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Scope 1/2/3 Emissions ​

GHG Protocol classification of direct, energy, and value chain emissions for wastewater treatment

Overview ​

The GHG Protocol Corporate Standard classifies greenhouse gas emissions into three scopes based on the source and organizational control. This framework enables comprehensive carbon accounting and identifies reduction opportunities across the value chain.

Scope Definitions ​

Scope 1: Direct Emissions ​

Emissions from sources owned or controlled by the organization.

┌─────────────────────────────────────────────────────┐
│                    SCOPE 1                          │
│              (Direct Emissions)                     │
├─────────────────────────────────────────────────────┤
│  • Process emissions (N2O, CH4)                     │
│  • Stationary combustion (boilers, CHP)             │
│  • Mobile combustion (vehicles)                     │
│  • Fugitive emissions (biogas leaks)                │
└─────────────────────────────────────────────────────┘

Scope 2: Energy Indirect Emissions ​

Emissions from purchased energy.

┌─────────────────────────────────────────────────────┐
│                    SCOPE 2                          │
│            (Energy Indirect)                        │
├─────────────────────────────────────────────────────┤
│  • Purchased electricity                            │
│  • Purchased steam                                  │
│  • Purchased heating/cooling                        │
└─────────────────────────────────────────────────────┘

Scope 3: Other Indirect Emissions ​

All other indirect emissions in the value chain.

┌─────────────────────────────────────────────────────┐
│                    SCOPE 3                          │
│            (Value Chain)                            │
├─────────────────────────────────────────────────────┤
│  UPSTREAM:                                          │
│  • Chemical production (embodied carbon)            │
│  • Capital goods (infrastructure)                   │
│  • Transportation (chemical delivery)               │
│                                                     │
│  DOWNSTREAM:                                        │
│  • Sludge transport and disposal                    │
│  • Effluent discharge (if CH4 released)             │
└─────────────────────────────────────────────────────┘

Scope 1 Details ​

Process Emissions ​

SourceGHGCalculation
NitrificationN2OEF × TKN_nitrified
DenitrificationN2OEF × NO3_denitrified
Anaerobic digestionCH4(1-eta) × CH4_produced
Biogas handlingCH4Leak rate × production

Stationary Combustion ​

FuelCO2 FactorCH4 FactorN2O Factor
Natural gas2.0 kg/m30.001 kg/m30.0001 kg/m3
Diesel2.68 kg/L0.00015 kg/L0.00004 kg/L
Biogas (CHP)0 (biogenic)0.001 kg/m30.0001 kg/m3

CHP Emissions ​

Combined heat and power using biogas:

$$E_{CHP} = V_{biogas} \times %CH_4 \times EF_{combustion}$$

Note: CO2 from biogas combustion is biogenic (excluded from totals)

Fugitive Emissions ​

Biogas System:

ComponentLeak RateDetection
Digester cover0.1-0.5%Flame ionization
Gas holder0.5-2.0%Soap bubble
Pipe flanges0.05-0.2%LDAR survey
Valves0.1-0.5%Infrared camera
Safety valvesVariableContinuous monitor

Scope 2 Details ​

Electricity Consumption ​

$$E_{electricity} = kWh \times EF_{grid}$$

Grid Carbon Intensity (kg CO2e/kWh) ​

Country/Region2024 FactorTrend
UK0.21Decreasing
Germany0.35Decreasing
France0.06Stable (nuclear)
USA (average)0.42Decreasing
Poland0.72Decreasing
Australia0.65Decreasing
China0.56Decreasing

Location vs Market-Based ​

MethodDescriptionUse Case
Location-basedGrid averageDefault reporting
Market-basedContractual instrumentsPPA, RECs, GoO

Example:

  • Location-based: 1,000 MWh × 0.42 kg/kWh = 420 tonnes CO2e
  • Market-based (100% renewable): 1,000 MWh × 0 = 0 tonnes CO2e

Energy Breakdown by Process ​

Process% of TotalTypical kWh/ML
Aeration50-60%150-300
Pumping20-25%60-125
Sludge treatment10-15%30-75
UV disinfection2-5%10-25
Mixing3-5%10-25
Buildings/HVAC3-5%10-25

Scope 3 Details ​

Upstream Emissions ​

Chemical Production (Embodied Carbon) ​

Chemicalkg CO2e/kgUse
Ferric chloride0.26P removal
Ferric sulfate0.18P removal
Alum0.40Coagulation
Polymer (synthetic)2.5-4.0Dewatering
Polymer (bio-based)0.5-1.0Dewatering
Lime (CaO)0.95pH control
NaOH (membrane)1.20pH control
NaOCl0.50Disinfection
Methanol0.70Carbon source
Acetic acid0.80Carbon source
Activated carbon3.5-8.5Adsorption

