One of the major concerns of today's world is water security. The rapid developments in biochemical studies have opened the door for more progress in the biological water treatment method. Moving-bed biofilm reactor (MBBR) system is one of the relatively new water treatment methods which have witnessed a rapid expansion in numbers during the past few years. In this work, an experimental MBBR system was built and monitored throughout a startup period for treatment efficiency until a constant

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... e of COD at 110 mg/l after 42 days when the reactor was considered efficiently started up. Different hydraulic retention times were evaluated and a treatment time of 6 h was chosen as the most efficient to reach the Syrian (Class a) irrigation water quality. Regression relationships of COD, TDS, NO3-, and PO4-3 indices before and after treatment were studied by implementing an increased influent load for each index with 6 h HRT treatment. Depending on regression equations, the maximum feeding concentration to reach the Syrian (Class a) irrigation water quality was calculated for each index. It was found that using the designed experimental system and 6 h HRT treatment, COD, TDS, NO3-, and PO4-3 in wastewater should be below 1997.4, 2122.86, 55.04, and 20.96 mg/l respectively.