The present invention relates to provide a carbon bed electrolyzer (CBE) unit for electrochemical treatment. More particularly the present invention relates to the treatment of recalcitrant wastewater, e.g. from chemical industry. Further the said CBE unit is useful for electrolytic treatment of liquid effluent having very high concentrations of Chemical oxygen Demand (COD), Total Kjeldahl Nitrogen (TKN) and Biochemical Oxygen Demand (BOD), and Total Dissolved Solids (TDS), and for improving biodegradability of the effluent. More particularly, the present invention relates to an electro oxidation process wherein the carbon bed gets regenerated in-situ continuously.