Long-term Continuous Experiment Research Articles

A Noninvasive Quantitative Method for Evaluating Intestinal Exposure to Microplastics Based on the Excretion and Metabolism Patterns of Microplastics and Their Additives.

Microplastics (MPs) pose potential health risks to the intestinal tract and gut microbiota, a topic that has garnered significant attention. However, the absence of quantitative assessment methods for human gut MP exposure impedes related health risk assessments. Here, we performed long-term continuous exposure experiments on mice using MPs that mimic actual human exposure characteristics. The daily excretion of fecal MPs and the concentrations of phthalates (PAEs) and their metabolites (mPAEs) in serum and urine were detected. The cumulative excretion rate of fecal MPs remains stable at about 93%. A significant linear correlation was observed between MP exposure and concentration of mPAEs in urine for both low MP (LMP; 150 μg of MPs/d) (R2 = 0.90) and high MP (HMP; 360 μg of MPs/d) groups (R2 = 0.97). Moreover, a strong correlation was found between daily PAEs exposure and total MP-associated PAEs exposure in both LMP (R2 = 0.77) and HMP (R2 = 0.88) groups. Based on these findings, we established a noninvasive model and evaluated multiple MP exposure parameters in the human gut across 6 continents, 30 countries, and 133 individuals. This study offers novel insights for the quantitative assessment of in vivo MP exposure and provides technical support for assessing the health risks of MPs.

Methane gas sensor based on direct absorption spectroscopy and the laser self-heating effect.

In this paper, a methane detection sensor based on direct absorption spectroscopy and the self-heating effect of lasers is proposed, which abandons the traditional method of relying on a thermoelectric cooler (TEC) to ensure stable gas concentration detection. The sensor can achieve stable concentration measurement in the temperature range of -10∘ to 40°C without the need for a TEC, which greatly simplifies the structure of the sensor and reduces the cost. The results of gas concentration calibration experiments show that the sensor has a good linear correlation (R 2=0.9993). Long-term continuous detection experiments show that the sensor maintains a relative detection error between -2.667% and 4.3% over the full test temperature range. In addition, signal-to-noise ratio analysis experiments further determine that the minimum detection limit of the sensor for methane gas is 27.33p p m⋅m (1σ). Given its advantages of simple structure, low cost, high accuracy, and stability, this methane detection sensor is well suited for natural gas leakage monitoring in home environments and can also be widely used in industrial safety detection and environmental monitoring applications. This technology provides a cost-effective solution for domestic and industrial methane detection.

Effect of different organic loads on the performance and microbial community mechanism of dry anaerobic digestion

In this study, the vertical continuous push-flow dry anaerobic digestion (AD) reactor was developed independently. Typical agricultural organic waste straw and cow dung were used as raw materials in this paper to carry out long-term continuous mixed dry AD experiments on a controlled laboratory scale. The experimental results showed that the system was in low-stress operation at an organic load rate (OLR) of 3 g VS L-1 d-1, the VS methane production rate was located at 225 ∼ 272 mL CH4 g VS-1, and the volumetric methane production rate was located at 0.95 ± 0.08 L (L·d)-1, and the combination of the volumetric methane production rate, VS methane production rate, methane content of the gas, and the VS removal rate showed that the system's operational performance in this stage was in the best condition in the whole set of experiments. When the OLR reached 25 g VS L-1 d-1, the content of VFAs all began to climb rapidly above 8000 mg/L, with the content of acetic acid increasing most significantly due to the fact that the activity of acetic acid-type methanogenic bacteria was the first to be inhibited. Eventually, because of the kinetic differences between the hydrolytic acidifying bacteria and the methanogenic archaea, the final acidification destabilisation of the anaerobic digestion reactor occurred and the system was irreversibly destabilised. The system performance at this stage was in the best condition in the whole set of experiments. The study of microbial community succession and metabolic mechanisms showed that Methanoculleus and Methanobacterium play a key role in sustaining methane production, and the increased abundance and dominance of hydrogen methanogens implies that methane is produced via the hydrogen methanogenic pathway under high organic loading conditions.

