•Arsenic effects on nitrification were revealed using FBR enriched cultures.•Nitrification was not affected by 100mg AsTOT/L at neutral pH.•150–200mg AsTOT/L inhibited ammonium oxidation by ...25%.•As(III) oxidation to As(V) decreased arsenic toxicity to nitrification.•FBR enrichment consisted of C. Nitrospira defluvii and other nitrifying species.
Mining and mineral processing of gold-bearing ores often release arsenic to the environment. Ammonium is released when N-based explosives or cyanide are used. Nitrification of simulated As-rich mining waters was investigated in batch bioassays using nitrifying cultures enriched in a fluidized-bed reactor (FBR). Nitrification was maintained at 100mg AsTOT/L. In batch assays, ammonium was totally oxidized by the FBR enrichment in 48h. As(III) oxidation to As(V) occurred during the first 3h attenuating arsenic toxicity to nitrification. At 150 and 200mg AsTOT/L, nitrification was inhibited by 25%. Candidatus Nitrospira defluvii and other nitrifying species mainly colonized the FBR. In conclusion, the FBR enriched cultures of municipal activated sludge origins tolerated high As concentrations making nitrification a potent process for mining water treatment.
Biological sulfate reduction is increasingly replacing chemical unit processes in mining biotechnology. Sulfate reducing bacteria (SRB) can be used for treating ground‐ and surface waters ...contaminated with acid mine drainage (AMD), and for recovering metals from wastewater and process streams. Biologically produced H2S precipitates metals as metal sulfides, while biogenic bicarbonate alkalinity neutralizes acidic waters. This paper reviews various passive and active SRB‐based alternatives as well as some process design aspects, such as reactor types, process configurations, and choices of substrates for sulfate reduction. The latest developments of using various low‐cost substrates together with new bioprocess designs are increasing the uses and applications of SRB‐based bioreactors in AMD control and selective metal recovery.
Bioprocesses based on sulfate reduction provide multiple options for the treatment of acid mine drainage as well as the recovery of metals from process waters. Various passive and active bioprocess alternatives are reviewed and recent design aspects are discussed.
•We used meta-analysis to investigate infants’ salivary cortisol reactivity to psychological stressors.•The results showed a small increase in salivary cortisol after psychological ...stressors.•Stressor type moderated the effect sizes, with only the separation paradigms showing consistent effects.•Age-related changes should be investigated with directly comparable psychological stressors across infancy.
Measurement of salivary cortisol is a practical and non-invasive tool for studying stress reactivity to various types of stressors even in young infants. Whereas studies using physical stressors during the first months of life have found robust cortisol responses to painful stimuli, research with older infants using psychological stressors (e.g., parental separation) has produced mixed findings, limiting our understanding of potential developmental changes in cortisol reactivity across infancy. In the present study, we used meta-analysis to systematically investigate whether psychological stressor paradigms are associated with measurable cortisol responses in infants under 18 months of age and whether the magnitude of the responses is moderated by the type of psychological stressor (i.e., separation, frustration, novelty, or disruption of parental interaction), infant age, and other potential moderators. Across 47 studies (N = 4095, age range: 3–18 months), we found that commonly used psychological stressor paradigms are associated with a small (Hedges’ g = .11) increase in salivary cortisol levels in typically developing infants. Stressor type moderated the effect sizes, and when effect sizes in each category were analyzed separately, only the separation studies were associated with a consistent increase in cortisol following the stressor. Age did not moderate the effect sizes either in the full set of studies or within the separate stressor types. These meta-analytic results indicate that the normative cortisol response to psychological stressors across infancy is small and emphasize the need for standardized stressor paradigms to assess cortisol responses systematically across infancy.
