📋 Case Study
Water Quality Model Validation for Singapore’s Deep Tunnel Sewerage System (DTSS) Supply Branch
Disinfectant residual dropping below 0.2 mg/L at farthest nodes despite design dosing; suspected wall reaction dominance
🏗️ Project Overview
Chlorine decay modeling across 42 km of precast concrete trunk mains supplying NEWater-integrated distribution zones
🎯 Challenge
Disinfectant residual dropping below 0.2 mg/L at farthest nodes despite design dosing; suspected wall reaction dominance
🔧 Design Approach
Dual-reaction chlorine decay model calibrated with 12-month field residual data + biofilm sampling at 18 locations
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Bulk Reaction Rate Constant
k_bulk = −ln(C/C₀)/t
Result: 0.32 hr⁻¹
Baseline bulk decay under laminar flow conditions
Wall Reaction Coefficient
k_wall = (2 × k_f × C_bulk) / D
Result: 1.82 × 10⁻⁵ s⁻¹
Quantifies biofilm-mediated chlorine sink
📊 Results
Model RMSE reduced from 0.41 to 0.07 mg/L; enabled targeted biofilm removal program; extended disinfectant contact time by 22 min through optimized dosing point relocation💡 Lessons Learned
- •Wall reactions dominate in low-velocity, aged concrete pipes
- •Biofilm sampling must be spatially stratified (upstream/mid/downstream)
- •Model validation requires simultaneous residual + TOC + temperature logging
✅ Key Takeaways
- 1Wall reactions dominate in low-velocity, aged concrete pipes
- 2Biofilm sampling must be spatially stratified (upstream/mid/downstream)
- 3Model validation requires simultaneous residual + TOC + temperature logging
📐 Prerequisites
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