Nitrogen Overload Research Articles

Nitrogen source type modulates heat stress response in coral symbiont (Cladocopium goreaui).

Ocean warming due to climate change endangers coral reefs, and regional nitrogen overloading exacerbates the vulnerability of reef-building corals as the dual stress disrupts coral-Symbiodiniaceae mutualism. Different forms of nitrogen may create different interactive effects with thermal stress, but the underlying mechanisms remain elusive. To address the gap, we measured and compared the physiological and transcriptional responses of the Symbiodiniaceae Cladocopium goreaui to heat stress (31°C) when supplied with different types of nitrogen (nitrate, ammonium, or urea). Under heat stress (HS), cell proliferation and photosynthesis of C. goreaui declined, while cell size, lipid storage, and total antioxidant capacity increased, both to varied extents depending on the nitrogen type. Nitrate-cultured cells exhibited the most robust acclimation to HS, as evidenced by the fewest differentially expressed genes (DEGs) and less ROS accumulation, possibly due to activated nitrate reduction and enhanced ascorbate biogenesis. Ammonium-grown cultures exhibited higher algal proliferation and ROS scavenging capacity due to enhanced carotenoid and ascorbate quenching, but potentially reduced host recognizability due to the downregulation of N-glycan biosynthesis genes. Urea utilization led to the greatest ROS accumulation as genes involved in photorespiration, plant respiratory burst oxidase (RBOH), and protein refolding were markedly upregulated, but the greatest cutdown in photosynthate potentially available to corals as evidenced by photoinhibition and selfish lipid storage, indicating detrimental effects of urea overloading. The differential warming nitrogen-type interactive effects documented here has significant implication in coral-Symbiodiniaceae mutualism, which requires further research.IMPORTANCERegional nitrogen pollution exacerbates coral vulnerability to globally rising sea-surface temperature, with different nitrogen types exerting different interactive effects. How this occurs is poorly understood and understudied. This study explored the underlying mechanism by comparing physiological and transcriptional responses of a coral symbiont to heat stress under different nitrogen supplies (nitrate, ammonium, and urea). The results showed some common, significant responses to heat stress as well as some unique, N-source dependent responses. These findings underscore that nitrogen eutrophication is not all the same, the form of nitrogen pollution should be considered in coral conservation, and special attention should be given to urea pollution.

The dynamic relation between fertilization, precipitation and the diffusion of agricultural non-point pollution in Hainan Island

With the increasing demand for crops, the excessive application of fertilizers has gradually become a significant factor affecting water quality. Therefore, studying the relationship between agricultural fertilizer runoff and water quality is crucial for the sustainable development of agricultural production. The present study sets up a new dynamic model of nitrogen fertilizer loss, introducing variables such as precipitation, fertilization application during dry and rainy seasons, and their lagged and interaction terms. The paper analyzed the issue of fertilizer runoff under the complex interactions of various factors, including spatial and temporal scales and climatic conditions, and explored the relationship between agricultural activities and water quality changes in the context of sustainable development. Due to Hainan Island’s independent river system, which is free from transboundary pollution, and its low level of industrial pollution, it provides an excellent sample for assessing the impact of agricultural non-point source pollution on water quality. Based on watershed monitoring data from Hainan Island, this study draws the following conclusions: 1. Precipitation exhibits a pronounced seasonal influence on total nitrogen concentration. 2. Nitrogen fertilizer enters into water bodies through precipitation, resulting in a lag effect on total nitrogen concentration. 3. The influence of grain and tropical crops on nitrogen loss is less significant, while cash crops will trigger the nitrogen overloading of rivers in scenarios where they account for a high proportion of the planting structure of the sown area.

