Manganese removal processes during start-up of inoculated and non-inoculated drinking water biofilters

Abstract

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

Start-up strategies for nitrification and manganese oxidation on a single stage RSF for drinking water production

“…that the durations required to complete manganese oxidation (between 25 and 40 days) are in the range of values found in literature (15-75 days(Bruins et al 2015b;Cheng et al 2018;Breda et al 2019)). …”

“…After the start-up period. Manganese oxidation in rapid sand filters is a complex phenomenon including biological oxidation and chemical heterogenous catalysis due to the production during biological reaction of solid manganese oxides with catalytic properties for Mn 2þ oxidation (Tekerlekopoulou et al 2013;Bruins et al 2014;Breda et al 2019). To investigate the influence of nitrite on the global manganese oxidation process, two pulses of nitrite were realized in influent water of the biofilter during experiment SUA3 at day 119 and day 122 (no modification of the raw water conditions).…”

“…However, regular interruptions of the process and addition of chemical agents (strong oxidant agents such as Cl 2 or KMnO 4 ) are needed to regenerate the catalytic oxidative potential of the reactive sand. Biological manganese oxidation is a slow process which leads to particulate manganese oxides which in turn promote the chemical oxidation pathway similarly to reactive sands (Bruins et al 2015a;Breda et al 2019). Evidence of such processes was reported for Pseudomonas manganoxidans (Gage et al 2001) and Leptothrix dischopora SS1 (Zhang et al 2002) or for Bacillus specie in the case of sewage activated sludge (Hasan 2010).…”

“…In real conditions, low temperature and low concentrations of ammonium and manganese lead to slow start-up of industrial biofilters (Ciancio Casalini et al 2020). Durations between 25 and 40 days for complete nitrification were reported by (Vandenabeele et al 1995;Cheng 2015;Albers et al 2018) and between 15 and 75 days for complete manganese oxidation (Bruins et al 2015a;Cheng et al 2018;Breda et al 2019). Hence, high volumes of water are wasted during this settling phase, as it is unsuitable for production.…”

Autochthonous tropical groundwater bacteria involved in manganese(ii) oxidation and removal

“…9,45 For this reason, the study of MOB for the development of inoculums that contribute to reducing the start-up time of biofilters is of interest. 29,35,46,47 Examples of proactive inoculation methods, listed by Breda et al, 47 include the addition of a concentrated source of microorganisms and/or catalytic surfaces like backwash sludge, matured filter sand, mixed culture bacteria or specific bacterial species. A different approach consists of the use of the indigenous bacteria present in well water containing manganese.…”