Updated: July 2002

1. Outline of system

Sewage which is subjected to secondary treatment and is then treated in this system can be turned into high-quality recycled water which is close to the tap water standard. This treated water provides better removal of salts (including nutrient salts) and bacteria-removing effect based on the membrane compared with the conventional sand filtration + activated carbon adsorption method.
Therefore, it can be used as water suitable for sanitary applications also, such as fountain water, disaster prevention water, industrial water, and water for miscellaneous use at facilities (cooling water).
1-1 Outline of system

(1) Micro Filtration (MF) membrane
Suspended solids and bacteria are completely removed.
This system adopts the MF membrane for treatment prior to the RO membrane.
In the MF membrane, SS and bacteria which cannot be removed easily in the sand filtration method are removed completely. In addition, this system adopts the gas back wash automatic back-washing system. Due to this system, substances which cause membrane clogging are discharged easily from the system. Therefore, high filtration performance is maintained and large quantities can be treated in the compact equipment.
(2) Reverse Osmosis (RO) membrane
Colors, salts, and organic substances are separated.
The RO membrane is the equipment which separates forced-fed MF treated water into permeated water in which colors, salts, and organic substances are removed and concentrated water in which they are concentrated. Because it is possible to vertically configure modules which are excellent in the volumetric efficiency, the equipment installation area can be reduced.

Fig.1 Structural diagram of MF membrane module

Fig.2 Image diagram

Fig.3 Conceptual diagram of RO membrane

1-2 System flow

System flow with a water production capacity of 100 m³/day (one line for normal service + one line as standby)

Fig.4 Membrane separation equipment system flow

2. Characteristics

(1) Treated wastewater can be reproduced and reused.
Because the quality of water subjected to advanced treatment is close to that of tap water, it can be used as fountain water, disaster prevention water, industrial water, water for miscellaneous use at facilities, etc.
(2) Stable treated water quality and high purification efficiency
Compared with sand-filtrated water, good quality treated water can be obtained because not only suspended solids and colloidal matter, but also algae, bacteria, etc. in water can be removed.
(3) The system is compact.
Compared with the sand filtration + activated carbon method, the equipment space can be greatly reduced.
(4) Completely automatic and unattended operation can be performed.
Due to the integration of the automatic back-washing device, completely automatic operation can be performed.
(5 )Reductions in the site work cost and work period
It is possible to reduce the site work cost and greatly shorten the work period because the membrane modules have skids.

3. Performance

This system has obtained the following performance based on the validation test carried out in the treatment plant K.

Table I Water quality data (Unit mg/l)

4. Applicability and objectives

(1) Advanced wastewater reuse plant
(2) Treatment plant which the salinity and hardness components are high. (for example : treatment plant located near the seashore)
(3) Treatment plants located in areas where the water rates are high.
*Details of the adoption of the membrane separation equipment for the sewage treatment plant in the City A
In the case of the sewage treatment plant in the City A, a large amount of hot spring waste water flows in, and thus, the hardness components and chlorine ion concentration are high. Therefore, in a case where sand-filtered water is reused as water for miscellaneous use with no modification, problems, such as pipe clogging and corrosion, were feared. Also, in the utilization of tap water, restrictions on water supply are possible due to such circumstances as a suspension of water supply and drought. These reasons and the consideration of stable securing of water and recycling of water have led to the adoption of the membrane separation equipment.

Fig.5 Membrane separation equipment