Deep-bed filters as post-treatment for ozonation in tertiary municipal wastewater treatment: impact of design and operation on treatment goals

• Published in: Environmental science water research & technology Vol. 7; no. 1; pp. 197 - 211
• Main Authors: Sauter, Daniel, D browska, Agata, Bloch, Robert, Stapf, Michael, Miehe, Ulf, Sperlich, Alexander, Gnirss, Regina, Wintgens, Thomas
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2021
• Subjects: Activated carbon; Adsorptivity; Anthracite; Biodegradability; Biodegradation; Biological activity; Carbonyl compounds; Carbonyls; Coagulants; Contact; Dissolved organic carbon; Dissolved oxygen; Ferric chloride; Filters; Influents; Iron chlorides; Municipal wastewater; N-Nitrosodimethylamine; Oxidation; Ozonation; Ozone; Ozonization; Phosphorus; Phosphorus removal; Removal; Sand; Tertiary; Wastewater treatment
• ISSN: 2053-1400; 2053-1419
• DOI: 10.1039/d0ew00684j

Ozonation followed by biological post-treatment is an established technology for abatement of organic micropollutants (OMP) from municipal wastewater. Although the necessity of biological post-treatment for oxidation by-product (OBP) removal is widely accepted, there is still discussion about the appropriate design and operation. The presented pilot-study investigates the impact of filter material and contact time on the removal efficiency of bulk organics, OMP, and OBP in three different deep-bed filters operated in parallel as post-treatment after ozonation (biological activated carbon (BAC) filter, dual-media filter sand/BAC and dual-media filter sand/anthracite). The use of BAC instead of non-adsorptive filter material resulted in higher removal of DOC and dissolved oxygen which indicates increased biological activity. Moreover, both BAC containing filters showed additional removal for a number of OMP even at high treated bed volumes of >50 000 whereas no removal was observed in the sand/anthracite filter. Analysis of N -nitrosodimethylamine (NDMA) and several carbonyl compounds revealed a clear formation of these biodegradable OBP during ozonation. A strong correlation was found between carbonyl formation and the specific ozone dose. Removal of OBP in the sand/BAC and the sand/anthracite filter was tested at different empty bed contact times (EBCT). While NDMA was efficiently removed independent of EBCT changes, there was a slightly negative impact of shorter EBCT on the reduction of carbonyl compounds. Furthermore, it was demonstrated that the integration of enhanced phosphorus removal into post-treatment is feasible with relatively low efforts by inline coagulant dosing (FeCl 3 ) in the filter influent. The removal of organic contaminants during post-treatment with deep-bed filters after ozonation in tertiary municipal wastewater treatment can be optimised by the choice of filter material and contact time.