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.

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.

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.

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.