Anaerobic Period Research Articles

Metagenomic insights into the mechanism of sophorolipid in facilitating co-anaerobic digestion of mushroom residues and cattle manure: Functional microorganisms and metabolic pathway analysis

The present study aimed to enhance the co-anaerobic digestion system of mushroom residues and cattle manure by incorporating biosurfactant sophorolipid. Results demonstrated that the addition of 75 mg/L sophorolipid increased cumulative methane production by 33.68%, acetate content by 9–10 times, and the abundance of Methanosarcina by 69.22%. The electroactive microorganisms (Bacteroides, Petrimonas, etc.) were enriched, while the up-regulation of functional genes associated with carbohydrate metabolism and methane metabolism was observed. The metagenomic analysis revealed the significant involvement of inter-microbial communication and extracellular electron transfer in anaerobic digestion. Petrimonas was identified as the predominant host involved in cellular processes and environmental information processing. The supplementation of sophorolipid significantly enhanced its abundance during the late anaerobic digestion period (by 12.30%–64.84%). The results emphasize the crucial function of sophorolipid as biosurfactant in enhancing the efficiency of anaerobic digestion.

Conversion of Oil Palm Empty Fruit Bunch Fiber Waste into Green Liquid Organic Fertilizer

Solid wastes generated from the oil palm industry contain valuable nutrients like nitrogen, phosphorus, and potassium that can significantly enhance plant growth and potentially elevate fertilizer production. This study aims to identify the optimal formulation of liquid organic fertilizer (LOF) derived from oil palm empty fruit bunch (OPEFB) fiber waste. Three formulations of LOF were prepared, comprising OPEFB waste, molasses, noni fruit, and cattle urine, designated as Formulation A, B, and C. These formulations underwent a 14-day anaerobic incubation period. The formulated OPEFB LOF was then analyzed for nutrient content, electrical conductivity, and total dissolved solids. This study also examines the soil properties and plant growth outcomes following the application of the formulated OPEFB LOF. The results indicated that Formulation A exhibited the highest nutrient concentrations, specifically 485 ppm nitrogen, 95 ppm phosphorus, and 1007 ppm potassium. In comparison to the other two OPEFB LOF formulations, Formulation A showed the lowest values for total dissolved solids (502 ppm) and electrical conductivity (8.14 dS/m). The findings demonstrated that Formulation A displayed the most favorable growth characteristics in terms of leaf count, plant height, leaf length, and leaf width. This is attributed to the nitrogen-boosting properties of cattle urine, along with the complementary effects of molasses and noni fruit as soil improver and bio-activator. This study confirms the viability of utilizing green organic fertilizer derived from OPEFB substrate in agriculture, replacing conventional inorganic fertilizers.

Greenhouse gas and volatile organic compound emissions of additive-treated whole-plant maize silage: part A—anaerobic fermentation period

