Vinasse wastewater of high organic content (COD = 131,000 mg/L) and low biodegradability (BOD5/COD = 0.11) cannot be easily managed and usually require several consecutive treatment steps. The objective of this work was to dilute vinasse wastewater with seawater and then subject them to electrochemical oxidation over boron-doped diamond (BDD) electrodes. The use of seawater is a rational and novel approach for plants close to the seashore since it may achieve the desirable levels of effluent concentration and conductivity without consuming other water resources and extra electrolytes. Experiments were conducted at initial COD values of 830–8,400 mg/L, NaCl concentrations of 34–200 mM and current densities of 70–200 mA/cm2 for up to 5 hours. The effect of current density and NaCl concentration was marginal on the electrochemical treatment, while the single most important parameter was the initial COD concentration. The order of reaction for COD reduction appears to be ‘first’ at low effluent concentrations and it decreases to ‘zero’ at higher concentrations, denoting the importance of the ratio of organics to reactive radicals concentration. Based on COD and total organic carbon data, it is postulated that degradation occurs predominantly through total oxidation (i.e. mineralization) to carbon dioxide and water, which is characteristic of BDD anodes.