Impacts of material characteristics on the anaerobic digestion kinetics and biomethane potential of American bourbon and whiskey stillage.

Stillage of American whiskey (e.g., bourbon) manufacturing is an abundant byproduct that is distinguished from fuel ethanol and malt whisky stillage materials by its highly inconsistent nature due to variability in mash bill composition. The impact of stillage physicochemical characteristics on biomethane production through anaerobic digestion was assessed by characterizing American whiskey stillage samples before batch biochemical methane potential tests of whole stillage. A maximum methane yield of 419 Nml CH4/g VS was obtained under food to microbe ratio (F: M) of 0.5 and organic loading rate (OLR) of 10 g VS/L while digester instability was noted under F: M ratios exceeding 0.5 under batch production. Methane production was significantly influenced by the mash bill composition with lowest methane yields obtained with higher rye content (rye whiskey) and highest methane yields obtained with higher corn content (bourbon or corn whiskey). A multiple linear regression model including C, P, N, and Na was able to accurately describe the methane yield (R2 = 0.93). This study provides valuable insights to aid the design of anaerobic digesters generating renewable natural gas from heterogeneous American whiskey stillage.

CH4 production potential of autotrophic nitrification bacteria produced in the submerged nitrification bioreactor in the laboratory and kinetic analysis.

In this study, CH4 production capacity of nitrification bacteria (NB) obtained from the submerged biofilter in the laboratory was investigated. Biochemical methane potential (BMP) test was carried out with the NB amount of zero (control, CR), 5% (R1), 10% (R2), and 15% (R3) at a temperature of about 37 ± 0.5°C. Compared to the CR, significantly higher cumulative CH4 volume of about 290, 490, and 715 mL were determined in the R1, R2, and R3, respectively. All the applied kinetic models gave good results (R2 ≥0.97), while the Transference Function and First-order models provided the better R2 values. The delay phase (λ) was not observed in the AD process, and CH4 production started immediately on the first day of operation. The predicted k value of 0.133 day-1 was high in CR, while it was approximately between 0.078 and 0.112 day-1 for the higher amount of NB containing BMP units, which indicated that the AD required long reaction time.

Hydrothermal pretreatment of press mud: Characterization and potential application of hydrochar and process water.

In the present study, press mud (PM), a major waste by-product from sugar industries, was subjected to hydrothermal pretreatment (HTP) to create resource recovery opportunities. The HTP process was performed with the PM samples in a laboratory scale high pressure batch reactor (capacity = 0.7 L) at 160 °C and 200 °C temperatures (solids content = 5 % and 30 %). The pretreatment resulted in separation of solid and liquid phases which are termed as solid hydrochar (HC) and process water (PW), respectively. High heating value (HHV) of HC was âˆ¼14-18 MJ kg-1, slightly higher than that of PM (14 MJ kg-1). The thermogravimetric analysis showed about 1.5-1.7 times higher heat release from HC burning compared to that observed from combustion of PM. Apart from this, the HC and PM showed no phytotoxicity during germination of mung bean (Vigna radiata). Moreover, the biochemical methane potential test on the PW showed a generation of 167-245 mL biogas per gram of chemical oxygen demand added. Hence, the HTP offers several resource recovery opportunities from PM which may also reduce the risks of environmental degradation.

Impact of food waste addition in energy efficient municipal wastewater treatment by aerobic granular sludge process.

Recently, one of the main purposes of wastewater treatment plants is to achieve a neutral or positive energy balance while meeting the discharge criteria. Aerobic granular sludge (AGS) technology is a promising technology that has low energy and footprint requirements as well as high treatment performance. The effect of co-treatment of municipal wastewater and food waste (FW) on the treatment performance, granule morphology, and settling behavior of the granules was investigated in the study. A biochemical methane potential (BMP) test was also performed to assess the methane potential of mono- and co-digestion of the excess sludge from the AGS process. The addition of FW into wastewater enhanced the nutrient treatment efficiency in the AGS process. BMP of the excess sludge from the AGS process fed with the mixture of wastewater and FW (195 ± 17 mL CH4/g VS) was slightly higher than BMP of excess sludge from the AGS process fed with solely wastewater (173 ± 16 mL CH4/g VS). The highest methane yield was observed for co-digestion of excess sludge from the AGS process and FW, which was 312 ± 8 mL CH4/g VS. Integration of FW as a co-substrate in the AGS process would potentially enhance energy recovery and the quality of effluent in municipal wastewater treatment.