BackgroundSilage emits climate- and environment-relevant gases during fermentation and feed-out periods. This trial aimed to determine the unknown carbon dioxide (CO2), methane, nitrous oxide, ethanol, and ethyl acetate emissions of constant maize silage material over both periods. The results will be published in two consecutive articles (Part A: anaerobic fermentation period, Part B: aerobic storage period).MethodsThe untreated control (CON) was compared with the chemical additive treatment (CHE; 0.5 g sodium benzoate and 0.3 g potassium sorbate per kg fresh matter) and the biological additive treatment (BIO; 108 colony-forming units (CFU) Lentilactobacillus buchneri and 107 CFU Lactiplantibacillus plantarum per kg fresh matter). Barrel silos (n = 4) were connected to gas bags to quantify gas formation during anaerobic fermentation (30 or 135 ensiling days). Glass jar silos (n = 12) were used for laboratory silage analysis.ResultsCHE produced significantly (p < 0.05) less gas (6.7 ± 0.3 L per kg dry matter ensiled material (kgDM) until ensiling day 14.0 ± 0.0) and ethanol (8.6 ± 1.5 mg kgDM–1) than CON did (8.5 ± 0.2 L kgDM–1 until ensiling day 19.5 ± 6.4; 12.2 ± 1.5 (mg ethanol) kgDM–1). BIO indicates prolonged gas formation (9.1 ± 0.9 L kgDM–1 until ensiling day 61.3 ± 51.9; 12.0 ± 2.1 mg kgDM–1). CO2 is the main component of the gas formed. All treatments formed methane and nitrous oxide in small quantities. CON emitted significantly more CO2eq emissions than BIO and less than CHE (p < 0.05). Additives had no effect on ethyl acetate gas emissions. For BIO, ethanol concentrations in the material (rS = 0.609, p < 0.05) and gas quantities (rS = 0.691, p < 0.05) correlate with ethyl acetate gas quantities. All the treatments exhibited decreasing gas and CO2 quantities, and the dry matter mass increased between ensiling days 14 and 30 (− 0.810 ≤ rS ≤ 0.442; p < 0.05 to p = 0.20).ConclusionSilage generates climate- and environmental-relevant gases during fermentation and silage additives affect this pattern. Gas formation exceeds the fixation potential, and the carbon footprint of silage fermentation is negative.Graphical

Mechanistic insights into sulfadimethoxine degradation via microbially driven Fenton reactions

Biodegradation, while cost-effective, is hindered by the requirement for specialized microorganisms and co-contaminants. Innovative biological technologies like the microbially driven Fenton reaction, hold promise for enhancing degradation efficiency. However, the intricate biochemical processes and essential steps for effective degradation in such systems have remained unclear. In this study, we harnessed the potential of the microbially driven Fenton reaction by employing Shewanella oneidensis MR-1 (MR-1). Our approach showcased remarkable efficacy in degrading a range of contaminants, including sulfadimethoxine (SDM), 4,4'-dibromodiphenyl ether (BDE-15) and atrazine (ATZ). Using SDM as a model contaminant of emergent contaminants (ECs), we unveiled that biodegradation relied on the generation of hydroxyl radicals (•OH) and involvement of oxidoreductases. Transcriptomic analysis shed light on the pivotal components of extracellular electron transfer (EET) during both anaerobic and aerobic periods. The presence of reactive oxidizing species induced cellular damage and impeded DNA repair, thereby affecting the Mtr pathway of EET. Moreover, the formation of vivianite hindered SDM degradation, underscoring the necessity of maintaining iron ions in the solution to ensure sustainable and efficient degradation. Overall, this study offers valuable insights into microbial technique for ECs degradation, providing a comprehensive understanding of degradation mechanisms during aerobic/anaerobic cycling.

A comparative study of algal-bacterial granular sludges and aerobic granular sludge at different C/N ratio: Granule characteristics, SND progress and Microbial community

The algal-bacterial synergistic effect in algal-bacterial granular sludge (ABGS) made its nitrogen metabolism mechanism different from that of aerobic granular sludge (AGS). In this study, the effects of algae on granules characteristics, SND process and community structure in ABGS were studied by treating wastewater with different C/N (13:1–20:1) ratios. The results showed that ABGS and AGS had excellent nitrogen removal capacity of 86 % and 91 %, respectively, and SND efficiency was above 90 %. ABGS granules were looser due to the phototaxis of algae, and the oxygen penetration depth was higher than that of AGS. The NH4+-N removal efficiency of AGS was higher than that of ABGS, but the SND efficiency of ABGS was better than that of AGS. In ABGS, photosynthesis provided organic carbon for denitrification in anaerobic period, and organic carbon might be more important than strict anaerobic environment. In aerobic period, The SND process in ABGS was mainly heterotrophic nitrification aerobic denitrification (HAND), while in AGS was conventional simultaneous nitrification denitrification (CSND). The results of this study would provide a theoretical foundation for further understanding the difference between ABGS and AGS nitrogen removal mechanisms and help to further expand the application of ABGS in practical engineering.

