Full scale performance of compost’s leachate treatment by biological anaerobic reactors

A wide range of treatment processes have been applied to leachate treatment with varying success. The aim of this research was to examine the performance of two hybrid biological anaerobic reactors in a new full-scale leachate treatment plant in Rasht composting facility, north of Iran. The studied plant was operated for nearly 12 months and treated up to 50 m³ day⁻¹ of fresh compost leachate with a relatively high BOD₅ to COD ratio of around 0.5. The average COD of the raw leachate was measured to be 81 000 mg L⁻¹. 30% of effective volume of each reactor was filled with clay blocks with a specific area of 87 m² m⁻³ as the fixed bed. The sequencing of reactors was down flow and up flow, respectively. The maximum COD removal efficiency of 91% was achieved with 4.5 kg COD m⁻³day⁻¹ of organic loading rate and 7500 mg L⁻¹ of volatile suspended solids. There was no significant difference in COD removal efficiency when the reactors were operated with an organic load between 2 and 5 kg COD m⁻³day⁻¹. Increasing the volumetric organic loading rate to greater than 6 kg COD m⁻³day⁻¹ caused a considerable reduction of COD removal efficiency. The COD removal efficiency decreased to less than 70% when the organic load rose to 10.8 kg COD m⁻³day⁻¹. Nevertheless, hybrid anaerobic reactors proved to be a feasible technique for the reduction of organic load from the composting leachate which was the subject of this study.