How to Use DBNPA (2,2-Dibromo-3-Nitrilopropionamide) in Water Treatment

Overview

DBNPA is a fast-acting, non-oxidizing biocide widely used for RO membrane systems and cooling water. Its key advantage: rapid kill of bacteria and biofilm within 30 minutes, followed by fast hydrolysis to non-toxic by-products — making it the only biocide safe for continuous contact with polyamide RO membranes.

Preparation & Dissolution

DBNPA is supplied as 20% solution (most common) or 10% solution.

No dilution needed — dose the 20% solution directly via metering pump.

Equipment: Chemical-resistant metering pump (Viton or PTFE wetted parts), HDPE tubing, injection point in RO feedwater line before cartridge filter.

Dosing Guide

Application	Dose (as 20% product)	Mode
RO biocide (intermittent)	30–50 ppm for 30 min	3x per week
RO biocide (continuous)	1–3 ppm	24/7 (rare, high-biofouling systems)
Cooling water shock	50–100 ppm for 2–4 hr	2–3x per week
Paper machine white water	50–100 ppm	Intermittent
UF/MF pretreatment	20–30 ppm for 30 min	As needed

Application Procedure

1. Calculate feed flow rate (m³/h)
2. Calculate DBNPA pump rate: Flow (m³/h) × dose (ppm) / product concentration (200 g/L for 20%) = L/h
3. Program timer to run pump for 30-minute intervals, 3x per week
4. Inject into feedwater line upstream of cartridge filters
5. Monitor differential pressure across cartridge filters (biofouling indicator)
6. Check total bacteria count monthly to verify biocide effectiveness

Monitoring & Control

Parameter	Frequency	Target
RO feed ΔP	Daily	Stable (increase = biofouling)
Total bacteria count	Monthly	< 10³ CFU/mL
DBNPA consumption	Weekly	Verify pump calibration

Common Mistakes

• Using DBNPA where chlorine is present: DBNPA is deactivated by reducing agents (sodium bisulfite). If your system uses bisulfite for dechlorination, inject DBNPA AFTER the bisulfite injection point.
• Expecting long-term residual: DBNPA half-life is 2–4 hours at neutral pH. It's a fast-kill, fast-decay biocide — not a persistent residual maintainer. Use glutaraldehyde or CMIT/MIT if you need long residual.
• Storing in sunlight: DBNPA degrades rapidly under UV light. Store in dark, cool area.

Storage & Handling

• Shelf life: 12 months at < 25°C. Shorter at higher temperatures.
• Temperature: Store 5–25°C. Do not freeze (crystallization at < 0°C).
• Safety: Toxic — causes skin sensitization and serious eye damage. Wear full PPE (chemical goggles, nitrile gloves, face shield for splashes). MSDS required on-site.