This study revealed that fluidized-bed denitrifying cultures tolerated soluble Ni concentrations up to 500 mg/L at 7-8 and 22°C. From 10 to 40 mg/L of feed Ni, denitrification resulted in complete ...nitrate and nitrite removal. The concomitant reduction of 30 mg/L of sulfate produced 10 mg/L of sulfide that precipitated nickel, resulting in soluble effluent Ni below 22 mg/L. At this stage, Dechloromonas species were the dominant denitrifying bacteria. From 60 to 500 mg/L of feed Ni, nickel remained in solution due to the inhibition of sulfate reduction. At soluble 60 mg/L of Ni, denitrification was partially inhibited prior to recover after 34 days of enrichment by other Ni-tolerant species (including Delftia, Zoogloea and Azospira) that supported Dechloromonas. Subsequently, the FBR cultures completely removed nitrate even at 500 mg/L of Ni. Visual Minteq speciation model predicted the formation of NiS, NiCO3 and Ni3(PO4)2, whilst only Ni3(PO4)2 was detected by XRD.
In addition to well-being, workplace learning has gained increasing interest in supporting employee and organizational development and success. Focusing on specific factors affecting workplace ...learning and well-being, this study examines the links between individual factors (basic psychological need satisfaction) and environmental factors (expansiveness of the workplace as a learning environment), job satisfaction, and turnover intention. Survey data were collected from the employees (
N
= 153) of two Finnish engineering companies from 2018 to 2019. The data were analyzed with correlation analysis and structural equation modeling (observed and latent variable path analysis). Results show that a more expansive workplace learning environment is associated with higher satisfaction of basic psychological needs. High levels of autonomy and competence need satisfaction, versatile work, promotion of learning, and acknowledgment of skills are positively associated with job satisfaction. Higher levels of autonomy and non-routine work tasks are associated with lower turnover intention. The results indicate that turnover intention is not necessarily associated with only negative conditions or perceptions, as high levels of competence and participation and understanding of the workplace are positively associated with turnover intention. The findings provide information about workplace factors that are relevant to improving employees’ workplace learning and well-being. The results also highlight the ambiguous nature of turnover intention.
Mining often leads to nitrate and metal contamination of groundwater and water bodies. Denitrification of acidic water was investigated in two up-flow fluidized-bed reactors (FBR) and using batch ...assays. Bacterial communities were enriched on ethanol plus nitrate in the FBRs. Initially, the effects of temperature, low-pH and ethanol/nitrate on denitrification were revealed. Batch assays showed that pH 4.8 was inhibitory to denitrification, whereas FBR characteristics permitted denitrification even at feed pH of 2.5 and at 7–8 °C. Nitrate and ethanol were removed and the feed pH was neutralized, provided that ethanol was supplied in excess to nitrate. Subsequently, Fe(II) and Cu impact on denitrification was investigated within batch tests at pH 7. Iron supplementation up to 100 mg/L resulted in iron oxidation and soluble concentrations ranging from 0.4 to 1.6 mg/L that stimulated denitrification. On the contrary, 0.7 mg/L of soluble Cu significantly slowed denitrification down resulting in about 45 % of inhibition in the first 8 h. Polymerase chain reaction—denaturant gradient gel electrophoresis demonstrated the co-existence of different denitrifying microbial consortia in FBRs.
Dechloromonas denitrificans
and
Hydrogenophaga caeni
were present in both FBRs and mainly responsible for nitrate reduction.
Sulphate-reducing biofilm and suspension processes were studied for treatment of synthetic wastewater containing sulphate, zinc and iron. With lactate supplemented wastewater with 170–230
mg/l Zn and ...58
mg/l Fe, the following precipitation rates were obtained: 250 and 350
mg/l
d for Zn in fluidized-bed (FBR) and upflow anaerobic sludge blanket reactors, respectively, and 80
mg/l
d for Fe in both reactors with hydraulic retention time of 16
h. The effluent Zn and Fe concentrations remained at less than 0.1
mg/l. The alkalinity produced in lactate oxidation increased the initial pH of 2.5–3, resulting in effluent pH of 7.5–8.5. The highest sulphate reduction rate was over 2000
mg/l
d. In terms of sulphate reduction, hydrogen sulphide production and effluent alkalinity, the start-up of the FBR with the 10% fluidization rate was superior to the FBRs with 20–30% fluidization rates. With increased loading rates, high recycling rate became an advantage. After process failure caused by intentional overloading, the sulphate reduction partially recovered within 2 weeks. Metal precipitates in the reactors were predominantly FeS
2, ZnS and FeS. The metal mass balance was as follows: 73–86% of Zn and Fe accumulated into the reactors and water level adjustors, 14–23% of the metals were washed out as precipitates and 0.05–0.15% remained as soluble metals. Biomass yield in the sulphate-reducing processes was 0.039–0.054
g dry biomass (VS or VSS) per g of lactate oxidized or 0.035–0.074
g dry biomass per g of sulphate reduced. The results of this work demonstrate that the lactate supplemented sulphate-reducing processes precipitated the metals as sulphides and neutralized the acidity of the synthetic wastewater.
