Soil organic matter priming: The pH effects.

Priming of soil organic matter (SOM) decomposition by microorganisms is a key phenomenon of global carbon (C) cycling. Soil pH is a main factor defining priming effects (PEs) because it (i) controls microbial community composition and activities, including enzyme activities, (ii) defines SOM stabilization and destabilization mechanisms, and (iii) regulates intensities of many biogeochemical processes. In this critical review, we focus on prerequisites and mechanisms of PE depending on pH and assess the global change consequences for PE. The highest PEs were common in soils with pH between 5.5 and 7.5, whereas low molecular weight organic compounds triggered PE mainly in slightly acidic soils. Positive PEs up to 20 times of SOM decomposition before C input were common at pH around 6.5. Negative PEs were common at soil pH below 4.5 or above 7 reflecting a suboptimal environment for microorganisms and specific SOM stabilization mechanisms at low and high pH. Short-term soil acidification (in rhizosphere, after fertilizer application) affects PE by: mineral-SOM complexation, SOM oxidation by iron reduction, enzymatic depolymerization, and pH-dependent changes in nutrient availability. Biological processes of microbial metabolism shift over the short-term, whereas long-term microbial community adaptations to slow acidification are common. The nitrogen fertilization induced soil acidification and land use intensification strongly decrease pH and thus boost the PE. Concluding, soil pH is one of the strongest but up to now disregarded factors of PE, defining SOM decomposition through short-term metabolic adaptation of microbial groups and long-term shift of microbial communities.

Rapid oxidative removal of Fe2+ and Mn2+ from acidic mining wastewater by a new-type biofilter system: application and mechanism.

Aimed at the problem of excessive concentration of Fe2+ and Mn2+ in acidic mining wastewater during mining and utilization, a new rapid oxidative removal technology of Fe2+ and Mn2+ by a new-type biofilter system was designed and tested. The new-type biofilter system was constructed using a bioreactor filled with special mature bioceramic pellets after continuous biofilm cultivation as the filter layers. The results indicated that the biofilter system could efficiently treat five times its volume of wastewater per hour. The Fe2+ concentration of the influent wastewater was about 500 mg/L, and its Mn2+ concentration was about 20 mg/L. The average Fe2+ and Mn2+ removal rates could reach 99.7% and 90.8%, respectively. In addition, scanning electron microscopy and energy dispersive spectroscopy-energy dispersive spectroscopy and X-ray photoelectron spectroscopy were applied to analyze the migration distribution and valence change of Fe and Mn ions to clarify the removal mechanism of Fe2+ and Mn2+ using the biofilter system. The results showed that iron oxidation products were mainly coated at the surface of the mature bioceramic pellets and could be easily washed out from the filter layer with flowing water, while manganese oxidation products tended to accumulate between the pores of the mature bioceramic pellets. Furthermore, the final filtration products were multivalent complex oxides, indicating that the high-valent oxidation products could adsorb Fe and Mn ions, which were mainly removed by the oxidation effect.

Geochemistry and microbiology of tropical serpentine soils in the Santa Elena Ophiolite, a landscape-biogeographical approach.

The Santa Elena Ophiolite is a well-studied ultramafic system in Costa Rica mainly comprised of peridotites. Here, tropical climatic conditions promote active laterite formation processes, but the biogeochemistry of the resulting serpentine soils is still poorly understood. The aim of this study was to characterize the soil geochemical composition and microbial community of contrasting landscapes in the area, as the foundation to start exploring the biogeochemistry of metals occurring there. The soils were confirmed as Ni-rich serpentine soils but differed depending on their geographical location within the ophiolite area, showing three serpentine soil types. Weathering processes resulted in mountain soils rich in trace metals such as cobalt, manganese and nickel. The lowlands showed geochemical variations despite sharing similar landscapes: the inner ophiolite lowland soils were more like the surrounding mountain soils rather than the north lowland soils at the border of the ophiolite area, and within the same riparian basin, concentrations of trace metals were higher downstream towards the mangrove area. Microbial community composition reflected the differences in geochemical composition of soils and revealed potential geomicrobiological inputs to local metal biogeochemistry: iron redox cycling bacteria were more abundant in the mountain soils, while more manganese-oxidizing bacteria were found in the lowlands, with the highest relative abundance in the mangrove areas. The fundamental ecological associations recorded in the serpentine soils of the Santa Elena Peninsula, and its potential as a serpentinization endemism hotspot, demonstrate that is a model site to study the biogeochemistry, geomicrobiology and ecology of tropical serpentine areas.

