Modified Gompertz Model Research Articles

Sustainable phycoremediation of mushroom farm wastewater using novel isolated microalga (Chlamydomonas asymmetrica SAG70.72): Experimental and kinetic studies

This study aimed to assess the mushroom farm wastewater (MFW) treatment potential using novel isolated microalga Chlamydomonas asymmetrica strain SAG70.72. Microalga was isolated from the Ganga River located in Haridwar, India, and identified using an 18S rRNA-based sequencing technique. For phycoremediation experiments, different concentrations of MFW (i.e., 0 % as control, 50, and 100 %) were used to cultivate isolated C. asymmetrica under laboratory conditions. The results showed that the maximum significant (p < 0.05) reduction in total dissolved solids (TDS: 87 %), biochemical oxygen demand (BOD: 93 %), chemical oxygen demand (COD: 92 %), total Kjeldahl's nitrogen (TKN: 87 %), and total phosphorus (TP: 97 %) were observed in 50 % MFW treatment. Moreover, proximate, biochemical, and fatty acids methyl esters (FAMEs) composition of C. asymmetrica were also found highest in 50 % MFW treatment. The first-order reaction-based kinetic model also depicted the highest value of rate constant (k) in the same treatment. Moreover, the growth of C. asymmetrica was best simulated using the logistic model as compared to the modified Gompertz models. The findings of this study suggested that the implementation of isolated C. asymmetrica in MFW treatment systems could contribute to the mitigation of environmental impacts associated with mushroom cultivation.

Co-digestion approach for enhancement of biogas production by mixture of untreated napier grass and industrial hydrolyzed food waste.

The co-digestion of untreated Napier grass (NG) and industrial hydrolyzed food waste (FW) was carried out in the batch reactor to investigate the effect of substrate ratios on biogas production performance. Two-stage anaerobic digestion was performed with an initial substrate concentration of 5g VSadded/L and a Food to Microorganism Ratio (F/M) of 0.84. The 1:1 ratio of the NG and FW showed the optimum performances on biogas production yield with a value of 1,161.33mL/g VSadded after 60 days of digestion. This was followed by the data on methane yield and concentration were 614.37mL/g VSadded and 67.29%, respectively. The results were similar to the simulation results using a modified Gompertz model, which had a higher potential methane production and maximum production rate, as well as a shorter lag phase and a coefficient of determination of 0.9945. These findings indicated that the co-digestion of Napier grass and hydrolyzed food waste can enhance biogas production in two-stage anaerobic digestion.

A kinetic modeling and energy conversion evaluation of biohydrogen production using a co-culture of green microalgae and wastewater activated sludge

Biohydrogen production is influenced by various parameters such as production formation rate, substrates degradation, and biomass utilization. Therefore, it is crucial to predict the kinetics of proper yield. This study was designed to perform a comprehensive kinetic analysis based on several linear or non-linear models. The experimental data analyzed was different co-culture ratios of microalgae and activated sludge with hexitols (glucose, sorbitol, mannitol) as carbon substrates. Results suggest that modified Gompertz model best predicts biohydrogen potential and acetate production in different co-cultures with high R2 values (>0.977 and > 0.982), respectively. A maximum of 9.8 % energy conversion efficiency is achieved in 10 g/L glucose supplemented co-culture, equivalent to traditional fuels. The linearized Luedeking–Piret model also indicates that biohydrogen production is influenced more by substrate degradation/utilization than microalgal biomass. These tools can be utilized to optimize the operational parameters and access the best fit of experimental data for enhanced yield.

