The addition of functional bacteria (FB) is low-cost and is widely applied in saline–alkali soil remediation, which may gradually become ineffective due to inter-specific competition with indigenous bacteria. To improve the adaptability of FB, the target FB strains were isolated from local saline–alkali soil, and the combined effects of FB and biochar were explored. The results showed that FB isolated from local soil showed better growth than the purchased strains under high saline–alkali conditions. However, the indigenous community still weakened the function of added FB. Biochar addition provided a specific niche and increased the relative abundance of FB, especially for Proteobacteria and Bacteroidota. As a result, the co-addition of 10% biochar and FB significantly increased the soil available phosphorus (AP) by 74.85% and available nitrogen (AN) by 114.53%. Zea Mays’s growth (in terms of height) was enhanced by 87.92% due to the decreased salinity stress and extra nutrients provided.

Due to its high toxicity, persistence, and bioaccumulation in the food chain, controlling cadmium (Cd) pollution in wastewater is urgent. Activated carbon is a popular material for removing Cd. To improve the Cd(II) adsorption efficiency by increasing the number of oxygen-containing functional groups, Phragmites australis-activated carbon (PAAC) was modified with mannitol at a low temperature (150 °C). The textural and chemical characteristics of PAAC and modified PAAC (M-PAAC) were analyzed by surface area analysis, elemental analysis, Boehm’s titration, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Batch adsorption experiments were conducted to investigate the influence of Cd(II) concentration, contact time, ionic strength, and pH on Cd(II) adsorption. The main adsorption mechanisms of Cd(II) on activated carbon were quantitatively calculated. The results showed that mannitol modification slightly decreased the S_BET (5.30% of PAAC) and increased the content of carboxyl, lactone, and phenolic groups (total increase of 43.96% with PAAC), which enhanced the adsorption capacity of PAAC by 58.59%. The adsorption isotherms of PAAC and M-PAAC were described well using the Temkin model, while the intraparticle diffusion model fitted the Cd(II) adsorption kinetics best. Precipitation with minerals was a crucial factor for Cd(II) adsorption on activated carbon (50.40% for PAAC and 40.41% for M-PAAC). Meanwhile, the Cd(II) adsorption by M-PAAC was also dominated by complexation with oxygen-containing functional groups (33.60%). This research provides a method for recovering wetland plant biomass to prepare activated carbon and efficiently treat Cd-containing wastewater.

Subsurface flow constructed wetland (SSFCW) has been applied for wastewater treatment for several decades. In recent years, the combination of ferric-carbon micro-electrolysis (Fe/C-M/E) and SSFCW was proven to be an effective method of multifarious sewage treatment. However, Ferric substrate created a relatively reductive condition, decreased the oxidation efficiency of NH₄⁺-N, and blocked the following denitrification process, which led to the low removal efficiencies of NH₄⁺-N and total nitrogen (TN). In this study, partial aeration was introduced into the ferric-carbon micro-electrolysis SSFCW (Fe/C-M/E CW) system to solve the problem above. The water quality and nitrogen-related functional genes of bacteria on the surface of substrate were measured for mechanism exploration. The results showed that, the removal efficiencies of NH₄⁺-N and total phosphorus (TP) in an aerated Fe/C-M/E CW system were 96.97% ± 6.06% and 84.62% ± 8.47%, much higher than 43.33% ± 11.27% and 60.16% ± 2.95% in the unaerated Fe/C-M/E CW systems. However, the TN removal in Fe/C-M/E CW system was not enhanced by aeration, which could be optimized by extending more anoxic section for denitrification.