12.2 Treatment technologies for water reclamation

Water reclamation is crucial for sustainable water management. Advanced treatment processes like oxidation, membrane filtration, and disinfection remove contaminants and pathogens from wastewater. These technologies enable the production of high-quality recycled water for various uses.

Designing effective water reclamation systems involves characterizing influent quality, identifying end-use requirements, and selecting appropriate treatment processes. Proper operation requires monitoring, maintenance, chemical management, and energy efficiency measures to ensure reliable performance and regulatory compliance.

Advanced Treatment Processes for Water Reclamation

Key water reclamation processes

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• Advanced oxidation processes (AOPs) utilize highly reactive oxidants such as hydroxyl radicals ($\cdot$OH) to degrade a wide range of organic contaminants including pharmaceuticals, personal care products, and endocrine disruptors
  • Common AOP methods combine ozonation with hydrogen peroxide (H$_2$O$_2$) or UV light, UV light with H$_2$O$_2$ or titanium dioxide (TiO$_2$), and Fenton's process using H$_2$O$_2$ and ferrous iron
• Membrane filtration physically separates contaminants using semi-permeable membranes in various configurations (hollow fiber, spiral wound, plate-and-frame, tubular)
  • Membrane types in decreasing pore size order: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO)
• Disinfection inactivates pathogenic microorganisms using methods such as chlorination (chlorine gas, sodium hypochlorite), UV irradiation, ozonation, chloramination (chlorine combined with ammonia), and membrane filtration as a physical barrier

Effectiveness of treatment technologies

• Advanced oxidation processes effectively degrade a wide range of organic contaminants but may not treat certain recalcitrant compounds or high contaminant concentrations and can be energy-intensive requiring careful process control
• Membrane filtration: MF and UF remove suspended solids, bacteria, and protozoa but not viruses or dissolved contaminants; NF and RO remove viruses, dissolved organic matter, and ionic species but require higher energy input and may foul; concentrate streams require proper management and disposal
• Disinfection: Chlorination effectively treats a wide range of pathogens but can form disinfection by-products (DBPs) with organic matter; UV disinfection treats most pathogens without forming DBPs but requires clear water and regular lamp maintenance; ozonation strongly oxidizes and disinfects but has high energy requirements and can form bromate in bromide-containing waters

Design and Operation of Water Reclamation Systems

Design of reclamation treatment trains

1. Characterize influent water quality by determining levels of suspended solids, organic matter, nutrients, pathogens, trace contaminants, and assessing variability in water quality and flow rates
2. Identify desired end-use requirements by consulting relevant regulations and guidelines for water quality standards based on intended use (irrigation, industrial processes, potable reuse) and considering additional treatment needs for specific end-uses (nutrient removal for irrigation, advanced disinfection for potable reuse)
3. Select appropriate treatment processes by combining technologies to target specific contaminants and meet end-use requirements, optimizing process design parameters (hydraulic retention times, chemical dosages, membrane flux rates) based on pilot studies or modeling
   • Example treatment train for potable reuse: secondary treatment → MF/UF → RO → advanced oxidation → disinfection

Operational requirements for reclamation systems

• Monitoring and control: Implement online monitoring for key water quality parameters (turbidity, pH, conductivity, residual disinfectant), establish control strategies and set points for process optimization and compliance, and develop a comprehensive sampling and analysis plan for offline monitoring
• Maintenance: Establish regular schedules for equipment maintenance (membrane cleaning, UV lamp replacement, filter backwashing), implement preventive practices to minimize downtime and extend equipment lifespan, and train operators on proper procedures and troubleshooting
• Chemical management: Ensure proper storage, handling, and dosing of treatment chemicals (coagulants, oxidants, cleaning agents), optimize dosages to minimize costs and environmental impacts while maintaining treatment effectiveness
• Energy efficiency: Assess energy consumption of treatment processes, identify optimization opportunities (variable frequency drives for pumps, high-efficiency blowers for aeration), and consider renewable energy sources (solar, biogas) to reduce grid electricity reliance and minimize carbon footprint