Nitrogen Degradation Research Articles

Benefited wastewater utilization via configurable, spatialized, and microorganisms-integrated biophotonic systems

The development of engineering microbiology is widely expected to advance carbon neutrality and sustainability in the wastewater industry. Engineering microbiology can deliver desired functions without high treatment costs, complex processes, massive greenhouse gas emissions, and resource waste. Here, we propose a complementary strategy to realize benefited wastewater utilization by configurable spatialized microorganisms-integrated biophotonic systems (CSMBs). The configurable spatialized microorganisms enable enhanced microbial synergy and empower on-demand waste-to-bioenergy conversion through optofluidic-assisted design. The developed CSMBs improve the reaction between light and microorganisms (light harvesting and microorganisms’ photosynthesis) via enhanced natural light photon capture and adjustable optical wavelength. Thanks to these features, in prospective wastewater treatment, the CSMBs breakthrough achieve 89.89% and 91.8% degradation of total nitrogen (TN) and total phosphorus (TP) and 91.98% removal of chemical oxygen demand (COD) within 72 h, respectively. The biomass (the absorbance of 680 nm), lipid content, and chlorophyll-a content of Chlorella in the CSMBs were increased by 56.95%, 62.91%, and 35.41%, respectively, compared to the growth of single Chlorella. The method possesses broad applicability and superior tunability, which can be extended to a wide variety of wastewater treatment and enable more ability in benefited waste utilization.

감태 분말 첨가 된장의 품질 특성

Doenjang (Korean soybean paste) was prepared by adding of Ecklonia cava powder (w/w 0.3.6,9%) to Meju fermented for 30℃ for 40 days. The pH level of all samples did not show any significant decrease or increase by days 20 and 30, but the pH level increased near the end of the fermentation process by day 40 compared to the early days of fermentation, with the highest pH for the control group with no added powder and the lowest for the 9% group. The titratable acidity in the 9% group was measured to be the highest, as all the samples increased from the initial fermentation on the 40th day of fermentation. At the start of fermentation, the control group showed the lowest levels of total nitrogen and amino acid content and the 9% group showed the highest. However, by day 40 of fermentation, the control group showed the highest levels and the 9% group showed the lowest levels. The nitrogen degradation rate (NDR) was increased as the fermentation process continued, the control group showed the highest levels by day 40, but the 9% group showed the lowest levels of NDR, showing a decreasing trend as more powder is added. As the fermentation process continued, the levels of reducing sugar decreased, with the control group showing the lowest level and the 9% group with the highest level. The total number of bacteria was significantly reduced from 7.12 to 8.28 log CFU/g at the beginning of fermentation to 6.00 to 6.15 log CFU/g by day 40 of fermentation. The total polyphenol content and % DPPH radical scavenging activity increased significantly with the addition of Ecklonia cava powder in both the early fermentation and the last day of fermentation, showing a higher polyphenol content on the last day of fermentation compared to the first day. In a survey of consumer preferences was showed that the control group with no addition of Ecklonia cava powder showed the highest values in appearance and aroma. However, although there were no significant differences in taste-related assessments (salty taste, umami, after taste) and overall acceptability, the preference for the group with 6% Ecklonia cava powder was the highest. Based on these findings, it was confirmed that soybean paste with 6% of Ecklonia cava powder had the best effect on the preference and functionality of soybean paste, and the possibility of manufacturing soybean paste using Ecklonia cava powder has potential in food development.

Identification of a Strain Degrading Ammonia Nitrogen, Optimization of Ammonia Nitrogen Degradation Conditions, and Gene Expression of Key Degrading Enzyme Nitrite Reductase

