Abstract: Ship ballast water (also called ship ballast water) plays a crucial role in ensuring ship stability and navigation safety. However, the pathogens and harmful organisms contained in ships’ ballast water also transfer globally along with ballast water , polluting the oceans and endangering humans. This article focuses on the analysis of the application technology for the treatment of ship ballast water filtration - UV sterilizers from the perspective of practicality . Filtration as a first stage pretreatment removes large suspended solids and microorganisms in seawater. The ship ballast water UV sterilizer is used as a secondary treatment to treat small microorganisms and bacteria that remain in seawater. The combined treatment method has an average inactivation rate of more than 98% , and the combined equipment is simple and easy to maintain , and the investment and maintenance cost is low . The treatment cost is about one- fifth of the traditional method . After analysis, the ship ballast water filtration - UV sterilizer is analyzed . The application technology is efficient and feasible.
Key words: ship ballast water, ship ballast water , filtration , UV , ship ballast water UV sterilizer, microorganism
Overview
Today, more than 90% of international cargo is delivered through ships. Ballast water plays an important role in maintaining the balance and stability of ships and the safe and effective operation of ships . Ship ballasting is a necessary condition for safe navigation of ships. Depending on the size and use of the ship, each ship ballast water can not carry the same, a few hundred kilograms less large and more than 100,000 tons. An estimated 10 billion tons of ballast water is transferred globally each year . The IMO Working Group on Ballast Water found that at least 7,000 organisms, etc., sailed with their ship's ballast water every day . Species invade each other and exacerbate the degradation of the marine ecological chain and environment. However, in many ballast water treatment methods, we cannot use a single method to treat ballast water so that it meets the requirements of the International Maritime Organization. Based on the effectiveness of filtration and UV technology for ballast water treatment, we analyzed the application of filtration - UV sterilizers in conjunction with ballast water applications.
2. Filtration - Research Status of Ultraviolet Radiation Treatment of Ship Ballast Water
In the study of the use of ultraviolet light on the ballast water treatment process found that : the turbidity of seawater will affect the penetration of ultraviolet light , which will reduce the effect of ultraviolet rays to kill bacteria and microorganisms. University of Maryland at the United States studied ballast water treatment technology combined with filtration and ultraviolet radiation. The results showed that solid suspended solids with a particle size of 50 μm or more can be filtered out in 5 experiments. The average inactivation rate of microorganisms above 50 μm is The average inactivation rate of microorganisms below 80% and below 50um is 95% . According to the IMO processing requirements, the filter filtration accuracy is designed to be 50um . Particles smaller than this precision are handled by the UV device.
3. Filtration - Advantages of treatment methods of ship's ballast water UV sterilizer
(1) Compact structure and small size;
(2) Light weight, easy to design and install;
(3) fewer system components, easy maintenance, adjustment and control;
(4) Filter - UV treatment is a mechanical and physical methods combined, without adding any chemical process, not cause secondary pollution.
In addition, the use of ship ballast water UV sterilizer to treat ballast water also has the following obvious advantages:
(1) High efficiency: the data indicate, at a flow 200Lh, 400Lh, when 800Lh, ultraviolet disinfection rates were 83% to 100%, from 84% to 100%, between 98% and 100% for some microorganisms and viruses , total inactivation rate above 99%, and almost instantaneous kill time, saving a lot of time.
(2) Broad spectrum: Ultraviolet light can kill almost all kinds of bacteria, viruses and algae.
(3) biologically immunity: UV treatment only changes the structure of DNA biological ballast water, while the conventional method, over a period of time can be effective, but a long time will have biological immunity handled effectively.
4. Filtration - Ultraviolet Technology Process Ballast Water Principle
Filtration can remove suspended solids and microorganisms in water without doubt. However, the smallest diameter of microorganisms in seawater is a few microns. If the filtering accuracy of the filter is designed to be high, although the filtering effect is good, the pressure needed is too large, and the backwashing is quickly required, otherwise the process will be difficult to proceed. Therefore, a proper filtration accuracy ( 50 μm ) is designed so that the microscopic microorganisms remaining in the ballast water will be subjected to UV treatment.