Rhizosphere iron and manganese-oxidizing bacteria stimulate root iron plaque formation and regulate Cd uptake of rice plants (Oryza sativa L.).

Iron plaque is the amorphous and/or crystalline layer of Fe and Mn (hydr)oxides formed on the root surface of wetland plants. It could adsorb and co-precipitate metal(loid)s at the rhizosphere, thus modulating the uptake and accumulation of metal elements in plants. In this study, the Fe(II)/Mn(II)-oxidizing bacteria Burkholderia sp. D416 (D416) and Pseudomonas sp. YGL (YGL) were isolated from Cd-contaminated rice field, both hydroponic experiment and pot experiment were performed to assess the impact of bacterial inoculation on iron plaque formation, elemental content of the plaque, plant dry mass, antioxidant enzyme activity and Cd content in rice plants. The results revealed that inoculation with D416, YGL, and D416+YGL stimulated iron plaque formation on the root surface of the hydroponic rice. The content of C, N, O, Na, Mg, Al, Si, P, S, Cl, K, Fe and Ca in the root plaque were affected by the bacterial inoculation and varied among different plant growth stages. The pot experiment indicated that inoculation with D416 increased the root dry biomass by 58.89%, and the combined inoculation of D416 and YGL increased the dry biomass of root, shoot and grain by 16.89%, 21.66% and 23.26%, respectively. Importantly, YGL inoculation decreased the Cd translocation from root to shoot and from glume to brown rice grain by 50.00% and 50.27%, respectively, and the Cd content in shoot and brown rice grain were decreased by 20.00% and 34.48%, respectively. Taken together, the elemental content of the iron plaque and Cd content in rice plants varied among different plant growth stages and when plants were inoculated with different bacterial strains. YGL dramatically reduced the Cd content in brown rice grain, thus it could potentially be used to reduce Cd content in rice crop grown in Cd-contaminated soils.

Performance and microbial community profiles in pilot-scale biofilter for the simultaneous removal of ammonia, iron and manganese at different manganese concentrations.

To accelerate extensive application of biological manganese removal technology, a pilot-scale biofilter for ammonia, iron and manganese removal was constructed to investigate the removal performance and microbial community profiles at different manganese concentrations. When manganese in influent increased from 1 to 10 mg/L, the pollutants were completely removed. Ammonia and iron was slightly changed along the filter depth, while manganese obviously increased. In 0 m of the filter depth, the abundance of Gallionella (iron oxidizing bacteria, IOB) increased, while Crenothrix (IOB) decreased. The abundance of Gallionella (manganese oxidizing bacteria, MnOB) in 0.4 and 0.8 m increased to 16.82% and 12.37%, respectively; and Crenothrix (MnOB) in 0.8 m increased to 19.95%, but decreased to 25.08% in 0.4 m. The abundance of ammonia oxidizing bacteria (AOB, Nitrosococcus) decreased in 0.4 and 0.8 m. The biofilter presented a high ability to remove manganese, and had a broad application prospect.

Removal of iron and manganese in groundwater through magnetotactic bacteria.

It is presented an alternative biological method based on biomineralization mechanisms of Magnetotactic Bacteria (MTB) for the removal in groundwater, of soluble elements such as Fe+2and Mn+2. In first place, it was compared the effectiveness of MTB retention methods for obtention of concentrated volumes in microorganisms, then, it was carried out an inoculation process in groundwater samples and evaluate the removal rate of Fe+2 and Mn+2 in constant conditions of pH and temperature. It was identified electromagnetic method is more efficient in MTB retention, and that the inoculation processes of an enriched solution with MTB in groundwater samples allow to get average removal rates of 47.86% for Fe+2 and 15.26% for Mn+2. In addition, it was evaluated the removal rate of other metals due to magnetic properties of biominerals inside of MTB magnetosome. The highest removal in all cases occurred between the interval of 3 and 5 min of interaction and tended to stabilize in time.

