Enhanced methane yield in anaerobic digestion of waste activated sludge by combined pretreatment with fungal mash and free nitrous acid.

This study explores a novel approach for enhancing anaerobic digestion of waste activated sludge (WAS) through the combined pretreatment of fungal mash and free nitrous acid (FNA). Aspergillus PAD-2, a fungal strain with superior hydrolase secretion, was isolated from WAS and cultivated in-situ on food waste to produce fungal mash. The solubilization of WAS by fungal mash achieved a high soluble chemical oxygen demand release rate of 548 mg L-1 h-1 within first 3 h. The combined pretreatment of fungal mash and FNA further improved the sludge solubilization by 2-fold and resulted in a doubled methane production rate of 416±11 mL CH4 g-1 volatile solids. The Gompertz model analysis revealed a higher maximum specific methane production rate and shortened lag time by the combined pretreatment. These results demonstrate that the combined fungal mash and FNA pretreatment offers a promising alternative for fast anaerobic digestion of WAS.

Utilization of Indole Acetic Acid with Leucadendron rubrum and Rhododendron pulchrum for the Phytoremediation of Heavy Metals in the Artificial Soil Made of Municipal Sewage Sludge.

The development of phytoremediation by garden plants is an effective way to deal with the dilemma of municipal sewage sludge disposal. In this study, two ornamental plants were used as phytoremediation plants to rehabilitate heavy-metal-contaminated municipal sewage sludge in field experiments, and the role of exogenous phytohormone IAA was also tested. Ornamental plants Loropetalum chinense var. rubrum (L. rubrum) and Rhododendron pulchrum (R. pulchrum) adapted well to the artificial soil made of municipal sewage sludge, and the concentrations of Cu, Zn, Pb, and Ni were decreased by 7.29, 261, 20.2, and 11.9 mg kg−1, respectively, in the soil planted with L. rubrum, and 7.60, 308, 50.1, and 17.7 mg kg−1, respectively, in the soil planted with R. pulchrum, accounted for 11−37% of the total amounts and reached significant levels (p < 0.05), except Cd. The concentration of Pb in all parts of the two ornamental plants was increased, as well as most heavy metals in L. rubrum root. As a result, three months after transplant, the phyto-extraction amounts in L. rubrum were 397, 10.9, and 1330 µg for Ni, Cd, and Pb, respectively, increased by 233% to 279%. The phyto-extraction amount in R. pulchrum were 1510, 250, and 237 µg for Zn, Pb, and Cu, respectively, increased by 143% to 193%. These results indicated a potential to remediate heavy metals of the two ornamental plants, especially L. rubrum. The results of correlation analysis implied that the interaction of heavy metals in the plant itself played an important role in the uptake of heavy metals. This seemed to explain why applying IAA in the experiment had little effect on plant growth and phytoremediation of heavy metals. This study provided a green and feasible idea for the proper disposal of municipal sewage sludge.

[Metal ions restrain the elimination of 4-tert-octylphenol by delta-MnO2].

The effect of metal ions on elimination of 4-t-OP by synthetic delta-MnO2 suspension at pH 4.0 was studied. Experiments indicated that the removal of 4-t-OP by delta-MnO2 achieved 100% at reaction time of 150 min. However, the removal of 4-t-OP by delta-MnO2 was restrained when metal ions were added, and the higher concentration of metal ion was, the stronger the inhibition produced. Additionally, there were apparent differences among the inhibitory effect of the tested metal ions. Firstly, Pb2+ and Mn2+ had the strongest effect at pH 4.0, followed by the transition metal ions, then the alkaline earth ions, while the alkali metal ions had little influence on the removal of 4-t-OP by delta-MnO2. Also comparing the adsorption results of metal ions by delta-MnO2, Pb2+ showed the greatest attraction with delta-MnO2, and among the other metal ions, transition metal ions were adsorbed a little more strongly on delta-MnO2 than alkaline earth metal ions. Consequences showed that the inhibitory effects of metal ions were due to their occupying reactive sites on delta-MnO2 surface, which competed with 4-t-OP. Moreover, the dissimilar suppressions were contributed by the different adsorption capacities, surface structure change of MnO2 and the difference of free metal ion percentage in solution as well as metal ions radii.