A novel alginate-embedded magnetic biochar-anoxygenic photosynthetic bacteria composite microspheres for multipollutant removal: Mechanisms of photo-bioelectrochemical enhancement and excellent reusability performance

Existing wastewater treatment technologies face the key challenge of simultaneously removing emerging contaminants and nutrients from wastewater efficiently, with a simplified technological process and minimized operational costs. In this study, a novel alginate-embedded magnetic biochar-anoxygenic photosynthetic bacteria composite microspheres (CA-MBC-PSB microspheres) was prepared for efficient, cost-effective and one-step removal of antibiotics and NH4+-N from wastewater. Our results demonstrated that the CA-MBC-PSB microspheres removed 97.23% of sulfadiazine (SDZ) within 7 h and 91% of NH4+-N within 12 h, which were 21.23% and 38% higher than those achieved by pure calcium alginate-Rhodopseudomonas palustris microspheres (53% and 45.7%), respectively. The enhanced SDZ and NH4+-N removal were attributed to the enhanced photoheterotrophic metabolism and excretion of extracellular photosensitive active substances from R. Palustris through the photo-bioelectrochemical interaction between R. Palustris and magnetic biochar. The long-term pollutants removal performance of the CA-MBC-PSB microspheres was not deteriorated but continuously improved with increasing ruse cycles with a simultaneous removal efficiency of 99% for SDZ and 92% for NH4+-N after three cycles. The excellent stability and reusability were due to the fact that calcium alginate acts as an encapsulating agent preventing the loss and contamination of R. palustris biomass. The CA-MBC-PSB microspheres also exhibited excellent performance for simultaneous removal of SDZ (89% in 7 h) and NH4+-N (90.7% in 12 h) from the secondary effluent of wastewater treatment plant, indicating the stable and efficient performance of CA-MBC-PSB microspheres in practical wastewater treatment.

Iron-based biochar derived from waste-activated sludge enhances anaerobic digestion of synthetic salty organic wastewater for methane production

Herein, synthetic iron-based biochar was used in anaerobic digestion of synthetic salty organic wastewater for methane production. The iron-based biochar synthesized at different pyrolysis temperatures improved methane production. An optimal methane production of 551 ± 4.0 mL/L was achieved by adding iron-based biochar prepared at 700℃. The rate of hydrolysis-acidification and methanogenesis was promoted by iron-based biochar as the NaCl concentration was less than 20 g/L. However, the catalytic effect of iron-based biochar on methane production of saline wastewater failed during the NaCl concentration of 40 g/L due to the complete suppression of methanogenesis. Analyzing the methanogenic activity of iron-based biochar modified anerobic systems and characterizing the physical-chemical properties of iron-based biochar demonstrated that the iron oxides and/or zero-valent iron generated on the biochar surface increased methane production. This study highlights the potential benefits of iron-rich sludge-based biochar on enhanced anaerobic digestion and treatment of salty organic wastewater.

Nano-Fe3O4-modified biochar promotes the formation of iron plaque and cadmium immobilization in rice root

Rice as a paddy field crops, iron-containing materials application could induce its iron plaque formation, thereby affecting cadmium (Cd) transportation in the rhizosphere and its uptake in root. In this study, a hydroponic experiment was conducted to investigate the effects of three exogenous iron materials, namely nano-Fe₃O₄-modified biochar (BC-Fe), chelated iron (EDTA-Fe), and ferrous sulfate (FeSO₄), on the iron plaque formation on the surface of rice root, and to investigate the effects of formed iron plaque on the absorption, migration, and transportation of Cd and Fe in rice plant. The results showed that yellow-brown and brown iron plaque was formed on surface cells of the Fe-treated rice root, and some black particles were embedded in the iron plaque formed by BC-Fe. The proportion of crystallized iron plaque (31.8%-35.9%) formed by BC-Fe was much higher than that formed by EDTA-Fe and FeSO₄. The Cd concentrations in the crystallized iron plaque formed by BC-Fe were 7.64-13.0 mg·kg^-1, and increased with the increasing of Fe concentrations in the plaque. The Cd translocation factor from root to stem (TF_r-s) and the Cd translocation factor from stem to leaf (TF_s-l) with BC-Fe treatment decreased by 84.7% and 80.0%, respectively. The results demonstrated that application BC-Fe promoted the formation of iron plaque and enhanced the sequestration of Cd and Fe in roots, thus reduced the transportation and accumulation of Cd in aerial rice tissues.