1.
Effects of the substrate depth on purification performance of a hybrid constructed wetland treating domestic sewage.
Ren, YX, Zhang, H, Wang, C, Yang, YZ, Qin, Z, Ma, Y
Journal of environmental science and health. Part A, Toxic/hazardous substances & environmental engineering. 2011;(7):777-82
Abstract
The depth of substrate in constructed wetlands (CWs) has a significant effect on the construction investment and the purification performance of CWs. In this study, a pilot scale CW system was operated in a domestic sewage treatment plant in Xi'an, China. The experimental systems included three-series CWs systems with substrate depths of 0.1m, 0.3 m and 0.6 m, respectively. Each series was composed of a hydroponic ditch, a horizontal subsurface flow CW and a vertical flow CW. The effluent from the primary clarifier in the sewage treatment plant was intermittently conducted to the wetlands at a flow rate of 0.3 m(3)/d. The hydraulic loading rate of each CWs system was regulated at 0.1 m(3)/m(2).d and the hydraulic retention time was 3 days. Canna indica L. was planted both in the hydroponic ditches and the CWs systems. Results showed that the highest removal efficiency of NH(+)(4)-N and TP was obtained in the hybrid CW with 0.1 m substrate depth. The average removal efficiency for NH(+)(4)-N and TP were 90.6 % and 80.0 %, respectively. The highest average removal efficiency of COD was obtained in hybrid CWs system with 0.6 m substrate depth. Therefore, a simultaneous removal of COD and nutrients can be achieved through the combination of different wetlands using different substrate depths. In addition, the substrate depth presents significant effects on the concentration of DO and root growth characteristics of canna in the system. As a result, the highest concentration of DO (>2 mg/L) and the highest amount of roots production were achieved in the 0.1 m substrate depth horizontal and vertical flow CWs.
2.
[Short-cut/Complete nitrification and denitrification in a pilot-scale plant treating actual domestic wastewater].
Ma, Y, Chen, LQ, Peng, YZ, Wu, XL
Huan jing ke xue= Huanjing kexue. 2006;(12):2477-82
Abstract
It is realized short-cut nitrification and denitrification in an A/O pilot-scale plant treating actual domestic wastewater controlling DO concentration (0.5 mg/L) in low level at normal temperature, the average nitrite accumulation rate reached 85 % or above. Three operational modes: low DO short-cut nitrification and denitrification (Mode 1), low DO complete nitrification and denitrification (Mode 2) and high DO complete nitrification and denitrification (Mode 3) were briefly compared, based on the nitrogen removal, operating cost, sludge characteristics and operational mechanism. Experimental results showed that the Model is the best modes of biological nitrogen removal, in terms of improving nitrogen removal and reducing operating cost. The net pH change in aerobic zones and anoxic zones is high for Mode 1, but the net pH change in anoxic zones is very small for Mode 3. The nitrification rate is the smallest for Mode 2, and the nitrification rate for Mode 3 is little higher than that of Mode 1; the denitrification rate for Model is larger than that of Mode 3 about 15 %. It is feasible using DO and pH on-line sensors to control the nitrification process.
3.
Fuzzy control of nitrogen removal in predenitrification process using ORP.
Peng, Y, Ma, Y, Wang, S, Wang, X
Water science and technology : a journal of the International Association on Water Pollution Research. 2005;(12):161-9
Abstract
In order to meet increasingly stringent discharge standards, new applications and control strategies for the sustainable removal of nitrogen from wastewater have to be implemented. In the past years, numerous studies have been carried out dealing with the application of fuzzy logic to improve the control of the activated sludge process. In this paper, fuzzy control strategies of predenitrification systems are presented that could lead to better effluent quality and, in parallel, to a reduction of chemicals consumption. Extensive experimental investigations on lab scale plant studies have shown that there was excellent correlation between nitrate concentration and ORP value at the end of the anoxic zone. Results indicated that ORP could be used as an on-line fuzzy control parameter of nitrate recirculation and external carbon addition. The optimal value of ORP to control nitrate recirculation and external carbon addition was - 86 +/- 2 mV and - 90 +/- 2 mV, respectively. The results obtained with real wastewater also showed the good performance and stability of the fuzzy controllers independently from external disturbances. The integrated control structure of nitrate recirculation and external carbon addition in the predenitrification system is also presented.