Anaerobic co-digestion of microalgal biomass, sugarcane vinasse, and residual glycerol from biodiesel using simplex-centroid mixture design: methane potential, synergic effect, and microbial diversity.

Microalgal biomass (MB) is a promising feedstock for bioenergy production. Nonetheless, the cell recalcitrance and the low C/N ratio limit the methane yield during anaerobic digestion. As an alternative to overcome these challenges, MB co-digestion with different feedstocks has been proposed. Thus, this study evaluated the anaerobic co-digestion (AcoD) of MB cultivated in wastewater with sugarcane vinasse (VIN) and residual glycerol from biodiesel production (GLY). Batch tests were conducted using augmented simplex-centroid mixture design to investigate the impact of AcoD on methane production (SMP), synergistic effects, and the influence on microbial community. When compared to MB digestion, 150 NmL CH4.g-1VS, binary and ternary AcoD achieved SMP increases from 120 to 337%. The combination of 16.7:16.7:66.7 (MB:VIN:GLY) showed the highest SMP for a ternary mixture (631 NmL CH4.g-1VS). Optimal synergies ranged from 1.3 to 1.4 and were primarily found for the MB:GLY AcoD. Acetoclastic Methanosaeta genus was predominant, regardless the combination between substrates. Despite the largest SMP obtained from the MB:GLY AcoD, other ternary mixtures were also highly synergetic and therefore had strong potential as a strategic renewable energy source.

A method for evaluating and verifying biochemical methane potential test completion performed with landfilled municipal solid waste.

The biochemical methane potential (BMP) test is significant for the landfill industry as it provides a means to evaluate the gas potential, and therefore potential degradability, of both incoming and in-place municipal solid waste (MSW). However, the BMP test is not standardized making comparison of BMP results across sites problematic. For example, the BMP test duration has historically ranged from 20 days to several months with most current BMP tests lasting 60 days. However, the gas generation data can potentially be modelled for any of those durations to produce a prediction of the ultimate BMP value (BMPULT). Currently, the predicted BMPULT values of 23 long-duration (115-150 days) BMP tests were used to determine the required quantity of data (i.e. number of days) needed to produce an accurate BMPULT prediction. Results showed that no single test duration produced both accurate and efficient results, so a novel performance-based endpoint was proposed. The relative change in predicted BMPULT values with respect to time (dBMPULT/dt) was chosen as a potential performance-based completion metric. Results indicate that once the absolute normalized dBMPULT/dt value is within <2.5, <1.5 and <0.6% day-1 that the predicted BMPULT is within 20, 10 and 5% of the true BMPULT, respectively. Overall, the use of performance-based metrics for determining BMP test completion will allow for the collection of partial data sets, reduced experimental times and verification of results.

Influence of zero-valent iron nanoparticles on anaerobic digestion of swine manure: effects on methane yield.

This study evaluated the effect of zero-valent iron nanoparticles (NZVI) on the anaerobic digestion of swine manure. A wide range of doses of NZVI was evaluated (5, 10, 15, 20, 25, 50, and 100 mgFe°/gVS). The maximum methane yield of 0.4506 L/gVSremoved was obtained with the concentration of 10 mgFe°/gVS representing an increase of 58.99% than the control system with 0.2834 L/gVSremoved, indicating that Fe° improves the methanogenic activity. However, when using doses greater than 20 mgFe°/gVS, there were decreases in the methane yield of 34.4-47.98%. Also, to observe the effect of NZVI in anaerobes was evaluated the activity in the electron transport system (ETS), where the control reactor showed an activity of 31.91 µg INTred/gVS•h, while in reactors with NZVI showed values of 39.48 µg INTred/gVS•h (10 Fe°mg/gVS), observing a stimulation of Fe° in microbial activity. However, the dose of 100 mgFe°/gVS showed the greatest decrease in methane yield (0.1474 L/gVSremoved) and a reduction in ETS was observed by 8.5% compared to the control. The effect on the composition of the volatile fatty acids was observed, where the control system obtained a maximum production of acetic acid of 639 mg/L, which was exceeded with the dose of 10 mg Fe°/gVS by 215% and a decrease of 41.15% with the inhibitory concentration of 100 mg Fe°/gVS. As a result, higher doses of NZVI affect the metabolic activity of anaerobes as well as the acetoclastic pathway causing a decrease in the methane production.