Ultraviolet (UV) is an electromagnetic wave having a wavelength between visible light (400 nm) and X -ray (100 nm) , and ultraviolet light can be divided into three wavelength bands: UV-A (long wave band 320-400 nm ); UV-B (medium wave band 280) - 320nm ); UV-C (short-range 100 - 280nm ), strong bactericidal action is provided by UV light with a wavelength of 253.7nm in the short-wavelength UV-C . Since UV - C has a high photon energy, when it irradiates microorganisms, it can penetrate the cell membrane and nucleus of microorganisms, destroy the molecular bonds of DNA , make them lose their ability to replicate or lose their activity, and soon they will die. We deal with the purpose of ballast water.
5. Filtration - ship ballast water UV sterilizer treatment device
5.1 filter processing device
Choose 50x250 mesh (50um) wire mesh as the filter material. Considering that low-carbon steel is not resistant to corrosion and rusting, the stainless steel filter is used for both marine filters and perforated screen filters. The stainless steel screen filter has good corrosion resistance, good seismic performance, and low cost. High efficiency is an ideal filter material. Based on the above considerations, the use of stainless steel fibers as a filter is more appropriate.
5.2 Ship Ballast Water UV Sterilizer Device
Ultraviolet sterilizers are divided into open canal UV sterilizers or closed UV sterilizers by design. The open canal type UV sterilizer is a device in which a UV sterilizing lamp covered and protected by a quartz tube is placed in a groove to allow the effluent to flow out; a closed UV sterilizer is a tube that covers the quartz tube and is protected by ultraviolet ray disinfection. The lamp is loaded into a cylindrically sealed reactor, the reactor is connected to the sewer, and the UV lamp is enclosed in a quartz tube, parallel or perpendicular to the flow of water. In contrast, the closed type is not as easy to monitor and maintain as the open channel type. However, the enclosed type has a larger amount of water than the open Channel type. For the characteristics that require a large amount of ballast water, we use a closed-type ultraviolet treatment device.
In order to be able to resist the effects of seawater erosion and UV radiation aging , the barrel can be made of non-toxic polyvinyl chloride impregnated with titanium , which is lighter, more durable and less costly than equipment made of stainless steel; the UV lamp should be The use of low-pressure mercury lamps; Quartz tube using high-strength quartz gas tube , requiring a transparency rate of not less than 80%, working pressure 0.45Mpa . Quartz tube can be isolated from the water in contact with the UV light, the lamp can be maintained at a working temperature of 40C jia most, because the UV lamp output and the surface temperature, when the temperature is 40C, the maximum ultraviolet output, available impregnated sleeve alcohol The gauze is cleaned once in half a year , and it can also be scrubbed with a grinding powder. Diffuser plate means, a gentle flow of water can be avoided to ensure that marine bacteria, microbes maximize contact with ultraviolet irradiation. The entire treatment unit is equipped with UV intensity monitoring and connected with an audible or visual alarm and an automatic shut-off device [7] .
5.3 Filtration - Flow chart of ship's ballast water UV sterilizer
6. Filtration - Feasibility analysis of ship ballast water UV sterilizer for ballast water treatment
6.1 Time Feasibility Analysis
Assume that the ship's weight is 50,000 tons, the maximum water capacity of the ship is 13,000 tons, and the rated flow of the ship's ballast water pump is 200 tons / hour.
From the above hypothetical data, the average treatment time of the ship for ballast water can be obtained.
T=13000/200/24=2.7d
This is calculated in accordance with the maximum amount and is actually related to the ship’s deadweight . The ballast water transfer must be less than the maximum ballast load . Therefore , this method can be reasonably used according to the time of port stop, the length of the route, and loading and unloading conditions . .
6.2 Filtration - Economic Feasibility Analysis of Ship Ballast Water UV Sterilizer Treatment
The operating cost of the ultraviolet treatment device itself is very low , only 0.005 to 0.01 yuan per ton of seawater is treated , and the effective use time of foreign UV lamps is above 12,000 hours , which can reach more than 200t/h .
Research shows that UV is highly effective in killing marine bacteria and microorganisms , but a few microorganisms are found to have strong resistance to UV rays during application. How to kill these microorganisms must be solved when the system is designed. For energy-saving considerations, marine diesel engine can be used to heat the ballast water was heated to about 35 ℃ ~ 45 ℃, and a period of time, so that can more effectively kill microorganisms and bacteria, domestic and related studies have begun.
7. Conclusion
In summary, the following conclusions can be drawn:
(1) filtration - UV ballast water disinfection treatment of ships' ballast water, which can effectively kill bacteria in the ballast water, microorganisms, this is feasible;
(2) How to improve filtration - The effectiveness, economy, system optimization, etc. of ship ballast water UV sterilizers need to be further studied and practiced.
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