Fubing Yao

Effectiveness and mechanisms of phosphate adsorption on iron-modified biochars derived from waste activated sludge

Excessive discharge of phosphate (P) into the surface water is the key factor to cause the eutrophication, so its removal has aroused much attention in recent years. In this study, different iron modification (chemical co-precipitation of Fe3+/Fe2+ or FeCl3 impregnation) was used to improve the phosphate adsorption capacity of waste activated sludge (WAS)-based biochar. Comparative tests demonstrated that the FeCl3-impregnated WAS-based biochar exhibited much superior phosphate adsorption capacity (111.0mg/g) in all as-prepared samples and performed well even under the interferences with pH and coexisting ions. X-ray diffraction (XRD) analyzes indicated that the iron in FeCl3-impregnated WAS-based biochar existed mainly in amorphous phase, as hematite and amorphous hydroxides forms, which was of great benefit to the phosphate adsorption. Besides, ligand exchange plays important role in the adsorption of phosphate. The WAS-based biochar kept over 60% phosphate removal efficiency after five recycles.

Effective adsorption/electrocatalytic degradation of perchlorate using Pd/Pt supported on N-doped activated carbon fiber cathode

In this work, Pd/Pt supported on N-doped activated carbon fiber (Pd/Pt-NACF) was employed as the electrode for electrocatalytic degradation of perchlorate through adsorption/electroreduction process. Perchlorate in solution was firstly adsorbed on Pd/Pt-NACF and then reduced to non-toxic chloride by the catalytic function of Pd/Pt at a constant current (20mA). Compared with Pd/Pt-ACF, the adsorption capacity and electrocatalytic degradation efficiency of Pd/Pt-NACF for perchlorate increased 161% and 28%, respectively. Obviously, positively charged N-functional groups on NACF surface enhanced the adsorption capacity of Pd/Pt-NACF, and the dissociation of hydrogen to atomic H* by the Pd/Pt nanostructures on the cathode might drastically promote the electrocatalytic reduction of perchlorate. The role of atomic H* in the electroreduction process was identified by tertiary butanol inhibition test. Meanwhile, the perchlorate degradation performance was not substantially lower after three successive adsorption/electrocatalytic degradation experiments, demonstrating the electrochemical reusability and stability of the as-prepared electrode. These results showed that Pd/Pt-NACF was effective for electrocatalytic degradation of perchlorate and had great potential in perchlorate removal from water.

Effect of nickel on the flocculability, settleability, and dewaterability of activated sludge

Short-term and long-term effects of nickel (Ni) (0.1-10mg/L) on the physicochemical properties of activated sludge, including the flocculability, settleability, and dewaterability, were investigated. It was found that these properties were unaffected after short-term exposure (1day) to Ni(II) even at the level of 10mg/L. After long-term exposure (60days) to 1 and 10mg/L of Ni(II), however, the sludge flocculability has seriously deteriorated, while the settleability, and dewaterability became gradually better than the control. The mechanism studies revealed that long-term exposure to Ni(II) resulted in the decrease of protein content in extracellular polymeric substances (EPS) and the damage to EPS structures. Although Ni(II) did not bring any adverse effect on the cell membrane, the relative hydrophobicity of activated sludge was significantly decreased. The negative effects on the flocculability and phosphorus removal performance of activated sludge could be completely eliminated by adding the chelator such as EDTA and citrate.

Complete bromate and nitrate reduction using hydrogen as the sole electron donor in a rotating biofilm-electrode reactor.