Analysis of biogas production from sewage sludge combining BMP experimental assays and the ADM1 model.

The Anaerobic Digestion Model No. 1 (ADM1) was employed to simulate methane (CH4) production in an anaerobic reactor (AR), and the associated bench-scale biochemical methane potential (BMP) assay, having sewage sludge (SWS) from a municipal wastewater treatment plant (WWTP) as feedstock. The SWS presented the following physical-chemical characteristics: pH (7.4-7.6), alkalinity (2,382 ± 100 mg CaCO3 L-1), tCOD (21,903 ± 1,000 mg L-1), TOC (895 ± 100 mg L-1), TS, TVS, and VSS (2.0%, 1.1%, and 0.8%, respectively). The BMP assay was conducted in six replicates under anaerobic mesophilic conditions (37 ± 0.1°C) for 11 days with a CH4 yield registered of 137.6 ± 6.39 NmL CH4 or 124 ± 6.72 CH4 g-1 VS-1. When the results obtained with the BMP bench-scale reactors were compared to the output generated with computational data by the ADM1 model having as input data the same initial sewage tCOD, similar cumulative CH4 production curves were obtained, indicating the accuracy of the ADM1 model. This approach allowed the characterization of the sludge and estimation of its biogas production potential. The combination of BMP assays, experimental data, and ADM1 model simulations provided a framework for studying anaerobic digestion (AD) processes.

Thermal hydrolysis of sewage sludge: Improvement in biogas generation and prediction of global warming potential.

Anaerobic digestion (AD) is a prominent treatment method for the sludge produced from sewage treatment plants. Poor solid reduction and longer retention time are the main drawbacks of AD. Thermal hydrolysis (TH) is a potential pretreatment method for solubilization of sewage sludge (SS) solids thereby improving biogas production during AD post-treatment. In this study, the SS sample (total solids = 1.75 wt% and total chemical oxygen demand (COD) = 15,450 mg L-1) was subjected to TH pretreatment (temperature = 140-180°C and reaction time = 60 minutes) in a 0.7-L capacity stainless-steel high-pressure reactor. At a reaction temperature of 180°C, the maximum solid solubilization (total dissolved solids = 4652 mg L-1) and improved dewaterability (time to filter = 4.7 s.L g-1) were observed. The biochemical methane potential test results showed almost doubling of methane generation from 145 to 284 mL gCOD-1 after TH pretreatment at 180°C. The life cycle assessment approach was used to compare various SS treatment and disposal scenarios, two of which included hydrothermal pretreatment. The scenarios involving hydrothermal pretreatments showed the least global warming potential.

Biochemical methane potential database: A public platform.

Diverse factors influence biogas production, such as material properties, testing conditions, reporting methods and other additional processing techniques. This complexity makes it difficult to compare biochemical methane potential (BMP) data, replicate experiments' results, and improve efficiencies associated with engineering applications. This study has taken preliminary attempts to build a sliced and structured BMP database, but optimizing the organization of data information and collecting more comprehensive and manually checked data information to cope with the increasing richness of the BMP test content. The first-generation BMP database contains 746 sets of data, covering 7 major substrate categories, including 187 key indicators and 26 supplementary indicators. It offers functions including data screening, comparing, uploading, and visual display of BMP data. The application of the database in comparing different types of substrates and additives is shown. In the future, the BMP database will be regularly upgraded to become more comprehensive.

Near-infrared reflectance spectroscopy for rapid prediction of biochemical methane potential of wastewater wasted sludge.

