Investigating the effect of copper and magnesium ions on nitrogen removal capacity of pure cultures by modified non-competitive inhibition model

Enhancement of cold-adapted heterotrophic nitrification and denitrification in Pseudomonas sp. NY1 by cupric ions: Performance and mechanism

Cupric ions can restrain biological nitrogen removal processes, which comprise nitrite reductase and nitric oxide reductase. Here, Pseudomonas sp. NY1 can efficiently perform heterotrophic nitrification and aerobic denitrification with cupric ions at 15 °C. At optimal culturing conditions, low cupric ion levels accelerated nitrogen degradation, and ammonium and nitrite removal efficiencies increased by 2.33%-4.85% and 6.76%-12.30%, respectively. Moreover, the maximum elimination rates for ammonium and nitrite increased from 9.48 to 10.26 mg/L/h and 6.20 to 6.80 mg/L/h upon adding 0.05 mg/L cupric ions. Additionally, low cupric ion concentrations promoted electron transport system activity (ETSA), especially for nitrite reduction. However, high concentrations of cupric ions decreased the ETSA during nitrogen conversion processes. The crucial enzymes ammonia monooxygenase, nitrate reductase, and nitrite reductase possessed similarly trends as ETSA upon exposure to cupric ion. These findings deepen the understanding for the effect of cupric ions on nitrogen consumption and bioremediation in nitrogen-polluted waters.

Acid-tolerant Pseudomonas citronellolis YN-21 exhibits a high heterotrophic nitrification capacity independent of the amo and hao genes

Heterotrophic nitrifying bacteria are found to be promising candidates for implementation in wastewater treatment systems due to their tolerance to extreme environments. A novel acid-resistant bacterium, Pseudomonas citronellolis YN-21, was isolated and reported to have exceptional heterotrophic nitrification capabilities in acidic condition. At pH 5, the highest NH4+ removal rate of 7.84 mg/L/h was displayed by YN-21, which was significantly higher than the NH4+ removal rates of other strains in neutral and alkaline environments. Remarkably, a distinct accumulation of NH2OH and NO3- was observed during NH4+ removal by strain YN-21, while traditional amo and hao genes were not detected in the genome, suggesting the possible presence of alternative nitrifying genes. Moreover, excellent nitrogen removal performance was displayed by YN-21 even under high concentrations of metal ion stress. Consequently, a broad application prospect in the treatment of leather wastewater and mine tailwater is offered by YN-21.

Efficient detoxication of hydroxylamine and nitrite through heterotrophic nitrification and aerobic denitrification by Acinetobacter johnsonii EN-J1

The co-existence of hydroxylamine (NH₂OH) and nitrite (NO₂ ^--N) can aggravate the difficulty of wastewater treatment. The roles of hydroxylamine (NH₂OH) and nitrite (NO₂ ^--N) in accelerating the elimination of multiple nitrogen sources by a novel isolated strain of Acinetobacter johnsonii EN-J1 were investigated in this study. The results demonstrated that strain EN-J1 could eliminate 100.00% of NH₂OH (22.73 mg/L) and 90.09% of NO₂ ^--N (55.32 mg/L), with maximum consumption rates of 1.22 and 6.75 mg/L/h, respectively. Prominently, the toxic substances NH₂OH and NO₂ ^--N could both facilitate nitrogen removal rates. Compared with the control treatment, the elimination rates of nitrate (NO₃ ^--N) and NO₂ ^--N were enhanced by 3.44 and 2.36 mg/L/h after supplementation with 10.00 mg/L NH₂OH, and those of ammonium (NH₄ ⁺-N) and NO₃ ^--N were improved by 0.65 and 1.00 mg/L/h after the addition of 50.00 mg/L NO₂ ^--N. Furthermore, the nitrogen balance results indicated that over 55.00% of the initial total nitrogen was transformed into gaseous nitrogen by heterotrophic nitrification and aerobic denitrification (HN-AD). Ammonia monooxygenase (AMO), hydroxylamine oxidoreductase (HAO), nitrate reductase (NR), and nitrite reductase (NIR), which are essential for HN-AD, were detected at levels of 0.54, 0.15, 0.14, and 0.01 U/mg protein, respectively. All findings confirmed that strain EN-J1 could efficiently execute HN-AD, detoxify NH₂OH and NO₂ ^--N, and ultimately promote nitrogen removal rates.

