Sundarban is the most important natural defense against natural calamities. We still have the live memory of cyclonic storm Sidr which took heavy a troll on coastal districts, with the death figure reaching more than 4,000. The figure could have been many times higher if Sundarban had not protected us. After the biggest oil spill in the River Shela, we are criticising how it could happen and what could be done. But, unfortunately, we are not focusing on how to resolve it immediately. Here are some ideas that might be considered in restoring life to Sandarban.
A three-step management strategy — (a) the removal of oil from the spot; (b) the reduction of oil toxicity and (c) the biodegradation of oil — could be taken.
Physical removal of oil
The first task would be the removal of oil as much as possible using skimmer and adsorbent. We can use our traditional net or cloth skimmers although there are modern skimmers available now. It is highly appreciable that local people have come forward to clean up the river. We should intensify our efforts. In addition, we can use hydrophobic and oleophilic materials such straws, plant materials, weeds, saw dust, rice husk and any kind of fibre such
as kapok or cotton to trap the oil. The oil adsorption capacity varies for the material used and it usually ranges between 25g to 50g per gram of material of the natural fibre.
Some optimistic studies have, however, shown that it could be much higher. For example, a study showed that 1g of kapok cotton can absorb as much as 200g of oil. Saw dust and rice husk can adsorb 4–7 times of oil. We can make rice husk or saw dust pad by putting them in between the two clothes and use them for oil removal. We can also make chain of rice straw bundle which can be potentially used. Another important available adsorbent of garments by-product popularly known as ‘jhut’, or garment wastes, might be used. Similarly, synthetic adsorbent like open-cell polyurethane can also be explored.
Reduction of oil toxicity
The next strategy should include measures that can reduce the environmental impact by detoxifying the soil and water by trapping the oil in sorbent which will stop the oil causing harm to environment. This measures might include use of dispersant to break down the slick of oil into smaller droplets that accelerates biodegradation and the use of hydrophobic materials such as activated carbon. I wonder whether we should use dispersant unless it is almost impossible to remove oil with physical methods as described above. Because this chemical is used to spread the oil. The activated carbon is a good choice but it is costly. However, we can make charcoal or biochar which also act as activated carbon. In scientific studies, it has been found that biochar can absorb oil ranged from 3.6 to 6.3 g/g while biochar also enhances microbial degradation of oil. Therefore, biochar can be produced from available materials easily and be applied.
Bioremediation of oil
The third and final one could be to break down the oil. An important way could be biodegradation. The faster the biodegradation is, the better it is. The biodegradation of oil depends on a number of factors such as the availability of oil degrading microorganisms, the availability of nutrient elements that help the smooth growth of theses microorganisms, the pH of water and the availability of oxygen. There is an array of different microorganisms (bacteria, fungi and yeast) such as Alcanivorax borkumensis, Pseudomonas species, that are present in nature and they use oil as their food (carbon) source.
We can collect potential microorganism of our environment and multiply them using biotechnological methods and finally use them for oil biodegradation. Alternatively, we can buy microbial inoculum from foreign countries and multiply and use them (scientifically known as seeding of microbes). There is always a question how foreign microorganisms will act in our environment. There is always a challenge that these microorganisms could be invasive and take over other microorganisms and cause serous imbalance in food chain of ecosystems. So, we should be careful.
Moreover, in scientific studies, it has been found that mineral nutrients, especially nitrogen and phosphorus, are limiting for microbial degradation of oil. So for bio-stimulation of the oil biodegradation, we can apply nitrogenous and phosphorous fertilisers after testing their status in sediments and soils of Sundarban. In addition, making floating pellets rich in bioremediation nutrients can be an excellent option for bioremediation as it can reach the deep forest. It can be made by inoculating carrier materials such as sawdust or rice husk with oil degrading microorganisms. The carrier materials should be provided with mineral nutrients to support microbial growth.
I would like to underscore forming a national expert team that will gather the current state of knowledge and technology about the oil spill, investigate the feasibility and apply them for the reclamation. Of course, the state should support the activities with sufficient funding.
Shamim Mia is an assistant professor in Patuakhali Science and Technology University.