Phase 4     Solids & Liquids Utilization

The digestate created in the AD stage is pumped to high solids screw presses (or centrifuges) for dewatering. The digestate is drawn on a daily basis and pumped to the presses for dewatering.The digestate is virtually contaminant free, is more than 75% of its way through the biological degradation cycle, is significantly reduced in volume, and has high fibre structure.

Step 8: Digestate Separation

Screw presses/centrifuging mechanically separates the digested material into solids and liquids after the retention time in the digester. The reclaimed liquids are captured and reused in the process water loop.

 

Dewatering Presses
         Internal View

Step 9: Dewatered Solids Utilization

The digested solids are typically used to make a final compost product.  Approximately 85% of the biological activity has been completed in the AD phase. There is a requirement to add bulking materials to allow greater porosity and oxygenation if the aerobic finishing of the digestate is implemented, which is typical. 

 

Digestate Close-Up
         Digestate Composting

Step 10: Reclaimed Liquids Utilization

Reclaimed liquids from the tipping floor drains, digestate solids/liquid separation, biogas dewatering and the dewatering of grit, heavies and rake fractions is stored in a buffer tank for reuse as process water. The facility is a net reclaimer of water due to the high moisture content in the organics. Excess liquids are typically discharged to the sewer.  Additional treatment prior to discharge is dependent on local requirements or alternative uses. 

 

Residuals Dewatering
         Optional Water Treatment