Phosphates in Wastewater

Q. Our city is cracking down on industry for phosphate content in wastewater. I am charged with finding the sources of phosphorus in our plant. Our main process effluents are from mass finishing and washing machines. I have not found significant phosphorus in these fluids, and yet, we are close to the limit. What am I missing? H.H.

A. The phosphorus occurring in industrial and household wastewater is almost entirely as phosphates. Phosphates are essential for plants and animals, but too much phosphate contributes to eutrophication—fertilization—of our streams, rivers, and lakes, allowing algae to grow so abundantly that it dies for lack of light; the decomposition of the algae uses the water’s dissolved oxygen, thereby causing the death of fish and other marine life. That explains why phosphorus is being regulated—16 states imposed tighter restrictions July 1, 2010.

There are many sources of phosphate in industrial and janitorial products because they are good cleaners and lubricants. The phosphorus in laundry and dishwash detergents has been limited by regulation in many states, to a maximum of 0.5%, down from previous limits of 8.7%. The problem, however, is bigger than that because urine accounts for about 60% of the phosphates in household wastewater—what percent in factories, or office buildings with hundreds of workers? In hot weather it is worse because of soft drink consumption. “Make mine a lemon phosphate, please.” Typical soft drinks have about the same phosphorus content—0.5%—as laundry detergents. Phosphate contribution from farms due to fertilizer and animal urine is another problem.

Unfortunately for the environment, industrial and commercial cleaners are exempted from this limit on phosphates, and it is common to find floor cleaners, parts washing compounds, and similar products with anywhere from 10% to 60% phosphates. For the most part, these high phosphate products will be found in powder form, although some liquid cleaners may also be high in phosphates. This is not necessary because excellent cleaning products are being made that fall within the 0.5% phosphate limit; this can even be accomplished without the use of harsh chemicals that are harmful to the operators. You may find that your janitorial cleaners account for the majority of the phosphates you are buying, with the possible exception of the soft drinks.