In this article the industrial wastewater specialists at WTS review the options for the in-field testing of wastewater quality available to business owners and plant operators.
The article highlights the important factors to consider when establishing a testing programme, and then goes on to consider a number of the most popular test methods, how they work and their advantages and disadvantages. It concludes with a brief look at considerations for water sampling, safety and environmental precautions.
Selecting the best in-field wastewater testing options
Companies and plant operators have a range of options and testing possibilities for monitoring the wastewater which their operation produces. The range of options is varied and might include titrimetric testing, colorimetric, electrometric, turbidity and other analysis methods. In most situations, more than one of these methods will be used to measure wastewater quality in-field. Chlorine levels, for example, can be measured using colorimetric, titrimetric or electrometric methods.
The key to successful on-site wastewater monitoring is establishing which of the methods – or which combination of test methods – is most appropriate for your situation. In order to do this, you should first understand what each method involves, and its limitations and advantages. This should help you narrow your decision.
What factors are important when monitoring wastewater quality?
Accuracy is just one of a whole host of factors which plant operators consider when deciding what wastewater testing methods to use. Costs for both the initial set-up and the ongoing cost per test should also be taken into account, along with the competence levels needed to perform the test, and how easily it can be repeated. Other factors might include portability; what sort of information you will get from the test or how easily the test materials can be disposed of after use.
There are several different in-field test methods suitable for monitoring wastewater quality, and here we’ll consider some of the most common.
Whichever method you use for testing your wastewater, taking an accurate sample is the key to success…
What is colorimetric testing?
In basic terms, a colorimetric test is based on a colour change in a solution, and will depend on the concentration of the “target” chemicals present in the sample.
Generally, the stronger the colour change, the greater the level of chemical detected. Sometimes, such as with the test for chlorine, the reaction causes an almost instant colour change. In other situations, such as when testing for phosphates or nitrates, you may have to wait up to 10 minutes for the colour change to take effect.
Occasionally, colorimetric tests work in the opposite way, so the greater the colour change, the less of the chemical detected. One of the most common examples of this is when testing for the presence of fluoride.
However, once the test has worked, the result is read by either comparing the colour in the solution against a chart supplied by the test manufacturer, or by using laboratory equipment to analyse the sample which will give the results digitally, usually in parts per million (ppm) or milligrams per litre (mg/L).
Limitations and benefits of colorimetric testing
Looking at differences in intensity of colour change can be affected by a range of factors, such as the level of lighting in a room, especially in areas lit by fluorescent lighting or strong sunlight. Different shades of blue or yellow can also be tricky to detect.
However, despite these drawbacks, this testing method is generally one of the least expensive, and is very easy to use. If you choose to use one of the systems which involves a photometer or other device to detect the colour change, then these are even easier to use. Most meters are designed to be fully portable. They work by passing a beam of light through the sample to measure the concentration of colour present, before displaying the result on screen. This cuts out the need to interpret the results and the result will not vary depending on background light. Meters that read colour tend to be more expensive than the manual methods, at least initially.
The other main benefit of colorimetric testing is that you get instant results when testing for some of the most commonly found wastewater contaminants such as iron, chlorine, copper, zinc, aluminium or sulphides.
Titrimetric testing of wastewater samples
In titration tests, a reagent chemical is added to the wastewater sample to produce a change in colour, drop by drop until the colour changes. The stage at which the colour changes is known as the “end-point”. There is a range of methods which can be used to drop the reagent chemical into your sample.
These wastewater test methods are generally fairly cost-effective and often the first choice in many situations. This is the method most commonly used for detecting acidity, alkalinity, dissolved oxygen or chlorine. Titration is the most commonly used method when monitoring corrosion in water supplies and helps water companies ensure that they are meeting the guidelines set for lead or copper corrosion.
What is turbidity testing?
