Treat the Water Right
Mubarak Ahmed Khan explores the feasibility of water treatment in Dhaka.
Policies to tackle environmental pollution have been receiving increasing attention throughout the world in recent years. Radiation processing using electron beam accelerators and gamma irradiators has shown very promising results in this area. Radiation processing in wastewater treatment is an additive-free process that uses the short lived reactive species formed during the radiolysis of water for efficient decomposition of pollutants therein. The rapid growth of the global population, together with the increased development of agriculture and industry, have led to the generation of large quantities of polluted industrial and municipal wastewater. The recognition that these polluted waters may pose a serious threat to humans has led technologists to look for cost effective technologies for their treatment. A variety of methods based on biological, chemical, photochemical and electrochemical processes are being explored for decomposing the chemical and biological contaminants present in the wastewaters.
The Textile industry is the fastest growing industry in Bangladesh. It provides almost 75% of the foreign currency in the country. But this sector is also a source of major environmental pollution. The wastewaters and other effluence produced by the textile sector, which are characterized by high alkalinity, high biological oxygen demand (BOD) and high-suspended solids, are often disposed off in nearby rivers, canals, ponds or lakes without proper treatment. Wastewater released by those industries contains toxic refractory dye at a high concentration. Disposal of effluence from textile industries has become a serious environmental concern in many countries. Most of the dyes used in the textile industry are non-biodegradable. Therefore, ordinary processes have had no affect on treating dye waste effluence. Most coloured materials undergo bleaching or colour changes when exposed to ionizing radiation. Ionizing radiation may be promising for the treatment of textile dye waste effluents because the effect of radiation can be intensified in aqueous solution, in which the dye molecules are degraded effectively.
Dhaka, has now become an overpopulated and polluted gray city. Because of highly dense population, lack of environmental consciousness among the inhabitants and absence of proper role of public agencies, Dhaka is headed to becoming one of the deadliest cities in the world . Dhaka already has a burgeoning list of environmental problems: huge extraction of ground water, crisis of pure drinking water, incapacitated drainage system, unplanned high rise buildings, discharge of industrial waste in rivers and water bodies, shortage of electricity and insufficient disposal facilities for solid waste appear most perturbing.
Some time ago there was an efficient network of natural canals within the Dhaka city, which served as means of draining the rain runoff and water during an event of flood. Those canals were also a good means of transportation. But this natural drainage system is almost unusable now. Man made drainage and sewerage systems used as drainage systems are not sufficient enough for this growing metropolis. Dhaka is surrounded by four rivers -- Buriganga, Shitalakhya, Turag and Balu--but all of them have been polluted unabatedly. Pollution of these rivers is directly related with city life.
River pollution occurs due to three reasons. Two main causes are discharge of municipal sewage and industrial effluence: 277 tanneries in Hazaribagh are discharging wastewater into the Buriganga without any treatment. Another important source is textile industrial effluents. Textile industry is the fastest growing industry in Bangladesh. It provides almost 75% of the foreign currency in this country. But this sector is one of the most environmentally polluted sectors and the effluents from dying and finishing are the major source of pollution. Its effects are becoming more evident with the increase in the number of textiles in the country. The wastewaters, which are characterized by high alkalinity, high BOD and high-suspended solids, are often disposed off to nearby rivers, canals, ponds or lakes without proper treatment. They contaminate and decrease the amount of fresh water, in addition to causing serious damage to ecology and aquatic lives. Therefore, under the circumstances it will be helpful to think of ways to treat the textile wastewater so that it can be friendly to the environment.
The new industries that are springing up in and around Dhaka city usually appear in Savar, Gazipur, and Narayangong and most of them are situated near rivers and canals. Most of these industries are disposing their wastewater and other contaminants into the nearby rivers, canals, ponds and even open grounds. Thus rivers like Burigonga, Shitalakhwa, Turag, Bongshai etc. are affected by old and new textile industries due to the disposal of highly toxic and hazardous effluents. Most of these industries generate and discharge a lot of wastewater without any treatment. From the investigations of NGOs, different organizations and monitoring authority, it is found that these wastewaters or partially treated wastewater contains contaminants, toxicants and chemicals over the acceptable limit, which may be disastrous to the environment. On the other hand some textile industries drain their wastewater and wastages onto the open ground, which leads to the reduction of soil fertility in the long run. It is also seen that wastewater disposed beside a busy roadside leads to odor and discomfort for the neighbouring people.
