Table Of Contents
Wastewater is a generic term for used water with solid and or liquid contaminants. For example, municipal wastewater has organic sludge, industrial wastewater carries industrial or inorganic sludge, etc.
Generation in large volume is the other aspect of wastewater, and therefore, the separation equipment needs to be able to process large amounts of contaminated fluid.
Wastewater from the sources, as mentioned earlier, contains bulk sludge, which is easier to separate. On the other hand, wastewater from mines and oilfield drilling operations contains fine, suspended solids requiring smaller mesh filtration or higher g-force centrifuges.
We also have industrial effluent water, which contains oil in addition to the solids or sludge. This application may need two different centrifuges to first separate the sludge and then the oil from the de-sludged water.
Filtration is not an option for this application, given the type and volume of wastewater that needs to be purified. Other separation technologies such as belt and filter presses have limited uses in wastewater separation duties. Again, these technologies have their drawbacks, including labor and equipment reliability issues that limit their widespread use in wastewater treatment plants.
Mechanical separation using a centrifuge has many advantages for the continuous processing of large quantities of wastewater. As with all technologies, centrifuges also have some drawbacks that we have highlighted below.
A wastewater centrifuge is a separation machine that utilizes a centrifugal force of 3,100 Gs to separate the wastewater from sludge. The sludge accumulates on the bowl periphery, which the internal auger scrapes towards the sludge discharge ports. The water flows out through the bowl's liquid outlet at the opposite end.
Three types of centrifuges apply to wastewater depending on the type and amount of sludge. The following section describes these broad categories.
A sludge dewatering or sludge thickening centrifuge is a decanter-type horizontal de-sludger that can remove water from slurries to thicken the sludge. In other words, a heavy-duty industrial centrifuge dewaters and concentrates (thickens) the sludge is also known as a sludge thickening machine. These machines are available in different sizes to process large quantities of sludge-laden water continuously.
Livestock farm manure, municipal sewage, car-washes, and oilfield drilling mud produce wastewater with high sludge content of up to 50%. The primary objective of such applications is to reduce the sludge volume to minimize handling and disposal costs. The recovered water is often clean enough to be reused or discharged with minimal environmental impact.
A wastewater clarifier centrifuge is a disc-stack type, high speed, self-cleaning separator that produces very high centrifugal forces that can separate micron-level suspended particles. The particles are pushed towards the bowl wall and automatically purged during the cleaning cycle. The cleared centrate discharges the bowl continuously through a centrally located outlet port.
Wastewater from mining applications is one such example. This stream contains minute silt and clay particles that are difficult to separate with a wastewater decanter. A high-speed, disc centrifuge has sufficient g-force to pull out these particles and clarify the water.
Industrial wastewater often carries oil in addition to the sludge. This oily water is a challenge because it cannot be disposed of into standard drains. A three-phase industrial centrifuge separates the oil from the water, which can make it disposable.
Industrial cleaning fluid containing shop-floor sludge and oil from the manufacturing run-off is ideal for separation with a liquid-liquid-solid separator.
Centrifuge offers many benefits compared to other dewatering and separation technologies. A brief description of some of the advantages follows.
Centrifuges produce dry sludge cake, which results in a significant reduction in transportation costs (up to 50%). Dry sludge also reduces disposal costs because the disposal volume is a fraction of the wet sludge.
Industrial decanters are heavy-duty machines that have long service lives. Their material of construction (Stainless Steel) provides corrosion resistance in corrosive processing applications.
These centrifuges have superior erosion protection in critical areas for enhanced wear protection. It is not uncommon for these dewatering machines to operate for decades without the need for replacement or even significant rebuilds.
Unlike belt and filter presses, centrifuges do not use any filter media, which is a significant benefit to these machines’ users. Also, this eliminates the labor cost related to media replacement.
The only operational expense associated with centrifuges is for maintenance. The only parts that need occasional replacement are the bearings because a decanter has fewer moving parts than filter presses.