The information of biochemical methane potential (BMP) of wasted sludge is essential to ensure the stable operation of sludge management processes. However, conventional anaerobic digestion (AD) approach for BMP test is time-consuming and labour-intensive. Currently, the technique of Near Infrared Spectroscopy (NIRS) is gaining prominence in the biogas production within AD process. Previous studies mostly focused on predicting BMP values for fibrous plant biomass and solid waste, with only a limited number of studies attempting to apply NIRS to obtain BMP values across a wide array of wasted sludge types. To obtain BMP values for this diverse range of wasted sludge efficiently and accurately, it is imperative to develop precise models for assessing BMP values using NIRS. In this study, the possibility of using NIRS to predict the BMP values of wasted sludge was evaluated. A total of 70 sludge samples from different sources were investigated to develop a BMP-prediction model by correlating the measured BMP values with the obtained NIR spectra. As a result, a reliable and successful BMP-prediction model was established with the determination coefficient of 0.90, residual prediction deviation of 3.50 and low root mean square error of prediction of 36.8 mL CH4/g VS. This BMP-prediction model is satisfactory for predicting BMP values of various types of sludge. It could provide support for plant operators to make decisions rapidly, thereby improving the process efficiency and optimizing sludge management procedures.

Assessment of biochemical methane potential of dairy wastewater with different co-substrates and evaluation of different kinetic models.

Dairy industry wastewater can be considered as an important source of pollution due to its high amounts and pollutant concentrations. Anaerobic treatment is seen as a suitable alternative over aerobic treatment which requires huge aeration systems. Biochemical methane potential (BMP) testing is a widely applied technique for estimating the performance of anaerobic digesters and still has no clear alternative. In the study, the biochemical methane potential change was investigated by mixing dairy wastewater with different co-substrates (cattle manure, chicken manure and slaughterhouse wastewater) at different rates. The highest biogas potential per gram of chemical oxygen demand added (CODadded) was determined as 574 mLbiogas in a mixture of 74% dairy wastewater + 2% chicken manure + 24% slaughterhouse wastewater inoculated with granular sludge. The highest methane potential was determined as 340 mLCH4 in the same co-substrate mixture inoculated with anaerobic sludge. In recent years, mathematical modeling offers an alternative to BMP tests and many different models are used for this purpose. In the study, six different mathematical models were used to simulate the BMP results, and the highest correlation coefficient in almost all mixtures ranged from 0.900 to 0.997 with the Modified Gompertz equation and Fitzhugh models.

Physico-chemical and rheological properties datasets related to batch mesophilic anaerobic digestion of waste activated sludge, primary sludge, and mixture of sludge with organic and inorganic matter.

The datasets included in this paper provide periodically measured physico-chemical and rheological properties of mesophilic batch anaerobic digesters' content for 30 days biochemical methane potential tests (BMP). Waste activated sludge (WAS) and primary sludge (PS) were the main substrates and digested sludge from a large scale mesophilic anaerobic digester was the inoculum. The substrates (F) and inoculum (I) were fed into the BMP rectors at different ratios of feed to inoculum (F/I = 1:1, 1:2, and 1:3). Experimental data on co-digestion of WAS with inorganic and organic additives were also reported. The reported characteristics such as total solids, volatile solids, total and soluble biochemical oxygen demand, ammonia, pH, as well as rheological properties over the duration of the BMP test could be used for analysing the changes in digestate properties as the anaerobic digestion process proceeds. The discussion and interpretation of the data have been provided in previous publications [[1], [2], [3]].

Enhancing methane production from anaerobic digestion of secondary sludge through lignosulfonate addition: Feasibility, mechanisms, and implications.

This study explores the feasibility of using lignosulfonate, a byproduct of the pulp and paper industry, to facilitate sludge anaerobic digestion. Biochemical methane potential assays revealed that the maximum methane production was achieved at 60 mg/g volatile solids (VS) lignosulfonate, 22.18 % higher than the control. One substrate model demonstrated that 60 mg/g VS lignosulfonate boosted the hydrolysis rate, biochemical methane potential, and degradation extent of secondary sludge by 19.12 %, 21.87 %, and 21.11 %, respectively, compared to the control. Mechanisms unveiled that lignosulfonate destroyed sludge stability, promoted organic matter release, and enhanced subsequent hydrolysis, acidification, and methanogenesis by up to 31.30 %, 74.42 % and 28.16 %, respectively. Phytotoxicity assays confirmed that lignosulfonate promoted seed germination and root development of lettuce and Chinese cabbage, with seed germination index reaching 170 ± 10 % and 220 ± 22 %, respectively. The findings suggest that lignosulfonate addition offers a sustainable approach to sludge treatment, guiding effective management practices.

