Endogenous Respiration Research Articles

Estimation of nitrifying and heterotrophic bacterial activity in biofilm formed on RAS biofilter carriers by respirometry

Biofilm, the aggregates of microbial layers that are attached on the surface of biofilter carriers, plays a central role in the removal and conversion of nutrients in recirculating aquaculture systems (RAS). The bacterial activity in biofilm involves autotrophic and heterotrophic processes. These biological processes are crucial for the water quality in RAS but are difficult to monitor. In this study, we demonstrate a new method based on intermittent respirometry to selectively estimate bacterial activity in biofilm following a spike in substrate concentration. The method was tested with three different biofilter carriers (extruded polypropylene, injection molded polypropylene and polymeric foam) from moving bed biofilm reactors in a common freshwater RAS. Oxygen consumption rates of biofilm-associated bacteria were measured in closed metabolic chambers under standard conditions. The protocol included sequential flushes of either pure tap water, or tap water spiked with nitrite, ammonium or acetate. The results showed consistent carrier-specific metabolic activities of endogenous respiration, nitrite-oxidizing bacteria (NOB), ammonia-oxidizing bacteria (AOB) and heterotrophic bacteria (HB) in biofilm. The highest activities normalized to volumetric oxygen consumption rates, were found in polymeric foam with values of 677 ± 125, 764 ± 156 and 166 ± 36 g O2·m−3·d−1 for NOB, AOB and HB, respectively. The biofilter performance evaluation based on respirometric data showed satisfactory accordance with the values from substrate degradation batch kinetic tests for all three tested carriers, confirming the feasibility and robustness of the method as a means to assessing biofilter performance. Our study provides an on-site tool in biofilter performance tests and leads to a better understanding of dynamic and relationship between biofiltration and water quality.

Mature landfill leachate treatment in a biological filter using scoria as media

Treatment of leachate and municipal wastewater has extended worldwide using already existing wastewater treatment plants. A biological aerated filter was used to treat leachate from Mexico City's largest landfill together with synthetic wastewater. After achieving stable operation of the filter under organic surface area loading rates of 8.1, 5.3, and 3.1 gCOD/m2·d, landfill leachate was added to the wastewater in volume proportions of 1, 2, and 3%. With leachate, COD removal decreases with increasing leachate concentration. Without leachate, complete nitrification was achieved with the two lower organic surface area loading rates and 93% NH4-N removal was achieved with the highest load. NH4-N removal was 71 and 39% with 2 and 3% leachate, respectively. The oxygen uptake rates decrease with increasing leachate concentration. With 3% leachate, O2 uptake rates for endogenous respiration are higher than for substrate respiration.

In-Situ Sludge Reduction in Membrane-Controlled Anoxic-Oxic-Anoxic Bioreactor: Performance and Mechanism.

Conventional and advanced biological wastewater treatment systems generate excess sludge, which causes socio-economic and environmental issues. This study investigated the performance of membrane-controlled anoxic-oxic-anoxic (AOA) bioreactors for in-situ sludge reduction compared to the conventional anoxic-oxic-oxic membrane bioreactor (MBRcontrol). The membrane units in the AOA bioreactors were operated as anoxic reactors at lower sludge recirculation rates to achieve hydrolysis of extracellular polymeric substances (EPS) and extensive endogenous respiration. Compared to MBRcontrol, the AOA bioreactors operated with 90%, and 80% recirculation rates reduced the sludge growth up to 19% and 30%, respectively. Protein-like components were enriched in AOA bioreactors while fulvic-like components were dominant in MBRcontrol. The growth of Dechloromonas and Zoogloea genra was promoted in AOA bioreactors and thus sludge reduction was facilitated. Metagenomics analysis uncovered that AOA bioreactors exhibited higher proportions of key genes encoding enzymes involved in the glycolysis and denitrification processes, which contributed to the utilization of carbon sources and nitrogen consumption and thus sludge reduction.

Impairment of Respiratory Chain Function and Involvement of Alternative Respiratory Pathway in Mitochondria of Potato Tubers Infected by Pectobacteriumcarotovorum subsp. carotovorum.