Effect of Particle Size Distribution on Kinetics and Overall Degradation in Anaerobic Digestion of Waste Biomass

Particle size distribution in pre-treated organic substrates significantly impacts microbial fermentation efficiency, with smaller particles offering greater specific surface area, potentially reducing retention times and operational costs, particularly beneficial for remote and urban areas. Laboratory tests compared manual chopping, shredding, grinding, and mincing techniques, finding manual methods more effective than shredders at pretreatment level 1. Non-treated tomato waste showed the highest fine particle distribution (41%), contrasting with grass waste (&lt; 2.9 mm), banana peel waste (&lt; 2 mm), and paper waste (&lt; 3 mm). Combining mincing, grinding, and extended processing increased methane output, particularly evident in higher pre-treatment levels with enhanced surface area. Among substrates, banana peel waste biomass (BPWSB) yielded the most methane (332 ± 36 Nml/gVS, 67% VSR), while grass waste biomass (GWSB) in semi-continuous tests produced 253 ± 29 Nml/gVS. The Biochemical Methane Potential (BMP) kinetic models consistently favored first-order kinetics over the modified Gompertz model across all substrates, attributing higher k-values to PTL4 due to its large surface area: BPWSB (0.59), GWSB (0.339), PWSB (0.59), and TWSB (0.59). These findings emphasized slower decay of larger particles and more rapid degradation of smaller fractions, crucial for optimizing biogas production efficiencies.

Modelling the Effect of mercury on the Growth Rate of an SDS-degrading Pseudomonas sp. strain Maninjau1

The SDS-degrading bacterium Pseudomonas sp. strain Maninjau1 experienced significant inhibition by mercury. Observations of bacterial growth at varying mercury concentrations revealed a sigmoidal pattern, with lag periods extending from 7 to 12 hours. Increasing mercury concentrations progressively impeded growth, with a concentration of 1.0 mg/L nearly halting bacterial activity. To analyze these effects, the modified Gompertz model was employed to determine growth rates across different mercury concentrations. These rates were then subjected to several models, including the modified Han-Levenspiel, Wang, Liu, Shukor, modified Andrews, and Amor models. Among these, the Amor model failed to appropriately fit the growth curves. Statistical analysis indicated that the Shukor model performed the best, evidenced by the lowest values for Root Mean Square Error (RMSE) and Akaike’s Information Criterion corrected (AICc), the highest adjusted correlation coefficient (adR2), and values of Accuracy Factor (AF) and Bias Factor (BF) closest to unity. The parameters obtained from the Shukor model, which are mmax (h-1) and Sm (mg L-1) and n which represent maximum growth rate, critical heavy metal ion concentration and empirical constant values were 0.187, 1.126 and 2.406, respectively. The Shukor model allows for the prediction of the critical heavy metals concentration which can completely inhibited bacterial growth. This robust modeling approach underscores the Shukor model's suitability for predicting the impact of mercury on the growth dynamics of Pseudomonas sp. strain Maninjau1 under toxic stress conditions.

Antibacterial Efficacy of Essential Oils from Four Spices against Salmonella typhimurium: Mathematical Modelling and Application in Enhancing Salad Cream Safety

The study was conducted to investigate the inhibitory effects of certain natural substances (finger root, clove, lemongrass, cardamom, and the combination of lemongrass with cardamom) against Salmonella typhimurium, a type of bacteria known to cause foodborne illnesses. The result showed that finger root, clove, lemongrass, cardamom, and the combination of lemongrass with cardamom exhibited strong inhibitory effects against S. typhimurium. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated. MIC values ranged from 0.049 to 0.781 µl/ml, and MBC values ranged from 0.049 to 6.250 µl/ml. Furthermore, the study aimed to develop mathematical models that accurately describe S. typhimurium survival in the presence of these essential oils. By understanding how the S. typhimurium respond to the oils over time, it was found that the mathematical models accurately described bacterial survival, with the modified Gompertz model fitting for finger root essential oil and the Weibull and modified Gompertz models suitable for the other oils. Additionally, the study sought to evaluate the practical viability of incorporating these essential oils into salad cream formulations, primarily aiming to assess their potential in reducing S. typhimurium counts and ensuring compliance with established quality standards. Specifically, the inclusion of finger root, clove, lemongrass, cardamom, and the combination of lemongrass with cardamom in salad cream formulations, maintained at a controlled temperature of 4 °C, yielded positive outcomes, meeting the required quality standards. Importantly, the presence of S. typhimurium was rendered undetectable, and an overall reduction in microbial count was observed when compared to cream formulations lacking these essential oils. This study effectively underscores the potential of the examined essential oils as natural antimicrobial agents suitable for incorporation in food products

