Dewatering of Juglans mandshurica Wood Using Supercritical Carbon Dioxide.

Supercritical carbon dioxide (ScCO2), known for such features as good solubility and mass transfer properties, can be an efficient drying medium for various materials, such as wood, by filling the pore space and dissolving water in the cell cavity without altering the microstructure. In this study, two specimens of Juglans mandshurica wood with a length of 30 mm and 140 mm were subjected to ScCO2 dewatering under four different pressure and temperature conditions. The results showed that the drying rate is mainly influenced by pressure and temperature, with pressure having the more significant effect. Moreover, the efficiency of dewatering was not dependent on the sample length under the same conditions. The moisture content (MC) was the same along the longitudinal direction throughout both the surfaces and core of the wood. While there were no significant differences in dewatering rate between tangential and radial directions and lengths of samples, significant MC gradient differences were noted along wood in radial and tangential directions. During ScCO2 dewatering, the dominant water transfer occurred from the middle towards the end surfaces along the wood's longitudinal directions. Furthermore, ScCO2 dewatering did not result in any shrinkage or significant drying stress, but it did cause some swelling in Juglans mandshurica wood.

Cationic cellulose nano-fibers (CCNF) as versatile flocculants of wood pulp for high wet web performance.

In recent years, cellulose nano-fibers (CNF) have been regarded as renewable, promising reinforcer to enhance the strength property of paper products. In this paper, the roles of cationic cellulose nano-fibers (CCNF) as versatile flocculants of wood pulp and fines in pulp slurry for high wet web performance have been studied. It was found that CCNF can induce significantly flocculation (CCNF-Fines complex) in pulp slurries. The mechanical properties of wet web can also be improved by the addition of CCNF. The study demonstrated that CCNF can act as effective flocculants of fines and form CCNF-Fines complex for improved wet-web strength, in addition, CCNF has little effect on the dewatering rate of wet-web. CCNF is more beneficial to the wet web performance when it is in higher charge density. The research paves a way to further study the comprehensive application of CCNF in the wet-web making process for high performance.

Improving the compression dewatering of sewage sludge through bioacidification conditioning driven by Acidithiobacillus ferrooxidans: dewatering rate vs. dewatering extent.

Prior to mechanical dewatering, sludge conditioning is indispensable to reduce the difficulty of sludge treatment and disposal. The effect of bioacidification conditioning driven by Acidithiobacillus ferrooxidans LX5 on the dewatering rate and extent of sewage sludge during compression dewatering process was investigated in this study. The results showed that the bioacidification of sludge driven by A. ferrooxidans LX5 simultaneously improved both the sludge dewatering rate and extent, which was not attained by physical/chemical conditioning approaches, including ultrasonication, microwave, freezing/thawing, or by adding the chemical conditioner cationic polyacrylamide (CPAM). During the bioacidification of sludge, the decrease in sludge pH induced the damage of sludge microbial cell structures, which enhanced the dewatering extent of sludge, and the added Fe2+ and the subsequent bio-oxidized Fe3+ effectively flocculated the damaged sludge flocs to improve the sludge dewatering rate. In the compression dewatering process consisting of filtration and expression stages, high removal of moisture and a short dewatering time were achieved during the filtration stage and the expression kinetics were also improved because of the high elasticity of sludge cake and the rapid creeping of the aggregates within the sludge cake. In addition, the usefulness of bioacidification driven by A. ferrooxidans LX5 in improving the compression dewatering of sewage sludge could not be attained by the chemical treatment of sludge through pH modification and Fe3+ addition. Therefore, the bioacidification of sludge driven by A. ferrooxidans LX5 is an effective conditioning method to simultaneously improve the rate and extent of compression dewatering of sewage sludge.

Cross-country analysis of faecal sludge dewatering.

Dewatering of faecal sludge (FS) is indispensable for adequate FS management. However, comprehensive knowledge is lacking on FS dewatering performance. This study compared the dewatering performance of FS from different countries and onsite sanitation technologies, to assess influential characteristics on dewatering, and to compare dewatering performance of FS with wastewater sludge. We collected 73 FS samples from septic tanks, lined pit latrines, unlined pit latrines and johkasou tanks in Uganda, Vietnam and Japan, and 18 samples of wastewater sludge in Switzerland. Capillary suction time (CST) and total solids (TS) of centrifuged sludge (%TSfinal) were determined as metrics of dewatering rate and dewaterability, respectively, together with relevant sludge characteristics. Data were analysed by bootstrapping comparison of median results of each sample category and by bootstrapping multiple regression analysis to quantify the relative importance of sludge characteristics on dewatering performance. Results showed that the dewatering rate was significantly different between FS from different technologies, whereas dewaterability was significantly different within the same technology. FS had a significantly lower dewatering rate than wastewater sludge. In contrast, FS dewaterability was greater than wastewater sludge. However, this could be attributed to higher concentrations of sand in FS. Electrochemical properties such as NH4-N and surface charge had the strongest correlation to dewatering rate, and solid properties such as sand content and total volatile solids to dewaterability. The results identify potential characteristics that could explain and predict the high variability of FS dewatering performance that is observed in the field.