Phosphorus limitation intensifies heat-stress effects on the potential mutualistic capacity in the coral-derived Symbiodinium

Coral reef ecosystems have been severely ravaged by global warming and eutrophication. Eutrophication often originates from nitrogen (N) overloading that creates stoichiometric phosphorus (P) limitation, which can be aggravated by sea surface temperature rises that enhances stratification. However, how P-limitation interacts with thermal stress to impact coral-Symbiodiniaceae mutualism is poorly understood and underexplored. Here, we investigated the effect of P-limitation (P-depleted vs. P-replete) superimposed on heat stress (31 °C vs. 25 °C) on a Symbiodinium strain newly isolated from the coral host by a 14-day incubation experiment. The heat and P-limitation co-stress induced an increase in alkaline phosphatase activity and reppressed cell division, photosynthetic efficiency, and expression of N uptake and assimilation genes. Moreover, P limitation intensified downregulation of carbon fixation (light and dark reaction) and metabolism (glycolysis) pathways in heat stressed Symbiodinium. Notably, co-stress elicited a marked transcriptional downregulation of genes encoding photosynthates transporters and microbe-associated molecular patterns, potentially undermining the mutualism potential. This work sheds light on the interactive effects of P-limitation and heat stress on coral symbionts, indicating that nutrient imbalance in the coral reef ecosystem can intensify heat-stress effects on the mutualistic capacity of Symbiodiniaceae.

Bioelectrochemical protein production valorising NH3-rich pig manure-derived wastewater and CO2 from anaerobic digestion

Microbial electrosynthesis (MES) cell use is an innovative approach for single-cell proteins (SCP) production. Coupling MES with the valorization of CO2 from anaerobic digestion and nitrogen from livestock effluents has beneficial environmental effects, reducing greenhouse gas emissions and nitrogen overloading. In addition, the reducing power needed can come from surplus renewable energy. In this study, MES with a biochar-functionalized cathode was tested at varying polarizations, i.e. non polarized, −0.6 V and −1.0 V vs Ag/AgCl, and biogas-derived CO2 and recovered ammonia from pig slurry was supplied.Negative polarization switched the microbial community from heterotrophic, typical of unpolarized MES, to a mix of both heterotrophic and autotrophic/electrotrophic communities at −0.6 V and to mainly autotrophic/electrotrophic at −1.0 V. The more negative polarization allowed the highest CO2 and N capture, i.e. 39 ± 2 % of the supplied CO2, and 6.7 ± 0.8 % supplied N. Microbial biomass characterization indicated a protein content on dry matter basis of 33.1 ± 1.3 % (unpolarized), 43.2 ± 0.6 % (−0.6 V) and 69.1 ± 1.0 % (−1.0 V). The amino acids profiles investigated showed a high nutritional value of the produced biomass, not far from those of conventional protein sources used for producing feed/food.

Exploring feedback mechanisms for nitrogen and organic carbon cycling in tropical coastal zones

The anthropogenic introduction of significant amounts of reactive nitrogen in the coastal zone particularly since the discovery and application of the Haber-Bosch process has profound consequences over organic carbon storage and transformations at both regional and global scales. Here, we review our current knowledge on cause-effect chains for nitrogen, especially dissolved inorganic nitrogen, on organic carbon cycling in coastal tropical systems. We focus on the feedback mechanisms for turnover of different organic carbon species to nitrogen excess and links to current environmental and climate changes. We pay special attention to organic carbon dynamics in tropical coasts due to their high primary productivity, rapid sedimentation, and significant needs of nitrogen for agriculture and industry usages. Together with land-use changes and economy development, we highlight the vulnerability of carbon storage in tropical coasts triggered by nitrogen overloading and outline possible industrial strategies with low carbon cycling disturbance to benefit the development of tropical countries.

Corticosteroid suppresses urea-cycle-related gene expressions in ornithine transcarbamylase deficiency

