Shengbing He

Removal of trivalent chromium from aqueous solution by zeolite synthesized from coal fly ash

The capability of 14 zeolites synthesized from different fly ashes (ZFAs) to sequestrate Cr(III) from aqueous solutions was investigated in a batch mode. The influence of pH on the sorption of Cr(III) was examined. ZFAs had a much greater ability than fly ash to remove Cr(III), due to the high cation exchange capacity (CEC) and the high acid neutralizing capacity (ANC) of ZFAs. The mechanism of Cr(III) removal by ZFAs involved ion exchange and precipitation. A high-calcium content in both the fly ashes and ZFAs resulted in a high ANC value and, as a result, a high immobilization capacity for Cr(III). The pH strongly influenced Cr(III) removal by ZFAs. Inside the solubility range, removal of chromium increased with increasing pH. Hydroxysodalite made from a high-calcium fly ash had a higher sorptive capacity for Cr(III) than the NaP1 zeolite from medium- and low-calcium fly ashes. On the other hand, at pH values above the solubility range, the efficiency of chromium removal by the ZFAs approached 100% due to the precipitation of Cr(OH)3 on the sorbent surfaces. It is concluded that ZFAs and high-calcium fly ashes may be promising materials for the purification of Cr(III) from water/wastewater.

Factors affecting simultaneous nitrification and de-nitrification (SND) and its kinetics model in membrane bioreactor.

Experiments have been carried out to investigate the effect of biological factors such as dissolved oxygen (DO), food/microorganism (F/M) ratio, carbon/nitrogen (C/N) ratio and pH on performance of SND in membrane bioreactor (MBR). It was found that a low DO was advantageous to SND on condition that nitrification was not inhibited, while F/M ratio and C/N ratio have reverse effects on SND, and pH should also be controlled in a suitable range. Based on the conventional activated sludge model, a deduction was conducted to illustrate that SND could take place from the theoretical aspect, and it was proved that high organics was effective in improving SND. In addition, a kinetic model for SND was constituted on the basis of batch test result, and the simulation nitrate saturation coefficient K(NO)(3) was much higher than that in a single-sludge wastewater treatment system.

Algal-based immobilization process to treat the effluent from a secondary wastewater treatment plant (WWTP).

Algal-based immobilization process was applied to treat the effluent from a secondary wastewater treatment plant. Batch test proved that algae could attach onto fiber-bundle carrier in 7 days, and then the algal-based immobilization reactor could reduce TN (total nitrogen) and TP (total phosphorus) significantly within 48 h. Based on the above investigations, the hydraulic retention time (HRT) of the algal-based immobilization reactor in continuous operation mode was determined to be 2 days. During the 91 days of experiment on the treating secondary effluent of Guang-Rao wastewater treatment plant, it was found that the fiber-bundle carrier could collect the heterobacteria and nitrifying bacteria gradually, and thus improved the COD removal efficiency and nitrification performance step by step. Results of the continuous operation indicated that the final effluent could meet the Chinese National First A-level Sewage Discharge Standard when the algal-based immobilization reactor reached steady state.

Preparation of ceramic filler from reusing sewage sludge and application in biological aerated filter for soy protein secondary wastewater treatment

Dehydrated sewage sludge (DSS) and clay used as raw materials for preparation of novel media-sludge ceramic filler (SCF) and SCF employed in a lab-scale up-flow biological aerated filter (BAF) were investigated for soy protein secondary wastewater treatment. Single factor experiments were designed to investigate the preparation of SCF, and the characteristics (microstructure properties, toxic metal leaching property and other physical properties) of SCF prepared under the optimum conditions were examined. The influences of media height, hydraulic retention time (HRT) and air-liquid ratio (A/L) on chemical oxygen demand (CODcr) and ammonia nitrogen (NH4(+)-N) removal rate were studied. The results showed that the optimum addition of DSS was approximately 25.0 wt% according to the physical properties of SCF (expansion ratio of 53.0%, v/v, water absorption of 8.24 wt%, bulk density of 350.4 kg m(-3) and grain density of 931.5 kg m(-3)), and the optimum conditions of BAF system were media height of 75.0 cm, HRT of 10.0 h and A/L of 15:1 in terms of CODcr and NH4(+)-N removal rate (91.02% and 90.48%, respectively). Additionally, CODcr and NH4(+)-N (81.6 and 15.3 mg L(-1), respectively) in the final effluent of BAF system met the national standard (CODcr ≤ 100 mg L(-1), NH4(+)-N ≤ 25.0 mg L(-1), GB 18918-2002, secondary standard).

The inverse correlation between growth rate and cell carbohydrate content of Microcystis aeruginosa

The cell carbohydrate content of cyanobacteria can alter buoyancy, and the ability to regulate the buoyancy is one of the most important mechanisms of cyanobacterial blooms. The net accumulation of carbohydrate in cell is affected by photosynthesis, respiration, synthesis of proteins, and other metabolisms, which are connected to the growth. The aim of this work is to seek the relationship between growth rate and intracellular carbohydrate content. The cell carbohydrate content in Microcystis aeruginosa cultures with different growth characteristics was investigated, and the relationship between growth rate and accumulated carbohydrate in cyanobacterial cells was analyzed. The result showed that the specific growth rate was inversely proportional to cell carbohydrate content. The growth rate was relatively high when the cell carbohydrate content was low. It can be indicated that high growth occurs when cells are buoyant, which favors blooms.