Performance and microbial community profiles in pilot-scale biofilter for ammonia, iron and manganese removal at different dissolved oxygen concentrations.

Dissolved oxygen (DO) is a significant operational parameter in biological systems. In this study, a pilot-scale biofilter was constructed to investigate the removal efficiency of ammonia, iron and manganese, as well as the microbial community structure evolution at different DO concentrations. Results indicated that when DO decreased from 8 to 4 mg/L, iron and manganese were still completely removed, however the concentration of ammonia in the effluent increased, and exceeded the permitted limit of 0.5 mg/L when DO was about 4 mg/L. The main functional microbes for ammonia and manganese removal were Nitrosomonas and Crenothrix, which was mainly distributed at 0.8 and 0.8 m of the filter bed with a corresponding abundance of 8.61% and 16.87% in sufficient DO considition, respectively; while iron was mainly removed by Crenothrix and Gallionella in 0 m with a corresponding abundance of 30.45% and 9.77%. With the decreasing of DO concentration, iron oxidizing bacteria (IOB, Crenothrix and Gallionella) was not affected, while the abundance of manganese oxidizing bacteria (MnOB, Crenothrix) increased to completely oxidize manganese. However, the amount of ammonia oxidizing bacteria (AOB, Nitrosococcus) at 0.4 and 0.8 m of the filter depth obviously decreased with increased ammonia in the effluent. Kinds of other bacteria which may be related to methane, hydrogen sulfide and organic matter removal, were also found. In addition, small part of archaea was also detected, such as Candidatus Nitrososphaera and Ferroplasma, which could oxdize ammonia and ferrous iron, respectively.

Membrane transporters mediating root signalling and adaptive responses to oxygen deprivation and soil flooding.

This review provides a comprehensive assessment of a previously unexplored topic: elucidating the role that plasma- and organelle-based membrane transporters play in plant-adaptive responses to flooding. We show that energy availability and metabolic shifts under hypoxia and anoxia are critical in regulating membrane-transport activity. We illustrate the high tissue and time dependence of this regulation, reveal the molecular identity of transporters involved and discuss the modes of their regulation. We show that both reduced oxygen availability and accumulation of transition metals in flooded roots result in a reduction in the cytosolic K(+) pool, ultimately determining the cell's fate and transition to programmed cell death (PCD). This process can be strongly affected by hypoxia-induced changes in the amino acid pool profile and, specifically, ϒ-amino butyric acid (GABA) accumulation. It is suggested that GABA plays an important regulatory role, allowing plants to proceed with H2 O2 signalling to activate a cascade of genes that mediate plant adaptation to flooding while at the same time, preventing the cell from entering a 'suicide program'. We conclude that progress in crop breeding for flooding tolerance can only be achieved by pyramiding the numerous physiological traits that confer efficient energy maintenance, cytosolic ion homeostasis, and reactive oxygen species (ROS) control and detoxification.

Evolution of river-aquifer disconnections and the migration and transformation of iron and manganese under non-time-varying/time-varying riverbed permeability.

