Citation: Vasilie, S.; Vitan, L.-D.; Tudoran, C.-A.; Manea, F. Flexible Electroflotocoagulation Reactor: New Design and Testing in Treatment of Real Surface Water. Water 2022, 14, 2990. https://doi.org/10.3390/ w14192990 Academic Editor: Alexandre T. Paulino Received: 12 August 2022 Accepted: 18 September 2022 Published: 23 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Flexible Electroflotocoagulation Reactor: New Design and Testing in Treatment of Real Surface Water Sergiu Vasilie 1 , Liviu-Danut Vitan 2,3 , Constantin-Adrian Tudoran 3 and Florica Manea 1, * 1 Department of Applied Chemistry and Engineering of Inorganic Compounds and Environment, Politehnica University of Timisoara, 300223 Timisoara, Romania 2 Department of Electrical Engineering, Politehnica University of Timisoara, 300223 Timisoara, Romania 3 Department of Design and Research, BeeSpeed Automatizari Ltd., 307221 Chisoda, Romania * Correspondence: florica.manea@upt.ro Abstract: A novel continuous and flexible electroflotocoagulation (EFC) reactor was built using concentric cylindrical Al and Fe electrodes, which can be operated either as anodes or cathodes linked to a DC connection. The reactor was operationally assessed related to various cell configurations that assured the required stages of coagulant dosage, mixing, reaction, and settling or flotation. The effects of several design variables and operational parameters (such as the electrode position that determines the reactor configuration, current density (i), flow rate (F), and the electrode area-treated volume ratio (Sel/V)) on the specific energy consumption versus the aluminum dose and charge loading rate were investigated. The most energy-efficient cell configuration using an aluminum anode and iron cathode was tested for the treatment of surface water (Bega river, Timisoara city, Romania) rich in hydrophobic natural organic matter (8.3 mg C·L -1 and specific UV absorbance parameter of 3.9 L·m -1 ·mg -1 ) and with a high turbidity of 92 NTU, under flood conditions. The best results that assured 97% turbidity removal, 87% for absorbance recorded at 254 nm, and 60% for DOC removal, through enhanced electroflotocoagulation, were achieved for an operational current density of 10 A·m -2 with specific energy and electrode consumption of 0.1 kW h·m -3 and 0.017 kg Al·m -3 , respectively. Keywords: flexible electrochemical reactor; electroflotocoagulation; water treatment; aluminum anode; iron cathode 1. Introduction Electroflotocoagulation (EFC) reactors have been built in a variety of configurations, each being characterized by its own set of advantages and disadvantages, with different degrees of treatment ability. The performance assessment of different reactor configurations is very difficult because the reactor geometry affects the main operational parameters, including floc formation bubble path and size, fluid flow regime, and mixing or settling characteristics via the current density and cell voltage [1–3]. An EFC unit can be operated by two approaches. Sometimes, an EFC unit is used simply as a replacement for chemical dosing systems and does not always take advantage of the electrolytic gases produced and floc formation in the electrocoagulation process. In this situation, the downstream units for reaction and settling are required to generate and remove the pollutants containing sludge from the water. However, a complete unitary system consisting of an in situ dosage of reagents, mixing, reaction, and sludge settling can be considered for designing an EFC reactor. Aluminum- or iron-based electrodes are commonly used in EFC units for wastewater or water treatment and various electrode geometries, e.g., horizontal [4,5], vertical [6], or cylindrical [7], in accordance with the reactor configuration, and different operation modes (batch or continuous) have been tested. In batch operation mode, the horizontal anode of iron reportedly allowed high efficiency for arsenic removal from real groundwater [4] and 70% of total organic carbon has been removed from surface water through aluminum Water 2022, 14, 2990. https://doi.org/10.3390/w14192990 https://www.mdpi.com/journal/water