Applications and kinds of dosing pumps
Dosing pumps have a lot of applications, including in addition to water treatment, industry, medicine and agriculture.
In water treatments' framework dosing pumps are used for the injection of products, as:
- chlorine or other products to cause a chemical reaction to inactivate pathogens;
- chemical products to maintain pH to a desired range or to avoid components to precipitate;
- flocculants products.
There are four main kinds of dosing pumps, which differ in their working and pumping mechanism and which are suitable for different chemical products, pressures and applications:
- diaphragm-type constant injection pump, in which there is a pump chamber filled and emptied by a piston, it has a diaphragm and inlet and outlet valves. When the chamber is full, the dosed volume is injected out at a constant flow rate, generally in the range of 6 – 250 l/hr. With an adequate control this pump kind can have a time-varying rate;
- diaphragm-type pulse injection pump, also this method employs a diaphragm mechanism, but this pump is controlled by a solenoid coil. The solenoid coil sucks in and injects the chemical product in pulses. The time-gap between the pulses provides the control of flow rate. This pump is generally less accurate than other types. However, it's very simple from both the mechanic and electric point of view and it's relatively inexpensive;
- lobe-type pump, this design allows the flux to pass through a set of meshing-gear-type impellers. The volume rate passing between these impellers can't be as accurate as in diaphragm pumps. The impellers have a surface quite susceptible to wearing, so this kind is suitable for very viscous and self – lubricating products. It's difficult to use this pump with small fluxes;
- peristaltic pumps, it consists of a flexible tube to carry the product. This tube has a semi-circular cross section. These pumps are used widely in the medical industry as they can be easily sterilized, and the pump mechanism can be quickly replaced if it is contaminated or damaged. Peristaltic pumps are highly accurate. However, they wear out quickly and they can’t handle pumping into a high pressure stream as they can only handle up to the burst pressure of their flexible tube.
What are ultraviolet devices?
The UV disinfection is a physical process that instantly neutralises microorganisms by ultraviolet rays radiated by a lamp immersed in the water. Ultraviolet (UV) rays are part of the light that is radiated from the sun to the Earth. The UV spectrum is higher in frequency ( and consequently in energy) than visible light and lower in frequency compared to x-rays.
UV radiation has three wavelength zones: UV-A, UV-B, and UV-C, this last region has germicidal properties for disinfection, in particular the wavelength between 240 e 280 nm. A low-pressure mercury arc lamp produces the UV light, almost monocromatic, in the range of 254 nm. The water flows as a thin film over the lamp. The typical UV treatment device consists of a cylindrical chamber housing the UV bulb along its central axis in a glass sleeve. Water flux is parallel to the bulb. There is a flow control device that prevents the water from passing too quickly over the bulb, assuring an appropriate exposition time. UV radiation affects microorganisms by altering their DNA in the cells and impeding reproduction. UV treatment does not remove organisms from the water, but it inactivates them and they become incapable to cause infection to human beings or to damage equipments and machines (for example biofilm). The process adds nothing to the water but UV light, and therefore, has no impact on the chemical composition or the dissolved oxygen concentration of the water.
UV devices' applications
UV devices are suitable in all the cases in which it's necessary a strong germicidal action and they are capable to disinfect water from:
- protozoa, included Giardia lamblia cysts or the Cryptosporidium oocysts (chlorine resistant).
UV devices' limitations and advantages
The UV device disinfection has some limitations: when it's used alone it doesn't improve the smell, the taste or the clarity of the water. Its disinfection can only occur inside the unit, there is no residual disinfection to inactivate bacteria that may survive or may be introduced after the water passes over the light source.
The effectiveness of the process depends on the contact time, the intensity of the UV light and inlet water quality.
In order to ensure that the system is always efficient it's necessary to replace the lamp in time, not having drops in its intensity. For this purpose in the system there is a warning device to alert the owner when lamp intensity falls below the germicidal range and it must be cleaned or replaced. It's very important to maintain the intensity in this range because if microorganisms don't sufficiently suffer a remarkable damage to their DNA, they are capable to reactivate thanks to the action of their enzymes, repairing their genetic material. The inlet water must be free, or with a very small concentration, of dissolved organic matter and suspended matter. Those components absorb UV radiation and shield microorganisms, resulting in a lower germicidal capability. The concentrations of iron and manganese must be very low, because they can affect the clarity of the glass hose, decreasing UV ray effectiveness. Lastly inlet water must not be hard, to prevent build-up of minerals on the lamp. For these reasons UV ray devices are often installed as final phases. They must be placed as near as possible to the point of use, also because the water could be contaminated in the intermediary passages. If the UV device is installed stand alone a chemical analysis of the inlet water must be done and it's necessary to establish a pretreatment system to remove the components which decrease system's effectiveness. UV devices are planned for a continuous work and they must be turn off only if the treatment must be not have effected for several days. A few minutes for lamp warm-up is needed before the system is used again following shut-down. In addition, the plumbing system should be flushed following a period of no use. Whenever the system is serviced, the entire plumbing system should be disinfected with a chemical such as chlorine. Keeping the mentioned limitations, compared with other disinfection methods, the UV disinfection has undoubted benefits, as:
- effectiveness and reliability, as in normal conditions up to 99,99% of the microorganisms are destroyed, more than with chlorine and chloroamines;
- chemical components free, so it's excellent from a safety point of view;
- environmental friendly, it has not by-products and it has low electrical needs;
- low maintenance it must be done every year and it has low cost, that includes the replacement of lamp and the flush of the plumbing system;
- quick process, the water flows through the system without holding tank or reaction times;
- water's taste and smell don't change, unlike chlorine.
PPM offers its services to:
- mechanic industry;
- chemical industry;
- paper industry;
- ceramic industry;
- pharmaceutical and cosmetic industry;
- galvanic industry;
- wood industry;
- leather and textile industry;
- petrochemical industry;
- plastic industry;
- agro – food industry;
- painting and graphic industry;
- car wash;
- Petrol stations;
- Urban waste water treatment for integrated water services, public authorities and large or tourist establishment.