Performance Assessment System for Energy Efficiency in Wastewater Systems
Abstract
:1. Introduction
2. Methodology
2.1. General Approach
2.2. PAS Development
2.3. PAS Validation and Consolidation
2.4. Reference Values Establishment
3. Results and Discussion
3.1. Consolidated PAS
- (1)
- Objective 1—Energy-use efficiency: ensures the efficiency in the use of energy in the operation of the wastewater systems and promote a sustainable use of the resource, targeting the specific inefficiencies of each system. The criteria associated with this objective focus on the adoption of best cleaning, operation, and maintenance practices in the replacement of equipment for more efficient ones or in the implementation of solutions to increase their efficiency and also in the control of undue inflows, among others.
- (2)
- Objective 2—Carbon neutrality: promotes mechanisms to control the emission of GHG associated with energy consumption in wastewater systems, reducing the respective impact in climate change. Encourages fast reductions in GHG caused by the several activities associated with system components that require energy supply. The proposed criteria for this objective focus on replacements at the equipment-, operation-, and maintenance-level actions and promotion of the use of clean energy (such as solar energy, wind energy, and hydropower).
- (3)
- Objective 3—Energy production and recovery: promotes the energy recovery practice and self-energy production in wastewater systems. The criteria associated with this objective relies on energy recovery (e.g., by turbines, Archimedes screw) and energy self-production.
- (4)
- Objective 4—Economical and financial sustainability: ensures efficiency in the use of economic resources associated with energy (e.g., reduce energy costs, energy recovery, equipment, operation, and maintenance).
3.2. Results from Application to Wastewater Utilities
3.3. General Recommendations for PAS Application
4. Conclusions
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A
Metric | Description | Formulation |
---|---|---|
Objective 1 | Energy-use efficiency | ||
Criterion 1.1: Energy efficiency of wastewater systems | ||
M1.1.1: Specific energy per total WW volume (kWh/m3) | Energy consumption per unit volume of collected or treated wastewater. | Total annual energy consumption/total annual collected or treated wastewater volume. Note: Variables are included in the Portuguese regulator annual report. |
M1.1.2: Specific energy per total elevated volume (kWh/m3) | Energy consumption per unit volume of elevated wastewater. | Total annual energy consumption for elevation/total annual elevated wastewater volume. Note: Energy consumption for elevation included in the Portuguese regulator annual report. Total annual elevated volume should be obtained from measurements. |
M1.1.3: Pumping stations energy efficiency (kWh/(m3.100 m)) [28] | Average pumping energy consumption in the system per 1 m3 at 100 m of head. | Energy consumption for elevation/standardization factor. Note: Standardization factor: m3/(year.100 m). |
M1.1.4: Percentage of total energy consumption used for elevation (%) | Energy consumption for elevation in relation to the total energy consumption. | Energy consumption for elevation/total energy consumption × 100. |
M1.1.5: Percentage of total energy consumption used for WW treatment (%) | Energy consumption for treatment in relation to the total energy consumption. | Energy consumption for treatment/total energy consumption × 100. Note: Energy consumption for treatment should be obtained from measurements. |
M1.1.6: Energy consumption for WWTP per population equivalent (kWh/e.p.) | Energy consumption for treatment per equivalent of population. | Energy consumption for treatment/population equivalent. |
M1.1.7: Percentage of pumps with acceptable efficiency (%) | Percentage of pumps with efficiency losses below 25% of their nominal value. | N. of pumps with efficiency losses below 25% of their nominal value/total n. of pumps × 100. Note: Requires audits data. |
Criterion 1.2: Practices of operation, cleaning and maintenance | ||
M1.2.1: Energy consumption for sewer network cleaning (tep/(100 km.year)) | Annual energy consumption used to clean each 100 km of the sewer network. | Energy consumption for sewer network cleaning/number of sewer km. Note: Energy consumption for sewer network cleaning should be obtained from measurements. |
M1.2.2: Energy consumption for septic tanks cleaning (tep/(km of travel.year)) | Annual energy consumption used for trucks per km travelled to empty septic tanks. | Energy consumption of trucks/total km travelled. |
M1.2.3: Operation practices improvement to lower elevation height (-) | Practices implemented at the wastewater utility to decrease the energy used for elevation (e.g., pumping operation levels adjustment). | - |
Criterion 1.3: Control of undue inflows | ||
