Antiscalant removes need for acid in wastewater RO
Steve Chesters, Managing Director, Genesys International LimitedField trials of a new scale-inhibiting chemical for use with reverse-osmosis membranes in wastewater reuse plants show that, at a low dose rate, it can increase the solubility of calcium phosphate by over one hundred times, obviating the need for using dangerous and costly acid.
Current design practices for large effluent reuse projects are focused on a combination of removing phosphate by precipitation prior to the RO plant and acid dosing to reduce pH to 6.0 and hence increase calcium phosphate solubility to prevent fouling.
Conventional antiscalants are ³ineffective at high phosphate and high recovery rates, and the only other option has been to dose large quantities of acid to reduce feed pH to below 6.2. Reducing the pH from 7.5 to 6.0 on a 2,700 m³/day plant would require 0.5 to 1 ton of 95% sulphuric acid per day. Handling this quantity of acid is an environmental, health, safety and logistical problem that many plant operators would like to move away from.
The results from the field trials show that using a highly active threshold inhibiting antiscalant such as Genesys PHO at a low dose rate of 2 -5 mg/L can increase the solubility of calcium phosphate by over one hundred times.
This article appeared in D&WR magazine's August/September 2008 issue.
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