Effects of salinity on glycerol conversion and biological phosphorus removal by aerobic granular sludge

Industrial wastewater often has high levels of salt, either due to seawater or e.g. sodium chloride (NaCl) usage in the processing. Previous work indicated that aerobic granular sludge (AGS) is differently affected by seawater or saline water at similar osmotic strength. Here we investigate in more detail the impact of NaCl concentrations and seawater on the granulation and conversion processes for AGS wastewater treatment. Glycerol was used as the carbon source since it is regularly present in industrial wastewaters, and to allow the evaluation of microbial interactions that better reflect real conditions. Long-term experiments were performed to evaluate and compare the effect of salinity on granulation, anaerobic conversions, phosphate removal, and the microbial community. Smooth and stable granules as well as enhanced biological phosphorus removal (EBPR) were achieved up to 20 g/L NaCl or when using seawater. However, at NaCl levels comparable to seawater strength (30 g/L) incomplete anaerobic glycerol uptake and aerobic phosphate uptake were observed, the effluent turbidity increased, and filamentous granules began to appear. The latter is likely due to the direct aerobic growth on the leftover substrate after the anaerobic feeding period. In all reactor conditions, except the reactor with 30 g/L NaCl, Ca. Accumulibacter was the dominant microorganism. In the reactor with 30 g/L NaCl, the relative abundance of Ca. Accumulibacter decreased to ≤1 % and an increase in the genus Zoogloea was observed. Throughout all reactor conditions, Tessaracoccus and Micropruina, both actinobacteria, were present which were likely responsible for the anaerobic conversion of glycerol into volatile fatty acids. None of the glycerol metabolizing proteins were detected in Ca. Accumulibacter which supports previous findings that glycerol can not be directly utilized by Ca. Accumulibacter. The proteome profile of the dominant taxa was analysed and the results are further discussed. The exposure of salt-adapted biomass to hypo-osmotic conditions led to significant trehalose and PO43−-P release which can be related to the osmoregulation of the cells. Overall, this study provides insights into the effect of salt on the operation and stability of the EBPR and AGS processes. The findings suggest that maintaining a balanced cation ratio is likely to be more important for the operational stability of EBPR and AGS systems than absolute salt concentrations.

A comprehensive floc model for simulating simultaneous nitrification, denitrification, and phosphorus removal

A comprehensive floc model for simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) was designed, incorporating polyphosphate-accumulating organisms (PAOs), glycogen-accumulating organisms (GAOs), intrinsic half-saturation coefficients, and explicit external mass transfer terms. The calibrated model was able to effectively describe experimental data over a range of operating conditions. The estimated intrinsic half-saturation coefficients of oxygen values for ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, ordinary heterotrophic organisms (OHOs), PAOs, and GAOs were set at 0.08, 0.18, 0.03, 0.07, and 0.1 mg/L, respectively. Simulation suggested that low dissolved oxygen (DO) environments favor K-strategist nitrifying bacteria and PAOs. In SNDPR, virtually all influent and fermentation-generated volatile fatty acids were assimilated as polyhydroxyalkanoates by PAOs in the anaerobic phase. In the aerobic phase, PAOs absorbed 997 % and 171 % of the benchmark influent total phosphorus mass loading through aerobic growth and denitrification via nitrite. These high percentages were because they were calculated relative to the influent total phosphorus, rather than total phosphorus at the end of the anaerobic period. When considering simultaneous nitrification and denitrification, about 23.1 % of influent total Kjeldahl nitrogen was eliminated through denitrification by PAOs and OHOs via nitrite, which reduced the need for both oxygen and carbon in nitrogen removal. Moreover, the microbial and DO profiles within the floc indicated a distinct stratification, with decreasing DO and OHOs, and increasing PAOs towards the inner layer. This study demonstrates a successful floc model that can be used to investigate and design SNDPR for scientific and practical purposes.