The significance of alternative respiratory pathway (AOXs) during the interaction between soft rot bacteria (Pectobacterium carotovorum subsp. carotovorum, (Pcc.)) and potato tubers is well-defined. However, the role of the AOXs in impaired mitochondrial respiratory chain function during the Pcc. infection is yet to be studied. In this study, the results show that with the aggravation of infection of Pcc., the capacity for alternative respiration in mitochondria of potato tubers increased gradually. The mitochondrial membrane potential increased more significantly after infection with Pcc. when the AOXs in potato tubers was partially blocked using salicylhydroxamic acid (SHAM) beforehand. In addition, the activity of complex III decreased more drastically while the activity of complex IV increased more significantly in the partial absence of the AOXs in the mitochondria. Furthermore, the mitochondrial endogenous respiration, mitochondrial respiratory state 3 and respiratory control rate (RCR) decreased more significantly and the value of RCR reached around 1.0 with the aggravation of infection of Pcc. in the partially absence of AOXs in the mitochondria.

Tributyltin in Wastewater: Influence on the Performance of Suspended Growth Biological Processes

The aim of this study was to evaluate the potential effect of tributyltin (TBT) on the performance of suspended-growth biological processes. The influence of TBT was evaluated for (i) the endogenous and exogenous respirations of heterotrophic micro-organisms in laboratory-scale batch reactors, taken from a municipal wastewater treatment plant and (ii) chemical oxygen demand (COD) removal, sludge production and oxygen consumption of a pilot-sale membrane bioreactor (MBR) system inoculated with heterotrophic micro-organisms taken from a MBR system. The batch experiments showed that the presence of TBT was likely to modify the activity of bacterial populations in endogenous conditions. The increase in endogenous oxygen needs suggested an increase in the maintenance requirements, essentially to manage the chemical stress induced by the presence of TBT. If the addition of TBT did not perturb COD removal in an MBR system, it limited sludge production and increased oxygen requirements; it is assumed that these modifications were linked with the necessity for the biomass to adapt in this stressful environment, as reflected by an increase in the maintenance requirements. These results emphasised that the respiratory activity of the bacterial cultures was modified by the presence of TBT, in the sense that an excess of oxygen was required to adapt to this chemical stress.

A novel approach to estimate and control denitrification performance in activated sludge systems with respirogram technology

Respirogram technology has been widely applied for aerobic process, however, the response of respirogram to anoxic denitrification is still unclear. To reveal such response may help to design a new method for the evaluation of the performance of denitrification. The size distribution of flocs measured at different denitrification moments demonstrated a clear expansion of flocs triggered by denitrification, during which higher specific endogenous and quasi-endogenous respiration rates (SOURe and SOURq) were also observed. Furthermore, SOURq increases exponentially with the specific denitrification rate (SDNR), suggesting that there should be a maximum SDNR in conventional activated sludge systems. Based on these findings, an index Rq/t, defined as the ratio of quasi-endogenous (OURq) to maximum respiration rate (OURt), is proposed to estimate the denitrification capacity that higher Rq/t indicates higher denitrification potential, which can be readily obtained without complex measurement or analysis, and it offers a novel and promising respirogram-based approach for denitrification estimation and control by taking measures to extend anoxic time to maintain its value at a high level within a certain range.

Comparative study of the auxins 2,4-D, fluroxypyr, dicamba, MCPA and hydrogen sulphide to inhibit postharvest calyx senescence and maintain internal quality of Valencia oranges

ABSTRACT The synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is sometimes applied commercially to delay calyx senescence, decay and maintain citrus fruit internal quality parameters, however, there is a need to find alternative treatments to reduce calyx senescence and maintain fruit quality during storage. In this study, the effectiveness of pre-storage dips of different auxin formulations, 2-(4-amino-3,5-dichloro-6-fluoropyridin-2yl) oxyacetic acid (fluroxypyr), 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), were assessed against the standard 2,4-D treatment using Valencia oranges at concentrations of 0.2 and 1 mM. Hydrogen sulphide (H2S) a gaseous signalling compound known to delay senescence in postharvest produce was also assessed by fumigating Valencia oranges at 100 µL L−1. During four weeks storage at 20°C, fluroxypyr produced the greatest reduction in calyx abscission, calyx browning and fruit decay and down regulation in endogenous ethylene production, respiration rate and ethanol formation, relative to other treatments. Fluroxypyr dip at 1 mM was most effective, with the 0.2 mM concentration still superior to 2,4-D. MCPA showed only modest activity, while dicamba was ineffective. H2S fumigation significantly reduced calyx deterioration and delayed the loss of internal quality factors. Therefore fluroxypyr or H2S, as a non-auxin treatment, have the potential to replace 2,4-D for commercial use.