Enhanced methane yield in anaerobic digestion of waste activated sludge by combined pretreatment with fungal mash and free nitrous acid.

This study explores a novel approach for enhancing anaerobic digestion of waste activated sludge (WAS) through the combined pretreatment of fungal mash and free nitrous acid (FNA). Aspergillus PAD-2, a fungal strain with superior hydrolase secretion, was isolated from WAS and cultivated in-situ on food waste to produce fungal mash. The solubilization of WAS by fungal mash achieved a high soluble chemical oxygen demand release rate of 548 mg L-1 h-1 within first 3 h. The combined pretreatment of fungal mash and FNA further improved the sludge solubilization by 2-fold and resulted in a doubled methane production rate of 416±11 mL CH4 g-1 volatile solids. The Gompertz model analysis revealed a higher maximum specific methane production rate and shortened lag time by the combined pretreatment. These results demonstrate that the combined fungal mash and FNA pretreatment offers a promising alternative for fast anaerobic digestion of WAS.

Growth Media Efficacy in Biochemical Methane Potential Assays.

The Biochemical Methane Potential (BMP) assay is a vital tool for quantifying the amount of methane that specific biodegradable materials can generate in landfills and similar anaerobic environments. Applications of the protocol are extensive and while simple in design, the BMP assay can use anaerobic seed from many different types of sources to determine the methane potential from most biodegradable substrates. Many researchers use differing protocols for this assay, both including and excluding the use of synthetic growth medias, intended to provide vital nutrients and trace elements that facilitate methanogenesis and leave the substrate being tested as the only limiting factor in methane generation potential. The variety of previous approaches inspired this effort to determine the efficacy of adding synthetic growth media to BMP assays. The presented findings suggest the use of M-1 synthetic growth media, defined in this study, at a volumetric ratio of 10% active sludge: 90% M-1 media yielded optimal results in terms of gas yield and reduced variability.

Anaerobic digestion of commercial PLA and PBAT biodegradable plastic bags: Potential biogas production and 1H NMR and ATR-FTIR assessed biodegradation.

Bioplastics aim to substitute conventional plastics in most applications, a critical one being the collection of organic wastes for composting or anaerobic degradation. The anaerobic biodegradability of six commercial bags composed of PBAT or PLA/PBAT blends and certified as compostable [1] was studied using 1H NMR and ATR-FTIR techniques. This study aims to elucidate if commercial bioplastic bags are biodegradable under conventional conditions found in anaerobic digestates. Results showed that all studied bags are hardly anaerobically biodegradable at mesophilic temperatures. The biogas yield resulting from the anaerobic digestion under laboratory conditions oscillated between 270.3 ± 45.5 L kgVS-1 for a trash bag composed of 26.64 ± 0.03%/73.36 ± 0.03% PLA/PBAT and 36.7 ± 25.0 L kgVS-1 for a bag composed of 21.24 ± 0.08%/78.76 ± 0.08% PLA/PBAT. The degree of biodegradation did not correlate with PLA/PBAT molar composition. However, 1H NMR characterization showed that the anaerobic biodegradation occurred mostly in the PLA fraction. No bioplastics biodegradation products were detected in the digestate fraction (<2 mm). Finally, none of the biodegraded bags comply with the EN 13432 standard.

Enhancement of biogas production rate from bioplastics by alkaline pretreatment.

The effect of alkali-based pretreatment on the methanization of bioplastics was investigated. The tested bioplastics included PHB [poly(3-hydroxybutyrate)], PHBH [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)], PHBV [poly(3-hydroxybutyrate-co-3-hydroxyvalerate], PLA (polylactic acid), and a PLA/PCL [poly(caprolactone)] 80/20 blend. Prior to methanization tests, the powdered polymers (500-1000 µm) at a concentration of 50 g/L were subjected to alkaline pretreatment using NaOH 1 M for PLA and PLA/PCL, and NaOH 2 M for PHB-based materials. Following 7 days of pretreatment, the amount of solubilized carbon for PLA and its blend accounted for 92-98% of the total initial carbon, while lower carbon recoveries were recorded for most PHB-based materials (80-93%), as revealed by dissolved total organic carbon analysis. The pretreated bioplastics were then tested for biogas production by means of mesophilic biochemical methane potential tests. Compared to unpretreated PHBs, methanization rates of pretreated PHBs were accelerated by a factor of 2.7 to 9.1 with comparable (430 NmL CH4/g material feed) or slightly lower (15% in the case of PHBH) methane yields, despite featuring a 1.4-2.3 times longer lag phases. Both materials, PLA and the PLA/PCL blend, were only extensively digested when pretreated, yielding about 360-380 NmL CH4 per gram of material fed. Unpretreated PLA-based materials showed nearly zero methanization under the timeframe and experimental conditions tested. Overall, the results suggested that alkaline pretreatment can help to enhance the methanization kinetics of bioplastics.