M1.3.1: Quarter energy peak factor (-) | Ratio between the average monthly consumption in the three months of highest consumption and the average monthly consumption. | Average energy consumption in the three months of highest consumption/average monthly energy consumption in the year. Note: Requires monthly energy consumption measurements. |
M1.3.2: Energy consumption seasonality (-) | Ratio between the average monthly consumption in the three months of highest consumption and the three months of lower consumption. | Average energy consumption in the three months of highest consumption/Average energy consumption in the three months of lowest consumption. Note: Requires monthly energy consumption measurements. |
M1.3.3: Percentage of energy equivalent to the volume generated in the served area used for elevation (%) | Total energy required to elevate the total volume generated in the served area if there were no limitations on the transport capacity of the network upstream of the pumping installation. | Energy consumption for elevation/energy consumption associated with the total volume generated in the served area × 100. Note: To obtain the energy consumption associated with the total volume generated in the served area it is necessary to measure the volume discharged or to have hydraulic models available. |
M1.3.4: Percentage of energy equivalent to the volume generated in the served area used for WW treatment (%) | Total energy used to treat the total volume from the served area if there were no limitations on the transport capacity of the network upstream of the pumping installation. | Energy consumption for treatment/energy consumption associated with the total volume generated in the served area × 100. |
M1.3.5: Effect of excessive inflows on energy consumption (%) | Percentage of energy consumption associated with undue inflows. | (Energy associated with the process/total volume of wastewater collected or treated) × (volume of excessive inflows of the dry weather pattern/total volume of wastewater collected or treated) × 100. Note: To obtain the volume of excessive inflows it is necessary to have daily flow patterns available. |
Objective 2 | Carbon neutrality | ||
Criterion 2.1: GHG emission in equipment, processes and transport | ||
M2.1.1: Specific GHG emissions associated with total WW volume (kg CO2 eq/m3) | Ratio between greenhouse gas emissions associated with the total energy consumption and the volume of wastewater collected or treated. | Total energy consumption × 7.04 × 10−4 (*)/total volume of wastewater collected or treated × 1000. Note: (*) Conversion factor: https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator (accessed on 12 January 2021). |
M2.1.2: Specific GHG emissions associated with elevated volume (kg CO2 eq/m3) | Ratio between greenhouse gas emissions associated with the energy consumption for elevation and the elevated volume. | Energy consumption for elevation × 7.04 × 10−4 (*)/elevated volume × 1000. |
M2.1.3: Specific GHG emissions associated with WW treated volume (kg CO2 eq/m3) | Ratio between greenhouse gas emissions associated with the energy consumption for treatment and the volume of wastewater collected or treated. | Energy consumption for treatment × 7.04 × 10−4 (*)/elevated volume × 1000. |
M2.1.4: Specific GHG emissions associated with volume generated in the served area (kg CO2 eq/m3) | Ratio between greenhouse gas emissions associated with the energy consumption associated with the total volume generated in the served area and the volume of wastewater collected or treated. | Energy consumption associated with the total volume generated in the served area × 7.04 × 10−4 (*)/total volume of wastewater collected or treated × 1000. |
M2.1.5: Specific GHG emissions associated with O&M (kg CO2 eq/m3) | Ratio between greenhouse gas emissions associated with the energy consumption for operation and maintenance and the volume of wastewater collected or treated. | Energy consumption for operation and maintenance × 7.04 × 10−4 (*)/total volume of wastewater collected or treated × 1000. |
Criterion 2.2: Use of clean energy | ||
M2.2.1: Percentage of total energy consumption from clean energy sources (%) | Percentage of total energy consumption that is associated with clean sources (e.g., solar, wind). | Energy consumption from clean sources/total energy consumption × 100. Note: Energy consumption from clean sources should be obtained from measurements. |
Objective 3 | Energy production and recovery | ||
Criterion 3.1: Self-energy production | ||
M3.1.1: Energy self-production (%) | Percentage of total energy consumption associated with self-production (e.g., biogas, solar). | Energy consumption from self-production/total energy consumption × 100. Note: Energy consumption for self-production should be obtained from measurements. |
Criterion 3.2: Energy recovery | ||
