In the field of electrocoagulation (EC), various studies on pollutant removal and on the use of different EC technologies have already been made. An EC process generates sludge, which is considered waste, resulting in increased operational costs that come from waste disposal. Sludge contains valuable materials, such as the nutrients or metals removed during water purification, along with metals, such as aluminum or iron, which come from the electrodes used in an EC system. Based on the principles of circular economy or based on existing legislations, reducing the production of valuable wastes, and increasing the valorization rate of as many materials as possible are important endeavors. This study is mainly a review of the existing sludge valorization studies. This review highlights the valorization of sludge as a fertilizer (mainly as struvite), pigment, construction material (mainly as blocks), adsorbent, and catalyst. While it has already been found that EC sludge is valorizable, more studies on EC sludge valorization and on the quality of sludge produced from the effluent of EC processes are warranted.

Batch electrocoagulation (BEC), continuous electrocoagulation (CEC), and chemical precipitation (CP) were compared in struvite (MgNH₄PO₄·6H₂O) precipitation from synthetic and authentic water. In synthetic water treatment (SWT), struvite yield was in BEC 1.72, CEC 0.61, and CP 1.54 kg/m³. Corresponding values in authentic water treatment (AWT) were 2.55, 3.04, and 2.47 kg/m³. In SWT, 1 kg struvite costs in BEC, CEC, and CP were 0.55, 0.55, and 0.11 €, respectively, for AWT 0.35, 0.22 and 0.07 €. Phosphate removal in SWT was 93.6, 74.5, and 71.6% in BEC, CEC, and CP, respectively, the corresponding rates in AWT were 89.7, 77.8, and 74.4%. Ammonium removal for SWT in BEC, CEC, and CP were 79.4, 51.5, and 62.5%, respectively, rates in AWT 56.1, 64.1, and 60.9%. Efficiency in CEC and BEC are equal in nutrient recovery in SWT, although energy efficiency was better in CEC. CP is cheaper than BEC and CEC.

Activated carbon from sawdust was produced with an environmentally friendly process involving single‐stage carbonization and activation with steam at 800°C. Production process is scalable because lignocellulosic biomass is ubiquitous worldwide as a waste or as a virgin material. Single‐stage production without any cooling steps between carbonization and activation is easier in larger scale production. Monometal adsorption and multimetal adsorption of cobalt, nickel, and zinc were investigated by using the produced carbon, with a commercial one as control. Effect of pH, initial metal concentration, adsorbent dosage, and adsorption time was evaluated in batch experiments. Multimetal experiments showed the order of the maximum adsorption capacities: zinc > nickel > cobalt. Experimental adsorption capacities were 17.2, 6.6, and 4.5 mg/g for zinc, nickel, and cobalt, respectively, in multisolute adsorption. In case of monometal adsorption, adsorption capacity was notably lower. Experimental data fitted into the single‐solute and multisolute Freundlich models. The best fit kinetic model varied among the metals. The Weber and Morris intraparticle diffusion model was used. Regeneration was performed with 0.1 M HNO₃, 0.1 M HCl, or 0.1 M H₂SO₄. The adsorption capacity remained at the same within three adsorption–desorption cycles.Practitioner points: Activated carbon was produced from sawdust with environmentally friendly process Monometal adsorption and multimetal adsorption with heavy metals were studied Best‐fitting models to the experimental data were single‐solute and multisolute Freundlich models Regeneration could be performed with diluted acids Worldwide available raw material successfully used as adsorbent for heavy metals

Sawdust was used as a precursor for the production of biomass-based activated carbon. Carbonization and activation are single-stage processes, and steam was used as a physical activation agent at 800 °C. The adsorption capacity towards zinc was tested, and the produced activated carbon proved effective and selectively adsorbent. The effects of pH, initial concentration, adsorbent dosage, time, temperature, and regeneration cycles were tested. The adsorption capacity obtained in this study was compared favorably to that of the materials reported in the literature. Several isotherms were applied to describe the experimental results, with the Sips isotherm having the best fit. Kinetic studies showed that the adsorption follows the Elovich kinetic model.