Experimental simulation and kinetic modeling of bioenergy potential of Eichornia crassipes biomass from the Volta River basin of Ghana under mesophilic conditions

The study presents the results of the laboratory experiment performed on the anaerobic digestion of water hyacinth biomass harvested from the Volta River basin of Ghana and Fruit waste sludge as the inoculum. Batch mode of experiment was performed under mesophilic conditions (29 ± 3 °C) with a hydraulic retention time of 61 days. The experimental setup was made up of three (3) fermenter bottles of 5.0 L capacity namely F1, F2 and F3. F1 served as the control whiles F2 and F3 served as the test fermenter bottles. Each of the fermenter bottles was fitted with BlueSens methane sensor and BlueVcount flowmeter for the measurement of methane composition and biogas volumes, respectively. The Theoretical Biomethane Potential (BMP) of the water hyacinth biomass was estimated to be 422.23 ml/gVS. The experimental BMP was determined to be 402.62 ml CH4/gVS and 356.03 ml CH4/gVS for F2 and F3, respectively. Consequently, a biodegradability value of 95.36 and 84.32 % was obtained from F2 and F3, respectively. Moreover, the F2 fermenter bottle recorded a cumulative net methane and biogas volumes of 5576.3 ml and 12,014 ml, respectively. Likewise, a total net cumulative methane and biogas volumes of 4931.0 ml and 11,384 ml were produced from the F3 fermenter bottle. Using the First order kinetic model, an average value of hydrolysis constant for water hyacinth biomass was determined as 0.051 day−1. Furthermore, the modified Gompertz model, the logistic function model and Transference function models were used to fit the experimental cumulative biogas and methane production data. The outcome of the study shows that, the production of biogas from water hyacinth biomass harvested the Volta River basin of Ghana could offer sustainable control solutions to its invasion on water bodies whiles providing a cheap and reliable means of biofuel to the riparian communities.

Anaerobic Co-Digestion of Vinasse and Pentose Liquor and the Role of Micronutrients in Methane Production within Sugarcane Biorefineries

Anaerobic digestion (AD) of residues from integrated first- and second-generation ethanol (1G2G) biorefineries is a sustainable method for energy recovery through biogas production. This study evaluated the co-digestion of 1G vinasse, 2G vinasse and pentose liquor (from the pretreatment of sugarcane bagasse for 2G ethanol production) compared to individual digestions using biochemical methane potential (BMP) assays. The results showed some “key” micronutrients from the substrates that affected methane (CH4) production, while their balance provided by co-digestion achieved high digestibility (95%). High iron (Fe) and nickel (Ni) concentrations, in addition to furfural (0.33 g L−1) in pentose liquor seemed to decrease its CH4 production potential. Despite these adverse effects observed in mono-digestion, co-digestion was beneficial for this substrate, increasing digestibility (52%) and BMP (118%). The highest BMP was observed in vinasse 2G (631 ± 6 NmL CH4 gTVS−1), with no significant difference compared to the adjusted modified Gompertz model (624 ± 10 NmL CH4 gTVS−1). The co-digestion system also presented the highest specific CH4 production rate (20 ± 1 NmL CH4 gTVS−1day−1) and shortened the lag phase by 19% compared to the AD of isolated 1G vinasse with the second lowest BMP value (494 ± 11 NmL CH4 gTVS−1).

