Drought-resistant and water-retaining tobermorite/starch composite hydrogel for the remediation of cadmium-contaminated soil.

The objective of this work is utilizing fly ash to synthesize tobermorite (TOB) with a higher specific surface area and layered structure, and incorporating it into the starch/acrylic acid network to boost the drought resistance, water retention and heavy metal adsorption properties. The water absorption and water retention performance and cadmium adsorption characteristics of tobermorite/leftover rice-based composite hydrogel (TOB@LR-CH) were evaluated by water absorption swelling test, soil evaporation test and batch adsorption experiment. By adjusting the addition of TOB and other synthesized conditions, the swelling property (from 114.80 g/g to 322.64 g/g), water retention (71.80 %, 144 h) and Cd2+ adsorption characteristics (up to 591.36 mg/g) were significantly enhanced. Adding a moderate amount of TOB (2 wt%) provided the most uniform tobermorite dispersion during synthesis, and TOB2@LR-CH exhibited the most stable three-dimensional network and highest proportion of effective TOB. The adsorption behavior of cadmium on TOB2@LR-CH was more consistent with the pseudo-second-order kinetics and Langmuir isotherm models. Additionally, the regeneration test results displayed that the adsorption removal rate of cadmium by TOB2@LR-CH adsorbent remained stable after 5 cycles. This study demonstrates that TOB@LR-CH has good water absorption and water retention potential in arid and semi-arid soils, and also has potential application prospects in remediating Cd(II)-contaminated soil.

The role of reagent adding sequence in the NH4+-N recovery by MAP method.

Ammonium-nitrogen (NH4+-N) recovery from high concentration of NH4+-N-containing wastewater by struvite (MgNH4PO4·6H2O, MAP) precipitation method has been realized, but whether NH4+-N recovery under different reagent adding sequence of NaOH, solid Mg salt and P salt can generate different effects, remains ambiguous. In view of the problem, four modes to add reagents were investigated in detail on the formation of struvite. The results show that the Mode IV (M-IV, i.e. using 50% NH4+-N wastewater to dissolve completely the Mg salt and the P salt, respectively and then simultaneously poured into a beaker to mix the solution evenly and adjust the pH to 9.5.) has the highest NH4+-N recovery efficiency (90.80%) and the maximum mass of precipitates (896 mg) because of the more amount of alkali and initial seed formation. From the morphology of the obtained precipitates, it can be seen that sample M-IV is more loose and porous than the others. XRD patterns show that the four products under the different modes basically agree with the standard MAP.

Ultrasound-Enhanced Catalytic Ozonation Oxidation of Ammonia in Aqueous Solution.

Excessive ammonia is a common pollutant in the wastewater, which can cause eutrophication, poison aquatic life, reduce water quality and even threaten human health. Ammonia in aqueous solution was converted using various systems, i.e., ozonation (O3), ultrasound (US), catalyst (SrO-Al2O3), ultrasonic ozonation (US/O3), ultrasound-enhanced SrO-Al2O3 (SrO-Al2O3/US), SrO-Al2O3 ozonation (SrO-Al2O3/O3) and ultrasound-enhanced SrO-Al2O3 ozonation (SrO-Al2O3/US/O3) under the same experimental conditions. The results indicated that the combined SrO-Al2O3/US/O3 process achieved the highest NH4+ conversion rate due to the synergistic effect between US, SrO-Al2O3 and O3. Additionally, the effect of different operational parameters on ammonia oxidation in SrO-Al2O3/O3 and SrO-Al2O3/US/O3 systems was evaluated. It was found that the ammonia conversion increased with the increase of pH value in both systems. The NH3(aq) is oxidized by both O3 and ·OH at high pH, whereas the NH4+ oxidation is only carried out through ·OH at low pH. Compared with the SrO-Al2O3/O3 system, the ammonia conversion was significantly increased, the reaction time was shortened, and the consumption of catalyst dosage and ozone were reduced in the SrO-Al2O3/US/O3 system. Moreover, reasonable control of ultrasonic power and duty cycle can further improve the ammonia conversion rate. Under the optimal conditions, the ammonia conversion and gaseous nitrogen yield reached 83.2% and 51.8%, respectively. The presence of tert-butanol, CO32-, HCO3-, and SO42- inhibited the ammonia oxidation in the SrO-Al2O3/US/O3 system. During ammonia conversion, SrO-Al2O3 catalyst not only has a certain adsorption effect on NH4+ but accelerates the O3 decomposition to ·OH.