Volatile Solids Reduction Research Articles

A pilot-scale evaluation of residual sludge quality in a worm-sludge treatment reed bed in the Mediterranean region

A pilot-scale study on sludge treatment reed beds investigated the combined effects of earthworms and Arundo donax on sewage sludge dewatering and residual sludge quality. Four units were tested: one planted with earthworms, one planted without earthworms, one unplanted with earthworms, and one control, each unit replicated. Over a year, 24 cycles of sludge (dry and volatile solid contents of 24.71 g.L−1, and 19.14 g.L−1) were fed onto the units at a sludge loading rate: 43.59 kg.DS.m−2.year−1. Afterward, the units experienced 132 days of resting period, increasing dry solids from 21 to 70 % and decreasing volatile solids from 81 to 69 % on average (40 % sludge volume reduction). The bottom layers of the planted unit with earthworms showed a 30 % reduction in volatile solids, indicating improved sludge stabilization. Macronutrient abundance in the residual sludge followed the sequence N > Ca > P > K > S > Mg. The planted unit with earthworms reduced micronutrient concentrations by 22 % compared to the control unit (Fe > Na > Mn > B > Mo). Earthworms also played a key role in reducing heavy metal concentrations by 11 % compared to the planted unit without earthworms (Zn > Cr > Pb > Ni > Cd). Heavy metal levels in the residual sludge met EU and Portugal standards, with a 99.9 % reduction in Escherichia coli and fecal coliforms. Cost estimation showed centrifugation and W-STRB scenarios cost 167 and 183 €.PE−1 for a ten-year operation, with O&M costs of 7 and 3 €.PE−1.year−1, respectively.

Poultry slaughterhouse waste management through anaerobic digestion with varying proportions of chicken litter

Nepal's burgeoning poultry industry which is a key sector in its economy leads to a considerable generation of slaughterhouse waste (SHW), necessitating effective and sustainable disposal methods. This study explores anaerobic digestion as an optimal solution for poultry SHW management, aiming to produce energy-rich biogas while efficiently mitigating pollution in these facilities. Particularly, the feasibility and effectiveness of co-digestion with chicken litter (CL) were investigated to enhance biogas production and waste utilization. Four distinct runs of anaerobic digestion were performed, each utilizing varying substrate compositions with SHW to CL ratios of 1:0, 4:1, 1:1, and 1:4. Throughout the process, essential parameters, including total solids (TS), volatile solids (VS), biological oxygen demand (BOD5), pH, temperature, biogas generation, were meticulously measured. The cumulative biogas production for each run was as follows: 14.87 liters and a biogas yield of 88.73 ml/gVS with a 17.39 % VS reduction for Run 1, 25.98 liters and a biogas yield of 147.21 ml/gVS with a 28.64 % VS reduction for Run 2, 78.32 liters and a biogas yield of 314.69 ml/gVS with a 54.32 % VS reduction for Run 3, and 89.195 liters and a biogas yield of 344.36 ml/gVS with a 63.05 % VS reduction for Run 4. Notably, as the proportion of CL increased in the mixture from 4:1 to 1:1, a considerable VS reduction was observed. Furthermore, when the ratio of SHW to CL reached 1:1 and 1:4, a significant BOD5 reduction of 50 % and 63.13 % was achieved, respectively, surpassing previous runs. The results reveal that the addition of CL in an appropriate ratio effectively manages poultry SHW, with the optimum SHW:CL ratio for significant biogas yield lying between 1:1 and 1:4.

High-solid digestion – A comparison of completely stirred and plug-flow reactor systems

