Treatment of waste products with anaerobic digestion
A waste stream is treated by anaerobic digestion. A process is described involves a step of separating solids from digestate, and returning separated solids to a digester. Optionally, there may be a step of solids separation in which larger solids are removed from the digester. A process and apparatus are described for treating waste sludge from a wastewater treatment plant in an anaerobic digester. Feed sludge is thickened or solids are separated from digestate and returned to the digester. Additional co-digestion waste may be added to the digester. The process and apparatus may be used in a retrofit of an existing wastewater treatment plant.
1. A process for treating waste sludge from a wastewater treatment plant comprising the steps of,
a) flowing the waste sludge to an anaerobic digester;
b) thickening the waste sludge before it enters the digester or recuperative thickening of digestate in the digester; and,
c) adding an external waste stream to the digester such that at least 30% of the volatile solids loading to the digester is derived from the external waste stream.
2. The process of claim 1 wherein digestate in the digester is mixed with hydraulic mixers.
3. The process of claim 1 wherein the digester is mixed intermittently.
4. The process of claim 1 comprising recuperative thickening of the digestate.
5. The process of claim 4 comprising grinding digestate before flowing the digestate to a thickener in a recuperative thickening loop.
6. The process of claim 1 comprising wasting digestate directly from the digester.
7. The process of claim 1 wherein digestate in the digester is maintained at a solids content of 3% or more.
8. The process of claim 1 wherein digestate in the digester is maintained at a solids content of 5% or more.
9. A process for treating waste sludge from a wastewater treatment plant comprising the steps of,
a) flowing the waste sludge to an existing anaerobic digester of the wastewater treatment plant; and,
b) recuperative thickening digestate in the digester.
wherein diqestate in the digester is maintained at a solids content of 5 % or more, and further comprising adding an external waste stream to the digester such that at least 30% of the volatile solids loading to the digester is derived from the external waste stream.
10. The process of claim 9 wherein the step of recuperative thickening comprises thickening digestate in a rotary screw press.
11. The process of claim 9 comprising mixing digestate in the digester with a hydraulic mixer.
12. A process for treating waste sludge from a wastewater treatment plant comprising the steps of,
a) flowing the waste sludge to an existing anaerobic digester of the wastewater treatment plant; and,
b) recuperative thickening digestate in the digester,
wherein digestate in the digester is maintained at a solids content of 5% or more, and further comprising mixing digestate in the digester intermittently.
13. The process of claim 12 wherein the step of recuperative thickening comprises thickening digestate in a rotary screw press.
14. The process of claim 12 comprising mixing digestate in the digester intermittently.