Comprehensive analysis of the start-up period of a full-scale drinking water biofilter provides guidance for optimization

Abstract

Abstract. The use of biofilters to produce drinking water from anaerobic groundwater is widespread in some European countries. A major disadvantage of biofilters is the long start-up period required for virgin filter medium to become fully functional. Although individual aspects of biofilter start-up have previously been investigated, no comprehensive study in full scale using inherent inoculation has previously been documented. A thorough investigation of a full-scale drinking water biofilter was carried out over 10 weeks of start-up. The many spatial and temporal changes taking place during start-up were documented using a holistic approach. In addition to collection of many samples over time (frequency) and space (filter depth), this study entailed the use of multiple sample media (water, backwash water and filter media) and multiple types of analyses (physical, chemical and microbiological). The decrease in filter effluent concentrations of individual substances to compliance levels followed a specific order that was shown to coincide with the spatiotemporal development of bacteria on the filter media. Due to the abiotic nature of the iron removal process, iron disappears at the earliest in the start-up period followed by substances that require growth of microorganisms. Ammonium disappears next, with nitrite appearing briefly near the end of ammonium removal, followed by manganese. The thorough overall picture obtained by these efforts provides guidance for optimization and monitoring of the start-up. Guidance for optimization includes shortening the start-up by focusing on kick-starting the ammonium removal; limiting the monitoring burden (at-line measurements of ammonium in finished water supplemented with manual manganese measurements when ammonium removal is complete); and improving filter design by isolating the removal processes in separate, smaller filters.

Predicting manganese and iron precipitation in drinking water biofilters

“…These increases in redox potential likely resulted from the oxidation of Fe and NH 4 (Mouchet, 1992;Stumm & Morgan, 1996;Tekerlekopoulou & Vayenas, 2008). Therefore, the PHREEQC model is consistent with observations in the literature, which have found that Fe and NH 4 are oxidized closer to the surface of the biofilter, while Mn is oxidized at depth Cheng, Nengzi, Xu, Guo, & Yu, 2017;Ramsay et al, 2018;Tekerlekopoulou & Vayenas, 2008).…”

“…These results suggest that Fe would be rapidly oxidized by oxygen and precipitate in the upper layers of the biofilters. In groundwater biofilters with aeration, Fe is often removed at the top of the biofilter immediately when the filter is put into service Ramsay et al, 2018). The additional information provided by this model over the Pourbaix diagram is useful for analyzing biofilters.…”

“…Additionally, substantial Mn removal is difficult to achieve in a biofilter unless most of the iron (Fe) and ammonium (NH 4 ) is removed (Bruins, Vries, Petrusevski, Slokar, & Kennedy, 2014;Ramsay, Breda, & Søborg, 2018). Notably, Fe and NH 4 oxidation both increase the oxidation-reduction (redox) potential, indicating that redox conditions may be important for Mn removal (Stumm & Morgan, 1996).…”

Exposure to Manganese in Drinking Water during Childhood and Association with Attention-Deficit Hyperactivity Disorder: A Nationwide Cohort Study

“…More important, functioning of a filter may suddenly be disrupted due to a number of reasons, including mechanical filter breaches, filter media replacements, and start-up of new filters. During such episodes of disrupted filtering, Mn concentrations in drinking water sharply increase, typically between 10-and 100-fold, and stay elevated for long periods, from several months to more than a year, before the removal of Mn is reestablished (Breda et al 2017;Bruins et al 2014;Gouzinis et al 1998;Ramsay et al 2018). Exposure to high levels of Mn through drinking water supplies based on simple-treated groundwater is therefore mainly governed by episodic water treatment failure.…”

Manganese removal processes at 10 groundwater fed full-scale drinking water treatment plants

“…(b) Mn versus NH 4 removal (percentage) over time (days 11, 27, 35, 39, 43, 67 and approximately 4 years) calculated based on the concentration of each substance in water samples collected over 20 cm depth intervals in relation to the inlet concentrations at DWTP9. All data were retrieved from Ramsay et al (2018) with the exception of observations at 4 years. Please refer to the online version of this paper to see this figure in colour: http://dx.doi.org/10.2166/wqrj.2019.006.…”