Introduction
Water is essential for human life as it comprises 70% of the human body, from domestic applications to industrial and agricultural use. Clean and sustainable water is required and therefore an efficient and low cost method of treatment is required. High rate water clarification and filtration are fundamental to the purification of water sources for domestic and industrial applications. For more than 100 years, water treatment companies have been treating water through filtration and clarification processes. For instance, companies like Siemens Water Technologies and Infilco Degremont offer high performance wastewater, sludge and water purification solutions for whichever population and practically every influent condition. Over the years, different water clarification techniques have been developed for example high-rate dissolved air floatation (Aquadaf), high-rate clarifier and thickener (DensaDeg) and solids contact clarifier (Infilco, “Aquadaf” p 1). In this study we will focus on Aquadaf technology to explain how the high rate water clarification process works, the efficiency of the process and the economical aspect of it. Aquadaf technology is a high-rate clarifier for algae-laden and low turbidity surface water. These Aquadaf plants are exceptionally engineered waste matter collection system that offers working rates unparalleled by conservative flotation technologies (Infilco, “Aquadaf” p 2).In brief, Aquadaf technology generates an exclusive flow pattern that leads to amplified bubble plane area for greater floatation and loading turn over to more than ten times as compared to usual DAF systems. The outcome of this technique is low energy consumption, lower costs of operation and high capacity for new and existing treatment plants with no negligible space required (Infilco, “Aquadaf” p 2).
Aquadaf Main Features
It is a compact footprint of unit tallness of 10 -14 feet and 10-20 gpm/ft2 loading rate and made up of stainless steel reprocess system. For this system, it has no or just limited polymers and consist of perfect membrane pretreatment machinery and further mechanical or hydraulic sludge removal alternatives. Beneath this system, there is retrofit sedimentation basins and wall layout. Never the less, Aquadaf technology has variety layout plans and can be tailored to any given size plan. Finally this system can easily be started up or shut down within few minutes (Infilco, “Aquadaf” p 3).
How It Works
The following are the six stages explaining how the high rate water clarification (Aquadaf technology works).
Raw Water Inlet
For high-rate dissolved air floatation technique, we have coagulated or viscous water coming in from a rapid mixer goes into a flow supply channel before going to the flocculation zone. These colloidal particles are destabilized by use of a coagulant such as ferric chloride hence facilitating particle aggregation. Once aggregation has been achieved, coagulated water is then pumped into flocculation zone (Infilco, “High-Rate Dissolved Air Flotation System” p 3).
Flocculation Zone
With the use of frequency mixers and tapered energy, coagulated water is uniformly divided to each unit and retained in this flocculation zone for about 8 to 10 minutes. The weakened particles agglomerate or comes together and results into bigger floc particles. As we know, technically the Aquadaf flotation process needs only the development of pinpoint, light particles and therefore the use of flocculant polymers is eliminated or considerably reduced.
Air-Water Dispersion Zone
From flocculation zone the flocculated water is transported to the bottom of the flotation region, where it goes through the introduction of a concentrated air-water recycle watercourse. This reprocess or recycle stream is generated by reprocessing about 8-12percent of filtered or clarified water to saturator vessel which is pressurized to about 70-90 psi (Infilco, “High-Rate Dissolved Air Flotation System” p 4). It is from this process that the generated recycle flows is subsequently depressurized through sequential discharge nozzles and then flooded and span the whole breadth of this transition region. Thousands of micro- bubbles are generated with the release of pressure and then distributed into the flotation region.
Flotation Zone
Flotation process involves the formation of a thick air blanket as a result of micro-bubbles generated during depressurizing process in the air-water dispersion zone within flotation region. The micro-bubbles and flocculate particulate or particles will agglomerate or come together and form single units as they come up to the surface consequently clarifying the water.
Sludge accumulation
As a result of agglomeration in stage 4, we have accumulation of floated solids on the surface leading to a dense sludge layer. There are two options for removing this sludge namely; mechanically in which moving bridge scraper machinery goes through and removes the solid film into the connected sludge or mud trough. Alternatively the mud coating can be removed hydraulically in which routine effluent barrier rises in a prearranged time. Afterward, the flotation region water height ascends and the mud is detached into an integral mud trough.
Collection
Finally we have the collection stage in which the clarified water is eventually collected homogeneously from corner to corner on a perforated or punctured collection floor. This outstandingly engineered system, coupled with supplementary process enhancements, leads to resistance above the flotation region, leading to consistent collection of water and competent or efficient hydraulics all through the basin. The outcome is the capacity to manage high descending velocities and the rate of DAF loading considerably greater than conservative DAF processes (Infilco, “High-Rate Dissolved Air Flotation System” p 4).
