Fine Bubble Diffuser Aeration From ABS: Energy Efficient Wastewater Management Solution To Rising Energy Costs
Global aeration system specialist, ABS, supplies an environmentally friendly waste water treatment solution, Fine Bubble Diffuser Aeration (FBDA) that delivers substantially reduced energy consumption for the mining, industry and waste water treatment plants. Environmentally sympathetic ABS is present in over 100 countries and uses 140 years of knowledge, fieldwork and continuous R&D to engineer, develop, manufacture and supply class leading eco-friendly purification systems for mining, municipal and other general industrial applications.
"Precious water sources are rapidly depleting across the globe and responsible without responsible management, this life giving commodity will be destroyed," says ABS General Manager, Hennie Basson. He adds that skillful, careful water purification management in a ‘water poor' country like South Africa is paramount to maintain water supply. In addition, ABS perceives a major shift in thinking by end users. The continuing steep upward trend in energy costs leaves end users with no alternative but to investigate energy efficient solutions for maximum savings. FBDA is accepted as the norm for water purification in Europe and South Africa is also moving in this direction.
"Local mining and industrial sectors use large quantities of water and while water purification is not their core business it is nevertheless crucial that they effectively manage purification to prevent contamination," Hennie continues. 'Because the water volumes involved are so massive, it is a challenge to identify a competent solution that is both cost effective and energy efficient. We all have a social responsibility and it is quite possible to run an eco friendly efficient plant by simply appointing a responsible supplier like ABS for the best solutions".
Rotating Bio-disc Contactors (RBCs) is the most commonly used water purification method for the mining sector while larger mines use surface aeration. Hennie points out that not only does either system remove harmful substances such as phosphorous nor nitrogen, but also that these systems also extremely greedy when it comes to energy consumption. The multiple RBC units use bio film on a plastic media on which the bacteria sits and as the drum rotates, foodstuffs cling to the plastic surface. Adsorption thus only takes place when the disc is in free air. According to Hennie, this short contact time reduces oxygen intake or aeration and thus purification. As much oxygen as is possible must be absorbed to achieve optimum aeration. The higher the transfer efficiency, the less energy is expended for oxidation. RBCs are also capital expensive as these large units usually cannot be repaired and must be replaced when mechanical failure occurs –a time and cost inefficient exercise for any plant.
Where water flow is too high for RBCs, mines rely on conventional sewage treatment systems. Hennie discusses the limitations of surface aeration: "Due to the layout of the system, so called ‘dead' areas, aerosol and waves cannot be avoided. ‘Dead' corners limit optimum aeration, aerosol causes waste build up on the surrounding areas, and wave action means more free board above the water level to prevent waves breaking over the sides in turn reducing water volumes vs. tank volume. "Moreover, mechanical surface aerators cannot be adjusted to deal with flow fluctuations and irrespective of whether flow demand is high or low, energy consumption remains high because mechanical surface aerators continue operating to maintain suspension. Other factors that add to running costs are the costs for support structures for bridges".
ABS's energy efficient, low noise level FBDA technology uses bio solids as a biological mass carrier in the water system to proficiently remove organic pollutants from waste water. "In other words, instead of forcing oxygen downward, FBDA applies the laws of physics; bubbles rise to the surface from diffusers placed at regular intervals along the floor of the basin for higher transfer efficiency, maximum oxygen absorption and minimum energy consumption".
"It is so important to realise that energy consumption is one of the most important and potentially highest cost saving areas". Hennie explains, "While cost control in many areas, including the price of energy, is difficult to control, energy efficiency can be achieved through intelligent utilisation of power consumption. Here, massive savings can be realised when taking into consideration that the biological process uses as much as 85% of total energy".
Hennie gives two examples to illustrate potential savings: "Our FBDA system saves 40% per hour on energy consumption at a typical high altitude water treatment plant; operating at 200kW installed power, the plant saves 80kW per hour. This energy that can be more profitably used elsewhere or the saving can be added to the bottom line. The projected average savings for a 20 mega liter coastal waste water treatment works with a 5 meter water depth. in accumulative energy costs is in the region of R50m plus in year five and R250m over a fifteen year period."
According to Hennie there is no total cost difference between the three purification systems – RBC's, mechanical surface aerators and FBDA – in terms of civil, mechanical, installation and electrical considerations. Hennie explains that if the initial capital expenditure for a FBDA system is higher, the installation of FBDA technology will allow these costs to be easily recouped through substantial savings on energy, operational, maintenance and life cycle costs that offer quick return on investment (ROI) and lower total cost of ownership (TCO). Hennie quotes as an example a large plant that invested an additional R7m for structure walls for the blower room. "The plant realised ROI within 19 months, a statistic which becomes even more meaningful when taking into consideration that the expected lifetime of a plant is calculated at 20 years."
Hennie continues, "Yet another compelling argument for energy efficiency is that our system allows air flow to be reduced to meet required oxygen. While mechanical surface aerators simply continue operating, our system is flexible and can speed up or down to meet the reduced oxygen demand related to water volume fluctuation. While sustainable daily efficiency remains high, less power is required, making up to an additional 30% energy saving possible."
As FBDA only has to overcome the hydrostatic pressure of the water, this pressure is relatively low i.e. 1m of water creates 100millibars of pressure. Whereas surface aeration is localised, the FBDA diffusers are positioned to use optimum tank geometry ensuring equal distribution of air flow, preventing ‘dead' areas. Value is added to any purification process as aerosol and wave formations are avoided, hence there is no build up of waste water droplets that can potentially damage surrounding areas. Because of the clean flat surface, the FBDA system does not require free board; in a 4 metre deep tank, for example, the system can use an additional 12.5% of the available volumetric capacity of the structure. A higher water level of 500 mm and additional capacity in the water tank means that a smaller footprint is required with related savings.
According to Hennie, a multi-channel FBDA system layout is quick and easy to clean and maintain, and maintenance costs are virtually zero. He supports this statement with examples of some FBDA installations that have been operating maintenance free for up to nine years. While every mechanical surface aerator requires a control panel, FBDA does not require any electrical cabling. In addition, filters for FBDA blowers cost the same as oil changes and filters that are required on gearboxes driving mechanical surface aerators, yet more cost saving benefits of FBDA.
Scientific data by Metcalf & Eddy show that FBDA can operate at double the efficiency of other systems. Hennie elaborates: "FBDA may be 40% more efficient in 3 metres of water and 50% more efficient in 5 metres of water. The deeper the tank, the more efficiently FBDA functions because contact time with oxygen in the air bubbles is increased. On the other hand, to maintain efficient surface aeration in deeper tanks require larger aerator cones and gearboxes to increase pumping action of the mechanical surface aerator".
Hennie cautions that the location of the plant in terms of altitude plays a role in the design and installation and therefore the cost of purification systems. "High altitudes with thinner air and less oxygen require more diffusers and larger blowers to ensure maximum oxygen for the purification process. But this also holds true for RBCs and surface aeration i.e. higher altitudes require more RBC units and larger surface aerators. Of course the reverse is true for low altitude installations where oxygen levels are higher."
ABS combines products, services and close to one and a half centuries of knowledge to identify the best possible waste water treatment systems, tailor made for specific purification requirements. The major savings on energy consumption and maintenance achieved by FBDA technology translates to rapid ROI and lower overall TCO, delivering a boost to the end-user's bottom line.
SOURCE: ABS