Thai Biogas Plants-High Rate Anaerobic Fixed Film Technology for Agroindustrial Wastewater
The Award Contest of Best Program on New and Renewable Sources of Energy (Off-Grid) in Year 2003
Laboratory for Waste Utilization and Management
Asst. Prof. Dr. Pawinee Chaiprasert
Biotechnology Program, School of Bioresources and Technology
Dr. Annop Nopharatana, Tanong Chayawattana, Chinnapong Wangnai
Warin Rukruem, Pratin Kullavanijaya
Pilot Plant Development and Training Institute
Assoc. Prof. Dr. Sakarindr Bhumiratana
Department of Food Engineering, Faculty of Engineering
Prof. Dr. Morakot Tanticharoen
National Center for Genetic Engineering and Biotechnology (BIOTEC)
Tel. 0-2470-9750 Fax. 0-2452-3455
Energy crisis, high oil price and decreased oil reserve in all over the world as well as the country's increased consumption of energy lead to promotion of renewable energy in the country to substitute of fossil fuel sources which have to be imported from other countries and have adverse impact on the environment. Biogas is another alternative of high-potential energy source in Thailand as there is a great quantity of raw materials obtained from waste from agro-industrial production processes where a lot of water is used and high quantity of wastewater is discharged e.g. industry producing flour from rice, tapioca or bean, food canning industry and palm oil industry.
Wastewater from these agro-product factories, if discharged into natural waterways, can cause severely adverse environmental impact. Typically, most factories use the open-pond wastewater treatment system by digging many open ponds and let water flow serially into the ponds. The wastewater will be let out in the last pond or some may permeate into the underground. This system reduces environmental impact only to some degree. It still has the problem of low efficiency and the bad smell from the open ponds. In addition, it may contaminate ground water with the wastewater permeating into the ground. The reason why factories have adopted for the open-pond system might be because in the past factories lacked knowledge and confidence in the existing technologies. Moreover, the technology used for wastewater treatment is costly, both in the initial investment and in the operation. It yields low financial rate of returns and becomes additional cost to the products. Consequently, most factories have chosen to hold wastewater in open ponds inside their facilities. Although this requires a lot of space, in case the price of land is cheap and it is more worthwhile than investing in construction of a wastewater treatment system in which there are expenses throughout the operation period.
A high rate treatment system has been developed. It has advantages over the open-pond system currently used in factories as follows:
During the past twenty years, King Mongkut's University of Technology Thonburi has been conducting research on treatment technology and use of waste from agro-industry. One of the research projects is the research and development of high-rate anaerobic reactor, which treats wastewater and produces biogas from wastewater that has carbohydrate as component i.e. wastewater from tapioca flour and rice flour factories. This project involves continuing research and development and has received funding from the National Center for Genetic Engineering and Biotechnology . The high rate anaerobic treatment system developed, which is ideal for the properties of wastewater in agro-industry, is the anaerobic fixed film reactor (AFFR).
- High efficiency in treatment. It can help solve environmental problems both in relation to water quality and smell.
- It requires small space.
- Most importantly, it yields biogas which can be used as alternative energy. Therefore, it is worth the investment. It reduces the burden of fuel costs in the situation where oil price is high.
|Properties and features
The anaerobic fixed film reactor is a close-type reactor. The media inside the reactor are neatly organized. Their function is to support the microorganisms. The microorganisms will stay on the media in form of bio-film. This system has advantages over other types of anaerobic treatment systems as follows:
From the above characteristics, we can see that the main features of the anaerobic fixed film reactor are: its easiness to operate, non-requirement of close control or supervision, non-requirement of many supervisors to check the quality of the input and output water, non-requirement of sophisticated measuring devices and low operational costs.
- It can keep microorganisms in the system for a long time.
- It is highly efficient in wastewater treatment and biogas production.
- It can work with wastewater with high quantity of suspended solids without requiring any pretreatment.
- It is more resistant to toxic wastewater than other systems.
- Low cost of chemicals used to operate and control the system.
- It does not require complicated maintenance. After start-up, it requires no specialists to supervise the system.
The fixed-film anaerobic wastewater treatment and biogas production system developed by KMUTT has already been constructed and operated in the industrial level. A 5,200 m3 reactor was built to treat wastewater of a rice flour factory. The reactor was designed to receive 2,000 m3 of wastewater a day. The concentration of wastewater in COD is 5,500 mg/litre. As the factory uses clean technology, the amount of wastewater is reduced to 1,200 m3. This water treatment system has been in operation since late 1999 and is currently working with good stability. Its effectiveness in organic substance elimination is 80-90% as expected. It can produce 2,500-3,000 m3 of biogas a day. An electricity generator has been installed supplying alternative energy of approximately 3,000 kWh a day. Thus, expenses on electricity are reduced.
The fixed film anaerobic reactor built in this rice flour factory and connected with a few existing open ponds can give the final treated water output with BOD lower than 20 mg/litre, meeting the standard requirements of the Department of Industrial Works. It also solved the odor issue which caused problems to the factory since this affected the neighboring community. In addition to reducing odor and pollution, it help saving expenses on chemicals used in treatment ponds by over 80% compared to the former system in the factory, biogas is obtained as alternative energy to generate electricity for internal use. This system received energy conservation subsidy from the Energy Conservation Promotion Fund, Office of Energy Policy and Planning.
This technology can be used with wastewater from agro-industry in general. The next goal of the Laboratory is to promote its use with the tapioca flour industry. KMUTT's study in 1997 indicates that production of one ton of tapioca flour produces as much as 11-33 m3 of wastewater (an average of 23 m3/ton of flour produced). However, nowadays many factories use clean technology in their production process, resulting in reduced amount of flour wasted and water used. The wastewater discharged from the production process is also reduced to approximately 10-15 m3/ton of flour produced in many factories. Yet, the wastewater still contains high quantity of organic substances in form of COD of 13,000-20,000 mg/litre.
The research findings and actual experience gained from the above-mentioned factory offer assurance of the efficiency of the fixed-film anaerobic reactor, that it is suitable for the properties of wastewater from tapioca flour factories. In a tapioca flour factory with the production capacity of 200 ton of flour which produces about 3,000 m3 of wastewater a day, with COD 16,000 mg/litre, the reactor has the efficiency of at least 80% for wastewater treatment. 3.84 million m3 of biogas a year can be produced, substituting the use of fuel oil of 1.8 million litres a year, an income from biogas of 14.4 million baht a year. This system requires approximately 40 million baht of investment and has a 3- years break-even period.
update : 28 September 2004