‘Green’ coagulant application with activated carbon: dosing sequence and removal of selected micropollutants and effluent organic matter from municipal wastewater

ABSTRACT

Combination of ‘green’ coagulation and powdered activated carbon adsorption was tested for removal of benzophenone (BP), benzophenone-3 (BP-3) and caffeine (CF) from treated municipal wastewater at realistic concentration levels (1–2 µg/L). At the same time it was tracked how the process affected effluent organic matter (EfOM) by measuring chemical oxygen demand (COD). Green coagulant was produced from dry common bean seed in laboratory. Combined coagulation-adsorption experiments were performed by applying different dosing sequences of process materials. Removal of hydrophobic BP and BP-3 by separate adsorption (from 79 to 98%) was not significantly hindered by the addition of the coagulant (activated carbon dose of 5 or 20 mg/L). However, in some cases negative effects were observed for hydrophilic caffeine, depending on the carbon dose, dosing sequence and presence of total suspended solids (TSS). Thus, when coagulant was firstly added into water without TSS before low activated carbon dose of 5 mg/L, caffeine removal dropped from 26% to 5%. Conversely, when TSS were present in the water sample, the removal of caffeine was not hindered under the same PAC dose and dosing sequence. The importance of the process optimisation related to removal of organic micropollutans of different hydrophilicity has been shown in this paper. Removal of around 30% of COD regardless of the dosing sequence was achieved.

GRAPHICAL ABSTRACT

KEYWORDS:

• Wastewater
• natural coagulant
• powdered activated carbon
• benzophenones
• caffeine

Acknowledgment

This work was supported by the Provincial Secretariat for Higher Education and scientific research (grant numbers 114-451-418/2015-03 and 142-451-2166/2019-01/02). The work of PhD student Minja Bogunović was supported by the fellowship (no 1445) from the Ministry of Education, Science and Technological Development of the Republic of Serbia, under the project grant OI172028. We would like to thank the company CABOT NORIT ACTIVATED CARBON for providing free carbon samples. The authors acknowledge the support of the Public Utility Company ‘Vodokanal’, Sombor.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Provincial Secretariat for Higher Education and Scientific Research, AP Vojvodina, Serbia [grant numbers 114-451-418/2015-03; 142-451-2166/2019-01/02]. The work of PhD student Minja Bogunović was supported by the fellowship (no 1445) from the Ministry of Education, Science and Technological Development (Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja) of the Republic of Serbia, under the project grant OI172028.