To achieve SDG 6.2 in full:
•6.6 billion people will have to gain access to safely managed sanitation between 2016 and 2030; and
•Not less than US$46 billion will be spent to achieve 100% coverage of safely managed sanitation in urban areas alone

This major investment is a challenge, but it also presents some opportunities to make better investment decisions in rapidly growing towns which are becoming cities.  With luck we can “lock in” carbon neutral or negative solutions but only if we improve our knowledge base.

CACTUS is developing models to enable estimation of Greenhouse Gas emissions from a range of sanitation systems.

CACTUS uses a combination of sources to model emissions from systems operating under a range of conditions.  The approach includes:

•Direct emissions from sludges and wastewater which are degrading and producing CH4 and NO2
•Operational emissions from burning fossil fuels (trucking, pumping, aeration)
•Embedded carbon

Calculations are modelled along the whole value chain for both onsite and offsite systems.

Full models and estimates will be uploaded during the next phaes of the project. Below is our model for estimating direct emissions from onsite systems.

Estimate of water use, energy use and GHG emissions in different urban sanitation systems

OSS Technologies (correspond to CH4 type)
Septic Tank Anaerobic environment. Half of BOD settles in tank.
Latrine Type 1 Household latrines in dry climate, with ground water table well below bottom of pit
Latrine Type 2 Communal latrines in dry climate, ground water table well below bottom of pit, Many users, higher volume of FS leading to a more anaerobic environment. These latrines are often poorly maintained.
Latrine Type 3 Wet climate/flush water use, ground water table higher than latrine. These types of latrine have more anaerobic conditions.
Latrine Type 4 UD and composting toilets,  aerobic environments. Regular sediment removal for fertiliser. Bucket latrines may also fall into this category providing waste is correctly disposed of.
Open Sewer Stagnant open sewers are often the site for illegal emptying of waste. They are heated by the sun which can lead to ideal conditions for methanogenesis however depending on the depth the sludge the top layers may be in aerobic conditions which would inhibit methane production.
N2O Category
A nitrification in the upper layers of the pits, not much denitrification is predicted to occur at the bottom
B simple latrines, where the conditions are predicted to be slightly less aerobic in the upper layers of the sludge
C account for both denitrification and some nitrification
D increased nitrification in VIPs and more denitrification occurring deeper within the pits
E simple latrines with less nitrification occurring at the surface
F septic tanks in warmer climated countries
G composting latrines designed for arobic decompositions and open defecation practices