In recent years, nitrogen pollutants have become one of the main causes of water pollution and eutrophication; thus, it is very important to increase the research on nitrogen removal in wastewater. In this study, a bacterium with outstanding ammonia nitrogen degradation capability was isolated from piggery wastewater and identified as Bacillus tequilensis (designated as A2). The ammonia nitrogen degradation rate of A2 reached the highest level (95%) when the incubation temperature was 42 °C, the initial pH was 7, the seed volume was 5%, the rotation speed was 160 r·min−1, the C/N was 10:1, and the carbon source was sodium citrate. A new nitrite reductase gene was successfully expressed in E. coli BL21 (DE3), and the result showed that the enzyme gene contained 2418 bp and 805 encoding amino acids, the recombinant enzyme was purified through an Ni2+ affinity chromatography column, it had a molecular weight of about 94 kDa, it displayed the maximum enzyme activity at 40 °C and pH 6.0, it exhibited good stability in the range of 25 °C to 35 °C, and it showed a pH of 6.0 to 7.0. A 1 mM concentration of Fe3+ promoted the enzyme activity, followed by a 1 mM concentration of Fe2+ and Mg2+. The kinetic parameters of Km, Kcat, and the Vmax of NiR-A2 were calculated to be 1.37 μmol·mL−1, 4.9 × 102 s−1, and 23.75 μmol·mg−1·min−1, respectively. This strain shows good prospects for wastewater treatment, especially in the treatment of high concentration ammonia nitrogen and nitrite degradation, because of its tolerance to and high degradation rate of high concentrations of ammonia nitrogen and high nitrite.

In vitro ruminal fermentation parameters of canola meal protein in response to incremental doses of gamma irradiation

Rapid ruminal degradation of canola meal (CM) limits its feed value for high-producing ruminants. Attempts to reduce ruminal degradability of CM through gamma irradiation have generated conflicting results. While this strategy has the potential to reduce CM degradability, the optimal radiation dose is unknown for this valuable co-product. Therefore, this in vitro ruminal fermentation study was designed to evaluate the efficacy of gamma irradiation to protect CM protein from ruminal degradation. Canola meal was irradiated at 0 (CM0), 15 (CM15), 30 (CM30), 45 (CM45), 60 (CM65), 75 (CM75), and 90 kGy (CM90). Irradiated CM was then analysed for proximate composition and incubated with rumen fluid to determine in vitro degradability of dry matter (DMD) and nitrogen (ND). The data were evaluated for linear and quadratic effects using response surface regression analysis. Neutral detergent fibre and acid detergent fibre linearly decreased as irradiation dosage increased. Quadratic responses were observed for total nitrogen (N) content, DMD12, and DMD36 in response to increasing irradiation dosage. Gamma irradiation linearly increased the rapidly soluble fraction (a) and effective degradability (ED) of dry matter. There were no irradiation effects on ND12, ND36, ND48, fractional rate constant (c), and potential degradability, but significant quadratic trends were observed for ND24, a, slowly degradable fraction (b), and ED of N. It was concluded that although gamma irradiation altered the chemical composition of CM, it was not an effective method to protect CM from extensive ruminal degradation

Response of nitrogen removal and microbial community to high concentration of humic acid in the anammox biofilm system

The anaerobic ammonium oxidation (anammox) process is highly effective to remove nitrogen from the wastewater with high ammonia concentration, such as landfill leachate and anaerobic digestion. This kind of wastewater generally contains high content of humic acid, and its effect on anammox is not clear. Therefore, this study investigated the effect of humic acid with high concentration (100–1000 mg/L) on the anammox biofilm system. The nitrogen degradation rates were greatly decreased at the high concentration of humic acid and the reaction time was prolonged by 4 h compared with that lacking humic acid. In the anammox biofilm system, the relative abundance of anammox bacteria Candidatus_Brocadia and Candidatus_Kuenenia decreased from 2.1 % and 15.01 % to 0.6 % and 8.32 %, respectively, while the denitrifying bacteria Thauera increased from zero to 8.86 %. Overall, the high humic acid concentration did not obviously inhibit nitrogen removal performance of anammox system, but affected anammox bacteria activity and microbial community structure.

Construction of CuS/ZnO Z-scheme heterojunction as highly efficient piezocatalyst for degradation of organic pollutant and promoting N2 fixation properties

Piezocatalytic technology has great potential in addressing water-system pollution and countering energy crises issues. Herein, high-performance CuS/ZnO Z-scheme heterojunction piezocatalyst was prepared by environmentally friendly solid-state chemistry approach and explored piezocatalytic performances toward degradation of organic methylene blue (MB) dye pollutant and nitrogen (N2) fixation activity under ultrasonic vibration. The CuS/ZnO piezocatalyst presents outstanding property in MB degradation process with high efficiency (94.7% in 40 min), high rate constant (0.06804 min−1) and good recyclability stability in comparison with the numerous ZnO-based piezocatalysts. In addition, this catalyst also exhibits superior piezocatalytic activity with a production rate of nitrogen fixation rate of 77.5 μmol L−1 gcat−1 h−1 in the reduction of N2 to ammonia process, which is approximately 4-folds higher than that of pristine ZnO. Such improvement was mainly attributed to the facilitating charge carriers separation via rational construction of Z-scheme heterojunction as well as enhanced redox capacity. A novel piezocatalytic Z-scheme heterojunction mechanism of CuS/ZnO has been proposed and elucidated. This work suggests that designing highly efficient CuS/ZnO piezocatalyst will be a promising candidate material for prospects application in coping with the environmental remediation pollutants and energy crisis problems.

