A lamella clarifier or inclined plate settler (IPS) is a type of clarifier designed to remove particulates from liquids.
Range of applications Lamella clarifiers can be used in a range of industries, including mining and metal finishing, as well as to treat groundwater, industrial process water and backwash from sand filters. Lamella clarifiers are ideal for applications where the solids loading is variable and the solids sizing is fine. They are more common than conventional clarifiers at many industrial sites, due to their smaller footprint. One specific application is pre-treatment for effluent entering membrane filters. Lamella clarifiers are considered one of the best options for pre-treatment ahead of ultrafiltration. Their all-steel design minimizes the chances that part of the inclined plate will chip off and be carried over into the membrane, especially compared to tube settlers, which are made of plastic. Further, lamella clarifiers may maintain the required water quality to the membrane with or without the use of chemicals. This is a cost-saving measure, both in purchasing chemicals and limiting damage to the membrane, as membranes do not work well with the large particles contained in flocculants and coagulants. Lamella clarifiers are also used in the municipal wastewater treatment processes. The most common wastewater application for lamella clarifiers is as part of the tertiary treatment stage. Lamella clarifiers can be integrated into the treatment process or stand-alone units can be used to increase the flow through existing water treatment plants. One option for integrating lamella clarifiers into existing plants is for conventional or sludge blanket clarifiers to be upgraded by attaching a bundle of inclined plates or tubes before the overflow in the so-called "clear water zone". This can increase the settling area by two-fold resulting in a decrease in the solids loading in the overflow.
Advantages and limitations The main advantage of lamella clarifiers over other clarifying systems is the large effective settling area caused by the use of inclined plates, which improves the operating conditions of the clarifiers in a number of ways. The unit is more compact usually requiring only 65-80 % of the area of clarifiers operating without inclined plates. Therefore, where site footprint constraints are of concern a lamella clarifier system is preferred. The reduced required area allows the possibility for the clarifiers to be located and operated inside, reducing some of the common problems of algae growth, clogging due to blowing debris accumulation and odour control, that occur when the machinery is outdoors. Operation within an enclosed space also allows for a better control of operating temperature and pressure conditions. The inclined plates mean the clarifier can operate with overflow rates 2 to 4 times that of traditional clarifiers which allow a greater influent flow rate and thus a more time efficient clarification process. Lamella clarifiers also offer a simple design without requiring the use of chemicals. They are therefore able to act as pre-treatment for delicate membrane processes. Where necessary flocculants may be added to promote efficiency. Lamella clarifier performance may be improved by the addition of flocculants and coagulants. These chemicals optimize the settling process and cause a higher purity of overflow water by ensuring all smaller solids are settled into the sludge underflow. A further advantage of the lamella clarifier is its distinct absence of mechanical, moving parts. The system therefore requires no energy input except for the influent pump and has a much lower propensity for mechanical failure than other clarifiers. This advantage extends to safety considerations when operating the plant. The absence of mechanical results in a safer working environment, with less possibility for injury. Whilst the lamella clarifier has overcome many difficulties encountered by the use of more traditional clarifiers, there are still some disadvantages involved with the configuration and running of the equipment. Lamella clarifiers are unable to treat most raw feed mixtures, which require some pre-treatment to remove materials that could decrease separation efficiency. The feed requires initial processing in advanced fine screening and grit and grease removal to ensure the influent mixture is of an appropriate composition. The layout of the clarifier creates extra turbulence as the water turns a corner from the feed to the inclined plates. This area of increased turbulence coincides with the sludge collection point and the flowing water can cause some re suspension of solids, whilst simultaneously diluting the sludge. This results in the need for further treatment to remove the excess moisture from the sludge. Clarifier inlets and discharge must be designed to distribute flow evenly. Regular maintenance is required as sludge flows down the inclined plates leaving them dirty. Regular cleaning helps prevent uneven flow distribution. Additionally, poorly maintained plates can cause uneven flow distribution and sacrifice the efficiency of the process. The closely packed plates make the cleaning difficult. However, removable and independently supported lamellar plates can be installed. Commercially available lamella clarifiers require different concrete basin geometry and structural support to conventional clarifications system widely used in industry, thus increasing the cost of installing a new (lamellar) clarification system.
Available designs Typical lamella clarifier design consists of a series of inclined plates inside a vessel, see first figure. The untreated feed water stream enters from the top of the vessel and flows down a feed channel underneath the inclined plates. Water then flows up inside the clarifier between the inclined plates. During this time solids settle onto the plates and eventually fall to the bottom of the vessel. The route a particle takes will be dependent upon the flow rate of the suspension and the settling rate of the particle and can be seen in the second figure. At the bottom of the vessel a hopper or funnel collects these particles as sludge. Sludge may be continuously or intermittently discharged. Above the inclined plates all particles have settled and clarified water is produced which is drawn off into an outlet channel. The clarified water exits the system in an outlet stream.
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