The sedimentation process in both water and wastewater treatment is a physical process which relies on gravity to settle and remove suspended solids. Advanced solids settling processes typically utilize lamella, commonly referred to as tube settlers or plate settlers, to reduce the vertical distance solids particles must fall until hitting a &#;settling surface&#;. Higher flow rates, better effluent quality, and more compact sedimentation basins can all be achieved with both types of lamella sedimentation equipment. Although both operate on the same principles of solids settling and can be used as basis of design in many cases, there are several notable differences between the two technologies.
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Tube settlers utilize multiple adjacent tubular channels that are sloped at a nominal 60° angle and combine to form an increased effective settling area. The size and shape of the tubular channels vary by manufacturer. Brentwood&#;s tube settler design features a trapezoidal shape created by thermoforming PVC sheets. You can learn more about our design process by reading our Thermoformed vs. Extruded Tube Settlers blog.
In contrast, plate settlers use a series of inclined plates, typically constructed of steel, which are spaced two to three inches apart from each other on a 55° to 60° angle to form an increased effective settling area. As a result of these design differences, typical design parameters for these two types differ.
It is important to note that there is a difference in application rate (flow rate/coverage area, expressed in gpm/ft²) between tube settlers and plate settlers as a result of different effective settling area terms used, despite settling principles being similar for the two technologies.
To provide a more direct comparison, the application rates of tube settlers can be converted to an equivalent &#;plate&#; application rate by taking into account the projected surface area of tubes (see Figure 1).
As illustrated, the equivalent maximum &#;plate&#; application rates of Brentwood tube settlers are in the same range as a generic plate settler, which has an average application rate of 0.30. IFR tube settlers are the most comparable to plate settlers in regard to coverage area because settler length is similar. However, Brentwood&#;s other tube settler modules are capable of treating required flow just as effectively with appropriate coverage area. Tube settlers also eliminate cross-flow and eddy currents, which makes flow hydraulics more stable and efficient.
In addition to varying design approaches, there are other advantages and disadvantages to consider when comparing tube settlers or plate settlers for your application.
When selecting lamella sedimentation equipment, a cumulative decision should be made based on performance and long-term economic impact. Tube settlers may not match the lifespan of plate settlers, but their lower initial cost and ease of installation can be enticing to a plant of any size. Their lightweight and easy to maintain characteristics, along with superior structural capabilities compared to other tube settler options on the market, make Brentwood&#;s equipment a clear choice.
To remove suspended solids, drinking and wastewater treatment facilities use tube settlers, often referred to as plate settlers or lamella clarifiers. The TSS (total suspended solids) loading might range from 50 to 500 mg/l or higher depending on the application. Solids will collect on the channel surface of the tube settler, slide down as sludge when the solid settling force is greater than all other drag forces. Similarly, we also have clarifiers for treating suspended solids in sewage.
In this blog, we will look at the differences between the tube settler and clarifier in sewage treatment plants. We will also look at the appropriate use of both the tube settler and the clarifier for sedimentation purposes.
Tube settlers use numerous tubular channels that are close to one another and inclined at an inclination of 60 degrees, to maximise the effective settling area. As a result, settling periods are shortened because the particle settling depth is substantially lower, than that of a traditional clarifier.
The larger floc can move to the tank bottom in a more settleable state because tube settlers catch the settleable fine floc, which escapes the clarifying zone beneath them. The solids are gathered in settler's channel into a tight mass. It encourages the solids to slide down the tube channel.
The performance of existing clarifiers and sedimentation basins in sewage treatment plants, can be enhanced at a low cost using tube settlers. By lessening the sediment loading on downstream filters, they can also lower the footprint needed in new installations, or enhance the functionality of existing settling basins.
Feasible settling surface must be provided by tube settlers while also avoiding channel obstruction. The following design elements are typically present in tube settlers to lessen the possibility of clogging:
· A smooth, anti-friction surface is created by lubricating additives, added to polypropylene or PVC material.
· A 60-degree channel inclination will provide a water and sludge counter-current flow. Because, settling materials do not obstruct raising barriers, particles settle more quickly in 60-degree inclined channels than in vertical ones.
· Application and TSS loading determine channel sizing or plate distance.
· A V-shaped groove is part of the channel geometry and is used for sludge accumulation and sliding.