Carbonate-bound Pb percentage distribution in agricultural soil and its toxicity: Impact on plant growth, nutrient cycling, soil enzymes, and functional genes

Metals pollution of lead in agricultural soils is a serious problem for food safety. Therefore, we investigated the toxic effects of carbonate-bound fraction Pb on agricultural soil from various aspects. The results revealed that a higher carbonate-bound fraction of Pb had more toxic effects on wheat growth, as evidenced by higher malondialdehyde (3.17 μmol g−1 FW) and lower catalase levels (9.77 μg−1 FW min−1). In terms of nutrient cycling, soil nutrients including carbon, nitrogen, and phosphorus would slow down transformation rates in high concentrations. Compared to carbon, nitrogen and phosphorus were more likely to be affected by the initial carbonate-bound fraction at the earlier stage. Increased Pb dosage may reduce the soil enzymes activity such as urease (119–50 U g−1) and phosphatase (3191–967 U g−1), as well as the functional genes of nitrogen degradation related nirK, nisS, and carbon related pmoA. Correlation analysis and structural equation modeling indicated that carbonate bound Pb could regulate nutrients cycle via functional genes inhibition, soil enzyme activity reduction and wheat growth suppression in agricultural soil. Our findings will help with polluted agricultural soil monitoring and regulation through microbial activity to ensure food safety.

A Review of Bubble Aeration in Biofilter to Reduce Total Ammonia Nitrogen of Recirculating Aquaculture System

Aeration becomes an essential aspect of biofilter performance to reduce ammonia nitrogen in the Recirculating Aquaculture System (RAS). Efficient aeration introduces air into water media and offers an aerobic environment in the biofilter for microbial degradation of organic matter and ammonia nitrogen. The efficiency of the bubble aeration depends on the size of the bubbles; these include coarse bubble, microbubble, fine bubble, and ultrafine bubble or nanobubble. This review highlights an overview of bubble aeration features in a biofilter to reduce ammonia nitrogen. Moreover, key aspects responsible for the ammonia nitrogen removal efficiencies, such as oxygen transfer, microbial community, and biofilm thickness, are evaluated in this review. In conclusion, the bubble size of aeration affects the microbial community of nitrifying bacteria, consequently determining the growth and thickness of biofilm to improve ammonia removal efficiency. It is emphasized that fine bubble and nanobubble aeration have very positive prospects on improving biofilter performance, though they are currently not widely used in RAS.

Enhanced treatment of landfill leachate by biochar-based aerobic denitrifying bacteria functional microbial materials: Preparation and performance.

In this work, polyvinyl alcohol (PVA) and sodium alginate (SA) were used as entrapped carriers and Artemisia argyi stem biochar (ABC) was used as an absorption carrier to immobilize aerobic denitrifying bacteria screened from landfill leachate, thus a new carbon-based functional microbial material (PVA/SA/ABC@BS) was successfully prepared. The structure and characteristics of the new material were revealed by using a scanning electron microscope and Fourier transform infrared spectroscopy, and the performance of the material for treating landfill leachate under different working conditions was studied. ABC had abundant pore structures and that the surface contained many oxygen-containing functional groups, carboxyl groups, and amide groups, etc. and it had good absorbing performance and strong acid and alkali buffering capacity, which was beneficial to the adhesion and proliferation of microorganisms. After adding ABC as a composite carrier, the damage rate of immobilized particles was decreased by 1.2%, and the acid stability, alkaline stability, and mass transfer performance were increased by 9.00, 7.00, and 56%, respectively. When the dosage of PVA/SA/ABC@BS was 0.017g/ml, the removal rates of nitrate nitrogen (NO3 --N) and ammonia nitrogen (NH4 +-N) were the highest, which were 98.7 and 59.4%, respectively. When the pH values were 11, 7, 1, and 9, the removal rates of chemical oxygen demand (COD), NO3 --N, nitrite nitrogen (NO2 --N) and NH4 +-N reached the maximum values, which were 14.39, 98.38, 75.87, and 79.31%, respectively. After PVA/SA/ABC@BS was reused in 5 batches, the removal rates of NO3 --N all reached 95.50%. PVA, SA and ABC have excellent reusability for immobilization of microorganisms and degradation of nitrate nitrogen. This study can provide some guidance for the great application potential of immobilized gel spheres in the treatment of high concentration organic wastewater.

