Effect of thermal hydrolysis pretreatment on the stabilization of sludge with different solid contents during autothermal thermophilic aerobic digestion

Fate of dissolved organic matter in thermal hydrolysis pretreatment aided autothermal thermophilic aerobic digestion of high solid sludge

Thermal hydrolysis pretreatment (THP) combined with autothermal thermophilic aerobic digestion (ATAD) process is a novel technology to achieve rapid stabilization of high solid sludge. In this study, the molecular transformation pathway of dissolved organic matter (DOM) during THP-ATAD process was analyzed by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS). The findings indicated that the removal of volatile solids from sludge containing 15% total solids achieved a rate of 40.3% following 6 d of ATAD treatment, facilitated by the conducive biodegradation environment established during the THP stage. Specifically, THP removed 24.22% of the O/C compounds and produced 45.66% of reduced organic matter. ATAD process effectively harnessed these reduced compounds from the THP stage, leading to the mineralization of organic matter through deamination and oxidation reactions, which was reflected by a 59.84-fold increase in the humification index. This work provides in-depth mechanistic insights into the transformation of organic matter during high solid sludge stabilization.

Effects of chitosan and rice husk powder on thermal hydrolysis-anaerobic digested sludge conditioning: Dewaterability and biogas slurry fertility

To enhance the dewaterability of anaerobic digested sludge and to make full use of the biogas slurry. This study set up five sludge conditioning methods: polymeric ferric sulfate, polymeric aluminum chloride, cationic polyacrylamide, chitosan, and chitosan combined with rice husk powder. Their effects on the dewaterability of thermal hydrolysis-anaerobic digested sludge, bacterial community, and biogas slurry fertility were studied to find a non-toxic and non-risk dewatering technology for the environment and biogas slurry. Compared with that of the control group, moisture content, normalization capillary suction time, and specific resistance to filtration were reduced by 12.8%, 97.7%, and 82.9%, respectively. Chitosan enlarges the sludge flocs and forms complexes with proteins, disrupting the structure of the extracellular polymeric substances, thereby exposing more hydrophobic groups and reducing the hydrophilicity of the sludge. The subsequent addition of rice husk powder enhances the adsorption of hydrophilic substances and provides a stronger drainage channel for the sludge. In addition, the biogas slurry obtained by this conditioning method used as a fertilizer increased the dry weight and fresh weight of corn seedlings by 59.3% and 91.0%, respectively. And the total chlorophyll content increased by 84.6%. Pearson's correlation analysis showed that chitosan and rice husk meal had no toxic effect on the biogas slurry compared to the other three flocculants. The results showed that the combined treatment of chitosan and rice husk powder resulted in the best dewaterability. Overall, chitosan combined with rice husk powder is a green dewatering technology with great potential for anaerobic digested sludge dewatering and biogas slurry recycling.