Anaerobic co-digestion of Unavoidable and Avoidable Food-Waste with addition of eggshells and applied kinetic studies

Food waste is a growing concern due to its contribution to harmful greenhouse gas (GHG) emissions. To address this issue, anaerobic digestion (AD) has been identified as an effective and sustainable method to treat organic waste. This study aimed to investigate the anaerobic co-digestion of avoidable and unavoidable food waste, along with calcined and uncalcined eggshells, using fresh cow dung as an inoculum in a 1:1 ratio. The use of eggshells in this study was based on their ability to preserve carbohydrates due to the presence of Ca(OH)2, an alkaline additive. The study was carried out in a batch process (1 L) at a mesophilic temperature range of 35 ± 2 °C, and kinetic parameters during biogas production were predicted by the first-order and modified Gompertz model. The results showed that the volatile solids % of food waste was reduced, indicating gas production during the process. However, the gas composition showed a negligible amount of methane production, likely due to the rise in pH caused by the addition of calcined eggshells, which inhibited the completion of the methanogenesis process. The decrease in the Volatile solids content was attributed to the addition of uncalcined eggshells, which requires a higher temperature (1000 °C) to calcine completely. The maximum biogas yields, predicted by the first order and the modified Gompertz model, are 1235 mL/gVS (experimental 1195 mL/gVS) and 1185 mL/gVS, respectively. However, the addition of eggshells to the co-digestion process must be carefully monitored to maintain the pH balance. Overall, this study suggests that the co-digestion of food waste and adding eggshells can be a viable and promising solution to food waste management to recover energy from it.

Synthesis, characterization, optimization and application of Pisum sativum peels S and N-doping biochars in the production of biogas from Ulva lactuca

This study assessed the usefulness of Pea Pisum sativum peels S-modified biochar (PPB–S) and Triethylenetetramine (TETA)-modified biochar (PPB-T) as improvers for biogas generation from green algae Ulva lactuca either individually or co-digested with Pea peels (PPs). BET, FTIR, TGA, XRD, XPS, SEM coupled with EDX were used to characterize the PPB-S and PPB-T biochars. EDX, FTIR, and XPS analyses proved the formation of sulphur and nitrogen groups on the surface of PPB-S and PPB-T. The kinetic study confirmed that the modified Gompertz model fits the experimental data satisfactorily, with R2 ranging between 0.948 and 0.991. The results suggested that adding 50 mg/L of PPB-S significantly increased the biogas production yield compared to all other studied treatments, either individually or in co-digestion with PPs. The extreme biogas production (498 mL/g VS) was formed when 50 mg/L of PPB-S was added to U. lactuca. According to Response surface methodology (RSM), the maximum biogas production among all experiments is 460.91 (ml/g VS), achieved for U. lactuca and PPB-S treatment corresponds to 54 days contact time and 50 mg/L of PPB-S dose. The direct electron transfer mechanism has been investigated in detail, and it is confirmed that conductive PPB-S can support electron transfer and promote methane production, as proved by the XPS and FTIR analyses, which the creation of sulphur groups on the PPB-S surface may propose. In this study, the use of PPB-S in biogas production aligns with the principles of a circular economy.

Simultaneous aerobic nitrogen and phosphate removal capability of novel salt-tolerant strain, Pseudomonas mendocina A4: Characterization, mechanism and application potential

A salt-tolerant strain, Pseudomonas mendocina A4, was isolated from brackish-water ponds showing simultaneous heterotrophic nitrification-aerobic denitrification and phosphorus removal capability. The optimal conditions for nitrogen and phosphate removal of strain A4 were pH 7–8, carbon/nitrogen ratio 10, phosphorus/nitrogen ratio 0.2, temperature 30 °C, and salinity range of 0–5 % using sodium succinate as the carbon source. The nitrogen and phosphate removal efficiencies were 96–100 % and 88–96 % within 24 h, respectively. The nitrogen and phosphate removal processes were matched with the modified Gompertz model, and the underlying mechanisms were confirmed by the activities of key metabolic enzymes. Under 10 % salinity, the immobilization technology was employed to enhance the nitrogen and phosphate removal efficiencies of strain A4, achieving 87 % and 76 %, respectively. These findings highlight the potential application of strain A4 in both freshwater and marine culture wastewater treatment.

