Electrochemical treatment as a pre-oxidative step for algae removal using Chlorella vulgaris as a model organism and BDD anodes

Abstract

An experimental work is presented in this paper on the inactivation of algae through electrochemical treatment. A green algae (Chlorella vulgaris) was adopted as a model. A commercial filter-press electrochemical reactor (Electro MP-Cell), equipped with a boron doped diamond (BDD) anode and a stainless steel cathode, was used to perform the electrolysis. The cell was inserted in a hydraulic circuit and used in either a closed loop, as a recirculating batch reactor, or in the continuous mode. The effects of current density and hydrodynamics were studied, as well as the formation of active chlorine and other chloride oxidation products. Active chlorine concentrations on the order of 0.3mmoldm−3 were obtained when algae were not present in the initial solution (batch experiments) or in the feed (continuous experiments). In the presence of algae, the value was 0.03mmoldm−3. The highest values were measured with i=75Acm−2 and flow conditions corresponding to a Reynolds number of 100 (batch experiments) or a hydraulic residence time of 4min (continuous experiments). The process led to the total inactivation of algae when 100mgdm−3 of chlorides was present in the solution, which is a typical value for natural waters. The results indicated that, under the adopted conditions, the prevailing mechanism was inactivation by means of long-life oxidants electrogenerated. A simple model of continuous stirred tank reactors (CSTRs) in-series was adopted to account for the non-ideal flow conditions in the continuous experiments, which was able to interpret the data under all the conditions tested.