Abstract—As petrochemical industrial wastewater contains many recalcitrant compounds, the potential of hybrid biological reactors may present a resource to be tapped, especially in the actual operation of an industrial wastewater treatment facility such as Al-Wafra industrial wastewater treatment plant in Kuwait treating primarily petrochemical industry wastewater. This paper examines possible scenarios for use of hybrid reactors in existing Al-Wafra industrial wastewater treatment plant to improve its efficiency due to loss of biomass in the activated sludge process caused by extreme conditions of the industrial wastewater it receives and its inhibitors. The main innovation in this study, the hybrid reactor was constructed using a biological carrier of the high surface area Random Packing type and was operated using real wastewater samples from Al-Wafra Industrial wastewater Treatment plant. The modalities of operation included high dissolved oxygen levels (4.0 mg/l), low dissolved oxygen levels (2.0 mg/l), and under ANNAMOX conditions. Results revealed that stable biomass have developed on the support media of the hybrid biological reactor with attached to suspended biomass ratio exceeding 70% and improved efficiency of the first sequence (hybrid-to-ASP) process for TOC removal of 11-17% and 19-26% for the second sequence (ASP-to-hybrid) combination depending on the operating conditions. These results clearly reflect the unfavorable conditions for biodegradation after the primary chemical treatment at Al-Wafra plant. In addition, the dominant bacterial species were identified as pseudomonas species favor less acidic environments which were achieved after the ASP. In terms of nitrification/denitrification, the process met the ammonia and total nitrogen Kuwait standards for irrigation water of 15 and 35 respectively. Index Terms—Hybrid biological reactors, industrial wastewater, wastewater treatment. I. INTRODUCTION Petrochemical industries are an important industrial sector in Kuwait and internationally as they use and produce considerable amounts of water and wastewater. Petrochemical wastewater is treated using a variety of technologies, including physical and chemical treatment processes such as electro-coagulation, electrochemical oxidation, dissolved air flotation, adsorption, and many others [1]. However, these technologies are costly, use specialized treatment equipment, use huge amounts of chemicals, and produce excessive amounts of sludge. Manuscript received March 19, 2019; revised May 25, 2019. This work was supported in part by the Kuwait Foundation for the Advancement of Science (KFAS) and Kuwait Institute for Scientific Research (KISR) for funding the study Project No. WT046C. The authors are with Kuwait Institute for Scientific Research, Water Research Center, Kuwait (e-mail: miahmed@kisr.edu.kw, rayaseen@kisr.edu.kw, amydlarczyk@kisr.edu.kw, ahadad@kisr.edu.kw). Biological processes are preferred since they are simple, inexpensive, and environmental friendly in their operation [1]. Biological processes can be one of three types, namely, suspended, attached, or hybrid processes. The suspended growth process utilizes suspended microorganisms to degrade contaminants in the wastewater; the attached growth process utilizes solid media to grow the microorganisms in order to reduce their loss rate, and the hybrid process is a combination of both and can be configured and operated in a variety of ways to maximize efficiency and maintain flexibility. In many instances integrated film biological reactors or biofilm reactor, intended by design, may actually be operating in a suspended and/or attached biological growth modes and, therefore, these reactors are termed “hybrid” biological reactors. The hybrid reactor process can be used as a normal wastewater treatment process the same way as an activated sludge process (ASP) or an attached growth process. In addition to their many advantages including good performance, simplicity of operation, and ability to absorb shock loads, hybrid biological reactors can be optimized to maximize degradation rates of organics including compounds of emerging concern and, hence, they are promising technology in treating industrial wastewaters [2]. In this paper, the research is focused on improving the performance of the activated sludge process of Al-Wafra industrial wastewater treatment plant in Kuwait. A hybrid biological reactor is proposed for this purpose. A background on Al-Wafra industrial wastewater treatment plant is given next. Al-Wafra Industrial Wastewater Treatment Plant. Al-Wafra Industrial Wastewater Treatment Plant is the only industrial wastewater treatment in Kuwait. The plant consists of preliminary treatment, chemical treatment and biological treatment at the secondary level. Disinfection by chlorination is then applied to effluent before storage in storage tanks. The plant does not utilize anaerobic processes or advanced treatment processes to further polish its effluent. Al-Wafra Industrial Wastewater Treatment Plant receives industrial wastewater from various industries via tankers to the maximum daily capacity of 7,500 m 3 . According to Al-Dhafeeri [3] around 300 tankers daily undergo testing before admitting their wastewater into the plant and in case tests indicate unsuitability some will be rejected. The accepted tankers are responsible for 5,000 m3/d load at which the plant is operating currently. This level of operation is maintained and imposed by the volume of generated sludge [3]. Industrial wastewater treatment in Kuwait has been briefly addressed in previous Kuwait Institute for Scientific Research (KISR) studies, mainly [3]-[5] and it is evident that Potential Use Scenarios of Hybrid Biological Reactor for Petrochemical Industry Wastewater Treatment Mohd Elmuntasir Ahmed, Rashed Al-Yaseen, Andrzej Mydlarczyk, and Adel Al-Haddad International Journal of Environmental Science and Development, Vol. 10, No. 8, August 2019 231 doi: 10.18178/ijesd.2019.10.8.1178