Electrochemical Removal of Nitrogen Compounds from a Simulated Saline Wastewater.

In the last few years, many industrial sectors have generated and discharged large volumes of saline wastewater into the environment. In the present work, the electrochemical removal of nitrogen compounds from synthetic saline wastewater was investigated through a lab-scale experimental reactor. Experiments were carried out to examine the impacts of the operational parameters, such as electrolyte composition and concentration, applied current intensity, and initial ammoniacal nitrogen concentration, on the total nitrogen removal efficiency. Using NaCl as an electrolyte, the NTOT removal was higher than Na2SO4 and NaClO4; however, increasing the initial NaCl concentration over 250 mg·L-1 resulted in no benefits for the NTOT removal efficiency. A rise in the current intensity from 0.05 A to 0.15 A resulted in an improvement in NTOT removal. Nevertheless, a further increase to 0.25 A led to basically no enhancement of the efficiency. A lower initial ammoniacal nitrogen concentration resulted in higher removal efficiency. The highest NTOT removal (about 75%) was achieved after 90 min of treatment operating with a NaCl concentration of 250 mg·L-1 at an applied current intensity of 0.15 A and with an initial ammoniacal nitrogen concentration of 13 mg·L-1. The nitrogen degradation mechanism proposed assumes a series-parallel reaction system, with a first step in which NH4+ is in equilibrium with NH3. Moreover, the nitrogen molar balance showed that the main product of nitrogen oxidation was N2, but NO3- was also detected. Collectively, electrochemical treatment is a promising approach for the removal of nitrogen compounds from impacted saline wastewater.

Simultaneous electrokinetic removal and in situ electrochemical degradation of a high nitrogen accumulated greenhouse soil

High nitrogen (N) concentration in farmland soil can easily cause the eutrophication of water bodies and a decline in soil fertility. As a new technology for quick in-situ nitrate restoration strategy, electrokinetic remediation has high efficiency, reliability, and competitive economic feasibility. However, the traditional electrokinetic remediation configuration will cause excessive acidification and alkalization of soil. The treatment of produced nitrogenous waste liquid was also necessary. In this study, the optimal design by the cation exchange membrane was adopted to solve the problems of soil over-acidification (pH<4) and over-alkalization (pH>10) caused by traditional electrokinetic remediation technology. Adding NaCl to the electrolyte, the anodic oxidation of ammonium was promoted, and the concentration of N in the electrolyte was reduced. Citric acid was added to stabilize pH and promote the conversion of NO3−-N. The removal efficiency of NO3−-N in the soil could reach 90%, 93%, and 97%, respectively, after 5, 10, and 15 days of electrokinetic treatment. The NO3−-N concentration in the processing solution was below 4 mg/L, the NH4+-N concentration was less than the method detection line, the total nitrogen concentration was not more than 8 mg/L, and the N in the waste liquid did not need secondary treatment. This study revealed the electrochemical behavior of nitrate on stainless steel electrodes, indicating that active chlorine can promote the anodic oxidation process of NH4+. At the same time, it was found that citric acid positively affected nitrate transformation. Based on the clarification of the transport and transformation mechanism, this study inspired optimizing our existing electric remediation technology to solve the problem of high N-accumulation in soils.

Technologies for pollutant removal and resource recovery from blackwater: a review.

Blackwater (BW), consisting of feces, urine, flushing water and toilet paper, makes up an important portion of domestic wastewater. The improper disposal of BW may lead to environmental pollution and disease transmission, threatening the sustainable development of the world. Rich in nutrients and organic matter, BW could be treated for resource recovery and reuse through various approaches. Aimed at providing guidance for the future development of BW treatment and resource recovery, this paper presented a literature review of BWs produced in different countries and types of toilets, including their physiochemical characteristics, and current treatment and resource recovery strategies. The degradation and utilization of carbon (C), nitrogen (N) and phosphorus (P) within BW are underlined. The performance of different systems was classified and summarized. Among all the treating systems, biological and ecological systems have been long and widely applied for BW treatment, showing their universality and operability in nutrients and energy recovery, but they are either slow or ineffective in removal of some refractory pollutants. Novel processes, especially advanced oxidation processes (AOPs), are becoming increasingly extensively studied in BW treatment because of their high efficiency, especially for the removal of micropollutants and pathogens. This review could serve as an instructive guidance for the design and optimization of BW treatment technologies, aiming to help in the fulfilment of sustainable human excreta management.