Residence Time Reduction in Anaerobic Reactors: Investigating the Economic Benefits of Magnetite-Induced Direct Interspecies Electron Transfer Mechanism

Existing research on direct interspecies electron transfer (DIET) has predominantly focused on the types and concentrations of conductive materials across diverse anaerobic digestion. However, insufficient understanding of the impact of residence time, a critical economic factor, prompted this investigation. Magnetite, a conductive material, was introduced into the anaerobic digestion of food wastewater, leading to a significant increase in ultimate methane production (Bu) with 25 mM-Fe3O4 (p &lt; 0.05). Despite a subsequent decline in methane production efficiency from 388.9% to 7.1% over the 15- to 65-day anaerobic digestion period, the initial impact of increased methane production due to magnetite addition was evident. Control’s maximum methane production rate (Rm) was 27.5 mL/day, reaching its highest point at 37.4 mL/day with 15 mM-Fe3O4, accompanied by a noteworthy 56.6% reduction in the attainment day of Rm (Rm-day), shortened to 8.2 days. Even with 100 mM-Fe3O4, while Bu showed no significant difference, Rm-day exhibited a substantial reduction of 22.8. Despite the lower overall anaerobic digestion efficiency under some magnetite input conditions, this study confirmed a substantial shortening of Rm-day, suggesting that the DIET mechanism induced by conductive materials such as magnetite could reduce the residence time in continuous-type anaerobic reactors, contributing to improved economic feasibility.

Long-term continuous degradation of carbon nanotubes by a bacteria-driven Fenton reaction

Very few bacteria are known that can degrade carbon nanotubes (CNTs), and the only known degradation mechanism is a Fenton reaction driven by Labrys sp. WJW with siderophores, which only occurs under iron-deficient conditions. No useful information is available on the degradation rates or long-term stability and continuity of the degradation reaction although several months or more are needed for CNT degradation. In this study, we investigated long-term continuous degradation of oxidized (carboxylated) single-walled CNTs (O-SWCNTs) using bacteria of the genus Shewanella. These bacteria are widely present in the environment and can drive the Fenton reaction by alternating anaerobic-aerobic growth conditions under more general environmental conditions. We first examined the effect of O-SWCNTs on the growth of S. oneidensis MR-1, and it was revealed that O-SWCNTs promote growth up to 30 μg/mL but inhibit growth at 40 μg/mL and above. Then, S. oneidensis MR-1 was subjected to incubation cycles consisting of 21-h anaerobic and 3-h aerobic periods in the presence of 30 μg/mL O-SWCNTs and 10 mM Fe(III) citrate. We determined key factors that help prolong the bacteria-driven Fenton reaction and finally achieved long-term continuous degradation of O-SWCNTs over 90 d. By maintaining a near neutral pH and replenishing Fe(III) citrate at 60 d, a degraded fraction of 56.3% was reached. S. oneidensis MR-1 produces Fe(II) from Fe(III) citrate, a final electron acceptor for anaerobic respiration during the anaerobic period. Then, ·OH is generated through the Fenton reaction by Fe(II) and H2O2 produced by MR-1 during the aerobic period. ·OH was responsible for O-SWCNT degradation, which was inhibited by scavengers of H2O2 and ·OH. Raman spectroscopy and X-ray photoelectron spectroscopy showed that the graphitic structure in O-SWCNTs was oxidized, and electron microscopy showed that long CNT fibers initially aggregated and became short and isolated during degradation. Since Shewanella spp. and iron are ubiquitous in the environment, this study suggests that a Fenton reaction driven by this genus is applicable to the degradation of CNTs under a wide range of conditions and will help researchers develop novel methods for waste treatment and environmental bioremediation against CNTs.

