Ostara reactors harvest phosphorus from raw sewage
By Ben Coxworth
March 31, 2010
Here’s something rather important that you might not know: there may be a worldwide phosphorus shortage within the next few decades. The majority of the world’s phosphorus is currently mined from non-renewable phosphate rock deposits, and widely used in crop fertilizers. Scientists have begun to question just how much more phosphorus is left, and what the agriculture industry will do once it runs out. The answer – or some of it, at least – could be bobbing in a pool of raw sewage. Ostara, a Canadian nutrient recovery company, has developed a method for harvesting phosphorus from municipal wastewater and converting it to fertilizer.
Ostara’s PEARL Nutrient Recycling Process, developed at Vancouver’s University of British Columbia, utilizes something called a proprietary fluidized bed reactor. The cone-shaped device is installed in a wastewater treatment plant, where it removes ammonia and most of the phosphorus from untreated sewage. Magnesium is added within the reactor, creating a concrete-like substance known as struvite. This struvite, in turn, is processed into a nitrogen/phosphorus/magnesium slow-release fertilizer sold as Crystal Green. Ostara claims that numerous trials have proven the fertilizer to be safe, and because of its slow-release properties, it stays in the soil instead of running off into waterways.
The removal of so much phosphorus, needless to say, makes the wastewater that much cleaner when it finally returns to the natural environment. Hopefully, Ostara’s system should decrease the occurrence of toxic blue-green algae blooms, which can occur when wastewater containing too many nutrients enters a body of water such as a river. While wastewater treatment plants already remove much of the phosphorus and other nutrients, the installation of a reactor would greatly reduce the bioload on the plant, allowing it to save a poopload (sorry) of power and operating costs.
While struvite is produced on purpose inside reactors, it also occurs naturally when phosphorus and nitrogen combine with magnesium in a wastewater treatment plant's sludge stream. This unasked-for struvite clogs lines and valves, reduces flow rates, and has to be removed either mechanically, or by running acid through the lines. By harvesting most of the phosphorus, a reactor is said to virtually eliminate struvite build-up, further lowering the plant’s operating costs, and increasing its capacity.
The system in use
With the combination of reduced operating costs, extra processing capacity, and revenue generated by fertilizer production, Ostara claims that a wastewater treatment plant utilizing a PEARL reactor could exceed $1 million in net savings per year. And it isn’t all just theoretical, either – Edmonton, Alberta’s Gold Bar wastewater treatment plant has been using a reactor since 2007, and has seen good results. Every day, the reactor extracts over 80% of the phosphorus and 15% of the ammonia from 500,000 liters of sludge (20% of the plant’s total sludge stream), and converts it to 500 kg (1,102 lbs) of ready-to-use Crystal Green. Pilot plants have also proven successful in British Columbia, Virginia and Oregon.
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