Calculation:

$$E_{chemical} = \sum (Q_i \times EF_i)$$

Where:

  • Q_i = Annual consumption (kg/y)
  • EF_i = Embodied carbon (kg CO2e/kg)

Chemical Transport ​

$$E_{transport} = Distance \times Load \times EF_{mode}$$

Modekg CO2e/tonne-km
Road (HGV)0.089
Rail0.028
Sea0.016

Downstream Emissions ​

Sludge Transport ​

$$E_{sludge transport} = m_{sludge} \times d \times EF_{road}$$

Where:

  • m_sludge = Dry tonnes/year
  • d = Distance to disposal (km)

Sludge Disposal ​

Methodkg CO2e/tonne DSNotes
Landfill200-500Methane generation
Incineration100-300Energy recovery credit
Land application50-150Fertilizer offset
Composting30-100Low processing
Pyrolysis-50 to 100Biochar credit

Infrastructure Embodied Carbon ​

Annualized over design life:

$$E_{infra} = \frac{\sum (m_i \times EF_i)}{Design Life}$$

Materialkg CO2e/kg
Concrete0.10-0.15
Reinforcing steel1.5-2.0
Stainless steel4.5-5.5
HDPE pipe2.0-2.5
PVC pipe2.5-3.0
Copper2.5-3.5

Typical annualized: 5-15% of total footprint

Scope Aggregation ​

Calculation Summary ​

$$Scope 1 = E_{process} + E_{combustion} + E_{fugitive}$$

$$Scope 2 = kWh_{purchased} \times EF_{grid}$$

$$Scope 3 = E_{chemicals} + E_{transport} + E_{disposal} + E_{infrastructure}$$

$$Total = Scope 1 + Scope 2 + Scope 3$$

Example Plant (20 MLD) ​

ScopeSourceCO2e (t/y)
Scope 1850
N2O emissions650
CH4 fugitive150
CHP combustion50
Scope 21,200
Electricity (3.5 GWh)1,200
Scope 3550
Chemicals200
Sludge disposal250
Infrastructure100
Total2,600
Per m30.36 kg

Reporting Configuration ​

ErgoPlanner Settings ​

json
{
  "carbonFootprint": {
    "scope1": {
      "processEmissions": true,
      "n2oModel": "process-based",
      "ch4Model": "mass-balance",
      "fugitiveEstimation": "component-level",
      "combustionTracking": true
    },
    "scope2": {
      "method": "location-based",
      "gridFactor": 0.21,
      "renewablePercentage": 0,
      "marketInstruments": []
    },
    "scope3": {
      "chemicals": true,
      "chemicalDatabase": "default",
      "transport": true,
      "disposal": true,
      "disposalMethod": "land_application",
      "infrastructure": false
    },
    "reporting": {
      "period": "annual",
      "boundaries": "operational-control",
      "format": "GHG-Protocol"
    }
  }
}

Reduction Strategies by Scope ​

Scope 1 Reductions ​

StrategyPotentialCost
N2O mitigation (DO control)30-70%Low
CH4 capture improvement50-90%Medium
LDAR program20-50%Low
Electric vehicles100%High

Scope 2 Reductions ​

StrategyPotentialCost
Energy efficiency20-40%Low-Medium
On-site solar20-50%Medium
Biogas CHP30-60%High
PPA (renewable)100%Variable
Grid decarbonizationAutomaticN/A

Scope 3 Reductions ​

StrategyPotentialCost
Chemical optimization10-30%Low
Local chemical sourcing20-40%Variable
Sludge land application50-70%Low
Low-carbon chemicals30-50%Medium
Infrastructure optimization10-20%High

Net Zero Pathway ​

Typical Reduction Roadmap ​

2024: Baseline
      │
2030: ─┼─ 30% reduction
      │   • Energy efficiency
      │   • N2O optimization
      │   • Biogas maximization
      │
2040: ─┼─ 60% reduction
      │   • On-site renewables
      │   • Electric fleet
      │   • Chemical substitution
      │
2050: ─┼─ Net Zero
          • 100% renewable
          • Residual offsetting
          • Carbon capture

Carbon Credits ​

For residual emissions:

  • Verified carbon offsets (VCS, Gold Standard)
  • Nature-based solutions
  • Carbon capture and storage (CCS)

References ​

  1. GHG Protocol (2015). Corporate Accounting and Reporting Standard
  2. GHG Protocol (2011). Corporate Value Chain (Scope 3) Standard
  3. DEFRA (2024). UK Government GHG Conversion Factors
  4. IPCC (2019). Guidelines for National GHG Inventories
  5. WRI/WBCSD (2015). GHG Protocol Scope 2 Guidance