# Phase 04 Waste & Water Factor Calculation Steps

All calculations use AR5 GWP values: CH₄ = 28, N₂O = 265. IPCC 2006 Guidelines Vol. 5 are used unless noted.

## 1. Managed landfill — `ng.waste.msw.landfill.managed`

**Composition selected:** Lagos metropolis mean from `msw_composition_nigeria.csv` (row 6). This is a single, Nigeria-representative urban composition with high confidence; it contains no residual `other_pct`.

| Component | % wet mass | DOC_j |
|-----------|-----------:|-------|
| Food      | 66.11      | 0.15  |
| Paper     | 10.02      | 0.40  |
| Plastic   | 13.93      | 0     |
| Metal     | 2.99       | 0     |
| Glass     | 2.36       | 0     |
| Textile   | 4.58       | 0.24  |
| Wood      | 0.00       | 0.43  |
| Other     | 0.00       | 0     |

DOC = Σ(frac_j × DOC_j) = 0.6611×0.15 + 0.1002×0.40 + 0.0458×0.24 = **0.15024**

Parameters (IPCC 2006 Vol. 5 Ch. 3 Tier 1):
- DOCf = 0.5
- F = 0.5
- OX = 0.1
- MCF = 1.0

EF_CH₄ (kg/t wet waste) = DOC × DOCf × F × (16/12) × (1 − OX) × MCF × 1000
= 0.15024 × 0.5 × 0.5 × 1.3333 × 0.9 × 1.0 × 1000
= **45.07 kg CH₄/t**

CO₂e = 45.07 × 28 = **1,262 kgCO₂e/t** → rounded **1,260 kgCO₂e/t**.

## 2. Open dump — `ng.waste.msw.open_dump`

Same DOC as above.
Parameters:
- DOCf = 0.5, F = 0.5
- OX = 0.0
- MCF = 0.4 (unmanaged deep dump, >5 m)

EF_CH₄ = 0.15024 × 0.5 × 0.5 × 1.3333 × 1.0 × 0.4 × 1000
= **20.03 kg CH₄/t**

CO₂e = 20.03 × 28 = **560.9 kgCO₂e/t** → rounded **561 kgCO₂e/t**.

## 3. Open burning — `ng.waste.msw.open_burning`

Source: IPCC 2006 Vol. 5 Ch. 5, Table 5.7 (`datasets/waste_water/derived/ipcc_default_parameters.csv`, rows 43–45). These are default EFs per tonne of waste open-burned:
- EF_CO₂ (fossil only) = **33 kg CO₂/t**
- EF_CH₄ = **6.5 kg CH₄/t**
- EF_N₂O = **0.2 kg N₂O/t**

CO₂e = 33 + (6.5 × 28) + (0.2 × 265) = 33 + 182 + 53 = **268 kgCO₂e/t**.

Nigeria-specific composition data (e.g., Lagos plastics/textiles shares) would allow a more refined fossil CO₂ estimate; the IPCC default fossil CO₂ factor is used here because country-specific fossil-carbon fractions were not available.

## 4. Composting — `ng.waste.organic.composting`

Source: IPCC 2006 Vol. 5 Ch. 4, Table 4.1 (wet-weight defaults):
- EF_CH₄ = 4 g/kg wet waste = **4.00 kg CH₄/t**
- EF_N₂O = 0.24 g/kg wet waste = **0.240 kg N₂O/t**

CO₂e = (4.00 × 28) + (0.240 × 265) = 112 + 63.6 = **175.6 kgCO₂e/t** → rounded **176 kgCO₂e/t**.

## 5. Domestic wastewater — `ng.waste.wastewater.domestic`

- Bo (IPCC default) = **0.6 kg CH₄/kg BOD**
- Weighted national MCF derived from NIR1 (2017)
  - TOW = 2,577,699,350 kg BOD (Table 7.4)
  - Reported CH₄ emissions = 547.6 Gg = 547,600,000 kg CH₄ (Table 7.13)
  - Effective EF = 547,600,000 / 2,577,699,350 = **0.2124 kg CH₄/kg BOD**
  - Effective MCF = 0.2124 / 0.6 = **0.354**
- Influent BOD from Oke-Afa WWTP = **127.5 mg/L = 0.1275 kg/m³**

Per m³:
- CH₄ = 0.2124 kg/kg BOD × 0.1275 kg BOD/m³ = **0.0271 kg CH₄/m³**
- CO₂e = 0.0271 × 28 = **0.758 kgCO₂e/m³**

The equivalent per-kg-BOD factor is **5.95 kgCO₂e/kg BOD**.

## 6. Industrial wastewater — `ng.waste.wastewater.industrial`

- Bo (IPCC default) = **0.25 kg CH₄/kg COD**
- Conservative industrial MCF (warm climate, limited treatment) = **0.3**

EF_CH₄ = 0.25 × 0.3 = **0.0750 kg CH₄/kg COD**
CO₂e = 0.0750 × 28 = **2.10 kgCO₂e/kg COD**.

## 7. Water supply — `ng.water.treatment.supply`

Local electricity intensity data for Nigerian waterworks was not available, so an international proxy was derived from UK DEFRA 2024:
- DEFRA water supply factor = 0.15311 kgCO₂e/m³
- UK grid EF = 0.20705 kgCO₂e/kWh
- Implied intensity = 0.15311 / 0.20705 = **0.739 kWh/m³**

Grid factor used: `ng.grid.national.location.2024` = **0.138611 kgCO₂e/kWh** (Nigeria national grid, AR5, location-based).

CO₂e = 0.739 × 0.138611 = **0.1025 kgCO₂e/m³** → rounded **0.103 kgCO₂e/m³**.

## 8. Wastewater treatment — `ng.water.treatment.wastewater`

UK DEFRA 2024 proxy:
- DEFRA water treatment factor = 0.18574 kgCO₂e/m³
- UK grid EF = 0.20705 kgCO₂e/kWh
- Implied intensity = 0.18574 / 0.20705 = **0.897 kWh/m³**

CO₂e = 0.897 × 0.138611 = **0.1243 kgCO₂e/m³** → rounded **0.124 kgCO₂e/m³**.