Phosphorous Discharge Limits and Drinking Water Corrosion Control Plans

How much can really be accomplished by focusing efforts here?

 

A trend is emerging to reduce algal blooms by lowering phosphorus discharge limits in wastewater through the elimination of blended phosphates from drinking water corrosion control programs. Surely, algal blooms are not just foul smelling and unsightly; they contain cyanobacteria that causes health problems for both humans and wildlife

 

When we take a close look at the numbers though, it is difficult to see how any meaningful reduction of phosphorus in public waterways can be achieved by focusing on drinking water phosphates.

 

More importantly, if blended phosphates are eliminated from drinking water, how will we be able to keep the public safe from the harmful effects of lead and copper?

 

To protect public health, the United States EPA regulates copper and lead in drinking water; both widely used in household and municipal plumbing materials. When lead levels reach 0.015 mg/L or copper climbs over 1.3 mg/L at the 90th percentile, action is required.

 

In these cases, the treatment plant must develop and submit a corrosion control plan that typically includes the use of blended phosphates.  Along with control of lead and copper, the addition of phosphates helps with sequestration in potable water. Sequestering iron and manganese helps control color and prevents calcium carbonate scale build-up which can be harmful to both public and private infrastructure.

 

Elemental Phosphorus (P) is not just a key component of the blended phosphates added to drinking water. It also finds its way into our daily lives through a large number of pharmaceutical and consumer products, and is added to foods as leavening agents, dairy emulsifiers, and to acidify soft drinks. All of the phosphorus found in these processes is ingested by humans and ends up in our wastewater systems. 

 

The following is a list of the milligrams per liter of phosphorus found in a number of foods and products.

  • Broccoli = 800 mg/L
  • Brussel Sprouts = 550 mg/L
  • Donuts = 1,000 to 10,000 mg/L
  • Brats = 1,000 mg/L
  • Bread = 1,000 mg/L
  • Cheese = 5,000 to 30,000 mg/L
  • Pizza = 3,000 mg/L
  • Soda = 200 to 1,000 mg/L
  • Beer = 160 mg/L
  • Toothpaste = 50,000 - 250,000 mg/L

Phosphates for corrosion control in drinking water = 0.30 to 1.30 mg/L

 

All of these sources combined, however, do not compare to the phosphorus that is found in runoff from agricultural applications such as animal feed and fertilizers. According to Iowa Geological Survey 2004, these account for 80% of the phosphorus found in our lakes and rivers.


As the graph below demonstrates, phosphorus from municipal drinking water contributes only about 2-10% of the phosphorus that ends up in wastewater treatment facilities. Furthermore, the phosphorus found in wastewater discharge only accounts for 20 percent of phosphorus found in our lakes and rivers.

 

 

 

Some alternatives to specialty phosphate blends have been proposed in the past. The use of silicates has been explored but quickly discarded since they are not as effective for corrosion control, cost 2 to 3 times as much as an equal amount of phosphates, and furthermore are far less effective for the sequestration of iron, manganese, or calcium carbonate.

 

One large Midwestern city went as far as to remove all of their lead lines at a cost of $15 million. For that amount, they could have fed phosphates for 150 years and yet they still did not address the existence of lead and copper pipes in consumer homes.

 

Clearly, concentrating on a factor that only contributes 1% of the problem, does not provide much of a solution. Furthermore, since alternative corrosion control technologies are not effective in dealing with lead and copper, municipalities that eliminate phosphates from drinking water run the risk of failing compliance with the US EPA lead and copper rule and putting their customers at risk.

 

Check out our webinar on Lead & Copper Control with Phosphates for more information on compliance with the Lead and Copper Rule.