Solid waste treatment with conversion to gas and anaerobic digestion
Waste solids are treated by pyrolysis at a temperature over 700 degrees C. to produce char and a gas. The gas is treated in an anaerobic digester. In one system, gas and digestate are brought into contact in a diffusion cone. In another option, headspace gas above the digestate is re-circulated through the digestate, for example by way of an eductor downstream of the diffusion cone.
1. A process comprising steps of,
a) producing a gas containing hydrogen and carbon monoxide from pyrolysis of a feedstock at a temperature of over 750 degrees C.; and,
b) adding the gas to an anaerobic digester,
wherein the feedstock comprises plastic.
2. The process of claim 1 wherein the feedstock comprises a mixture of biogenic and non-biogenic material.
3. The process of claim 1 wherein the anaerobic digester is coupled with or part of a municipal wastewater treatment plant.
4. The process of claim 1 comprising producing a gas containing hydrogen and carbon monoxide from pyrolysis of a feedstock at a temperature of 800 degrees C. or more.
5. An apparatus for transferring syngas to digestate comprising a diffusion cone in a sidestream loop wherein the diffusion cone defines an outer surface of part of the sidestream loop with a downwardly increasing cross sectional area.
6. The apparatus of claim 5 having an eductor in the sidestream loop downstream of the diffusion cone and connected to a headspace of the digester.
7. A process for treating wastewater comprising,
a) treating the wastewater to generate a sludge;
b) feeding the sludge to an anaerobic digester to produce biogas and digestate;
c) dewatering the digestate to produce a cake;
d) thermally drying the cake to produce a dried cake;
e) pyrolysing the dried cake at a temperature of over 700 degrees C. or more to produce char and syngas;
f) feeding the syngas to the anaerobic digester;
g) monitoring one or more indicators of carbon monoxide inhibition in the anaerobic digester.
8. The process of claim 7 comprising pyrolysing the dried cake at a temperature of over 800 degrees C. or more.