THRIVE combined with i-gel laryngeal mask for prolonging apneic oxygenation time in retrograde intrarenal surgery

To explore the effect of THRIVE combined with i-gel laryngeal mask on the safety of oxygen therapy in apnea and surgical precision of retrograde intrarenal surgery. A total of 120 patients undergoing retrograde intrarenal surgery under general anesthesia with laryngeal mask were randomized into 3 groups (n=40), and after the flexible ureteroscope entered the renal pelvis and located the stones, the patients received assisted ventilation in APPV mode (control group), ventilation with small tidal volume and high respiratory rate (group H), or THRIVE combined with laryngeal mask for oxygen supply without using the ventilator (THRIVE group). The time for lithotripsy by the surgeons, surgeons' satisfaction, diaphragm mobility, and times of urinary tract mucosal injury were recorded, and arterial blood pressure, heart rate, SpO2, PaO2, PaCO2, and pH value were measured before, during and after lithotripsy. Among the 3 groups, THRIVE group had the shortest time for lithotripsy, best satisfaction of the surgeons, the lowest diaphragmatic mobility of the patients, and the smallest number of mucosal injuries. The arterial blood pressure, heart rate, and SpO2 of the patients did not differ significantly among the 3 groups. At 20 min and 30 min after the start of lithotripsy, PaO2 decreased significantly in group H and THRIVE group; in THRIVE group, PaCO2 increased and pH decreased significantly at 10, 20 and 30 min after the start of lithotripsy. No significant difference was found in oxygenation indicators among the 3 groups upon discharge from the PACU. In retrograde intrarenal surgery, THRIVE combined with i- gel laryngeal mask for oxygen therapy during the anaerobic period can improve the surgical accuracy and maintain the patient's oxygenation index in a controllable range within 30 min.

Research on the Promotion of Sludge Anaerobic Fermentation with Sodium Citrate under Low Concentrations of Polyaluminum Chloride

Polyaluminum chloride (PAC) is used widely and increasingly in wastewater treatment plants, resulting in its inevitably high production in sludge. Previous studies have indicated that the production of short-chain fatty acids (SCFAs) is inhibited by the existence of PAC in sludge anaerobic fermentation, so it is necessary to study how to promote sludge anaerobic fermentation under low concentrations of PAC. In this study, sodium citrate (SC) was first used to improve the efficiency of anaerobic fermentation under low concentrations of PAC. The results showed that the production of SCFAs increased with SC, especially when the ratio of PAC to SC was 1:2, and the maximum production of SCFAs reached 2890 mg/L, which is 2.5 times more than when PAC only exists. The mechanism studies showed that SC could remove the Al3+ in the sludge floc, which led to deflocculation of the sludge floc, accelerated the destruction of extracellular polymers (EPS), and released soluble substances in the sludge. At the same time, the key enzymes that were bound and hidden originally in the sludge were also released, which promoted the further degradation of organic matter and shortened the anaerobic fermentation period. However, the higher concentration of SC was not conducive to sludge dehydration. Therefore, the optimal distribution ratio of PAC to SC should be 1:1. This study provides a new idea for the research and practical application of sludge anaerobic fermentation.

Conversion of Materials and Energy in Anaerobic Digestion of Sewage Sludge with High-Pressure Homogenization Pretreatment

High pressure homogenization (HPH) pretreatment can improve sludge anaerobic digestion; however, the relationship among the material, energy conversion, and gas production efficiency was unclear under different operating conditions in sludge anaerobic digestion by HPH pretreatment. In this study, the performance of HPH pretreatment before sludge anaerobic digestion was investigated, and the relationship among the material, energy conversion, and gas production efficiency was explored. HPH pretreatment induced organic solubilization, and a maximum soluble chemical oxygen demand (SCOD)/total chemical oxygen demand (TCOD) of about 30% was achieved. Results showed that HPH pretreatment significantly improved the biogas production of sludge anaerobic digestion; the maximum increase in CH4 yield was 57%; and the anaerobic digestion period was shortened by about 10 days. The ratio of CH4 yield increment to volatile dissolved solids (VDS) increment was 0.21 mL/mg. The CH4 yield increment of 1 L/g volatile solid (VS) required a specific energy of 0.10 MJ/kg total solid (TS) by increasing the pressure with one cycle and 0.72 MJ/kg TS by increasing the cycle at 60 MPa. The minimum additive energy consumption of HPH pretreatment was 125 J/mL CH4 yield increment at 20 MPa with one cycle. Considering CH4 yield improvement and energy conservation, HPH pretreatment should maintain a pressure of no more than 60 MPa in one cycle. This study provides a theoretical reference for the practical application of HPH pretreatment in anaerobic digestion. HPH holds promise as a potential strategy for sewage sludge pretreatment to produce CH4 in anaerobic digestion.