Enhanced electrochemically mediated calcium phosphate precipitation for phosphorus recovery simply by carbon felt barrier cathode

Phosphorus removal and recovery from wastewater is crucial for environmental pollution control and sustainable phosphorus fertilizer production. Electrochemical technologies are promising, but disadvantages like high energy consumption remain. Here, we improved the electrochemical system's performance by placing carbon felt in front of the cathode at a distance of 3 mm with a current density as low as 1 A/m2, which separated the reactor into two parts: near the cathode area and bulk solution. The phosphorus removal near the cathode can reach 75 % in 1 h, while it takes 8 h for the bulk solution to achieve 75 % removal efficiency. The main reason for the enhancement was the retention of OH− ions between the cathode and carbon felt with enriched calcium ions, providing an appropriate environment for calcium phosphate precipitation. The functional groups on the carbon felt surface were another reason for the retention of OH− ions. Furthermore, our results show that the carbon felt system has considerable stability under different mass transfer efficiencies. By adjusting the stirring rate, we could control the proportion of precipitation on the carbon felt or cathode, thereby reducing the scaling on the cathode and avoiding significantly reduced removal efficiency. A long-term continuous flow experiment also illustrated this. Interestingly, we observed that the phosphorus removal had a specific correlation with pH and fit an empirical formula. Therefore, we could estimate the removal efficiency by simply measuring the effluent pH of the solution after treatment. In treating real phosphorus-rich wastewater, the carbon felt system removed 63 %–87 % of 1500 mg/L P after 8 h to 48 h treatment at 20 A/m2, respectively, resulting in lower energy consumption (31 kWh/kg P, 8 h) compared to the system without carbon felt (48 kWh/kg P, 8 h). This study provides a simple yet efficient method for enhancing electrochemical phosphorus recovery.

New evidence of the arsenic uptake and translocation in As-hyperaccumulator fern Pteris cretica using a modified hydroponic system

Pteris cretica is a native fern in temperate regions known for its ability to hyperaccumulate arsenic (As). However, the uptake and translocation of As in hydroponic conditions have remained poorly understood. In this study, we modified a hydroponic cultivation system, combining 24 plants into one unit, to suppress individual differences among plants and evaluate As uptake and translocation in P. cretica. The 7-day short-term As removal experiment results revealed that the As uptake rate by P. cretica appears to be dependent on the initial As concentration in the hydroponic medium. Furthermore, the rhizomes play a role in regulating As translocation from roots to fronds in P. cretica was observed. In the 27-day long-term continuous flow experiment, approximately 1 mg/d of As was removed by P. cretica with 200 μg/L As applied. Moreover, the long-term translocation factor (TF) between rhizomes and roots and between fronds and rhizomes from the 27-day long-term continuous flow experiment demonstrated the same pattern as the short-term TF from the 7-day short-term As removal experiment, further indicating the role of rhizomes in regulating As translocation from roots to fronds in P. cretica.

Response of partial nitritation-anammox process to substrate concentration and temperature variations in a single-stage airlift circulation system: Performance and microbial community dynamics

Low-strength ammonia and temperature challenge the application of partial nitritation-anammox (PNA) process in the treatment of mainstream wastewater. In this study, we operated a single-stage PNA process under various substrate concentrations (250, 150, and 50 mg/L) and temperatures (32, 25, 15 °C). Changes in nitrogen removal performance, biochemical reaction rate, and specific activity were investigated via the long-term continuous experiment and batch tests. Microbial diversity, community structure, and metabolic pathways in response to the various conditions were explored. When the temperature declined to 15 °C, the nitrogen removal efficiency decreased from 83.9 % to 51.5 % with the influent of 50 mg-NH4/L, while the nitrogen removal rate dropped to 0.33 kg N/m3/d. Meanwhile, the relative abundances of Candidatus Brocadia and Nitrosomonas reached 14.1 % and 1.5 %, respectively. The results showed that the mechanisms of performance degradation caused by low ammonia concentration and low temperature were significantly different. Moreover, the substrate concentration mainly affected the reaction rate and activity of anammox bacteria and hardly affected the relative abundance of functional bacteria. But temperature reduction resulted in a significant decline in the relative abundance of anammox bacteria. Changes in metabolic pathways suggested that this PNA system may respond to low substrate concentrations and low temperatures by facilitating substance transport and reducing energy consumption. These results provide a deep insight into the microbial community dynamics and interactions in the treatment of mainstream wastewater by PNA process.