High-solid digestion (HSD) for biogas production is a resource-efficient and sustainable method to treat organic wastes with high total solids content and obtain renewable energy and an organic fertiliser, using a lower dilution rate than in the more common wet digestion process. This study examined the effect of reactor type on the performance of an HSD process, comparing plug-flow (PFR) type reactors developed for continuous HSD processes, and completely stirred-tank reactors (CSTRs) commonly used for wet digestion. The HSD process was operated in thermophilic conditions (52 °C), with a mixture of household waste, garden waste and agricultural residues (total solids content 27–28 %). The PFRs showed slightly better performance, with higher specific methane production and nitrogen mineralisation than the CSTRs, while the reduction of volatile solids was the same in both reactor types. Results from 16S rRNA gene sequencing showed a significant difference in the microbial population, potentially related to large differences in stirring speed between the reactor types (1 rpm in PFRs and 70–150 rpm in CSTRs, respectively). The bacterial community was dominated by the genus Defluviitoga in the PFRs and order MBA03 in the CSTRs. For the archaeal community, there was a predominance of the genus Methanoculleus in the PFRs, and of the genera Methanosarcina and Methanothermobacter in the CSTRs. Despite these shifts in microbiology, the results showed that stable digestion of substrates with high total solids content can be achieved in both reactor types, indicating flexibility in the choice of technique for HSD processes.

Evaluating the influence of calcined eggshells and ultrasonication in the Co-digestion of avoidable and unavoidable Food Waste and OLS regression analysis of the reactor system

The technological advancements in the bio-conversion of food waste (FW) into biogas signify substantial advancements in the field of waste management. However, persistent operational challenges like rapid acidification and difficulties in maintaining the C/N ratio in mono-digestion remain, despite extensive research efforts. The present study aims to evaluate the reactor performance in co-digestion, specifically using a 1:1 ratio of unavoidable food waste (UAFW) and avoidable food waste (AFW), with the addition of calcined eggshells as an additive. Further, the study employs Ordinary Least Square (OLS) regression modeling to predict the biogas production from the co-digestion process. The experimental process involves ultrasonication pretreatment, focusing on calcined eggshells for their ability to preserve carbohydrates via Ca(OH)2, an alkaline material. The semi-continuous operation of the reactor spanned for 120 days and was divided into three phases with varying Organic Loading Rates (OLR) from 0.6 to 2.2 gVS/l/d. Characterization studies such as SEM, FTIR and TGA-DTA were performed to validate the pretreatment method and addition of egg-shells. Results indicated increased OLR led to higher Volatile Solids (VS) reduction. This was attributed to the calcined eggshells' role in adsorbing NH4+ and NO3− ions while maintaining pH levels, resulting in significantly higher biogas production. The multiple regression models used in the study yielded promising results, surpassing simple linear regression, with an adjusted R-squared value > 0.9 and p-value <0.05. The model effectively anticipated the specific methane yield, demonstrating the capability to improve energy production by co-digesting AFW and UAFW. The study presents an opportunity to divert organic waste from landfills, reduce greenhouse gas emissions, and promote sustainable waste management by using bio-waste additives, reducing reliance upon synthetic chemicals.

Fuzzy-decision tree modeling for H2S production management in an industrial-scale anaerobic digestion process

H2S is a byproduct in anaerobic digesters (ADs), causing significant challenges due to its negative impact on biogas quality and equipment corrosion. As a solution, previous researchers developed complex mechanistic models that are computationally expensive due to solving equations with many variables. These models were only tested within normal H2S ranges. This research introduces a novel hybrid fuzzy-decision tree (F-DT) model to predict H2S production from primary/secondary sludge ratio (P/S), dry solids (DS), and volatile solid (VS) reduction parameters in the Qom wastewater treatment plant in Iran. Notably, the H2S concentrations in this facility consistently surpass the acceptable thresholds reaching levels as high as 6500 ppm, in contrast to the designed accepted limit of 3000 ppm. The process involved collecting and pre-processing data, creating a decision tree classifier for rule generation, developing a fuzzy model suited for complex systems like AD, and optimizing it with a genetic algorithm. The analysis of the final model revealed that the P/S ratio significantly influences elevated H2S levels, indicating that maintaining a P/S ratio > 1.2 holds promise as an effective strategy. The model is both simple and interpretable, with decent accuracy in predicting H2S compared to previous models. This study not only introduces a useful method for optimizing industrial-scale ADs, but also aims to uncover the reasons behind high H2S levels.

