[kleton]

There aren't a lot of places that use anaerobic digesters (fermenting waste to methane) to treat wastewater. Anheuser-Busch does it at their breweries because their wastewater is particularly rich. If more municipalities built those at their wastewater treatment plants, then it would be a sizeable amount of carbon-neutral fuel. There are already 1200 municipal wastewater treatment plants in the US that do this according to the EPA, but there are many major cities that do not. https://www.epa.gov/anaerobic-digestion/types-anaerobic-dige...

[toomanybeersies]

The energy generated from biogas recovery at Melbourne's two main sewerage plants (~100 GWh) isn't even enough to make them net generators [1].

The main environmental benefit isn't actually from the carbon footprint of biogas, it's the reduced methane and NOx emissions from capturing the gas.

[1] https://www.melbournewater.com.au/water-data-and-education/e...

[noaccnt]

Ya, but I would guess the story is a bit more complicated. Consider (off the top of my head):

I imagine there's a real concentration problem there. Sewage is incredibly diluted if you think about it (divide your estimate of how much organic waste you generate by the amount of water used in your water bill).

If, instead, houses had grey water systems (i.e. the sink in you bathroom is used to fill up your toilet tank), or if black waters had a separate sewer (sure, not feasible in suburbia), the energy budget would change considerably.

Either way, the affluent is full if nutrients even if we can't recover the energy. Nutrients our soil is rapidly being depleted of (thanks to our modern use of sewers!)

[toomanybeersies]

At the end of the day, there's just not a lot of energy in human waste. Poop is what's left after your body has extract all the energy it can from food.

[noaccnt]

That's a key qualifier though, energy we can extract.

I don't think energy recovery from sewage is feasible, not in the short term, not with our current infrastructure. But either way we should be treating our waste more deferentially in an attempt to recover the minerals 6 billion people poop every day. Except for water, everything in pee and poop is valuable if recovered (urea ->energy, phosphate ->mineral, sulphur ->mineral, starch ->energy)

Instead it all gets dumped to the oceans and the ocean dies from too much nutrients

[lostlogin]

I don’t think you are correct. A lot of places spread it on crop fields historically and many still do. It can be treated to remove (reduce?) the risk of disease transmission.

Animal manure is very good for plants and many gardeners seek out chicken, horse or cow manure.

[toomanybeersies]

Manure is used as a source of nitrogen for crops, not energy. Plants usually get their energy from the sun.

[pchristensen]

affluent -> effluent. Affluent means wealthy.

[noaccnt]

thnx

[istjohn]

I imagine it also greatly improves the air quality for anyone down wind from the treatment plants.