Inclined Plate Clarifier Design and Sizing Procedure
Inclined plate clarifiers are typically considered very simple devices. However, several factors that could potentially affect safety, efficiency, and proper management must be given careful consideration prior to the installation or modification of any clarifier or clarification system:
- Flow Rate
In general, clarifiers are sized by the flow rate verses the separation chambers “effective” surface area (or, as it is more commonly called. the “projected” surface area). Therefore, the effectiveness of any clarifier is affected by the flow rate. The slower the flow, the better the results.
- Design Capacity
A clarifier has upper limits to the amounts of suspended solids that can effectively accumulate while it is in operation. If too much “sludge” or settled suspended solids accumulate on the plates, it may carry over into the wastewater outlet chamber and end up being discharged to the environment. Proper clarifier design will take the plate spacing into consideration and also allow for the removal and storage of accumulated sludge from the clarifier to ensure that the accumulated products do not effect the operation of the clarifier.
- Maintenance Practices
The ability of any clarifier to function properly depends upon the timely performance of required service and maintenance. Clarifiers must be monitored and maintained by competent personnel who understand how the systems operate. Clarifiers should be given the same close attention shown to any other important piece of equipment. The operators, users, and maintainers of the clarifier must be clear on who will be responsible for monitoring, inspecting, maintaining, and servicing the system. Frequent inspections should be made of the system and all associated piping, valves, etc. to prevent operational and mechanical failures or inefficiencies. Sludge needs to be regularly removed from the clarifier to keep it operating properly. Additionally, leaks from clarifiers can result in environmental pollution, which can trigger costly investigative studies and cleanups. Rigorous implementation of a clarifier inspection and maintenance plan can prevent discharges from the clarifier that may contaminate the environment.
- Suitability of Inclined Plate Clarifier System to Process
A clarifier designed and installed to meet a past process requirement may no longer be suitable when process requirements change and/or the original maintenance plan is no longer followed. A clarifier that is put to a use for which it was not originally designed may be damaged or may not function properly, and could become an environmental liability. For example, a clarifier designed to receive the wastewater discharge from a small heavy metal precipitation system will not be able to properly treat larger wastewater volumes for removing chrome from a tannery effluent. Process changes can also result in changes to the physical/chemical makeup of the wastewater being treated by a clarifier.
- Contaminants Contained in the Wastewater Stream
Metallic particles in the wastewater will settle into the sludge at the bottom of the clarifier. Solvents or fuel compounds may also be entrained in the clarifier’s sludge. This sludge could require management under the Resource Conservation and Recovery Act (RCRA) as a hazardous waste, if it exhibits certain toxicity characteristics. Therefore, it is important to prohibit the discharge of certain types of potential contaminants into a clarifier, and to regularly analyze sludge samples to determine toxicity prior to disposal. General improvements in spill/drip control and containment of hazardous materials and solvents will also reduce the amount of contamination in clarifier discharges.
Determining the hydraulic loading ratio required to meet your effluent requirements (ppm, mg/l) is an important step in the design and sizing of any clarification system. A small change in the hydraulic loading ratio can result in a large change in the size of the specified clarifier. For example look at the following spreadsheets.
The only change in the above spreadsheets was the “Hydraulic Loading Ratio”. All other variables remain the same.
On the first spreadsheet the “Hydraulic Loading Ratio” was input at .25. On the second spreadsheet the “Hydraulic Loading Ratio” was input at .40. You will note that the model #’s (which represent the total cubic feet of media required) changed from a high of 139 cubic feet to a low of 74 cubic feet. That is a 46% change in the total size of the separator.
Both examples are suitable for 100 gallons per minute. Both examples will remove the targeted suspended solid. The real world difference between all the listed clarifiers is overall clarifier efficiency.
This example should reinforce the importance of accurately conducting the “Test for Determination of Clarifier Hydraulic Loading Ratio” and the “Clarifier Settling Rate” studies. If you size a clarifier without knowing the target “Hydraulic Loading Ratio”, you will have to greatly over size the clarifier, because erring on the safe side, you will have to size the clarifier for maximum efficiency.
Inputting the Accumulated Data to the HydroFlo Clarifier Sizing Spreadsheet to Accurately Size a Clarifier or Clarification System for Your Application
The final step is to insert the data into the “Stinger Clarifier Sizing Spreadsheet“.
If you go to ten different clarifier manufacturers and ask them to size a clarifier for a specific application (even when giving them a written specification), you will get ten different answers. Everyone bases the efficiency of their clarifier on their clarifier’s projected surface area. But, other design variables are all over the map. Plate spacing will vary from 3/4″ to 2″, and more. The angles and configurations of the plates are vastly different from manufacturer to manufacturer. Overall clarifier volume, from the largest to the smallest designs, can fluctuate as much as 150%, or more.
When comparing one manufacturer to another, it is best to compare the volume of the separation chamber (or size of the plate pack) in cubic feet verses the sell price. This ratio should give you the clarifiers cost per cubic foot of plate pack. This is important because the physical size of the clarifier is the greatest factor in the cost, as well as the efficiency, of the device. The published projected surface area has a much smaller impact on the clarifier’s overall cost and performance.