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; 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.
2. The process of claim 1 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.
3. The process of claim 1 wherein the step of recuperative thickening comprises thickening digestate in a rotary screw press.
4. The process of claim 1 comprising mixing digestate in the digester with a hydraulic mixer.
5. A process for treating WWTP sludge comprising the steps of,
feeding the WWTP sludge at 4% TS or less to an anaerobic digester;
operating the anaerobic digester at 5 to 6% TS; and,
providing recuperative thickening for the digester by way of a side stream thickener; and,
adding a polymeric thickening aid in the side stream.
6. The process of claim 5 wherein waste digestate is dewatered separately from the side stream.
7. The process of any of claim 5 further comprising mixing the digester with a hydraulic mixer.
8. The process of claim 5 comprising mixing digestate in the digester intermittently.
9. The process of claim 5 wherein the step of recuperative thickening comprises thickening digestate in a rotary screw press.
10. The process of claim 5 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.