A Dual Media Filter using Zeolite and Mortar for the Efficient Removal of Heavy Metals in Stormwater Runoff

Stormwater runoff from expressways contains high concentrations of various heavy metals. However, heavy metal removal in most current runoff treatment facilities, using infiltration and filtration, is limited and poses substantial risks. Therefore, this study proposes and evaluates a dual media system of mortar and Na-zeolite, which are inexpensive and readily available, using long-term continuous column experiments for the removal of heavy metals. The results showed significant Cu2+ removal with Na-zeolites that was improved by the addition of a thin mortar layer, while a sand layer provided negligible improvements. The removal of Cu was further enhanced by increasing mortar layer thickness. The removal of Cu2+, Zn2+, Fe3+, and Ni2+ in a mixture was enhanced as the mortar layer’s thickness increased, while the contribution of Na-zeolite was significant in 232 h experiments with a fixed empty bed contact time (EBCT) of 1.8 min. Moreover, the media were not saturated with Fe throughout the operation period. These results suggest that the dual media system is cost-effective and efficient in the removal of heavy metals from stormwater runoff via precipitation, filtration, and adsorption with a short EBCT.

PMo12 as a redox mediator for bio-reduction of Cr(VI): Promotor or inhibitor?

Slow reduction rate and low reduction ability were the main limitations of bio-reduction of Cr(VI). As an efficient redox mediator, how phosphomolybdic acid (PMo12) affected bio-reduction of Cr(VI) was worthy of exploration. In this study, short-term and long-term effects of PMo12 on Cr(VI) reduction were investigated to reveal the relevant mechanism. After evaluating the short-term effect of PMo12 concentration from 0.05 to 1.00 mM on Cr(VI) bio-reduction, 0.50 mM was found to be optimum by improving Cr(VI) reduction rate by 16.3 % and microbial electron transport system activity (ETSA) by 43.0 % with Cr(VI) reduction efficiency of 100 % in short-term (22 h) batch experiments. By contrast, in long-term (28 days) continuous flow experiments, 0.50 mM PMo12 exhibited serious inhibition on Cr(VI) bio-reduction. The cumulative toxicity of Mo, strong oxidative stress (reactive oxygen species increased by 16.5 %), the inhibition of extracellular polymeric substances production and the reduction of microbial activity were proved to be the main inhibition mechanism. In terms of microbial electron transport system, the main electron carriers including flavin mononucleotide (FMN), nitrate reductase (NAR), nitrite reductase (NIR) were seriously inhibited. BugBase analysis confirmed that the relative abundance of biofilm forming bacteria decreased after PMo12 addition, and the relative abundance of oxidative stress tolerance bacteria continued to increase.

Halophilic Martelella sp. AD-3 enhanced phenanthrene degradation in a bioaugmented activated sludge system through syntrophic interaction

