In this article the wastewater treatment specialists at WTS consider the benefits of treating industrial wastewater and trade effluent streams prior to discharge or re-use.
The article looks at how good wastewater treatment practices can help businesses achieve regulatory compliance and improve total environmental performance. It examines the role of pre-treatment technologies, what they involve, and how they work with a review of the most common chemical and filtration methods currently used in industry.
Why is the treatment of industrial wastewater important?
Industrial wastewater is created during many different business activities, and in some cases, the used water can be discharged straight into the local drainage system if it is clean enough, or reused in the same operation. In most cases though, the contaminated water will not be clean enough for immediate reuse or discharge, and will need to go through some other treatment process to make it suitable to put into the local sewers. This process is commonly known as wastewater treatment (or pre-treatment) and is often essential to ensure environmental compliance standards are met.
If as a business you are not cleaning up your wastewater to a sufficient standard before disposing of it into the local sewer system, then you are risking damaging the local environment, heavy fines, and perhaps even legal action. It’s certainly not a topic which can be ignored.
What does the treatment of industrial wastewater involve?
The first stage of any industrial wastewater treatment process involves the chemical analysis of the contaminated water, and a study of the circumstances under which it would be discharged into the drains. The aim of the pre-treatment process is to remove metals, other suspended materials, dissolved solids and chemicals from the water. There are various ways of doing this, but the main pre-treatment methods usually involve a mix of both filtration, and the use of special water treatment chemicals.
Using chemicals in the treatment of wastewaters
The starting point once you have your chemical analysis of your wastewater is to review the minimum standards required as part of your trade effluent discharge consent or licence, and then work out what you need to do to bring the wastewater (trade effluent) up to that standard.
You’ll often find that many of the particulates created in industrial processes are far too small to be removed by even the finest filters, so you will need a chemical treatment to do some of the initial work. Water treatment chemicals can help you remove ions and other unwanted solids from the wastewater. The three main chemical groups commonly used for the treatment of industrial wastewaters are:
- pH Adjusters
One of the first steps in the treatment process is usually to adjust the pH of the wastewater. Raising the pH will help to bring any metal contaminants out of solution, before adding in a specially selected chemical called a coagulant. The role of the coagulant is to get the solid particles contaminating the wastewater to form into small clumps so they can be removed more easily. Once these small clumps or flocs have formed a special chemical called a flocculant can be added to the wastewater to encourage the solids to settle out, or to float, for easy removal.
Using pH adjusters
A pH adjusting chemical works by manipulating the pH level of the water. The chemical reaction that takes place will help to increase the number of negatively charged hydroxide ions, which will in turn cause the positively charged metal ions to bond with them. This reaction creates solid particles of the metals which can then be filtered out more easily.
Using wastewater coagulants
In treatment systems where solids suspended in water are an issue, a coagulant can be used to bring all the solids together, making them much easier to remove. Wastewater coagulant can be either organic or inorganic.
The most common inorganic coagulants tend to be based on aluminium or iron and are often more cost effective, they are ideal for use in water with low turbidity. Inorganic coagulants work to form either iron or aluminium precipitates which then absorb any impurities in the water. The problem with this is that inorganic coagulants can increase the amount of sludge created, which then needs to be removed from the treated water. Organic coagulants on the other hand are used in smaller quantities, and also produce less sludge.
Using flocculants to treat industrial wastewater
The job of a flocculant chemical is to make it easier to remove suspended solids in water by encouraging them to clump together into flakes, which are also known as flocs. These flakes then either sink to the bottom of the tank, or float on the top. Flocculants and coagulants are commonly used together, but can also be used separately.
Wastewater treatment using filtration technologies
Once the wastewater has been chemically treated, the next step is to run the water through a filter system to get rid of the larger particles causing the contamination in the water. Some treatment processes incorporate a filtration system immediately following on from chemical treatment, whereas others incorporate a settlement tank for additional clarification or to allow solids to be floated off.
There are lots of options for filtering out waste contamination, but the main technologies used are centrifuges, filter presses, and belt presses. Each method has its own advantages and disadvantages.
Using a centrifuge to literally “spin” contaminants out of industrial wastewater has been a technique used for a long time. This method uses a fast-spinning cylinder to remove the solids from a liquid.
Once the liquid has been removed from your waste, you are left with a thick sludge which is easier to store in tanks, or to further process and separate out for reprocessing. However, centrifuges use a lot of energy while operating, and can be very expensive to set up initially, which often makes them prohibitively expensive.
Belt filter presses have been around since the 1970s and are used as a way of removing excess water from sludge to make it easier to treat. They work through a combination of drainage through gravity, and pressure, applied mechanically.
Usually, the wastewater to be treated first flows into a gravity drainage system, allowing water to flow away and the slurry to thicken up. Then pressure is gradually applied, using a system of belts and rollers to squeeze even more water out of the slurry.
The slurry will first flow through several sets of rollers, with each set having a smaller diameter. The forces exerted by the squeezing and shearing pressures help to remove excess water until the solids become even more concentrated.
Most belt presses will only work after coagulant or flocculant chemicals have been added into the wastewater treatment system, and they can be time-consuming to maintain and keep running. However, a belt press can be kept running constantly, rather than treating the water in batches.
Filter presses use pumps to create pressure which forces solids out of the wastewater. A typical system will involve sludge being forced at high-pressure through a succession of filters until all of the contaminants have been separated out from the water.
This technology has been around the longest and at the end of the process the solids are formed in to what are called “cakes” that can be easily removed.
The filters are most commonly made from plastic, with a hole in the middle. Joining the plates together provides a chamber for the wastewater, which is then forced out through a fine filter to catch the particulates. Modern filter presses are usually fully automated, and don’t require the addition of extra chemicals. Although low-tech, this is one of the most reliable filtration methods used for the treatment of industrial wastewaters.
Expert industrial wastewater and trade effluent solutions
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