Characterization and Performance Evaluation of Anaerobic Night Soil Biodegrading Inoculum

The efficiency of anaerobic night soil (human excreta) biodegradation depends on the characteristics of the inoculum used. This anaerobic microbial inoculum (AMI) contains a microbial consortium, including rate-limiting methanogens whose growth depends on various physicochemical and biological parameters necessitating the inoculum characterisation essential for optimum night soil (NS) biodegradation. The inoculum contained 24.567 g/L (±0.07) total solid, 5.022 (±0.57) g/L total dissolved solid, 18.148 (±0.0.058) g/L volatile solid (VS), and 7.0±0.2 pH. The Gas chromatography analysis confirmed the presence of a small amount of volatile fatty acid (VFA), (≤ 4 mM except propionate) showing rapid conversion of VFA to methane, and 55% methane. Further, the presence of methanosaetaceae group of methanogens was detected through Taqman probe-based real-time PCR. The inoculum performance was evaluated for NS biodegradation in semicontinuous mode of feeding in four 2 L anaerobic biodigesters (2D HRT, 4D HRT, 5D HRT, and 10D HRT) with varying hydraulic retention time (HRT) (2, 5, 8, and 10 days, respectively) at mesophilic temperature (35°C). After 5 HRT, VS reduction for 2D HRT and 5D HRT was &lt;40% while for 8D HRT and 10D HRT was &gt;45-50% and &gt;45-60%, respectively. The methane content was &lt;20% in biogas for 2 and 5 days HRT while for 8 and 10 days &gt;45-50% and 50-65% methane, respectively. The % VS reduction and methane content showed the overfeeding of NS in biodigesters 2D HRT and 5D HRT while 8D HRT showed towards optimum and 10D HRT optimum with improved VS reduction and methane content.

A novel additive for enhancing biomass energy production from agro-industrial wastes: synthesis of hydrophobic nanoporous silica aerogel and its effect on methane production

AbstractAnaerobic digestion (AD) is one of the most preferred processes for the treatment of organic waste. However, additional processes such as co-digestion, pretreatment, and additive addition continue to be explored to remove the limits on the applicability of AD. This study investigated the effects of hydrophobic nanoporous silica aerogel (NpSA) synthesized from waste rice husks on the anaerobic co-digestion (AnCD) of the mixture consisting of sewage sludge and fruit processing industry wastes. All bioreactors containing NpSA-free, 0.1 g, 0.2 g, 0.5 g, and 1 g NpSA (0.03–0.3 gNpSA/gVSadded) were operated in a mesophilic-batch process. Biogas and methane yields increased from 346 mL/gVS (NpSA-free) to 387 mL/gVS and from 231 mL/gVS (NpSA-free) to 288 mL/gVS, respectively, with 0.1 g NpSA addition. NpSA additive increased biogas production in all bioreactors compared to the blank. However, biogas production rate and methane content increased faster at lower doses of NpSA. Maximum soluble chemical oxygen demand (sCOD), protein, carbohydrate, and volatile solid (VS) reductions were between 45–71%, 35–54%, 44–65%, and 34–91% for NpSA added mixtures, respectively. The hydrophobic NpSA additive was effective in improving the AnCD performance and biogas/methane production. Experimental results fit the kinetic models frequently preferred in such AD processes. In addition, the possible energy and financial potential of the produced methane were also discussed, and it was determined that the direct sale of methane gas produced by the addition of NpSA in the global market could provide 1.4 $/Lmixture more financial gain than the mixture NpSA-free. Graphical Abstract

Assessing the impact of alkali pretreatment of rice husk on its composition and product portfolio: Tradeoff between biogas and valuable materials recovery for sustainability