Changes in the composition, structure, and thickness of riverbed sediments caused by riverbed clogging strongly affect the hydraulic connection, migration and transformation of nutrients between river water and groundwater in groundwater source areas. However, previous studies have not extensively investigated the mechanisms of river-aquifer disconnection and the migration and transformation processes of iron and manganese under non-time-varying and time-varying conditions of riverbed permeability. This study developed a model using the COMSOL Multiphysics platform to characterize the riverbed clogging-groundwater exploitation-disconnection process, considering microbial growth and related biogeochemical processes, and investigated feedbacks between the reactive migration of iron and manganese and physical clogging-groundwater exploitation processes or bioclogging processes. The research findings showed that under non-time-varying conditions of riverbed permeability, the evolution of river-aquifer disconnection was strongly affected by the thickness and permeability coefficient of riverbed sediments. The dissolved oxygen attenuation rate in the disconnection zone decreased by up to 88.8 %. Additionally, the Mn2+ and Fe2+ generation rates in sediment pore water decreased by 65.8 % and 62.7 %, respectively. In contrast, during the riverbed bioclogging process, as the biofilms on the surface of the riverbed sediments developed, the sediment pores gradually clogged, leading to a significant reduction in the porosity and permeability coefficient. Consequently, the hydraulic connection between the river and aquifer transitioned from a saturated connection to a disconnection. However, reduced permeability due to riverbed bioclogging primarily controlled the release of Fe and Mn. When the river-aquifer was in complete disconnection, compared to the saturated connection state, the Mn2+ and Fe2+ generation rates increased by up to 5.8 and 3.8 times, respectively. This study deepens our understanding of the biogeochemical cycling mechanisms of Fe and Mn under riverbed clogging conditions in groundwater source areas and contributes to ensuring a secure and stable water supply in these areas.

Microbial consortium involved in ferromanganese and francolite biomineralization in an anchialine environment (Zinzulùsa Cave, Castro, Italy).

Tidally-influenced subterranean settings represent natural geomicrobiological laboratories, relatively unexplored, that facilitate the investigation of new biomineralization processes. The unusual water chemistry of Zinzulùsa Cave and its oligotrophic and aphotic conditions have allowed the development of a unique ecosystem in which complex bacterial activities induce rare biomineralization processes. A diversified microbial community develops on centimeter-thick crusts that form in the submerged part of the cave. The crusts are formed of Ca-phosphate minerals, mostly carbonate-fluoroapatite (francolite), covered by a black crust, few microns in thickness, composed of ferromanganiferous oxides (hematite and vernadite). Diffuse coccoidal and filamentous bacteria and amorphous organic matter are mixed with the minerals. The micromorphologies and comparative 16S rRNA gene-based metabarcoding analyses identify a "core microbiota" also common to other natural environments characterized by FeMn and Ca-phosphate mineralization. The microbiota is characterized by nitrifying, sulfide/sulfur/thiosulfate-oxidizing and sulfate/thiosulfate/sulfur-reducing bacteria. In addition, manganese-oxidizing bacteria include the recently described "Ca. Manganitrophus noduliformans" and an abundance of bacteria belonging to the Planctomycetes-Verrucomicrobia-Chlamydiae (PVC) superphylum, as well as Haliangiales (fruiting body-forming bacteria) and Hyphomicrobiales (stalked and budding bacteria) that are known to produce extracellular polymers that trap iron and manganese oxides. 16S rRNA gene metabarcoding analysis showed the presence of bacteria able to utilize many organic P substrates, including Ramlibacter, and SEM images revealed traces of fossilized microorganisms resembling "cable bacteria", which may play a role in Ca-phosphate biomineralization. Overall, the data indicate biomineralization processes induced by microbial metabolic activities for both ferromanganiferous oxide and francolite components of these crusts.

Transformation of As and Cd associated with Fe-Mn-modified biochar during simultaneous remediation on the contaminated soil.

Here, Fe- and Mn-modified biochar (BC-Fe-Mn) was applied to simultaneously stabilize As and Cd in the contaminated soil. The removal efficiencies for NaHCO3-extractable As and DTPA-extractable Cd by BC-Fe-Mn were 60.8% and 49.6%, respectively. The speciation analyses showed that the transformation to low-crystallinity Fe-bound (F3) As, Fe-Mn oxide-bound (OX) of Cd, and residual As and Cd was primarily attributed to stabilizing the two metal(loid)s. Moreover, the correlation analyses showed that the increase of As in F3 fraction was significantly and positively associated with the increase of OX fraction Mn (r = 0.64). Similarly, OX fraction Cd was increased notably with increasing OX fraction Fe (r = 0.91) and OX fraction Mn (r = 0.76). In addition, a novel dialysis experiment was performed to separate the reacted BC-Fe-Mn from the soil for intensively investigating the stabilization mechanisms for As and Cd by BC-Fe-Mn. The characteristic crystalline compounds of (Fe0.67Mn0.33)OOH and Fe2O3 on the surface of BC-Fe-Mn were revealed by SEM-EDS and XRD. And FTIR analyses showed that α-FeOOH, R-COOFe/Mn+, and O-H on BC-Fe-Mn potentially served as the reaction sites for As and Cd. A crystalline compound of MnAsO4 was found in the soil treated by BC-Fe-Mn in the dialysis experiment. Thus, our results are beneficial to deeper understand the mechanisms of simultaneous stabilization of As and Cd by BC-Fe-Mn in soil and support the application of the materials on a large scale.

