Applying AD to Waste Management
The nature of anaerobic digestion inevitably means that its applications to waste management are relatively large-scale operations, there being no effective equivalent of home composting. Hence, whether the application is as an onsite treatment for process effluent or as part of a centralised municipal waste initiative, the approach relies heavily on engineering, a schematic plant being shown in Figure 8.2. This is in clear contrast with composting and, together with the attendant additional...
Practical Toxicity Issues
The general factors which influence toxicity have already been set out earlier in this discussion, but before moving on to consider wider practical issues it is helpful to mention briefly the manner in which the toxic action of pollutants arises. There are two main mechanisms, often labelled 'direct' and 'indirect'. In the former, the effect arises by the contaminant combining with cellular constituents or enzymes and thus preventing their proper function. In the latter, the damage is done by...
Biological Waste Treatment
The aims of biological treatment are relatively straightforward and can be summed up in the following three points 1. Reducing the potential for adverse effects to the environment or human health. 2. Reclaiming valuable minerals for reuse. 3. Generating a useful final product. Broadly speaking, this effectively means the decomposition of the biowaste by microbes to produce a stable, bulk-reduced material, during which process the complex organic molecules originally present are converted into...
Manufacturing
In the manufacturing sphere, it seems certain that there will be increasing pressures to continue the reductions in pollution and waste production. These are related issues, of course, and both may be addressed by one of two general approaches a priori methods to avoid the problem in the first place or a posteriori to clean it up more efficiently after the event. Clean production methods, which have been variously discussed in Chapters 4 and 10, seem likely to play a growing part in achieving...
Semiochemical agents
However, perhaps one of the best examples of the use of such biological technologies in pest control is the development of isolated or synthesised semiochemical agents. Semiochemicals are natural messenger substances which influence growth, development or behaviour in numerous plant and animal species and include the group known as pheromones, a number of which are responsible for sexual attraction in many insects. This has been successfully applied to control various forms of insect pests,...
Endocrine disrupters
To date, there are chemicals, including xenobiotics, which still resist degradation in the environment. This may be due to a dearth, at the site of contamination, of organisms able to degrade them fully or worse, microbial activity which changes them in such a way that they pose a bigger problem than they did previously. One such example is taken from synthetic oestrogens such as 17a-ethinyloestradiol commonly forming the active ingredient of the birth control pills, and the natural oestrogens...
Extremophiles
As has been previously mentioned, in general the use of biotechnology for environmental management relies on mesophilic micro-organisms which have roughly similar environmental requirements to ourselves, in terms of temperature, pressure, water requirement and relative oxygenation. However, often some of their abilities, which are directly instrumental in enabling their use in this context, arose in the first instance as a result of previous environmental pressures in the species (pre)history....
Biodiesel
Returning to the central consideration of bioenergy, it would be wrong to discuss this topic without at least some passing reference to biodiesel, even though, since it revolves around a chemical refining process, it is not strictly produced by biotechnology. Like the increasing number of mineral oil substitutes currently available or under development, biodiesel is derived from vegetable oils. Modern diesel engines demand a clean-burning fuel of uniform quality which can function under all...
Ex situ techniques
Again, there are three principal approaches in common use, namely land farming, soil banking and soil slurry bioreactors. Though inevitably there are distinct similarities between all applications of bioremediation, for obvious reasons of fundamental biology, these techniques are generally more distinct and separate. The major benefits of ex situ methods are the greater ease of process optimisation and control, relatively shorter treatment time and the increased potential for the safe...
Examples of developments in plant GE
The purpose of these examples is to illustrate the potential plant genetic engineering could bring to future practical applications in the field of environmental biotechnology. In some cases the intention is to reduce the amount of herbicide and pesticides, or other agricultural chemicals required to produce a given crop yield, in others it is to improve tolerance of harsh conditions or to protect the plants from attack thus reducing wastage. The intention is to note the technical details here,...
Carbon sequestration
Their use as a carbon sink is a simpler process, only requiring the algae themselves. However, even as a functional algal monoculture, just as with the joint algal bacterial bioprocessing for effluents, without external intervention to limit the standing burden of biomass within the bioreactor, reduced efficiency and, ultimately, system collapse is inevitable. In nature, huge amounts of many elements are held in global reservoirs, regulated by biogeochemical cycles, driven by various...
Membrane Bioreactors
This system, instead of utilising conventional methods of gravity settlement, achieves the desired biomass retention by means of a cross-flow filtration process, as shown in Figure 6.8. The development of effective methods of micro- and ultra-filtration has opened up the potential for using membrane bioreactor technology on various forms of domestic and industrial effluents. There are three general types of reactor systems which have been developed, namely solid liquid separation, gas permeable...
Fermentation and respiration
The electrons derived from the catabolism of the carbon source are eventually either donated to an organic molecule in which case the process is described as fermentation, or donated to an inorganic acceptor by transfer along an electron chain. This latter process is respiration and may be aerobic where the terminal electron acceptor is oxygen, or anaerobic where the terminal electron acceptor is other than oxygen such as nitrate, sulphate, carbon dioxide, sulphur or ferric ion. Unfortunately,...
