Haiping Yuan

Adsorption and Fenton-like degradation of naphthalene dye intermediate on sewage sludge derived porous carbon

A sewage sludge derived porous carbon (SC), which was prepared by physicochemical activation and carbonization (600°C), was applied for the adsorption and degradation of 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) in the presence of H(2)O(2) and the performance was compared to that of pure Fe(3)O(4) magnetic nanoparticles (MNPs). The prepared SC showed mesoporous structure with magnetic property, which made it favorable for solid-liquid separation application. Further experiments revealed that SC had a higher adsorption capacity and degradation efficiency of 1,2,4-Acid than bare Fe(3)O(4). The Langmuir and Freundlich model fitted the isotherm data and illustrated that the equilibrium adsorption amount of 1,2,4-Acid onto SC (95.1 mg g(-1)) was quadruple as large as that on Fe(3)O(4) (26.4 mg g(-1)). The subsequent degradation experiments were conducted at conditions (pH 5.0 in the presence of 15 mM H(2)O(2)) with regard to 1,2,4-Acid degradation efficiency and metal ions leach. The 120 mins treatment in SC/H(2)O(2) system achieved 94% of 1,2,4-Acid (from 150 mg L(-1) after adsorption equilibrium to 9 mg L(-1)) and 48.1% TOC reduction, far higher than the efficiency of 46% and 24.3% by using Fe(3)O(4) MNPs. Further analysis evidenced the co-catalytic effect of iron, carbon, silicon and aluminum, which existed in large quantities in sludge derived SC. The carbonaceous phase along with silica contributes to an increase in the dispersion of catalytic centers and an adsorbent to concentrate organic pollutant whereas the iron oxide as well as alumina provides the catalytic centers for a Haber-Weiss initiated reactions.

Dewaterability characteristics of sludge conditioned with surfactants pretreatment by electrolysis

The potential benefits of electrolysis-conditioned sludge dewaterability treatments with surfactants were investigated in this study. Capillary suction time (CST) and specific resistance of filtration (SRF) were used to evaluate the sludge dewaterability. Extracellular polymeric substance (EPS) content, viscosity and zeta potential were determined in an attempt to explain the observed changes in the conditioning process. The results indicated that SDS (Sodium Dodecyl Sulphate) and Triton X-100 have negative effect on the dewaterability of sludge pretreated both with and without electrolysis. However, with a combination of CTAB (Cetyl Trimethyl Ammonium Bromide) and electrolysis pretreatment presented clear advantages over surfactant conditioning alone for improving sludge dewaterability. The optimal dosage of CTAB to give maximal dewaterability was found to be 2000 mg/L, which generated sludge with optimal EPS concentration (150-300 mg/L), viscosity (55-62 mpa s) and zeta potential (-2.12 to -1.19 mV).

Chemical and microbial changes during autothermal thermophilic aerobic digestion (ATAD) of sewage sludge.

Autothermal thermophilic aerobic digestion (ATAD) is a promising process for sewage sludge stabilization. Batch experiments were conducted on sewage sludge collected from a municipal wastewater treatment plant in Shanghai, China, to evaluate the effectiveness of the ATAD system by determining changes in volatile suspended solids (VSSs) and to study its microbial diversity by denaturing gradient gel electrophoresis of 16S rRNA gene sequences amplified by PCR. The digestion system achieved rapid degradation of the organic substrate at 55 degrees C. The VSS was removed by up to 45.3% and 50.4% at 216 h and 264 h, respectively, while NH(4)(+)-N, chemical oxidation demand and total organic carbon of supernatant as well as total nitrogen did not exhibit obvious declines after 168 h. The microbial diversity changed during the thermophilic process as thermophiles belonging to the Hydrogenophilaceae, Thermotogaceae, Clostridiaceae and the genus Ureibacillus replaced less temperature-tolerant microorganisms such as Sphingobacteriaceae and the genus Trichococcus.

New sludge pretreatment method to improve dewaterability of waste activated sludge

The enhancements of electrolysis-pretreated conditioning were investigated in this study. Normalized capillary suction time (CST) was used to evaluate sludge dewaterability. Extracellular polymeric substance (EPS) concentration, viscosity and scanning electron microscopy (SEM) were determined to explain the observed changes in conditioning process. It indicated that pretreatment at 50 v and 5 min with Ti/RuO(2) anode was determined to be the optimal condition, which generated the lowest normalized CST and optimal soluble EPS concentration, leading to the decreasing of viscosity. EPS had positive correlation with the normalized CST. Subjecting to a combination of electrolysis pretreatment and flocculants conditioning, 50% dosage of cationic polyacrylamide (PAM) could be reduced. When co-conditioned with electrolysis and polymerization ferric sulfate (PFS), it did not present any clear advantages over PFS conditioning alone. Furthermore, SEM investigation indicated that electrolysis pretreatment could rupture sludge, release the interstitial water and extracellular substances, especially protein and polysaccharide, and consequently enhance its dewaterability.

Near-infrared photocatalyst of Er3+/Yb3+ codoped (CaF2@TiO2) nanoparticles with active-core/active-shell structure

A novel near-infrared (NIR) photocatalyst of Er3+/Yb3+-(CaF2@TiO2) was synthesized with optically active centers (Er3+/Yb3+) presented both in the CaF2 cores and TiO2 shells, and the corresponding upconversion luminescence properties increased greatly, which was helpful for the organic dye solution removal efficiency under NIR irradiation.

Leaching behavior of heavy metals from sewage sludge solidified by cement-based binders.