The burning of agricultural crop residues has evolved into a significant global issue with far-reaching implications for public health and environmental integrity. Utilizing biochemical methodologies to valorize these residues presents a dual advantage, mitigating disposal challenges while concurrently fostering wealth generation through bioenergy production and the creation of value-added materials. Nevertheless, the biodegradation of residues faces impediments due to the presence of recalcitrant silica and lignin. To assess the efficacy and elucidate the performance of biochemical approaches, this study investigates the impact of NaOH treatment (2%, 4%, 6%, 8%, and 10% w/v) on rice husk (RH) at 90 °C for 2 h initially followed by anaerobic digestion (AD) for biogas generation. This recovers silica, yielding residual pulp devoid of lignin, a raw material for biogas generation. Analytical investigation through FE-SEM reveals mild fissures and surface ruptures in 4% NaOH-treated RH, while XRD shows a crystallinity index increase from 43.3% (untreated RH) to 69.4% (NaOH-treated RH). The optimal NaOH concentration, yielding 0.16 g/g of silica and 0.206 L/g VSadded of biogas is 4%. These results highlight tailored NaOH's potential for enhancing silica recovery and biogas production from RH. Spearman's correlation analysis reveals a strong correlation (0.9–1.0) among the reduction in volatile solids (VS %), total solids (TS %), methane yield (mL/g VSadded), and biogas yield (mL/g VSadded). P values for artificial neural network (ANN) and fuzzy models consistently range from 10−4 to 10−19. Achieving sustainability necessitates balancing the trade-off between maximizing biogas production and optimizing silica recovery for an environmentally sound and efficient system.

Along‐Strike Variations of Alaska Subduction Zone Structure and Hydration Determined From Amphibious Seismic Data

AbstractWe develop a 3‐D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land‐based seismographs to investigate along‐strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land‐based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high‐velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from VS reduction and VP/VS are larger than those determined using VP reduction in prior studies, likely due to water in cracks affecting VS more than VP. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments.

Anaerobic co-digestion of food waste and bio flocculated sewage sludge towards bio-methane production

The existing sewage treatment plants are energy consumers rather than producers and integration of anaerobic reactor can be a viable approach for enhancing their commercial viability. Therefore, anaerobic co-digestion of food waste and bio-flocculated sewage sludge was studied in a continuous stirred tank reactors (R1 and R2) having a working volume of 6.5 Litre at organic loading rates of 2.5 and 2.4 g VS L−1D−1. At mesophilic temperature, the stabilisation of inoculum was performed in batch mode for 60 days followed by continuous mode feeding for 120 days. The feeding ratio was decided based on availability of food waste and bio-flocculated sewage sludge from a typical domestic household for analysing the effect of volatile fatty acids accumulation on reactor performance. The R1 was fed with equal proportion of bio-flocculated sewage sludge and food waste while R2 was fed in 98:2 (v/v), respectively. To analyse the mixing and temperature distribution within the digester, the velocity and temperature profiles were obtained using Ansys Fluent. In R1, more biogas yield were observed than R2 due to 80% average VS reduction as compared to 55% in case of R2. The highest volatile fatty acids accumulation of 10951 mg L−1 was observed in R1 whereas R2 showed 2800 mg L−1, respectively. The more fluctuations in pH were observed in R1 as compared to R2 due to more food waste concentration and maximum bio-methane production was 133 and 233 mL CH4 g−1 VSadded in R1 and R2, respectively.

Enhancing Single- and Two-Stage Anaerobic Digestion of Thickened Waste-Activated Sludge through FNA-Heat Pretreatment

This study aimed to investigate the effect of combined Free Nitrous Acid (FNA)-Heat (i.e., FNH) pretreatment on single- and two-stage anaerobic digestion (AD) of thickened waste-activated sludge (TWAS). Single-stage AD was conducted in batches, while two-stage AD involved acidogenic fermentation under semi-continuous flow followed by batch methanogenesis. FNH pretreatment was applied before the acidogenic stage, using 1.4 mg HNO2-N/L FNA concentration at 25 °C, 37 °C, and 60 °C for 24 h. Among the scenarios, the most promising results were observed with two-stage AD fed with FNH-pretreated TWAS at 60 °C, showing higher COD solubilization and a reduction in volatile solids. Combined FNA-Heat pretreatment in two-stage AD yielded elevated methane production (363–415 mL CH4/g VS added) compared to single-stage digestion. Methane yields from FNA-Heat pretreated single-stage ranged from 332 to 347 mL CH4/g VS added, contrasting with 212 mL CH4/g VS added for untreated TWAS. Methane generation commenced early in both untreated and pretreated samples, attributed to soluble substrate abundance.

