Novel Approaches for the Dewatering of Anaerobic Digestate from Food Waste: EPS Stripping Coupled Skeletal Reconstruction

Digestate dewatering challenges have been recognized as the bottleneck in applying anaerobic digestion of food waste. The study demonstrated that the content and composition of extracellular polymeric substances (EPSs) played crucial roles in the dewaterability of food waste anaerobic digestate (FWAD). The protein of tightly bound EPS (TB-EPS-PN) showed a significant correlation with capillary suction time (CST) (r = 0.95, p < 0.001) which was a key factor influencing FWAD dewaterability. Subsequent investigations showed that the Fenton oxidation was effective in stripping EPS from FWAD. However, the FWAD floc structure would be disturbed by EPS stripping, which would deteriorate its dewaterability. An innovative strategy for EPS stripping coupled skeletal reconstruction has been proposed. The heterogeneous Fenton oxidation based on iron-doped biochar (BC-Fe) could enhance the dewaterability of FWAD to streamline the process and reduce iron sludge production. Results indicated that the removal rate of TB-EPS-PN reached 90.8%, the reduction rate of CST reached 91.2% under the optimal dosages of BC-Fe of 0.25 g/g of TS and H2O2 of 0.07 g/g of TS, and the water content was reduced to 75.9%. Heterogeneous oxidation conditioning in improving FWAD dewaterability was feasible with a 30% cost saving compared to conventional dewatering methods and offered great potential for catalyst reuse and pH adjustment-free operation. This study provided a viable alternative to the problems in the FWAD industry.