Grit Samplers​

4. Slotted Dual pipe vertically Integrated sampler (VIS)

The most recent version of our VIS is the front slot, dual pipe vertical sampler.  This style of sampler allows the user to sample the entire height of the water column, similar to the pipe-in-a-pipe design but is lighter, stiffer, and narrower.  The combination of lighter and smaller allows us to get the sampler into the narrower channels and deeper channels, but not lose the ability to sample the entire height. The front pipe serves as the slotted pipe and is connected to the rear via a U-trap that funnels all flow into the suction pipe.  This design is cleaner, simpler, and easily modified to fit each particular application.  The bottom cap is also slotted to the center of the cap to allow any grit moving along the bottom of the channel to be sampled.  The slot is designed to collect a sample from the entire height of the water column.  The width of the slot is designed to allow flow to enter at the same speed as the wastewater is moving in the channel.  If we know the plant flow, and we know the width and height of the water column, and the sampling pump speed, we can estimate the slot width. Because the flows will likely change throughout the study,  a slot is created that is thinner than we need.  This allows adjustments to be made to the flow entering the sampler by increasing or decreasing the pump speed.  The sampler is lowered to the bottom of the channel and secured, and the suction pipe is attached to a trash pump with a suction hose.  The sampler can be moved side-to-side to collect a sample from the entire area of the water column if need be.

This is by far our most universal, and most successful version of the sampler to date!  

Pros: - moderately easy to build.  Collects a more representative sample that the siphon tube.  Allows for the use of a single grit settler and a single sample to be collected.

Cons: - channel access may prevent a VIS from being installed, although they may be scaled down to fit behind gates.  A deep or fast waste stream requires a thin slot that may become plugged with rags, requiring periodic cleaning. Because the suction pipe is close to the bottom, the sample may be biased towards the bottom.

 2. Multi-Siphon Tubes

Several siphon tubes are secured at different elevations within the water column. Each tube is feeding a dedicated grit settler.  The entire rack is moved periodically from side-to-side, capturing grit from the entire width of the water column.

Pros: -  Provides a more complete profile across the height and width of the channel. Having separate grit settlers allows for a profile to be created for different levels in the channel.

1. Single-Siphon Tubes

A siphon tube is constructed of a length of one-inch tubing with an elbow at the end which faces into the flow of the waste stream.  The tube is secured in the waste stream, attached to a length of flexible hose which is dropped off the side of the structure, and backfilled with water.  Once the water is released, a siphon is created that sucks wastewater through the pipe and hose and feeds a grit settler. The apparatus is periodically raised and lowered and moved side-to-side to sample the entire area of the water column.  In instances where there is insufficient elevation to create a siphon, a pump may be used.

Cons: - having multiple settlers is difficult to maintain.  Because flow rates need to be periodically monitored, and each setup requires hosing and associated hardware, it is difficult to manage.  For example, a performance evaluation will require an influent and effluent setup. Assuming three levels are to be sampled, a total of six siphon tubes and six settlers will be needed.  Additionally, total performance will require "weighting" the concentrations for each level sampled because it is likely that each of the six settlers will produce slightly different feed rates.

3. Vertically Integrated Sampler (VIS) (Pipe in a Pipe)

A Vertically Integrated Sampler (VIS) is created by cutting a slot along the length of a four-inch piece of PVC pipe, capping the bottom, and inserting a length of two-inch pipe into the larger pipe.  The small pipe serves as the suction pipe and is secured two-inches from the bottom of the slotted pipe.  The cap is also slotted to the center of the cap to allow any grit moving along the bottom of the channel to be sampled.  The slot is designed to collect a sample from the entire height of the water column.  The width of the slot is designed to allow flow to enter at the same speed as the wastewater is moving in the channel.  If we know the plant flow, and we know the width and height of the water column, and the sampling pump speed, we can estimate the slot width. Because the flows will likely change throughout the study,  a slot is created that is thinner than we need.  This allows adjustments to be made to the flow entering the sampler by increasing or decreasing the pump speed.  The sampler is lowered to the bottom of the channel and secured, and the suction pipe is attached to a trash pump with a suction hose.  The sampler can be moved side-to-side to collect a sample from the entire area of the water column.

Pros: - Easy and cheap.  Their small size allows them to be slipped behind gates when channel access is limited.

Cons: - Only samples a single point at any given time.  Because the concentration of grit varies depending on the time of day (i.e. peak daily                 flow events), the single-point siphon tube will likely miss  "slugs" of grit that occur.

          - Utilizes a smaller one-inch sampling area so clogging is more pronounced.