Nutrient Overload

When I was a kid growing up in a small Kentucky town we were surrounded by farmland and pastures. In those fields were farm ponds, and as young boys we had permission to fish those ponds. But we all knew not to go to the pond below the hog lot because it was always covered in slime and we never caught anything except turtles. I now understand what was happening, and is still happening, in situations like this – nutrient overload.

One nutrient that contributes to nutrient overload is phosphorous (Chapter 2, page 28). Controlling phosphorous discharged from municipal and industrial wastewater treatment plants is a key factor in preventing eutrophication of surface waters. Phosphorous is one of the major nutrients contributing to the increased eutrophication of lakes and natural waters.

Phosphorous is a necessary nutrient for plants to live and is normally the limiting factor for plant growth in many freshwater ecosystems. The addition of phosphorous promotes excessive plant growth and decay, and causes a severe reduction in water quality.

When the algae die they are decomposed and the nutrients contained in the organic matter are converted into inorganic form by bacteria. The decomposition process uses the dissolved oxygen in the water and deprives the fish and other organisms of the oxygen they need to survive, therefore causing fish deaths.

Phosphorous in the water causes many water quality problems including increased purification costs, decreased recreational and conservation value of impoundments, loss of livestock, and the possible lethal effect of algal toxins in drinking water.

Municipal wastewaters may contain from 5 to 20 mg/l of total phosphorous, of which 1-5 mg/l is organic and the rest is inorganic. Normally, secondary treatment can only remove 1-2 mg/l, so a large excess of phosphorous is discharged in the final effluent, causing eutrophication in surface waters.

The removal of phosphorous from wastewater involves the incorporation of phosphate into total suspended solids and the subsequent removal from these solids. Phosphorous can be incorporated into either biological solids (e.g. micro organisms) or chemical precipitates. Make sure that your facility is participating in one of these methods to reduce the amount of phosphorous that is being released in the final effluent.

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