M3.2.1: Recovered energy (%) | Percentage of the total energy that is recovered by the wastewater utility. | Energy recovered/total energy consumption × 100. Note: Energy recovered should be obtained from measurements. |
Criterion 3.3: Use of purely gravity systems | ||
M3.3.1: Percentage of sewer network not associated with pumping stations (%) | Percentage of the total sewer network that is purely gravity. | Km of purely gravity network/total km of network. |
Objective 4 | Economical and financial sustainability | ||
Criterion 4.1: Wastewater system associated costs (except maintenance) | ||
M4.1.1: Percentage of cost of total energy equivalent to the volume generated in the served area used for elevation (%) | Cost of total energy required to elevate the total volume generated in the served area if there were no limitations on the transport capacity of the network upstream of the pumping installation. | Costs of energy consumption for elevation/costs of energy consumption associated with the total volume generated in the served area × 100. |
M4.1.2: Percentage of cost of total energy equivalent to the volume generated in the served area used for WW treatment (%) | Cost of total energy required to treat the total volume generated in the served area if there were no limitations on the transport capacity of the network upstream of the pumping installation. | Costs of energy consumption for treatment/costs of energy consumption associated with the total volume generated in the served area × 100. |
M4.1.3: Percentage of the cost of total energy consumption used for elevation (%) | Cost of energy consumption for elevation in relation to the total energy consumption. | Costs of total energy consumption for elevation/total energy costs × 100. |
M4.1.4: Percentage of the cost of total energy consumption used for WW treatment (%) | Cost of energy consumption for treatment in relation to the total energy consumption. | Costs of total energy consumption for treatment/total energy costs × 100. |
M4.1.5: Cost associated with the quarter energy peak factor (-) | Ratio of costs with the average monthly consumption in the three months of highest consumption and the average monthly consumption in the year. | Costs of the average energy consumption in the three months of highest consumption / costs of the average monthly energy consumption in the year. |
M4.1.6: Cost associated with energy consumption seasonality (-) | Ratio of costs with the average monthly consumption in the three months of highest consumption and the three months of lower consumption. | Costs of the average energy consumption in the three months of highest consumption / costs of the average energy consumption in the three months of lowest consumption. |
M4.1.7: Percentage of cost associated with energy self-production (%) | Percentage of total energy costs associated with self-production (e.g., biogas, solar). | Costs of energy consumption from self-production/total energy costs × 100. |
M4.1.8: O&M costs of energy consumption reduction by control of undue inflows (%) | Energy costs of operating and maintenance practices regarding the control of undue inflows to foster the reduction of energy consumption. | Energy costs of operating and maintenance practices regarding the control of undue inflows/total energy costs × 100. Note: Energy consumption associated with operating and maintenance practices regarding the control of undue inflows should be obtained from measurements. |
Criterion 4.2: Maintenance costs | ||
M4.2.1: Repair or replacement costs of pumping equipment (€/(equipment .year)) | Annual costs associated with the repair or replacement of pumps and/or pump components. | Costs associated with the repair or replacement of pumping equipment/total number of repaired equipment. |
M4.2.2: Cleaning operations costs of energy (€/(100 km.year)) | Annual costs associated with cleaning practices in the sewer network. | Costs of energy associated with cleaning practices in the sewer network/number of sewer km. Note: Energy consumption associated with cleaning practices should be obtained from measurements. |
M4.2.3: Solids removal operations costs of energy [€/(kg.year)] | Annual costs associated with operations regarding the removal of solids in the sewer network. | Costs of energy associated with solids removal operations/kg of solids removed. Note: Energy consumption associated with solids removal operations should be obtained from measurements. |
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WU/Type | Number of Effective Service Lodges | Network Extension (km) | Number of Pumping Stations | Number of WWTP |
---|---|---|---|---|
WU1/Type A | 35,204 | 32 | 3 | 23 |
WU2/Type A | 311,490 | 447 | 192 | 65 |
WU3/Type B | 19,772 | 546 | 66 | 9 |
WU4/Type A | 488,725 | 1498 | 380 | 176 |
WU5/Type B | 55,363 | 1539 | 85 | 16 |