Current Concentrations of Zn, Cu, and As in Piggery Wastewater Compromise Nutrient Removals in Microalgae–Bacteria Photobioreactors Due to Altered Microbial Communities

Simple Summary

Photobioreactor systems based on consortia of microalgae and bacteria are a promising, efficient and sustainable alternative for treatment of wastewaters with high nitrogen content, such as piggery wastewater. In these biological systems, microorganisms play a key role in wastewater treatment by degradation of organic matter and accumulation of nutrients into the generated biomass. However, these wastewaters often contain high concentrations of zinc, copper and arsenic, which can severely affect the activity and growth of microorganisms, and so, the wastewater treatment performance. This article studies the effect of high concentrations of zinc, copper and arsenic on microbial communities, specifically microalgae and bacteria, in photobioreactors treating piggery wastewater, with the aim of elucidating their impact on wastewater treatment performance. For this purpose, the growth of microalgae and the composition and structure of bacterial communities exposed to these pollutants were studied. The performance of the reactors was also evaluated by determining the removal of nutrients, zinc, copper and arsenic. The results showed that high concentrations of zinc, copper and arsenic in piggery wastewater significantly affect the microbiome of the reactors without recovery after exposure to these contaminants, resulting in poorer performance of the reactors and compromising the environmental and health impact of treated effluents.

Abstract

The treatment of pig manure is a major environmental issue, and photobioreactors containing consortia of microalgae and bacteria have proven to be a promising and sustainable treatment alternative. This work studies the effect of Cu, Zn and As, three toxic elements frequently present in piggery wastewater, on the performance and microbiome of photobioreactors. After dopage with Zn (100 mg/L), Cu (100 mg/L), and As (500 µg/L), the high biomass uptake of Zn (69–81%) and Cu (81–83%) decreased the carbon removal in the photobioreactors, inhibited the growth of Chlorella sp., and affected heterotrophic bacterial populations. The biomass As uptake result was low (19%) and actually promoted microalgae growth. The presence of Cu and As decreased nitrogen removal, reducing the abundance of denitrifying bacterial populations. The results showed that metal(loid)s significantly affected 24 bacterial genera and that they did not recover after exposure. Therefore, this study makes an important contribution on the impact of the presence of metal(loid)s in piggery wastewater that compromises the overall performance of PBRs, and so, the environmental and health impact of treated effluents.

Insight into halotolerance of a robust heterotrophic nitrifying and aerobic denitrifying bacterium Halomonas salifodinae

Studies toward biotreating hypersaline wastewater containing different salts and halotolerant mechanism of robust strains are important but still rare. Here an isolated bacterium Halomonas salifodinae can perform simultaneous nitrification and denitrification (SND) at 15% salinity, showing high nitrogen removal efficiencies of over 98% via response surface methodology optimization. Besides NaCl, this robust strain had high resistance to other salts (KCl, Na₂SO₄, and K₂SO₄) and can efficiently remove nitrogen in saline wastewater containing heavy metals such as Fe(II), Mn(II), Zn(II), Cr(VI), Ni(II), and Cu(II). After repeated-batch culturing at different salinities, the treated strains with different halotolerant capabilities were used as single strain model to study halotolerant mechanism via metabolic analysis. The halotolerant bacterium can convert D-proline and glutamic acid to glutamine as well as lactulose to trehalose. The accumulated intracellular compatible solutes can resist high osmotic pressure and bound water molecule in hypersaline wastewater to accomplish high-efficiency SND processes.

Effects of copper and florfenicol on nirS- and nirK-type denitrifier communities and related antibiotic resistance in vegetable soils

