Cong Li

Adsorption of Pb(II) on activated carbon prepared from Polygonum orientale Linn.: kinetics, isotherms, pH, and ionic strength studies.

Low-cost activated carbon was prepared from Polygonum orientale Linn. (PL) by phosphoric acid activation. Its ability to adsorb Pb(II) ions from aqueous solutions was examined. Through SEM, XRD, BET, and FTIR analyses, the PL-activated carbon (PLAC) was found to have a porous structure with a surface area of about 1400 m(2)/g. Carboxyl groups played an important role in the adsorption of Pb(II) through blocking studies. The sorption system followed a pseudo second-order kinetic model, and the equilibrium time was obtained after 30 min. The adsorption isotherms were simulated well by the Langmuir model. The adsorption of Pb(II) on PLAC was strongly dependent on pH and ionic strength, indicating an ion-exchange mechanism. Regeneration studies showed that PLAC could be used several times by desorption with an HCl reagent.

Impact of COD/N ratio on nitrous oxide emission from microcosm wetlands and their performance in removing nitrogen from wastewater

Constructed wetlands (CWs) are considered to be important sources of nitrous oxide (N(2)O). In order to investigate the effect of influent COD/N ratio on N(2)O emission and control excess emission from nitrogen removal, free water surface microcosm wetlands were used and fed with different influent. In addition, the transformation of nitrogen was examined for better understanding of the mechanism of N(2)O production under different operating COD/N ratios. It was found that N(2)O emission and the performance of microcosm wetlands were significantly affected by COD/N ratio of wastewater influent. Strong relationships exist between N(2)O production rate and nitrite (r=0.421, p<0.01). During denitrification process, DO concentration crucially influences N(2)O production rate. An optimal influent COD/N ratio was obtained by adjusting external carbon sources for most effective N(2)O emission control and best performance of the CWs in nitrogen removal from wastewater. It is concluded that under the operating condition of COD/N ratio=5, total N(2)O emission is minimum and the microcosm wetland is most effective in wastewater nitrogen removal.

Preparation of activated carbon from cattail and its application for dyes removal

Activated carbon was prepared from cattail by H3PO4 activation. The effects influencing the surface area of the resulting activated carbon followed the sequence of activated temperature > activated time > impregnation ratio > impregnation time. The optimum condition was found at an impregnation ratio of 2.5, an impregnation time of 9 hr, an activated temperature of 500 degrees C, and an activated time of 80 min. The Brunauer-Emmett-Teller surface area and average pore size of the activated carbon were 1279 m2/g and 5.585 nm, respectively. A heterogeneous structure in terms of both size and shape was highly developed and widely distributed on the carbon surface. Some groups containing oxygen and phosphorus were formed, and the carboxyl group was the major oxygen-containing functional group. An isotherm equilibrium study was carried out to investigate the adsorption capacity of the activated carbon. The data fit the Langmuir isotherm equation, with maximum monolayer adsorption capacities of 192.30 mg/g for Neutral Red and 196.08 mg/g for Malachite Green. Dye-exhausted carbon could be regenerated effectively by thermal treatment. The results indicated that cattail-derived activated carbon was a promising adsorbent for the removal of cationic dyes from aqueous solutions.

Influence of organic shock loads on the production of N2O in denitrifying phosphorus removal process

In this work, the influences of short-term organic shock loads on N₂O production during denitrifying phosphorus removal were investigated by changing the influent COD concentrations (100, 200, 350, and 500 mg/L). After switching the COD concentrations from 200 to 350 or 500 mg/L, N₂O-N production amount increased from 1.62% to 7.12% or 3.29% of the TN removal, respectively, while the corresponding effluent phosphorus concentrations increased from 1.84 to 16.55 and 56.08 mg/L, respectively, which were higher than the influent phosphorus concentration (4.93 mg/L). Furthermore, when the COD concentration was decreased to 100 mg/L, N₂O-N production amount was only 1.20%. All results suggested that higher organic shock loads increased N₂O production. The main reason was that higher organic shock loads increased anaerobic poly-β-hydroxyalkanoates (PHA) synthesis, which resulted in higher nitrite accumulation. The influences of higher organic shock loads on N₂O production could be minimized by adopting continuous nitrate addition strategy.

