Professionals follow a precise 7-step chlorination process for water tank disinfection. This WHO-approved method ensures 99.9% pathogen elimination while meeting NEMA safety standards in Nairobi.
Step 1: Pre-Service Assessment
Technicians inspect tank condition, measure capacity (in liters), and test initial water quality using coliform swabs. They isolate the tank by shutting inlet/outlet valves and draining 60-80% of water via pump to expose all surfaces. Safety gear (PPE, harnesses for rooftops) and tools (high-pressure scrubbers, pH meters) get deployed.
Step 2: Mechanical Cleaning
Heavy-duty brushes and 100-150 bar pressure washers remove algae, sediment, and biofilms from walls, baffles, and inlets. Vacuum extraction pulls sludge; concrete tanks get crack sealing if needed. This prevents chlorine from reacting with organic matter, ensuring effective disinfection.
Step 3: Chlorine Dosage Calculation
For 50 ppm target (50 mg/L free chlorine), professionals calculate: Grams of HTH granules = (Tank liters ÷ 1000) × 1.7 (adjusting for 65% available chlorine). A 5,000L tank needs ~85g dissolved in 20L clean water. pH testing (ideal 7.2-7.8) guides exact dosing.
Step 4: Solution Application and Circulation
Chlorine solution pours evenly through all openings. Submersible pumps circulate for 30-60 minutes, ensuring 100% surface contact. Temperature monitoring prevents degradation (optimal 20-25°C). Tank seals for 12-24 hours contact time.
Step 5: Contact Time Monitoring
Technicians use DPD test kits hourly, maintaining 40-60 ppm free chlorine. Digital logs record levels per NEMA requirements. Most bacteria die within 6 hours; viruses/amoebas need full 24 hours.
Step 6: Triple Rinsing Protocol
Tank drains completely. Fresh water flushes 3x tank volume (15,000L for 5,000L tank). Each rinse tests <0.5 ppm residual chlorine via colorimeter. Pipes/valves flush separately to eliminate downstream contamination.
Step 7: Final Testing and Certification
Post-rinse coliform test (<1 CFU/100ml) confirms safety. Turbidity (<1 NTU), pH (6.5-8.5), and taste verification complete the process. Bestcare issues NEMA-compliant certificate with before/after readings. Tank refills; clients get maintenance schedule.
This systematic approach eliminates DIY risks like under-dosing (surviving pathogens) or over-chlorination (health hazards). Professionals complete service in 1-2 days, tank size dependent.
