Water quality and sources of pollution - Eutrophication and algal blooms(Source: Australian Government - Department of the Environment)
Eutrophication occurs when the major plant nutrients - nitrogen and phosphorus - accumulate in water (or sediments). Given the right conditions, elevated concentrations of nutrients stimulate the growth of aquatic flora to nuisance levels. Examples include microscopic algae in the water column which may result in algal blooms...
Algal blooms are a natural occurrence, however, due to human activities (such as land clearing, destruction of riparian vegetation, water extraction, decreased flow and flow variability associated with weirs and dams, discharge of sewage and intensive agriculture), higher quantities of nitrogen and phosphorus have been reaching inland waters. Periods of low or no flow in many rivers have also increased due to high water extraction and river regulation. The combination of high nutrient levels and long periods of low or no flow provide ideal conditions for algal blooms to develop.
Blue-green algal blooms are of most concern in inland waters as certain species produce toxins that may cause skin irritations, gastrointestinal disorders, influenza-like symptoms and, in extreme cases, permanent organ damage and death (ANZECC/AWRC 1992). Many of the toxins produced by blue-green algae can affect people, livestock, birds and fish. ...
For human uses, blue-green algal blooms in drinking water resources is the most serious issue. Traditional water treatment methods are unable to remove the algal toxins from algae-contaminated water, while other alternative water treatment methods are expensive. Blue-green algal blooms may affect the recreational use of a waterway by decreasing its aesthetic amenity and posing a health risk to individuals who have direct contact with the algae.
"A $40 a tonne increase in the US in December has led Australian farmers paying up to $200 a tonne more for the fertiliser diammonium phosphate (DAP)."Point sources of nitrogen and phosphorus include sewage treatment plants, intensive agriculture (such as cattle feedlots and piggeries) and industry. Although in most river systems, point sources only contribute to 5% to 35% of the total amount of nutrients entering the waterway (Environment Australia 1996; NPI 2000), their impact can be proportionally greater.
Point-source discharges are usually continuous and often contain high levels of nitrate and phosphate, forms of nitrogen and phosphorus that can be readily used by algae.
In dry weather, diffuse source nutrient pollution is generally low and point sources are the largest source of nutrients. The greater stability of the water column in dry weather is generally more favourable to the development of algal blooms (SKM 2001) and there is also less flow in river systems to dilute point-source discharges.
Although there is information on the quantity of nutrients discharged from sewage treatment plants (NPI 2000), there is no comprehensive information on other point sources. ... The contribution to nutrient loads from intensive livestock enterprises is potentially considerable as these facilities are widespread, often poorly regulated and generate wastes that are high in nutrients (e.g. manure).
Figures 13 and 14 show the quantities of phosphorus and nitrogen discharged to inland waters by sewage treatment plants each year. As New South Wales has the highest inland population, its sewage treatment plants also discharge the highest quantity of nutrients. The four river systems that receive the highest loads of nitrogen (greater than 100 tonnes per year) and phosphorus (greater than 30 tonnes per year) from sewage treatment plants are the Murrumbidgee, Hawkesbury-Nepean, Namoi and Hunter.
Struvite (magnesium ammonium phosphate) Recovery
"Ostara’s Pearl® technology created at the University of British Columbia recovers ammonia and phosphate from nutrient rich fluids."Ostara’s proprietary wastewater treatment technology, called the Pearl® Nutrient Recovery Process, recovers phosphorus and other nutrients from sludge liquids preventing the buildup of struvite scale in plant infrastructure and converting the recovered nutrients into a premium commercial fertilizer (Crystal Green®)
The pellets are then harvested from the reactor and formulated to become Crystal Green®, a high-quality environmentally friendly, slow-release, commercial fertilizer that provides revenue for the system’s operator.
Ostara’s Pearl® technology is based on a proprietary fluidized bed reactor that recovers ammonia and phosphate from nutrient rich fluids. The technology, created at the University of British Columbia, uses a proprietary fluidized bed reactor design which removes approximately 85% of the influent phosphorus, but also results in the formation of a fertilizer in granular form consistent with that used in the fertilizer industry.
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Incitec Pivot Phosphorus Fertilisers
Ammonia MoleculeDAP (Diammonium Phosphate) is manufactured by reacting ammonia with phosphoric acid. Because it has a high nitrogen and phosphorus content, DAP allows savings to be made in storage, freight and application. It is a very economical nitrogen and phosphorus fertiliser and is widely used throughout the world. In Australia, DAP is used in cropping and on grass pastures, both on its own and in blends, e.g. for sugarcane and horticulture.