Abstarct: This thesis aims to investigate the effectiveness of micro-nano bubble technology in wastewater treatment in a potato chips factory (Case study: Topis Co.). The Topis wastewater treatment plant (WWTP) is baxsed on a conventional activated sludge system. The hydraulic retention time for treating effluent of the anaerobic pond with COD of 400-500 mg/L and reducing the COD to 100-150 mg/L is 43.75 h. The treatment plant faces problems such as low efficiency of aeration ponds, high energy consumption, and high maintenance costs of blowers. The use of micro-nano bubble as aeration system on a pilot scale was investigated. The micro-nano bubble generator was submerged in a 2000 L tank with a working volume of 1800 L. 30 % of the tank was fed with activated sludge from Topis WWTP, and 70 % was fed with the effluent of an anaerobic pond and aerated for one week. After the preparation of microbial culture, half of the experiment were performed in summer (25-35℃) and half in autumn (10-15℃). Suspended growth and attached growth experiments were performed. For each experiment, 70% of the tank was discharged and fed with an anaerobic pond's effluent, and COD removal after 3 h, 6 h and 9 h was measured for suspenden and attached growth experiments. The results of the suspended growth tests revealed 65% and 39% COD removal after 9 hours of aeration with MNBs in warm and cold weathers, respectively. In addition the results of attached growth in cold weather showed 54% COD removal in 9 hours. Results revealed that the attached growth was more tolerabale for cold weather and in all tests the COD was meet the statndards (less than 200 mg/L). Therefore, aeration with MNB reduced HRT, improve COD removal eeficiency, reduced electricity consumption and eliminated the high maintenance costs of blowers. In addition, MNB can be considered an optimal and environment-friendly approach for wastewater treatment.