Dongsu Bi

The global issue of ecological ditches being poor in removing nitrogen and phosphorus under cold winter temperatures has been identified. This study introduced three types of biochar (reed, rice, and corn) into ecological ditch sediments via two application methods: rhizosphere and mixed addition. The purpose was to explore how these methods affect the removal of nitrogen and phosphorus, as well as their influences on microbial communities in sediments. The results indicated that the addition of biochar to ecological ditches significantly enhanced the removal of nitrogen and phosphorus. Among the three types of biochar, the mixed addition of corn biochar yielded the greatest results, achieving removal rates of 77.1% for total nitrogen (TN), 93.3% for NH₄⁺-N, and 90.3% for total phosphorus (TP). The growth of Vallisneria natans was greatly improved by the mixed addition method, resulting in an average increase of 154%. This improvement was superior to the rhizosphere addition group, which led to a growth increase of 125%. In comparison, the control group (CK) showed a decrease of 4.8% in growth. Different methods of biochar addition resulted in changes in the physicochemical properties and stoichiometry of the plants. Microbial analyses showed that the addition of biochar reduced the diversity and abundance of the substrate microbial community.

In this study, one type of layered double hydroxide (LDH), the meta-aluminate intercalated mafic-modified hydrotalcite (LDH-2), was engineered through an unprecedentedly facile, affordable one-step procedure. In the interest of meticulous perception regarding our superior strategy, the conventional two-step synthesis method—the fabrication of optimal mafic-modified hydrotalcite through the coprecipitation and roasting process followed by a second aging step (LDH-1)—was also synthesized. After scrutinization of as-derived nanostructures, the adsorption capacity of both structures for bromate remediation was elaborated. When the effect of experimental variation was optimized and the impact of various ions was investigated, the more astounding performance of LDH-2 (0.97 mg/g) was detected when compared with conventional LDH-1 (0.90 mg/g). Therefore, the novel approach for the engineering of meta-aluminate intercalated mafic hydrotalcite not only introduces facile and practical procedures, but also furnishes a much more efficient adsorption system. In the matter of structure durability, the as-synthesized LDH-2 presented exceptional resistance, maintaining activity after five consecutive cycling runs. This investigation sheds light on the facile and affordable synthesis of the LDH construction.

2-methylisoborneol (2-MIB) is a common taste and odor compound caused by off-flavor secondary metabolites, which represents one of the greatest challenges for drinking water utilities worldwide. A TiO₂-coated activated carbon (TiO₂/PAC) has been synthesized using the sol-gel method. A new TiO₂/PAC photocatalyst has been successfully employed in photodegradation of 2-MIB under UV light irradiation. In addition, the combined results of XRD, SEM-EDX, FTIR and UV-Vis suggested that the nano-TiO₂ had been successfully loaded on the surface of PAC. Experimental results of 2-MIB removal indicated that the adsorption capacities of PAC for 2-MIB were higher than that of TiO₂/PAC. However, in the natural organic matter (NOM) bearing water, the removal efficiency of 2-MIB by TiO₂/PAC and PAC were 97.8% and 65.4%, respectively, under UV light irradiation. Moreover, it was shown that the presence of NOMs had a distinct effect on the removal of MIB by TiO₂/PAC and PAC. In addition, a simplified equivalent background compound (SEBC) model could not only be used to describe the competitive adsorption of MIB and NOM, but also represent the photocatalytic process. In comparison to other related studies, there are a few novel composite photocatalysts that could efficiently and rapidly remove MIB by the combination of adsorption and photocatalysis.

TiO2-C hybrid aerogels containing submicrometer anatase and carbon nanoparticles were prepared with TiCl4 and resorcinol-furfural. A modified polyvinylidene fluoride (PVDF) ultrafiltration membrane was prepared through phase inversion after dispersing the TiO2-C hybrid aerogel into a PVDF solution. The surface features, structure, and hydrophilicity of the membrane were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, contact angle measurement, and pure water flux. The mechanical strength of this membrane was also determined. The photocatalytic performance of the modified membrane was investigated using reactive brilliant red (X-3B) as a representative contaminant. Characterization results indicated that the TiO2-C hybrid aerogels were distributed evenly in the PVDF membrane, showing enhanced hydrophilicity, mechanical strength, and pure water flux. Furthermore, the photodegradation rate of X-3B through the modified membrane was significantly high owing to the photocatalytic action of the TiO2-C hybrid aerogels distributed in the modified membrane.

Activated graphene adsorbents (G-KOH) were synthesized by a one-step alkali-activated method, with a high specific surface area (SSA) and a large number of micropores. As a result, the SSA of the final product greatly increases to ∼512.6 m²/g from ∼138.20 m²/g. The resulting G-KOH was used firstly as an adsorbent for the removal of ciprofloxacin (CIP) in aqueous solutions. Experimental results indicated that G-KOH has excellent adsorption capacity (∼194.6 mg/g). The alkali-activation treatment introduced oxygen-containing functional groups on the surface of G-KOH, which would be beneficial to improving the adsorption affinity of G-KOH for the removal of CIP. Kinetic regression results showed that the adsorption kinetic was more accurately represented by a pseudo-second-order model. The overall adsorption process was jointly controlled by external mass transfer and intra-particle diffusion, and intra-particle diffusion played a dominant role. A Langmuir isotherm model showed a better fit with adsorption data than a Freundlich isotherm model for the adsorption of CIP on G-KOH. The remarkable adsorption capacity of CIP onto G-KOH can be attributed to the multiple adsorption interaction mechanisms (hydrogen bonding, π–π electron donor–acceptor interactions, and electrostatic interactions). Results of this work are of great significance for environmental applications of activated graphene with higher SSA as a promising adsorbent for organic pollutants from aqueous solutions.

Three laboratory-scale digesters were operated in parallel under anaerobic, anoxic and aerobic conditions to reveal the release mechanisms of phosphorus when digesting enhanced biological phosphorus removal (EBPR) sludge. The variation rates of the parameters associated with phosphorus release were calculated and compared with that of a typical EBPR anaerobic process. The results show that both phosphorus-accumulating organisms (PAOs) and denitrifying phosphorus-accumulating organisms (DPAOs) played important roles in the phosphorus release during the digestion processes. Under anaerobic conditions, the PAOs hydrolyzed internal polyphosphorus (poly-P) into PO43−-P concurrent with synthesis of polyhydroxyalkanoates (PHA). Under anoxic or aerobic conditions, PAOs and/or DPAOs assimilated part of the PO43−-P from the digestive liquid using nitrate or oxygen as terminal electron acceptors. Nevertheless, the biological activities of PAOs under anaerobic conditions and DPAOs under anoxic conditions were limited. Moreover, it was the biomass hydrolysis degree that determined the phosphorus release capacity of the sludge, regardless of whether anaerobic, anoxic or aerobic conditions were adopted. Assuming that nitrate was the sole electron acceptor during anoxic digestion of EBPR biomass, the relationship between the consumption of nitrate and uptake of PO43−-P associated with the denitrifying phosphorus removal (DPR) can be expressed as ΔP = 0.11 × ΔN.