Effects and Mechanisms of Microbial Agents and Carbon Sources on Aquaculture Environment

Improving aquaculture environment through microbial manipulation has been a hot topic in aquaculture research in recent ten years. The effectiveness of microbiological agents in improving aquaculture water quality, especially in the degradation of inorganic nitrogen, remains controversial. One of the reasons is the lack of understanding of the pathway through which microbiological agents affect the environment. The effects of carbon sources and two microbial agents on ammonia nitrogen conversion in a cultured environment were studied by two in-situ experiments. The results showed that the inorganic carbon and organic carbon increased significantly in the sterilized and non-sterilized groups. The conversion trend of inorganic nitrogen was the same. The ammonia nitrogen and nitrite did not decrease, and the nitrate decreased significantly. The results indicated that there was no significant change in the function and unextinguished effect of nitrifying bactericide after sterilization. The effect of adding microbial agents on the conversion of inorganic ammonia in the environment might be due to the role of carbon source itself.

Influence of supplemental flavomycin on growth performance, carcass characteristics, and nutrient digestibility in calf-fed Holstein steers.

The objective of this study was to evaluate the influence of supplemental flavomycin on cattle growth performance, carcass characteristics, diet digestibility, and ruminal fermentation characteristics of calf-fed Holstein steers. One hundred Holstein steers (123 ± 7 kg) were balanced by weight and assigned to 20 pens. Dietary treatments consisted of a steam flaked corn-based diet supplemented with (dry matter basis): 1) control, no feed additive; 2) 6.6 mg/kg flavomycin; 3) 13.2 mg/kg flavomycin, and 4) 30 mg/kg monensin (MON). There were no treatment effects (P ≥ 0.17) on live weight, average daily gain (ADG), and gain efficiency. Flavomycin did not affect dry matter intake (DMI; P ≥ 0.24). Flavomycin supplementation did not affect (P ≥ 0.37) the ratio of observed vs. expected DMI. However, MON decreased (P = 0.02) observed vs. expected DMI by 3.7%. There were no treatment effects (P ≥ 0.44) on ruminal pH or temperature. Flavomycin did not affect (P ≥ 0.13) carcass characteristics and liver abscess among steers. Four Holstein steers (463 ± 20 kg) with ruminal cannulas were used in 4 × 4 Latin square experiment to study treatment effects on site and extent of digestion, ruminal pH, and volatile fatty acid (VFA) molar proportions. Dietary treatments were the same as experiment 1. Flavomycin tended to increase (linear effect, P = 0.07) ruminal organic matter (OM) digestion, associated with increased (linear effect, P < 0.01) ruminal starch digestion. Supplementing flavomycin at 13.2 mg/kg decreased net microbial N synthesis (quadratic effect, P = 0.03). Compared with control, MON tended to increase (P = 0.10) ruminal neutral detergent fiber (NDF) digestion and increased (P < 0.01) ruminal starch digestion. Monensin did not affect (P = 0.39) net microbial N synthesis, but decreased (P = 0.01) ruminal degradation of feed nitrogen (N). There were no treatment effects (P > 0.10) on total tract apparent digestion of DM, OM, NDF, and starch. Flavomycin decreased ruminal pH (quadratic effect, P < 0.01) measured 4 h postprandial. Compared with control, MON increased ruminal pH (P = 0.03). Flavomycin increased (linear effect, P = 0.03) ruminal propionate molar proportion and decreased (linear effect, P ≤ 0.04) ruminal molar proportions of acetate and butyrate, and decreased (linear effect, P = 0.02) acetate:propionate molar ratio and estimated methane production. We conclude that supplementing flavomycin at 6.6 or 13.2 mg/kg had no major effects on cattle growth performance, carcass characteristics, diet digestibility, and ruminal fermentation characteristics.

