Advanced wastewater treatment consumes significant energy through various processes. Aeration, pumping, mixing, and sludge processing are major energy users. Advanced technologies like membrane filtration and UV disinfection add to energy demands beyond conventional treatment.

Energy consumption is influenced by wastewater characteristics, treatment design, operational parameters, and equipment efficiency. Different technologies have varying energy intensities. Electricity costs impact operational expenses, but energy recovery and efficiency measures can help reduce costs and environmental impact.

Energy Consumption in Advanced Wastewater Treatment

Energy-consuming processes in wastewater treatment

• Aeration consumes significant energy by providing oxygen for biological treatment processes (activated sludge) and mixing to keep solids in suspension
• Pumping requires energy for moving influent, effluent, and recirculating wastewater and sludge throughout the treatment plant (lift stations, return activated sludge pumps)
• Mixing ensures homogeneous conditions in treatment tanks, prevents sedimentation, and maintains solids in suspension (mechanical mixers, jet aerators)
• Sludge processing involves thickening, dewatering, and drying of sludge, as well as anaerobic digestion for biogas production, all of which consume energy (centrifuges, belt presses, heat drying)
• Advanced treatment technologies such as membrane filtration (MBR, UF, NF, RO), advanced oxidation processes (AOPs), activated carbon adsorption, and UV disinfection have additional energy requirements beyond conventional treatment

Factors influencing energy consumption

• Wastewater characteristics influence energy consumption, including organic load (BOD, COD), nutrient concentrations (nitrogen, phosphorus), and presence of recalcitrant or toxic compounds that may require more intensive treatment
• Treatment process design and configuration factors such as selection of treatment technologies, process optimization and control strategies, and hydraulic profile and pumping requirements impact energy usage
• Operational parameters like solids retention time (SRT), dissolved oxygen (DO) levels, recirculation rates, and chemical dosing rates affect energy consumption in various treatment processes
• Equipment efficiency of aeration systems (diffusers, blowers), pumps and mixers, and sludge processing equipment plays a role in overall energy consumption
• Influent flow variations, including diurnal and seasonal fluctuations and peak flow management, can impact energy requirements for pumping and treatment processes

Energy intensity of treatment technologies

• Conventional activated sludge (CAS) has moderate energy intensity due to aeration and pumping requirements
• Membrane bioreactors (MBRs) have higher energy intensity compared to CAS due to membrane operation, but may have reduced aeration requirements due to higher MLSS concentrations
• Advanced oxidation processes (AOPs) have high energy intensity due to the use of UV lamps, ozone generators, or hydrogen peroxide
• Granular activated carbon (GAC) adsorption has moderate energy intensity for pumping and regeneration of GAC
• Nutrient removal processes vary in energy intensity:
  1. Enhanced biological phosphorus removal (EBPR) has lower energy intensity
  2. Nitrification-denitrification has higher energy intensity due to aeration and recirculation
• Disinfection technologies also differ in energy intensity, with UV disinfection having high intensity due to UV lamps, while chlorination has lower intensity

Impact of energy on operational costs

• Electricity costs contribute significantly to overall operational costs and depend on local energy prices and tariff structures
• Potential for energy recovery exists through biogas production from anaerobic digestion, combined heat and power (CHP) generation, and using biogas for process heating or electricity generation
• Energy efficiency measures can reduce costs, including process optimization and control, variable frequency drives (VFDs) for pumps and blowers, high-efficiency aeration systems (fine bubble diffusers), and heat recovery from wastewater or exhaust gases
• Life cycle cost analysis considers capital costs, operational costs, and energy consumption over the plant's lifetime, balancing energy efficiency with treatment performance and effluent quality requirements