Insight of CO2 and ethanol emission from maize silage: A case study with real-time identification of aerobic and anaerobic microbial respiration using a multi-sensor-fusion method

Silage is produced worldwide for both livestock feeding and biogas production. Sustainable silage production requires characterization and mitigation of potential effects on environmental quality, particularly from greenhouse gas emissions during the production cycle. Ex-situ sampling has demonstrated that major emissions are carbon dioxide (CO2) and ethanol (EtOH). In-situ gas measurements from farm silo and bale silage are rare and may be important to improve our knowledge of the physical and biochemical causes, and constraints on these gas emissions. This study focused on tracking the kinetics of CO2 and EtOH emissions from bale maize silage, with real-time identification, quantification and separation of aerobic and anaerobic respiratory components in the period following opening of the silage. For this, an automatic multi-sensor gas-flux chamber (AMGC) was developed. Three bales (mean weight: 890 kg) of maize silage were tested (n = 3). Oxygen (O2) and temperature (Tsi) sensors were co-located at 10- and 20-cm behind the open face of the bales. Over the two weeks of the experiment we observed: (i) significant initial discharge of CO2 across the open face (1.68–2.55 mol m−2 h−1) and EtOH (0.027–0.034 mol m−2 h−1); (ii) peak CO2 emission occurred when O2 concentration (10 cm depth) was 3∼8% vol., while peak EtOH emission occurred below 2% vol. O2, (iii) dynamic conversion of O2 to CO2 from aerobic respiration; and (iv) the cumulative emission of EtOH during the anaerobic period was 4–6 times greater than that during aerobic plus semi-aerobic periods. These novel measurements provide mechanistic understanding, and may facilitate improved management of silage production to minimize environmental impact and aerobic loss of silage.

Lessons learned from in situ corrosion experiments in the HADES URL

Abstract A wide range of metals have been studied as a candidate container material to be considered in the geological disposal concept of high-level radioactive waste and spent fuel in Belgium. More than 40 years ago, SCK CEN started studies on the corrosion of these metals. The HADES underground research laboratory (URL) played an important role in the corrosion research as it enabled in situ corrosion experiments to be carried out that simulate realistic disposal conditions as closely as possible. These experiments consisted of placing metallic coupons on a steel support tube, heated from the inside, that was installed in Boom Clay, thereby exposing the coupons to various conditions representative of the disposal concept that was considered at that time. Test durations lasted from 6 months to approximately 7.5 years. This paper summarizes the results from the various corrosion studies and discusses their implications in the choice of disposal concept. One of the main outcomes of these experiments was a change of rationale regarding the choice of the container material from carbon steel (corrosion-allowance) to stainless steel (corrosion-resistant). The main arguments for this change were the need to avoid severe pitting corrosion during the aerobic period and to minimize the generation of hydrogen gas during the subsequent anaerobic period.

Model-based evaluation of simultaneous nitrification and denitrification in aerobic granular sludge systems.