Denitrification play an important role in nitrogen cycle and is affected by veterinary drugs entering agricultural soils. In the present study, the effects of copper and florfenicol on denitrification, related antibiotic resistance and environmental variables were characterized using real-time quantitative PCR (qPCR) and amplicon sequencing in a short-term (30 d) soil model experiment. Drug additions significantly decreased the nirS gene abundance (P < 0.05) but maximized the abundance of gene nirK in soil containing florfenicol and moderate copper levels (150 mg kg^-1). Surprisingly, copper additions decreased the fexB gene abundance, however, the abundance of gene pcoD significantly increased in soils containing florfenicol, moderate copper levels (150 mg kg^-1), and florfenicol and low copper levels (30 mg kg^-1), respectively (P < 0.05). Overall, the nirK-type community composition was more complex than that of nirS-type but Proteobacteria predominated (> 90%) in both communities. Correlation analysis indicated that the gene abundance of fexB was highly correlated with NH₄⁺-N (P < 0.05) and NO₃^--N (P < -0.01), and floR gene abundance was positively correlated with nirK (P < 0.01). Besides, the abundance of nirS-type genera Bradyrhizobium and Pseudomonas were obviously related to total organic matter (TOM), total nitrogen (TN) or total phosphorus (TP) (P < 0.05), while the abundance of nirK-type Rhizobium, Sphingomonas and Bosea showed a significantly correlated with TOM, TN or copper contents (P < 0.05). Taken together, copper and florfenicol contamination increased the possibility of durg resistance genes spread in agricultural soils through nitrogen transformation.

Blended municipal compost and biosolids materials for mine reclamation: Long-term field studies to explore metal mobility, soil fertility and microbial communities

Application of stable soil amendments is often the key to successful phytostabilization and rehabilitation of mine tailings, and microbial guilds are primary drivers of many geochemical processes promoted by these amendments. Field studies were set up at a tailings management area near Sudbury, Ontario to examine performance of blends of lime stabilized municipal biosolids and compost at nine different rates over thick (1 m) municipal compost covers planted with agricultural crops. Based on biogeochemical variability of the substrates four and ten years after application of the initial compost cover, the experimental plots could be classified into three categories: "Low" rate (0-100 t ha^-1 biosolids), "Medium" rate (200-800 t ha^-1), and "High" rate (1600-3200 t ha^-1) treatments. The addition of biosolids materials to the thick compost cover at rates higher than 100 t ha^-1 significantly reduced C:N ratio of the substrates, available phosphorus, and some of the nutrient cations, while notably increasing inorganic carbon and the potential solubility of Ni and Cu. This suggests that increasing biosolids application rates may not equivalently ameliorate soil quality and geochemical stability. Correspondingly, microbial communities were altered by biosolids additions, further intensifying the negative impacts of biosolids on long-term efficiency of the initial compost cover. Abundance of cellulose, hemicellulose, and lignocellulose decomposers (as key drivers of mineralization and humification) was significantly reduced by "Medium" and "High" rate treatments. Most DNA sequences with high affinity to denitrifiers were detected in "High" rate treatments where geochemical conditions were optimal for higher microbial denitrification activities. These findings have implications for improving the long-term efficiency of reclamation and environmental management programs in mine tailings of northern temperate climates.

Dose-response analysis of toxic effect from palm oil mill effluent (POME) by-products on biohydrogen producing bacteria - A preliminary study on microbial density and determination of EC50

The stimulant and toxicity effects of reported organic (acetic acid, propionic acid, butyric acid, formic acid, oil & grease) and inorganic (copper) by-products presented in palm oil mill effluent on anaerobic bacterial population were examined in this paper. The toxicity test had shown that acetic, propionic and butyric acids tend to stimulate the bacterial density level (survival rate more than 50%), while formic acid, copper, oil and grease were shown to have suppressed the density level (survival rate less than 50%). The highest biomass recorded was 1.66 mg/L for the concentration of acetic acid at 216 mg/L and lowest biomass concentration, 0.90 mg/L for copper at 1.40 mg/L. Biohydrogen-producing bacteria have a favourable growth rate around pH 5.5. The comparison of half maximal effective concentration (EC₅₀) values between two test duration on the effects of organic and inorganic by-products postulate that bacteria had a higher tolerance towards volatile fatty acids. While acetic, butyric and propionic acids had exhibited higher tolerance EC₅₀ values for bacteria, but the opposite trend was observed for formic acid, copper and oil & grease.