Most sludge-thickening and dewatering centrifuges are fully automatic. The control systems have built-in sensors that have self-correcting features to allow operator-free processing.
Other methods mentioned above need manual service to replace media or perform other periodic functions.
Centrifuges are compact when compared to other dewatering equipment. For equivalent capacity, a decanter footprint is often a fraction of other comparable machines. This small size makes them a viable option for wastewater de-sludging in confined areas in treatment plants.
The centrifuge equipment’s compact size means that its location can be changed or moved to the worksite for ease of use and flexibility.
Centrifuge specifications and sizing are highly dependent on the manufacturer and the customer’s capacity throughput requirements. Listed below are some specific technical details and sizes of the commonly used dewatering separators from Alfa Laval.
|Manufacturer||Alfa Laval Decanter|
|Rated Capacity||170 GPM||80 GPM|
|Capacity on Wastewater with 5% Sludge||100 GPM||40 GPM|
|Capacity on Wastewater with 10% Sludge||60 GPM||25 GPM|
|Motor Power||20 ~ 25 HP||10 ~ 15 HP|
|Weight||4,000 Lbs||2,500 Lbs|
|Size / Dimensions||3′ x 10′ x 4′ (H)||3′ x 8′ x 4′ (H)|
|Material of Construction (MOC)||316L Stainless Steel||316L Stainless Steel|
|Wear Protection – Auger||Tungsten Carbide Hard Surfaced Auger||Tungsten Carbide Hard Surfaced Auger|
|Wear Protection – Sludge Ports||Stellite Bushings||Stellite Bushings|
|Wear Protection – Inlet Feed Zone||Hard Surface or Stellite Insert||Hard Surface or Stellite Insert|
|Manufacturer||Alfa Laval Separator|
|Type||Hi-Speed; Disc-Stack; Self-Cleaning|
|Efficiency||Solids Particles down to 0.5 µ|
|Rated Capacity||100 GPM||20 GPM|
|Capacity with 5% Sludge (Max.)||80 GPM||15 GPM|
|Motor Power||15 HP||5 HP|
|Skid Weight||4,000 Lbs||2,500 Lbs|
|Size / Dimensions||6′ x 7′ x 7′ (H)||4′ x 5′ x 6′ (H)|
|Bowl Material of Construction (MOC)||316L SS w/ Some Red Metal Parts|
|Disc Stack Configurations||2-Phase or 3-Phase|
|Control System||Fully Automatic PLC & Touchscreen|
Dolphin Centrifuge has supplied industrial decanter and disc-stack clarifiers for a wide range of wastewater applications. Some of these applications are listed below.
A small municipality in the mid-west needed a sludge-thickener for their sewage treatment operation. Dolphin Centrifuge supplied an Alfa Laval NX-418B-31 Decanter centrifuge with Chemical Dosing attachment. Municipal sewage dewatering is a common application and the decanter works as expected to produce dry cake minimizing disposal costs.
Dolphin Centrifuge carries a range of Alfa Laval wastewater centrifuges in stock. The following are the various models available for the three types of wastewater centrifuges with additional options.
|Alfa Laval NX 418B-31G||20 to 100 GPM||Feed Pump w/ VFD Control & Torque Lock|
Fluid Tank w/ Level Sensor & Pump
Sludge Auger w/ Motor & Gear Reducer
Bearing Temp. Monitoring System
Automatic Back-Drive Control System
|Alfa Laval NX 314 B-31G||3 to 40 GPM|
|Sharples P 3400||20 to 100 GPM|
|Sharples P 3000||3 to 40 GPM|
|Alfa Laval MOPX 213|
|Up to 80 GPM||Feed Pump w/ VFD Control|
Sludge Tank w/ Sludge Pump
Clean Fluid Tank w/ Return Pump
Pre & Post Duplex Filters
Flow-Meter w/ Auto Pump Control
|Alfa Laval WHPX 405|
|Up to 15 GPM|