Inorganic phosphorus (P)-solubilizing bacteria (IPSB) and organic P-mineralizing bacteria (OPMB) were isolated from bacteria that were first extracted from the rhizosphere soil of a natural wetland and then grown on either tricalcium phosphate or lecithin medium. The solubilizing of inorganic P was the major contribution to P availability, since the isolated bacteria released much more available P from inorganic tricalcium phosphate than lecithin. IPSB No. 5 had the highest P release rate, that is, 0.53 mg·L⁻¹·h⁻¹ in 96 h, and R10′s release rate was 0.52 mg·L⁻¹·h⁻¹ in 10 days. The bacteria were identified as Pseudomonas sp. and Pseudomonas knackmussii, respectively. R10 released as much as 125.88 mg·L⁻¹ dissolved P from tricalcium phosphate medium, while R4 released the most dissolved P from organic P medium among the isolates, with a concentration of 1.88 mg·L⁻¹ and a releasing rate of 0.0078 mg·L⁻¹·h⁻¹ in ten days. P releasing increased with a pH decrease only when it was from inorganic P, not organic lecithin, and there was no significant correlation between the culture pH and P solubilizing. High-throughput sequencing analysis revealed that the dominant phylum in the studied wetland rhizosphere consisted of Acidobacteria, Proteobacteria, Bacteroidetes and Chloroflexi, accounting for 34.9%, 34.2%, 8.8% and 4.8%, respectively.

The imbalance of inorganic nutrients in micro-polluted source water poses a huge threat to aquatic environments and human health. To pretreat micro-polluted source water, some biological reactors have been conducted at lab-scale. However, using phototrophic biofilms to pretreat micro-polluted source water at pilot-scale has yet to be explored, and the effects of light on the practical operation of phototrophic biofilms are poorly understood. In this study, the potential of pretreating micro-polluted source water by phototrophic biofilms was explored. The high light intensity (4500 lx, 60.75 μmol/m²/s) promoted the growth of phototrophic biofilms and the secretion of extracellular polymeric substance. The removal efficiency of inorganic nitrogen and total phosphorus in synthetic micro-polluted water was 56.82% and 40.90%, respectively. When interacting with actual micro-polluted source water, the nutrients in the actual micro-polluted source water were reduced by the stable pilot-scale phototrophic biofilms. The final concentration of effluent nutrients was lower than the Grade II surface water quality standard in China. Therefore, using phototrophic biofilms as a pretreatment facility in water treatment plants is a promising solution to this issue.

Moving bed biofilm reactor (MBBR) is considered as a promising technology for wastewater treatment owing to the high biomass retention and low cost. In this study, the performance of using MBBR for partial denitrification (PD) was investigated. Denitrifying biofilm was successfully formed after 40 days with the biomass and nitrite reduction rate of 40.83 mg VSS/g carriers and 51.52 mg N/(gVSS·h), respectively. Morphology analysis by scanning electron microscope (SEM) showed that the biofilm surface was dominant by cocci, filamentous bacteria, and extracellular polymeric substances (EPS). Investigation about the influencing factors of PD found that the optimal COD/NO₃⁻-N and pH for efficient nitrite production (nitrate to nitrite ratio: 96.49%) was 3 and 9, respectively. Moreover, Saccharimonadales was proved to be dominant functional microbes in the constructed PD systems with different influent conditions because its relative abundance exhibited good correlation with the nitrite accumulation. By analyzing the biofilm characteristics under different conditions, PD was observed to mainly occur in the range of 300–700 μm inside the biofilm, where most of the dissolved oxygen was consumed. This study confirmed the feasibility and superior performance of PD-MBBR system.

Flue gas desulfurization (FGD) gypsum is increasingly considered a secondary raw material, but gypsum purity and bulk mineralogy alone do not fully describe the environmental behavior of associated trace elements. Three Serbian FGD gypsum materials were investigated: FGD-A and FGD-B from two wet-FGD operating streams of the Nikola Tesla A Thermal Power Plant and FGD-C from Kostolac B. Bulk characterization, X-ray diffraction, sequential extraction, and aqueous leaching were combined. FGD-A and FGD-B contained >98.6 wt.% CaSO₄·2H₂O, whereas FGD-C contained 87.47–92.06 wt.%; gypsum nevertheless remained the predominant crystalline phase in all three materials. Operationally defined non-residual fractions (F1–F3) accounted for 74.4%–82.8% of As, 91.9%–95.4% of Cd, and 89.9%–96.8% of V, whereas 81.5%–88.3% of Sb was retained in the residual fraction. Aqueous release was generally low but element- and material-dependent: Zn reached 5.25 µg L⁻¹ in FGD-B, V reached 0.98 µg L⁻¹ in FGD-C, and Pb remained below the validated detection limit in all leachates. The non-residual fraction was not directly proportional to aqueous release, showing that sequential fractionation and water leaching provide complementary information. The results demonstrate that FGD gypsum materials with broadly similar gypsum-rich characteristics can nevertheless exhibit distinct trace-element partitioning and short-term aqueous release.