15A novel biosorbent derived from agricultural residue -walnut shell (WS) is reported to remove cesium from aqueous 16 solution. Nickel hexacyanoferrate (NiHCF) was incorporated into this biosorbent, serving as a high selectivity trap 17 agent for cesium. Field emission scanning electron microscope (FE-SEM) and thermogravimetric and differential 18 thermal analysis (TG-DTA) were utilized for the evaluation of the developed biosorbent. Determination of kinetic 19 parameters for adsorption was carried out using pseudo first-order, pseudo second-order kinetic models and 20 intra-particle diffusion models. Adsorption equilibrium was examined using Langmuir, Freundlich and
Heavy metals (HMs) immobilization in sewage sludge was investigated by using subcritical water technology (SCWT) in this study. The characteristics of sludge and toxicity of HMs were analyzed after SCWT process. The results showed that besides large reduction in sludge volume, SCWT had some positive effect on HMs dissolution into liquid phase, while the majority of HMs was still accumulated in solid phase. The direct toxicity and bioavailability of HMs in sludge was greatly decreased with no toxicity fractions of HMs highly increased. Pb was always at low risk level and the risk of other HMs was greatly reduced from low risk to no risk after SCWT treatment. Moreover, the leaching toxicity of HMs declined after SCWT and the best result was obtained at 280 with the metal concentrations in leachate decreased by 97.46%, 93.91%, 86.14%, 73.67%, 71.93% and 10.71% for Cu, Cd, Zn, Cr, Ni and Pb, respectively.
Hydrothermal treatment (HTT) at 200°C was applied to immobilize heavy metals (HMs) and the effect of rice husk (RH) addition was investigated based on total HMs concentration, fractionation and leaching tests. The results indicated that a synergistic effect of RH addition and HTT could be achieved on reducing the risk of HMs from medium and low risk to no risk. Metals were redistributed and transformed from weakly bounded state to stable state during the HTT process under RH addition. Notably at a RH/sludge ratio of 1/1.75 (d.w.), all the HMs showed no eco-toxicity and no leaching toxicity, with the concentrations of leachable Cr, Ni, Cu and Cd decreased by 17%, 89%, 95% and 93%, respectively. This synergistic effect of RH addition and HTT on the risk reduction of HMs implies that HTT process with RH addition could be a promising and safe disposal technology for sewage sludge treatment in practice.
This study focused on the behavior of phosphorus (P) and its effect on cadmium (Cd) immobilization in sludge during hydrothermal treatment (HTT). The results showed that, after HTT other forms of P in sludge were almost completely converted into apatite P (AP) and the eco-toxicity and leachability of Cd was sharply decreased, signaling the immobilization effect of HTT on Cd in the sludge. Hydroxyapatite (HAP) addition showed a synergetic effect with HTT on Cd risk reduction, implying the immobilization effect of HTT on Cd could be partly attributed to the strong binding capacity of phosphorus with Cd. P content was found to have a strong relationship with the existing forms of Cd during HTT. The present results suggest that HTT with HAP addition could be a promising method for the safe disposal of Cd-contaminated sludge.
Using lignocellulosic materials as substrates, ruminal microbiota were co-inoculated with anaerobic sludge at different loading rates (LR) to study the microbial community in the semi-continuous mode. The results indicated that the highest CH yield reached 0.22 L/g volatile solid at LR of 4 g/L/day, which obtained 56-58% of the theoretical value. In the steady stage with LR of 2-4 g/L/day and slurry recirculation, copies of total archaea increased. Especially the Methanobacteriales increased significantly (p < 0.05) to 3.30 × 10 copies/mL. The microbial communities were examined by MiSeq 16S rRNA sequencing. Enriched hydrolytic bacteria mainly belonged to Clostridiales, including Ruminococcus, Ruminiclostridium, and Ruminofilibacter settled in the rumen. High-active cellulase and xylanase were excreted in the co-inoculated system. Acid-producing bacteria by fermentation were affiliated with Lachnospiraceae and Bacteroidales. The acidogen members were mainly Spirochaetaceae and Clostridiales. Syntrophic oxidation bacteria mainly consisted of Synergistetes, propionate oxidizers (Syntrophobacter and Pelotomaculum), and butyrate oxidizers (Syntrophus and Syntrophomonas). There had no volatile fatty acid (VFA) accumulation and the pH values varied between 6.94 and 7.35. At LR of 6 g/L/day and a recirculation ratio of 1:1, the hardly degradable components and total VFA concentrations obviously increased. The total archaea and Methanobacteriales then deceased significantly to 8.56 × 10 copies/mL and 4.14 × 10 copies/mL respectively (p < 0.05), which resulted in the inhibition of methanogenic activities. Subsequently, microbial diversity dropped, and the hydrolytic bacteria and syntrophic oxidizers obviously decreased. In contrast, the abundances of Bacteroidales increased significantly (p < 0.05). Acetate, propionate, and butyrate concentrations reached 2.02, 6.54, and 0.53 g/L, respectively, which indicated "acidification" in the anaerobic reactor. Our study illustrated that co-inoculated anaerobic sludge enriched the ruminal function consortia and hydrogenotrophic methanogens played an important role in anaerobic digestion of lignocelluloses.
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