A lab-scale granular sludge sequencing batch reactor (G-SBR) system was operated using synthetic wastewater. The total nitrogen removal efficiency of 85% was obtained together with the achievement of complete total phosphorus removal with average granule diameter of 400µm. Dual-step nitrification and denitrification model with fixed biofilm thickness was used for performance analysis. The denitrification mode only contributed to TN removal with 25% which can be calculated with process stoichiometry. The remaining nitrogen removal could be explained by simulating simultaneous nitrification and denitrification which was responsible for 75% denitrification during aerobic period. In addition, low NO3- concentration at the beginning of the fill period provided advantage for securing a prolonged anaerobic period for enhanced biological phosphorus removal (EBPR). The model parameters of boundary layer thickness (zBL = 50µm) and half-saturation of O2 for nitrite-oxidizing bacteria (KO2,NOB = 0.5 gO2/m3) were tuned to fit NO2 and NO3 profiles in SBR cycle.

The interaction between temperature and citric acid treatment in the anaerobic fermentation of Chinese cabbage waste

Temperature is a crucial environmental factor for recycling Chinese cabbage waste. Herein, we evaluated the impacts of temperatures (15, 25 and 35 °C) on the effects of citric acid treatment (1.11% dry matter) on the anaerobic fermentation of Chinese cabbage waste. The results indicated that citric acid treatment improved the acetic acid concentration, reduced the ammonia nitrogen levels, upregulated lipid metabolism, and increased the Lactobacillus and Pediococcus abundances but reduced the Weissella, Naumovozyma, Monascus and Alternaria abundances during the anaerobic period. After aerobic exposure, citric acid treatment during the anaerobic period at 15 and 35 °C improved aerobic stability, reduced organic acid degradation, inhibited ammonia nitrogen formation, upregulated replication and repair pathways, enhanced the competition among fungi, and increased the Acetobacter, Naumovozyma and Kazachstania abundances but reduced the Bacillus, Pseudomonas and Trichosporon abundances; citric acid treatment during the anaerobic period at 25 °C enhanced aerobic deterioration, resulted in a 77.12% (p < 0.05) increase in the pH value and a 167.71% (p < 0.05) increase in the ammonia nitrogen content, upregulated amino acid metabolism, enhanced commensalism or mutualism between bacteria and fungi, and enriched Zygosaccharomyces and Bacillus. Collectively, citric acid treatment at 15 and 35 °C improved short-chain fatty acid production, improved aerobic stability and reduced alkaline pollutant generation during Chinese cabbage waste fermentation, whereas at 25 °C, it exacerbated aerobic deterioration, which was associated with variations in dominant microbes, microbiome topologies and functional pathways.

Effect of time and temperature of pretreatment and anaerobic co-digestion of rice straw and swine wastewater by domesticated paddy soil microbes

Rice straw and swine wastewater are abundant, easy to obtain, and inexpensive biomass materials. Anaerobic digestion of rice straw and swine wastewater effectively regulates the carbon-to-nitrogen ratio and also improves methane production efficiency. The dense lignocellulosic structure, unsuitable carbon-to-nitrogen ratio, and light texture of rice straw hinder its application in anaerobic digestion. Effective pretreatment technologies can improve degradation efficiency and methane production. Our study is the first to apply domesticated paddy soil microbes to enhance the efficiency of hydrolytic acidification of rice straw and swine wastewater at varying temperatures and times. The results show that the highest total organic carbon (1757.2 mg/L), soluble chemical oxygen demand (5341.7 mg/L), and organic acid concentration (4134.6 mg/L) appeared in the hydrolysate after five days of hydrolytic acidification at 37 °C. Moreover, the use of hydrolysate produced 13% more gas and reduced the anaerobic digestion period by ten days compared to the untreated control. This suggests that using domesticated paddy soil microbes as a pretreatment might be a sustainable and cost-effective strategy for improving the degradation efficacy and methane production from lignocellulosic materials.

