Removing Solids from the Waste Stream

Question:

We have several vibratory finishing machines using a fast cutting ceramic media. Each machine has its own settling tank, and inattention to the tanks leads to slurry build-up in the floor drains. This is a very expensive problem, often involving outside contractors. Is there some way to automate the cleaning of the settling tanks, perhaps using a drag conveyor or similar device? B.E.

Answer:

I don’t know of any successful installation for automating the cleanout of individual settling tanks. The answers to this problem are expensive and eliminate settling tanks. What you do depends upon the size and proximity of the machines to each other. One consideration is to put a small centrifuge at each location. A centrifuge is basically a high-speed settling tank. Set up the centrifuge to re-processes the effluent many times. This is easy, since even a small centrifuge can process many times the fluid requirement of even the largest mass finishing machine. The fines are compressed by centrifugal force into a semi-dry cake that can usually be disposed of as non-hazardous waste. Before sending the effluent to drain, pass it through a final filter to prevent the remaining small fines from settling in the drain lines.

If it is practical to pump all the effluent to a central location, a centrifuge system can handle all the effluent. A final filter before going to drain should follow this.

An alternative method for central treatment of the effluent is to use a flocculating system. A filter press, or continuous filter, usually follows this prior to going to drain. Flocculating has a lower initial investment than a centrifuge, but the semi-solid residue is not as convenient. If a filter press is in the system, the investment is about the same, but the centrifuge requires less manpower—it can even be automated.

You did not mention the possibility of re-using the fluid after separating the solids. This is known as a closed-loop system. If you are going to spend what it takes for one or more centrifuges, or a central flocculating system, you should consider biting the bullet and going all the way to zero effluent. In that case, the centrifuge approach will be more successful, but it should be followed by a polishing filter, or even ultra-filtration. The topic is too long to address here, and we will send you additional information.