Updated: July 2002

1. Outline

Excessive water consumption and contaminated wastewater seriously affects the ecosystem. The use of re-circulated water in plants is an important issue when considering the environment and lost reductions. However, water is, economically and technologically, one of the most difficult materials to recycle.
The system introduced here freezes and concentrates wastewater to produce clean ice, stores the ice in a tank, for process cooling or air conditioning. The freeze concentration method is considered to consume much energy, however, in this system, the energy required in freeze concentration and separation is reserved as ice and the latent heat is re-used is almost, therefore, the energy required for separation nears zero. Also, if the heat is stored at night when electric a low, the energy cost for air conditioning or process cooling will be lower than usual. In addition, freeze concentration results in reduced volume of water allowing in reduced treatment space.
The major function of this system is to separate wastewater into clean ice and concentrated wastewater by freeze concentration. It is an extremely multifunctional system, making effective use of cold heat, recycling of water, and effective use of concentrated wastewater. We consider that the keyword of a system capable of achieving the social targets such as harmony with the environment, zero emissions, and sustainable development is multifunctionability. Namely, the system must be environmentally friendly and economical for both production and social activities.

2. Features

Features of the freeze concentration and separation system are as follows:
* Separation of only the water from solution.
* Allows clean water to be separated.
* Allows all components (smell, suspended solids, and others) to remain in the concentrated solution.
* Causes no heat damage because separation is performed at the freezing point.
* The energy required for separation is the latent heat of fusion of water (80 kcal/kg) which is approximately 1/7 of the latent heat of vaporization (550 kcal/kg) in the evaporation method.
* Easy operation because it uses a physical wastewater processing method.
* Requires a smaller water tank because of its short hold period.
* Allows the wastewater, in which microorganisms are hard to be decomposed, to be separated and processed.
* Allows even suspended solids to be processed without any problems.

3. Performance

The performance depends upon the types and densities of the wastewater. As an example, the performance of simulated glucose waste solution of 5000 ppm is shown below.
Concentration rate = Raw water volume/Condensate volume = Approximately 5 times
Separation efficiency = (Raw water concentration - Ice concentration)/Raw water concentration×100 = 99% or more
Ice making speed = 15 mm/h

4. Scope of Application and Objects to Be Processed

For the system to be introduced, the amount of cold heat required for the plant must be examined beforehand. If the amount of latent heat of ice used effectively, the economy of the system will be impaired. On the other hand, it is important to design the amount of wastewater to be freeze-concentrated according to the amount of cooling required by the plant.
Specifically, the system can be used to reduce the volume drainage from the following.
* High water content waste fluid (cutting lubricant, oil for washing, waste solution)
* Waste acid (plating liquid, waste sulfuric acid, waste hydrochloric acid)
* Waste alkali (Waste soda fluid, metallic soap and water)
* Cleaning solvent used in semiconductor plants
* Drainage from medical laboratories
* Collection of precious metals from waste fluid

5. Others

In recent years, global warming, air and water pollution have become a social problem, and the awareness about environmental protection is increasing. Accordingly, the realization of a zero emission plan has become strongly desired.
Industrial waste is noted as a load on the environment and using the refrigerating technology, freeze-concentration this load can be reduced with less energy.
We consider that the spreading of this system can contribute to reducing a load on the global environment.