Simultaneous reduction of bromate and nitrate was investigated using a rotating biofilm-electrode reactor (RBER) with graphite carbon (GC) rods as anode and activated carbon fiber (ACF) bonded with steel ring as cathode. In RBER, the community of denitrifying bacteria immobilized on the cathode surface could completely utilize hydrogen (H2) as the electron donor, which was internally produced by the electrolysis of water. The short-term test confirmed that the RBER system could reduce 150-800μg/L bromate to below 10μg/L under autotrophic conditions. The reduced bromate was considered to be roughly equivalent to the amount of bromide in effluent, indicating that bromate was completely reduced to bromide without accumulation of by-products. The long-term test (over 120 days) showed that the removal fluxes of bromate and nitrate could be improved by increasing the electric current and decreasing the hydraulic retention time (HRT). But nitrite in effluent was significantly accumulated when the electric current was beyond 10mA and the HRT was less than 6h. The maximum bromate reduction rate estimated by the Monod equation was 109.12μg/Lh when the electric current was 10mA and HRT was 12h. It was proposed that the electron transfer process in RBER produced H2 on the surface of the ACF cathode, and the microbial cultures attached closely on the cathode which could completely utilize H2 as electron donors for reduction of bromate and nitrate.

Hydrated lanthanum oxide-modified diatomite as highly efficient adsorbent for low-concentration phosphate removal from secondary effluents

The requirement to the phosphorus (P) emission from wastewater treatment plants (WWTPs) is becoming increasingly strict, which makes an advanced treatment for the low-concentration phosphate removal from secondary effluents indispensable. In present work, hydrated lanthanum (La) oxide-modified diatomite composites (La-diatomite) were fabricated by a facile method and employed as the highly efficient adsorbent for the low-concentration phosphate removal from simulating secondary effluents. Comparative experiments indicated that the La-diatomite treated by 0.1 mol/L LaCl3 exhibited the highest La availability (P/La molar ratio of 2.30) and performed good selectivity to phosphate adsorption even with the coexistence of competing anions and humic acid. The maximum P adsorption capacity reached to 58.7 mg P/g and the 96% P was removed quickly within 30 min at initial phosphate concentration 2 mg P/L. Insignificant La leaching was observed during the process due to the La stabilization by macroporous diatomite. Eight cycles of adsorption-desorption experiments revealed that the excellent repeated use property of La-diatomite. At the column test, La-diatomite showed superior treatment capacities of 3455 kg water/kg La-diatomite for simulated secondary effluents. The La-diatomite maintained high and stable adsorption effectiveness in wide pH range, which should be attributed to the synergistic effect of electrostatic interactions, ligand exchange and Lewis acid-based interaction. This work might provide a candidate for low-concentration phosphate removal from secondary effluent to alleviate the eutrophication.

Sulfate radical induced degradation of Methyl Violet azo dye with CuFe layered doubled hydroxide as heterogeneous photoactivator of persulfate

Persulfate (PS)-based advanced oxidation processes have aroused considerable attentions due to their higher efficiency and wider adaptability to the degradation of bio-recalcitrant organic contaminants. In this study, Cu-Fe layered doubled hydroxide (CuFe-LDH) was employed to degrade Methyl Violet (MV) through heterogeneous photo-activation of PS under visible-light irradiation. The reaction kinetics, degradation mechanism, catalyst stability were investigated in detail. Under the conditions of CuFe-LDH (3:1) dosage 0.2 g/L, PS concentration 0.2 g/L and without initial pH adjustment, 20 mg/L MV was almost completely degraded within 18 min. Electron Spin Resonance (ESR) test and radical quenching experiment indicated that sulfate radicals (SO4-) were the dominant reactive oxidants for the MV decolorization, while hydroxyl radicals (OH) were also involved. The CuFe-LDH/PS/Vis system was applicable at wide range of pH level (3-9). However, extreme pH level would lead to the reduction or transformation of SO4-. The catalyst CuFe-LDH exhibited excellent stability and maintained relatively high catalytic activity to PS even after four recycles. Mechanism study revealed that the redox cycle of Fe3+/Fe2+ and Cu2+/Cu3+ assisted by visible-light irradiation accounted for the enhanced generation of radicals in CuFe-LDH/PS/Vis system, resulting in the improved degradation of organic contaminants. Overall, the CuFe-LDH/PS/Vis process could be a promising approach for the removal of refractory organic pollutants in wastewater.