By lowering the vertical distance, tube settlers boost the settling capacity of circular clarifiers or rectangular sedimentation basins. Before clumping together to create larger particles, the floc particles would settle. The settlers make use of numerous tubular channels that are placed next to one another, and sloped at an inclination of 60° to provide a larger effective settling area.
As a result, settling periods are shortened because the particle settling depth is substantially lower, than that of a traditional clarifier. The larger floc can move to the tank bottom in a more settleable state, because tube settlers catch the fine floc that escapes the clarifying zone beneath them. Solids are gathered by the settler's channel and compacted.
Flow chart for Tube settler in STPs
1. Wide wetted area; narrow hydraulic radius.
2. Particle deposition is free from interference from turbulent flow, due to good laminar flow conditions.
3. The greatest water quality is achieved when the effective payload is designed to meet 3-5 t/m2, V is controlled within 2.5-3.0 mm/seconds, and the oblique tube length is 1 metre.
4. If a tube settler is used in the water intake and is 2.0 to 3.0 metres long, it can perform well in a high turbidity tank with a sediment concentration of 50 to 100 kilogrammes per cubic metre.
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5. When a tube settler is used in a sedimentation tank, the treatment capacity is 2-3 times greater than that of an accelerating clarification tank, and 2-3 times greater than that of a pulse clarification tank.
Any clarifier or basin can benefit from tube settlers' advantages such as:
· These allow clarifiers and basins to run at 2 to 4 times the average pace, of clarifiers/basins without them.
· While, retaining a decreased influent turbidity to the treatment plant filters, the coagulant dosage can be reduced by up to 50%.
· Significant operating cost savings for both water and electricity result from less frequent filter backwashing.
· The enhanced flow capacity is allowed for the design of smaller new installations utilizing tube settlers.
· Tube settlers can be added to existing water/sewage treatment facilities to enhance flow.
· By raising the settling capacity and the pace at which sediments are removed from settling tanks, tube settlers raise the maximum flow capacity that is permitted.
Wherever the concentration of suspended particulates in raw or wastewater is higher, clarifiers are necessary. Sedimentation tanks or clarifiers in almost every treatment facility are circular in shape, and occasionally rectangular.
Clarifiers operate on the settling principle of gravity. Due to quiescent circumstances offered in by Clarification zone, heavier suspended materials settle in clarifier. With the aid of moving scraper blades, the settled solids are swept to the middle well designed for collecting sludge.
Every conventional sewage treatment facility has primary and secondary clarifiers, which are different but equally important components.
While, primary clarifiers are built downstream of the plant's screening and grit chambers, to separate settleable solids from the raw wastewater influent, secondary clarifiers are built downstream of the biological treatment or activated sludge facility, to separate the treated sewage from the biological mass used for treatment.
Both of these clearing methods use gravity to separate the solids from the feed water, which goes into the clarifiers. Their design configurations are comparable.
Clarifiers used in STPs
Let us discuss in detail about the primary clarifiers and the secondary clarifiers used in sewage treatment plants.
The first step in the water/sewage treatment process for removing suspended solids (TSS), oil, and grease is primary clarification, sometimes referred to as sedimentation. Prior to biological treatment, this stage involves the removal of big water or wastewater flow particles, and solids that are surfacing at the surface.
A rake is used to gather the sludge that has collected at the bottom of the clarifier basins, before it is removed by a sludge removal system. In the meantime, grease and oil float to the top and are skimmed off. A typical primary clarifier removes 30 to 40% of the biological oxygen demand (BOD) and 60% of the suspended solids.
After biological treatment, activated sludge is returned with the help of secondary clarity. The biomass from microorganisms sinks to the bottom during the secondary clarifying, process in the form of activated sludge.
The biomass of microbes is returned to the aeration tank after settling over time, and the cycle is repeated until the effluent is clean before being transported for filtering, or disinfection. Prior to digestion, waste sludge is removed and thickened.
There are various designs for circular clarifiers, such as segmented rakes, spiral scrapers, and hydraulic removal types. There are 3-shaft and 4-shaft rectangular Chain and Scraper clarifier systems, as well as moulded, filament wound, and stainless steel chains available.
Basin length and solids loading are used to determine selection. Ballasted clarification using either circular or rectangular clarifiers significantly boosts treatment capacity, aids in meeting restrictions, and generates effluent quality that is substantially superior to conventional options, while having a lower life-cycle cost.
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