Application of zeolitic material synthesized from thermally treated sediment to the removal of trivalent chromium from wastewater.

Zeolitic materials were synthesized from thermally treated sediment by alkali treatment using different NaOH/sediment ratios. Characterization of the materials was done by XRD, FTIR, cation exchange capacity and specific surface area. Use of high NaOH/sediment ratio favored the formation of zeolite. The potential value of the zeolitic materials for the retention of trivalent chromium from water was examined. The maximum of Cr(III) sorption by the zeolitic materials, determined by a repeated batch equilibration method, ranged from 38.9 to 75.8 mg/g which was much greater than that of the thermally treated sediment (6.3 mg/g). No release of sorbed Cr(III) by 1.0M MgCl(2) at pH 7 was observed but Cr(III) desorption by ionic electrolyte increased with decreasing pH. The zeolitic materials could completely remove Cr(III) from wastewater even in the presence of Na(+) and Ca(2+) with high concentrations with a dose above 2.5 g/L. The pH-dependent desorption behavior and the high selectivity of zeolitic material for Cr(III) were explained by sorption at surface hydroxyl sites and formation of surface precipitates.

Comparison of microbial communities in different sulfur-based autotrophic denitrification reactors

Sulfur-based autotrophic denitrification is a useful approach for the eutrophication control in lakes and rivers, yet the microorganisms in this process are still not clearly known. In order to reveal the bacterial composition in these denitrification reactors, high-throughput sequencing was performed over the sludge samples. And the results indicated that when using thiosulfate, elemental sulfur, and sulfide as electron donors, the microbial communities were clearly different. Besides the well-known Thiobacillus, many other genera of denitrifiers were identified. Chlorobaculum, Dechloromonas, and Acinetobacter were the most predominant genera in thiosulfate, elemental sulfur, and sulfide systems, respectively, while Janthinobacterium accounted for the most in the heterotrophic reactor with ethanol as electron donor. Thiobacillus existed abundantly in every system, even in the heterotrophic one. PCA comparison revealed that the microbial communities in the denitrification systems may vary greatly according to the electron donor, the running condition, sampling position, and other factors.

Nitrogen removal by the enhanced floating treatment wetlands from the secondary effluent

Three novel floating treatment wetlands, including autotrophic enhanced floating treatment wetland (AEFTW), heterotrophic enhanced floating treatment wetland (HEFTW) and enhanced floating treatment wetland (EFTW) were developed to remove nitrogen from the secondary effluent. Results showed that the analogously excellent nitrogen removal performance was achieved in AEFTW and HEFTW. About 89.4% of the total nitrogen (TN) was removed from AEFTW at a low S/N of 0.9 and 88.5% from HEFTW at a low C/N of 3.5 when the hydraulic retention time (HRT) was 1d in summer. Higher nitrification and denitrification performance were achieved in AEFTW. Addition of electron donors effectively reduced the N2O emission, especially in summer and autumn. High-throughput sequencing analysis revealed that the electron donors distinctly induced the microbial shifts. Dechloromonas, Thiobacillus and Nitrospira became the most predominant genus in HEFTW, AEFTW and EFTW. And autotrophic and heterotrophic denitrification could simultaneously occur in HEFTW and AEFTW.

Treatment of chromite ore processing residue by pyrolysis with rice straw.

Chromite Ore Processing Residue (COPR) is the byproduct of chromate production process, which contains a large amounts of Cr(VI). The present work developed a new technique to treat COPR, and the process involved mixing the COPR with rice straw followed by pyrolysis. It was found that the gaseous organic fraction generated during pyrolysis of straw was beneficial to Cr(VI) reduction. In the study, process variables, such as the amount of straw added to COPR, heating temperature and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were all investigated. After pyrolysis, Cr(VI) decreased greatly, from 3400 for untreated COPR to less than 30 mg kg(-1) for treated COPR at 600 degrees C.

Impact of pyrolysis process on the chromium behavior of COPR.

The effect of pyrolysis process with sewage sludge on the chromium behavior of chromite ore processing residue (COPR) was examined in this study. The behavior of chromium was characterized in term of chromium oxidation test, pH-static leaching tests, column leaching test and sequential extraction test. As a sequence of pyrolysis process, the Cr(VI) in COPR was effectively reduced from 5057 mg kg(-1) for untreated COPR to 8.6 mg kg(-1) for treated COPR at temperature over 600 degrees C, which is far below the New Jersey Department of Environmental Protection regulatory limit of 240 mg kg(-1). As a result, the amount of exchangeable and carbonate-bound Cr fractions, the most mobile for the environment, were largely reduced. At the same time, the amount of the other three Cr fractions which are much less mobile become augmented. pH static test showed that the chromium in the treated COPR at pyrolysis temperature above 400 degrees C was quite stable at pH>7. Column study also indicated that only negligible amount of chromium of the treated COPR at above 600 degrees C can be released by the acid rain.