Effect of biowaste and construction waste additives on mechanical dewaterability of lake sediment for brick production.

Nowadays, when the zero-waste strategy is an inevitable component of the circular economy, the reuse of waste, including dredged sludges, has drawn the attention of many researchers. This study evaluated four kinds of bio-wastes (corn core powder, rice husk powder, sugarcane bagasse powder, and peanut shell powders) and two kinds of construction wastes (autoclaved aerated concrete-AAC and pavement stone) in enhancing the dewaterability of dredged sludge from the lake, in which the sludges would then be reused for brick production. The results showed that the moisture contents decreased from 62 ± 0.14% to 57 ± 1.89% after mixing and then to 35 ± 8.31% after compressing for the construction waste-blended sludge. Among the bio-wastes, the sugarcane bagasse additive performed the best at a mixing ratio of 1:3 by weight and rice husk powder worked best at a mixing ratio of 1:5 by weight. The organic matter was increased up to 80% when the bio-wastes were added, while it was decreased to 5% for the case of construction wastes. The optimum percentage of sludge in the mixture to meet all the oxide contents in the brick and energy saving shall be about 30%. The results have revealed a potentially green route for brick production with lake sediment and bio-waste/construction wastes.Implications: It is the first time the reuse of agro-wastes/construction waste was evaluated to mix with lake sediment to partly replace clay for brick production; Among the bio-wastes, the sugarcane bagasse additive performed the best at a mixing ratio of 1:3 by weight; Moisture contents decreased from 62 ± 0.14% to 57 ± 1.89% after mixing and then to 35 ± 8.31% after compressing for the blended sludge; The optimum percentage of mixed sludge, possibly replaced the clay in brick production, considering oxide contents and energy saving shall be up to 30%.

Effects of CO2 and temperature on phytolith dissolution.

Phytoliths, silica structures derived from plant residues in silicon (Si)-accumulating plant species, have recently been recognized as a sink and source of nutrients and a hosting phase for carbon sequestration in soil. While the solubility of phytoliths in relation to their respective nature and solution chemistry has been intensively studied, the combined effects of CO2 and temperature, two highly variable parameters in soil, have not been fully understood. We hypothesized that changes in CO2 and temperature may affect the dissolution rate, thereby resizing the soil phytolith pool. Rice straw phytoliths were obtained from either open burning or controlled heating of straw from 300 to 900 °C and used to determine their batch incubation kinetics in a closed chamber at CO2 concentrations of 0 to 15% vol. and a temperature range of 20 to 50 °C for six days. The results revealed a contrasting effect in which temperature and CO2 were correspondingly found to accelerate or decelerate the dissolution rate of phytoliths. Under the most dissimilar conditions, i.e., 0% vol. CO2 and 50 °C and 15% vol. CO2 and 20 °C, the discrepancy in solubility was approximately six-fold, indicating a high vulnerability of phytoliths to CO2 and temperature changes. This finding also suggests that the soil phytolith pool can be diminished in the case of either increasing soil temperature or decreasing CO2 flux. Calculations based on these data revealed that the dissolution rate of phytoliths could be increased by an average of 4.5 to 7.3% for each 1 °C increase in temperature. This finding suggests a possible impact of current global warming on the global biogenic silica pool, and more insight into the relationship between this pool and climate change is, therefore, necessary to maintain the function of the phytolith phase in soil.

Colloidal Dynamics of Freshly Formed Iron Oxides under the Influence of Silicic Acid.

Silicic acid and soluble Fe are among the most abundant components in acid mine drainage. During the oxidation of Fe(II), the interaction between silicic acid and freshly formed Fe oxides might change the colloidal dynamics, altering surface charge properties. However, the effects of silicic acid on colloidal Fe oxides formed from acid mine drainage are not fully understood. In this work, we examined the colloidal dynamics of freshly formed Fe oxides in synthetic acid mine drainage (prepared from FeSO solution) under the effect of silicic acid as a function of changes in pH and ionic strength. The results demonstrate that through adsorption, silicic acid progressively slows oxidation and enhances the dispersion of freshly formed Fe oxides by shifting the surface charge toward more negative values. This effect was most prominent between pH 5 and 9. The current results demonstrate that silicic acid enhances the dispersion and transport of freshly formed Fe oxides and suggest that aggregation-based techniques for the treatment of Fe-rich drainage may require further consideration of this effect.