Polycyclic aromatic hydrocarbons (PAHs) are a group of common recalcitrant pollutant in industrial saline wastewater that raised significant concerns, whereas traditional activated sludge (AS) has limited tolerance to high salinity and PAHs toxicity, restricting its capacity to degrade PAHs. It is therefore urgent to develop a bioaugmented sludge (BS) system to aid in the effective degradation of these types of compounds under saline condition. In this study, a novel bioaugmentation strategy was developed by using halophilic Martelella sp. AD-3 for effectively augmented phenanthrene (PHE) degradation under 3% salinity. It was found that a 0.5∼1.5% (w/w) ratio of strain AD-3 to activated sludge was optimal for achieving high PHE degradation activity of the BS system with degradation rates reaching 2.2 mg⋅gVSS−1⋅h−1, nearly 25 times that of the AS system. Although 1-hydroxy-2-naphthoic acid (1H2N) was accumulated obviously, the mineralization of PHE was more complete in the BS system. Reads-based metagenomic coupled metatranscriptomic analysis revealed that the expression values of ndoB, encoding a dioxygenase associated with PHE ring-cleavage, was 5600-fold higher in the BS system than in the AS system. Metagenome assembly showed the members of the Corynebacterium and Alcaligenes genera were abundant in the strain AD-3 bioaugmented BS system with expression of 10.3±1.8% and 1.9±0.26%, respectively. Moreover, phdI and nahG accused for metabolism of 1H2N have been annotated in both above two genera. Degradation assays of intermediates of PHE confirmed that the activated sludge actually possessed considerable degradation capacity for downstream intermediates of PHE including 1H2N. The degradation capacity ratio of 1H2N to PHE was 87% in BS system, while it was 26% in strain AD-3. These results indicated that strain AD-3 contributed mainly in transforming PHE to 1H2N in BS system, while species in activated sludge utilized 1H2N as substrate to grow, thus establishing a syntrophic interaction with strain AD-3 and achieving the complete mineralization of PHE. Long-term continuous experiment confirmed a stable PHE removal efficiency of 93% and few 1H2N accumulation in BS SBR system. This study demonstrated an effective bioaugmented strategy for the bioremediation of saline wastewater containing PAHs.

Simultaneous removal of aromatic pollutants and nitrate at high concentrations by hypersaline denitrification:Long-term continuous experiments investigation

If we can use toxic aromatic compounds as supplementary carbon source, the simultaneous removal of nitrate (NO3−) and aromatic compounds may be achieved at much lower chemical costs. This study uses the expanded granular sludge bed (EGSB) reactors to investigate the hypersaline (> 3%) denitrification performance, the removal of aromatic compounds, i.e., aniline, phenol, and their mixture, and the mechanisms involved in. The four reactors exhibit high removal efficiency of NO3− (> 92.8%) and aromatic compounds (> 73.9%) at 0–1200 mg/L of aromatic compounds. The formation of toxic intermediates such as catechol and azo dyes is revealed by gas chromatography mass spectrometry (GC–MS) with and without N,O-Bis(trimethylsilyl) trifluoroacetamide (BSTFA) derivation, and their toxic effects lead to the lower cell survival ratios after exposing to phenol (64.2% ∼ 68.9%) than to aniline and mixture (72.7% ∼ 78.0%). The stable performance is associated with the more secretion of extracellular polymeric substances (EPS) and the adsorption of pollutants on EPS, and this was indicated from the higher fluorescence intensity in three-dimensional excitation-emission matrix (3D-EEM). Moreover, the Halomonas and Azoarcus show high abundance and play important roles in the removal of both NO3− and aromatic compounds. Besides, quantitative real time PCR (RT-qPCR) results demonstrate the key role of highly abundant nosZ and nirS genes in denitrification. The toxic organics in industrial wastewaters are potentially feasible carbon sources for denitrification even under high-salinity stress.

Autotrophic denitrification of NO for effectively recovering N2O through using thiosulfate as sole electron donor

To reclaim nitrous oxide (N2O) as an energy resource economically, this study developed an autotrophic denitrification-based system with thiosulfate (S2O32-) and nitric oxide (NO) as electron donor and acceptor, respectively. NO from flue gases is absorbed on Fe(II)EDTA to overcome its low solubility in liquid phase by forming Fe(II)EDTA-NO. Short-term batch tests and long-term continuous experiments were conducted to investigate the N2O production profile and NO conversion efficiency from thiosulfate-based denitrification under varied Fe (II)EDTA-NO conditions (5–20 mM). Up to 39% of NO was converted to gaseous N2O at 20 mM Fe(II)EDTA-NO amid batch test due to the inhibition of key enzymatic activities by NO and the acidic conditions following thiosulfate oxidation. Higher Fe(II)EDTA-NO levels induced lower enzymatic activities with N2OR being suppressed harder than NOR. Microbial diversity was reduced in the continuous thiosulfate-driven Fe(II)EDTA-NO-based denitrification system. NO-resistant bacteria and sulfide-tolerant denitrifiers were enriched, facilitating NO conversion to N2O thereafter.