Anaerobic digestion of an invasive aquatic plant Ludwigia grandiflora by thermal hydrolysis pretreatment: Correlations between methane kinetics and substrate composition

Ludwigia grandiflora, an emerging aquatic weed, has become a global waterway invader, causing various environmental issues. Anaerobic digestion (AD) of lignocellulosic biomass is a cost-effective treatment method. To enhance methane yield, pretreatment is required to break the rigid lignocellulose structure, which hampers the biodegradability of the biomass. Therefore, in this study, we examined the impact of thermal hydrolysis (TH) pretreatment on L. grandiflora through batch AD tests at temperatures ranging from 150 to 210 °C, with durations of 10 and 30 mins. At 180 °C for 30 mins (severity factor of 3.8), methane yield increased significantly by 142.7 % compared to the untreated condition. Significant methane production differences were observed at temperatures equal to or above 165 °C. Longer retention times, such as 30 mins, were crucial for enhancing methane yield. Additionally, the Modified Gompertz model was a good fit for the AD process, with R2 values ranging from 0.996 to 0.935 and lag phase reduction from 0.273 (untreated) to 0.102-0.000 days for the pretreated conditions. Methane yield and production rates increased from 88.85 mL g-VS−1 and 15.01 mL g-VS−1 day−1 (untreated) to 110.48-206.41 mL g-VS−1 and 30.76-71.33 mL g-VS−1 day−1, respectively. Pearson correlation revealed a positive correlation between cellulose and methane yield enhancement, while lignin, crystallinity index, and pH showed negative correlations. Despite these negative correlations, their impact on the AD process was limited. Overall, changes in lignocellulosic structure and increased cellulose content were the main factors enhancing methane production. Additionally, the study recommends a new cost-effective reactor design for TH pretreatment.

Enhanced Biogas Production from Rice Husks and Okra Stalks by Co-digestion with Ostrich Dung and Cow Manure

In this study, two sides were studied. First one included single and combined pretreatment which were performed to treat milled rice husks compared to increase the production of biogas untreated rice husks. The other side included investigate the effect of two types of mixing: mixing rice husks and okra stalks using three mixing ratios inoculated with ostrich dung compared to rice husks and okra stalks inoculated with ostrich dung separately and mixing ostrich dung and cow manure using three mixing ratios with rice husks compared to using rice husks inoculated with ostrich dung and cow manure separately. The ten reactors, which were carried out in this study, were in batch mode. Single pretreatment included hydrothermal and oxidative pretreatment with 50% (v/v) H2O2, while combined pretreatment consisted of both hydrothermal and H2O2 pretreatment. The cow manure was used as inoculum in this anaerobic co-digestion process. The results clarified that the increase of biogas productions were by 5.42%, 48.05%, and 59.07% for hydrothermal, H2O2, and combined pretreatment of hydrothermal and H2O2, respectively. For first mixing, 25:75 ratio (rice husks: okra stalks) was better than other ratios in the production of biogas (48.77 ml/g VS). In the second case of mixing, 75:25 ratio (ostrich dung: cow manure) was better than other ratios in the production of biogas (21.85 ml/g VS). Kinetic study was applied using modified Gompertz model, and there was well agreement between the predicted and measured values of the all pretreatments with correlation coefficient &gt; 0.95. The pretreatment samples of rice husks and the mixing of materials improve the production of biogas and methane.

