Archive for December, 2011


Earthworms and arsenic

Arsenic poisoning in groundwater is a global calamity and millions of people are affected arsenic related diseases due to drinking groundwater contaminated with very high concentration of arsenic. Arsenic concentration > 10 ppb is recorded in groundwaters of theBengalBasinand nearly 60% of the population consuming such groundwater is affected by arsenic related diseases. This is more severe inBangladesh. This problem is existing for the last few decades. Children below the age of 12 are seriously affected.  Arsenic content in groundwater varies from less than 1 ppb to 3200 ppb. From water this problem has entered the food chain due to the prevalence of tube well irrigation in a large part ofWest Bengal. Over 5,50,000 bore wells operate now constantly pumping groundwater to the rice fields and the farmers have a happy, contended life since they can grow rice round the year without knowing the dark clouds that are lingering above them and their children!!.

Groundwater being used for irrigation has arsenic concentration about 10 to 32 ppm and it has been established now that the rice roots concentration all the arsenic from the irrigated water. The concentration of arsenic in the roots from rice cultivated in Nadia and Murshidabad districts of West Bengal varies from 56 to 136 ppm and the concentration of arsenic in rice grain is also high, over 3 ppm.

Since this practice of irrigation with arsenic rich groundwater is in place over centuries in India and other countries, and due to the age old practice of ploughing the roots back into the soil is being practiced by the farmers, the soil, over the period of time is accumulating arsenic to levels beyond ones imagination. Some of it enters the shallow aquifers due to subsequent crop cultivation seasons. 

There is no easy solution to this problem since its implementation needs political will. There are hundreds of short term solutions being proposed by a variety of scientists spending millions of rupees,  both from national and international organizations.  But the problem is not showing any downgrade trend but entering the subsequent generation of the population.

Several scientific papers appeared over the last two decades on the behaviour of earthworms in soils contaminated and uncontaminated with arsenic. Perhaps these papers may provide some clues to contain this problem. The solution to arsenic problem could be  earthworms! Earthworms are known to inhabit arsenic rich metalliferous soils and accumulate arsenic in their body and develop resistance to arsenic toxicity. The amount accumulated depends on the soil properties such as soil pH, organic content, microbial content etc. All of know that earthworms are the principal organisms responsible for mixing soil constituents. Countries where traditional agricultural practices are in place, farmers depend on earthworms to “plough” the soil before seeds are sowed. These animals help in soil fertility by removing partially decomposed litter (especially the stems and roots that were left after the harvest) from the soil surface, ingesting it and transporting it to the root zones. Since the earthworms are prey to many birds and animals, the toxic substances ingested by them from the soil is transferred to higher trophic levels. Arsenic concentration in soils is controlled by phosphorus, iron and organic carbon and redox state of the soils. Inorganic arsenic in soils are converted to organo-arsenic compounds by soil mirco-organisms. The toxic state of arsenic follows the order from most toxic to less toxic:

        arsenic gas> inorganic arsenic (III)> organic arsenic (III)> inorganic arsenic (V)> As (element).

 Earthworms are known to inhabit arsenic-rich metalliferous soils  and tend to accumulate arsenic in their bodies and are immune to arsenic toxicity. Chemoreceptor and sensory tubercles in the earthworms makes them very sensitive to chemical environment thus avoiding toxic environment.  But this sensitivity is selective! Experiments have shown that they are sensitive to sodium arsenate only when the concentration is > than 5000 ppm!! Although all species accumulate arsenic in the body, a few species like Eisenia fetida have a very high bio concentration factor ( ~ 10 – 18). This bio concentration factor is independent of the concentration of arsenic in the soil. It is not clear what control this factor. Again these features are earthworm species specific! The entire investigation suggests that, over a long period of time, earthworms are able to sequester arsenic in the tissues in less toxic form

 Again it all depends on the species. For example Lumbricus rubellus  can adopt both under toxic and non toxic conditions. Those adopted to non-toxic conditions can not survive in soils that have high arsenic concentration. Laboratory experimental results reported in the literature show that the above species adopted to toxic conditions are able to sustain arsenic concentration of 2000 ppm in soils and the tissues were able to accumulate 230 ppm of arsenic while the same species adopted to non-toxic conditions dies when exposed to such toxic conditions. Some earthworms of the same species develop yellow pigmentation when their tissues get enriched with arsenic. The above reported results on earthworms indicate that there are several species that are able to sustain high arsenic levels in the soils and some species are able to methylate arsenic in an organic form and pass the toxicity to higher trophic levels.

 Since earthworms are friends of the farmers, arsenic contaminated soils like those inWest Bengalcan find a solution to the perennial problem of arsenic contamination in irrigated soils.



Finally the Special Report on Renewable Energy (SRREN) sources and Climate Change mitigation (Final Release) was released in May 2011 by IPCC. This report gives the status of Wind, Solar, Geothermal and other renewables in the context of ongoing debate on carbon dioxide emissions, climate change and future plan of action for all the countries, especially for those countries under non-OECD. ighlights of the report related to geothermal energy are as follows:

The available heat that can be extracted from the depth of 3 km in the earth is 34 x 106 EJ. Theoretically an amount of 146 EJ/Y of electric power can be generated from this energy.  Technology for generating electric power from hydrothermal sources is very matured and is in place for the last 100 years or more and at present over 11,000 MWe being generated across the countries.  Ground heat sources technology to cool or heat space is also very well developed and in some countries it is mandatory to use ground source heat pumps to cool or heat residential space and districts. The status of electricity generated and direct application through geothermal is regularly updated during the world geothermal congress held every five years. With regard to direct application, during 2009 63% geothermal energy was used for space heating of buildings, 25% for balneology, 5% for greenhouse cultivation, 3% for dehydration, 3% for fish farming and 1% for snow melting.


