New and Innovative Design of a Grit Chamber for Applications in Municipal Wastewater Treatment

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A crucial first step in the treatment of wastewater is the removal of inorganic grit from the influent to the wastewater treatment plant (WWTP). In Canada, WWTPs often use aerated grit chambers for grit removal and this requires the creation of two dissimilar flows in the same chamber. An energetic turbulent flow is required to separate organic coatings from the heavy inorganic grit particles, and a quiescent flow is required to allow settling of the grit particles. Generating these dissimilar flow conditions in the same chamber is very difficult in terms of both the design and operation. This problem can be solved by performing the two functions in separate chambers, which would be more efficient and cost effective than existing aerated grit chambers. In Canada, there are many WWTPs that have been upgraded to meet national effluent standards by the addition of secondary and tertiary treatment processes but with no modification of their grit removal systems. Therefore, upgrades to existing grit removal systems are urgently needed if WWTPs are to be able to cope with the increasingly large amounts of fat, oil and grease (FOG) and grit, associated with the growth of cities and industry. The proposed NSERC CRD Program will develop an innovative grit chamber design that will be more efficient and have larger capacity than existing grit chambers. The addition of a pre-mixing chamber equipped with cross-jets is proposed that will effectively separate FOG from grit and this cleaned grit can then be removed more efficiently in a downstream settling chamber. Pilot-scale experiments will be conducted to determine the cross-jet configuration and operating conditions that produce large dispersion numbers in the pre-mixing chamber as well as to determine the operating conditions that produce large absolute velocity gradients and homogeneous flow fields. Moreover, experiments at the Gold Bar WWTP will be performed to determine if the new grit removal system operates effectively when processing real wastewater. The proposed research results can be directly applied to existing Canadian WWTPs to improve grit removal efficiency and enhance the entire wastewater treatment process.