Thermal Equations of State of Magnesite: Implication for the Complex Mid‐Lower Mantle Seismic Scatterers

AbstractMagnesite (MgCO3) entering the lower mantle together with the subducted oceanic crust is an important carbon carrier. The reaction between magnesite and mantle minerals has been documented, but its influence on the density and velocity profiles of lower mantle remains unexplored. To decipher the deep carbon transportation and its associated effect, here we determined the thermal equations of state of magnesite up to 120 GPa and 2600 K using X‐ray diffraction in laser‐heated diamond anvil cells. The obtained thermal elastic parameters of magnesite facilitated a comprehensive understanding on the influence of magnesite‐SiO2 reaction, variation of carbon and SiO2 content, and temperature on the origin of lower‐mantle scatterers at 1,000–1,800 km depth. Our modeling revealed that the depth of the lower‐mantle VS scatterers is mainly controlled by the Al2O3 content in SiO2, while its magnitude depends on the SiO2 content. Along normal geotherm, the magnesite‐SiO2 reaction would occur before the post‐stishovite transition, consuming substantial SiO2 in the subducted oceanic crust. Depending on the amount of residual SiO2, the post‐stishovite transition can produce a 2.5–5.2 (2)% VS reduction, compatible with the observed seismic scatterers in Izu‐Bonin and Mariana subduction zones. Along slab geotherm, this reaction occurs after the post‐stishovite transition, generating a greater VS reduction of 4.4–6.4 (4)%. We thus propose that the reaction between sinking MgCO3 and SiO2 in the slab is one of the potential factors influencing the magnitude of the lower‐Vs scatterers at 1,000–1,900 km depth. Our results provide new insights into the deep‐mantle carbonate transportation influencing regional geophysics.

Anaerobic Treatment of Food Waste with Biogas Recirculation under Psychrophilic Temperature

Food waste has emerged as a pressing concern, and thus advanced techniques to valorize food waste into nutrition rich materials as well as renewable energy are highly important. The exceptional biodegradability of food waste renders it a highly suitable substrate for anaerobic treatment. This leads to energy production and a reduction in the carbon footprint. Nevertheless, in frigid territories like Canada, the conventional mesophilic anaerobic digestion at 30–40 °C can require substantial amounts of energy. Consequently, this study introduces a new approach to treat food waste at psychrophilic temperatures (1–20 °C). Lower temperatures can negatively impact cellular processes during anaerobic treatment, rendering substrates less accessible to microscopic organisms. To address this challenge associated with lower temperatures, the study introduces an innovative biogas recirculation strategy. The primary objectives of this study are to assess the viability of anaerobic treatment for food waste at psychrophilic temperatures and to investigate the effectiveness of reintroduction of the produced biogas to the anaerobic system in enhancing biomethane generation and stability of the system. Batch experiments were conducted on food waste in various assessments, both with and without biogas recirculation. The outcomes revealed a methane concentration ranging from 68% to 93% when biogas recirculation was employed, whereas without this technique, methane concentration varied between 10% and 45%. Moreover, with biogas recirculation, the reduction in volatile solids reached a maximum of 92%, and there was an 82% decrease in chemical oxygen demand. In conclusion, the utilization of the recirculation of biogas at the psychrophilic temperature range enhanced biomethane production and reduction of volatile solids and chemical oxygen demand. This study underscores the potential of employing anaerobic treatment with reintroduction of produced biogas into the system in cold regions as an economically viable and sustainable choice for treating food waste with nominal energy consumption.

Digestão anaeróbia de dejetos de poedeiras alimentadas com dietas contendo diferentes fontes minerais e níveis de óleo de alecrim

ABSTRACT: This study evaluated the stability of anaerobic digestion and biogas production from the manure of laying hens fed diets containing different mineral sources and rosemary oil concentrations. Manure was obtained from 288 semi-heavy laying hens, 30 weeks old, and collected for 112 days. A completely randomized design was used in a 2×3 factorial scheme with repeated measures, considering two mineral sources (inorganic and organic) and three concentrations of rosemary oil (0, 100, and 200 mg kg-1). Twelve continuous bench digesters (7.5 kg) were operated with a hydraulic retention time of 30 days and daily loads of 5% total solids, for 90 days. A weekly analysis of influents and effluents was performed by measuring the values of total solids (TS), volatile solids (VS), pH, ammonia nitrogen (ammonia N), intermediary alkalinity (IA), partial alkalinity (PA), and the relationship IA:PA; biweekly analysis of total nitrogen (N) and total phosphorus (P) concentrations; and daily measurement of biogas production data to calculate the biogas production potential of the manure. Manure from laying hens fed with organic minerals has greater potential for biogas production and greater TS and VS reduction than manure from hens supplemented with inorganic minerals. Laying hen diets containing up to 200 mg kg-1 of rosemary oil do not present the risk of anaerobic digestion failure.

