Removal of metals and hydrocarbons from stormwater using coagulation and flocculation

• Published in: Water research (Oxford) Vol. 182; p. 115919
• Main Authors: Nyström, Fredrik, Nordqvist, Kerstin, Herrmann, Inga, Hedström, Annelie, Viklander, Maria
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2020
• Subjects: Centre - Centre for Stormwater Management (DRIZZLE); Centrumbildning - Centrum för dagvattenhantering (DRIZZLE); Coagulation/flocculation; Hydrocarbons; Metals; Pollutant removal; Stormwater treatment; Treatment efficiency; Urban Water Engineering; VA-teknik; Hydrocarbons; Coagulation/flocculation; Stormwater treatment; Pollutant removal; Metals; Treatment efficiency
• ISSN: 0043-1354; 1879-2448; 1879-2448
• DOI: 10.1016/j.watres.2020.115919

As the understanding of how stormwater pollutants are fractioned and need for mitigation has increased, so has the investigation into more advanced treatment techniques. The present study investigated the treatment efficiency of coagulation/flocculation and sedimentation in semi-synthetic stormwater. Five coagulants were evaluated in terms of reducing particle content, organic carbon, total and dissolved metals, hydrocarbon oil index, and polycyclic aromatic hydrocarbons (PAHs). Changes in the resulting particle size distribution as a consequence of the coagulation treatment were also investigated. The pollutants in the semi-synthetic stormwater were predominantly in the particulate phase. The medium and longer chained hydrocarbons dominated the hydrocarbon oil index, while medium to high molecular weight PAHs were most abundant. Iron chloride was the only coagulant that affected particle size distribution post-treatment, shifting the distribution toward larger particles. In terms of total metal removal, the performance of the coagulants was similar, with over 90% removal on average. Concentration of zdissolved copper, one of the metals found in the dissolved phase, was reduced by 40% via coagulation treatment. The iron chloride coagulant increased dissolved Zn, a change attributed to a considerable drop in pH resulting in higher ion mobility. Similarly, the reduction in organic content (total organic carbon, oil, and PAHs) was over 90% for most coagulants. [Display omitted] •Over 90% reduction in concentration of particulate metal, polycyclic aromatic hydrocarbons and hydrocarbon oil index.•Dissolved copper was removed on average by 40%.•Dissolved zinc was mobilized due to changes in pH with the use of metal salt coagulants.•Chitosan demonstrated good removal of both dissolved copper (72%) and zinc (51%).•Analysis of particle size distribution indicated coagulation treatment had an effect on smaller particles (<10 μm).