Chemical Precipitation treatment of leachate
This is a process which utilises physical separation by precipitation to remove the contaminants from leachate, and will remove COD, ammoniacal nitrogen, heavy metals etc.
There have been variants on this process, however, chemical precipitation would normally involve the dosing of magnesium hydroxide (Mg(OH2)), and phosphoric acid (H3PO4), into the leachate. These react with leachate to form magnesium-ammonium-phosphate (MgNH4PO4.6H2O) which is insoluble and which precipitates during settlement.
Magnesium-ammonium-phosphate is also known as struvite, and can be used as a fertiliser subject to the acceptability of metal concentrations etc present
Unfortunately, capital costs are high for the chemical dosing system required, and settlement tanks, clarification, or filtration adds further to the cost. Also, the precipitation tends not to cease within the settlement tanks, and continues through the pipework. These plants are reported to suffer from high maintenance costs due to pipe furring, and eventual blockage if not regularly cleaned. Cleaning is time consuming as struvite furring can be quite hard and tenaciously adhere to pipe surfaces, and thus require high pressure jetting to remove.
The chemical dosing required is also a cost, and normally the resulting leachate quality would not be sufficiently high to allow any other than a sewer discharge.
As a result, chemical precipitation is a process which has in most instances not proceeded beyond trials stages.
|
Newsletter