Calcium carbonate (CaCO₃) is a widely used inorganic powder, but its industrial applications are limited by its hydrophilicity and oleophobicity. Surface modification of CaCO₃ can improve its dispersion and stability in organic materials and further improve its potential value. In this study, CaCO₃ particles were modified with silane coupling agent (KH550) and titanate coupling agent (HY311) combined with ultrasonication. The oil absorption value (OAV), activation degree (AG), and sedimentation volume (SV) were employed to evaluate the modification performance. The results showed that the modification effect of HY311 on CaCO₃ was better than that of KH550, and ultrasonic treatment played an auxiliary role. Based on response surface analysis, the optimal modification conditions were determined as follows: the HY311 dosage was 0.7%, the KH550 dosage was 0.7%, and ultrasonic time was 10 min. The OAV, AG, and SV of modified CaCO₃ under these conditions were 16.65 g DOP/100 g, 99.27%, and 0.65 mL/g, respectively. The SEM, FTIR, XRD and thermal gravimetric analyses indicated successful coating of HY311 and KH550 coupling agents on the surface of CaCO₃. The optimization of the dosages of two coupling agents and ultrasonic time improved the modification performance significantly.

A large amount of sludge is produced in the process of municipal sewage treatment. The recovery and utilization of large amounts of sugar, protein, lipids and other organic matter from sewage sludge (SS) is of great significance for reducing environmental pressure and producing clean energy. In this study, microwave combined with thermal-alkaline pretreatment was used to accelerate the dissolution of primary sedimentation sludge and the release of intracellular substances, and to promote the extraction of sugar from SS. The results showed that the yield of crude sugar and the extraction efficiency of pure sugar increased with the increase in NaOH dosage. The extraction of crude sugar reached the equilibrium at about 30 min. During the response surface analysis, the optimal pretreatment conditions were determined as follows: the dosage of NaOH was 9.93 mL, and the leaching time and the microwave time were 27.65 min and 33.2 s, respectively. The crude sugar yield and extraction efficiency obtained under this condition were 39.80 ± 3.57% and 89.74 ± 3.61%, respectively. The pretreated sludge and crude sugar were characterized with scanning electron microscopy and Fourier transform infrared spectroscopy. The results showed that the combined use of thermal-alkaline and microwave effectively destroyed the structure of the sludge and increased the yield of crude sugar.

Adsorption is a promising technology for phosphate removal to alleviate eutrophication. In this study, thermally modified calcium aluminate decahydrate (TCAH) was prepared via low-temperature thermal treatment of calcium aluminate decahydrate (CAH₁₀) to develop a cost-effective and high-performance phosphate adsorbent. The optimal modification temperature was determined to be 120 °C, which reduced the crystallinity of CAH₁₀, enhanced its porosity, and induced the formation of amorphous calcium aluminate phases. Batch adsorption experiments showed that TCAH exhibited a maximum adsorption capacity of 199.80 mg P/g at 25 °C. The adsorption kinetics followed the pseudo-second-order model, while the adsorption isotherms were well fitted by the Redlich–Peterson model. TCAH maintained high removal efficiency over a wide pH range of 3.0–11.0 and showed high selectivity against common coexisting anions. Characterizations using SEM-EDS, XRD, FTIR and XPS suggested that phosphate removal by TCAH was dominated by synergistic amorphous precipitation and inner-sphere complexation. In tests with real phosphorus-releasing liquor derived from excess sludge, TCAH achieved nearly complete phosphate removal at a dosage of 5 g/L within 6 h. Owing to its readily available raw materials, low preparation temperature, and outstanding phosphate capture performance, TCAH is a promising candidate for efficient phosphate capture and recovery from wastewater.