Grit Washing Plants

Q: "Why is grit washing needed?"

"In municipal wastewater treatment, grit is separated in a grit trap. This separation takes place by sedimentation, i.e. the grit settles in the grit chamber after sufficient retention time. However, since there are not only mineral substances such as grit in the wastewater, but also many organic solids, these also settle to a greater or lesser extent. As a result, when the grit is discharged from the grit chamber, it sometimes contains a large amount of organic solids. This contamination of the grit with organic matter hinders, among other things, cost-effective landfilling or reuse of the grit.\r\nGrit washing with a HUBER Grit Washer RoSF4 solves this problem and produces clean grit with an organic content of less than 3% loss on ignition, the HUBER Grit Washer RoSF G4E reduces the organic content to \u2264 5%."

Q: "What are the characteristics of a good grit washing system?"

"A good grit washing system is characterised by its ability to wash out the organic substances in the grit so that the loss on ignition in the washed grit is < 3%. In addition to the effective separation of organic and mineral components, the retention of fine sands is also decisive in practice, which is taken into account in the design of HUBER Grit Washing Plants."

Q: "Can sewer grit be washed together with sewage treatment plant grit?"

"HUBER has solutions for the processing of sewer grit and grit from sewage treatment plants as well as road sweepings. Depending on the quantities and composition of the material to be processed as well as other general conditions, we design a tailor-made HUBER solution for grit treatment."

Q: "Why should subsequent grit washing be implemented after grit separation?"

"Conventional grit classifiers separate virtually all solids contained in the grit trap effluent. This classified and partly dewatered grit is usually more or less contaminated with organic particles. With further treatment in a subsequent grit washer, the organics are separated from the mineral particles."

Q: "What is the difference between a grit washer and a grit classifier?"

"Both the grit washer and the grit classifier are fed with a grit-water mix. In the machine, the grit is separated from the water.\r\nIn contrast to the grit classifier, the grit washer is able to wash the separated grit. This means that the separated grit is freed from organic components as far as possible. The grit washer thus produces grit that is almost free of organic matter, whereas the separated grit in the grit classifier may contain a considerable amount of organic matter."

Q: "What is the advantage of classification with simultaneous grit washing compared to simple classification?"

"Due to the additional washing, the organic content in the discharged grit can be guaranteed below 3%. This leads to possible lower disposal costs and volumes."

Separation of organics from the mineral particles.

The clean grit is removed through a classifying screw, statically dewatered and discharged into a container.

Grit from grit traps of wastewater treatment plants

The grit contained in the wastewater is usually removed in grit traps by gravity or centrifugal force to protect downstream equipment. Various different grit trap systems are available for this purpose which however separate not only the grit but frequently also many of the organic particles, dependent upon the hydraulic load (inflow). The separated particles are then pumped from the grit trap to a grit classifying unit (screw or pilgrim step classifier) which remove the solids from the flow without any differentiation. As a result, the loss on ignition of the classified grit trap material varies from 10 % to 80 % depending on the screen bar spacing and inflow. The water content of the grit trap material is accordingly high (50 - 80 %). The result are inevitably high costs for removal, transport and disposal, and in addition very bad hygienic conditions.

Grit from sewer systems, gully waste, road refuse

These raw materials are more or less contaminated with organics (sludge, leaves, etc.), but they contain also foreign matter that is similar to domestic waste (such as cans, screenings, stones, etc.), and a considerable amount of water. Additionally, the individual raw materials (grit, organics, foreign matter) vary seasonally so that their loss on ignition will range from 5 % to 80 % and their water content from 40 % to 90 %. This results in inevitably high costs for dewatering, removal, transport and disposal.

FAQ

Frequently Asked Questions

In municipal wastewater treatment, grit is separated in a grit trap. This separation takes place by sedimentation, i.e. the grit settles in the grit chamber after sufficient retention time. However, since there are not only mineral substances such as grit in the wastewater, but also many organic solids, these also settle to a greater or lesser extent. As a result, when the grit is discharged from the grit chamber, it sometimes contains a large amount of organic solids. This contamination of the grit with organic matter hinders, among other things, cost-effective landfilling or reuse of the grit.

Grit washing with a HUBER Grit Washer RoSF4 solves this problem and produces clean grit with an organic content of less than 3% loss on ignition, the HUBER Grit Washer RoSF G4E reduces the organic content to ≤ 5%.

A good grit washing system is characterised by its ability to wash out the organic substances in the grit so that the loss on ignition in the washed grit is < 3%. In addition to the effective separation of organic and mineral components, the retention of fine sands is also decisive in practice, which is taken into account in the design of HUBER Grit Washing Plants.

HUBER has solutions for the processing of sewer grit and grit from sewage treatment plants as well as road sweepings. Depending on the quantities and composition of the material to be processed as well as other general conditions, we design a tailor-made HUBER solution for grit treatment.

Conventional grit classifiers separate virtually all solids contained in the grit trap effluent. This classified and partly dewatered grit is usually more or less contaminated with organic particles. With further treatment in a subsequent grit washer, the organics are separated from the mineral particles.

Both the grit washer and the grit classifier are fed with a grit-water mix. In the machine, the grit is separated from the water.

In contrast to the grit classifier, the grit washer is able to wash the separated grit. This means that the separated grit is freed from organic components as far as possible. The grit washer thus produces grit that is almost free of organic matter, whereas the separated grit in the grit classifier may contain a considerable amount of organic matter.

Due to the additional washing, the organic content in the discharged grit can be guaranteed below 3%. This leads to possible lower disposal costs and volumes.