Muhammad Rizwan Azhar and  Emadadeen Ali,  Periodic Control of a Wastewater Treatment Process to Improve Productivity.   journal   = {International Journal of Environmental and Ecological Engineering}, [online]. World Academy of Science, Engineering and Technology.
    April 2013, vol. 76(4). 209 - 214
    [viewed 09 December 2019]. Available from: https://publications.waset.org/pdf/4473.