EBT Presentation Slides

EBT Presentation

Reduction of CO2 emission

Increase in the concentration of CO2 in the atmosphere has of late become a global issue. It is probably linked with the rise in atmospheric temperature causing the so-called ‘Green House Effect’. The green house gases (GHGs) include, CO2, CH4, CFC (chlorofluorocarbon) and water vapour.

Present models suggest that for the doubling of CO2 level in the atmosphere, global temperature can increase by around 1.5-5˚C. This would lead to the rise of sea levels, erratic rain-fall, shifting of vegetation zones and their effects on agriculture in general.

This is led to the thinking of devising means of possible reduction of CO2 emissions. Along with the chemical approaches, the possibility of biotechnological reduction is also being thought of and investigated in different parts of the world as an alternative approach.

Use of microalgal photosynthesis

An efficient mechanism for CO2 reduction, as they would be able to generate more O2 than the amount of CO2 consumed per unit biomass than in case of higher plants.

Industrially generated CO2 is higher (20%) than its normal level in the air. CO2 reduction from such high concentration would thus require algal forms or strains which can tolerate high CO2 level, eg. Increased alcohol tolerance by yeats. In this respect, genetic manipulation with chemical mutagens like EMS (ethylmethane sulphonate) or NMU (nitrosomethyl urea) and others yielding higher CO2 tolerant mutants in Anacystis nidulans and Synechococcus is encouraging. This has also led to the discovery of a number of strains, high higher CO2 tolerance, of other algae like Chlorococcum and Oocystis.

Alternatively, using gene cloning technique it may perhaps be possible to develop strains with faster growth rate to yield larger biomass of the concerned algae. Changes in sedimentation and flocculation behavior would be another advantage with respect to harvesting algal biomass as it can be a part of the overall process economics.

Biological Phosphorus Removal from Waste Water

Phosphorus is an ecological factor that is very significant in algal productivity. As algal blooms can be directly related with eutrophication of a certain water body, it is important to keep phosphorus discharge at bay, or at least under control. Usual practice is to precipitate them chemically with salts of calcium, iron, aluminum or magnesium.

An equation on how phosphorus is precipitated using calcium salts is as follows:
5Ca + 7OH +3H2PO4 → Ca5OH(PO4)3 + 6H20

However, there is also an alternate method which is biotechnological, where phosphate-metabolizing bacteria assist in this process. The energy needed for this is made by the release of phosphorous bound as polyphosphate in volutin granules in the bacterial protoplasm. The bio-P removal has the advantage that additions of chemicals can be avoided and it helps in the reduction of sludge volumes. The principle of biological treatment plant lies in the exposure of the organisms to alternating anaerobic and aerobic conditions. Nitrogen removal can be achieved in this method, with an anoxic condition.

Examples of this so-called Bio-P bacterium include, Acinetobacter, Pseudomonas and Nocardia.

The method as to how the bacteria utilize the phosphorus is as follows:
Under anaerobic conditions, the transportation and storage of certain acetates in the bacteria require energy, which is obtained from polyphosphates reserves of the bacteria, which results in the expulsion of phosphorus. To reverse this and reduce the amount of phosphorus in the water, the subsequent stage of aerobic conditions is initiated by the bacteria. The organic matter is oxidized to produce energy and reclamation of phosphates into polyphosphates. The excess phosphorus stored in the water would then be stored in the bacterial cell.

Case Study

Switzerland, phosphate precipitation gave soluble phosphorus removal rates of up to 40%. Phosphate concentration was reduced from around 1.1 to 0.7 mole/m3 after 4 hours by progressively increasing the pH up to 8.1 at a temperature of 15.8°C.

Another example but in a lower pH, phosphate concentrations were reduced from nearly 0.8 to around 0.65 mole/m3 during two abrupt pH increase phases to 7.7, but returned to around 0.77 mole/m3 when pH was returned to around 7 (total experiment time 7 hours). Thus, it is shown at a higher pH, the concentration deficit produced is more, though higher than the one with a lower pH. However, the higher pH gives stable concentrations that stay low, unlike the one with a lower pH, which will spike back up in the concentration level. Adding on to that, experiment time is lesser.

Applications

And to apply such methods in the real world, one can incorporate the anaerobic and aerobic tanks before entering a riparian zone. Adding on the prevention policy to reduce nutrient concentrations before discharging, this biotechnological method has to be more applied. For example, municipal discharge will go through a series of treatment methods like the method with phosphate-metabolizing bacteria, to reduce the amount of phosphates in the effluent. Adding on that, the bacteria can be incorporated with other treatment systems to improve the sludge quality. From there, the effluent can be further discharged into a riparian zone for further nutrient stabilization ecologically or directly into the sea, depending on the quality of the effluent. Therefore, the phosphate-metabolizing bacteria, though non-significant, it will still help in the further reductions of phosphorus concentrations in waste water.

