GRAVER LAMELLA CLARIFIER
INTRODUCTION TO WASTEWATER CLARIFICATION
New England Sales is proud to represent the Graver Lamella Clarifier in the 6 New England Sales and Upstate New York. By way of introduction, a lamella type clarifier consists of a number of inclined surfaces in the form of plates. The settling surface area of each plate is equivalent to its horizontal projection. Since the lamella plates are normally spaced two inches apart, a relatively large projected settling area (PSA) can be concentrated within a relatively small footprint. Stacking the inclined plates results in a clarifier having up to ten times the clarification area of a conventional circular clarifier occupying the same floor space. Put another way, a lamella requires 1/10 the space for the equivalent throughput.
CLARIFIER PRINCIPLES OF OPERATION
The lamella plates are stacked as shown above and divide the lamella tank into a multiplicity of integral sections or chambers. Only one side of each chamber (the top surface of a plate) provides a settling surface. The chemically preconditioned feed stream enters the lamella tank and transverses through bottomless distribution feed ducts along each side of the lamella plate housing(s). The mixed liquid/solids feed stream then enters each plate chamber near the bottom section of the plates and flows upward between them. As the feed stream moves upward, solids settle downward by descending a short
THE GRAVER LAMELLA CLARIFIER (CONT’D)
distance onto the surface area provided by the plates. The solids then continue to slide down the plate surfaces to a collection hopper. Of primary importance is the continued flow of clarified water up between the lamella plates, without entraining or impeding the descent of the already settled solids.
It is extremely important that the particles (i.e. solids) to be removed from the process stream be of a minimal size so they are able to “sink” under the forces of gravity. This assumes particle density is greater than the liquid portion of the stream. If not, it is vital that the constituents are transformed to obtain this property. Some constituents will naturally possess the ability to settle. Still other materials must be pretreated physically and/or chemically to promote the formation of a settleable mass. Additional pretreatment steps can further improve settling velocities by causing smaller individual particles to form larger masses, called floc. The formation of suitable floc directly impacts performance. Again, the material to be removed must be settleable, or the installation of a lamella clarifier will not bring about the desired results. Settling velocities for a particular stream are determined from experience or by bench scale testing representative samples.
The solids continue to move downward to the sludge collection area, undisturbed by the movement of the feed flow. The sludge is periodically removed for disposal or further treatment. It is important to remove liquid sludge regularly to prevent build up in the lamella plate area. The liquid sludge level is easily monitored by the operator, using sample valves to collect and visually inspect samples.
Since liquid sludge removal is important, the sludge collection area must also be designed with inclined walls to keep the liquid sludge moving to the point of discharge. An effective
arrangement for a majority of applications is in inverted pyramid type hopper in which all walls are sloped a minimum of 60° toward the discharge point. This eliminates the need for mechanical scraping mechanisms or internal collector piping that can clog or plug.
The hopper is also designed with a hold-up volume to allow liquid sludge to accumulate. This usually eliminates having to continuously operate the sludge blowdown system and results in higher dry solids concentrations. By accumulating sludge, the water is squeezed (compressed) from the liquid sludge, decreasing the daily volume of blowdown.
Whenever a higher dry solids concentration is desired or required, the lamella can be combined with a thickener, which replaces the sludge collection hopper. The thickener
THE GRAVER LAMELLA CLARIFIER (CONT’D)
slowly agitates the sludge to release a larger percentage of mechanically removable water while providing positive movement and removal.
Since the circular thickener section is an integral part of the lamella, the released water moves upward along with the clarified water, eliminating any decanting or repumping requirements. The thickener height and diameter are designed to maximize the dry concentration. The bottom floor is concentrically sloped to a center pit to ensure positive sludge removal.
Standard units can be manufactured for flows from 25 gpm up to 3000 gpm (5 to 680 m3/hr) and above, in single above-grade tanks, limited only by shipping requirements. One-piece prefabricated tanks are available in a range to process 1500 gpm (340 m3/hr) with 3000 ft2 (280 m2) of PESA. Larger units are also prefabricated and shipped knocked down in match-marked pieces for final fit-up and erection in the field. Optionally, a concrete tank design can be used with prefabricated internals to treat unlimited flow rates. If headroom is a problem, a standard unit can be customized into a “low profile” design by modifying the internals to change overall tank dimensions.
FEATURES & ADVANTAGES
Flow Entry - Inlet flow enters from the bottom of both sides of the lamella plates, thus maintaining distribution velocities at a minimum. This optimizes the hydraulic flow regime resulting in a higher projected “effective” surface area (PESA) through more efficient utilization of the available PSA.
Effluent Weir Take off - An adjustable weir launder is used to provide a level and more effective weir length than other designs. The weir is of the orifice type with orifices placed so that each plate is serviced by two orifices, one on each side of the plate. This insures uniform collection of the clarified effluent and thus higher quality.
Removable Plates - Individual plates in the GRAVER lamella are easily removable, even when the unit is in operation. This design permits a single operator to easily inspect, clean, or remove plates without the assistance of mechanical lifting devices, making the unit easier to maintain than competitive designs. This feature also offers the flexibility needed to handle changes in influent characteristics.
THE GRAVER LAMELLA CLARIFIER (CONT’D)
Hopper Arrangement - Several options are available for sludge storage. The standard arrangement is a four sided inverted pyramid hopper bottom with a structural steel support frame. A second option is to mount the lamella on top of a mechanical sludge thickener in order to achieve a higher solids concentration, while at the same time providing a large sludge storage volume.
AVAILABLE OPTIONS
Flash mix / flocculation tank with preselected mixers
Full FRP or stainless steel tank construction
Built on site concrete construction
Special lining and plate materials suitable for potable service
Integral mechanical sludge thickener
Access ladder and platform
Cover
Automatic desludging
Instrumentation and controls
Chemical feed equipment
THE GRAVER LAMELLA CLARIFIER
FOR MORE DETAILS PLEASE CONTACT US AT:
SALES@NEWENGLANDSALESINC.COM
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