Turbidity testing is one of the analysis methods which does not depend on a colour change to deliver results. After the wastewater sample has been taken, a reagent is added which produces cloudiness, or turbidity in the sample. The greater the level of cloudiness, the higher the concentration. Again, the results can be read from a chart supplied by the manufacturer, or inserted into a colorimeter for a digital result. This is a common method for testing wastewaters for the presence of sulphates or potassium. Turbidity testing kits are usually simple to use and completely portable.
Electrometric testing of wastewater
Another method of testing, electrometric testing involves putting a small electrode into the water sample. A small electrical current is then passed through the sample and the result is read off using a meter. This is the sort of test which is most often used for identifying conductivity and pH levels, but the technique can also be used to test wastewater samples for chlorine, nitrates or calcium.
Some level of skill is required to perform these tests as the water sample will require to be pre-treated, or the test meter will need to be calibrated before testing. The equipment also needs a higher level of maintenance than other types of testing. There are cost-effective pH and conductivity meters on the market, which many companies find ideal for running quick system checks on their wastewater.
Gravimetric testing is based on gravity, and in simple terms it looks at how many solids settle at the bottom of a wastewater sample. The testing technique starts by taking a known volume of water, mixing it in a settlometer or Imhoff settling cone, and then allowing the solids to settle at the bottom. Measurements of settled solids are then taken at specific time intervals. These tests can help wastewater operators manage sludge volumes, and determine which treatment chemicals should be added into the waste. It’s a relatively simple testing method which doesn’t require the addition of any extra chemicals or reagents, and can often provide quick and valuable data to operators of the treatment plant.
Nephelometric turbidity analysis
Nephelometric analysis is used to measure turbidity. Using a special piece of equipment which sends a beam of light into the wastewater sample, where the light is scattered by any suspended particles of silt, dirt or other solids. This scattering of the light beam is measured by a photodiode, the results are interpreted and displayed on the meter.
Wastewater treatment systems, whether public or private, use this method for monitoring settlement tanks or how effectively the wastewater filtration system is performing. In this sort of plant, a continuous monitoring system is the norm, and there are also some portable monitors for use in remote locations.
Considerations for taking wastewater samples
Whichever method or methods you decide to use for testing your wastewater, taking an accurate sample is the key to success. It is important that you always choose the correct point in your wastewater treatment system to take the sample from, and if using a tap, allow it to run for a short period before sampling to ensure the sample is truly representative. Take care to measure the volume of the sample correctly as many test results will only be accurate with the correct volume of wastewater.
After testing is completed, dispose of the sample and any waste chemicals safely and correctly, and clean out the testing equipment following the manufacturer’s instructions. Deviating from their recommendations risks skewing any future testing results. Never mix test reagents made by different companies, especially when using colour-based testing, unless you are sure they are exactly the same concentration.
Important safety and environmental considerations
Many of the chemicals and reagents used in water and wastewater testing kits can be dangerous. You should always read the safety instructions before starting any tests, and consult the safety data sheets supplied by the manufacturer to get detailed information on the associated risks.
Some reagents have a use-by date, and should be discarded after that point as they may not work as intended and give inaccurate results.
Importantly, there are particular risks associated with testing for heavy metals, and these tests are usually prohibited for domestic use. Extremely hazardous chemicals such as sodium cyanide are often used to test for lead, mercury or cadmium so these tests should be left to the professionals. Always seek advice from wastewater testing professionals such as Water Treatment Services or kit manufacturers if you have any queries about testing correctly.
Expert industrial wastewater treatment solutions
Water Treatment Services offer a comprehensive range of innovative water and wastewater management solutions for business. Our experts can provide advice and support to help you identify the most appropriate strategies for the identification, investigation and implementation of environmentally sensitive testing, monitoring and treatment solutions for industrial wastewaters and trade effluents.
With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained engineers and wastewater treatment specialists we offer cost effective environmental support solutions across the whole of the UK and internationally.
Contact us today to learn how our wastewater solutions can help you reduce costs and improve environmental performance.