Introduction: Organic compounds are one of the most important quality characteristics in wastewater treatment. The aim of this study is to make comparison of the efficiency of wetland and extended aeration activated sludge in the removal of organic compounds from sanitary wastewater based on response surface methodology.

Methods: In this experimental study 100 mixed samples were taken from wetland and extended aeration reactors. According to type of wastewater treatment and operating time, COD, BOD5 and TSS were measured. Sampling, transportation, storage and measurement performed according to standard methods. Experiment setting, modeling, removal equation of organic compounds and optimal condition was obtained by response surface methodology.

Results: Maximum removal of COD, BOD5 and TSS (in summer) in wetland were 95.67, 93.4 and 87.41%; in extended aeration was 97, 65.1 and 80.2%, respectively. Efficiency of extended aeration was better than wetland in all seasons and all parameters. R2: 0.8- 0.89 confirms the effect of operating time on wastewater treatment efficiency. Validity and accuracy in wetland and extended aeration were 12.64-17.65 and 16.01-19.37, respectively. Removal model in both wetland and extended aeration was linear.

Conclusion: Efficiency of extended aeration is more than wetland. Response surface methodology properly describes organic compound removal efficacy by extended aeration and wetland.