Grit Removal Systems

Screening is typically the first stage of wastewater treatment, where large solids are removed from the wastewater stream to prevent operational problems in downstream treatment processes.

The next stage involves removing smaller heavy inorganic particles such as sand, grit, gravel, and fine glass particles. If these materials are not removed, they can cause abrasion and damage to pumps and other mechanical equipment. Grit can also accumulate in pipe bends, channels, and other low-velocity areas, reducing hydraulic capacity and potentially causing blockages in wastewater conveyance systems.

Grit removal tanks are designed to reduce the wastewater velocity sufficiently to allow heavy inorganic particles to settle while keeping lighter organic solids in suspension.

Types of Grit Removal Systems

Three common types of grit removal systems are used in wastewater treatment plants:

Gravity Grit Chambers

Gravity grit chambers are designed to maintain an optimum wastewater velocity that allows most grit particles to settle at the bottom of the chamber while lighter organic solids remain suspended.

The chamber dimensions and hydraulic conditions are selected according to the required flow rate and particle removal performance.

Aerated Grit Chambers

Aerated grit chambers are typically long, deep, and relatively narrow tanks equipped with coarse-bubble diffusers.

Air is introduced into the chamber to create a controlled circulation pattern that helps separate grit from lighter organic solids. Aerated grit chambers are commonly used in larger wastewater treatment plants and can be equipped with mechanical grit collection systems.

Vortex Grit Removal Systems

Vortex-type grit removal systems, such as Pista and Jetta configurations, use controlled circular flow patterns inside a mechanically designed chamber to separate grit from wastewater.

The generated vortex promotes the settling and collection of heavy inorganic particles while allowing lighter organic matter to remain in suspension.

Mojan Reciprocating Bridge Grit Collection System

Mojan equips grit removal chambers with reciprocating bridge systems designed for efficient collection of settled grit and floating scum.

The bridge travels back and forth along the walls of the concrete grit chamber using two carriage assemblies. The reciprocating bridge is equipped with grit collection paddles and surface scum skimmers.

During the forward movement of the bridge, floating scum and grease accumulated on the water surface are collected by the surface skimmer and transferred to a dedicated scum collection tank located near the chamber wall.

During the return movement, settled grit is collected by the grit collection paddles and directed toward the grit hopper.

The collected grit is then transferred to a grit washing and dewatering unit. The washing process removes organic matter attached to the collected grit, helping improve grit quality and allowing the separated organic material to return to the wastewater treatment process.

Deep Aeration System

Mojan grit collection systems can be equipped with a deep aeration system.

Controlled air injection inside the grit chamber helps prevent relatively light organic particles from settling together with the heavier grit. Aeration also helps reduce the formation of unpleasant odors within the grit removal unit.

This combination of mechanical collection and controlled aeration improves the separation between inorganic grit and organic solids.

Main Components

A typical Mojan reciprocating bridge grit removal system may include:

• Reciprocating bridge
• Bridge carriage assemblies
• Grit collection paddles
• Surface scum skimmer
• Grit collection hopper
• Scum collection tank
• Grit washing and dewatering system
• Deep aeration system
• Coarse-bubble air diffusers
• Drive and control system
• Supporting and guide structures

The exact configuration is selected according to the chamber dimensions, wastewater flow rate, grit characteristics, and project requirements.

Key Features

• Effective separation of solid and liquid phases
• Efficient removal of sand, grit, and heavy inorganic particles
• Integrated grit and surface scum collection
• Low energy consumption
• Economical design
• Low maintenance requirements
• Simple installation
• Long service life
• Controlled aeration for improved grit separation
• Reduced accumulation of organic matter with collected grit
• Suitable for municipal and industrial wastewater treatment plants

Applications

Mojan Grit Removal Systems are suitable for:

• Municipal wastewater treatment plants
• Industrial wastewater treatment plants
• Preliminary wastewater treatment
• Grit and sand removal
• Protection of pumps and mechanical equipment
• Large and medium-capacity wastewater treatment facilities
• Systems requiring integrated grit and scum collection

Customized Design by Mojan

Mojan designs grit removal and collection systems according to the hydraulic and operational requirements of each wastewater treatment project.

Design considerations may include:

• Design and peak wastewater flow
• Grit particle characteristics
• Required grit removal efficiency
• Grit chamber dimensions
• Hydraulic retention conditions
• Aeration requirements
• Grit collection method
• Scum collection requirements
• Grit washing and dewatering requirements
• Site and installation conditions

The resulting system provides efficient grit separation, reliable collection, reduced equipment wear, and improved overall performance of downstream wastewater treatment processes.