Effects of CO2 enrichment on the anaerobic digestion of sewage sludge in continuously operated fermenters

The effect of CO2 enrichment in sewage sludge anaerobic digestion (AD) as a potential strategy to improve the biogas yield was assessed at increasing organic loading rates (OLR). Effects on process performance and resilience were evaluated in long-term continuous AD experiments at lab-scale. The specific methane production (SMP) was sustainably enhanced in the test digester compared to a control at elevated OLRs, reaching an increase of 6 ± 12% on average at the highest OLR tested (4.0 kgVS/(m3·d)). The reduction of CO2 via homoacetogenesis, facilitating acetoclastic CH4 formation is proposed as the dominant conversion pathway. Results suggest that sufficient load of easily degradable substances is a prerequisite for intrinsic formation of the reduction equivalent H2 via acidogenesis. The enhanced resilience of the process under CO2-enriched conditions in response to acid accumulation further qualifies this approach as a viable option for improving AD performance by converting a waste stream into a valuable product.

A new method for determining air permeabilities of wood-based panels

In this study, a new apparatus for measuring the air permeability of wood-based panel specimens without using water displacement was developed with the aim of decreasing the influence of variation in atmospheric pressure on permeability measurement. Validation experiments were conducted using plywood, oriented strand board (OSB), particleboard, and medium-density fiberboard (MDF) panels and a control specimen sealed with an epoxy resin. The background (leakage) flow of the apparatus was evaluated based on the experimental results of the control specimen. A methodology for the determination of air permeability based on Darcy’s law for gases and the evaluated background flow rate was proposed. The results of the current study were compared with those obtained in a previous study, indicating that the new method provides valid measurements for wood-based panels with high and low air permeability. No significant influence of variation in atmospheric pressure on the experimental results was observed, suggesting that the proposed method is suitable for a long-term continuous experiment for evaluating a specimen with extremely low permeability

Catalytic Wet Peroxide Oxidation of Cylindrospermopsin over Magnetite in a Continuous Fixed-Bed Reactor

The development of cost-efficient and environmentally friendly technologies for the removal of cyanotoxins from water is crucial, given the increasingly frequent appearance of toxic cyanobacterial blooms. In this work, the application of catalytic wet peroxide oxidation (CWPO) promoted by natural magnetite for the removal of the highly toxic cyanotoxin cylindrospermopsin (CYN) has been investigated. A fixed-bed reactor packed with magnetite powder and granules was used to treat a continuous flow of CYN-bearing water. Experiments were carried out under ambient conditions and circumneutral pH (pH0 = 5). The effect of the main variables of the process, viz. magnetite load (8–14 g), feed flow rate (0.1–0.25 mL min−1), H2O2 dose (0.5–8 mg L−1) and initial CYN concentration (25–100 μg L−1), were systematically analyzed. CYN conversion values and kinetic constants were calculated to evaluate the feasibility of the catalytic system. The process was highly effective in the removal of the cyanotoxin, achieving up to 80% CYN conversion under optimized conditions (flow rate = 0.2 mL min−1, [H2O2]0 = 5 mg L−1, WFe3O4 = 14 g, pH0 = 5, T = 25 °C). It also showed reasonable activity (~55% CYN conversion) in two real samples (pond and river water). The decay on CYN conversion in these cases was mainly due to the scavenging of hydroxyl radicals by the co-existing species present in the matrices. Remarkably, the catalytic system showed high stability with limited iron leaching (the iron leached at the end of the experiments represented less than 0.2 wt.% of the catalyst’s initial iron content) in all cases. Its stability was further confirmed in a long-term continuous experiment (60 h time on stream). Furthermore, the magnetite granules at the top layer of the packed bed avoided the loss of magnetite powder from the reactor, confirming the suitability of the system for continuous long-term application.

