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Nutrients in Wastewater: Reducing Phosphorus and Nitrogen
Nutrient loading of freshwater systems is one of the most common forms of contamination originating from industrial and municipal wastewater treatment plants, agriculture and other human sources. Carbon, nitrogen and phosphorusare essential nutrients for plants and algae. When assimilated by freshwater and saltwater organisms, can increase their activity and productivity, and alter natural ecosystems. Phosphorus and nitrogen in high concentrations, can trigger blue green algal bloom, toxic to aquatic life and harmful to human health.
Nutrient sources
Sources of nitrogen (nitrates) include human and animal waste, and fertilisers, while sources of phosphorus (phosphates) include human and animal waste, fertilisers, soaps and detergents, and food waste.
Nutrient pollution
Since nitrogen and phosphorus are plant nutrients (they are both added to fertilisers used to stimulate rapid crop growth), they fuel algal growth, which can result in algal blooms in both freshwater systems and coastal bays. Once these algal cells have utilised all the available nutrients, they die off, stripping oxygen from the water as they decompose. This results in eutrophication, which in turn causes water quality to deteriorate, leading to a loss of biodiversity in affected aquatic systems. In extreme cases, it can lead to a hypoxic environment devoid of oxygen that is unable to support aquatic life. Green algae blooms can be extremely toxic resulting in large fish kills. In addition to the environmental impacts, algal toxins and nutrient pollution can also have economic and health impacts.
Health impacts of nitrogen pollution
Exposure to nitrite in drinking water can lead to methemoglobinaemia (blue baby syndrome) in infants. Blue baby syndrome is a potentially fatal condition that arises when an infant ingests nitrite in drinking water. Nitrite reacts with oxyhemoglobin — the oxygen-carrying protein in the blood — to form methemoglobin, which is unable to carry oxygen. As a result, the body becomes starved of oxygen. Nitrite is regulated to maximum 3 mg/L as nitrite. Nitrate in drinking water is currently regulated at maximum 10 mg/L as nitrogen. Epidemilogial research shows that at this concentration nitrate still causes large number of digestive system cancers, low birth weight and pre-term birth in humans. Recommended new concentration for nitrate is maximum 4 mg/L as nitrogen,
Health impacts of phosphorus pollution
If you read the label on food packaging of any processed food, you will find that the food product invariably contains phosphates — a form of phosphorus. Phosphorus can occur naturally in foods such as meat, diary and plants, but is often added to processed foods during the food production process as an enhancer or to extend the shelf-life. While the levels of phosphates found in food products are generally too low to pose a health risk to humans, exposure to high concentrations of phosphorus can pose a significant risk. The negative health impacts associated with exposure to high levels of phosphorus include toxic symptoms such as diarrhea, as well as chronic cardiovascular, kidney and bone disease arising from the body's inability to absorb important minerals such as iron, magnesium, calcium and zinc. However, the greatest danger of phosphorous pollution of water bodies is triggering of algal blooms. The blue green algae toxins are some of the most potent in nature, comparable with dioxins and more powerful than snake venom.
Water Quality Standards for Nutrients
The EPA recommends the following criteria for monitoring phosphorus in wastewater effluent:
1. No more than 0.1 mg/L when discharging into streams which do not empty into reservoirs;
2. No more than 0.05 mg/L when discharging into streams that discharge into reservoirs; and
3. No more than 0.025 mg/L when discharging directly into a reservoir.
However, since the environmental impact of nutrient loading in aquatic systems is affected by other factors (for example, available light, slit load, etc), in Australia, the recommended nutrient guideline maximum thresholds can vary according to the freshwater environment they are discharged into. According to findings in the 1995 report titled: Preliminary Nutrient Guidelines for Victorian Inland Streams, depending on the water body being discharged into, the recommended maximum threshold for phosphorus varies between 0.03-0.05 milligrams per liter, while the maximum threshold for nitrogen varies between 0.150-1.0 milligrams per liter.
Efficient Wastewater Treatment is Key
In order to safeguard environmental and public health, municipal wastewater treatment plants and industrial wastewater treatment facilities alike are required to implement measures to ensure that nutrients and other potentially hazardous pollutants present in effluent are reduced to acceptable environmental health standards before the effluent is discharged into the environment.
Wastewater treatment strategies commonly employed by the industrial sector such as food and beverage processors, for example, are effective at reducing nitrogen. However, until now, reducing phosphorus to levels that meet environmental health standards has continued to be somewhat problematic. Phosphorous could trigger algal blooms from concentration as low as 0.03 mg/L Currently, many wastewater treatment plants are not as efficient as they could and should be. Yet, there is new technology available that is very effective at removing phosphorus. By making use of innovative technologies now available to reduce phosphorus, water utilities and industrial wastewater treatment facilities can improve their efficiency, which will in turn protect the environment and improve their companies environmental performance too.