Treating sewage and wastewater is critical for the conservation of water environment such as rivers, lakes and inland sea. In Japan, the Water Pollution Control Law was laid down in 1970 aimed mainly at reducing BOD and COD that reveal the amount of organic matters. The law has decreed the limit for the pollutant concentration in the industrial and household effluent water. This regulation has been very effective in cleaning up the bodies of water as witnessed by the high compliance rate and by the casual everyday observation. However, closed bodies of water such as lakes, and bays of Tokyo, Ise and Osaka, and the Inland Sea, has not seen much improvement. The extent of accomplishment of the standard in these areas has been stagnant. The frequent annual growths of water bloom and red tide in these places disclose the shortfall in the safekeeping of the place of relaxation for the people. The 1993 amendment of the Water Pollution Control Law has added Nitrogen and Phosphorus to the controlled elements for the purpose of reducing nutrient salts that cause water blooming and red tide. The results, however, has not been encouraging. Subsequently, a major change has been made in the Sewage Law Enforcement Regulations in 2003 that has added Nitrogen and Phosphorus to the list of controlled constituents of the effluent water, and the legal ground has been set for the adoption of advanced treatment facilities. Along with the tightening of regulations described above, introduction of new technologies from abroad, and development of treatment technologies have taken place, resulting in the implementation of new applications. We report here on the history of such technological innovations and the future trend of the advance water treatment technology.
This is an introduction to the Katsushika Incineration plant that we built and delivered to The Clean Association of Tokyo 23 last December. This plant thoroughly recovers the thermal energy from the Refusedisposal incineration. It generates electricity that is used to melt its own combustion ashes and also those received from other incineration facilities. A test operation was conducted over a period of six months, and it has proven that the incineration and melting units perform up to the design capacity. The exhaust gas analysis and molten slag leachate test have also shown to meet the regulatory limits.
In November of 2006, we completed, on a turnkey basis, Yala Green Power Plant, a biomass power generation facility for Gulf Yala Green Co. located in Yala province in the south of Thailand. This facility generates 23 MW of electricity by burning wood waste from a rubber wood plywood factory.
This plant consists of steam generator, turbine generator, cooling tower and other necessary facilities for biomass power generation, including fuel handling system, ash handling system, raw water and waste water treatment system and 115 kV transmission switch yard.
In this article, we report on the outline of this biomass power plant facilities, and its operation.
We have a gas turbine packaging contract with Siemens Industrial Turbomachinery Ltd. that dates back to 1990. Here is the outline of the unit No. 1 and No.2 of our cogeneration package TCP-12000 that we delivered recently. It incorporates SGT-400, the two-shaft gas turbine of 12.9MW capacity newly developed by Siemens.
Co-generation using natural gas is known for its excellent contribution to the reduction of the global environmental burden through the reduction of carbon dioxide by recovering waste heat from the gas turbine. SGT-400 model has the ISO basic power generation capacity of 12.9MW, and its shaft-end efficiency is 34.8%, the best in its class in the world, and its exhaust gas temperature is as high as 555℃. Having the world's highest overall efficiency, it is the most advanced model well suited for the co-generation application.
As demand for utilization of sewage resource and its advanced treatment is increasing lately, re-using treated sewage water and reducing COD require advanced treatment in addition to the biological process, raising its cost. In contrast to the traditional advanced treatment that uses ozone and biological activated carbon, we have developed a new system that employs an advanced oxidation process using a hydroxy radical that is a more powerful oxidant than ozone, enabling a more efficient treatment using less ozone.
Our goal was set at CODMn 3mg/L for the secondary effluent, and conditions to achieve this have been established. The running cost has been reduced, and the contents of the treated water have been found to be within the safety zone, assuring that this is an effective ultra-advanced secondary sewage effluent treatment system.
We wish to add that this achievement has come from the joint research between Japan Sewage Works Agency and Takuma, called "Development of the Technology for Reducing Environmental Risks such as Hard-biodegradable Material."
Due mainly to the revision of Sewage Control Regulations, use of sand filtration is expected to increase at sewage treatment facilities that discharge effluents into closed bodies of water. As many existing sewage treatment facilities lack sufficient space to install conventional high-rate filtration equipment, we have developed a compact version of the moving-bed, up-flow sand filter that has been adopted widely as a means of high-rate filtration.
The filtration speed reaches the maximum of 700m/day (1,000m/day hourly maximum), far superior to the 300m/day maximum (450m/day hourly maximum) of the conventional system, greatly reducing its installation space requirement.
Furthermore, its power consumption is slashed drastically, establishing itself as energy-saving equipment.
In March 2007, this technology was awarded the Construction Technology Review and Certification by Japan Institute of Wastewater Engineering Technology.
Conventional mechanical thickeners for sewage sludge are high in energy consumption. An energy-saving, high-efficiency thickener is badly needed for reducing the cost and preventing global warming.
With this background, we have developed a rotating-drum type thickener that performs as well as the conventional mechanical systems but saves on electricity.
A demonstration test using sludge from a concentrated sludge treatment facility has proven that this thickener is capable of stable operations (thickened sludge concentration: better than 4% ; SS recovery rate : over 95%). A comparison with a centrifugal thickener of the conventional design in the areas of initial equipment cost, chemicals usage for 15 years and the power use, has shown 90% reductions in the power usage and the greenhouse gas emission. This new thickener has proven to save as much as 40% in the total cost over the centrifugal unit.
Looking for a new desalination technology, we have examined a diffusion dialysis method and a piezodialysis method using an amphoteric-charged membrane developed by ourselves. The amphoteric-charged membrane system is characterized by its ability to separate electrolyte from non-electrolyte, preventing concentration polarization, with easy operation and low energy demand.
We have developed a variety of amphoteric-charged membranes with different salt permeability by changing the preparation condition. The membranes also have high monovalent ion permeabilities such as Na+, K+, Cl- and so forth. A test of piezodialysis confirmed its excellent salt permeability, assuring that it can be used as a competent membrane for piezodialysis.