Full-scale demonstration of a floating seal for enhanced biological nutrient removal in a sequencing batch reactor establishing chemical-free environment in wastewater treatment at low carbon source availability

ABSTRACT Due to the cyclical nature and changing water levels in the sequencing batch reactor (SBR), oxygen diffusion and utilization can be difficult to control particularly in light of the need to conserve the limited quantity of carbon source required to optimize biological nutrient removal. During the fill period, oxygen penetration may be undesirable since heterotrophic and autotrophic organisms cause a reduction in the readily biodegradable carbon source (rbCOD). This carbon source is essential and often limited in the anaerobic and anoxic periods. As a consequence, unwanted oxygen penetration can hinder efficient biological phosphorus and nitrogen removal. The purpose of the present research was to verify the advantage of a floating seal on the continuously moving surface of an SBR reactor to minimize undesirable oxygen penetration. In the floating seal-covered SBR both nitrification and denitrification efficiency proved to be higher due to insulation, and even during wintertime biological phosphorus removal met target removals without chemical dosing. The SVI values in the two SBR trains proved to be close to each other, despite the high difference in chemical dosing. Having experienced the higher efficiency of the seal-covered train, microbiome compositions of the two differently operated systems were investigated to determine potential differences via 16S rRNA gene amplicon sequencing experiments. In the samples taken from the seal-covered system, higher ratios of fermentative bacteria and phosphate accumulating organisms (PAOs) as well as glycogen accumulating organisms (GAOs) could be observed as compared to the samples deriving from the uncovered system. Highlights Seal-covering the periodically decreasing open water surface increased SBR efficiency Seal-covering the open water surface increased nitrification efficiency by insulation No chemical dosing was necessary for phosphorous removal in the Test system Metagenome investigations provided almost doubled amount of fermentative bacteria Production of GAOs indicated nutrient deficiency due to phosphorous removal.

Sequencing Batch Reactor Performance Evaluation on Orthophosphates and COD Removal from Brewery Wastewater

The discharge of industrial effluent constituting high orthophosphates and organic pollutants in water receiving bodies compromises freshwater quality and perpetuates eutrophication. In this study, an anaerobic–aerobic sequencing batch reactor (SBR) under activated sludge was investigated for orthophosphates and chemical oxygen demand (COD) removal from brewery wastewater. Raw brewery wastewater samples were collected on a daily basis for a period of 4 weeks. The findings of the study are reported based on overall removal efficiencies recording 69% for orthophosphates and 54% for total COD for a sludge retention time (SRT) of 7 days and hydraulic retention time of 18 h at mesophilic temperature conditions of ±25 °C. Moreover, the SBR system showed stability on orthophosphate removal at a SRT ranging from 3 to 7 days with a variation in organic volumetric loading rate ranging from 1.14 to 4.83 kg COD/m3.day. The anaerobic reaction period was experimentally found to be 4 h with the aerobic phase lasting for 14 h. The SBR system demonstrated feasibility on orthophosphates and COD removal with variation in organic loading rate.

Insights into the denitrifying phosphorus removal decay processes by profiling of the response mechanism of denitrifying phosphate-accumulating organisms to starvation stress

Starvation conditions were inevitably encountered by biological wastewater treatment systems. Four anaerobic starvation periods (5, 10, 16 and 20 days) were conducted to investigate the response mechanism of denitrifying phosphate-accumulating organisms (DPAOs) in order to dissect denitrifying phosphorus removal (DPR) decay processes. The denitrifying phosphorus removal performance suffered with the decay rate of 0.162 ± 0.022 d−1 during 20-day starved duration. Metabolic activity decay was responsible 93.20 ± 0.11% for the damaged DPR performance, while biomass decay contributed to 6.79 ± 0.68%. The genus Dechloromonas affiliated to DPAOs exerted stronger survival adaptability to starvation with the abundance increasing from 1.98% to 3.15%, depended upon the endogenous consumption of intracellular polymers. In view of PHA-driven DPR mechanism of DPAOs, the metabolic activity was restricted by the depletion of available PHA. These results revealed the poorer stability but preponderant recovery of DPR system encountering with starvation.