Mesophilic methane fermentation performance and ammonia inhibition of fish processing wastewater treatment using a self-agitated anaerobic baffled reactor

The performance of the self-agitated anaerobic baffled reactor (SA-ABR) was investigated by increasing the organic loading rates (OLRs) from 0.46 to 9.50 g-COD/L/d. A good performance was achieved by the SA-ABR for the treatment of fish processing wastewater (FPW). The maximum OLR was 6.77 g-COD/L/d and the biogas production rate reached 2.16 L/L-reactor/d with a methane content of 69% at this OLR. The COD, carbohydrate, protein, lipid and VS removal efficiencies were as high as 64, 65, 68, 78 and 79%, respectively. Ammonia inhibition was assumed with inhibition concentrations of 10% (IC10) and 20% (IC20) at 4140 and 5780 mg/L. However, it was found that the reactor could tolerate ammonia at a high concentration range of 4500–6373 mg/L after a long-term continuous experiment. Ammonia inhibition was addressed by diluting the substrate and the sludge in the reactor with tap water.

Management duration controls the synergistic effect of tillage, cover crop, and nitrogen rate on cotton yield and yield stability

Resilient agroecosystems are foundational for stable and profitable food, feed, and fiber production in the face of increasing climatic perturbations and environmental stresses. Enhanced soil and environmental benefits of cover crops applied to conservation tillage systems has been well documented. However, little is known about the timespan for interactions of no tillage and cover crops to achieve enhanced yield and yield stability while lowering N fertilization. Using a long-term continuous cotton experiment in southeastern USA, we analyzed yield data collected from 1986 to 2018 from 32 management systems to identify how management duration controls the synergistic effect of applied mineral N rates (0, 34, 67, and 101 kg ha−1), cover crops (no cover [NC], hairy vetch [HV], crimson clover [CC], and winter wheat [WW]), and tillage practices (no tillage [NT] and conventional tillage [CT]) on cotton yield and yield stability. Yield stability was analyzed using Finlay—Wilkinson regression model, Wricke’s Ecovalance, and coefficient of variation, and a mixed model approach was used to compare the yield and yield stability within three time phases (1−10 years, 11–20 years, and 21−33 years) at the 95% confidence level. During the initial 10 yr period (phase 1) CT resulted in greater cotton yield (7%) and yield stability than NT. However, in phase 2 (11–20 years) and phase 3 (21−33 years) NT led to greater yield (7%) and yield stability for almost all cover crop × N interactions, except for zero N following NC and WW. Increased N during the initial phase reduced both yield and yield stability under legume cover crops. During phases 2 and 3, however, the higher N rates (67 and 101 kg N ha−1) increased cotton yield, although management systems with 0 and 101 kg N ha−1 showed the largest temporal yield variability. Legume cover crops increased yield and yield stability under low N rates. The maximum combined yield and yield stability benefit was obtained from HV cover on NT with additional application of 34 kg N ha−1. Our results suggest that after the initial phase NT delivers the most consistent yield benefits while enhancing yield stability against unfavorable environmental conditions. Long-term integration of legume cover crops (particularly HV) to NT systems was effective in maintaining high yield and increasing yield stability while lowering N rates.

Capturing of gaseous and particulate pollutants into liquid phase by a water/oil column using microbubbles

A new method was developed to remove gaseous and particulate pollutants by capturing them in water using microbubbles. The capture efficiency of gaseous toluene and ultrafine carbon particles, which are hydrophobic substances, was remarkably improved compared to water-only conditions by adding a small amount of oily substances (4% volume fraction of water) to the water surface. The physicochemical properties of four types of oily substances were investigated. Rapeseed and mineral oil exhibited good capture efficiency during a capture experiment of high-concentration gaseous toluene for 96 h. Additionally, a long-term continuous capture experiment for 24 days revealed that the capture mechanisms of rapeseed and mineral oil were different. The toluene concentration in rapeseed oil reached saturation in the middle of the experiment while the capture efficiency of mineral oil remained constant. It was also shown that the emulsion formation greatly affected the capture of rapeseed oil. Thus, it is expected that a new gaseous pollutant treatment technology that can capture and remove gaseous/particulate pollutants regardless of their hydrophilic/hydrophobic properties could be developed in the future.