Impact of primary treatment methods on sludge characteristics and digestibility, and wastewater treatment plant-wide economics.

Biogas production from anaerobic sludge digestion plays a central role for wastewater treatment plants to become more energy-efficient or even energy-neutral. Dedicated configurations have been developed to maximize the diversion of soluble and suspended organic matter to sludge streams for energy production through anaerobic digestion, such as A-stage treatment or chemically enhanced primary treatment (CEPT) instead of primary clarifiers. Still, it remains to be investigated to what extent these different treatment steps affect the sludge characteristics and digestibility, which may also impact the economic feasibility of the integrated systems. In this study, a detailed characterization has been performed for sludge obtained from primary clarification (primary sludge), A-stage treatment (A-sludge) and CEPT. The characteristics of all sludges differed significantly from each other. The organic compounds in primary sludge consisted mainly of 40% of carbohydrates, 23% of lipids, and 21% of proteins. A-sludge was characterized by a high amount of proteins (40%) and a moderate amount of carbohydrates (23%), and lipids (16%), while in CEPT sludge, organic compounds were mainly 26% of proteins, 18% of carbohydrates, 18% of lignin, and 12% of lipids. The highest methane yield was obtained from anaerobic digestion of primary sludge (347 ± 16 mL CH4/g VS) and A-sludge (333 ± 6 mL CH4/g VS), while it was lower for CEPT sludge (245 ± 5 mL CH4/g VS). Furthermore, an economic evaluation has been carried out for the three systems, considering energy consumption and recovery, as well as effluent quality and chemical costs. Energy consumption of A-stage was the highest among the three configurations due to aeration energy demand, while CEPT had the highest operational costs due to chemical use. Energy surplus was the highest by the use of CEPT, resulting from the highest fraction of recovered organic matter. By considering the effluent quality of the three systems, CEPT had the highest benefits, followed by A-stage. Integration of CEPT or A-stage, instead of primary clarification in existing wastewater treatment plants, would potentially improve the effluent quality and energy recovery.

Effects of hydrothermal pretreatment on methane potential of anaerobic digestion sludge cake of cattle manure containing sawdust as bedding materials.

OBJECTIVE: The purpose of this study was to analyze the effect of the hydrothermal pretreat-ment of anaerobic digestion sludge cake (ADSC) of cattle manure on the solubilization of organic matter and the methane yield to improve the anaerobic digestion efficiency of cattle manure collected from the sawdust pens of cattle. METHODS: Anaerobic digestion sludge cake of cattle manure was thermally pretreated at 160°C, 180°C, 200°C, and 220°C by a hydrothermal pressure reactor, and the biochemical methane potential of ADSC hydrolysate was analyzed. Methane yield recovered by the hydrothermal pretreatment of ADCS was estimated based on mass balance. RESULTS: The chemical oxygen demand solubilization degree (CODs) of the hydrothermal hydrolysate increased to 63.56%, 67.13%, 70.07%, and 66.14% at the hydrothermal reaction temperatures of 160°C, 180°C, 200°C, and 220°C, respectively. Considering the volatile solids content obtained after the hydrothermal pretreatment, the methane of 10.2 Nm3/ton-ADSC was recovered from ADSC of 1.0 ton, and methane yields of ADSC hydrolysate increased to 15.6, 18.0, 17.4, and 17.2 Nm3/ton-ADSC. CONCLUSION: Therefore, the optimal hydrothermal reaction temperature that yielded the maximum methane yield was 180°C based on mass balance, and the methane yield from cattle manure containing sawdust was improved by the hydrothermal pretreatment of ADSC.