Conventional vs. recycled water treatment

Question: What is the main difference between a conventional water treatment plant and a water recycling plant?

Raul Borrero
Puerto Rico

Answer: Regarding conventional water treatment and water recycling, your question is a good one, however, one that’s difficult to answer.
Basically, conventional treatment is the process of taking surface water from source such as a lake, river, ocean or groundwater from a well, and treating it, primarily for potable purposes.

Recycling involves taking water that has been used for any purpose (industrial rinsing, cooling towers, human uses, etc.), treating it and reusing.

It’s typically assumed wastewater is harder to treat than raw water because it contains more contaminants; however, this is not necessarily true.  Seawater contains 30,000-50,000 mg/L of dissolved salts and, as such, is very expensive to treat.

Virtually all municipalities use the available raw water source to produce potable water, but many non-potable applications—including both commercial and industrial—recycle some of their water, particularly in areas of the world where water of any kind is scarce.

Spot-free rinse water for bus washer—three answers
Question: Can you provide any insight as to the best process to use to produce 3-to-5 gpm of spot-free rinse water for our bus washer application? The use of potable drinking water has resulted in etched glass or polycarbonate panels on the side windows of our buses (not hard water spots). The washing takes place at night and window blow-drying is not feasible. The conservation of water and electrical power is of some concern, as industrial sewer discharge fees rise.

Stephen Watt
Long Beach, Calif.

Reverse osmosis
Answer:  The typical solution is reverse osmosis, which provides a cost-effective rinse. It’s hard to believe the use of city water causes etching of the windows. A more likely cause is the detergent used in the wash cycle. Consider changing the formulation or quantity. By the time you rinse the damage has already been done.

Jim Hunt
DWC Division, Duff Co.

Reverse osmosis
Answer: The most practical technology for spot-free rinse water generation is reverse osmosis. In general, the water quality produced by this process will not leave a spot when it evaporates. Conservation of water can be a problem, as anywhere from 10-to-50 percent of the feed water to reverse osmosis systems is discharged as concentrate. It is possible to reuse the concentrate in other concentration, perhaps as makeup water for the washing solution. Any of the water conditioning dealers that handle commercial and industrial applications should be able to help you with this. Good Luck.

Peter S. Cartwright, P.E., CWS-VI
Cartwright Consulting Co.

Buyer beware
Answer: Recently we conducted an evaluation for a car wash operation that wanted to get rid of white pinhead spots from calcium carbonate deposits on vehicles washed using city water. The customer asked us to evaluate a device to cure this problem. The manufacturer claimed conversion of the depositing crystalline calcium carbonate to a form that would slide off the washed vehicles without white deposits. Our study could not validate the manufacturer’s claims. The take home lesson is: “Buyer Beware.” I am sure you’ll get offers to fix your problem.

Henry Nowicki, Ph.D.

Treating recycled cooling water for bottles and cans

Question: We recycle our water that’s used to cool cans and bottles as part of our food processing system. Can you recommend the standard water treatment devices/systems that are usually found in this type of closed loop?

Deryck Taylor

Answer: The technology required to accomplish this will depend on what contaminants are picked up in your process and the water quality requirements of your cooling system. It is difficult to answer your question on recycled water without knowledge of the first use of that water. Most often recycled water is processed by ultrafiltration. This results in excellent water clarity and should provide excellent cooling water. More than likely, the optimum technology will be a membrane process; however, we can only be sure after we receive a more detailed water analysis.


Comments are closed.