Nitrous oxide (N2O) is a significant greenhouse gas, and biological nitrogen removal systems have been shown to be a significant N2O source. To evaluate the control parameters for N2O emission in the wastewater treatment process, N2O emissions were compared in the activated sludge from anoxic–aerobic sequencing batch reactors (A/O SBRs) acclimated under different aeration rates, and fed with synthetic wastewater. Results showed that a higher aeration rate led to a smaller N2O emission, while reactors acclimated under mild aeration performed the best in terms of nitrogen removal efficiency. Most of the N2O was produced during the aerobic phase, regardless of the aeration rate. Trace studies showed that incomplete denitrification appeared to be the major process responsible for high N2O emission at a low aeration rate (Run 1), while incomplete nitrification was the reason for N2O emission at a higher aeration rate (Run 2 and Run 3). For enhancing the efficiency of nitrogen removal while lowering energy consumption and reducing N2O emission, the optimal aeration rate would be 2.7 Lair/(Lreactor • h), in terms of the synthetic wastewater used.

Low cost activated carbon was prepared from Polygonum orientale Linn by phosphoric acid activation. Its ability to remove the basic dyes, malachite green (MG) and rhodamine B (RB) was evaluated. The surface area of P. orientale Linn activated carbon (PLAC) was found to be 1398 m2/g. The effects of experimental parameters such as initial concentration, contact time, pH, ionic strength and temperature on the adsorption were investigated. Alkaline pH was more favorable for MG adsorption, whereas acidic pH was better for RB uptake. Adsorption of dyes on PLAC was weakly dependent on ionic strength. The adsorption kinetics was found to be best represented by the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. The equilibrium adsorption data was well described by the Langmuir model. Thermodynamic study showed that the adsorption was a spontaneous, endothermic process.

The adsorption of methyl orange and methyl violet from aqueous solutions by Phragmites australis activated carbon (PAAC) was studied in a batch adsorption system. The adsorption studies include both equilibrium adsorption isotherms and kinetics. Several isotherm models were investigated and the adsorption isotherm data were best represented by the Temkin isotherms. The kinetic data were well described by the pseudosecond-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. The results indicate that PAAC could be employed as a low-cost alternative for the removal of the textile dyes from effluents.

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°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.

In this paper, an activated carbon was prepared from Typha orientalis and then treated with KMnO4 and used for the removal of Basic Violet 14 from aqueous solutions. KMnO4 treatment influenced the physicochemical properties of the carbon and improved its adsorption capacity. Adsorption experiments were then conducted with KMnO4-modified activated carbon to study the effects of carbon dosage (250-1500 mg/L), pH (2-10), ion strength (0-0.5 mol/L), temperature, and contact time on the adsorption of Basic Violet 14 from aqueous solutions. The equilibrium data were analyzed by the Langmuir and Freundlich isotherms and fitted well with the Langmuir model. The pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to evaluate the kinetic data and the pseudo-second-order kinetics was the best with good correlation.

Constructed wetlands (CWs) are considered to be important sources of nitrous oxide (N2O). In order to investigate the effect of influent COD/N ratio on N2O 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 N2O production under different operating COD/N ratios. It was found that N2O emission and the performance of microcosm wetlands were significantly affected by COD/N ratio of wastewater influent. Strong relationships exist between N2O production rate and nitrite (r=0.421, p<0.01). During denitrification process, DO concentration crucially influences N2O production rate. An optimal influent COD/N ratio was obtained by adjusting external carbon sources for most effective N2O 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 N2O emission is minimum and the microcosm wetland is most effective in wastewater nitrogen removal.

