Dosing and disinfection

What are chemical products dosing pumps for water treatment?

A dosing pump is a small, positive displacement pump. It is designed to pump a very precise amount of a chemical components or other substances into a water flow.

Dosing pumps are usually quite small and they are powered by either a small electric motor or an air actuator. They are controlled either by an external control system or more commonly by an internal pump controller that can alter the flow rate, the on/off function and also alarms and warnings for run dry, degassing and low product levels.

The delivering in the flow of a substance can be done with different methods, but it generally involves drawing a measured amount into a chamber and then injecting this volume into the pipe or tank being dosed.

Dosing pumps' structure

The pumps' structure changes based on the producer and the application, but the main components are:

  • the chemical tank or container of the product that is being dosed;
  • the foot valve, that is a one way valve that is attached to a suction line. It is placed into the drum of product and allows the pump to remain primed. It should have a weight on it so it remains in the bottom of the drum of product and sometimes it has a float switch attached to it so the pumps have an alarm activate if the product runs out;
  • the pump itself, it can vary in size and materials but it is generally made of chemical resistant plastic materials (PVC, PE or similar), rubbers or stainless steel. It has a suction line attached to the inlet and the dosing line is attached to the suction;
  • the dosing line is generally a fairly rigid PVC or PE tube or a reinforced hose. The line can have a variety of bleed, pressure relief, air release valves included into it but generally it is just a line;
  • the injector, that is at the point where the product is injected and it's a one way valve so that when the dosing pump pushes an amount of product into the line it can overcome the pressure in the delivery pipe and allows the product out into the flow. In the case the pump stops, the one way valve stops the liquid in the delivery line from going up the dosing line and damaging the pump. The injector has also a spout so that the product is delivered into the middle of the flow rather than towards the side wall. Over time certain products especially acids and oxidisers like chlorine or peroxide can corrode the walls of a pipe if released right at the edge of the stream. Releasing the product into the middle of the stream also allows the product to mix properly because of the turbulence;
  • the control system is installed when it's necessary to ensure that the dosing pump is accurate and that it turns on and off at particular time intervals. The control system can be as simple as a timer or a flow switch connected to a full SCADA or a similar central control system with sensors for pH, chlorine and others and variable rate control to raise and lower the level being dosed. It may also be integrated into a more complex operations system.

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:

  1. 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;
  2. 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;
  3. 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;
  4. 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:

  • virus;
  • bacteria;
  • 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.

Our plant

Installation place: military zone
Plant flow rate: 70 mc/day
Problem to solve: the necessity to have potabilization systems and waste waters disposal systems in a military camp. The plants must be able to be carried where there are the necessity.

Kind of plant: Design and supply of n. 2 potabilization and waste waters disposal systems. Every system is composed by the following sub - systems: n.1 reverse osmosis potabilitazion plant for fresh, salt or brackish waters; n.1 reverse osmosis desalination plant for sea waters, n.1 BC module for the treatment of water contaminated with war biological and chemical agents, composed by pre – filtration, ultrafiltration and reverse osmosis plants; n.1 wastewater disposal plant with activated sludge bioreaction process and ultrafiltration membranes. Depending on the necessities and on the working conditions, every module can be employed separately. The two potabilization systems are collocated in ISO standard containers, in order to move them easly. Every systems is equipped with all the hydraulic and electric components and with a PLC programmed by the PPM expert staff, that guarantees its correct functioning. The potabilization plants are equipped with two UV rays disinfection systems model SH-5000. Those devices are composed by two vertically arranged debacterization rooms, the parts in contact with water are made in inoxidizable steel or in ultrapure quartz glass. The lamp's efficiency can be monitored by a digital display. The maximum working temperature is 35°C and the instantaneous flow rate is 5000lt/hr. The lamps' medium life time is 9000 hours and the irradiation is 30000 micwS/cmq.

Our customers

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;
  • Autolavaggi;
  • Petrol stations;
  • Urban waste water treatment for integrated water services, public authorities and large or tourist establishment.

How do we work

The first phase of the realization of a water treatment plant is the data collection, that it's necessary for the planning: inlet water's characteristics, costumer's requirements, final water's characteristics. The chemical and physical analysis of the inlet water and visits are done during this phase.
The second phase is the designing, where the preparatory data are investigated and the most suitable solution for the problem is determined. Dosing pumps are used to inject in the plants defined amounts of products with different purposes: to maintain an appropriate pH range, to prevent compounds precipitation, disinfection, etc... Dosing pumps' planning is performed on the basis of the conditions which must be maintained in the plant, the control systems which manage the pumps must be carefully evaluated. If during the planning the integration of UV disinfection system is decided, in this phase its insertion point and the control system for the proper functioning are defined. The following phase is the plant implementation, assembling the structure and the different components, both hydraulic and electronic, with the best materials available on the market.The plant is installed and tested at its final position.

PPM remains available to its customers offering maintenance and assistance services for the plant during all its life stages.