Kill two birds with one stone: Ceramisite production using organic contaminated soil

Surfactant-enhanced anoxic degradation of polycyclic aromatic hydrocarbons (PAHs) in aged subsurface soil at high temperature (60 °C)

Thermally enhanced anoxic biodegradation is emerging as a promising method for removing PAHs from subsurface soil. However, some PAHs still remain in soil following remediation with thermally enhanced anoxic degradation due to low bioavailability of these residual PAHs. The effects of five surfactants (Tween 80, TX 100, Brij 30, SDS, and SDBS) on the desorption of PAHs, anoxic degradation of PAHs, and native bacteria in soil at high temperature (60 °C) were evaluated in this study. The desorption of PAHs in soil increased as surfactant concentration increased. Low doses of surfactants (0.08%, w/w) enhanced the growth of potential PAHs degrading bacteria and promoted the anoxic degradation of PAHs, whereas high doses of surfactants (0.3%-0.8%, w/w) displayed the opposite effect, and the degree of inhibition increased with increasing surfactant concentration. The results also indicated that the inhibitory effect of anionic surfactants (SDS and SDBS) on microbial growth and PAHs degradation is stronger than that of nonionic surfactants (Tween 80, TX 100 and Brij 30) at the same concentration. These results suggest a feasible way of enhancing the anoxic degradation of PAHs in soil where heat cannot be effectively utilized when in situ thermal desorption (ISTD) technology is used.

Immobilization of heavy metals in ceramsite prepared using contaminated soils: Effectiveness and potential mechanisms

Heavy metal contaminated soils pose a serious threat to the environment, and preparing ceramsite using contaminated soils was proposed as an effective method to address this threat in this study. Specifically, two typical soils (i.e., contaminated clay and sandy soil) were mixed with different ratios and calcined at temperature 1000-1200 °C to prepare ceramsite. Special attentions were paid to evaluating the immobilization of heavy metals in ceramsite and identifying the corresponding immobilization mechanisms. Using the leachability of heavy metals from ceramsite as evaluation criteria, the optimum mixing ratio of clay/sandy soil and sintering temperature were determined as 0.6:0.4 and 1200 °C. Moreover, based on the spectroscopic characterizations and thermodynamic calculation, high sintering temperature well facilitated the liquid phases formation, promoting the reactions between heavy metals and aluminosilicates and the valence state conversion of heavy metals. Accordingly, heavy metals were well immobilized in ceramsite by forming thermodynamically stable minerals, being encapsulated in solid matrix, and transforming to valence states with low mobility. The leaching conditions including pH and temperature had minimal effect on the immobilization of heavy metals in ceramsite. In summary, ceramsite prepared by contaminated soils was environmentally friendly and had good potential in engineering application as building materials.

Resource Utilization of Lake Sediment to Prepare “Sponge” Light Aggregate: Pore Structure and Water Retention Mechanism Study

Nitrogen, phosphorus, and metals’ pollutants discharged from industrial sources eventually accumulate in lake sediment, hence increasing the difficulty of sediment treatment and disposal. In this work, the water storage ceramsite is prepared from dredged lake sediment and cyano-bacterial powder. The effects of pyrolysis temperature and cyanobacterial sediment on the porosity of ceramsite were investigated. The results showed that the pyrolysis of organic matter and the de-composition of compounds or salts can produce gas, causing a rich pore structure inside the ceramsite. When the temperature increased to 1150 °C, vitrification would collapse the pore structure inside the material. At the cyanobacterial-to-sediment ratio of 3:7, the porosity and water absorption of the material could reach 81.82% and 92.45% when the pyrolysis temperature was 500 and 1050 °C, respectively. The internal macropore structure of ceramsite improved the water absorption performance, and the mesoporous structure was responsible for its long water release time and stable water release structure. The ceramsite exhibited a superior metals’ retention effect. Under different pH and temperature conditions, the consolidation rates of Fe, Ni, Mn, Cr, and Pb in ceramsite were all more than 99%, suggesting the safety of the material in environmental applications. This study demonstrates the feasibility of the resourceful production of water storage ceramsite from lake sediment and cyanobacterial slurry, which helps to reduce the impact of solid waste on the environment. Thus, this work provides a practical basis for guiding water storage ceramsite in the construction of sponge cities.