Honour for wastewater treatment pioneer
K. S. RAJGOPAL
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The technology is especially suited for developing countries
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TOMORROW THE international environmental community will honour Gatze Lettinga by conferring on him the prestigious 2007 Tyler Prize for Environmental Achievement. The Tyler Prize is one of the leading awards presented in the fields of environmental sciences, energy and medicine.
This prize for the Dutch scientist is special for many reasons.
At the present time when patenting products and inventions has become the order of the day and is projected as the only means to further research and development, it comes as a pleasant surprise that there was a scientist who developed a technology in 1972 and made it available to the society sans any patent.
Concept open for all
"The ... concept is still completely open for everyone, particularly also to the citizens in developing countries, and that is what I wanted and still want, Lettinga was quoted as saying in the Water and Wastewater.com.
Lettinga, was based in Wageningen University, the Netherlands, when he developed the upflow anaerobic sludge blanket (UASB) technology to treat industrial and domestic wastewater.
Today, his technology is used across the world and more so in the developing countries, including India. Lettinga's technology is used in more than 70 per cent of anaerobic wastewater treatment by different industries.
It was originally designed to treat wastewater of the sugar-beet industry in the Netherlands.
Simple concept
The technology is based on a simple concept. Wastewater is made to flow into a tank in an upward direction.
The anaerobic bacteria present in the sludge bed come in contact with the wastewater. The bacteria are so chosen that they exhibit a very special characteristic of forming granules (pellets) of 0.5 to 2 mm diameter. The bacteria encapsulate the wastewater substances that are to be degraded. The heavy granules settle to the bottom despite the wastewater moving in an upward direction.
The highlight of the technology is ensuring the right choice of bacteria to maximise the granule formation and its settling down than allowing them to be dispersed all along the tank.
Four stages
The anaerobic degradation produces methane gas as a by-product. It is produced at the end of a four-stage process of hydrolysis, acidogenesis, acetogenesis, and finally the methanogenesis. In the methanogenesis, carbon dioxide and water are produced in addition to water.
This gas moves upward, enhancing the mixing of the wastewater present in the tank.
The device provides 75 per cent to 90 per cent reduction in BOD. BOD — biochemical (biological) oxygen demand — is a test used to measure the concentration of biodegradable organic matter (carbon source) present in a sample of water. It can be used to infer the general quality of the water and its degree of pollution by biodegradable organic matter. As we know that the increase in organic matter in waste water leads to an increase in pollution of water we have to remove this organic matter content to purify the water, and if we have removed 75 to 90 per cent BOD it means that 75 to 90 per cent of organic matter has been removed from water.
If this organic matter is not removed from waste water and if this water is dumped in any river body then the presence of the organic matter reduces the oxygen content of the water thus leading to the death of other aquatic animals which are used by humans as food.
Higher the BOD higher is the oxygen demand to decompose the organic matter in wastewater.
Removing impurities
According to Mr. A. Vijay Bharat Sastri, Environmental Engineer, R&D, UPL Environmental Engineers Limited, Vadodara, biologically treated waste water may still have some impurities which are removed in post treatment. After such treatment the waste water can be finally discharged in any water body without causing any harm to the aquatic life of that water body.
The effluent from the reactor contains sloughed (detached biomass) biological growth, which has to be separated which may otherwise increase the turbidity of the wastewater and the water source in which it is dumped. Hence post treatment is required in this system.
Great opportunity
What makes UASB stand out is the great opportunity to use the methane that is produced as a by-product, particularly in the developing countries.
It is in total contrast to the energy intensive aerobic wastewater treatment technologies.
The UASB thus solves two problems.
First, it treats industrial wastewater and second, it produces renewable energy.
UASB technology is suitable in a developing world urban context as it is efficient, simple, low-cost, needs low capital and maintenance costs and has low land requirements.
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