# Phase 04 Waste & Water Factor Notes

## Overview
This note records the assumptions, conservative default choices, data-quality flags, and gaps for the eight Phase 4 emission factors calculated in `phase_04_factor_calculation.csv`.

## General assumptions

- **GWP basis:** AR5 — CH₄ = 28, N₂O = 265. This matches the AR5 basis used by existing NEFDB grid-electricity factors (e.g., `ng.grid.national.location.2024`).
- **Biogenic CO₂:** Excluded from all waste factors (landfill methane, open-burning fossil CO₂ only, composting biogenic CO₂ excluded), consistent with IPCC and GHG Protocol Scope 1/3 practice.
- **All factors are candidate values** intended for review and possible adoption into `src/factors/waste.ts` and `src/factors/water.ts`.

## Factor-by-factor assumptions and flags

### 1. `ng.waste.msw.landfill.managed`
- **Composition:** Lagos metropolis mean from `msw_composition_nigeria.csv` (row 6). High-confidence, Nigeria-representative urban data. The row has no residual `other_pct`, so DOC can be computed directly.
- **IPCC defaults used:** DOCf = 0.5; F = 0.5; OX = 0.1; MCF = 1.0.
- **Flag:** Real Nigerian sanitary landfills are rare; most disposed waste is open-dumped. Treat this as a *managed landfill* (controlled/engineered) scenario rather than the dominant current practice.

### 2. `ng.waste.msw.open_dump`
- **Composition:** Same Lagos metropolis mean as above.
- **IPCC defaults used:** DOCf = 0.5; F = 0.5; OX = 0; MCF = 0.4 (unmanaged deep dump, >5 m).
- **Flag:** If Nigerian dumps are shallow (<5 m), MCF should be lower (~0.2). The 0.4 value is the IPCC default for deep unmanaged dumps and is conservative for deeper sites.

### 3. `ng.waste.msw.open_burning`
- **EFs:** IPCC 2006 Vol. 5 Ch. 5 Table 5.7 defaults: fossil CO₂ = 33 kg/t; CH₄ = 6.5 kg/t; N₂O = 0.2 kg/t.
- **Flag:** Nigeria-specific studies (e.g., Okafor et al. 2022) estimate a higher fossil CO₂ share because Nigeria's plastic fraction is rising; this would raise the factor toward ~320 kgCO₂e/t. The IPCC default is retained until Nigeria-specific fossil-carbon fractions are agreed.

### 4. `ng.waste.organic.composting`
- **EFs:** IPCC 2006 Vol. 5 Ch. 4 Table 4.1 wet-weight defaults: CH₄ = 4 g/kg; N₂O = 0.24 g/kg.
- **Flag:** Assumes well-managed mixed-windrow composting. Industrial-scale, poorly turned piles would emit more CH₄.

### 5. `ng.waste.wastewater.domestic`
- **Bo:** IPCC default 0.6 kg CH₄/kg BOD.
- **MCF:** A national weighted MCF of 0.354 was derived from NIR1 2017 aggregate emissions (547.6 Gg CH₄) and total organically degradable material (2,577,699,350 kg BOD). This avoids needing an urban high/low income split, which is not given in NIR1.
- **BOD concentration:** Oke-Afa WWTP influent BOD = 127.5 mg/L = 0.1275 kg/m³.
- **Flag:** Does **not** include N₂O from domestic wastewater. IPCC estimates N₂O from protein load; add a separate factor if required.
- **Fallback:** `nigeria_waste_water_inputs.csv` was not available; NIR1 Tables 7.4 and 7.13 were used directly.

### 6. `ng.waste.wastewater.industrial`
- **Bo:** IPCC default 0.25 kg CH₄/kg COD.
- **MCF:** Conservative 0.3 (overloaded aerobic / partial anaerobic conditions). Site-specific industrial effluent treatment can range from ~0.1 (clean, aerobic) to 0.8 (anaerobic lagoon).
- **Flag:** Very limited Nigeria-specific industrial effluent data. Treat as a conservative order-of-magnitude factor.

### 7. `ng.water.treatment.supply`
- **Electricity intensity proxy:** UK DEFRA 2024 water supply factor (0.15311 kgCO₂e/m³) divided by UK grid EF (0.20705 kgCO₂e/kWh) → 0.739 kWh/m³.
- **Grid factor:** `ng.grid.national.location.2024` = 0.138611 kgCO₂e/kWh (Nigeria national grid, AR5, location-based).
- **Flag:** No measured electricity intensity for Nigerian State Water Agencies was found in the local docs. Proxy may understate pumping energy in Nigerian systems with high non-revenue water and diesel backup.

### 8. `ng.water.treatment.wastewater`
- **Electricity intensity proxy:** UK DEFRA 2024 water treatment factor (0.18574 kgCO₂e/m³) divided by UK grid EF (0.20705 kgCO₂e/kWh) → 0.897 kWh/m³.
- **Grid factor:** Same as above.
- **Flag:** Very few Nigerian WWTPs operate continuously; actual energy use is likely lower at poorly performing plants and higher at aerated/lift stations. Proxy should be validated against plant-level data when available.

## Data gaps and recommended next steps

1. **National MSW composition:** No national composition table was found in Nigeria's BUR2/NIR1. Current factors rely on Lagos data.
2. **Fossil carbon fraction for open burning:** Obtain Nigeria-specific plastic/synthetic textile shares and carbon content to refine fossil CO₂.
3. **Industrial wastewater MCF:** Collect treatment-type shares by sector (food & beverage, textiles, oil & gas, etc.).
4. **Water/WWTP electricity intensity:** Extract energy-use data from WASHNORM utility mapping or directly from SWAs/WWTP operators.
5. **N₂O from wastewater:** Add a separate domestic-wastewater N₂O factor using IPCC protein-based methodology.
6. **Gas flaring/landfill gas recovery:** Managed landfill factor assumes no CH₄ recovery; update if recovery becomes material.

## Sources used
- `datasets/waste_water/derived/msw_composition_nigeria.csv`
- `datasets/waste_water/derived/wastewater_treatment_params.csv`
- `datasets/waste_water/derived/ipcc_default_parameters.csv`
- `docs/regulatory_mrv/11_Nigeria_NIR1_2000_2017.md` (Tables 7.4, 7.5, 7.13)
- `docs/waste_water/oke_afa_wwtp_lagos_2021.md`
- `docs/waste_water/Environ-09-02-11.md` (open-burning context only)
- `datasets/international_ef_databases/ghg-conversion-factors-2024-FlatFormat_v1_1.xlsx` (DEFRA water factors)
- `src/factors/grid_electricity.ts`
- IPCC 2006 Guidelines Vol. 5 Chapters 3–6