Anaerobic digestion of distillery wastewater and napier grass: Characterization and process performance parameters

The BOD/COD ratio of napier grass (NG) + distillery wastewater (DWW) was found to be 0.4982, which reflected that the biodegradability of organic material is high and can be degraded and treated efficiently via biological processes. Moreover, further reductions in total solids (TS) and volatile solids (VS) were observed after thermal pretreatment at temperatures of 60°C and 100°C. VS/TS ratio also increased from 0.8767 to 0.9508 indicating a more significant proportion of organic matter are favorable for biogas production. This was evidenced by the resulting removal efficiencies ranging from 15% to 32% and 23% to 42%, for TS and VS, respectively. Overall, the study reported relevant effects of the application of thermochemical pretreatment in the process performance parameters in anaerobic digestion.

Effect of alkali pretreatment time on kitchen waste anaerobic digestion performance enhanced by alkali pretreatment combined with bentonite: performance enhancement, microbial community structure, and functional gene analysis.

Kitchen waste was mainly composed of carbohydrates, lipids, and proteins. Anaerobic digestion (AD) of kitchen waste usually occurred acidification and further deteriorated. In our previous study, alkali pretreatment combined with bentonite (AP/Be) treatment was proved to enhance high solid AD of kitchen waste. However, effects of AP time on AP/Be were not yet studied. This study investigated the effects of AP time on AP/Be treatment on enhancing high solid AD. The results showed that compared with the control group, the cumulative methane production rate could be increased by 3.30 times (149.7mL CH4/g VS) and the volatile solids (VS) reduction rate increased by 63.36%. Microbial community analysis showed that the relative abundance of Methanosarcina and Methanosaeta were increased from 6.49 and 7.83% to 47.14 and 16.39% respectively. Predictive functional analysis showed that AP/Be treatment increased the abundance of energy production and conversion, coenzyme transport, and metabolism. This study revealed the potential mechanism of AP/Be enhanced kitchen waste AD performance and AP/Be was a potential strategy to strengthen AD.

Anaerobic digestion of the organic fraction of municipal solid waste in a simulated bioreactor to improve predictive modeling of landfill systems

Municipal solid waste (MSW) generation is increasing globally, containing up to 57 % organic matter. Trapping and extraction of methane (CH4) produced via anaerobic digestion (AD) of the organic fraction of MSW (OFMSW) reduces CH4 released from landfills into the atmosphere. To estimate CH4 production from OFMSW, mathematical models are frequently used, but their accuracy varies under the non-ideal conditions that are inevitable in real landfilling scenarios. This work calibrates first-order decay (FOD) and Gompertz models for predicting CH4 production from the OFMSW based on experimental results from a pilot-scale landfill bioreactor operating under non-ideal conditions, namely under dry and mesophilic conditions with low leachate recirculation inteded to represent landfills in developing countries. This study achieved a 73 % and 66 % reduction in volatile solids (VS) and total solids (TS), respectively, demonstrating successful organic degradation. Models were calibrated using laboratory data, showing high correlation and accuracy >80 % in a Chemical Oxygen Demand (COD) mass balance. The experiment produced 104.3 mL CH4 g−1 VS with accurate predictions from calibrated models Non-calibrated models, however, overestimated methane production by 75 %. Work highlights the importance of modifying models for non-ideal conditions, and results provide useful information for landfills in developing countries.

