The majority of wastewater treatment plant operators are aware that their facilities, perform best at a certain ideal pH and that a certain level of alkalinity is necessary, to maintain the health of the microorganisms. But all too frequently, the terms "pH" and "alkalinity" are employed improperly to mean the same thing, and the full significance of each parameter in terms of biological stability, and optimal performance is lost in the translation.
Let’s see how we can solve your wastewater treatment plants' problems, with alkalinity adjustment.
There are a lot of possibilities for alkalinity adjustment, but when it comes to Wastewater Treatment Plants (WWTPs), there are three main solutions that are commonly available: magnesium hydroxide, lime slurry, and caustic soda.
The following blog provides the advantages and disadvantages of each, providing the necessary direction for WWTP decision-making. The decision ultimately rests with the plant's final specifications, and is determined by the facility's discharge permit.
Why is alkalinity vital in the treatment of water?
The rate of nitrogen is most frequently caused by the usage of lime and caustic soda, which is the most used alkaline pH modifiers and alkalinity boosters. When used to meet pH requirements, they may do so successfully, but they are unlikely to be able to meet the demand for alkalinity, without adversely raising pH above physiologically appropriate levels. Furthermore, it remains virtually impossible to maintain pH stability and homogeneity, throughout complete treatment basins.
As a result, it's crucial to consider all available options for pH and alkalinity modifications, and ensure a thorough understanding of how each will affect the system. For instance, it has been noted that when considering the nitrification process alone, having a constant, slightly raised pH and adequate alkalinity can significantly improve the denitrification.
How should alkalinity in water be handled?
Typical substances us?ed to raise pH and alkalinity includes:
· Either calcium hydroxide or calcium oxide (as lime slurry)
· Hydroxide of sodium (caustic soda)
· Either sodium bicarbonate or sodium carbonate (soda ash)
· Magnesium bicarbonate or magnesium hydroxide
1: Calcium hydroxide
CaO quicklime, commonly known as hydrated lime, is a very popular product that may be made into slurry, by mixing water with dry lime powder. This slurry is frequently used in potable water to "soften," or remove hardness minerals like calcium and magnesium from drinking water. It can be used to treat wastewater to enhance pH and alkalinity.
The impacts of potential scaling in the water distribution system are reduced, by lime slurries. Due to its low cost and numerous treatment advantages, including helping to remove manganese and iron from water, it is also the most widely used product to maintain alkalinity levels.
Due to its high solubility, lime slurry has some drawbacks. Before perfect alkalinity levels and process stability can be achieved, maintaining proper pH levels frequently becomes biologically impractical. Another significant issue is that lime slurry would increase waste sludge, often by as much as 50%, increasing the operation's disposal expenses.
Adding hydrated lime slurry to collection systems raises the expense of operations, and maintenance associated with the build-up of scale and solids/sludge. In extreme situations, this may result in line blockages.
2: Sodium hydroxide
Sodium Hydroxide, sometimes known as caustic soda, it is also known as NaOH. Surprisingly, while it is frequently found in homes, its primary industrial purpose is the neutralisation of alkalis. A typical, well-liked method to neutralise and subdue all types of acids is to use caustic soda, which may be found in a variety of quantities. Due to its solubility, it is also thought to be simple to introduce into the system.
However, handling it properly throughout the treatment process requires taking various precautions, because it is exceedingly dangerous to handle at high doses. At the very least, these would consist of improved PPE (personal protective equipment), and readily available wash stations.
Due to Caustic Soda's high solubility, pH frequently crosses the physiologically threshold extremely fast, just like Lime Slurry. This frequently increases the risk of killing off the microorganisms by elevating the pH, before you can make modifications.
It's also crucial to consider how temperature and caustic concentration relate to one another because, above a 50% concentration, caustic has a 60°F freezing point, which limits its use to warm climates or necessitates heating tanks. Using Caustic soda in lesser concentrations lowers the freezing point and lessens some of these difficulties, but you will eventually spend more in freight to export the blend's "water content."
3: Baking soda
Baking soda has little effect on the pH in general, however soda ash (sodium carbonate) can be used to drastically increase, and manage alkalinity and pH. Under the direction of the water treatment process, soda ash is a good choice to utilize if you're aiming to boost pH.
4: Magnesium Hydroxide
Also known as milk of magnesia, this substance has the dual purposes of stabilising alkalinity and neutralising acids. Magnesium Hydroxide's self-buffering properties make it largely worry-free, for changes in alkalinity. Magnesium Hydroxide is safe to use because it won't dissolve and produce a pH above 8.5, making it unlikely that biological activity will burn out (pH above 9) at that pH.
Magnesium hydroxide has various disadvantages
The slurry (usually 60–66%) separates and needs to be stirred or circulated continuously. With the right equipment selection, this problem can be easily fixed and without stress. The advantages of alkalinity and pH stability will lead to more predictable reaction times, and with its self-buffering properties, will ensure more stable settings for biological organisms used in wastewater treatment to function as effectively as possible - without killing them.
How much should you use?
For the WWTP industry, caustic soda and lime slurry are unquestionably the go-to chemistries, since they provide the necessary pH changes. But, when comparing those two and magnesium hydroxide on a pound-for-pound basis, there is an important distinction to make that has less to do with pH or alkalinity, and more to do with the actual amount needed to address the problem.
For instance, 100 mg/L of magnesium hydroxide may be needed, to elevate the pH of a particular water sample to 8.8. It would take 138 mg/L of caustic soda and 135 mg/L of lime to process the same sample.
Comparing magnesium hydroxide, caustic soda, and lime slurry, it can be seen that while all three can provide the necessary benefits, the best overall treatment should be chosen based on some of the adverse effects of each.
Magnesium hydroxide can be tricky to store if done incorrectly, but it can provide a microbial wastewater system with much more alkalinity in a bio-available form, without negatively influencing pH. This improves the environment for BOD and nutrients, like nitrogen and phosphorus to be bio-remediated.
Additionally, magnesium hydroxide contributes to the production of a denser, more readily dewatered sludge with a higher proportion of cake, because it provides a lightweight, divalent cation as opposed to the monovalent sodium, in caustic and heavier calcium in lime.
Manufacturer of wastewater treatment plants
A wide range of industrial and commercial water filtration and water purification equipment’s’ are available from Netsol Water, and they may be customised to meet the demands and requirements of any particular project. In addition, we provide top-notch RO plants, water softeners and activated carbon filters that can be used for any tertiary water treatment, or water purification application.