Nitrogen combined with biochar changed the feedback mechanism between soil nitrification and Cd availability in an acidic soil

Inorganic nitrogen (N) inputs increase soil nitrification, acidification and trace metal toxicity e.g. cadmium (Cd). Biochar (B) has been widely used for metal immobilization. However, little is known about how the combination of N fertilizers with biochar (N-B) changes soil Cd availability through altering nitrification process. Here, (NH₄)₂SO₄ or CO(NH₂)₂ was applied in combination with biochar to an acidic, artificially enriched Cd contaminated soil. Not as we expected, available Cd did not increase following (NH₄)₂SO₄ or CO(NH₂)₂ addition. Nitrification and acidification of Cd contaminated soils were greatly inhibited, accompanied by elimination of ammonia-oxidizing bacteria (AOB). Exchangeable H⁺ of Cd contaminated soils was significantly lower than that of uncontaminated soils, thus inhibiting Cd itself from mobilization. N-B addition nearly halved soil available Cd and significantly increased nitrification by promoting AOB recovery. However, the restored nitrification did not cause soil acidification, due to the high buffering and slow liming effects of biochar. Available Cd continuously decreased with decreasing soil acidity and exchangeable Al. This study firstly demonstrated a feedback between soil nitrification and Cd after N application, and how biochar modified the feedback. Biochar, therefore, provides a feasible strategy for eliminating potential Cd toxicity on both soil biological and chemical processes.

Nitrous oxide produced directly from ammonium, nitrate and nitrite during nitrification and denitrification

A hypothermia aerobic denitrifying bacterium, Pseudomonas taiwanensis strain J488, can effectively remove multiple nitrogen sources from wastewater at 15 °C. The ammonium, nitrate and nitrite removal efficiencies were 100 %, 92.61 % and 92.49 %, respectively. Strain J488 could survive with hydroxylamine as sole nitrogen source and its removal efficiency was 97.71 %. The removal efficiency of ammonium was 100 % even in the presence of the classical inhibitors of nitrification allylthiourea and diethyldithiocarbamate. These findings fundamentally changed the picture that the ammonia monooxygenase could be inhibited by the copper chelators of allylthiourea or diethyldithiocarbamate. Similarly, the nitrite removal capacity of strain J488 was not sensitive to inhibition by Pb²⁺, and its removal efficiency was also 100 %. Additionally, by identifying the intermediates accumulation of nitrification and denitrification, using nitrification and denitrification inhibitors, measuring enzyme activities and determining N₂O concentrations, it was demonstrated that N₂O could be produced directly from ammonium, nitrate and nitrite.

Bioreactor performance using biochar and its effect on aerobic granulation

The effects that rice husk (biochar-rh), rice bran (biochar-rb) and walnut shell (biochar-ws) biochar had on aerobic granulation and reactor performance during the treatment of petroleum wastewater have been investigated. The different biochars reduced aerobic granulation time by 15 days compared with the control and also increased resistance to shock loading. The average COD and TN removal increased by 3.2%-5.1% and 10%-13%, respectively. Bacteria having functional metabolisms associated with the treatment of petroleum wastewaters were enriched in granular sludge that contained biochars. The reactor containing biochar-rb was the most stable and removed the most nutrients. The reactor containing biochar-rh had the largest initial granule size. This study provides insights into how the physicochemical properties of different biochars influence aerobic granular sludge systems.

Inhibition effect of magnetic field on nitrous oxide emission from sequencing batch reactor treating domestic wastewater at low temperature

This study aims to investigate the effect of a magnetic field on nitrous oxide (N₂O) emission from a sequencing batch reactor treating low-strength domestic wastewater at low temperature (10°C). After running for 124 days in parallel, results indicated that the conversion rate of N₂O for a magnetic field-sequencing batch reactor (MF-SBR) decreased by 34.3% compared to that of a conventional SBR (C-SBR). Meanwhile, the removal efficiencies for total nitrogen (TN) and ammonia nitrogen (NH₄-N) of the MF-SBR were 22.4% and 39.5% higher than those of the C-SBR. High-throughput sequencing revealed that the abundances of AOB (Nitrosomonas), NOB (Nitrospira) and denitrifiers (Zoogloea), which could reduce N₂O to N₂, were promoted significantly in the MF-SBR. Enzyme activities (Nir) and gene abundances (nosZ nirS and nirK) for denitrification in the MF-SBR were also notably higher compared to C-SBR. Our study shows that application of a magnetic field is a useful approach for inhibiting the generation of N₂O and promoting the nitrogen removal efficiency by affecting the microbial characteristics of sludge in an SBR treating domestic wastewater at low temperature.