Lifespan of Medical Ultrapure Water Equipment

Figure 1 Lifespan of Medical Ultrapure Water Equipment

The medical ultrapure water machine system is a multifunctional fully automatic device composed of a pre-treatment, reverse osmosis (RO) system, and electro-deionization (EDI) system. It is a fully automatic complete set of equipment with safe and convenient use, low operating costs, and stable water quality. The equipment is mainly used for centralized water supply in hemodialysis rooms, biochemistry rooms, dental clinics, central laboratories of supply rooms, preparation rooms, operating rooms, etc.

I. Technical Requirements and Process Flow

The medical ultrapure water machine adopts automatic control (manual control can also be used at the same time), and the automatic backwash and regeneration programs can be set during system operation. The first-stage and second-stage reverse osmosis have reflux pipelines, and the reverse osmosis equipment is equipped with chemical cleaning and disinfection devices. The reverse osmosis membrane uses DuPont membrane imported from the United States to ensure the long-term stable operation of the reverse osmosis equipment.

The reverse osmosis pipeline adopts stainless steel and UPVC materials. Online conductivity meters are installed in the first-stage and second-stage reverse osmosis equipment, and the reverse osmosis system is equipped with low-pressure and high-pressure protection switches. The reverse osmosis water recovery rate is adjustable, with a recovery rate of 50-75% for first-stage reverse osmosis and 80-90% for second-stage reverse osmosis. The circulating transportation pipeline is equipped with ultraviolet sterilizers and microporous filters to ensure that the pure water meets hygiene requirements.

Figure 3 The process of using high-efficiency reverse osmosis with EDI

II. Equipment and Consumables Technology

The pure water machine equipment uses reverse osmosis technology for water treatment. In addition to using materials such as stainless steel and UPVC for the equipment and pipes used in reverse osmosis equipment to improve the basic material guarantee, we can also perform initial purification of tap water before the reverse osmosis pure water machine to achieve the RO water quality requirements, protect the reverse osmosis RO membrane, and enable the normal operation and prolong its lifespan. Improvements in pure water machine processing can be made through the following components.

Figure 3 Pure water equipment

1. Selection of Melt-Blown Filter Elements

Melt-blown filter elements can filter out suspended particles in water larger than 5-10μm. The aperture size is non-uniform, and the number of apertures of different sizes follows a normal distribution, with a large value (peak) occurring at 5-10μm. The diameter of the fiber and pore size of the PP fibers are related to factors such as the melt temperature, indoor air temperature and humidity, airflow size and speed, and receiving distance. 

High-quality melt-blown filter elements have progressively denser pore sizes from the outside to the inside of the PP fiber, with a large number of impurities filtered out on the surface and inside of the filter element, and have a high pollution absorption capacity and long service life. However, the manufacturing equipment is complex and expensive, and the price of filter elements is high.

2. Use of Ceramic Filter Elements

Although melt-blown filter elements are inexpensive, they are disposable. Ceramic filter elements can be used instead of melt-blown filter elements. Although ceramic filter elements are more expensive and require a larger initial investment, they can be repeatedly cleaned and have a much longer service life. As long as the design of the entire machine considers easy filter element installation and removal, using ceramic filter elements instead of melt-blown filter elements is a good choice. 

The raw material used for ceramic filter elements should be diatomaceous earth, which is fired in a tunnel kiln. The ceramic filter element should be light in weight, have good water absorption, and have high porosity. Poor-quality ceramic filter elements have a relatively rough and uneven surface and are heavier due to impurities. Another simple method is to drip water on the surface of the ceramic filter element. If the water is quickly absorbed and no droplets remain on the surface, it indicates good hydrophilicity and high porosity.

3. Microfiltration-Ultrafiltration Dual Membrane Method

Some water purifier manufacturers use a combination of hollow fiber microfiltration – granular activated carbon – hollow fiber ultrafiltration for the pre-treatment stage, which is a good combination. 

The first stage uses a PVDF hollow microfiltration membrane with enhanced support to remove suspended solids and bacteria. The membrane can be removed and rinsed if it becomes dirty, and will not break. The second stage uses activated carbon to remove residual chlorine, organic matter, colloids, odors, and more. The third stage uses a PS hollow ultrafiltration membrane to further remove suspended solids, microorganisms, and colloids. This thorough pre-treatment not only extends the service life of the RO membrane but also increases the recovery rate of pure water. 

4. Activated Carbon Fiber Filter Element

Activated carbon fiber (ACF) is made from viscous fiber or polyacrylonitrile-based fiber with a fiber diameter of about 10-20μm. The average pore size of the micropores is 17-26A for the former and 10-20A for the latter. Activated carbon fiber is often made into a felt that is 1-5mm thick. It has more micropores than granular activated carbon and is larger.

5. Granular Activated Carbon Filter

Activated carbon has a significant role in removing residual chlorine, adsorbing colloids and organic matter, removing odors, and protecting reverse osmosis membranes. Its performance is mainly reflected in its ability to remove COD. The ability to remove COD is related to the flow rate and contact time design of the water purifier. According to the JB/T2932 “Technical Conditions for Water Treatment Equipment” standard, the filter can remove the residual chlorine in water (the effluent residual chlorine Ag2+ > Ag+, inhibiting bacterial growth and ensuring that the silver ion content in water does not exceed the standard).

6. Purification Column

A purification column sometimes called an ultra-purification column, is designed to deeply desalinate reverse osmosis purified water to achieve primary or ultra-pure water levels based on the customer’s water quality needs. The principle behind it is ion exchange. The lifespan of the purification column is indicated by the online resistivity. If the resistivity is below a certain specific level, it means that the purification column has expired, which is a straightforward indication. In addition to the amount of water used, the filling amount of the ion exchange resin and the quality of the resin itself during production and design by each manufacturer are especially important factors in the lifespan of the purification column. 

7. Installation of Pressure Relief Pump

When the water pressure is too high, a pressure relief pump must be installed. If the incoming water pressure is consistently higher than 0.3 MPa or the pressure fluctuates greatly, it may cause damage to the ultrafiltration membrane. Therefore, a pressure relief pump should be installed when necessary to ensure that the water pressure reaches the normal working standards of the water purifier.

III. Equipment Operation, Maintenance, and Use

Figure 4 Maintenance of ultra pure water equipment

Firstly, the machine must be operated correctly according to the correct procedure, and secondly, its maintenance and upkeep must be done to make its performance more stable. The filter cartridges used to filter the water quality in the ultra-pure water machine are consumables and have a certain service life. If consumables are not replaced in a timely manner, the entire system’s operating status will be poor, resulting in a gradual decline in performance.

Therefore, during the daily use of the system, it is necessary to strengthen the supervision of the machine’s performance indicators and identify problems in a timely manner to resolve them. For example, regularly cleaning the reverse osmosis equipment can remove residual pollutants from the equipment and extend the life of the pure water machine.

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