Remediating thiacloprid-contaminated soil utilizing straw biochar-loaded iron and manganese oxides activated persulfate: Removal effects and soil environment changes.

Thiacloprid (THI) has accumulated significantly in agricultural soil. Herein, a novel approach to removing THI was explored by straw biochar-loaded iron and manganese oxides (FeMn@BC) to activate the persulfate (PS). The factors influencing the removal of 5 mg kg-1 THI from the soil by FeMn@BC/PS were investigated, including FeMn@BC dosing, PS dosing, temperature, and soil microorganisms. The feasibility was demonstrated by the 75.22% removal rate of THI with 3% FeMn@BC and 2% PS at 7 days and a 92.50% removal rate within 60 days. Compared to the THI, NH4+-N and available potassium were 3.96 and 3.25 times, and urease and phosphatase activities were increased by 22.54% and 33.28% in the FeMn@BC/PS at the 15 days, respectively. THI was found to seriously alter the structure of the genus in the 15 days by 16 S rRNA analysis; however, the FeMn@BC/PS group alleviated the damage, compared to the THI with 658 more operational taxonomic units. Actinobacteriota accounted for 51.48% of the microbial community in the FeMn@BC/PS group after 60 days, possibly converting transition products of THI into smaller molecules. This article provides a novel insight into advanced oxidative remediation of soils.

Gravity-driven membrane system treating heavy metals-containing secondary effluent: Improved removal of heavy metals and mechanism.

This study aimed at investigating the removal performance of the gravity-driven membrane (GDM) system in treating the heavy metals-containing secondary effluent, as well as evaluating the respective roles of Fe and Mn addition on the removal of heavy metals. GDM process with the formation of biocake layer exerted effective removals of Cr, Pb and Cd, with an average removal efficiency of 98%, 95% and 40%, respectively, however, after removing the biocake layer, the removal efficiencies of Cr, Pb and Cd reduced to 59%, 85% and 19%, respectively, indicating that the biocake layer played a fundamental role in removing heavy metals. With the assistance of Fe, the removal efficiency of heavy metals increased, and exhibited a positive response to the Fe dosage, due to the adsorption by the freshly generated iron oxides. On the contrary, the Mn involvement would result in the reduction of Cd removal due to the competitive adsorption of residual dissolved Mn2+ and Cd. Furthermore, the addition of a high dosage of Fe increased the diversity of eukaryotic communities and facilitated the elimination of heavy metals, however, the involvement of Mn would lead to a reduction in microbial diversity, resulting in a decrease of heavy metal removal efficiency. These findings are expected to develop new tactics to enhance heavy metal removal and promote widespread application of GDM technology in the fields of deep treatment of heavy metals-containing wastewater and reclamation of secondary effluent.

The abiotic removal of organic micropollutants with iron and manganese oxides in rapid sand filters for groundwater treatment.

Rapid sand filters (RSFs) have shown potential for removing organic micropollutants (OMPs) from groundwater. However, the abiotic removal mechanisms are not well understood. In this study, we collect sand from two field RSFs that are operated in series. The sand from the primary filter abiotically removes 87.5% of salicylic acid, 81.4% of paracetamol, and 80.2% of benzotriazole, while the sand from the secondary filter only removes paracetamol (84.6%). The field collected sand is coated by a blend of iron oxides (FeOx) and manganese oxides (MnOx) combined with organic matter, phosphate, and calcium. FeOx adsorbs salicylic acid via bonding of carboxyl group with FeOx. The desorption of salicylic acid from field sand indicates that salicylic acid is not oxidized by FeOx. MnOx adsorbs paracetamol through electrostatic interactions, and further transforms it into p-benzoquinone imine through hydrolysis-oxidation. FeOx significantly adsorbs organic matter, calcium, and phosphate, which in turn influences OMP removal. Organic matter on field sand surfaces limits OMP removal by blocking sorption sites on the oxides. However, calcium and phosphate on field sand support benzotriazole removal via surface complexation and hydrogen bonding. This paper provides further insight into the abiotic removal mechanisms of OMPs in field RSFs.