If we want to save the rivers from pollution we have to take care of the wastewater discharged from different industries. But unfortunately most of the industries in and around Dhaka city do not possess effluent treatment plants. A World Bank study said four major rivers near Dhaka the Buriganga, Shitalakhya, Turag and Balu -- receive 1.5 million cubic meters of waste water every day from 7,000 industrial units in surrounding areas and another 0.5 million cubic meters from other sources.
Present wastewater treatment technologies:
At the present time wastewater treatment technologies have improved significantly In developed countries wastewater is treated as a source of energy. Waste-to-energy has become a sustainable point of view towards wastewater treatment. The more the water is organic, the more energy it contains. So, we can actually think of wastewater as a source of energy.. But the problem is, in Dhaka city, we do not treat the wastewater we produce everyday. A few industries are using some conventional wastewater treatment technologies, most of which are not very effective in treating the effluence. This does not mean that we do not have effective wastewater treatment technologies, it simply means we do not utilize it much.
Hundreds of wastewater treatments technologies depend on the type of wastewater to be treated. Some of the most used treatment technologies in our country are based on conventional chemical treatments, which are less effective. But we have to look for a cost-effective wastewater treatment technology. Such wastewater treatment technology can be Ultraviolet Radiation Treatment of wastewater or electron beam radiation treatment. This has been proved to be very cost-effective in treating industrial wastewater.
EB wastewater treatment
Right now many countries such as Australia, Hungary, India, Japan, Jordan Poland, Portugal Turkey, USA are using EB radiation for wastewater treatment for various purposes like decontamination of wastewater and municipal waste, reducing the concentration of toxic pesticides, non-biodegradable materials, disinfections of microbio-logically contaminated drinking water etc.
Electron Beam Treatment in Korea
In South Korea, an electron beam treatment pilot plant for treating 1,000 m3/day of dyeing wastewater was constructed in Daegu and has been in operation since 1998. It utilizes an accelerator having the energy of 1MeV and producing beam power of 40 kW. The system is shown schematically in Fig. 3. For the uniform irradiation of water, nozzle type injector with the width of 1.5 m is used. The wastewater is injected under the E-beam irradiation area through the injector to obtain the adequate penetration depth. The speed of injection can be varied to achieve a certain dose. This plant is combined with a biological treatment system. It demonstrated the reduction of chemical reagent consumption, and also the reduction in retention time with the increase in removal efficiencies of up to 30~40 times.
Removal of organic and petrochemical pollutants in Brazil
Researchers in Brazil have performed studies to predict how the electron beam treatment of industrial effluents can be considered a practical technology in removing organic contaminants in water treatment plants. One of their studies compared the use of electron beam processing with activated carbon adsorption to clean up a real industrial effluent. The electron beam treatment was performed using an electron beam accelerator from Radiation Dynamics Inc. Brazilian researchers also compared the results of treating water polluted with three petrochemical pollutants with electron beam dose of 50 kGy with those processed by a convention treatment using activated carbon. They concluded from the results that the EB process shows organic removal efficiency similar to that of the more conventional treatment using the activated carbon process if adequate irradiation dose was delivered to the organic pollutant.
Feasibility of a radiation induced wastewater treatment plant
Radiation induced wastewater treatment can be potentially beneficial in treating industrial and municipal wastewater in Dhaka city. This decontaminated waster contains nitrogen compound and could be used for irrigation. A laboratory scale plant has been developed in the Radiation and Polymer Chemistry Laboratory of Bangladesh Atomic Energy Commission to treat the textile effluent. The result was promising. Here we can propose wastewater trements, which involve the integration of biological treatment of the wastewater with electron beam accelerator. Fig 4. Shows a proposed design for a possible radiation induced waste-water treatment facility.
Radiation treatment technology represents a viable solution to the problem of wastewater treatment. Several countries have already taken the initiative of implementing electron beam in the irradiation of wastewater. It is expected that the spread of use of this technology will provide the impetus for the accelerator industry to produce linacs specially designed for this application. It is hoped that the increase in number of units produced would help the cost of such technology to decline to a level that makes it affordable and economically attractive to many countries. Scientists of Bangladesh Atomic Energy Commission able to design and establish such wastewater treatment plant in our country to save Dhaka city from wastewater pollution.
Dr. Mubarak Ahmed Khan, Chief Scientific Officer, Bangladesh Atomic Energy Commission