Jacopa® Crossflow™ Grit Treatment

The Jones+Attwood Crossflow™ Detritor™ grit separator is used at raw sewage inlets, and should ideally be positioned downstream from sewage screens. This type of grit removal system has two key elements, a) grit-collecting mechanism and b) grit-classifying mechanism. Both elements operating separately, but in hydraulic connection with one another.

The Crossflow™ grit separator is used at raw sewage inlets, and should be positioned downstream from sewage screens. These screens require medium to fine spaces. Where two stage screening is applied, the Crossflow™ unit can be installed after the medium spaced screen, thus protecting the fine screening mechanism from abrasive detritus. The collection tank is a wide, shallow, square proportioned channel. The inlet channel is near parallel to the inlet side of the tank, and has a series of vertical baffles to assist the distribution of flow entering the collection tank. The Jones + Attwood™ chamber design enhances flow equalization across the chamber.

The Detritors removal efficiency shall be 95% for grit particles > 200 micron with a SG of 2.65 whilst the incoming flow rate remains at or below the specified flow rate.

Flow is in a single direction across the tank to the outlet side. The outlet is a sharp edged weir, which has a drowned discharge during higher flow rates. The normal form of hydraulic control is a Standing Wave Flume. This doubles as the means of flow measurement. The characteristics of the flume are ideal to control the critical crossflow velocities within the trap. The flume has to be positioned downstream of the Crossflow™ chamber. This design forms a recessed, circular sump. This has a diameter equivalent to the length of the square sides of the tank. The level floor of this sump is the bed upon which the grit and other similar solids will settle. This accumulation of solids is collected and transported by a slowly rotating scraper mechanism supported on the bridge spanning the tank. The collected solids are delivered to a hopper on the periphery of the tank. From here the grit is separated and dewatered by a Classifier. Various grit classification methods are available, and are selected by preference, site limitations and, in some instances, the effectiveness of the primary screening. Operation is most efficient when velocity is maintained at a specific value over the whole range of flow. At this velocity, grits of the specified size and specific gravity will be collected. Sizing, positioning and hydraulic control are of the utmost importance.

Grit classification separates, as far as possible, any other solids present with the grit at the point of collection. It is also the means by which the grit is dewatered, thus providing a suitable product for disposal. Jones + Attwood™ have developed a number of grit classifying methods, all of which can be applied to the Crossflow™ grit removal system. Sewage and sewer systems vary to such an extent that design flexibility is essential. The options provided allow for: variations in screening, the height and depth of the installation, and the point of dewatered grit collection

Key Features & Benefits:

• Classification for floating solids, settled solids and liquids
• Mild steel coated or stainless steel construction
• Free standing unit can be located next to collection container for disposal
• Suitable for most grit removal systems
• Auto-lubrication
• Automatic operation
• Standardized equipment for tanks up to 12.0m diameter
• Wide selection of grit handling methods available
• Flexibility of automatic and hand controls

 

Jacopa will provide a design solution that we consider offers the best valued solution to the purchaser based on over 50 years of experience of this type of plant.