La3+@BC500-S2O82- system for removal of sulfonamide antibiotics in water.

Sulfonamide antibiotics (SAs) widely used have potentially negative effects on human beings and ecosystems. Adsorption and advanced oxidation methods have been extensively applied in SAs wastewater treatment. In this study, compared with Al3+@BC500 and Fe3+@BC500, La3+@BC500 for activating persulfate (S2O82-) had the best effect removal performance of sulfadiazine (SDZ) and sulfamethoxazole (SMX). Morphology, acidity, oxygen-containing functional groups, and loading of La3+@BC500 were analyzed by techniques, including EA, BET, XRD, XPS, FT-IR. XRD results show that with the increase of La3+ loading, the surface characteristics of biochar gradually changed from CaCO3 to LaCO3OH. Through EPR technology, it is proved that LaCO3OH on the surface of La3+@BC500 can not only activate S2O82- to generate SO4-•, but also to produce •OH. In the optimization experiment, the optimal dosage of La3+ is between 0.05 and 0.2 (mol/L)/g. SDZ had a good removal effect at pH (5-9), but SMX had a good removal effect only at pH=3. Zeta potential also proves that the material is more stable under acidic conditions. The removal process of SDZ is more in accord with pseudo-first-order kinetics (R2=0.9869), while SMX is more in line with pseudo-second order kinetics (R2=0.9926).

Removal of polybrominated diphenyl ethers by biomass carbon-supported nanoscale zerovalent iron particles: influencing factors, kinetics, and mechanism.

In this study, nanoscale zerovalent iron (NZVI) immobilized on biomass carbon was used for the high efficient removal of BDE 209. NZVI supported on biomass carbon minimized the aggregation of NZVI particles resulting in the increased reaction performance. The proposed removal mechanism included the adsorption of BDE 209 on the surface or interior of the biomass carbon NZVI (BC-NZVI) particles and the subsequent debromination of BDE 209 by NZVI while biomass carbon served as an electron shuttle. BC-NZVI particles and the interaction between BC-NZVI particles and BDE 209 were characterized by TEM, XRD, and XPS. The removal reaction followed a pseudo-first-order rate expression under different reaction conditions, and the k obs was higher than that of other NZVI-supported materials. The debromination of BDE 209 by BC-NZVI was a stepwise process from nona-BDE to DE. A proposed pathway suggested that supporting NZVI on biomass carbon has potential as a promising technique for in situ organic-contaminated groundwater remediation.

The removal of chromium (VI) and lead (II) from groundwater using sepiolite-supported nanoscale zero-valent iron (S-NZVI).

In this study, the synthesis and characterization of sepiolite-supported nanoscale zero-valent iron particles (S-NZVI) was investigated for the adsorption/reduction of Cr(VI) and Pb(II) ions. Nanoscale zero-valent iron (NZVI) supported on sepiolite was successfully used to remove Cr(VI) and Pb(II) from groundwater with high efficiency. The removal mechanism was proposed as a two-step interaction including both the physical adsorption of Cr(VI) and Pb(II) on the surface or inner layers of the sepiolite-supported NZVI particles and the subsequent reduction of Cr(VI) to Cr(III) and Pb(II) to Pb(0) by NZVI. The immobilization of the NZVI particles on the surface of sepiolite could help to overcome the disadvantage of NZVI particles, which have strong tendency to agglomerate into larger particles, resulting in an adverse effect on both the effective surface area and reaction performance. The techniques of XRD, XPS, BET, Zeta potential, and TEM were used to characterize the S-NZVI and interaction between S-NZVI and heavy metals. The appropriate S-NZVI dosage was 1.6 g L(-1). The removal efficiency of Cr(VI) and Pb(II) by S-NZVI was not affected to any considerable extent by the presence of co-existing ions, such as H2PO4(-), SiO3(2-), Ca(2+) and HCO3(-). The Cr(VI) and Pb(II) removal kinetics followed a pseudo-first-order rate expression, and both Langmuir isotherm model and Freundlich isotherm model were proposed. The results suggested that supporting NZVI on sepiolite had the potential to become a promising technique for in situ heavy metal-contaminated groundwater remediation.

Enhanced adsorptive removal of selected pharmaceutical antibiotics from aqueous solution by activated graphene.

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 m(2)/g from ∼138.20 m(2)/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.

Enhanced dewaterability of waste-activated sludge by combined cationic polyacrylamide and magnetic field pretreatment.

The potential function of combining magnetic field (MF) pretreatment with cationic polyacrylamide (CPAM) additive on enhancing the dewaterability of waste-activated sludge was investigated in the present work. Two reactors were involved in a specially designed experimental apparatus, one of which was built with MF accessories. Several parameters were conducted, including CPAM dosages, MF strengths and processing times, respectively. Capillary suction time (CST) and specific resistance to filtration (SRF) were used to evaluate sludge dewaterability. Extracellular polymeric substances (EPS) concentration was also determined in an attempt to identify the observed changes in dewaterability. It was indicated by the results that both CPAM conditioning and MF pretreatment on sludge can lower CST and SRF values. However, subjecting to a combination of MF pretreatment and CPAM conditioning, sludge dewaterability was significantly enhanced beyond the level observed of CPAM addition alone. The lowest CST and SRF values of 36.5 s and 0.75×10(12) m kg(-1), respectively, were obtained when sludge was co-conditioned by CPAM (at a dosage of 40 mg L(-1)) and MF (at an induction of 40 mT) for 30 min, suggesting the optimal condition for enhancing sludge dewaterability. It is also shown from the significant correlations between EPS, protein, polysaccharide and CST/SRF that the increment of EPS concentration in sludge supernatant may be the major reason for the enhancement of dewaterability.

Phosphorus release mechanisms during digestion of EBPR sludge under anaerobic, anoxic and aerobic conditions.

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 PO4(3-)-P concurrent with synthesis of polyhydroxyalkanoates (PHA). Under anoxic or aerobic conditions, PAOs and/or DPAOs assimilated part of the PO4(3-)-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 PO4(3-)-P associated with the denitrifying phosphorus removal (DPR) can be expressed as ΔP = 0.11 × ΔN.

Characteristics of various forms of phosphorus and their relationships in the sediments of Haizi Lake, China.

The phosphorus (P) distribution in the sediments of Haizi Lake from the middle reach of the Yangtze River region, China, was investigated using a sequential chemical extraction procedure. P forms and concentrations of sediment samples taken at 25 sites over the whole lake were measured. The relationships between various forms of P in sediments and dissolved P in the overlying water were also discussed. Results showed that the concentrations of total P (TP) in the sediments ranged from 404 to 670 mg kg⁻¹, with an average of 503 mg kg⁻¹. The exchangeable P (Ex-P), Al-bound P (Al-P), Fe-bound P (Fe-P), occluded P (Oc-P), authigenic carbonate fluorapatite + biogenic apatite + CaCO3-associated P (ACa-P), detrital apatite + other inorganic P (De-P) and organic P (Or-P) accounted for, on average, 0.52, 0.04, 10.9, 32.0, 7.4, 20.1 and 29.0% of TP, respectively. Relevance analysis indicated that Oc-P, ACa-P and De-P, as the majority forms of inorganic P, were less correlated to others. The significant correlations between Ex-P, Al-P, Fe-P, Or-P and TP suggested the probability of reciprocal transformation. It was suggested that Ex-P, Al-P, Fe-P, Or-P and TP in the sediments might be released easily to the water interface, resulting in sustained lake eutrophication.