The use of Nanobubbles in water, waste water treatment, agriculture and aquaculture and other application has witness recent massive advancement. We will be exploring the benefits of application of Nanobubbles in water and waste water treatment
Currently, in many developing countries, water resources are facing extreme challenges such as water scarcity, drought and other environmental problems. Hence, the need to develop a water and waste water treatment technology that can effectively address these challenges. The use of nanobubbles have emerged as a useful and potential technology for the successful extraction of harmful contaminants from water and waste water.
Defining Nanobubbles
Nanobubbles are extremely small gas bubbles that are less than 200 nanometers (nm) in diameter. They are nanoscopic gaseous (typically air) cavities in aqueous solutions that have the ability to change the normal characteristics of water. They can be formed using any gas and injected into any water. Due to their size, nanobubbles exhibit several unique properties that make them useful for water treatments and different from normal bubbles.
Physical Properties of Nanobubbles
I. Bubble Size: Nanobubbles are the smallest bubble size known, 500 times smaller than a microbubble, or about the size of a virus. At this scale, far more nanobubbles can fit in the same volume of water compared to other bubbles.
II. Neutral Buoyancy: Ordinary bubbles have a diameter which range from 1 µm and larger. These quickly rise to the surface of a liquid and collapse. Nanobubbles lack enough buoyancy to reach the surface instead follow Brownian motion and can remain suspended in water for months until they dissolve.
III. Surface Charge: Nanobubbles have a strong negative surface charge that prevents them from coalescing and enables them to physically separate small particles and droplets like emulsified fats, oils, and grease from water.
IV. Surface Area: Nanobubbles have more than 400 times the surface area of a typical microbubble, measured at 40 micrometers in diameter. The larger surface area allows for increased mass transfer, ensuring virtually any gas is effectively delivered to water.
V. High Transfer Efficiency: Nanobubbles have an oxygen transfer efficiency (OTE) of over 80% per foot of water when compared with conventional aeration system. This system transfers only 1% to 3% of oxygen per foot of water due to their size and corresponding rapid rise rate thereby making conventional aeration highly inefficient.
VI. Oxidation: When nanobubbles are stimulated, they destabilize and collapse, releasing the hydroxyl radical. The hydroxyl radical (HO) is one of the strongest known oxidizers commonly used to destroy hard to treat and hard to kill contaminants in water.
The Use of Nanobubbles in Water and Waste water treatment
The physical properties of nanobubbles makes them useful in techniques of water and waste water purification such as floatation, aeration, ozonation, degradation and disinfection.
Ø Aeration Process
The aeration process for water purification is a successful treatment for harmful substances, such as dissolved gases, volatile organic compounds, and industrial solvents. It is effective for precipitating dissolved iron and manganese. Aeration increases the pH of water, and its treatment involves passing vast amounts of air through water and, afterward, venting it outside. Oxygen is not only an essential component of water treatment for the preservation of the life of aquatic species but also a biochemical reaction substrate for the degradation of oxidative pollutants so it needs aeration to transport oxygen. However, conventional mechanical aeration requires a significant amount of electrical energy, but the oxygen transmission efficiency is only 6-10%. Nanobubbles for aeration can enhance oxygen mass transfer, increase dissolved oxygen concentration, and strengthen oxidation. In the synthetic wastewater treatment system with nanobubbles, the oxygen utilization rate and volume mass transfer coefficient are about twice that of the traditional bubble aeration system.
Ø Ozonation
Wastewater from the textile and dye processing industry is considerably colorful and is mostly not naturally biodegradable. Ozonation is a conventional technique because it can break conjugated double bonds in colored compounds and prevent sludge formation. It can increase the rate of decolorization by generating more OH radicals in the presence of H2O2 (hydrogen peroxide) or UV. With the use of nanobubbles to purify textile waste water, decolorization rate and reduction in organic matter are significantly higher than that of the traditional bubble contactor with limited amount of ozone used.
Ø Odour Control
Most offensive odours produced in wastewater are the gaseous by-product of decomposed organic matter. The most common of these is hydrogen sulphide (H2S), which is formed from the anaerobic degradation of organic matter containing sulphur or from mineral sulphates and sulphites. Hydrogen sulphide is known for its rotten egg smell and can adversely impact human health at levels above 10 ppm. One means of treating odours, including H2S, is to prevent the water from going anaerobic by increasing dissolved oxygen (DO) or oxidation reduction potential (ORP) using air, oxygen or other oxidants. Nanobubbles effective gas-injection technology delivers a high volume of air or oxygen nanobubbles, efficiently maintaining DO and preventing the anaerobic conditions that lead to odorous compound formation.
Ø Degradation of organic pollutants and water disinfection
Pollutant oxidation and pathogen disinfection using ozone is a promising method for purifying wastewater. Studies show that gas bubbles of ozone due to their powerful disinfection ability successfully treat water even with short contact time and low concentration. The effectiveness of this method has frequently increased its application for chemical-resistant spore-forming bacteria (e.g., Cryptosporidium parvum and Bacillus subtilis). Using nanobubbles make this process more efficient, as kinetic disinfection demonstrates a faster decrease rate of Escherichia coli (99% reduction), with a relatively small water tank and a lesser amount of ozone than the normal ozone disinfection process.
Ø Floatation
Flotation has also been a major separation process in the area of water purification. The most specific substances that need to be removed from flotation are dust, chemicals, organic matter, metal ions, and oils. The efficiency of the separation process is closely linked with the size of bubbles. In flotation, nanobubbles are commonly used to remove pollutants from the water with greater efficiency. They promote longer contact time and higher adhesion efficiency of bubbles and suspended solids due to their unique advantages of large specific surface area, and long residence time in water.
Ø Soil and Groundwater Remediation
In situ bioremediation are one of the most common and environmental friendly methods to remediate soil and groundwater. Nanobubbles can greatly enhance bioremediation by accelerating the oxygen transfer process while this process is capable of adsorbing small impurities so as to remove pollutants through its excellent adsorption capacity.
The use of nanobubbles as an innovative technology for applications in water and waste water treatment is to reduce the size of the system structures, operating time, the operating costs of processing plants, and increase efficiency in eliminating water pollutants.
Safebrooks has developed her brand of Nanobubbles generator for efficient water treatment. We provide sustainable water solutions and chemical free water treatment systems that can be used in a wide range of industrial water and waste water treatment applications where highly efficient treatment method is required.
If you have any water and waste water issues, please get in touch with us for a free consultation. An advice may save you and/or your client a great deal.