Table 7.
Chlorine decay in ten recycled water systems.
| Site | System Practices a | Characteristic | Decay Model | R2 | Decay Rate |
|---|---|---|---|---|---|
| CA-18 | Plant with 350 MG/yr capacity using MBR followed by UV disinfection. System with drip irrigation. Water has 1 day shelf-life in the distribution system. | Distance | y = 2E − 17x + 0.1 | 0 | 0 (No decay) |
| Temperature | y = 3E − 16x + 0.1 | 0 | |||
| TOC | y = 7E − 15x + 0.1 | 0 | |||
| FL-1 | 20 MGD sewage plant with 5-stage biological nutrient removal (BNR; i.e., Bardenpho system) with enhanced removal of nitrogen and phosphorus. System was well pressurized, and the water was used rapidly (i.e., within 1–3 days). | Distance | y = 1.0424e−1.04x | 0.739 | 1.16 mg Cl/°C |
| Temperature | y = 2E − 15e1.1629x | 0.870 | |||
| TOC | y = 8E − 13e6.6594x | 0.837 | |||
| NC | 50 MG/yr using AS technology. Effluent disinfected with UV and chlorine. Booster disinfection at the furthest point sampled ( i.e., DS3; not included in the decay model). | Distance | y = 0.4176e0.134x | 0.576 | 0.104 mg/°C |
| Temperature | y = 0.104x − 1.5489 | 0.940 | |||
| TOC | y = 1E − 0.8e2.8477x | 0.438 | |||
| CA-3 | 110 MGD wastewater plant by AS, tertiary treatment and dual media (anthracite/sand) filtration. System had multiple pressure zones (40–200 psi). | Distance | y = −0.0505x + 1.3543 | 0.872 | 0.051 mg Cl/mile |
| Temperature | y = 0.3513x + 8.879 | 0.387 | |||
| TOC | y = −0.2615x + 2.3947 | 0.008 | |||
| CA-2 | Facultative ponds (lagoons; 3 mg DO/L) followed by multiple ponds with aerators to attain 8–10 mg DO/L). Water subjected to DAF (at 70 to 80 psi), creating microbubbles. System branched but without any dead ends. Reservoir is aerated. Water used within 2 days or discharged into river. | Distance | y = −0.0695x + 0.2117 | 0.8126 | 0.07 mg Cl/mile |
| Temperature | y = 0.0176x − 0.2998 | 0.424 | |||
| TOC | y = 0.0383x − 0.1065 | 0.027 | |||
| CO-5 | 40 MG/yr AS with extended aeration (DO to approximately 1 mg/L to drive nitrification. UV disinfection (fluence of 40,635.28 mJ/cm2) and chlorine gas (10 to 15.l b gas/day in 1000 gal/min.) then filtered through a pack of eight cloth filters. Reservoir was aerated. | Distance | y = 0.0087x + 0.1387 | 0.073 | 0.22 mg Cl/mg TOC (R2 low due to other characteristics e.g., heavy algal growth in reservoir) |
| Temperature | y = 0.0011x + 0.1718 | 0.008 | |||
| TOC | y = −0.0287e0.2211x | 0.352 | |||
| CA-1 | 16 MGD AS process with an anoxic phase to facilitate nitrification combined with a fine bubble diffuser. Clarified liquid was filtered through thick anthracite and coal filtration beds. The filtered water was disinfected with UV (fluence of 144,000–180,000 mJ/cm2) before chlorination. | Distance | y = 0.0095x + 0.0659 | 0.145 | 0.015 mg Cl/°C (R2 low due to other characteristics e.g., multiple pressure zones with 14 to 90 psi) |
| Temperature | y = 0.0153x − 0.2456 | 0.337 | |||
| TOC | y = −0.0119x + 0.1703 | 0.043 | |||
| AZ-8 | Production capacity of 0.28 MGD. The aeration tanks had an anoxic zone where the mixed liquor dissolved solids attained a low DO (0.07 mg DO/L). Disinfection was achieved with chlorine gas followed by gravity-fed filtration (sand and anthracite). Distributed through a looped system. | Distance | y = −0.0353x + 0.1411 | 0.151 | 0.031 mg Cl/mg TOC (R2 low due to other characteristics e.g., disinfectant retention by filters) |
| Temperature | y = 0.0056e0.1894x | 0.157 | |||
| TOC | y = 0.0313x + 0.0249 | 0.609 | |||
| TX-3 | 60 MGD plant with an activated sludge process. System had some dead ends. The dissolved oxygen was greatly diminished in the distribution system as well and the water was rusty due to corrosion. | Distance | y = 0.3058e−0.745x | 0.336 | 1.69 mg Cl/mg TOC (R2 low due to other factors e.g., corrosion) |
| Temperature | y = 2E − 15e1.3472x | 0.069 | |||
| TOC | y = 7E − 07e1.6884x | 0.377 | |||
| FL-5 | The anaerobic-anoxic-oxic (i.e., A2O) plant had a 2.75 MGD capacity. The treatment process removed BOD and TSS as well as reduced nitrogen and phosphorus. | Distance | y = 0.4263e−0.246x | 0.347 | 0.304 mg Cl/°C (R2 low due to other characteristics e.g., multiple dead ends and pressure zones) |
| Temperature | y = 0.3041x − 7.6502 | 0.457 | |||
| TOC | y = 0.137e0.2437x | 0.421 |
a AS = Activated sludge; BNR = biological nutrient removal; MG = Million gallons; MBR = membrane bioreactor; DAF = dissolved air floatation; DO = dissolved oxygen.