Production of medium chain fatty acids from ensiled potato peels; effect of inoculum type and kinetic study

Medium chain fatty acids (MCFAs) are fatty acids containing 6 to 12 carbon atoms with a wide range of industrial application. They can be produced by the fermentation of waste biomass through a process called chain elongation (CE). During CE, the type of inoculum used plays a key role in determining the optimal yield of MCFAs. In this study, we showed, for the first time, the use of three different inocula including leachate, rumen fluid and digestate from a biogas reactor for the batch fermentation of ensiled potato peels for MCFAs production. Results showed that the highest chain elongation was obtained when leachate was used as inoculum with a maximum yield of 57, 4 and 26 g/kgVS for caproic acid, heptanoic acid and caprylic acid respectively. A kinetic study shows that the production of MCFAs from ensiled potato peels was better described by the first-order model than by the modified Gompertz model.

Influence of Pre-Incubation of Inoculum with Biochar on Anaerobic Digestion Performance.

The application of biochar as an additive to enhance the anaerobic digestion (AD) of biomass has been extensively studied from various perspectives. This study reported, for the first time, the influence of biochar incubation in the inoculum on the anaerobic fermentation of glucose in a batch-type reactor over 20 days. Three groups of inoculum with the same characteristics were pre-mixed once with biochar for different durations: 21 days (D21), 10 days (D10), and 0 days (D0). The BC was mixed in the inoculum at a concentration of 8.0 g/L. The proportion of the inoculum and substrate was adjusted to an inoculum-to-substrate ratio of 2.0 based on the volatile solids. The results of the experiment revealed that D21 had the highest cumulative methane yield, of 348.98 mL, compared to 322.66, 290.05, and 25.15 mL obtained from D10, D0, and the control, respectively. Three models-modified Gompertz, first-order, and Autoregressive Integrated Moving Average (ARIMA)-were used to interpret the biomethane production. All models showed promising fitting of the cumulative biomethane production, as indicated by high R2 and low RMSE values. Among these models, the ARIMA model exhibited the closest fit to the actual data. The biomethane production rate, derived from the modified Gompertz Model, increased as the incubation period increased, with D21 yielding the highest rate of 31.13 mL/gVS. This study suggests that the application of biochar in the anaerobic fermentation of glucose, particularly considering the short incubation period, holds significant potential for improving the overall performance of anaerobic digestion.

The study of the influence of tetracycline and sulfadiazine on biomethane production from manure and apple pomace

Anaerobic digestion is the most popular technic for obtaining biomethane from substrates like cow manure and other organic materials, however, chlortetracycline (CTC) and sulfadiazine (SDZ) which are commonly used in animal husbandry and present in cow manure can adversely affect biomethane yields. In this paper, the results of the influence of an increasing dose of CTC between 10 and 1000 mg×kg−1 and dose of SDZ between 10 and 500 mg×kg−1 on biomethane yield and kinetics for co-fermentation of cow manure and apple pomace experiment was presented. The obtained data during 21 days of lasting batch tests performed under mesophilic conditions allowed the determination of kinetics parameters of biomethane production according to the modified Gompertz model. The biomethane yield for the experiment with CTC differs from 233 to 353 mlCH4, while for the experiment with SDZ from 396 to 455 mlCH4. The kinetics parameters varied in a broad range. The ymax, λ, and Rm were 232–531 ml, 18–66 ml d−1, and –2.9-(–1.7) d for CTC, and 533–653 ml, 20–21 ml d−1, and –4.5-(–0.8) d for SDZ, respectively. With the high antibiotics dose, the biomethane yield decreased due to the inhibitive effect on microorganisms. The experiment showed that antibiotics had an inhibitory effect on biomethane production, at high doses. The biomethane yield had been reduced by 32.3 % at 1000 mg×kg−1 of CTC and by 13.9 % at 500 mg×kg−1 of SDZ. Interestingly, small doses (<100 mg×kg-1) did not affect significantly methane yield and sometimes increased it. Obtained results showed that the co-fermentation of apple pomace and manure performance may be affected by high doses of antibiotics. Depending on the dose and the antibiotic type it affects the biomethane yield, production rate, or lag phase differently.

