The flocculation and settling was achieved spontaneously at the pH of zero point charge (pHzpc), straight after blending the two waste streams (i.e. the acidified anaerobic digestate and the wood ash), without the use of centrifugation. Further treatment of the liquor via aeration or addition of antifoam chemicals would be sufficient to remove the bubbles from the surface of the liquid.
This video was recorded while performing the steps to attain the pHzpc as previously reported (https://doi.org/10.1016/j.nbsj.2022.100014). The experimental unit that is examined in this video is similar to the one reported in the Fig. S.8 (https://doi.org/10.1016/j.nbsj.2022.100014). The steps to reproduce these conditions of dewaterability of the anaerobic digestate are:
1. Acidify the anaerobic digestate with a common dose (0.24 mol H+/kg anaerobic digestate) of a commercial acid (e.g. H2SO4, HCl, and HNO3): Add 10 mL of the acid solution to each gram of anaerobic digestate. In total were around 20 mL of acid solution added to 2 g of anaerobic digestate.
2. Add 10 mL of the deionized water to each gram of wood ash. In total were around 5 mL of milli-Q water added to 0.5 g of wood ash. The purpose of this step is to fluidize the wood ash for easy handling. It would be possible to apply several rounds of washing to the wood ash to remove the impurities and improve sorption capacity.
3. Blend the 2 fluidized streams: Flocculation and settling occurs spontaneously.