Arundo donax root carbon (ADRC), a new adsorbent, was prepared from Arundo donax root by carbonization. The surface area of the adsorbent was determined 158m2/g by N2 adsorption isotherm. Batch adsorption experiments were carried out for the removal of malachite green (MG) from aqueous solution using ADRC as adsorbent. The effects of various parameters such as solution pH (3-10), carbon dose (0.15-1.0 g/100 ml) and initial MG concentration (10-100 mg/l) on the adsorption system were investigated. The effective pH was 5-7 and the optimum adsorbent dose was found to be 0.6 g/100 ml. Equilibrium experimental data at 293, 303 and 313K were better represented by Langmuir isotherm than Freundlich isotherm using linear and non-linear methods. Thermodynamic parameters such as △G, △H and △S were also calculated. The negative Gibbs free energy change and the positive enthalpy change indicated the spontaneous and endothermic nature of the adsorption. The adsorption equilibrium time was 180 min. Adsorption kinetics was determined using pseudo-first-order model, pseudo-second-order model and intraparticle diffusion model. The results showed that the adsorption of MG onto ADRC followed pseudo-second-order model.

Activated carbon was prepared from an inexpensive and renewable carbon source, Typha orientalis, by H3PO4 activation and then impregnated with different Mn salts and tested for its Neutral Red (NR) adsorption capacities. The amount of Mn impregnated in the activated carbon was influenced by the anion species. Impregnation with Mn decreased the surface area, changed the pore size and crystal structure, and introduced more acidic functional groups such as carboxyl, lactone and phenol groups. The optimum adsorption performance for all the activated carbons was obtained at pH 3.7, Mn–Carbon dose of 0.100 g/100 ml solution and contact time 4.5 h. The adsorption isotherms fit the Langmuir isotherm equation. The kinetic data followed the pseudo-second-order model. The thermodynamic parameters indicated that the processes were spontaneous and endothermic. According to these results, the prepared Mn modified activated carbons are promising adsorbents for the removal of Neutral Red from wastewater.

A pilot subsurface wastewater infiltration system filled with a mixed soil of red clay + 25% cinder was constructed in a village located in Dianchi valley in south west China to treat rural sewage. At first, the system was continuously fed with rural sewage at a hydraulic loading of 2 cm d-1 for over 4 months. The removal of COD, T-P, NH4 +-N, and T-N over the operation period was achieved at average rates of 82.7, 98.0, 70.0, and 77.7%, respectively. Compared to T-P removal, the lower nitrogen removal rates were attributed to reductive soil condition in the system, which was unfavorable for the nitrification process. An intermittent operation was adopted to improve nitrogen removal. The same performances of COD and T-P removal were achieved in the intermittent operation mode. NH4 +-N removal was increased from 70% in the continuous feeding mode to over 90%, and T-N removal rate was elevated over 80% even with the average hydraulic loading as high as 8 cm d-1. Nitrogen balance calculation suggested that nitrification–denitrification was the main mechanism of nitrogen removal that eliminated 57–76% of the fed T-N. Soil redox potential measurement showed that the oxidative environment was increased through intermittent operation, encouraging nitrification. Correspondingly, soil nitrification potential was increased from less than 0.8 mg-N kg-1 h-1 in the continuous feeding mode to about 1.6 mg-N kg-1 h-1 in the intermittent operation mode.

中国北方地区城市纳污河道内的污染河水具有水量、水质、水温季节性变化大的特点，这给人工湿地污染河水处理系统的持续性运行造成很大困难。通过1a多的连续性运行，对潜流人工湿地污染河水处理系统的可持续运行问题进行了系统研究，年平均水力负荷为15cm/d。结果表明，季节变化对氨氮的去除效果影响很大，夏季氨氮去除效果良好，去除率达70%以上，而冬季水温降低到15V以下时，氨氮去除率降低到30%以下，但季节变化对COD去除效果的影响较小。人工湿地在夏季雨季时期可以承受较大的短期洪水水力冲击负荷，在100cm/d的负荷下，对氨氮和COD的去除率分别可以达到52%和36%。基质脱氢酶活性与温度和污染物去除效果的季节性变化存在一定的正相关关系。