Technical Note 8 - Applicability of support medium based of polyurethane foam for systems used to post-treatment of anaerobic effluents

Several technologies have been applied to post-treat anaerobic effluents. For most of those, a rigorous sludge management is needed. In this case, the use of sponge-based packing media in biofilm systems tends to significantly contribute to the minimization of sludge production and effluent quality improvement. Endogenous respiration and predation are important mechanistic processes explaining such improvements, which is related with the increase of the sludge retention time by the retention of biomass within the sponge. Depending on the operational condition, nitrogen removal is also observed in addition to the notorious performance for organic matter removal. Considering the advances for the post-treatment of anaerobic effluents with the use of sponge-based biofilm systems, this Technical Note aim to present: (i) fundamentals of biofilm systems using polyurethane sponge as support media; (ii) full-scale experiences with emerging sponge-based technologies; (iii) performance of sponge-based biofilm systems and operational conditions usually practiced; (iv) a preliminary critical analysis regarding implementation and operational costs; (v) advantages and disadvantages. The potential and limitations regarding the use of sponge-based reactors as post-treatment of anaerobic effluents are finally remarked.

Metabolism of exogenous and endogenous dissolved organic carbon for bacterioplankton production and respiration in reservoirs

全球气候变化和人类活动的加剧影响水生生态系统中溶解性有机碳（DOC）的种类和浓度.浮游细菌生产和呼吸过程对碳源变化的响应，可能影响水体乃至区域的碳循环特征.本研究选取了南京市11座中小型水库，利用碳稳定同位素技术和双端元混合模型定量分析浮游细菌在生产和呼吸代谢过程中对内外碳源的利用.依据DOC中内外碳源的比例，将11座水库划分为内源型水库（内源碳占比>50%）和外源型水库（外源碳占比>50%）.内源型水库DOC浓度、叶绿素a浓度以及营养指数均显著高于外源型水库.分析发现，水体初级生产力提高显著促进了浮游细菌对内源DOC的代谢速率，内源型水库中浮游细菌生产利用内源碳速率提高，而外源型水库中浮游细菌呼吸分解内源碳速率提高.不仅如此，水体初级生产力提高促进外源型水库浮游细菌对DOC的总代谢速率.水体溶解性无机氮和磷与浮游细菌的呼吸作用存在显著的相关关系，内源型水库中随着营养盐浓度升高细菌呼吸作用减弱，而外源型水库中细菌呼吸作用增强.上述研究结果提示，以外源输入为主的水体，随着营养水平提高浮游细菌呼吸过程显著增加，可能引起温室气体释放通量增加.;Global climate change and intensive anthropogenic activities are affecting the variety and contents of dissolved organic carbons (DOC) in the aquatic systems. The potential response of planktonic bacteria to the changing carbon sources could influence the characteristics of carbon cycling in local waterbodies and even regional areas. In this study, eleven small and medium reservoirs were selected to quantificationally analyze the utilization of exogenous and endogenous organic carbon during the bacterial production and respiration using the stable carbon isotope analysis and a two-source mixing model. The eleven reservoirs were subsequently classified into exogenous (exogenous DOC/DOC>50%) and endogenous (endogenous DOC/DOC>50%) reservoirs according to the ratio of the two kinds of DOC sources. Results indicated that the concentrations of DOC and chlorophyll-a (Chl.a) and trophic level index were significantly higher in the endogenous reservoirs than in the exogenous reservoirs. It was observed that the bacterial metabolic rates of endogenous DOC could be significantly elevated with increasing primary productivity in the reservoirs. Specifically, the metabolic rates of endogenous DOC were improved for bacterial production in the endogenous reservoirs and bacterial respiration in the exogenous reservoirs, respectively. Moreover, the overall bacterial metabolic rates of DOC were promoted in the exogenous reservoirs with increasing primary productivity. In addition, a significant relationship was observed between dissolved inorganic nitrogen/phosphorus and bacterial respiration, indicating that the bacterial respiration could be suppressed with increasing nutrition concentration in the endogenous reservoirs but be strengthened with increasing nutrition concentration in the exogenous reservoirs. These results suggested that the release flux of greenhouse gas can be increased owing to the improvement of bacterial respiration with the elevating eutrophication levels in the exogenous reservoirs.

