Rotary drum screen
A key to successful wastewater filtration
What is a rotary drum filter?
The rotary drum screen, or rotary sifter, is part of the equipment usually found in municipal and industrial water treatment processes. This is the second pre-treatment process used in wastewater treatment plants after screening. It is generally placed upstream of the system, i.e. at the discharge of the pumping station which is in charge of collecting the wastewater.
In addition, the sifter can collect mechanically fine and coarse debris such as trash rack debris (RAG), thick sands or grease…
This way, the waste will not be mixed with sludge and will not interfere with the downstream process.
How does it work?
The purpose of the rotary drum screen is to sort out various fine and coarse matters. The water first flows into a container and is poured onto a circular drum screen. Raw water mixed with debris will then pass through the drum screen gravitationally to be sifted.
Through its slow rotation, the debris is trapped on the surface of the drum screen. This will eliminate any build up and clogging of the sifters. This waste will be then drained and scraped off the surface of the screen by an outer scraper mounted on a ressort system
All the waste will fall into a hopper, garbage can or dumpster and will be discharged to the outside later. Finally, the drum screen is cleaned with high or medium-pressure water after being scraped.
Fine separation with the sifter
The rotary drum screen ensures a fine screening based on the selected mesh size. These sizes range from 0.25 mm to 2.5 mm and the most common are 1 mm.
In addition, there are two types of rotary drum screens commonly used:
- with triangular wire
- with perforated metal sheet
Besides, triangular wire drum screens offer three benefits :
- best transition coefficient
- Its shape allows the finest particles to slide inside without blocking the slots.
- No rough side, instead of the flat plate, which has a rough side because of its manufacturing process.
Fixed screen VS Rotary screen
Sieves are essential equipment in wastewater pre-treatment. They are used to remove suspended solids before subsequent treatment stages. Of the various types of sieve, the most commonly used are the rotary sieve and the fixed sieve. Here is a detailed comparison of these two types of sieve. At 1h2o3, we have chosen to integrate the rotary screen into our wastewater treatment solutions to provide high-quality equipment and meet the challenges of sustainable management of water resources.
Benefits of the rotary drum screen
Basically, all rotary drum screens have similar features:
- Compactness: rotary drum screens have a small footprint
- Low maintenance: Rotary drum screens require low maintenance. You should check that the drum screen runs perfectly, is well scraped, and that the spouts are not clogged, and you should grease the bearing.
- Easy to operate: the sifters work automatically through their self-cleaning system. When the pumps in the elevation station begin to work, the drum screen also begins to work.
- Sorting: a rotary drum screen ensures solid/liquid separation. The finer the mesh, the more effective the separation. a fine sifter is used to collect rejects from the screenings separately. Therefore, it does not end up in the sludge.
- Securing the downstream process: removing coarse waste at the head of the treatment process secures the entire process: clogging of pumps, solenoid valve lockouts, build-up of sand in the basins, etc.
The various application areas
Sifters are widely used in many activities:
- Wastewater pretreatment for municipal and industrial wastewater
- Storm overflow collection
- Wastewater treatment with high content of solids including fibers, wool, feathers and films.
- Effluents from paper mills
- Textile industry like dyeing, bleaching, etc…
- Chemical and pharmaceutical industry
Rotary drum screens are highly recommended for any fixed culture process such as MBBR.
- Solid/liquid separation for the food industry:
- meat processing factories
- slaughterhouses
- dairies
- fast food
- Viticultural and vinicultural effluents,
- fish industry
- potato processing
- canning factories
- animal feeding
Rotary drum screen VS rotary screen
In fact, it’s almost the same thing. We use the expression ” rotary screen ” when it comes to the separation of solids and liquids. The word rotary screen is used to describe equipment that separates solids from solids, such as composting equipment.
Focus: The rotary drum screen for wastewater treatment
The rotary drum screen is suitable for special applications requiring fine screening. Among them, there is the wastewater treatment which uses the drum screen as the first step of the pre-treatment before the primary treatment or flotation.
According to a study by Irstea, fine screening of wastewater can eliminate up to 80% of suspended solids larger than 1 mm. Screening wastewater treatment plant effluent is very important. On the one hand, it allows to sort out a certain amount of debris to avoid having large waste in the sludge. In addition, it protects the downstream process, i.e. the entire wastewater treatment plant. Moreover, with a drum screen, you will have no more pump clogging and much less filthy crusting on the primary clarifier. It is therefore an essential step, especially if the downstream processes use filters for example.
- Protection of downstream equipment: By removing large debris, the rotary screen protects downstream equipment (such as pumps and flotation systems) from clogging and damage.
- Reduced maintenance costs: By preventing clogging and build-up of solids, the rotary screen reduces maintenance costs and extends equipment life.
- Improved treatment efficiency: Fine screening effectively removes suspended solids, improving the efficiency of subsequent treatment stages, such as primary settling and biological treatment.
- Prevention of filtrate crusting: The use of a rotary screen prevents the formation of filtrate crusting on the primary clarifier, which is essential to maintain optimum operation of the treatment plant.
A survey of 50 wastewater treatment plants in France carried out by IFEP in 2020 revealed that 76% of them were equipped with a rotary screen for wastewater pre-treatment.
Pre-treatment : screening or sieving?
Screening and rotary drum screen
The main difference between a rotary screen and a bar screen is the size of the elements filtered. However, the two facilities complement each other.