Optimization and microbial community analysis for anaerobic digestion of water hyacinth (Eichhornia crassipes) with waste sludge at different solid contents and temperatures

In this study, optimum operating conditions for anaerobic digestion of water hyacinth (Eichhornia crassipes) with waste sludge was investigated at varying total solid (TS) content of the digestion solution (3.3%, 4.3%, 5.3%, 6.3%, 7.3% and 8.3%) and digestion temperature (35, 40, 45, 50 and 55 °C) to produce methane with high yield. The highest biogas yield reached experimentally was 163.2 mL/g TVS (with high CH4 content of 81.1 vol%) at 6.3% of TS content and digestion temperature of 35 °C. Kinetic parameters were estimated by using modified Gompertz, Cone and first-order kinetic models in which modified Gompertz model gave the lowest fitting errors (−1.0 to 3.7%). The effect of temperature on methane production rate was simulated by Ratkowsky model and optimum digestion temperature was found between 41.5 and 44 °C for maximum methane production at 6.3% TS. The experimental methane yields were 61.9–132.3 mL CH4/g TVS. The metagenomic sequencing was used to characterize microbial community structure of the anaerobic digestate at varying conditions and acetoclastic/hydrogenothrophic methanogenesis was equally dominated methane-producing pathways. The most abundant bacterial populations were found to be Proteobacteria, Firmicutes, Chloroflexi and Actinobacteria. Based on alpha diversity indices, it can be concluded that effect of digestion temperature on microbial richness and diversity was higher than the effect of TS content.

Hydrothermal carbonization of food waste: Process parameters optimization and biomethane potential evaluation of process water

Food waste (FW) is one of the major biomasses produced in large quantities in urban areas, which contributes to more than one-third of global greenhouse gas emissions. FW must be properly managed to minimize its environmental consequences. Hydrothermal carbonization (HTC) of FW is a promising technology compared to conventional methods. The objective of the present study is to maximize the mass yield (MY), higher heating value (HHV) and energy yield (EY) of FW by optimizing the operational variables of HTC process. Additionally, process water generated during HTC of FW under optimal conditions was evaluated for methane yield using anaerobic digestion. To optimize the HTC process, three operational variables, including solid-to-liquid (S/L) ratio, temperature, and reaction time, were manipulated using response surface methodology (RSM). According to RSM studies, the optimum operating conditions are 198.5 °C for 150 min with a 0.2 S/L ratio, resulting in MY, HHV and EY as 62.5%, 21.24 MJ/kg and 81.71%, respectively. Proximate and elemental analysis for the hydrochars synthesized at various operating conditions reveals that the temperature and reaction time have a significant impact on fixed carbon and carbon percentage. The anaerobic digestion results showed that the combination of process water and hydrochar, yielded a maximum cumulative methane production of 298.5 ± 16.34 mL/g COD. To mimic methane production, the modified Gompertz model was utilized. Thus, this finding contributes towards the commercialization of the HTC process to produce solid fuel (hydrochar) and provides a way to find an alternative energy source that enhances the HTC process and tackles the problem of process water disposal.

Growth kinetic model of Bacillus pasteurii under different pH and temperature conditions in sodium carboxymethyl cellulose solid-free drilling fluid

