The continued growth in the market for mineral waters, bottled waters and flavoured waters is good news for the food and beverage sector. To ensure that products have a long shelf life, disinfection of both water and flavour concentrates is critical, and traditional water disinfection processes have used oxidising biocides like sodium hypochlorite, chlorine dioxide or ozone. Chlorine based chemicals can produce a range of potentially carcinogenic by-products including trihalomethanes (THMs), haloacetic acids (HAAs) and nitrosodimethylamine (NDMA). All of these by-products will pass through reverse osmosis membranes into the product water. With consumers becoming more discerning, and wanting the products they buy to be free from chemicals and as natural as possible, ultraviolet (UV) irradiation has become the technology of choice for liquid disinfection in the food and beverage sector.
UV disinfection uses electromagnetic waves in the UV-C band – a natural component of sunlight – to inactivate bacteria and a variety of other microbes. It is a broad-spectrum technique that inactivates a wide range of micro-organisms and is entirely chemical-free with no health and safety or environmental issues. All it needs is an electricity supply. However, in order to get the best out your UV system, it has to be properly designed and that means providing the UV supplier with 5 key items of information to be able not only to select the right size of reactor but also to consider what other features will need to be included.
We strongly believe in providing flexible, tailored UV disinfection systems, and understand that there are a vast variety of needs depending on your industry type and a wide range of other factors. Here are 5 of the most important pieces of information you should provide to your UV supplier to make sure you will have the right system to meet your business needs.
1. DEFINING THE FLOW RATE
The first thing to define is the flow rate of the liquid you want to treat. That sounds easy enough but they will want not only the maximum, average and minimum flows but also the pattern of use.
For example, if the normal average flow is 5m3/h for 6 hours per shift but the maximum is 10m3/h for 2 hours it may be better to use two 5m3/h units with one normally off-line and just brought into service for the maximum flow.
2. DEFINING WHETHER THE FLOW IS CONTINUOUS OR INTERMITTENT
Then is the flow continuous, and do you need a standby stream to cover for maintenance or breakdown? The minimum flow is important because some large UV reactors need a minimum flow to keep them cool.
Equally important is whether the flow is intermittent. If the flow stops it may be necessary to switch the reactor off, but then, when it restarts it will need a warm-up time before it can guarantee to deliver the full germicidal dose and this may necessitate a run to waste or a recycle line.
3. DEFINING THE LIQUID CHARACTERISTICS FOR UV DISINFECTION
Next is the liquid characteristics – most UV systems treat water but UV is also used to treat sugar syrup. Your supplier will need to know the density, viscosity and temperature of the liquid including any maximum and minimum variations. For UV disinfection to occur, the radiation has to pass through the liquid and the critical parameter here is the UV transmittance (UVT). This measures how much of the radiation power is lost by absorption or scattering of the rays in a 1cm path length through the liquid. It is usually measured in percentage so a liquid with UVT of 80% means that 20% of the UV lamp intensity will be lost in a 1cm path.
Knowing this allows the supplier to rate the reactor to compensate for this loss. Other useful characteristics are turbidity (a measure of colloidal particles that scatter light), colour and UV254 absorbance both of which indicate how much light is absorbed by the liquid. There are quite a few different units used for these measurements so make sure that you tell the supplier what they are.
4. ESTABLISHING THE CORRECT UV DOSE
Finally the UV dose (or fluence). A single pass through a standard UV system delivering a UV dose of 40 mJ/cm2 will typically achieve better than a 4 Log reduction (99.99%) of most bacteria and protozoans like Cryptosporidium. However some yeasts and moulds require much higher doses so, if possible, let your supplier know what species are (or could be) present. Evoqua has a range of UV products to fit your specific needs.
For UV to be effective it has to be delivered uniformly to all parts of the reactor so make sure that there is a UV monitor built into the reactor to check that the required dose is being received. But that’s only part of the story.
A single monitor can only check a single point in the reactor. Being certain that the applied dose is reaching all areas of the reactor depends on the reactor design.
Reactor performance can be validated by type testing using independent third party bioassay with live, surrogate microorganisms (typically bacteriophage T1 and MS2) against standardised test methods – the internationally accepted protocol is that of the US EPA so ask for a validation certificate to this effect.
5. LASTLY, PREPARATION IS KEY…
Collating all this information before talking to your UV supplier will pay dividends in ensuring that your system meets all your requirements and provides you with years of trouble-free operation.