By Jared Alder, MS
There has been a big focus in domestic wastewater on the removal of phosphorus and the potential for excess phosphorus to cause eutrophication in receiving water. Treatment facilities of all different shapes and sizes with inadequate phosphorus treatment technologies have the potential for excess phosphorus release.
The removal of phosphorus from wastewater can be performed using physico-chemical methods, biological treatment, and/or combinations of both. Physico-chemical processes of phosphorus removal have been widely used. Such physico-chemical processes are generally effective, reliable, and do need a lot of large capital equipment; however, they are not without limitations. For example, adding chemicals to treatment processes can impact the pH of the treatment process, thus resulting in the need for additional chemicals to adjust the pH before the treated water can be discharged. In some cases, because of the chemical usage, a chemical sludge can be created and there may need to be additional treatment steps for removing the sludge.
The most common chemical phosphorus removal options utilize dosing metal salts—such as ferric chloride as part of pre-treatment—into activated sludge reactors or as part of the secondary clarifier process. Ferric chloride (or similar metal salts) precipitates phosphorus in the wastewater and the resulting solids residuals are removed either by settling under gravity or by filtration. The subsequent precipitates may be rich in phosphorus but, since it is chemically bound, it can make recovering the phosphorus challenging—which presents a disadvantage over Enhanced Biological Phosphorus Removal (EBPR) systems because it reduces the economic benefits of the phosphorus-rich sludge.
Removal rates for phosphorus are typically proportional to the mass of the chemical added, which influences the amount of extra solids produced; therefore, a balance between the two is critical. Phosphorus effluent concentrations of 1 mg/L or greater can generally be achieved by gravity settling. Techniques including filtration and tertiary-ballasted flocculation are sometimes combined with metal-salt dosing to achieve lower phosphorus levels, even down to concentrations of < 0.50 mg/L.
Since chemical dosing is generally reliable and widely accepted, it is the most commonly used treatment option.
Related Posts
Live Aid: Music That Fed the World (and Filled My Parents’ Basement)
This Week In Ag #124: Live Aid: Music That Fed the World (and Filled My Parents’ Basement) This past Sunday marked the 40th anniversary of the greatest PR and musical event in history. It was held at Wembley Stadium in London. And at JFK Stadium in Philadelphia. It was viewed by nearly 40% of the world’s population. The event was Live Aid, a benefit concert to raise money and awareness for famine relief in Africa. It was the event that forged a generation, my generation, Gen X. I’ll never forget that day. Dad was among the first in our neighborhood to purchase a satellite dish. I threw a party that day, attended by seemingly every college-aged aggie in the county (or at least dad seemed to think so)
This Week in Ag #60
“They’re on 30s, we’re on 36s.” The cultural practice of row width is often as defining to a farm as the color of tractors they drive. Row width speaks to how far apart you plant your rows. This can vary greatly depending on the crop, geography, agronomic challenges and what the farmer wants to achieve. Here’s a look
Just Another Snake Oil?
by Heather Jennings, PE For years, the wastewater industry has been plagued with products that meet only half the expectations of the users or make matters worse. I get it. I personally questioned the efficacy of Micro Carbon Technology® (MCT—the nutrient carrier for all our liquid nutrient and biostimulant products) when I started with Probiotic