Phytoremediation, the all-in-one solution to land, air and water pollution

Phytoremediation is an emerging technology that uses plants to clean up soil, water, and air contaminated with environmental pollutants through degradation, extraction, or immobilization of contaminants. However, there are still limitations in this technology as some natural occurring plants lack the capacity to tolerate or clean-up contaminants from the environment. Hence, there is a clear need to improve the performance of naturally-occurring plant species, in order to obtain commercially-significant phytoremediation performance.

Transgenic plants are genetically engineered organism. They generally had a better germination percentage, greater growth rate, and higher accumulation of some metals than non transformed plants.

In genetic engineering, a foreign piece of DNA from various plants, animal or bacteria species is integrated into the plant to enhance their functionality in different aspect. The foreign gene may induce enzymatic activity in the plant to become up-regulated (over expression) or down-regulated, or it can bring in a totally new enzymatic activity. The presence of enzymes can be controlled to be present all the time, in every tissue or, only in some selected tissue (e.g. only in leaves) or at certain times. With such control at hand, it is possible to create a new breed of more efficient plants that is specially made to clean out a specific waste problem in a particular site under defined conditions.

 

Different Forms of Phytoremediation

 

Phytoextraction

Phytoextraction is the use of plant to take up metal contaminants from soil through the absorption by plant roots. The metal absorbed are stored or accumulated in the aerial portions of the plants (Stems & Leaves).  Plants intended for this application are called hyper accumulators. These species of plants have high tolerance to heavy metals and are capable of absorbing larger amount of metal in comparison to other plants. Today, researchers are developing genetically engineered hyper accumulators that have a higher metal accumulation and tolerance capacity.

After the plants are allowed to absorb the contaminants for some time, they are harvested to either be disposed by incineration or be composted to recycle metals. Although plants that were incinerated will be disposed off in a hazardous waste landfill, the volume of the plant ash generated will be below 10% of the volume that would be produce if contaminated soil were excavated for treatment.

The plants take up the contaminant through the system of roots and store them in the roots or transport them up into the stems and leaves. The plants will carry on absorbing contaminants until it is being harvested. After the harvest, the soil will contain a lower concentration of contaminant. As such, this growth and harvest cycle is usually repeated for a number of times to achieve a considerable clean up. After the process, the remediated soil can be put into other beneficial uses.

Gene to improve Phytoextraction

A problem in the use of phytoaccumulator is that they do not have enough biomass and growth rate to be applied in large scale practices. To resolve this problem, phytoextraction can be further improve by transfer of genetic traits from hyper accumulator into plants that has high biomass and growth rate. In this way, plants with high biomass and growth rate will also have the ability to take up high quantity of metals.

For example, Poplar and willow do not accumulate metals to high concentration. However, they are still effective remediators because of their deep root system and biomass. Hence, they became excellent candidate to be genetically engineered to have traits of hyper-accumulators.

Metals accumulated poses significant risk to consumers of plants. As such, plants capable of producing substances that deter or discourage herbivores from feeding them can be transformed to have improved metal tolerance and capabilities. With such a system in place, it will help prevent the transfer of metals to food chain.

Transfer of gene extracted from bacteria or animals into plants systems are attempts to improve the potential of remediation. Some bacteria have the genetic characteristic to detoxify toxic elements. Today, the transfer of such genes into plants had already produced promising results.

For instances, no plants have been shown to be able tolerate some elements such as mercury or lead. This can possibly be changed by transferring genes from bacteria that has the ability to detoxify these metals (mercury & lead) into plants. With the transfer of the expressing gene, plants can be genetically altered to be used clean up these metals which were once seemed to be impossible.

The use of transgenic plants also addresses the problem of mix contamination that is happening in a polluted site. Methods which involve introducing several genes at once into plants have help in the removal of complex and mixed pollutants.

Advantages:

1. Owing to incineration, the volume of harvested plant biomass that requires disposal is dramatically reduced
2. In some cases, additional source of revenue can be obtained by extraction of metals from metal rich ash; so therefore, it can be used to offset the cost of remediation.
3. Cheaper than most clean-up methods
4. In comparison to conventional methods which typically disrupt soil structure and productivity, phytoextraction is capable of remediating heavily metal contaminated soil without impairing the soil quality.

Disadvantages:

1. As the process relies solely on plants, the remediation time is relatively longer than other anthropogenic soil clean-up processes.

 

 

Phytostabilization

In phytostabilization, soil contaminants are immobilized through absorption by roots, adsorption onto root surface and precipitation within the area of plant roots. As such, the plant and plant roots are employed to prevent the spread or migration of contaminants through wind and water erosion, soil dispersion and leaching. Phytostabilization influences the contaminant’s mobility in several ways:

• The amendments directly change the soil condition that influences the mobility of metal contaminants (acidic or alkaline conditions, organic matter, oxygen levels).

