There should be lots of info on truck wash / wash rack recycling systems on the internet. But, there are several issues that will impact this operation. Since the washing will take place at a saleyard, I would expect that you don't have a rigid spec for the quality (TDS, chloride content, pH, etc) of the recycled water. As long as it looks relatively clean and doesn't smell then it should perform okay. And if you set a reasonable percent blowdown to sewer, then you don't have to worry about high chloride content and possible metal corrosion issues.
The real problem that you have, I suspect, is that the dirty wash water is loaded with high solids and organic load. Most commercial recycling systems consist of an oil water separator and various forms of filtering, not good for this application. You don't have any oil to remove and the solids/organic load will quickly foul the system. High solids, such as mud, can usually be handled by some type of settling basin followed by filtration. But, you also have an organic load of animal origin and that can be a problem.
A bio treatment unit is likely to be a better choice but the organic load might be too high for the bugs. This could result in anaerobic conditions and the generation of H2S, not good. Also, in dealing with cattle, I would suspect that e. coli is a concern. These bio systems typical employ minimal treatment of the final effluent. In studying these systems, one vendor claimed that system performance improved over time as the "bugs" distributed themselves throughout the system (clean water tank, yard sump, and influent piping). With the "bugs" present in the recycled water, the H&S people were not too comfortable in approving the system regardless of vendor claims as to how benign his bugs were.
You could use biocide to sterilize the water, but that could end up killing the bugs. Some systems use ozone injection to control odor (to prevent the system from going septic), but they do not use enough to reduce the organic load and sterilize the water. You could add bleach to the treated water but this increases cost and it's more equipment that needs to be monitored and maintained. And, USDA/local water agency regulations may or may not allow you to use recycled water (some require sterile water if there is any potential for human contact).
Overall, I'm not a big fan of these recycling systems. There are many hidden costs to keep the system running correctly and the savings in water does not justify the increased use of chemicals, electricity, supplies, and labor. Why buy a $25K (or more) system + thousands for labor to achieve a reduction in water use when you can get the same level of reduction by installing a $15 shut-off nozzle? Attack the issue of proper water use first and the justification for many of these systems goes away.
I hope this helps.
Mike Callahan, PE
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