•High rate, high efficiency autotrophic denitrification was demonstrated in a FBR.•Complete nitrate and nitrite removal was achieved at HRTs as low as 10min.•The nitrate and nitrite loading rates ...reached 600 and 228mgL−1h−1, respectively.•The biofilms were dominated by T. denitrificans and tolerated pHs as low as 5.8.•The optimal temperature for nitrate removal was 26.6°C based on Ratkowsky modeling.
High rate, high efficiency thiosulfate-driven autotrophic denitrification and denitritation with Thiobacillus denitrificans dominated biofilms were achieved in fluidized-bed reactors (FBRs) operated at 20.0±2.0 and 30.0±0.2°C. Complete nitrate removal was obtained even at nitrate loading rate and hydraulic retention time (HRT) of 600mgL−1h−1 and 10min, respectively. Further decrease of HRT to 5min resulted in 50% of nitrate removal efficiency. Nitrite did not accumulate when nitrate was used as electron acceptor unless HRT was decreased to 5min. Effluent pH remained at 5.8 during denitrification. When nitrite was supplemented as the electron acceptor, denitritation effectively proceeded with the highest nitrite loading rate of 228mgL−1h−1. Similar denitrification and denitritation performances were obtained at 20.0±2.0 and 30.0±0.2°C. Batch assays conducted at temperature range from 1 to 46°C, however, showed a significant impact of temperature on autotrophic denitrification. Ratkowsky model was used to estimate the minimum, optimal and maximum growth temperatures of T. denitrificans dominated culture that were below 1, 26.6 and 50.8°C, respectively.
The dispersion of nitrogenous compounds and heavy metals into the environment is frequent during mining activities. The effects of nickel (Ni) and cobalt (Co) on denitrification of simulated mine ...waters were investigated in batch bioassays and fluidized-bed reactors (FBRs). At pH 7, batch tests revealed that Co did not exhibit inhibition on denitrification even at 86.6 mg/L. Ni showed to be inhibitory at 50 and 100 mg/L by decreasing nitrate removal efficiencies of 18 and 65 %, respectively. In two FBRs, operated at 7–8 and 22 °C, 5.5 mg/L Ni did not affect nitrate and nitrite removals because of FBR potential of diluting soluble Ni feed concentration. On the contrary, the effluent pH clearly decreased in both FBR1 and FBR2 because of nickel sulfide precipitation and Ni inhibition of the last two steps of denitrification. When Ni injection was stopped, the process recovered more slowly at 22 than 7–8 °C. This is the first study reporting the effect of Ni on denitrification in biological FBRs.
Seasonal and diurnal fluctuations of pH, dissolved oxygen (DO) and temperature were investigated in a pilot-scale advanced integrated wastewater pond system (AIWPS
®) treating tannery effluent. The ...AIWPS
® was comprised of advanced facultative pond (AFP), secondary facultative pond (SFP) and maturation pond (MP) all arranged in series. The variations of pH, DO and temperature in the SFP and MP followed the diurnal cycle of sunlight intensity. Algal photosynthesis being dependent on sunlight radiation, its activity reached climax at early afternoons with DO saturation in the SFP and MP in excess of over 300% and pH in the range of 8.6–9.4. The SFP and MP were thermally stratified with gradients of 3–5°C/m, especially, during the time of peak photosynthesis. The thermal gradient in the AFP was moderated by convective internal currents set in motion as a result of water temperature differences between the influent wastewater and contents of the reactor. In conclusion, the AFP possessed remarkable ability to attenuate process variability with better removal efficiencies than SFP and MP. Hence its use as a lead treatment unit, in a train of ponds treating tannery wastewaters, should always be considered.
PDF
