Manganese removal is a typical concern in drinking water production. Biofiltration may be used when treating groundwater sources but the onset of manganese removal in virgin biofilters can vary considerably. The aim of this study was to investigate the effect of different filter media on manganese oxidation and bacterial diversity in biofilters during the start-up. The onset of manganese oxidation in four virgin granular filter media (quartz, calcium carbonate, polystyrene, and manganese oxide) and one matured medium (quartz) was followed during the start-up. Immediate manganese removal was achieved by manganese oxide, while 48, 57 and 72 days were required by virgin quartz, calcium carbonate and polystyrene, respectively. The bacterial community was investigated using DAPI staining, quantitative polymerase chain reaction (qPCR), 16S rRNA gene pyrosequencing, and bacterial enrichments. Bacterial abundance was greatest on polystyrene and matured quartz. Molecular community analysis and bacterial enrichments suggested the presence of manganese oxidizing bacteria on all media coatings after the start-up period. Virgin quartz and calcium carbonate showed similar bacterial communities whereas manganese oxide and polystyrene were distinct. This investigation suggests that when inoculating different filter media with an identical water source, the bacterial diversity and onset of manganese oxidation during start-up is strongly influenced by the filter media type.

Due to the potential health risks at very low concentrations, the criterion for arsenic in drinking water has been debated. High-income, low-dose countries are uniquely positioned to follow WHO’s recommendation of keeping concentrations “as low as reasonably possible.” In this policy analysis, 47646 arsenic analyses from Denmark are used to follow the effect of lowering the national criterion from 50 to 5 μg/L. The first 3 years (2002–2004) following the criterion change, 106 waterworks were identified as noncompliant. An additional 64 waterworks were identified as noncompliant in the next 12 years (2005–2016). Of the 106 waterworks initially (2002–2004) aware of the violation, an average concentration drop from 6 to 3 μg/L was observed during a 6 year period following a lag time of 1 year. After this point, no further improvements were observed. Thirteen years after regulation was imposed, 25 of 170 waterworks were still in violation. The results suggest that legislation alone is insufficient to ensure better drinking water quality at some waterworks and that stakeholders’ drivers and barriers to change also play an important role. In an exploration of five legislation scenarios, this study showed that a criterion of 1 μg/L would require action by more than 500 Danish waterworks, with treatment costs from 0.06 to 0.70 €/m3. These scenarios illustrate that it can be technically feasible and affordable to lower the arsenic criterion below 5 μg/L in low-dose, high-income countries. However, more information is needed to apply a cost–benefit model, and comparative studies from other counties are warranted.

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.

Manganese removal in drinking water biofilters is facilitated by biological and physico-chemical processes, but knowledge regarding the relative role of these mechanisms during start-up is very limited. The aim of this study was to identify the dominant process for manganese removal occurring during the start-up period of sand filters with and without inoculation by addition of matured sand collected from an operating groundwater-based waterworks. Inoculation with matured filter sand is frequently used to accelerate the start-up in virgin biofilters and to rapidly obtain compliant water quality. The non-inoculated filter took 41 days to comply with manganese quality criteria, whereas the inoculated filter with 20% matured sand showed removal from Day 1 and compliance from Day 25. By Day 48, the inoculated filter showed two times higher manganese removal rates and manganese oxides deposits. Using sodium azide as an inhibitor of microbial activity, it was found that manganese removal in the non-inoculated filter was dominated by biological processes, whereas physico-chemical processes were of more importance in the inoculated filter (Day 35, 39 and 48).16S rDNA sequencing of the microbiota collected during filter maturation indicated a limited immediate effect of inoculation on the microbial community developed on the remaining filter material. I. L. Breda (corresponding author) P. Roslev

Manganese (Mn) removal in drinking water filters is facilitated by biological and physico-chemical processes. However, there is limited information about the dominant processes for Mn removal in full-scale matured filters with different filter materials over filter depth. Water and filter material samples were collected from 10 full-scale drinking water treatment plants (DWTPs) to characterise the Mn removal processes, to evaluate the potential use of enhancers and to gain further insight on operational conditions of matured filters for the efficient Mn removal. The first-order Mn removal constant at the DWTPs varied from 10−2 to 10−1 min−1. The amount of Mn coating on the filter material grains showed a strong correlation with the amount of iron, calcium and total coating, but no correlation with the concentration of ATP. Inhibition of biological activity showed that Mn removal in matured filters was dominated by physico-chemical processes (59–97%). Addition of phosphorus and trace metals showed limited effect on Mn removal capacity, indicating that the enhancement of Mn removal in matured filters is possible but challenging. There was limited effect of the filter material type (quartz, calcium carbonate and anthracite) on Mn removal in matured filters, which can be relevant information for the industry when assessing filter designs and determining returns of investments. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).