Guest Column | November 27, 2017

WWEMA Window: Grit Removal — Anticipating Future Challenges And Equipment Selection

By Adam Neumayer, Hydro International

ScrewPumps

Plant processes are interdependent, and all existing and future processes should be considered when making design decisions. Grit, for example, is a significant cause of unforeseen maintenance costs and lower-than-expected performance and capacity. Effectively removing grit keeps the entire plant operating at the intended design capacity and helps ensure long-term, reliable performance.

Why Remove Grit?

Wastewater grit should be taken seriously. If allowed to enter a plant, it has detrimental long-term effects throughout the plant. Grit abrades operationally critical technologies and can smother processes such as aeration basins, which significantly increases runtime and energy use. When effectively designed and implemented, headworks grit removal extends the life and preserves the capacity of many downstream processes.  

Grit-related maintenance costs can be the downfall of a project.
Plant designers, operators, and owners need to think about the impact of grit at the early stages of any plant design or upgrade. If overlooked, challenges rapidly become apparent in increased maintenance costs and parts replacement. Grit settling in tanks can result in tons of material hidden beneath the surface. Removing these deposits requires draining down the tank and is difficult, labor-intensive, time-consuming, and expensive.

The impacts of a high peak-to-average flow ratio.
Peak flows can significantly increase the amount of grit that enters a plant. The wider the range from average to peak, the higher the grit load is likely to be. This can be significant in combined sewer oveflow (CSO) systems. Elevated flow surges will scour large quantities of grit deposited throughout the collection system into a facility. Specifying a system with appropriate solids handling capacity is critical when peak flow hits a facility. 

Design to minimize maintenance.
Unforeseen maintenance costs can quickly become apparent after a grit system that was not designed to match the site-specific behavior of the material is brought online. Finer grit particles are the easiest to overlook but can be the most insidious given grit’s abrasive potential. Plant designers will be well served to understand the nature of the site-specific grit as it relates to the complete facility design. Grit-related maintenance tasks often show up in surprising ways and can be a real challenge for operators for years to come. Combining a clear understanding of the material to be removed with a grit system’s operating efficiency and performance can create a robust and resilient process.

What Can Be Done To Prevent Grit?

The good news is that grit can be controlled. Removing it in the headworks before it enters downstream processes is often the most efficient and effective way. A clear understanding of the behavior of the material entering the plant combined with downstream process sensitivities, facility maintenance goals, and overall plant performance should all be at the forefront of equipment selection decisions. Selecting a grit removal system to match site-specific needs and the plant’s existing and future downstream processes is a sure path to reduce operational costs and challenges.

WWEMA Can Help

The Water and Wastewater Equipment Manufacturer’s Association (WWEMA) is a group of some of the best and most knowledgeable technology providers in the industry.  WWEMA’s mission is to inform, educate, and provide leadership on issues affecting the worldwide water and wastewater equipment industry. Whether you are searching for the right grit-removal system or another wastewater technology, WWEMA can help you find solution providers who bring quality, value, and the knowledge necessary to solve important challenges.

Adam Neumayer, PE, is Managing Director for Hydro International’s Wastewater Division located in Hillsboro, OR. He is a member of the Water and Wastewater Equipment Manufacturers Association (WWEMA) Board of Directors. For more information about WWEMA, go to www.wwema.org

Image credit: "Screw pumps and solar wall," Jason Turgeon, 2014, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/