Re-circulation on engineered landfill or absorption or biological filter media or sand or soil filteration.

because of high COD in this type of wastewater you should use biological methods including aerobic and anaerobic methods.

Is the bottom sealed? The system should be designed for given parameters of this specific leachate, but you have to remember that this parameters will probably significantly differ throughout the year and will dramatically shift after several seasons. Recirculation is a kind of solution, especially when local climate is quite hot and dry, because of reduction of leachate volume by evaporation, however, those contaminants that aren't volatile will be concentrated. When you still want to process the leachate,  it is always good to have two stage treatment system, e.g biological and physiochemical, in any arrangement. If you have enough solar energy, maybe photocatalysis  is a good choice?

Commonly the treatment systém is designed according to quality of influent leachate and requested parameters of effluent after treatment. Without these parameters you can hardly design any treatment systém including lkeachate treatment.

Best regards Vit

Dear Sir,

Assuming that this is about a young active landfill, then the COD would indeed be high. In that case we apply high-rate anaerobic digestion (HRAD) to convert up to 90% of the COD-load to biogas (methane) as green energy. For old inactive landfills we apply advanced aerobic biological treatment to crack and biodegrade the recalciitrant organics. If interested, I can send you more information via email.

Regards, Bruno