood crops commercially, there is a clear opportunity for a sizeable vegetable oil industry to develop, though the attitude of heavy industry will prove crucial.

While there is no denying the burgeoning interest in biolubricants, the actual machinery to be lubricated is extremely expensive, and enforced downtime can be very costly. Understandably as a result, few equipment operators are willing to risk trying these new, substitute oils, as original equipment manufacturers (OEMs) are seldom willing to guarantee their performance, not least because vegetable products are often wrongly viewed as inferior to traditional oils.

Simple biosubstitutions

Not all biosubstitutions need be the result of lengthy chemical or biochemical synthesis or processing and far simpler forms of biological production may provide major environmental benefits. The production of biomass fuels for direct combustion under short rotation coppicing management, described in Chapter 10, is one example. The use of what have been termed ‘eco-building materials’ formed from hemp, hay, straw and flax and then compressed, as an ecological alternative to conventional materials in the construction industry, is another.

Traditional building approaches have a number of broadly environmental problems. Adequate soundproofing, particularly in home or work settings where traffic, industrial or other noises are a major intrusive nuisance can be difficult or costly to achieve for many standard materials. Walls made from eco-materials have been found to be particularly effective at sound suppression in a variety of applications, including airports, largely due to a combination of the intrinsic

86 Environmental Biotechnology

natural properties of the raw materials and the compression involved in their fabrication. In a number of trials of these materials, principally in Austria, where they originated, eco-walls have consistently been shown to provide significant improvements in the quality of living and working conditions. In addition, construction and demolition waste, consisting of concrete rubble, timber fragments, brick shards and the like, poses a considerable disposal problem for the industry, particularly with increasingly stringent environmental regulation and rising storage and landfill costs. Though various recycling initiatives and professional codes of practice have helped ease the situation, there is an obvious advantage in a relatively inexpensive, lightweight and sustainable material which is truly biodegradable. At present, the use of this technology has been limited to small-scale demonstrations, though wider uptake is currently being promoted through the European Union’s Innovation Relay Centre network. The appeal of this, and other biological materials production methods for use in construction, the automotive and aerospace industries is clear, but it is very early days in their development. How successful they will ultimately prove to be remains to be seen.

Closing Remarks

As this chapter has shown, pollution and its mitigation have major ramifications in many diverse fields both for industry and in the wider sphere of general human activities. The potential contributions of clean technologies discussed in the final section have enormous bearing on the reduction of contamination ab initio, and, clearly, avoiding a problem in the first place is far better than cleaning it up after it has occurred. However, in most cases, current applications of environmental biotechnology to treat pollutants and wastes far outnumber the practical examples of clean biomanufacturing and so the rest of this book will address this more common use.

References

BioWise, UK Department of Trade and Industry (2001) Biotechnology Improves Product Quality, Crown copyright.

Georgis, R. (1996) Present and future prospects of biological insecticides, Proceedings of the Cornell Community Conference on Biological Control, April 11 – 13, Cornell University.

Holland, H., Khan, S., Richards, D. and Riemland, E. (1986) Biotransformation of polycyclic aromatic compounds by fungi, Xenobiotica, 16: 733 – 41.

Rai, C. (1985) Microbial desulfurization of coals in a slurry pipeline reactor using

Thiobacillus ferrooxidans, Biotechnology Progress, 1: 200 – 4.

Rai, C. and Reyniers, J. (1988) Microbial desulfurization of coals by organisms of the genus Pseudomonas, Biotechnology Progress, 4: 225 – 30.

Pollution and Pollution Control 87

Case Study 4.1 Microbial Pollution Control (Maine, USA)

Pollution control often involves either minimising existing problems or dealing with their aftermath and biological treatment can frequently be a very cost-effective option in either case.

Caldwell Environmental of Acton, USA have developed a number of proprietary biological approaches to deal with environmental contamination. One of the most successful is BioRem ST, an affordable microbial process designed to liquefy the solid waste build up in septic tanks, keeping the system in optimum working order, while odour problems are also largely eliminated. Routine applications also help to prevent drain blockage, which is often a problem for these installations. The formulation uses Class 1 classified bacteria, as defined by the American Type Culture Collection, which are safe to humans, animal and plant species, and approved for use in federally inspected meat and poultry processing plants. Able to reduce nitrogen and break down fats, carbohydrates, starches, oils, greases and detergents, the treatment offers an effective alternative to reliance on corrosive or toxic chemicals.