BackgroundOrnithine transcarbamylase deficiency (OTCD) is most common among urea cycle disorders (UCDs), defined by defects in enzymes associated with ureagenesis. Corticosteroid administration to UCD patients, including OTCD patients, is suggested to be avoided, as it may induce life-threatening hyperammonemia. The mechanism has been considered nitrogen overload due to the catabolic effect of corticosteroids; however, the pathophysiological process is unclear.MethodsTo elucidate the mechanism of hyperammonemia induced by corticosteroid administration in OTCD patients, we analyzed a mouse model by administering corticosteroids to OTCspf−ash mice deficient in the OTC gene. Dexamethasone (DEX; 20 mg/kg) was administered to the OTCspf−ash and wild-type (WT) mice at 0 and 24 h, and the serum ammonia concentrations, the levels of the hepatic metabolites, and the gene expressions related with ammonia metabolism in the livers and muscles were analyzed.ResultsThe ammonia levels in Otcspf−ash mice that were administered DEX tended to increase at 24 h and increased significantly at 48 h. The metabolomic analysis showed that the levels of citrulline, arginine, and ornithine did not differ significantly between Otcspf−ash mice that were administered DEX and normal saline; however, the level of aspartate was increased drastically in Otcspf−ash mice owing to DEX administration (P < 0.01). Among the enzymes associated with the urea cycle, mRNA expressions of carbamoyl-phosphate synthase 1, ornithine transcarbamylase, arginosuccinate synthase 1, and arginosuccinate lyase in the livers were significantly downregulated by DEX administration in both the Otcspf−ash and WT mice (P < 0.01). Among the enzymes associated with catabolism, mRNA expression of Muscle RING-finger protein-1 in the muscles was significantly upregulated in the muscles of WT mice by DEX administration (P < 0.05).ConclusionsWe elucidated that corticosteroid administration induced hyperammonemia in Otcspf−ash mice by not only muscle catabolism but also suppressing urea-cycle-related gene expressions. Since the urea cycle intermediate amino acids, such as arginine, might not be effective because of the suppressed expression of urea-cycle-related genes by corticosteroid administration, we should consider an early intervention by renal replacement therapy in cases of UCD patients induced by corticosteroids to avoid brain injuries or fatal outcomes.

Can nitrifiers from the sidestream deammonification process be a remedy for the N-overload of the mainstream reactor?

The combination of sidestream deammonification and bioaugmentation of the mainstream reactor using ammonia oxidizers from partial nitritation (PN) was not achieved before. This novel solution not only enables the efficient sidestream nitrogen removal, but also improves mainstream resistance to stress situations such as biomass washout or nitrogen overload. This feature is important for wastewater treatment plants (WWTPs) equipped with reject water deammonification as its implementation leads to lower nitrifier mass in the mainstream reactor and therefore diminish ability to cope with rapid increase in the loading rate (i.e. due to sidestream process failure). The proposed approach presents the use of the excess sludge from a modified PN process to boost the mainstream nitrification in unfavourable conditions. In a long-term laboratory experiment, the operation of an existing WWTP at low temperature was simulated in two reactors using real wastewater fluxes. One of them was augmented with the excess sludge from a PN reactor that treats reject water containing 20% of the WWTP N-load. The treatment efficiency in both reactors was tested under different nitrogen loading rates, as well as in the case of the of biomass loss. The bioaugmentation intensity was set according to the actual nitrogen load balance of the modelled WWTP, resulting in a daily seed volume only equal to 0.28% of the reactors' influent. Two incidents were simulated, where the nitrogen load increased by about 24.5% and 34%. In both cases, the nitrification efficiency in the non-augmented reactor dropped by about 45%, while the augmented reactor maintained efficient ammonium removal. The bioaugmentation effect was also noticeable during biomass washout — only in the non-augmented reactor nitrification was insufficient for over 60 days. These results undoubtedly show the possibility of combining two different approaches for sidestream nitrogen removal into one technology demonstrating the advantages of both component solutions.

Nitrogen Overload: Environmental Degradation, Ramifications, and Economic Costs

Nitrogen Overload: Environmental Degradation, Ramifications, and Economic Costs

Intellectualized Control System for Anaerobic Bioconversion of Liquid Organic Waste

The use of methods for the biological conversion of organic waste with the production of biogas while solving environmental issues from pollution is an urgent task. The aim of this work is the development of intellectualized control system of parameters of anaerobic bioconversion of organic waste liquid, including parameters of heating supply system of a biogas plant with optimization of the combustion process of biogas, while using the method of optimization of the anaerobic bioconversion of organic waste due to the multiple supply substrate to the bioreactor, ensuring the efficiency and stability of anaerobic bioconversion of organic matter. The developed system allows optimizing the process of biogas combustion with obtaining the heat carrier in the required quantity and quality while minimizing emissions of biogas combustion. Maintaining the optimal rate of supply of the daily dose of the substrate in the bioreactor allows to increase the resistance to organic matter overload; to increase resistance to ammonium nitrogen overloads; to reduce pH fluctuations in the bioreactor.

