# Notes on Common Misconceptions in Microplastics Removal from Water
## 3 Microplastics Removal from Water
### Coagulation/Flocculation
In addition, a mutual comparison between two studies is impracticable, because each WWTP treats wastewater with different physical-chemical properties and the concentration of contaminants (including microplastics) is \"unique\" for every one of them. [PERSON] et al. investigated removal of microplastic particles via coagulation followed by sedimentation with spherical polystyrene particles of two diameters, 1 um and 6.3 um. Ferric chloride, polyaluminium chloride and polyamine were compared and the highest removal efficiency was achieved with ferric chloride and polyaluminium chloride (up to 99%) [42]. [PERSON] and [PERSON] tested the removal of microplastic (<65 um) particles at different stages of tertiary treatment in WWTPs and the results were compared with the primary and secondary treatment stages. It was determined that the primary and secondary stages were able to remove 75-92% of microplastic particles. However, considering the scale of water treated in WWTPs, a large number of microplastics was still present in water [43]. Aluminum coagulation was combined with different tertiary treatment technologies (ozonation, membrane disc-filter and rapid sand filter) and it was found out that such combination helped to increase the removal efficiency exceeding 99%. Without application of additional tertiary treatment technologies, removal efficiency via coagulation was up to 95%. The positive effect of coagulant dosing enhancing microplastic particles removal was also confirmed [44]. It was reported that weathered microparticles revealed higher removal efficiency via coagulation and flocculation than fresh particles, due to changes on their surface roughness [45]. Aluminum coagulation is reported to be more efficient and studies on iron coagulation are not as intensively reported as aluminum coagulation. The reason might be in the different character of the sludge. Aluminum sludge contains more water than Fe sludge and that may be the reason why microplastic particles are better removed (not only adsorption on sludge surface but also water volume capture). [PERSON], [PERSON] and [PERSON] focused on the removal of PE beads (300\(-\)355 \(\upmu\)m) from fresh water using electrocoagulation with aluminum electrodes. The authors tested various process parameters for the best performance of electrocoagulation and they achieved more than 99% removal efficiency at a pH of 7.5, NaCl concentration of 2 g/L, current density = 11 A/m\({}^{2}\) and time of reaction of 60 min [46]. The authors do not report on coagulant dose, as this is the crucial parameter during coagulation studies. They put dose of coagulant in relation with current density, but it must be given in relation with current intensity. Current intensity is the parameter to be calculated with Faraday's Law. Another study that focused on the removal of microplastic particles via electrocoagulation as a consecutive step of sewage water treatment plants was made by [PERSON] and [PERSON]. They focused on the removal of various types of PTFE plastics using an aluminum electrode. The authors achieved more than 90% removal efficacy by electrocoagulation of particles that could not be removed with other methods [47]. Electrocoagulation is considered an alternative to standard chemical coagulation with significantly reduced use of chemicals, because the coagulating chemical is replaced by an electrochemical substitute in the form of a sacrificial electrode [48].