Feasibility of nutrients removal and its pathways using integrated anaerobic-aerobic sequencing batch reactor

This research is a continuous work for a previous study, which contemplates the performance of the proposed bioreactor called integrated anaerobic-aerobic sequencing batch reactor (IAASBR) regarding the nutrients removal. This investigation is accomplished by two schemes; firstly, choosing the best anoxic/oxic time ratio in the Anx/O SBR compartment, secondly, changing the anaerobic hydraulic retention time (HRTan) to enhance the nutrients removal and sludge maintaining in it. The overall removal efficiencies of SCOD and NH3-N were high (94 ± 4% and 91 ± 10% as average) comparing with the overall removal efficiencies of TN and PO43−, where they were 38% and 6%, respectively in the best operating condition (Anx/O = 3.5 h/1.5 h). Nitrate removal by means of endogenous respiration is the most likely pathway. Furthermore, a conceptual corrigendum; DO concentration in the anoxic phase cannot be maintained at the level below 0.5 mg/L in the SBR unless there is an addition of organic matters.

Effects of Heat Waves During Post-natal Development on Mitochondrial and Whole Body Physiology: An Experimental Study in Zebra Finches.

Human-induced climate change is increasing the frequency, duration, and intensity of heat waves and exposure to these extreme temperatures impacts individual physiology and performance (e.g., metabolism, water balance, and growth). These traits may be susceptible to thermal conditions experienced during embryonic development, but experiments focusing on post-natal development are scant. Documented effects of heat waves on whole-body metabolism may reflect changes in mitochondrial function, but most studies do not measure physiological traits at both the cellular and whole organism levels. Here, we exposed nests of zebra finches to experimentally simulated heat waves for 18 days after hatching and measured body mass, growth rate, whole-body metabolic rate, body temperature, wet thermal conductance, evaporative water loss, and relative water economy of chicks at three ages corresponding to ectothermic (day 5), poikilothermic (day 12), and homoeothermic (day 50) stages. Additionally, we measured mitochondrial bioenergetics of blood cells 80 days post-hatch. While early-life exposure to heat wave conditions did not impact whole body metabolic and hygric physiology, body temperature was lower for birds from heated compared with control nests at both 12 and 50 days of age. There was also an effect of nest heating at the cellular level, with mitochondria from heated birds having higher endogenous and proton-leak related respiration, although oxidative phosphorylation, maximum respiratory capacity, and coupling efficiency were not impacted. Our results suggest that early-life exposure to high ambient temperature induces programming effects on cellular-level and thermal physiology that may not be apparent for whole-animal metabolism.

Analyzing sensitivity of the energy metabolism in the tissues of the heart, liver, kidney, and blood lymphocytes in rats to the effect of local vibration and pharmacological protection by a succinate-containing antihypoxanth