Measurement of Total Nitrogen Concentration in Surface Water Using Hyperspectral Band Observation Method

Nitrogen overload is one of the main reasons for the deterioration of surface water quality. Hence, monitoring nitrogen loadings is vital in maintaining good surface water quality. Increasingly, the use of spectral reflectance to monitor nitrogen concentration in water has shown potentials, but it poses some problems. Therefore, it is necessary to explore new methods of quantitative monitoring of nitrogen concentration in surface water. In this paper, hyperspectral data from surface water in the Ebinur Lake watershed are used to select sensitive bands using spectral transformation, the spectral index, and a coupling of these two methods. The particle swarm optimization support vector machine (PSO-SVM) model, constructed on the basis of sensitive bands, is used quantitatively to estimate the total nitrogen concentration in surface water and subsequently to verify its accuracy. The results show that the bands near 680, 850, and 940 nm can be used as sensitive bands for estimation of the total nitrogen concentration of surface water in arid regions. Compared with the best estimation models constructed by sensitive bands selected using the spectral transformation or the spectral index alone, the best model based on the coupling of these two measures is more accurate (R2 = 0.604, Root Mean Square Error (RMSE) = 1.61 mg/L, Residual Prediction Deviation (RPD) = 2.002). This coupling method leads to a robust, accurate, and strong predictability model, and can contribute to improved quantitative estimation of water quality indexes of rivers in arid regions.

A constitutive knockout of murine carbamoyl phosphate synthetase 1 results in death with marked hyperglutaminemia and hyperammonemia.

The enzyme carbamoyl phosphate synthetase 1 (CPS1; EC 6.3.4.16) forms carbamoyl phosphate from bicarbonate, ammonia, and adenosine triphosphate (ATP) and is activated allosterically by N-acetylglutamate. The neonatal presentation of bi-allelic mutations of CPS1 results in hyperammonemia with reduced citrulline and is reported as the most challenging nitrogen metabolism disorder to treat. As therapeutic interventions are limited, patients often develop neurological injury or die from hyperammonemia. Survivors remain vulnerable to nitrogen overload, being at risk for repetitive neurological injury. With transgenic technology, our lab developed a constitutive Cps1 mutant mouse and reports its characterization herein. Within 24 hours of birth, all Cps1 -/- mice developed hyperammonemia and expired. No CPS1 protein by Western blot or immunostaining was detected in livers nor was Cps1 mRNA present. CPS1 enzymatic activity was markedly decreased in knockout livers and reduced in Cps1+/- mice. Plasma analysis found markedly reduced citrulline and arginine and markedly increased glutamine and alanine, both intermolecular carriers of nitrogen, along with elevated ammonia, taurine, and lysine. Derangements in multiple other amino acids were also detected. While hepatic amino acids also demonstrated markedly reduced citrulline, arginine, while decreased, was not statistically significant; alanine and lysine were markedly increased while glutamine was trending towards significance. In conclusion we have determined that this constitutive neonatal mouse model of CPS1 deficiency replicates the neonatal human phenotype and demonstrates the key biochemical features of the disorder. These mice will be integral for addressing the challenges of developing new therapeutic approaches for this, at present, poorly treated disorder.

