Interference of manganese removal by biologically-mediated reductive release of manganese from MnOx(s) coated filtration media.

Discontinuing application of pre-filter chlorine is a common water treatment plant practice to permit a bioactive filtration process for the removal of soluble Mn. However, soluble Mn desorption has sometimes been observed following cessation of chlorine addition, where filter effluent Mn concentration exceeds the influent Mn concentration. In this paper it is hypothesized that Mn-reducing bacteria present in a biofilm on the filter media may be a factor in this Mn-release phenomenon. The primary objective of this research was to assess the role of Mn-reducing microorganisms in the release of soluble Mn from MnOx(s)-coated filter media following interruption of pre-filtration chlorination. Bench-scale filter column studies were inoculated with Shewanella oneidensis MR-1 to investigate the impacts of a known Mn-reducing bacterium on release of soluble Mn from MnOx(s) coatings. In situ vial assays were developed to gain insight into the impacts of MnOx(s) age on bioavailability to Mn-reducing microorganisms and a quantitative polymerase chain reaction (qPCR) method was developed to quantify gene copies of the mtrB gene, which is involved in Mn-reduction. Results demonstrated that microbially-mediated Mn release was possible above a threshold equivalent of 2 × 102 S. oneidensis MR-1 CFU per gram of MnOx(s) coated media and that those organisms contributed to Mn desorption and release. Further, detectable mtrB gene copies were associated with observed Mn desorption. Lastly, MnOx(s) age appeared to play a role in Mn reduction and subsequent release, where MnOx(s) solids of greater age indicated lower bioavailability. These findings can help inform means of preventing soluble Mn release from drinking water treatment plant filters.

Survival of Antibiotic Resistant Bacteria and Horizontal Gene Transfer Control Antibiotic Resistance Gene Content in Anaerobic Digesters.

Understanding fate of antibiotic resistant bacteria (ARB) vs. their antibiotic resistance genes (ARGs) during wastewater sludge treatment is critical in order to reduce the spread of antibiotic resistance through process optimization. Here, we spiked high concentrations of tetracycline-resistant bacteria, isolated from mesophilic (Iso M1-1-a Pseudomonas sp.) and thermophilic (Iso T10-a Bacillus sp.) anaerobic digested sludge, into batch digesters and monitored their fate by plate counts and quantitative polymerase chain reaction (QPCR) of their corresponding tetracycline ARGs. In batch studies, spiked ARB plate counts returned to baseline (thermophilic) or 1-log above baseline (mesophilic) while levels of the ARG present in the spiked isolate [tet(G)] remained high in mesophilic batch reactors. To compare results under semi-continuous flow conditions with natural influent variation, tet(O), tet(W), and sul1 ARGs, along with the intI1 integrase gene, were monitored over a 9-month period in the raw feed sludge and effluent sludge of lab-scale thermophilic and mesophilic anaerobic digesters. sul1 and intI1 in mesophilic and thermophilic digesters correlated positively (Spearman rho = 0.457-0.829, P < 0.05) with the raw feed sludge. There was no correlation in tet(O) or tet(W) ratios in raw sludge and mesophilic digested sludge or thermophilic digested sludge (Spearman rho = 0.130-0.486, P = 0.075-0.612). However, in the thermophilic digester, the tet(O) and tet(W) ratios remained consistently low over the entire monitoring period. We conclude that the influent sludge microbial composition can influence the ARG content of a digester, apparently as a result of differential survival or death of ARBs or horizontal gene transfer of genes between raw sludge ARBs and the digester microbial community. Notably, mesophilic digestion was more susceptible to ARG intrusion than thermophilic digestion, which may be attributed to a higher rate of ARB survival and/or horizontal gene transfer between raw sludge bacteria and the digester microbial community.

Effect of drinking water treatment process parameters on biological removal of manganese from surface water.

Soluble manganese (Mn) presents a significant treatment challenge to many water utilities, causing aesthetic and operational concerns. While application of free chlorine to oxidize Mn prior to filtration can be effective, this is not feasible for surface water treatment plants using ozonation followed by biofiltration because it inhibits biological removal of organics. Manganese-oxidizing bacteria (MOB) readily oxidize Mn in groundwater treatment applications, which normally involve pH > 7.0. The purpose of this study was to evaluate the potential for biological Mn removal at the lower pH conditions (6.2-6.3) often employed in enhanced coagulation to optimize organics removal. Four laboratory-scale biofilters were operated over a pH range of 6.3-7.3. The biofilters were able to oxidize Mn at a pH as low as pH 6.3 with greater than 98% Mn removal. Removal of simulated organic ozonation by-products was also greater than 90% in all columns. Stress studies indicated that well-acclimated MOB can withstand variations in Mn concentration (e.g., 0.1-0.2 mg/L), hydraulic loading rate (e.g., 2-4 gpm/ft(2); 1.36 × 10(-3)-2.72 × 10(-3) m/s), and temperature (e.g., 7-22 °C) typically found at surface water treatment plants at least for relatively short (1-2 days) periods of time.

Effect of silver nanoparticles and antibiotics on antibiotic resistance genes in anaerobic digestion.