For geothermal to reach its full capacity in climate change mitigation, it is necessary to overcome technical and non-technical barriers. These barriers can be overcome by making amendments in renewable energy policies. Geothermal resources are either site specific (hydrothermal sources) or site independent (EGS and GHPs). The distance between electricity markets and sources becomes a significant factor in the economics of power generation and direct use. These are technical barriers. Non-technical barrier include lack of information and awareness related to geothermal energy resources among the public. This can be overcome by disseminating information through a variety of media and also holding seminars and symposia. Institutional barriers include lack of specific laws governing geothermal resources. In many countries geothermal resources are considered as mining or water resources.

Policies should be clear regarding the use of GHPs. For example, heating/cooling individual domestic homes does not need any specific policy but implementation of district heating system requires  different policy framework. Policies that support R and D programmes would benefit geothermal technologies, especially emerging technologies like EGS. Fiscal incentive, public finance for research and demonstration, subsidies, guarantees, tax write-offs to cover commercial upfront exploration costs, including high risk drilling costs are a few issues that a policy should address to encourage geothermal resources. Equally important is the feed in tariff that needs to be attractive for the investors.  Experience with the countries that are successful in the development of  geothermal energy for power generation and for direct applications shows that such developments are closely linked to the government policies, regulations, incentives and initiatives.

Geothermal energy resources are independent of weather conditions of any region, provides base-load electricity, reduces GHG emissions and provides solutions for Clean Development Mechanism (CDM).  Geothermal energy sources can generate  substantial carbon credits under CER. For example the Darajat III geothermal power plant of Indonesia, established in 2007 has so far generated 650000 carbon credits per year thereby reducing the life cycle cost of geothermal energy by about 2 to 4%. This is a substantial amount! Geothermal energy does not pose any environmental problems. The GHGs that are emitted by geothermal power plants is very small and such gases any how would have escaped into the atmosphere through natural vents eventually. In the case of EGS supported power plants, the GHG emissions are nil. Electric power  enerated from geothermal power plants can easily be integrated to any type of grid or can also be developed as stand-alone systems especially in remote villages. Since the geothermal power plants provide base load power,  scaling up the old power plants or integrating new ones with the old ones is not a major issue.

Drilling of production and injection of geothermal wells have a success rate of 60 to 90% and the cost of wells depends on permeability, porosity, depth of drilling, temperature of the reservoir, availability of drilling rigs, composition of the fluids etc. These factors take 20 to 35 % of total investment. Geothermal projects in general, are financed in two different ways with different return rates. One is on equity basis and the other on debt basis. Equity rates are generally higher than the debt rates. The capital structure of geothermal-power projects are  commonly composed of 55 to 70% debt and 30 to 45% equity, but in some countries like the USA, debt lenders usually require 25% of the resource capacity to be proven before lending money. Operation and maintenance costs include variable and fixed costs that are directly related to the power generated from a geothermal power plant.  It is necessary, over a period time, to drill new wells to maintain the fluid/steam flow rate. These are make-up wells and they will add to the cost of the project..

Land requirements for geothermal power plants are very small. By designing proper  surface installation systems ( pipes, roads, steam/fluid separators, drilling pads, power stations) and adopting  directional drilling techniques, the land area above the geothermal resources site can be developed for other purposes such as farming, horticulture, forestry etc. as has been developed at Mokai and Rotokawa in New Zealand and national park in Olkaria geothermal site in Kenya.  Land requirement, for example, for a 110 MWe geothermal flash plant is 1260 m2/MWe and for a 20 MWe binary plant is 1415 m2/MWe. The electricity output is substantial. For example 20 MWe binary power plant installed in an area of 1415m2/MWe would generate 170 GWh/yr.

The IPCC Fourth Assessment Report (AR4) estimated a potential contribution of geothermal to world electricity supply by 2030 of 633 TWh/yr (2.28 EJ/yr). Climate policy is likely to be one of the main driving factors of future geothermal development, and under the most favourable policy of CO2 emissions (<440 ppm) geothermal deployment by 2020, 2030 and 2050 could be  higher by several factors.

In a nutshell,  the geothermal-electricity market appears to be accelerating as seen from the increase in the installed and planned generation capacity.  Gradual introduction of new technologies like the EGS is expected to enhance the power production to 160 GWe by 2050. Power generation with binary plants permits the possibility of producing electricity in countries that have no high-temperature resources. Investigations are on in using CO2 as a working fluid in EGS based power projects. CO­2 has more efficient than water in extracting heat from the  underground reservoirs. This would provide means to sequester CO­2 and the same time generating energy with low carbon emission.

Oil fields can also be used to extract geothermal energy.  Abandoned oil and gas wells capable of supplying temperatures higher than 120º C. The advantage here is lowering of project cost due to availability of drilled wells. The only cost involved here is cleaning the wells.