Spatiotemporal distributions and environmental drivers of diversity and community structure of nosZ-type denitrifiers and anammox bacteria in sediments of the Bohai Sea and North Yellow Sea, China

Denitrification and anammox processes are major nitrogen removal processes in coastal ecosystems. However, the spatiotemporal dynamics and driving factors of the diversity and community structure of involved functional bacteria have not been well illustrated in coastal environments, especially in human-dominated ecosystems. In this study, we investigated the distributions of denitrifiers and anammox bacteria in the eutrophic Bohai Sea and the northern Yellow Sea of China in May and November of 2012 by constructing clone libraries employing nosZ and 16S rRNA gene biomarkers. The diversity of nosZ-denitrifier was much higher at the coastal sites compared with the central sites, but not significant among basins or seasons. Alphaproteobacteria were predominant and prevalent in the sediments, whereas Betaproteobacteria primarily occurred at the site near the Huanghe (Yellow) River estuary. Anammox bacteria Candidatus Scalindua was predominant in the sediments, and besides, Candidatus Brocadia and Candidatus Kuenenia were also detected at the site near the Huanghe River estuary that received strong riverine and anthropogenic impacts. Salinity was the most important in structuring communities of nosZ-denitrifier and anammox bacteria. Additionally, anthropogenic perturbations (e.g. nitrogen overloading and consequent high primary productivity, and heavy metal discharges) contributed significantly to shaping community structures of denitrifier and anammox bacteria, suggesting that anthropogenic activities would influence and even change the ecological function of coastal ecosystems.

Coniferous coverage as well as catchment steepness influences local stream nitrate concentrations within a nitrogen-saturated forest in central Japan

High concentrations of nitrate have been detected in streams flowing from nitrogen-saturated forests; however, the spatial variations of nitrate leaching within those forests and its causes remain poorly explored. The aim of this study is to evaluate the influences of catchment topography and coniferous coverage on stream nitrate concentrations in a nitrogen-saturated forest. We measured nitrate concentrations in the baseflow of headwater streams at 40 montane forest catchments on Mount Tsukuba in central Japan, at three-month intervals for 1 year, and investigated their relationship with catchment topography and with coniferous coverage. Although stream nitrate concentrations varied from 0.5 to 3.0 mgN L−1, those in 31 catchments consistently exceeded 1 mgN L−1, indicating that this forest had experienced nitrogen saturation. A classification and regression tree analysis with multiple environmental factors showed that the mean slope gradient and coniferous coverage were the best and second best, respectively, at explaining inter-catchment variance of stream nitrate concentrations. This analysis suggested that the catchments with steep topography and high coniferous coverage tend to have high nitrate concentrations. Moreover, in the three-year observation period for five adjacent catchments, the two catchments with relatively higher coniferous coverage consistently had higher stream nitrate concentrations. Thus, the spatial variations in stream nitrate concentrations were primarily regulated by catchment steepness and, to a lesser extent, coniferous coverage in this nitrogen-saturated forest. Our results suggest that a decrease in coniferous coverage could potentially contribute to a reduction in nitrate leaching from this nitrogen-saturated forest, and consequently reduce the risk of nitrogen overload for the downstream ecosystems. This information will allow land managers and researchers to develop improved management plans for this and similar forests in Japan and elsewhere.

Evaluation of four seagrass species as early warning indicators for nitrogen overloading: Implications for eutrophic evaluation and ecosystem management

Seagrasses are major coastal primary producers and are widely distributed on coasts worldwide. Seagrasses show sensitivity to environmental stress due to their high phenotypic plasticity, and therefore, we evaluated the use of constituent elements in four dominant seagrass species as early warning indicators for nitrogen eutrophication of coastal regions. A meta-analysis was conducted with published data to develop a global benchmark for the selected indicator, which was used to evaluate nitrogen loading at a global scale. A case study at three bays was subsequently conducted to test for local-scale differences in leaf C/N ratios in four seagrasses. Additionally, morphological and physiological metrics of seagrasses were measured from the three locations under varied nitrogen levels to develop further assessment indexes. The benchmark and local study showed that leaf C/N ratios of Zostera marina were sensitive to nitrogen discharge, which could be a highly valuable early warning indicator on a global scale. Moreover, the threshold value of seagrass leaf C/N was determined according to the benchmark to differentiate eutrophic and low nitrogen levels at a local scale. Of the eight phenotypic metrics measured, leaf width, total chlorophyll (a + b), chlorophyll ratio (a/b), and starch in the rhizome were the most effective at discriminating between the three locations and could also be promising indicators for monitoring eutrophication.

