Tertiary treatment technologies offer advanced wastewater purification but come with significant costs. Capital expenses include equipment and installation, while operating costs cover energy, chemicals, and maintenance. Understanding these costs is crucial for effective wastewater management.

Economic analysis tools like life-cycle cost analysis and sensitivity analysis help compare treatment alternatives. These methods consider long-term expenses and identify key cost factors, enabling informed decision-making for wastewater treatment facilities.

Economic Considerations for Tertiary Treatment

Costs of tertiary treatment technologies

• Capital costs include construction and installation of treatment units (clarifiers, filters), land acquisition, engineering and design fees, and permitting and legal fees
• Operating costs driven by energy consumption for pumping, aeration, mixing, and UV disinfection
  • Chemical costs for coagulants (alum), flocculants (polymers), disinfectants (chlorine), and pH adjustment (lime)
  • Labor costs for skilled operators and maintenance personnel
  • Maintenance and replacement costs for membranes (RO), media (activated carbon, sand), and equipment repair and upkeep

Life-cycle cost analysis for alternatives

• Life-cycle cost analysis (LCCA) considers all costs over the entire life of the treatment system, allowing for comparison of different treatment alternatives (MBR vs. CAS)
• Components of LCCA include initial capital costs, annual operating and maintenance costs, replacement costs, salvage value, and discount rate
• Net present value (NPV) converts future costs to present value, allowing for direct comparison of alternatives
  • Calculated using the formula: $NPV = \sum_{t=0}^{n} \frac{C_t}{(1+r)^t}$, where $C_t$ is cash flow at time $t$, $r$ is discount rate, and $n$ is project lifetime

Economic benefits of tertiary treatment

• Water reuse opportunities for irrigation (agricultural, landscape, golf courses), industrial processes (cooling water, boiler feed water), groundwater recharge, and potable reuse (indirect or direct)
  • Cost savings from reduced need for freshwater extraction and treatment, delayed expansion of water supply infrastructure
• Regulatory compliance benefits include avoidance of fines and penalties, improved public perception, and increased opportunities for growth and development (new housing, businesses)

Sensitivity analysis for cost-effectiveness

• Sensitivity analysis identifies the most influential factors affecting cost-effectiveness, aiding in decision-making and risk assessment
• Key parameters to consider include discount rate, energy costs, chemical costs, membrane or media replacement intervals, influent water quality, and effluent water quality requirements
• Scenario analysis evaluates the impact of different combinations of key parameters, helping identify the most robust and cost-effective solution (worst-case, best-case)

Tertiary Treatment Technologies and Their Costs

Costs of tertiary treatment technologies

• Membrane filtration (MF, UF, NF, RO)
  • Capital costs: Membrane modules, pressure vessels, pumps, piping, instrumentation
  • Operating costs: Energy for pumping, membrane cleaning and replacement, chemical costs (citric acid, sodium hypochlorite)
• Advanced oxidation processes (AOPs)
  • Capital costs: Oxidant generation equipment (ozone generators, UV lamps), reaction vessels, pumps, piping
  • Operating costs: Energy for oxidant generation, chemical costs (hydrogen peroxide), lamp replacement
• Activated carbon adsorption
  • Capital costs: Carbon contactors, pumps, piping
  • Operating costs: Carbon regeneration or replacement (thermal, chemical), pumping energy
• Ion exchange
  • Capital costs: Ion exchange vessels, resin (cation, anion), pumps, piping
  • Operating costs: Resin regeneration chemicals (acid, base), pumping energy, resin replacement
• Constructed wetlands
  • Capital costs: Land acquisition, earthwork, vegetation (cattails, bulrush), liners, pumps, piping
  • Operating costs: Vegetation management, sediment removal, pumping energy