Increasing the bonding force between broken blocks to form a complete borehole wall is essential to solving borehole wall destabilization in broken strata, and introducing microbial-induced calcite deposition (MICP) technology into the field of drilling fluids establishes a novel research idea for manifesting this technical method. However, during drilling, the pH value and temperature of the drilling fluid constantly change, affecting the activities of microorganisms and the effect of MICP. Therefore, exploring the growth law of microorganisms in drilling fluid environments under different temperatures or pH conditions is necessary. This study used experimental research and theoretical analysis to compare the growth of Bacillus pasteurii in sodium carboxymethyl cellulose (CMC) solid-free and xanthan gum biopolymer solid-free drilling fluid. The growth of B. pasteurii in CMC solid-free drilling fluid in pH = 7.0–9.8 and temperatures from 30 to 50 °C was studied, and the growth kinetic model of B. pasteurii was constructed. The mean square error, decision coefficient (R2), accuracy factor (Af), and deviation factor (Bf) were used to verify the accuracy of the model. CMC solid-free drilling fluid is more suitable for B. pasteurii survival than XG solid-free drilling fluid. The optimum growth temperature of B. pasteurii in CMC solid-free drilling fluid was 32 °C, and the OD600 reached 2.146 at 24 h pH = 8.2 was the optimum pH environment for B. pasteurii in CMC solid-free drilling fluids; the OD600 reached 2.065 at 24 h. As a first-order growth kinetic model, the modified Gompertz model accurately described B. pasteurii growth in CMC solid-free drilling fluid under different temperature strips or pH values. As a secondary growth kinetic model, the square root model accurately described the pattern of pH (7.0–8.2) and temperature effects on the maximum specific growth rate (μmax), with R2 = 0.961, Af = 1.084, Bf = 0.9979, and an error of less than ±0.05. The Arrhenius model accurately described the pattern of pH effects on B. pasteurii (μmax) at pH = 8.6–9.8, with R2 = 0.9996, Af = 1.0036, Bf = 0.999, and an error of less than ±0.02. The effect of temperature was inversely proportional to the growth of B. pasteurii; the higher the temperature, the lesser the B. pasteurii growth. In the pH range of 7.0–8.2, the higher the pH value, the better the B. pasteurii growth; however, at an increased pH range of 8.6–9.8, the higher pH value decreased the B. pasteurii growth. This study is the first to investigate the effect of temperature or pH on B. pasteurii growth in CMC solid-free drilling fluid. Our study provides a scientific basis and theoretical reference for the subsequent research on the induced domestication of B. pasteurii in high-temperature and strong alkaline environments and its engineering application.

Advanced steam-explosion pretreatment mediated anaerobic digestion of municipal sludge: Effects on methane yield, emerging contaminants removal, and microbial community

Advanced steam explosion pretreatment, i.e., the Thermal hydrolysis process (THP) is applied mainly to improve the sludge solubilization and subsequent methane yield in the downstream anaerobic digestion (AD) process. However, the potential of THP in pretreating the high solids retention time (SRT) sludges, mitigating the risk of emerging organic micropollutants and effects on anaerobic microbiome in digester remains unclear. In this study, sludge from a sequencing batch reactor (SBR) system operating at a SRT of 40 days was subjected to THP using a 5 L pilot plant at the temperature ranges of 120–180 °C for 30–120 min. The effect of THP on organics solubilization, methane yield, organic micropollutant removal, and microbial community dynamics was studied. The highest methane yield of 507 mL CH4/g VSadded and volatile solids (VS) removal of 54% were observed at 160°C- 30min THP condition, i.e., 4.1 and 2.6 times higher than the control (123 mL CH4/gVSadded, 20.7%), respectively. The experimental values of hydrolysis coefficient and methane yield have been predicted using Modified Gompertz, First order, and Logistics models. The observed values fitted well with all three models showing an R2 value between 0.96 and 1.0. THP pretreated sludges showed >80% removal of Trimethoprim, Enrofloxacin, Ciprofloxacin, and Bezafibrate. However, Carbamazepine, 17α-ethinylestradiol, and Progesterone showed recalcitrant behavior, resulting in less than 50% removal. Microbial diversity analysis showed the dominance of Proteobacteria, Firmicutes, Chloroflexi, and Bacteroidetes, collectively accounting for >70–80% of bacterial reads. They are mainly responsible for the fermentation of complex biomolecules like polysaccharides, proteins, and lipids. The THP-mediated anaerobic digestion of sludge shows better performance than the control digestion, improved methane yield, higher VS and micropollutants removal, and a diverse microbiome in the digester.