Anaerobic digestion and electromethanogenic microbial electrolysis cell integrated system: Increased stability and recovery of ammonia and methane

Abstract The integration of anaerobic digestion (AD) and a microbial electrolysis cell (MEC) with an electromethanogenic biocathode is proposed to increase the stability and robustness of the AD process against organic and nitrogen overloads; to keep the effluent quality; to recover ammonium; and to upgrade the biogas. A thermophilic lab-scale AD, fed with pig slurry, was connected in series with the bioanode compartment of a two-chambered MEC. In turn, the biocathode of the MEC was poised at −800 mV vs Standard Hydrogen Electrode and fed with CO2 to increase the methane production of the system. After doubling its organic and nitrogen loading rate, the AD operation became stable thanks to the connection of a recirculation loop with the MEC effluent. Ammonium removal in the anode compartment of the MEC achieved 14.46 g N-NH4+ m−2 d−1, while obtaining on average 79 L CH4 m−3 d−1 through the conversion of CO2 in the cathode compartment. The microbial analysis showed that methylotrophic Methanossiliicoccaceae family (Methanomassiliicoccus genus) was the most abundant among the metabolically active archaea in the AD during the inhibited state; while, on the cathode, Methanobacteriaceae family (Methanobrevibacter and Methanobacterium genus) shared dominance with Methanomassiliicoccaceae and Methanotrichaceae families (Methanomassiliicoccus and Methanothrix genus, respectively).

Microbial fuel cells for polishing effluents of anaerobic digesters under inhibition, due to organic and nitrogen overloads

BACKGROUND Bioelectrochemical systems have been proposed as a possible polishing step for anaerobic digestion (AD). They can also be useful to overcome AD instability in case of AD inhibition while, at the same time recovering ammonia. Continuous assays with a microbial fuel cell (MFC) fed with digested pig slurry were performed to evaluate its operation during malfunction periods of the AD reactor and its feasibility as a strategy to recover ammonia, either by introducing VFA pulses in the MFC or by inducing AD inhibition. A microbial community assessment was performed to study MFC changes over its operation when fed with the digestate. RESULTS The MFC achieved COD removal efficiencies of 50% during AD inhibition, reaching a maximum of ammonium removal of 31% (11.19 gN m−2 d−1). A high throughput 16S rRNA gene based sequencing assessment revealed that the anode biofilm was different from the digestate fed, showing a reduction in microbial population diversity in the anode after a 182-day-operation period with digested pig slurry. The main enriched populations in the anode belonged to Bacteroidetes (Flavobacteriaceae), Chloroflexi (fermentative bacteria Anaerolineaceae), Methanosarcinaceae and hydrogenotrophic methanogens belonging to Methanobacteriaceae. CONCLUSION MFCs have proven to be a reliable technology to complement the operation of AD, improving the quality of the effluent and recovering ammonia, particularly during AD inhibition.

Impacts of Rac- and S-metolachlor on cyanobacterial cell integrity and release of microcystins at different nitrogen levels

Pesticide residues and nitrogen overload (which caused cyanobacteria blooms) have been two serious environmental concerns. In particular, chiral pesticides with different structures may have various impacts on cyanobacteria. Nitrogen may affect the behavior between pesticides and cyanobacteria (e.g., increase the adverse effects of pesticides on cyanobacteria). This study evaluated the impacts of Rac- and S-metolachlor on the cell integrity and toxin release of Microcystis aeruginosa cells at different nitrogen levels. The results showed that (both of the configurations: Rac-, S-) metolachlor could inhibit M. aeruginosa cell growth under most conditions, and the inhibition rates were increased with the growing concentrations of nitrogen and metolachlor. However, cyanobacterial growth was promoted in 48 h under environmental relevant condition (1 mg/L metolachlor and 0.15 mg/L nitrogen). Therefore, the water authorities should adjust the treatment parameters to remove possible larger numbers of cyaonbacteria under that condition. On the other hand, the inhibition degree of M. aeruginosa cell growth by S-metolachlor treatments was obviously larger than Rac-metolachlor treatments. S-metolachlor also had a stronger ability in compromising M. aeruginosa cells than Rac-metolachlor treatments. Compared to control samples, more extracellular toxins (12%–86% increases) were detected after 5 mg/L S-metolachlor treatment for 72 h at different nitrogen levels, but the variations of extracellular toxins caused by 5 mg/L Rac-metolachlor addition could be neglected. Consequently, higher concentrations of metolachlor in source waters are harmful to humans, but it may prevent cyanobacterial blooms. However, the potential risks (e.g. build-up of extracellular toxins) should be considered.

