A two-in-one unit from Schreiber removes grit and grease from wastewater streams in parallel channels, helping to protect downstream processes.
Grit in wastewater is a well-known nuisance that if not efficiently removed can damage downstream process equipment and cause maintenance headaches.
But grease can cause its own set of issues, such as by forming grease balls in aeration basins and clarifiers that have to be removed manually. A technology from Schreiber is designed to remove both grit and grease in adjoining channels.
The Grit & Grease system has an aerated channel where grit settles to the bottom and is pumped out, along with a parallel channel where grease floats to the surface and is skimmed off. Improvements to the system have enhanced reliability, reduced maintenance, and simplified programming of operations to adapt to specific treatment plant flows and grit characteristics.
Larry Willingham, director of sales processes, talked about the technology in an interview with Treatment Plant Operator.
TPO: What market need drove development of this technology?
Willingham: Grit is a nuisance component of wastewater that can cause abrasive wear on mechanical equipment. A combination of grit and grease becomes even more abrasive. Getting those components out early in the process benefits the operation and maintenance of a facility throughout its service life. A combined removal system is very beneficial.
You get both materials out, as opposed to neglecting the grease.
TPO: How does this system remove the grit efficiently?
Willingham: The primary component is an aerated grit chamber with a traveling bridge carrying a pump for removing grit that accumulates in the bottom trough. Our system differs from a conventional aerated grit chamber using a length-width ratio of 8-to-1 to 10-to-1, versus conventional units with a ratio of about 5-to-1. It has the typical design parameter of a three- to five-minute detention time, but the greater length means more opportunity to accumulate the grit on the floor of the basin.
TPO: Is the footprint about the same as for a conventional aerated grit basin?
Willingham: It’s narrower than a conventional chamber but also longer, and so the overall area is about the same.
TPO: What is the advantage of a grit channel that is aerated?
Willingham: Coarse-bubble diffusers run the length of the channel. We aerate very heavily at the influent end where the heaviest grit settles out. Organics are often bound up with the grit. The turbulence, the roll that we create with aeration, helps slough off the organic material from the grit and keep it in suspension. As the flow travels down the channel, we reduce the agitation so that the finer grit particles can settle out. The system is adaptable to a wide range of flows without deterioration of grit removal because it controls the aeration and agitation independent of the hydraulic flow.
TPO: How is the grit that settles removed from the system?
Willingham: A grit pump mounted to a traveling bridge lifts the collected grit to an elevated trough to transfer the grit slurry to a classifier for further washing and dewatering.
TPO: How does the system remove grease along with the grit?
Willingham: There are two separate linear channels. One is a deep channel where we settle the grit. Next to that a divider baffle wall protrudes just below the water surface and separates the two channels. The baffle wall keeps the turbulence in the aerated grit channel from transferring to the grease channel. The grease needs a quiescent area where it can float on the surface. The air rolls that agitates the grit and separates the organics also assists in floating the grease to the surface and to the other channel. The grease slips underneath the baffle wall and onto the surface of the grease channel, where we remove it with an air/water skimming mechanism.
TPO: How does the skimming mechanism function?
Willingham: The skimming system directs air or water onto the surface and transports the floating grease and scum to the far end of the channel. There it enters a screw conveyor that runs continuously and rotates very slowly, removing and dewatering the grease. Since the screw conveyor sits at an angle of about 20 degrees, the water drains back down into the structure, and we end up with relatively dry grease balls about an inch to an inch-and-a-half in diameter. The material is very easy to dispose of at a landfill because most of the water has been removed. The volume is reduced tremendously.
TPO: What are some of the latest upgrades to this technology?
Willingham: The mechanical drive systems have improved with direct-drive gearboxes. This and other modifications have reduced the time and resources needed to maintain and service the equipment. And a new bridge arrangement makes it much easier to access and retrieve the grit pump for servicing.
TPO: How much operator attention does this system require?
Willingham: The system is highly automated. Mainly, it just needs a periodic visual inspection. Operators have flexibility to use a touch screen to adjust the sequence time for grit pump operation based on the characteristics of the grit.