Introduction. Modern technological processes that generate ultra- and infrasound, electromagnetic, vibration-noise radiation significantly exceed the background effects and inevitably create an unfavorable technogenic load on the human body. A special place is occupied by vibration, primarily associated with such professional groups as mining enterprises, gold and diamond processing plants, aircraft plants, thermal power plants and hydroelectric power plants, and aluminum industry enterprises. Vibration exposure leads to a number of biochemical disorders in the homeostasis system. Mitochondrial dysfunctions are among the leading elements in the hierarchy of pathogenesis of many pathological syndromes and diseases. The aim of the study was an experimental analysis of tissue-specific features of the myocardium, kidneys, liver energy production system activity as well as the enzyme status of rat lymphocytes in relation to the activity of succinate dehydrogenase (SDH) on the background of 7 episodes of local vibration with a frequency of 27-30 Hz for 90 minutes daily before and after protection with succinate-containing antihypoxant "Yantar-cardio" at a dose of 100 mg/kg/day. Materials and methods. The study of the energy-dependent reactions of the native mitochondria of the organs was carried out by the polarographic method using a closed Clark-type membrane electrode. The activity of SDH of rat blood lymphocytes was studied by a modified method of quantitative cytochemical analysis. Results. Functional rearrangement in the respiratory chain (RC) of the mitochondria confirmed the NAD-dependent site's inhibition and activation of the oxidation system of endogenous succinic acid, most pronounced in the myocardial tissue. On the vibration background, the specific SDH activity of lymphocytes (Q) significantly increased by 52%, and the variability (V) - by three times. The use of "Yantar-cardio" limited the growth rate of endogenous respiration of the most significant in the heart (70%, p<0.05), restored oxidative and conjugating activity NAD-dependent link of RC, improve the structure and condition of the cell population of lymphocytes based on their energy status and warned the mismatch of the leading parameters of the population variability of the cellular pool of blood lymphocytes in experimental animals. Conclusions. The intensity of vibration-mediated bioenergetic hypoxia in the form of inhibition of the NAD-dependent link of the respiratory chain and activation of the endogenous succinic acid oxidation system is tissue-specific and is most pronounced in the myocardial tissue. The succinic acid oxidation system is highly sensitive to vibration effects and a pharmacological drug that supports the function of RC under conditions of the stress of the homeostatic functions of tissues involved in the pathological process.

ACTIVITY OF THE MICROSOMAL OXIDATION SYSTEM IN RAT LIVER UNDER THE INFLUENCE OF SODIUM FLUORIDE

Summary. The pathogenesis of fluoride intoxication at the molecular, cellular and functional levels has not been sufficiently studied. There are very few modern data on these issues, so they are contradictory, since the effects of this trace element are multifaceted and cannot be characterized unambiguously.
 The aim of the study – to learn the state of the monooxygenase system of rat hepatocytes under conditions of the formation of fluoride intoxication.
 Materials and Methods. In the experiment, we used 30 sexually mature rats (N=30) of the Wistar population weighing 200–210 g for 1.5 months. Sodium fluoride solution was administered orally at doses of 1/10 DL50, which was 20 mg/kg of animal body weight.
 Results. The results of experiments on the study of oxygen consumption by rat liver microsomes under fluoride intoxication indicated that the rate of endogenous respiration of microsomes, the rate of NADPH oxidation, the rate of NADH oxidation in the presence of EDTA, and the rate of lipid peroxidation increase under the influence of fluorides. Sodium fluoride stimulated an increase in all parameters of microsomal oxidation, except for cytochrome b5. It should be assumed that in this case there is an increase in the generation of reactive oxygen species, free radicals, which stimulate the development of free radical processes in the body and are, most likely, the leading link in oxidative stress.
 Conclusions. These changes indicate a violation of the bioenergetics of hepatocytes associated with the mitochondrial apparatus and the development of hypoxic processes, which lead to a decrease in the activity of redox reactions occurring at the level of intracellular membranes and organelles.

The role of beneficial microorganisms in an anoxic-oxic (AO) process for treatment of ammonium-rich landfill leachates: Nitrogen removal and excess sludge reduction

This study comprehensively investigated the performances of the anoxic-oxic processes with (AO-M) and without the beneficial microorganisms (AO-N) for the treatment of the ammonium-rich landfill leachates. Although the AO-M had the lower concentrations of the mixed liquor suspended solids (MLSS, 3230 mg L−1) and mixed liquor volatile suspended solids (MLVSS, 2480 mg L−1) compared to the AO-N process (MLSS = 7790 mg L−1; MLVSS = 5260 mg L−1), dissolved organic compounds and nitrogen species could be more effectively removed using the AO-M process (removal efficiency of dissolved organic carbon (DOC) = 99.0%; removal efficiency of total nitrogen (TN) = 79.2%) than the AO-N process (removal efficiency of DOC = 98.6%; removal efficiency of TN = 75.1%). Moreover, the excess sludge production was also less pronounced for the AO-M process than the AO-N process since the enhanced endogenous respiration and relative enzyme activity of microorganisms in the oxic bioreactor of the AO-M process via the inoculation of the beneficial microorganisms reduced the excess sludge production significantly. These observations suggest that the variations in the relative abundances of microorganisms through the inoculation of the beneficial microorganisms into the sludge digestion tank might enhance the removal of nitrogen species and the reduction of the excess sludge production during the during the treatment of the ammonium-rich landfill leachates.