Water resource recovery facilities have been described as creating breeding ground conditions for the selection, transfer, and dissemination of antibiotic resistance genes (ARGs) among various bacteria. The objective of this study was to determine the effect of direct addition of antibiotic and silver nanoparticles (Ag NPs, or nanosilver) on the occurrence of ARGs in thermophilic anaerobic digesters. Test thermophilic digesters were amended with environmentally-relevant concentrations of Ag NP (0.01, 0.1, and 1.0 mg-Ag/L; corresponding to approximately 0.7, 7.0, and 70 mg-Ag/kg total solids) and sulfamethoxazole (SMX) that span susceptible to resistant classifications (1, 5, and 50 mg/L) as potential selection pressures for ARGs. Tetracycline (tet(O), tet(W)) and sulfonamide (sulI, sulII) ARGs and the integrase enzyme gene (intI1) associated with Class 1 integrons were measured in raw sludge, test thermophilic digesters, a control thermophilic digester, and a control mesophilic digester. There was no apparent effect of Ag NPs on thermophilic anaerobic digester performance. The maximum SMX addition (50 mg/L) resulted in accumulation of volatile fatty acids and low pH, alkalinity, and volatile solids reduction. There was no significant difference between ARG gene copy numbers (absolute or normalized to 16S rRNA genes) in amended thermophilic digesters and the control thermophilic digester. Antibiotic resistance gene copy numbers in digested sludge ranged from 10(3) to 10(6) copies per microL (approximately 8 x10(1) to 8 x 10(4) copies per microg) of sludge as result of a 1-log reduction of ARGs (2-log reduction for intI1). Quantities of the five ARGs in raw sludge ranged from 10(4) to 10(8) copies per microL (approximately 4 x 10(2) to 4 x 10(6) per microg) of sludge. Test and control thermophilic digesters (53 degrees C, 12-day solids retention time [SRT]) consistently reduced but did not eliminate levels of all analyzed genes. The mesophilic digester (37 degrees C, 20-day SRT) also reduced levels of sulI, sulII, and intI1 genes, but levels of tet(O) and tet(W) were the same or higher than in raw sludge. Antibiotic resistance gene reductions remained constant despite the application of selection pressures, which suggests that digester operating conditions are a strong governing factor of the bacterial community composition and thus the prevalence of ARGs.

Application of XPS and solution chemistry analyses to investigate soluble manganese removal by MnO(x)(s)-coated media.

X-ray photoelectron spectroscopy (XPS) was applied to investigate Mn(II) removal by MnO(x)(s)-coated media under experimental conditions similar to the engineered environment of drinking water treatment plants in the absence and presence of chlorine. Macroscopic and spectroscopic results suggest that Mn(II) removal at pH 6.3 and pH 7.2 in the absence of chlorine was mainly due to adsorption onto the MnO(x)(s) surface coating, while removal in the presence of chlorine was due to a combination of initial surface adsorption followed by subsequent surface-catalyzed oxidation. However, Mn(III) was identified by XPS analyses of the Mn 3p photoline for experiments performed in the absence of chlorine at pH 6.3 and pH 7.2, suggesting that surface-catalyzed Mn oxidation also occurred at these conditions. Results obtained at pH 8.2 at 8 and 0.5 mg·L(-1) dissolved oxygen in the absence of chlorine suggest that Mn(II) removal was mainly due to initial adsorption followed by surface-catalyzed oxidation. XPS analyses suggest that Mn(IV) was the predominant species in experiments operated in the presence of chlorine. This study confirms that the use of chlorine combined with the catalytic action of MnO(x)(s) oxides is effective for Mn(II) removal from drinking water filtration systems.

Use of XPS to identify the oxidation state of Mn in solid surfaces of filtration media oxide samples from drinking water treatment plants.

X-ray photoelectron spectroscopy (XPS) was used to identify Mn(II), Mn(III), and Mn(IV) in the surfaces of pure oxide standards and filtration media samples from drinking water treatment plants through the determination of the magnitude of the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line. The Mn 3p region has been widely studied by applied physicists and surface scientists, but its application to identify the oxidation state of Mn in heterogeneous oxide samples has been limited. This study shows that the use of both the Mn 3s multiplet splitting and the position and shape of the Mn 3p photo-line provides a feasible means of determining the oxidation state of manganese in complex heterogeneous, environmentally important samples. Surface analysis of filtration media samples from several drinking water treatment plants was conducted. While Mn(IV) was predominant in most samples, a mixture of Mn(III) and Mn(IV) was also identified in some of the filtration media samples studied. The predominance of Mn(IV) in the media samples was felt to be related to the maintenance of free chlorine (HOCl) at substantial concentrations (2-5 mg*L(-1) as Cl2) across these filters. XPS could be a useful tool to further understand the specific mechanisms affecting soluble Mn removal using MnOx-coated filtration media.

Manganese-oxidizing and -reducing microorganisms isolated from biofilms in chlorinated drinking water systems.

The interaction of chemical, physical and biological factors that affect the fate, transport and redox cycling of manganese in engineered drinking water systems is not clearly understood. This research investigated the presence of Mn-oxidizing and -reducing bacteria in conventional water treatment plants exposed to different levels of chlorine. Mn(II)-oxidizing and Mn(IV)-reducing bacteria, principally Bacillus spp., were isolated from biofilm samples recovered from four separate drinking water systems. Rates of Mn-oxidation and -reduction for selected individual isolates were represented by pseudo-first-order kinetics. Pseudo-first-order rate constants were obtained for Mn-oxidation (range: 0.106-0.659 days(-1)), aerobic Mn-reduction (range: 0.036-0.152 days(-1)), and anaerobic Mn-reduction (range: 0.024-0.052 days(-1)). The results indicate that microbial-catalyzed Mn-oxidation and -reduction (aerobic and anaerobic) can take place simultaneously in aqueous environments exposed to considerable oxygen and chlorine levels and thus affect Mn-release and -deposition in drinking water systems. This has important implications for Mn-management strategies, which typically assume Mn-reduction is not possible in the presence of chlorine and oxidizing conditions.