Application of using surface constructed wetland for removal of chemical oxygen demand and ammonium in polluted river water

Abstract River water was mostly polluted in northern China in the past decades and the major contaminants were organic matter and ammonia. In this study the performance of the pilot-scale and full-scale surface constructed wetlands for removing COD (chemical oxygen demand) and ammonium from polluted river water was evaluated. Results showed that the effluent COD and NH4 +-N concentrations in the pilot scale wetland systems were 10.72–19.34 mg l−1 and 0.18–0.90 mg l−1, respectively, which met Grade-III (COD 20 mg l−1, NH4 +-N 1 mg l−1) of national surface water standards in China. The maximal COD and NH4 +-N removal efficiency was 96.18% and 99.78%. COD and NH4 +-N removal in spring and summer were better than that in fall and winter based on the k–C∗ model. Combined with research results of the two-year full-scale study, it indicated that the surface wetland system was a promising technology for treating polluted river water to meet the requirement of Grade-III water quality in northern China.

Effect of Ammonia Stress on Physiological and Biochemical Character of Phragmites australis in Constructed Wetland

The function of a constructed wetland system may be affected by high ammonia concentrations, which are toxic to wetland plants. This research was conducted to assess the tolerance of Phragmites australis to ammonia. P. australis is a reed species commonly used in constructed wetlands. The photosynthetic rate (Pn), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) activities and the proline and malondialdehyde (MDA) contents were investigated under different concentrations of ammonia (0, 80, 160, 320, and 640 mg L-1). P. australis grew well at ammonia concentrations of up to 160 mg L-1, but growth was inhibited at higher levels. Ammonia also induced the activity of antioxidative enzymes such as SOD, POD, and CAT, suggesting that ammonia can cause oxidative stress. Oxidative stress may be part of the mechanism of ammonia toxicity. Thus, ammonia concentrations should be managed to maintain the effectiveness of constructed wetland systems.

Response of greenhouse gas emissions and microbial community dynamics to temperature variation during partial nitrification

This study investigated the greenhouse gas emission characteristics and microbial community dynamics with the variation of temperature during partial nitrification. Low temperature weakened nitrite accumulation, and partial nitrification would shift to complete nitrification easily at 15 °C. Based on CO2 equivalents (CO2-eq), partial nitrification process released 2.7 g of greenhouse gases per gMLSS per cycle, and N2O accounted for more than 98% of the total CO2-eq emission. The total CO2-eq emission amount at 35 °C was 45.6% and 153.4% higher than that at 25 °C and 15 °C, respectively. During partial nitrification, the microbial community diversity greatly declined compared with seed sludge. However, the diversity was enhanced at low temperature. The abundance of Betaproteobacteria at class level increased greatly during partial nitrification. Proteobacteria abundance declined while Nitrospira raised at low temperature. The nosZ community abundance was not affected by temperature, although N2O emission was varied with the operating temperature.

Kinetics and Equilibrium Isotherms on Methyl Violet Adsorption by Arundo Donax Root Activated Carbon

Arundo donax root was used to prepare activated carbon by H 3 PO 4 activation for the removal of methyl violet (MV). The activated carbon has a micro-mesoporous structure with BET surface area 1392 m 2 /g. Pseudo-second-order model could predict the adsorption kinetics for the entire process. The sorption involved several stages and the actual rate controlling step was film diffusion for the whole process. The equilibrium data were better represented by Freundlich model than Langmuir model. The adsorption of methyl violet onto Arundo donax root activated carbon was spontaneous and endothermic.