This Aquadaf technology replaces old conservative DAF systems of water clarification such as solid contact clarifier and gravity filter method. These methods are less efficient and of high cost as compared to the Aquadaf technology. Moreover the conservative DAF methods are less compact and therefore occupy more space.
Advantages of Aquadaf Technology
- This technology yields unmatched loading rates of 10-20 gmp/ft2.
- It has mechanical or hydraulic flocculation and drift removal options.
- Extended plant capability without supplementary basins.
- No or very little polymer and low waste matter turbidities guarantees extended filter runs.
- The technology provides flexible float elimination which easily adjusts to plant needs.
- Easy design for straightforward maintenance and operation.
- Compact design results in less capital costs and space savings.
- Algae elimination more than 90%.
- With Aquadaf technique there is less flocculation time under 10 minutes.
- Phosphorus elimination below 0.1 mg/l TP.
Plant in Smith Falls in Ontario, Canada
As compared to other technology of the same scale, it turns out that Aquadaf technology more efficient but less costly. The plant at Smith Falls is a treatment plant is built on a small piece of land with a production capability of about 19million litres of clean water (McConnell, para. 1). The plant on Rideau River banks is a complex plant as it incorporates a lot of modern water treatment technological process. In Ontario, the original plant was tendered at a whooping figure of $33 million, which was far beyond Canada-Ontario Municipal Rural Infrastructure Fund (COMRIF). With some design modification, the overall building footprint reduced to approximately one third. A comparable reduction were employed to the in ground reservoir capability. After all those design modification, the cost of the plant was brought down to about $21.8 million yet above initial municipal budget (McConnell, para. 2).
To increase plant efficiency, the design consists of double medium gravity sieves with GAC caps, principal disinfection with UV-light, deposit management system and secondary antiseptic with chlorine. It functions using elevated lift pumps and 2200 cm3 features, in-ground solid reservoir (McConnell, para. 3).
Conclusion
Dissolved stream or air floatation (DAF) is a perfect solution for filtering or clarifying water which has high degree of algae and some low-density elements that may not be easily eliminated resourcefully by sedimentation. The economical polymer free dissolved air flotation flocculates water which has undergone preheating with coagulant. By eliminating the use of polymers, there is reduction in the costs involved and also increases the lifespan of whole design. What puts Aquadaf ahead of other dissolved air flotation technology is effluent gathering system which is superb. The Aquadaf system creates a conical flow prototype surrounded by the DAF basin that leads to thick air bed and greater bubble cross-section area for considerably higher.
In this study we have focused on Aquadaf technology and explained how high rate water clarification process works, the efficiency of the process and the economical aspect of it. Aquadaf technology is a high-rate clarifier for algae-laden and low turbidity surface water. These Aquadaf plants are exceptionally engineered waste matter collection system offers working rates unparalleled by conservative flotation technologies. In brief about its operation, Aquadaf technology generates exclusive flow pattern that leads to amplified bubble plane area for greater floatation and loading turn over to more than ten times as compared to usual DAF systems. The outcome of this technique is low energy consumption, lower costs of operation and high capacity for new and existing treatment plants with no negligible space required. Further the Aquadaf technology offers flexible float elimination which easily adjusts to plant needs and easy design for straightforward maintenance and operation. Sometime to due limited space it may not be easy to construct a water clarification plant but thanks to this design which has a compact design result into less capital costs and space savings. Finally we have seen that after necessary modification the Aquadaf technology eliminates more than 90% of algae are compared to other less efficient yet costly designs like solid contact clarifier and gravity filters.
In conclusion, Aquadaf saves lots of time, energy and manpower as water flocculates in less than 10 minutes and has a capability eliminating phosphorous even below 0.1 mg/1 TP. We have seen that Aquadaf technology replaces old conservative DAF systems of water clarification such as solid contact clarifier and gravity filter method. These methods are less efficient and of high cost as compared to the Aquadaf technology. Moreover the conservative DAF methods are less compact and therefore occupy more space yet the outcome is not worthy as compared to the cost and manpower involved in engineering those technologies. Therefore Aquadaf is the best method of clarifying water as witnessed in Ontario project in Canada.
Works Cited
Infilco, Degremont. Aquadaf. November 2009. Web.
Infilco, Degremont.High-Rate Dissolved Air Flotation System. 2002. Web.
McConnell, Patrick. Small Plant in Smith Falls Ontario. 2009. Web.