Model for Microalgae-Bacteria Systems with Nitrification and Photoinhibition

Microalgae-bacteria (MAB) systems are a useful technology for treating domestic wastewater. They combine the oxygen producing capability of microalgae with the chemical oxygen demand (COD) and total nitrogen degradation efficiency of aerobic bacteria in a synergistic manner. This work proposes a new mathematical model that incorporates two recently observed phenomena: photoinhibition during bacterial nitrification and heterotrophic growth of microalgae in the dark. The model is corroborated with experimental data, showing good prediction capabilities.

Investigation of the nitrogen removal performance and microbial community structure in a full-scale A/O1/H/O2 coking wastewater treatment system.

Biological treatment processes are an effective method for removing the nitrogen-containing contaminants that exist in coking wastewater. However, little is known about microbial composition and keystone taxa involved in biological nitrogen removal processes. In order to improve the removal efficiency of nitrogen-containing contaminants in anaerobic-aerobic-hydrolytic-aerobic (A/O1/H/O2) system, the microbial composition and interactions of keystone taxa should be clarified. The present work clarifies the removal performance of nitrogen-containing contaminants in the A/O1/H/O2 system, identifies the microbial community involved in various bioreactors, and reveals the keystone taxa within the microbial communities. Combined the processes of ammoniation, denitrification, and nitrification, total nitrogen decreased from 248 to 31 mg L-1 and achieved a removal efficiency of 87.5% in the full-scale A/O1/H/O2 system. High-throughput MiSeq sequencing revealed that Proteobacteria was the most abundant phylum in the A/O1/H/O2 system with relative abundances of 24%-50%. Thiobacillus dominated in bioreactors A and O1 with relative abundances of 2.90% and 4.44%, respectively, while Nitrospira was identified as the most dominant genus in bioreactors H and O2, accounting for 13.33% and 18.38%, respectively. The microbial community composition and co-occurrence network analysis showed that the keystone taxa belonged to Thiobacillus, Nitrospira, Bdellovibrio, Planctomyces, Desulfotomaculum, and Sphingobium, which are related to nitrogen degradation.

Fungus Pichia kudriavzevii XTY1 and heterotrophic nitrifying bacterium Enterobacter asburiae GS2 cannot efficiently transform organic nitrogen via hydroxylamine and nitrite.

Heterotrophic nitrification is a process of organic nitrogen degradation completed by the participation of heterotrophic nitrifying microorganisms, which can accelerate the nitrogen transformation process. However, the current research mainly focuses on heterotrophic nitrifying bacteria and their ammonium degradation capacities. And there is little accumulation of research on fungi, the main force of heterotrophic nitrification, and their capacities to transform organic nitrogen. In this study, novel heterotrophic nitrifying fungus (XTY1) and bacterium (GS2) were screened and isolated from upland soil, and the strains were identified and registered through GenBank comparison. After 24 h single nitrogen source tests and 15N labeling tests, we compared and preliminarily determined the heterotrophic nitrification capacities and pathways of the two strains. The results showed that XTY1 and GS2 had different transformation capacities to different nitrogen substrates and could efficiently transform organic nitrogen. However, the transformation capacity of XTY1 to ammonium was much lower than that of GS2. The two strains did not pass through NH2OH and NO2 - during the heterotrophic nitrification of organic nitrogen, and mainly generated intracellular nitrogen and low N2O. Other novel organic nitrogen metabolism pathways may be existed, but they remain to be further validated.

Synergistic removal of ammonia nitrogen by UV photo-electrocatalytic process: Heterogeneous reaction pathways and mechanism

UV photo-electrocatalytic process has emerged as a promising approach for the abatement of ammonia nitrogen in wastewater. However, the radical chemistry for ammonia nitrogen removal in this process requires further clarification. The heterogeneous reaction pathways and mechanism of ammonia nitrogen oxidation in the UV photo-electrocatalytic process were investigated in this study. Photocurrents of the Ti/RuO2-IrO2-TiO2 electrodes with good electrocatalytic behavior were enhanced by UV radiation. Compared with the electrocatalytic process, the removal rates of ammonia nitrogen were improved by 12.4%∼20% at the Cl− concentration of 50 mM in the photo-electrocatalytic process. The ammonia nitrogen was mainly transferred into N2, meanwhile, the formation of nitrogenous by-products, active chlorine, and chloramines was inhibited in the photo-electrocatalytic process. The contribution of UV radiation was to photo-decompose the active chlorine and chloramines, generating free radicals. The removal efficiency of ammonia nitrogen reached more than 64% after the elimination of free radicals. The electro-generated HOCl was the principal species for ammonia nitrogen removal, and the synergistic effect for the acceleration of ammonia nitrogen oxidation resulted from the photo-generated chlorine radicals. This investigation provides insight into the electrochemistry, photochemistry, and radical chemistry for the heterogeneous catalytic degradation of ammonia nitrogen by UV photo-electrocatalytic process.