Short-term seawater inundation induces metal mobilisation in freshwater and acid sulfate soil environments.

Climate change is leading to global sea level rise. Storm surges and higher tides will generate short-term 'pulses' of seawater into freshwater systems, often for the first time in over 3000 years. The effect of increased seawater inundation upon soil geochemistry is poorly understood. We identified 12 sites in South Australia which are predicted to be inundated by seawater storm surges in the next 20 years. Within these 12 sites are three distinct environments; fresh water streams and lakes, hypersaline saltmarsh and mangroves, and acid sulfate soils. Soils were inundated with seawater under laboratory conditions to replicate a short-term (two weeks) inundation by a storm surge. Lowering of redox potential and dissolution of high concentrations of reactive Mn and Fe in freshwater environments lead to the release of dissolved Fe and Mn in the soils from freshwater environments. Soils also released As, Cu, Ni, Cd and Co, while Zn and Pb were less mobilised. Concentrations of metals released exceeded water quality guidelines to protect freshwater aquatic ecosystems in most cases. By comparison, hypersaline soils only released minor amounts of Mn, Fe, Cd and Ni, and only in some of the soils. The moderately acidic acid sulfate soil (pH 5.41) reductively dissolved Mn and Fe releasing significant amount of Fe and Mn as well as As, Cu, Ni, Cd and Co, whereas almost all metal species decreased in the porewaters of the strongly acidic acid sulfate soil (pH 2.77). The response to short-term seawater inundation in acid sulfate soils was dependent upon the baseline soil acidification status. This study highlights the need for further research on seawater inundation of coastal soils as sea levels rise and storm surges penetrate further inland.

Cadmium isotope fractionation during transport processes within agricultural soil profiles in a mining area: Implications for source tracing.

Cadmium (Cd) isotope fractionation patterns within soil profiles and the underlying mechanisms remain unclear and poorly documented. Here, Cd concentrations and isotope compositions of metal ore, surface soils and soil profile samples around a lead-zinc mine in southwest China were determined, and the relationships between soil properties and Cd isotope fractionation within the soil profiles were investigated. Cadmium concentrations of eleven surface soil samples were 0.49-66.1 mg kg-1 and the samples with high Cd concentrations had Cd isotope compositions similar to the metal ore (δ114/110Cd = 0.02‰), indicating that mining activity was the main Cd source at the study areas. Within three soil profiles with different Cd pollution levels the δ114/110Cd values gradually increased with increasing depth from 0 to 40 cm (Δ114/110Cd = 0.08-0.18‰), reaching a maximum at 30-40 cm depth, and then remained fairly constant or decreased with increasing soil depth below 40 cm. Soil δ114/110Cd values were negatively correlated with free iron and manganese oxides contents, which decreased at 0-40 cm depth then increased below 40 cm. This indicates that light Cd isotopes within 0-40 cm depth preferentially migrated downward with free iron and manganese oxides, leaving the soils at a depth of 0-40 cm enriched in heavy Cd isotopes. At 40-90 cm depth the preferential retention of heavy Cd isotopes by hydroxides may be responsible for the gradual decrease in δ114/110Cd values with increasing soil depth. These observations demonstrate that the vertical migration of Cd can induce detectable isotope fractionation within soil profiles and alter the δ114/110Cd values including those of the surface soils. Our study highlights the need to consider Cd mobilization and transport in soil profiles when tracing metal sources using isotope techniques.

Sand from groundwater treatment coated with iron and manganese used for phosphorus removal from wastewater.

