The Lamella Clarifier

Cross-flow lamellar clarification is a technology used in industrial environments to remove oils and solids from residual water. It takes advantage of the natural tendency of oils to float, and the decantation principle for suspended solids that are denser than water. The originality of this process is the combination of natural flotation and clarification techniques in one system. The strip decanter performs as well as conventional clarifiers, but is more compact and occupies a smaller area. The process is mainly used for dealing with oils and grease present in residual liquids emanating from industrial activities in the petrochemical, chemical, mechanical, metallurgical and food-processing sectors. Depending on the specific design criteria (available space, quantity and quality of water to be treated, structural and hydraulic constraints, budget limits and need for mobility), the equipment can be housed in a circular or rectangular reservoir, or can consist of mechanical components attached to a below-grade concrete tank. If the oils are partially or completely emulsified, the cross-flow lamellar clarifier can be equipped with a coalescer, which uses a physical process to trigger separation of the oil and water phases. The coalescer is filled with various elements (rings, plastics, honeycombs, other appropriate materials ...) which maximize the potential contact surface. The accretion of microglobules to these elements leads to phase separation. System performance depends on the specific nature of the effluent to be treated and varies according to the type of industry. Depending on the particular situation, removal of free oils and greases, and of suspended solids, varies from 90 to 99%. With no chemical amendment (i.e. demulsifying agent), 20-40% removal of emulsified oils and greases can be achieved. The addition of an agent enables the process to achieve 50-99% removal, depending on the application.

This technology is designed to handle effluents containing a maximum of 10,000

mg/1 of grease, and 3,000 mg/1 of solids. Hydraulic load is not a limiting factor. The cross-flow lamellar clarifier consists of the following basic units: primary screening chamber, separator plate cell, sludge silo, oil and grease storage chamber. First, water is pretreated in the primary screening chamber to remove part of the floating oil and grease and to allow sedimentation of large solid particles (> 500mm). Then the effluent feeds through the plate cell where separation of phases is accomplished as follows: oils are deflected upwards by the plates to form a film on the surface of the water, sludges settle to the bottom and the purified water flows horizontally to the reservoir outlet. Before leaving the system, water passes through a calibrated opening which controls the unit's hydraulic load. Sludges are recovered in a conical extraction silo which aids their compaction and provides easier handling. Dryness rates of 1 to 5% are achieved depending on sludge type. The sludge is kept apart from water to be treated, so as not to draw it back into the process flow. Floating oils are recovered from the water surface and channeled into a storage reservoir located beneath the sludge silo. Equipment installation and start-up take less than a week. Running the system requires no energy input except for the effluent pump. Maintenance is limited to monthly testing, and cleaning of the separator plates once every six months. If needed, various products (polymers, demulsifiers and coagulants) can be added to the process to improve its performance. Running the system requires no special safety measures. If required, the equipment can be designed to provide a safe environment for treating effluents containing volatile compounds with risk of explosion.

Various parameters are taken into account in designing a cross-flow lamellar clarifier. These include:

• suspended matter load;

• hydrocarbon load;

• desired performance;

• space available for clarifier's installation.

The investment required to set up a treatment unit complete with coalescer varies from $750 to $2,500 per cubic meter of water to be treated, depending on unit size and available space. Operating costs are low.

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