For example, a soil’s pH have an effect on the retention and mobility of metals in soil columns. The pH is a controlling factor in precipitation-solubilization reactions. This affects the solubility of nutrient elements and toxic elements, and it affects the ion exchange that binds nutrients and toxicants to soil particles.

• Enzymes and proteins secreted by plant roots into adjacent soil results in immobilization and precipitation of the contaminants in soil or on root surface.

• Contaminant accumulated in plant tissue becomes insoluble and or immobilized after absorption through plant roots.

• When the surface of the soil is vegetated, the vegetation serves as a barrier for physical contact and to minimize erosion by wind and water.

Advantages

• Phytostabilization does not produce secondary waste that needs treatment.
• Compared with other remediation technologies, such as excavation, materials that were used and handled are lesser, and costs are typically lower.
• Usually the technology enhances the soil fertility. It may combine treatment with ecosystem restoration
• Water removal is improved with more plants that reduce water infiltration. With that, soluble contaminants are unable to leach into soil and contaminate ground water.
• Improved Aesthetic
• Vegetation offers a protective covering to help reduce the impact of wind, over watering and rainfall; they will also stabilize the properties of soil and thus, prevent soil erosion. As a result, impact on aquatic life will be greatly reduced due to lesser sediment deposition

Disadvantages

• The contaminants are left in place, so the site must be monitored continuously to maintain the stabilizing conditions.
• If the contaminant concentrations increase to a high level, toxic effects may prevent plants from growing
• If soil additives are used, there may be a need to reapply them over and over again in order maintain the immobilization effectiveness of contaminants.

Rhizofiltration

Rhizofiltration shares similarity in concept with phytoextraction. However, it is used to remediate contaminated groundwater instead of polluted soil. The contaminants are either adsorbed onto the root surface or are absorbed by the plant roots. Plants intended for rhizofiltration are not planted directly onsite but are adjusted to the pollutant first.

 

Phytodegradation

Phytodegradation which is also known as phyto-transformation is the breakdown of contaminants taken up by plants through metabolic processes within the plant, or the breakdown of contaminants surrounding the plant through the effect of enzymes produced by the plants. Plants are able to produce enzymes that catalyze and accelerate degradation. Hence, organic pollutants are broken down into simpler molecular forms and are incorporated into plant tissues to aid plant growth.

Enzymes in plant roots break down (degrade) organic contaminants. The fragments are incorporated into new plant material.

[Case Study]

Trinitrotoluene (TNT) is one of the world’s most persistent and dangerous explosives. The use and disposal of TNT has resulted in the contamination of many sites. Furthermore, methods available to clean up such sites are so costly that only a few of them are have been remediated.

There are many plant species that are able to break down TNT in their own tissue. However, this process tremendously affects the plant’s growth and development. Owing to this limiting factor, it prevents their application in large-scale phytodegradation system.

An Entereo cloaca, a soil bacterium was discovered to be able to utilize ester explosive as its source of nitrogen. Enzymes produced by this bacterium are PETN reductase and nitroreductase. Both of these enzymes degrade TNT into less harmless product. The genes expressing the production of these 2 enzymes are introduced into the tobacco plant Tobacco (Nicotiana tabacum).

Subsequently, a study on the transgenic was carried out. The tobacco plant and the wild type plant were both exposed to 0.25mM of TNT. The wild type plant became chlorotic and lost mass, while the transgenic plant continues to grow. The enzymes that were over expressed in the transgenic helped to metabolized TNT at faster rates than the control plants. More importantly, transgenic plant became more resistant to TNT concentration in comparison to non-transformed plants that are greatly affected in their development.

Rhizodegradation

Rhizodegradation, also known as phyto-stimulation, is the degradation of contaminants in the rhizosphere (area of soil surrounding the roots of the plants) by means of microbial activity which is enhanced by the presence of plant roots.

Microorganisms such as yeast, fungi or bacteria consume these contaminants as their source of energy and nutrition. In this process of biodegradation, certain microorganisms are capable of breaking down hazardous pollutants such as fuels or solvent into nontoxic and harmless product. Biodegradation is aided by plants. Plants released natural carbon containing substances such as sugar, alcohols and acid and thereby, providing the microorganisms with additional nutrients which stimulate their activity.

It is possible to develop transgenic plants with improved plant-microbe interaction. The plant would be enhanced in their ability to secrete natural substances which stimulates microbial activity.

 

Phytovolatilization

Phytovolatilization is a process, in which plants take up contaminants from soil and release them as volatile form into the atmosphere through transpiration. The process occurs as growing plants absorb water and organic contaminants. As water travels from the roots to the leaves along the vascular system of the plant, it is changed and modified along the way. Then, some of the contaminants move through the plants to the leaves and evaporate or volatilize into the atmosphere. Phytovolatilization has been primarily used to remove mercury; the mercuric ion is converted into less toxic elemental mercury.