Investigating organic nitrogen production in activated sludge process: Size fraction and biodegradability

The effect of sludge retention time (SRT) on the production of organic nitrogen (ON) fractions (particulate, colloidal and soluble) and the biodegradability of produced soluble ON in an activated sludge process was investigated. Synthetic wastewater with no ON was fed to the four laboratory-scale reactors operated at SRTs of 2, 5, 10 and 20 d, respectively. Effluent ON from each reactor was fractionated into particulate, colloidal, and soluble ON (pON, cON, and sON). The effluent total ON contained 5.7 to 11.9 mg/L pON, 3.6 to 3.8 mg/L cON, and 2.3 to 4.6 mg/L sON. cON fraction can be larger than sON fraction in the secondary effluent. Therefore, besides focusing on sON, water resource recovery facilities aiming to meet stricter effluent TN limits should also identify appropriate technologies to target cON. More than 50% of effluent sON was biodegradable under SRTs of 2, 5, and 10 d but the biodegradability decreased to 31% at 20-d SRT. Large fractions of non-biodegradable sON (69%) at SRT of 20-d could be contributed by extracellular polymeric substances and soluble microbial products, specifically biomass associated products due to endogenous respiration. Thus, sON generated at long SRTs may take longer to decompose in receiving waters.

Explore the sludge stabilization process in sludge drying bed by modeling study from mesocosm experiments

Sludge drying bed (SDB) treatment is a valuable alternative to conventional sludge treatment methods. However, changes in sludge hydrotexture during dewatering present a barrier for direct modeling of the SDB process. This study proposes a modeling strategy to simulate the sludge stabilization process in SDB treatment by separating sludge dewatering and sludge solids stabilization into independent processes. Two cell decay theories widely used by activated sludge models (ASM), death-regeneration concept and endogenous respiration theory, are compared to describe the biokinetic processes of sludge digestion. Both cell decay theories are found to adequately describe effluent total COD, NH4–N, NO3–N, and sludge layer composition, but have pronounced differences in describing effluent COD compositions. Results show that natural aeration does not maintain adequate aerobic/anoxic sludge digestion within the sludge layer to fully nitrify NH4–N released by cell decay. Results also indicate that the kinetics of sludge digestion are adaptable over time, indicating the need to adopt lumped values for biokinetic simulations. While lowered sludge dewatering rates (outflow) can increase biodegradable COD for cell metabolism, increased sludge loading rates (inflow) lead to higher effluent COD and NH4–N concentrations. Contrary to conventional judgement, this study demonstrates the merit of sludge layer formation to reduce leaching loss of biodegradable COD. Overall, the proposed modeling strategy is proven capable of simulating deposited sludge digestion processes in an SDB.

ABACO: A New Model of Microalgae-Bacteria Consortia for Biological Treatment of Wastewaters

Microalgae-bacteria consortia have been proposed as alternatives to conventional biological processes to treat different types of wastewaters, including animal slurry. In this work, a microalgae-bacteria consortia (ABACO) model for wastewater treatment is proposed, it being calibrated and validated using pig slurry. The model includes the most relevant features of microalgae, such as light dependence, endogenous respiration, and growth and nutrient consumption as a function of nutrient availability (especially inorganic carbon), in addition to the already reported features of heterotrophic and nitrifying bacteria. The interrelation between the different populations is also included in the model, in addition to the simultaneous release and consumption of the most relevant compounds, such as oxygen and carbon dioxide. The implementation of the model has been performed in MATLAB software; the calibration of model parameters was carried out using genetic algorithms. The ABACO model allows one to simulate the dynamics of different components in the system, and the relative proportions of microalgae, heterotrophic bacteria, and nitrifying bacteria. The percentage of each microbial population obtained with the model was confirmed by respirometric techniques. The proposed model is a powerful tool for the development of microalgae-related wastewater treatment processes, both to maximize the production of microalgal biomass and to optimize the wastewater treatment capacity.