WU6/Type B | 158,303 | 977 | 26 | 16 |
WU7/Type B | 2220 | 55 | 2 | 0 |
WU8/Type B | 29,722 | 444 | 17 | 1 |
Metric | Reference values |
---|---|
Objective 1 | Energy-use efficiency | |
Criterion 1.1: Energy efficiency of wastewater systems | |
M1.1.1: Specific energy per total WW volume (kWh/m3) |
A: [0, 0.5]; ]0.5, 0.6]; ]0.6, +∞[ B: [0, 0.2]; ]0.2, 0.3]; ]0.3, +∞[ |
M1.1.2: Specific energy per total elevated volume (kWh/m3) |
A: [0, 0.5]; ]0.5, 1.7]; ]1.7, +∞[ B: [0, 0.09]; [0.09, 0.12]; [0.12, +∞[ |
M1.1.3: Pumping stations energy efficiency [kWh(m3.100 m)] – metric from [28] | [0.27, 0.45]; ]0.45,0.68]; ]0.68,5[ |
M1.1.4: Percentage of total energy consumption used for elevation (%) |
A: [0, 15]; ]15, 30[; [30, 100] B: [0, 5]; ]5, 40[; [40, 100] |
M1.1.5: Percentage of total energy consumption used for WW treatment (%) |
A: [0, 5]; ]5, 50[; [50, 100] B: [0, 5]; ]5, 30[; [30, 100] |
M1.1.6: Energy consumption for WWTP per population equivalent (kWh/e.p.) | [0, 20]; ]20, 50[; [50, +∞[ |
M1.1.7: Percentage of pumps with acceptable efficiency (%) | - |
Criterion 1.2: Practices of operation, cleaning, and maintenance | |
M1.2.1: Energy consumption for sewer network cleaning [tep/(100 km.year)] | - |
M1.2.2: Energy consumption for septic tanks cleaning [tep/(km of travel.year)] | - |
M1.2.3: Operation practices improvement to lower elevation height (-) | - |
Criterion 1.3: Control of undue inflows | |
M1.3.1: Quarter energy peak factor (-) | [1.0, 1.25[; [1.25, 1.75[; [1.75, +∞[ |
M1.3.2: Energy consumption seasonality (-) | [1.0, 1.75[; [1.75, 2.5[; [2.5, +∞[ |
M1.3.3: Percentage of energy equivalent to the volume generated in the served area used for elevation (%) | [95, 100]; [80, 95[; [0, 80[ |
M1.3.4: Percentage of energy equivalent to the volume generated in the served area used for WW treatment (%) | [95, 100]; [80, 95[; [0, 80[ |
M1.3.5: Effect of excessive inflows on energy consumption (%) | [0, 2.0[; [2.0, 5.0[; [5.0, 100] |
Objective 2 | Carbon neutrality | |
Criterion 2.1: GHG emission in equipment, processes, and transport | |
M2.1.1: Specific GHG emissions associated with total WW volume (kg CO2 eq/m3) | [0, 0.3]; ]0.3, 0.5]; [0.5, +∞[ |
M2.1.2: Specific GHG emissions associated with elevated volume (kg CO2 eq/m3) | [0, 0.4]; ]0.4, 0.5]; ]0.5, +∞[ |
M2.1.3: Specific GHG emissions associated with WW treated volume (kg CO2 eq/m3) | [0, 0.2]; ]0.2, 0.4]; [0.4, +∞[ |
M2.1.4: Specific GHG emissions associated with the volume generated in the served area (kg CO2 eq/m3) | - |
M2.1.5: Specific GHG emissions associated with O&M (kg CO2 eq/m3) | [0, 1×10−4]; [1×10−4, 2×10−4]; [2×10−4, +∞] |
Criterion 2.2: Use of clean energy | |
M2.2.1: Percentage of total energy consumption from clean energy sources (%) | - |
Objective 3 | Energy production and recovery | |
Criterion 3.1: Self-energy production | |
M3.1.1: Energy self-production (%) | [20, 100]; [10, 20[; [0, 10[ |
Criterion 3.2: Energy recovery | |
M3.2.1: Recovered energy (%) | - |
Criterion 3.3: Use of purely gravity systems | |
M3.3.1: Percentage of sewer network not associated with pumping stations (%) | - |
Objective 4 | Economical and financial sustainability | |
Criterion 4.1: Wastewater system associated costs (except maintenance) | |
M4.1.1: Percentage of cost of total energy equivalent to the volume generated in the served area used for elevation (%) | - |
M4.1.2: Percentage of cost of total energy equivalent to the volume generated in the served area used for WW treatment (%) | - |
M4.1.3: Percentage of the cost of total energy consumption used for elevation (%) | - |
M4.1.4: Percentage of the cost of total energy consumption used for WW treatment (%) | - |
M4.1.5: Cost associated with the quarter energy peak factor (-) | [1, 1.5]; [1.5, 2.5[; [2.5, +∞[ |
M4.1.6: Cost associated with energy consumption seasonality (-) | [1, 2]; [2, 3[; [3, +∞[ |
M4.1.7: Percentage of the cost associated with energy self-production (%) | - |
M4.1.8: O&M costs of energy consumption reduction by control of undue inflows (%) | - |
Criterion 4.2: Maintenance costs | |
M4.2.1: Repair or replacement costs of pumping equipment [€/(equipment.year)] | - |
M4.2.2: Cleaning operations costs of energy [€/(100 km.year)] | - |
M4.2.3: Solids removal operations costs of energy [€/(kg.year)] | - |
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Jorge, C.; Almeida, M.d.C.; Covas, D. Performance Assessment System for Energy Efficiency in Wastewater Systems. Water 2021, 13, 1807. https://doi.org/10.3390/w13131807
Jorge C, Almeida MdC, Covas D. Performance Assessment System for Energy Efficiency in Wastewater Systems. Water. 2021; 13(13):1807. https://doi.org/10.3390/w13131807
Chicago/Turabian StyleJorge, Catarina, Maria do Céu Almeida, and Dídia Covas. 2021. "Performance Assessment System for Energy Efficiency in Wastewater Systems" Water 13, no. 13: 1807. https://doi.org/10.3390/w13131807