Sewage sludge was stabilized and solidified (S/S) with cement-based binders prior to landfill in order to reduce the potential hazard of heavy metals. The leaching behavior and chemical speciation of heavy metals in the solidified sludge were studied by semi-dynamic leaching test, toxicity characteristic leaching procedure (TCLP) and sequential extraction procedures. The effectiveness of S/S treatment was evaluated by determining diffusion coefficients (De) calculated from the data achieved in semi-dynamic leaching test. High De values under low pH (4.0 compared to 7.0 and 10.0) and high temperature (35°C compared to 10°C and 25°C) conditions were always recorded. Acid-assisted S/S product showed lower De values and leaching tendency from TCLP test results for all the selected heavy metals (Ni, Cu, Zn and Pb) compared to traditional S/S product using the same binders. More heavy metals were converted into stable fractions by acid-assisted S/S than usual S/S according to sequential extraction test.

Degradation pathway of the naphthalene azo dye intermediate 1-diazo-2- naphthol-4-sulfonic acid using Fenton's reagent.

Degradation of naphthalene dye intermediate 1-diazo-2- naphthol-4-sulfonic acid (1,2,4-Acid) by Fenton process has been studied in depth for the purpose of learning more about the reactions involved in the oxidation of 1,2,4-Acid. During 1,2,4-Acid oxidation, the solution color initially takes on a dark red, then to dark black associated with the formation of quinodial-type structures, and then goes to dark brown and gradually disappears, indicating a fast degradation of azo group. The observed color changes of the solution are a result of main reaction intermediates, which can be an indicator of the level of oxidization reached. Nevertheless, complete TOC removal is not accomplished, in accordance with the presence of resistant carboxylic acids at the end of the reaction. The intermediates generated along the reaction time have been identified and quantified. UPLC-(ESI)-TOF-HRMS analysis allows the detection of 19 aromatic compounds of different size and complexity. Some of them share the same accurate mass but appear at different retention time, evidencing their different molecular structures. Heteroatom oxidation products like SO(4)(2-) have also been quantified and explanations of their release are proposed. Short-chain carboxylic acids are detected at long reaction time, as a previous step to complete the process of dye mineralization. Finally, considering all the findings of the present study and previous related works, the evolution from the original 1,2,4-Acid to the final products is proposed in a general reaction scheme.

Enhancement of waste activated sludge aerobic digestion by electrochemical pre-treatment

Electrochemical technology with a pair of RuO(2)/Ti mesh plate electrode is first applied to pre-treat Waste Activated Sludge (WAS) prior to aerobic digestion in this study. The effects of various operating conditions were investigated including electrolysis time, electric power, current density, initial pH of sludge and sludge concentration. The study showed that the sludge reduction increased with the electrolysis time, electric power or current density, while decreased with the sludge concentration. Additionally, higher or lower pH than 7.0 was propitious to remove organic matters. The electrochemical pre-treatment removed volatile solids (VS) and volatile suspended solids (VSS) by 2.75% and 7.87%, respectively, with a WAS concentration of 12.9 g/L, electrolysis time of 30 min, electric power of 5 W and initial sludge pH of 10. In the subsequent aerobic digestion, the sludge reductions for VS and VSS after solids retention time (SRT) of 17.5 days were 34.25% and 39.59%, respectively. However, a SRT of 23.5 days was necessary to achieve equivalent reductions without electrochemical pre-treatment. Sludge analysis by Scanning Electron Microscope (SEM) images and infrared (IR) spectra indicated that electrochemical pre-treatment can rupture sludge cells, remove and solubilize intracellular substances, especially protein and polysaccharide, and consequently enhance the aerobic digestion.

Conditioning of sewage sludge with electrolysis: effectiveness and optimizing study to improve dewaterability.

The potential benefits of electrolysis-conditioned sludge dewatering treatment were investigated in this paper. Focuses were placed on effectiveness and factors affecting such novel application of electrolysis process. Experiments have demonstrated that a significant improvement of sludge dewaterability evaluated by capillary suction time (CST) could be obtained at a relative low value of electrolysis voltage. A Box-Behnken experimental design based on the response surface methodology (RSM) was applied to evaluate the optimum of the influencing variables. The optimal values for electrolysis voltage, electrode distance and electrolysis time are 21 V, 5 cm and 12 min, respectively, at which the CST reduction efficiency of 18.8+/-3.1% could be achieved, this agreed with that predicted by an established polynomial model in this study.

Isolation, identification and utilization of thermophilic strains in aerobic digestion of sewage sludge

Two representative thermophilic bacterial strains (T1 and T2) were isolated from a one-stage autothermal thermophilic aerobic digestion pilot-scale reactor. 16S rRNA gene analysis indicated that they were Hydrogenophilaceae and Xanthomonodaceae. These isolated strains were inoculated separately and/or jointly in sewage sludge, to investigate their effects on sludge stabilization under thermophilic aerobic digestion condition. Four digestion conditions were tested for 480 h. Digestion without inoculation and inoculation with strain T2, as well as joint- inoculation with strains T1 and T2, achieved 32.6%, 43.0%, and 38.2% volatile solids (VS) removal, respectively. Removal in a digester inoculated with stain T1 only reached 27.2%. For the first 144 h, the three inoculated digesters all experienced higher VS removal than the digester without inoculations. Both specific thermophilic strains and micro-environment significantly affected the VS removal. DGGE profiles revealed that the isolated strains T1 and T2 can successfully establish in the thermophilic digesters. Other viable bacteria (including anaerobic or facultative microbes) also appeared in the digestion system, enhancing the microbial activity.