Branched Medium Chain Fatty Acids: Iso-Caproate Formation from Iso-Butyrate Broadens the Product Spectrum for Microbial Chain Elongation.

Chain elongation fermentation can be used to convert organic residues into biobased chemicals. This research aimed to develop a bioprocess for branched medium chain fatty acids (MCFAs) production. A long-term continuous reactor experiment showed that iso-caproate (4-methyl pentanoate, i-C6) can be produced via ethanol based chain elongation. The enriched microbiome formed iso-caproate from iso-butyrate at a rate of 44 ± 6 mmol C L–1 day–1 during the last phase. This amounted to 20% of all formed compounds based on carbon atoms. The main fermentation product was n-caproate (55% of all carbon), as a result of acetate and subsequent n-butyrate elongation. The microbiome preferred straight-chain elongation over branched-chain elongation. Lowering the acetate concentration in the influent led to an increase of excessive ethanol oxidation (EEO) into electron equivalents (e.g., H2) and acetate. The formed acetate in turn stimulated straight chain elongation, but the resulting lower net acetate supply rate towards straight chain elongation led to an increased selectivity towards and productivity of i-C6. The electrons produced via oxidation routes and chain elongation were apparently utilized by hydrogenotrophic methanogens, homoacetogens, and carboxylate-to-alcohol reducing bacteria. Further improvements could be achieved if the acetate-producing EEO was minimized and limitations of ethanol and CO2 were prevented.

3D MnO2 hollow microspheres ozone-catalysis coupled with flat-plate membrane filtration for continuous removal of organic pollutants: Efficient heterogeneous catalytic system and membrane fouling control

A heterogeneous catalytic ozonation/membrane filtration (HCOMF) system was fabricated by integrating a flat-plate polyvinylidene fluoride (PVDF) membrane module along with a slurry catalytic ozonation reactor. The performance and catalytic activity of HCOMF was evaluated for degradation of model wastewater containing bisphenol A (BPA) and humid acid (HA) under different permeation flux in long-term continuous experiments. The membrane fouling was investigated by trans-membranous pressure (TMP), membrane filtration resistance, scanning electronic microscopy (SEM), and fluorescence spectra. The results showed that HCOMF system exhibited an excellent and stable catalytic activity in long-term continuous experiments owning to integration of 3D MnO2 hollow microsphere ozone-catalysis with flat-plate membrane filtration. The TMP of HCOMF system didn’t increase significantly, and the membrane resistance Rp and Rc declined from 4% and 16% to 1% and 4%, respectively, thus, the membrane fouling of HCOMF system was mitigated compared to MF system. The mitigation of membrane fouling in HCOMF system was attributed to the increase of hydrophilicity of membrane surface and change of HA fractions.

Anaerobic digestion of chicken manure: Mitigating process inhibition at high ammonia concentrations by selenium supplementation

In this study, the anaerobic digestion of nitrogen-rich chicken manure from egg-laying hens was investigated via long-term continuous experiments with and without the addition of different trace elements. With trace element supplementation, a CH4 yield of 0.26 ± 0.03 m3 kg−1 of volatile solids (VS) added was achieved at an organic loading rate (OLR) of 3.62 kg m−3 day−1 based on VS and total ammonia nitrogen (TAN) content greater than 7200 g m−3. Selenium (Se) was identified as the critical trace element for the stable anaerobic digestion of chicken manure. The dominant methanogen in the reactors was the hydrogenotrophic methanogen Methanoculleus bourgensis. Therefore, we concluded that at elevated TAN concentrations, the CH4 production stimulated by Se supplementation likely occurred through syntrophic acetate oxidation. Without trace element supplementation, severe acetic and propionic acid accumulation occurred, causing the CH4 yield to decrease below 0.12 m3 kg−1 of VS added.