Raw water biofiltration for surface water manganese control

Abstract

Manganese (Mn) control in surface water systems is a challenge for the drinking water industry, especially through a sustainability framework. Current methods for removing manganese from surface water use strong oxidants that embed carbon and can be expensive and harmful to human health and the environment. In this study, we used a simple biofilter design to remove manganese from lake water, without conventional surface water pre-treatments. Biofilters with aerated influent removed manganese to concentrations below 10 µg/L when receiving influent water containing > 120 µg/L of dissolved manganese. Manganese removal was not inhibited by high iron loadings or poor ammonia removal, suggesting that removal mechanisms may differ from groundwater biofilters. Experimental biofilters also achieved lower effluent manganese concentrations than the full-scale conventional treatment process, while receiving higher manganese concentrations. This biological approach could help achieve sustainable development goals.

Figure 1

Conceptual diagram of raw water biofiltration experiment compared to the conventional surface water treatment plant hosting the experiment (a) and diagram of raw water biofiltration experimental conditions.

Figure 2

Raw water (i.e., water feeding the control filters) dissolved oxygen concentration (a), unfiltered manganese and iron concentrations (b), pH (c) and TOC concentration (d) over time. Error bars represent standard deviation. Dashed lines represent the division between lake stratification and destratification. The gap in data represents the period of COVID interruption.

Figure 3

Mean dissolved manganese across raw water biofilters, grouped by influent condition. Error bars represent standard deviation. Vertical dashed lines represent the division between lake stratification and destratification.

Figure 4

Iron fractogram for an untreated Bennery Lake sample taken on day 116.

Figure 5

Relationship between ATP and effluent dissolved manganese (a) as a scatterplot with time and (b) as an empirical cumulative distribution function for manganese with multiple ATP values as thresholds.

Figure 6

Effluent dissolved manganese for raw water biofilters and BLDWTP full-scale filter after destratification. Error bars represent maximum and minimum values. Concentration given in legend represent average influent manganese concentration during this period.