Effects of thermal pretreatment and biotin supplementation on the anaerobic digestion of pineapple (Ananas comosus) wastes, kinetics of methane production, and statistical analysis

The anaerobic digestion (AD) of pineapple wastes (PW) was employed to understand the effects of design parameters, namely thermal pretreatment (TP) temperature (X1) and reaction time (X2), and biotin concentration (X3), to methane production. Kinetic parameters were evaluated by utilizing sigmoidal growth functions, whereas modified Gompertz (MGM) and Logistic function (LF) best described the system among all batch assays. Principal components analysis (PCA) and Pearson correlation matrix were used to understand the correlation and relationship between the design parameters, evaluated kinetic parameters, methane yield (Y), and process performance parameters, wherein it was found that the significantly statistical correlations were Rm-A, λ-X1, A-Y, A-%VS reduction, A-%pH change, Rm-Y, Y-%VS reduction, Y-%pH change, and %VS reduction-%pH change. Furthermore, the cumulative methane production profile in all reactors showed an increase of 19.2–169.2 % in Y compared to the control, suggesting that TP and biotin supplementation were suitable for the optimization of Y from the AD of PW. The Y among all reactors followed the order of A0 <A1 <A2 <A4 <A7 <A3 <A5 <A8 <A6 wherein the lowest Y from pretreated PW was observed at A1 (77.6478 mL/gVS), while the highest was recorded at A6 (175.3053 mL/gVS). The ANOVA results demonstrated that the contribution of main and interaction parameters to Y (X3 >X1X3 >X2X3 >X1 >X2 >X1X2) were statistically significant (p < 0.05), and therefore relevant in the microbial syntrophies during the AD of PW. From the regression analysis, a surrogate mathematical model was constructed with a goodness of fit R2adj= 0.998. Herein, the optimum design conditions in the methane production from AD of PW were found to be X1 = 80ºC, X2 = 120 min, and X3 = 0.25 mg/L.

Ruminal content biochar supplementation for enhanced biomethanation of rice straw: Focusing on biochar characterization and dose optimization

Anaerobic digestion (AD) of agricultural wastes is a promising approach for energy recovery and crop residue management. However, its recalcitrant chemical structure hinders microbial hydrolysis and reduces biomethane production under AD. Biochar supplementation has been proven to promote the digestibility and biomethanation of lignocellulosic substrates. Therefore, this study investigated the influence of different pyrolysis temperatures (450 °C, 550 °C, and 650 °C) on the physicochemical properties of biochar. Furthermore, the impact of ruminal content biochar supplementation (1 %, 2 %, and 3 %) on the AD of rice straw with rumen fluid as inoculum has been investigated. The ruminal content biochar (RUCB) supplemented reactors showed an increment in biomethane yield and the highest cumulative biomethane yield 243.11 mL/g volatile solids (VS)) was recorded at 2 % RUCB supplementation, followed by 227.12 mL/g VS at 1 % RUCB supplementation and 162.86 mL/g VS at 3 % RUCB supplementation (P > 0.05). Compared to the control reactors (128.68 mL/g VS), RUCB supplemented reactors exhibited 1.88-fold, 1.76-fold, and 1.26-fold increments in biomethane yield due to pH stabilization and facilitation of microbial biofilm formation on the biochar. The correlation analysis showed that biomethane production is positively correlated with VS reduction (R2 = 0.9852). This study proposed a potential strategy to utilize ruminal content waste as a feedstock for biochar production and its application in AD for accelerating the biomethanation of rice straw.

Enhancing thermophilic anaerobic digestion of municipal sludge: An investigation

Thermophilic anaerobic digestion (TAD), although less explored as opposed to mesophilic AD is a viable strategy to reduce the volume of municipal sludge and generate renewable energy in the form of biogas simultaneously. In this study, biochemical methane potential was tested to compare three different pretreatments i.e., ultrasonication, biochar (black spruce wood and bark, California almond hull), enzyme (cocktail of endoglucanase, β-glucosidase, xylanase) for their ability to enhance TAD of municipal sludge. In addition to conventional parameters such as chemical oxygen demand (COD), volatile solids (VS), and biogas, the respiratory value and the pathogen removal were also evaluated. Ultrasonication for 20 min was found to be the best pretreatment in terms of higher COD removal, biogas generation and VS reduction. This is possible due to the increase in soluble fraction of organic matter after ultrasonication which facilitated effective hydrolysis and reduction in start-up time. However, pathogen removal was mostly facilitated by AD and the contribution of pretreatment was minimal.