Unravelling the active microbial community in a thermophilic anaerobic digester-microbial electrolysis cell coupled system under different conditions

Thermophilic anaerobic digestion (AD) of pig slurry coupled to a microbial electrolysis cell (MEC) with a recirculation loop was studied at lab-scale as a strategy to increase AD stability when submitted to organic and nitrogen overloads. The system performance was studied, with the recirculation loop both connected and disconnected, in terms of AD methane production, chemical oxygen demand removal (COD) and volatile fatty acid (VFA) concentrations. Furthermore, the microbial population was quantitatively and qualitatively assessed through DNA and RNA-based qPCR and high throughput sequencing (MiSeq), respectively to identify the RNA-based active microbial populations from the total DNA-based microbial community composition both in the AD and MEC reactors under different operational conditions. Suppression of the recirculation loop reduced the AD COD removal efficiency (from 40% to 22%) and the methane production (from 0.32 to 0.03 m3 m−3 d−1). Restoring the recirculation loop led to a methane production of 0.55 m3 m−3 d−1 concomitant with maximum MEC COD and ammonium removal efficiencies of 29% and 34%, respectively. Regarding microbial analysis, the composition of the AD and MEC anode populations differed from really active microorganisms. Desulfuromonadaceae was revealed as the most active family in the MEC (18%–19% of the RNA relative abundance), while hydrogenotrophic methanogens (Methanobacteriaceae) dominated the AD biomass.

Overcoming organic and nitrogen overload in thermophilic anaerobic digestion of pig slurry by coupling a microbial electrolysis cell

The combination of the anaerobic digestion (AD) process with a microbial electrolysis cell (MEC) coupled to an ammonia stripping unit as a post-treatment was assessed both in series operation, to improve the quality of the effluent, and in loop configuration recirculating the effluent, to increase the AD robustness. The MEC allowed maintaining the chemical oxygen demand removal of the whole system of 46±5% despite the AD destabilization after doubling the organic and nitrogen loads, while recovering 40±3% of ammonia. The AD-MEC system, in loop configuration, helped to recover the AD (55% increase in methane productivity) and attained a more stable and robust operation. The microbial population assessment revealed an enhancement of AD methanogenic archaea numbers and a shift in eubacterial population. The AD-MEC combined system is a promising strategy for stabilizing AD against organic and nitrogen overloads, while improving the quality of the effluent and recovering nutrients for their reutilization.

Reduction of nitrogen excretion and emission in poultry: A review for organic poultry

ABSTRACTOrganic poultry is an alternative to conventional poultry which is rapidly developing as a response to customers' demand for better food and a cleaner environment. Although organic poultry manure can partially be utilized by organic horticultural producers, litter accumulation as well as excessive nitrogen still remains a challenge to maintain environment pureness, animal, and human health. Compared to conventional poultry, diet formulation without nitrogen overloading in organic poultry is even more complicated due to specific standards and regulations which limit the application of some supplements and imposes specific criteria to the ingredients in use. This is especially valid for methionine provision which supplementation as a crystalline form is only temporarily allowed. This review is focused on the utilization of various protein sources in the preparation of a diet composed of 100% organic ingredients which meet the avian physiology need for methionine, while avoiding protein overload. The potential to use unconventional protein sources such as invertebrates and microbial proteins to achieve optimal amino acid provision is also discussed.