Rumen microbiota responses to the enzymatic hydrolyzed cottonseed peptide supplement under high-concentrate diet feeding process.

In current dairy production, dietary energy is always excessively provided with a high-concentrate diet feeding to improve milk production. However, this feeding practice disturbed the rumen microbial ecosystem and the balance between ruminal energy and nitrogen, resulting in decreased nutrient fermentability, which in turn declined the milk yield of dairy cows. Therefore, supplementation of dietary degradable nitrogen may be helpful for high dairy production. In this study, we evaluated the regulatory effects of easily utilized enzymatic hydrolyzed cottonseed peptide (EHP) supplements on rumen microbiota communities and rumen nutrient fermentability under high-concentrate feeding. For this purpose, a gradient concentrate of EHP (from 0.2 to 1.0%) was added to the high-concentrate basal substrates for an in vitro experiment. Each treatment contained three replicates, with three bottles in each replicate. Rumen fermentable parameters included microbial protein content, volatile fatty acids, and ammonia-N; the rumen nutrient degradability of dry matter, crude protein, neutral detergent fiber, acid detergent fiber, ether extracts, calcium, and phosphorus were further investigated after in vitro fermentation for 72 h. Then, rumen microbiota communities and their correlation with ruminal fermentation parameters and rumen nutritional degradability were analyzed to understand the regulatory mechanism of the EHP supplements on rumen fermentability. Results indicate that treatment with 0.6% of EHP supplements had the highest content of acetate, butyrate, and neutral detergent fiber degradability among all treatments. Furthermore, EHP supplements significantly increased the relative abundance of rumen cellulose and starch-degrading bacteria such as Ruminococcus, Bifidobacterium, and Acetitomaculum, and the high nitrogen utilizing bacteria Butyrivibrio and Pseudobutyrivibrio, which may further promote the rumen carbohydrate and nitrogen metabolism. In summary, supplementation of easily degraded small peptides helps reestablish rumen energy and nitrogen balance to promote the rumen fermentable functions and nutritional degradability under high-concentrate diet feeding circumstances. These findings may further promote dairy production.

Land use and land cover changes in coastal and inland wetlands cause soil carbon and nitrogen loss

AbstractAimNatural wetlands are widely considered important for mitigation of climate change, but they have been impacted by land use and land cover change (LULCC), often resulting in ecosystem degradation and significant changes in soil carbon (C) and nitrogen (N) dynamics. However, the impact of various LULCC types on wetland soil C and N dynamics remains unclear.LocationGlobal.Time period1982–2021.Major taxa studiedWetland.MethodsWe present a global meta‐analysis using a database of 487 sites compiled from the literature, demonstrating the response of soil C and N concentrations and stocks in coastal wetlands, riparian wetlands and peatlands to various types of LULCCs, including agricultural lands, drained wetlands, aquaculture ponds, pastures and constructed wetlands.ResultsThe conversion of coastal wetlands, riparian wetlands and peatlands to most LULCC types decreased the mean soil C and N concentrations and stocks by 17.8 ± 10.3, 25.3 ± 13.4 and 23.2 ± 6.3%, respectively. The loss of wetland soil C owing to LULCC is estimated to cause a potential CO2 emission of 1.8–22.8 Mg CO2 equivalent emission/ha/year, except for conversion to constructed wetlands. The soil C and N contents were more sensitive to LULCCs, relative to the stocks. We also found that the patterns of soil C and N variations were closely related to the conversion time since completion of LULCC. After LULCC, the response of soil C and N variables was sensitive to changes in plant biomass, soil water conditions, bulk density, pH and NH4+‐N concentration, with the major controlling factors varying with the conversion age.Main conclusionsOur results highlight the important role of LULCC in triggering soil C and N loss in natural wetlands, which enhances the greenhouse effect. As such, our study calls for sustainable land management strategies aiming at wetland conservation as a powerful tool to mitigate climate warming.