A bar screen is a coarse filtration device that uses bars or grids to trap large debris and solids in the water. It is often installed upstream in water treatment systems to protect downstream equipment (lift station pumps), then the sieve refines the filtration at the discharge. The rotary screen retains finer particles than a conventional bar screen, thanks to smaller mesh sizes or perforations.
To choose the right size for your rotary screen, you need to take a number of parameters into account: the peak flow rate to be treated, the nature and size of the elements to be filtered, and the space available. It is advisable to seek specialist advice.
Sifting and screening are both wastewater pretreatment processes with their own characteristics.
Screening
Screening is one of the important steps in wastewater treatment to remove large waste from wastewater. Indeed, the screening involves:
- to separate large materials that could interfere with the effectiveness of subsequent treatments
- protect the structures at the beginning of the plant from damage that can be caused by large objects in the wastewater flow
Screeners are very frequently installed on wastewater treatment plants.
Sifting
Sifting, meanwhile, ensures a finer solid/liquid separation. While most screeners have a mesh size of 6 to 20 mm, sifters have a mesh size of about 1 mm. The finer the drum screen, the more particles it will remove from the wastewater.
Sifters are usually placed at the head of small treatment plants. The screeners racks of the pumping stations upstream on the network act as coarse screeners.
The carbon load removed by a sifter is about 5%.
How to design a rotary drum screen?
The design of a rotary drum screen is based on several parameters:
- The peak flow rate: the higher the flow rate, the larger the drum must be
- Desired filtration mesh: 250 µ, 500 µ, 750 µ, 1 mm, 1.5 mm, 2 mm, 2.5 mm. The larger the opening, the larger the flow rate
- The type of application where it will be used: urban effluents are quite similar and contain little grease. Agri-food effluents are different.
- Water salinity (g/l salt): important for the choice of materials
With these criteria, we can determine the required drum screen surface (m²) and the suitable model.
1h2o3 rotary drum screen concept
Technical description of the sifting machines
The sifter is a necessary equipment to protect your downstream process. It removes all rough waste above the selected mesh size. Also, it allows to separate some of the grease and sand. Separate waste collection greatly improves the quality of the sludge. Their valorization or spreading is then easier.
All our sifters are made of :
- A stainless steel frame
- A stainless steel triangular wire drum
- Stainless steel bearings
- A hopper to prevent splashing
- A small engine training system
- A backwash ramp powered by a solenoid valve
- An inner distributor box with integrated by-pass
Specific advantages of 1h2o3 drum screens
Our rotary drum screens stand out through :
-
- their medium pressure operation: only 3 bars (drinking water network pressure) are needed to feed the cleaning nozzle, while other drum screen technologies require an intermediate pressure pump to reach 6 to 8 bars
- the sturdy concept of the triangular wire drum: stainless steel, anti-clogging shape and good passage coefficient. The drum screen is carried by stainless steel bearings with indirect drive. The frame itself is made of stainless steel.
- the built-in distribution boxinside the drum screen, which allows the fluid to be distributed over the entire surface
- with wear-resistant scraper and constant pressure on the drum
- With the possibility to associateour drum screens with sand removal, oil removal, buffer tanks or all 3 combined.
- For the reuse of treated water at the outlet of the plant when the rotary drum screen is used together with a 1h2o3 lamella clarifier offering the “industrial water” option
- Internal bypass: in case of high flow, part of the flow goes directly behind the drum. Hence, there is no need to add an additional bypass line
- Their economical function: a small engine running when the pumping station starts and water coming either from the network or from the industrial water reserve of the lamella clarifier.
- The non-spill hood that is fitted to every screen we manufacture
Used rotary drum screen
Sometimes we have used rotary drum screen for sale. For more information, please contact us!
Why should I rent a rotary drum screen?
Renting a rotary drum screen may be a very good idea to test its efficiency on your process. We offer rent-to-own, so before you invest in any significant civil engineering work, test the pretreatment of your effluent by sifting.
We invite you to contact us to learn more!
Combining other processes 1h2o3 with a sifter
Grit removal
As the name implies, the grit removal unit is used to remove sand.
Indeed, the sifters remove some of the sand but this is not their primary function. When effluents are loaded with sand (e.g. potato washing), it is recommended to combine the rotary screen with a grit removal system. It will collect sand that is finer than the mesh size of the drum screen.
Therefore, these sands will not end up downstream of the industry. Fine sand may gather in some structures or block small solenoid valves.
This is why it is preferable to recover it in the pretreatments. Did you know that when cleaned, this sand can be recycled?
Oil Remover
The purpose of the oil remover is to separate liquids from light greasy substances contained in the wastewater.
Some effluents, such as in the food industry, are loaded with oil and grease. The sifter will remove the larger blocks but some of the oil will pass through. In this case, we recommend using the rotary drum screen together with hot water for the nozzles.
After the sifter, an oil remover is strongly recommended to trap residual oil and grease.
Buffer tank
The buffer tank is used to store and smooth the pumped effluent obtained after sifting.
With the buffer tank, it is possible to smooth the flow over the day and thus avoid hydraulic and organic overloads. It offers several advantages:
- Biological treatment can be more compact
- Installed power for ventilation is reduced.
MBBR biological treatment
Any MBBR process must be protected by a rotary drum screen. The accumulation of fillings in the biological ponds is undesirable. In addition, they will disrupt treatment over the long term.
The MBBR biological treatment is efficient in removing COD, BOD5 and NH4. To ensure this performance over time, a sifter should be placed at the top.