A good example of its large-scale use is the clean-up of accidental pollution from a food market in Maine, USA. The facility, which was located less than 75 metres (250 feet) from a lake, had a 250 litre (1000 gallon) septic tank. Unbeknown to the owners, the soakaway zone had failed and the discharge was going directly into the water body, this fact only coming to light during a routine inspection by the local authorities, using a dye tracer. Subsequent pollution control began with the daily dosing of the soakaway zone with the bacterial formulation, while controlled levels of additional nutrients were pumped in to bioenhance the area, thus optimising microbial action. Nine months later, the treatment was complete, and the necessary operational certifications granted for its continued use.

The value and effectiveness of this intervention would appear to have been more than adequately demonstrated, since the site owners have instigated an ongoing preventative maintenance regime, involving continued systematic microbial dosing, to avoid any repetition in the future.

5

Contaminated Land

and Bioremediation

Contaminated land is another example of a widely appreciated, yet often poorly understood, environmental problem, in much the same way as discussed for pollution in the last chapter. That this should be the case is, of course, unsurprising, since the two things are intimately linked, the one being, in essence, simply the manifestation of the other. The importance of land remediation in cleaning up the residual effects of previous human activities on a site lies in two spheres. Firstly, throughout the world, environmental legislation is becoming increasingly stringent and the tightening up of the entire regulatory framework has led to both a real drive for compliance and a much greater awareness of liability issues within industry. Secondly, as the pressure grows to redevelop old, unused or derelict socalled ‘brown-field’ sites, rather than develop previously untouched ‘green-field’, the need to remove any legacy of previous occupation is clear. A number of technologies are available to achieve such a clean-up, of which bioremediation, in its many individual forms, is only one. Though it will, of course, provide the main focus of this discussion, it is important to realise that the arguments presented elsewhere in this book regarding the high degree of specificity which governs technology selection within biotechnological applications also applies between alternative solutions. In this way, for some instances of contamination, expressly nonbiological methods of remediation may be indicated as the best practicable environmental option (BPEO). It is impossible to disassociate contextual factors from wider issues entirely. Accordingly, and to establish the relevancy of the wider setting, alternative remediation techniques will be referred to a little later in this chapter.

The idea of ‘contaminated land’ is something which is readily understood, yet, like pollution, somewhat more difficult to define absolutely. Implicit is the presence of substances which, when present in sufficient quantity or concentration, are likely to cause harm to the environment or human health. Many kinds of sites may give rise to possible contamination concerns, such as asbestos works, chemical works, garages and service stations, gas works, incinerators, iron and steel works, metal fabrication shops, paper mills, tanneries, textile plants, timber treatment plants, railway yards and waste disposal sites. This list is not, of course, exhaustive and it has been estimated that in the UK alone something in the region

90 Environmental Biotechnology

of 360 000 hectares (900 000 acres) of land may be affected by contamination in one form or another (BioWise 2001). Much of this will, of course, be in prime urban locations, and therefore has the potential to command a high market price, once cleaned up.

Since the whole question of contaminated land increasingly forms the basis of law and various professional codes of practice, there is an obvious need for a more codified, legal definition. The version offered in Section 57 of the UK Environment Act 1995 is a typical example:

any land which appears. . . . .to be in a condition that. . . . .significant harm is being caused or there is a significant possibility of significant harm. . . . (or). . . . .pollution of controlled waters.

In this, harm is expressly defined as to human health, environment, property . As was mentioned earlier, land remediation continues to grow in importance

because of pressures on industry and developers. The motive force is, then, a largely commercial one and, consequently, this imposes its own set of conditions and constraints. Much of environmental biotechnology centres on the ‘unwanted’ aspects of human activity and the clean-up of contaminated land is no exception to this general trend. As such, it is motivated by necessity and remedies are normally sought only when and where there is unacceptable risk to human health, the environment and occasionally to other vulnerable targets. In broad terms it is possible to view the driving forces on remediation as characterised by a need to limit present or future liability, increase a site’s value, ease the way for a sale or transfer, comply with legislative, licensing or planning requirements, or to bolster corporate image or public relations. Generally, one or more of these have to be present before remediation happens.

Having established the need for treatment, the actual remedies to be employed will be based on a realistic set of priorities and will be related to the risk posed. This, of course, will require adequate investigation and risk assessment to determine. It is also important to remember in this context that, since the move to remediate is essentially commercial, only land for which remediation is either necessary or worthwhile will tend to be treated and then to a level which either makes it suitable for its intended use or brings it to a condition which no longer poses an unacceptable risk.

