ORIGINAL PAPER Online monitoring of the nanoscale zero-valent iron process for trichloroethylene wastewater treatment R.-F. Yu • F.-H. Chi • W.-P. Cheng • M.-H. Wang Received: 18 May 2013 / Revised: 2 January 2014 / Accepted: 10 March 2014 / Published online: 9 April 2014 Ó Islamic Azad University (IAU) 2014 Abstract In this study, a batch-type, nanoscale, zero- valent iron process was used to treat trichloroethylene wastewater. Variations in oxidation–reduction potential (ORP) and pH in the reactor were monitored online for use in developing the model for process control. After the addition of nanoscale, zero-valent iron, the pH value increased rapidly, from 5.0–6.0 to around 8.5–9.5, whereas the ORP decreased dramatically, from around 300 mV to -700 to -800 mV. The degradation of trichloroethylene reached equilibrium at a reaction time of about 120 min. The use of a dose of 1.5 g/L to treat an influent that had a trichloroethylene concentration of 50 mg/L resulted in a removal efficiency of 94 %. Two models, i.e., a multiple regression model and an artificial neural network (ANN) model, were used to develop the control model to predict the trichloroethylene removal efficiencies. Both the regression model and the ANN model performed precise prediction results for the trichloroethylene removal effi- ciencies, with correlation coefficients of about 0.87 and 0.98, respectively, resulting in great potential for control- ling the trichloroethylene removal. Keywords Artificial neural network  Monitoring and control  Nanoscale zero-valent iron  Oxidation–reduction potential  pH  Trichloroethylene Introduction Trichloroethylene (TCE) is discharged in the industrial wastewater produced by metal degreasing processes, electronic processes, and dry cleaning, which are most critical sources for the dense, non-aqueous-phase liquid (DNAPL) contaminants in groundwater that are difficult to remediate (Cho and Choi 2010; Haest et al. 2012; Wang et al. 2012). Industrial wastewaters that contain TCE typ- ically have been treated by various chemical technologies, including chemical adsorption and oxidation processes (West et al. 2008). However, the nanoscale zero-valent iron (nZVI) process has emerged as one of the most innovative and effective technologies for soil and groundwater reme- diation, as well as for treating industrial wastewaters, due to its strong redox potential and large specific surface area (Crane and Scott 2012; Hua et al. 2012). The nZVI process has been used to reduce various pollutants, including chlorinated hydrocarbons (Lookman et al. 2004; He et al. 2007; Smuleac et al. 2011), nitrochlorobenzene (Dong et al. 2011), dyes (Lin et al. 2008; Shu et al. 2007, 2010; Moon et al. 2011), heavy metals (Uzuma et al. 2008; Zhang et al. 2010; Shi et al. 2010; Dua et al. 2012), and nitrites (Ryu et al. 2011; Liu et al. 2012). The nZVI process also has been used to inactivate microbes and remove antibi- otics from aqueous effluents (Diao and Yao 2009; Ghauch et al. 2009). However, investigations concerning process monitoring and control of the nZVI process are relatively rare. The monitoring of oxidation–reduction potential (ORP), dissolved oxygen (DO), and pH provides economical, flexible, and effective control parameters for the various wastewater treatment processes (Chang et al. 2004; Olsson 2012; Zanetti et al. 2012) that have been applied success- fully to control systems that remove biological nutrients R.-F. Yu (&)  W.-P. Cheng  M.-H. Wang Department of Safety, Health and Environmental Engineering, National United University, Miao-Li 360, Taiwan, ROC e-mail: rfyu@nuu.edu.tw F.-H. Chi Department of Environmental Engineering, Kun-Shan University of Technology, T’ai-nan 710, Taiwan, ROC 123 Int. J. Environ. Sci. Technol. (2015) 12:1647–1656 DOI 10.1007/s13762-014-0567-2