Wastewater COD characterization: RBCOD and SBCOD characterization analysis methods

Wastewater characterization is the basis for process design and operation optimization of wastewater treatment plants (WWTPs). In this work, a comprehensive study of the respirometry method has been performed to evaluate the biodegradable organic matters of wastewater. First, the optimal initial substrate to biomass ratio (S0/X0) was confirmed. Second, under the optimal S0/X0, the degradation curves of wastewater carbon oxygen demand (COD) components rapidly biodegradable COD (RBCOD) and slowly biodegradable COD (SBCOD) were obtained. Third, the Mann–Kendall test was performed to confirm the time point (t2) when endogenous respiration levels were reached, and the hydrolysis model was used to determine the time point (t1) of the SBCOD degradation stage. Considering the results, an adequate wastewater COD characterization method for RBCOD and SBCOD has been proposed. This study provides strong support to carry out effective and feasible process design, process diagnosis and optimization capability, can help achieve refined and stable operational management of WWTPs.

Acute inhibitory impact of sulfamethoxazole on mixed microbial culture: Kinetic analysis of substrate utilization biopolymer storage nitrification and endogenous respiration

This study explored acute impact of sulfamethoxazole (SMX) on mixed microbial culture by means of respirometric analysis and modeling of process kinetics. The culture was developed in a laboratory-scale activated sludge reactor fed with peptone mixture. The reactor was maintained at steady state at SRT of 10 days allowing the culture to sustain both heterotrophic and autotrophic fractions. Response of biomass under pulse feeding of 50 mg/L and 200 mg/L SMX was determined by monitoring corresponding oxygen uptake rate (OUR) profiles. Model calibration of OUR profiles enabled numerical assessment of the repressive action of SMX on all processes, heterotrophic growth; substrate binding and storage; two-step nitrification; endogenous respiration. The maximum growth rate of Nitrite Oxidizing Bacteria (NOB) was reduced by 35 %, compared to a slight decrease for Ammonia Oxidizing Bacteria (AOB). Upon exposure, significant substrate binding of around 40–50 % by SMX was observed, drastically reducing the amount of available carbon source for microbial growth. Substrate was directed towards storage with a 15–25% increase in the maximum storage rate. Pulse exposure to 200 mg/L of SMX induced a 50 % increase in the endogenous respiration rate, presumably to meet a higher need for maintenance energy potential for resistance and survival.

Enhancing methane production of synthetic brewery water with granular activated carbon modified with nanoscale zero-valent iron (NZVI) in anaerobic system

Anaerobic digestion is an effective treatment technology for wastewater. However, long HRT and low CH4 production limit the application of anaerobic treatment. Iron-based materials, carbon-based materials and Fe-C composite particles have been used in anaerobic processes. However, the strengthening effect of Fe-C composite particles on anaerobic systems requires further research. In this study, granular activated carbon (GAC) loaded with nanoscale zero-valent iron (NZVI) was prepared by a co-precipitation method and its morphology was characterized. Different concentrations of GAC-NZVI particles were used in the batch experiment to study the enhancing effect of the anaerobic biological treatment process. The water quality, sludge properties and microbial community were analyzed. The degradation rate of COD and total CH4 production increased by 9.38% and 14.29% with particles at a concentration of 1000 mg/L, respectively. The average methane yield was 169.86 mL CH4/g-COD removed, which was 9.39% higher than that of the control. The measurement results of extracellular polymeric substance (EPS), conductivity, cyclic voltammetry (CV) and Fe concentration indicated that the composite particles showed excellent electrical conductivity and promoted microorganism metabolism, which accelerated the use of substrates and methane generation. The 3-dimensional excitation (Ex) – emission (Em) matrix (3D-EEM) fluorescence spectroscopy of soluble microbial product (SMP) and EPS indicated that the particles could affect the endogenous respiration of microorganisms. Microbial community analysis revealed that the dominant genus Methanothrix (acetoclastic methanogens) increased by 13.32%, which could strengthen acetoclastic methanogenesis and lead to higher CH4 production. The abundance of hydrogenotrophic archaea decreased after the addition of GAC-NZVI. These results provide an alternate method for enhancing anaerobic wastewater treatment using conductive particles.