RO Biocides - Reverse Osmosis Treatment

Advanced Reverse Osmosis Technology

RO Biocides - Non-oxidizing, non-ionic biocides can be used either on line or as part of a cleaning program to control biofouling in RO membranes. When used as an on-line treatment, the biocide should be dosed prior to the RO system to control bio-growth in the membranes. Application frequency will depend on biological loading and biofilm growth rate. The program should be used to control differential pressures in the RO plant to reduce cleaning frequency. Application rates and frequency of application (biocide program costs vs. effectiveness) vs. reduction in cleaning frequency, down time, membrane life (operating costs without biocide program) should be balanced to determine the most cost effective biocide dosing frequency.

Dosing biocide further back in the pre-treatment will help control bio-growth but will greatly increase demand and application costs. The main goal of an effective biocide program is to control biofouling in the membranes to an acceptable and cost effective level compared to cleaning program costs (and associated costs).

The two products widely used are 2,2-dibromo-3-nitrilopropionamide (DBNPA) and isothiazolone. These products are fully compatible with polyamide (PA) and cellulose acetate (CA) membranes.

DBNPA

DBNPA is fast acting and readily decomposes to harmless by-products on discharge. On-line, it is dosed just prior to the RO system to control biofouling in the membranes. Dose rate is typically 100 ppm for 1 hour. Frequency of application depends on degree of biological contamination in the feed water and rate of biofilm growth in the membranes. Typically frequency of application can vary from every other day to once a month. The half-life of DBNPA is reduced with the increase of pH. In high pH feed waters (>8.5) the dose rate and contact time should be doubled.

DBNPA biocide should not be dosed with stainless steel injection quills as corrosion of the injection assembly will occur.

Isothiazolone

Isothiazolone has a longer contact time than DBNPA. Dose rate is typically 50 – 100ppm for 4 hours contact. Isothiazolone is more effective than DBNPA in waters with high organic loading. Isothiazolone can also be used at low dose rates on a continuous basis (10 – 20ppm).

Hydrogen Peroxide Silver Blend

ROCbio Silver, an innovative blend of hydrogen peroxide and silver, is an eco-friendly, multi-component oxidising biocide utilising a stable combination of Hydrogen Peroxide (H2O2) and Silver(Ag) ions to form a highly effective sanitising solution. This synergistic combination is so effective it creates a biocide twenty times more powerful than that of hydrogen peroxide alone.

For further information or assistance please contact Reverse Osmosis Chemicals International on +44 (0) 161 877 2334 or e-mail info@rochemicals.com.