This article presents investigations into the removal of PO4-P from biologically treated wastewater using raw material taken from drinking water treatment filters - quartz sand grains coated with iron and manganese oxide coating (OG). The experiments carried out in laboratory stands used real household wastewater and demonstrated that OG filter media accumulated and removed from wastewater two times more PO4-P than known reactive filter media Filtralite P. The mean effectiveness of PO4-P removal from wastewater by filtering at a rate of 2.2 m/h and using OG filter media reached 68%. The pH of the filtrate from OG filter media was stable and reached 7.7 ±â€¯0.2 thus meeting requirements for the discharge of treated wastewater into the natural environment. OG grains are mechanically resistant, do not pollute the filtrate and could therefore be used as filter media for tertiary wastewater treatment.

Interactions between Escherichia coli survival and manganese and iron oxides in water under freeze-thaw.

Pathogenic survivals were dramatically affected by Fe3+ and Mn2+ under freeze-thaw (FT), and the dissolutions of manganese and iron oxides (MIOs) were also accelerated under FT. But the mutual influences of pathogenic bacterial survival and MIOs under FT have not been profoundly explored yet. In this work, aqueous systems containing Escherichia coli as well as synthetic ferrihydrite (Fh) and manganese dioxide (MnO2) were experimented under simulated FT cycles to study the mutual influences of metal oxides and bacteria survival while oxide dissolutions and appearances, bacterial morphology and activities (survival number, cell surface hydrophobicity (CSH) and superoxide dismutase (SOD)) were obtained. The results showed that broken E. coli cells by ice growth were observed, but both oxides promoted E. coli survival under FT stress and prolonged bacterial survival time by 1.2-2.9 times, which were mainly attributed to the release of Fe3+ and Mn2+ caused by FT. The dissolutions of Fh and MnO2 under FT, which took place at a low level in absence of E. coli cells, were markedly enhanced with bacterial interferences by 2-8 times and higher dissolved manganese concentrations were detected than iron. This was probably because that concentrated organic matters which were released from broken cells, rejected into unfrozen liquid layer and acted as electron donors and ligands to oxide dissolution. Compared with Fh system, more significant promotion of E. coli survival under FT in MnO2 systems were found because of more SOD generations associated with high dissolved manganese concentrations and the stronger cellular protection by MnO2 aggregations. The results suggested that FT significantly influenced the interactions between metal oxides and bacterial in water, resulting to changes in pathogen activity and metal element cycling.

[Removal Efficiency and Mechanism of Ammonia Nitrogen in a Low Temperature Groundwater Purification Process].

To explore the mechanism and efficiency of ammonia nitrogen removal, a pilot-scale biofilter for the simultaneous removal of high concentrations of iron, manganese, and ammonia nitrogen[Fe(Ⅱ) 11.9-14.8 mg·L-1, Mn(Ⅱ) 1.1-1.5mg·L-1, and NH4+-N 1.1-3.2 mg·L-1] from low temperature(5-6℃) groundwater was operated in a water supply plant in Northeast China. Results indicated excellent performance for ammonia nitrogen removal during the initial start-up stage. According to theoretical analysis and experimental verification, TNloss was driven by the adsorption of ammonia nitrogen by iron oxides, and the conversion of ammonia nitrogen into nitrate nitrogen occurred via biological nitrification. When the concentration of ammonia nitrogen increased, due to limited adsorption sites, the adsorption capacity of iron oxides remained stable at approximately 1 mg·L-1. For the same period, the amount of ammonia nitrogen removal via oxidation continued to increase, with higher quantities removed in the upper filter layer than in the lower filter layer. Dissolved oxygen(DO) is the limiting factor in the further increase in the removal of ammonia nitrogen by oxidation. With an increase in the filtration rate, the adsorption time of ammonia nitrogen by iron oxides was shortened, and the adsorption amount was reduced. Meanwhile, the shortening of EBCT reduced the ammonia nitrogen removed by nitrification under the action of nitrifying bacteria in the unit volume of the filter material. Based on these findings, it is recommended that the thickness of the filter layer should be increased to improve ammonia nitrogen removal performance.