It should be apparent, then, from the preceding discussion that the economics of remediation and the effective use of resources are key factors in the whole contaminated land issue. Hence, in purely economic terms, remediation will only take place when one or more of the driving forces becomes sufficiently compelling to make it unavoidable. It will also tend towards the minimum acceptable standard necessary to achieve the required clean-up. This is not an example of industrial self-interest at its worst, but rather the exercise of responsible management, since resources for remediation are typically limited and so their effective use is of great importance. To ‘over’ remediate any one given site could seriously

Contaminated Land and Bioremediation 91

compromise a company’s ability to channel sufficient funds to deal with others. The goal of treating land is to make it suitable for a particular purpose or so that it no longer poses unacceptable risk and, once the relevant aim has been achieved, further treatment is typically not a good use of these resources. Generally it would be judged better to devote them to cleaning up other sites, which maximises the potential reuse of former industrial land thereby protecting urban open spaces and the countryside from development pressure. In the long term, the sustainable use of land largely depends on making sure that it is maintained at a level which enables its continued best use for its current or intended purpose. In this respect, discussions of absolute quality become less relevant than a consideration of minimum acceptable standards.

The choice of method and the determination of the final remediation standard will always be chiefly governed by site-specific factors including intended use, local conditions and sensitivities, potential risk and available timeframe. For this reason, it is appropriate to take a brief overview of the available technologies at this point, to set the backdrop for the discussions of the specifically biotechnological methods to come.

Remediation Methods

The currently available processes for soil remediation can be divided into five generalised categories:

•biological;

•chemical;

•physical;

•solidification/vitrification;

•thermal.

Biological

Biological methods involve the transformation or mineralisation of contaminants to less toxic, more mobile, or more toxic but less mobile, forms. This can include fixation or accumulation in harvestable biomass crops, though this approach is discussed more fully later in Chapter 7.

The main advantages of these methods are their ability to destroy a wide range of organic compounds, their potential benefit to soil structure and fertility and their generally nontoxic, ‘green’ image. On the other hand, the process end-point can be uncertain and difficult to gauge, the treatment itself may be slow and not all contaminants are conducive to treatment by biological means.

Chemical

Toxic compounds are destroyed, fixed or neutralised by chemical reaction. The principal advantages are that under this approach, the destruction of biologically

Contaminated Land and Bioremediation 93

on no more than where the treatment takes place – on the site or off it – but since the techniques within each do share certain fundamental operational similarities, the classification has some merit. Accordingly, and since the division is widely understood within the industry, these terms will be used within the present discussion.

In situ

The major benefit of approaches which leave the soil where it is for treatment, is the low site disturbance that this represents, which enables existing buildings and features to remain undisturbed, in many cases. They also avoid many of the potential delays with methods requiring excavation and removal, while additionally reducing the risk of spreading contamination and the likelihood of exposing workers to volatiles. Generally speaking, in situ methods are suited to instances where the contamination is widespread throughout, and often at some depth within, a site, and of low to medium concentration. Additionally, since they are relatively slow to act, they are of most use when the available time for treatment is not restricted.

These methods are not, however, without their disadvantages and chief amongst them is the stringent requirement for thorough site investigation and survey, almost invariably demanding a high level of resources by way of both desktop and intrusive methods. In addition, since reaction conditions are not readily controlled, the supposed process ‘optimisation’ may, in practice, be less than optimum and the true end-point may be difficult to determine. Finally, it is inescapable that all site monitoring has an in-built time lag and is heavily protocol dependent.

Ex situ

The main characteristic of ex situ methods is that the soil is removed from where it originally lay, for treatment. Strictly speaking this description applies whether the material is taken to another venue for clean-up, or simply to another part of the same site. The main benefits are that the conditions are more readily optimised, process control is easier to maintain and monitoring is more accurate and simpler to achieve. In addition, the introduction of specialist organisms, on those occasions when they may be required, is easier and/or safer and generally these approaches tend to be faster than corresponding in situ techniques. They are best suited to instances of relatively localised pollution within a site, typically in ‘hot-spots’ of medium to relatively high concentration which are fairly near to the surface.

Amongst the main disadvantages are the additional transport costs and the inevitably increased likelihood of spillage, or potential secondary pollution, represented by such movement. Obviously these approaches require a supplementary area of land for treatment and hence they are typically more expensive options.

As Figure 5.1 illustrates, the decision to use in situ or ex situ techniques is a comparatively straightforward ‘black-or-white’ issue at the extremes for either