Specific Biogas Production Rate Research Articles

Influence of the Construction Materials Properties of the Biodigester on the Biogas Production and Electricity Generated by the Slaughterhouse Waste

The objective of this study was to carry out a comparative analysis of the influence of the properties of the construction materials of the biodigester based on three different materials (steel, plastic PVC, and concrete) to predict the rate of biogas production from the anaerobic digestion of slaughterhouse waste. The input parameters were substrate temperature, ambient temperature, biogas temperature, biodigester temperature, specific biogas production rate, and material properties. A thermal model was developed using MATLAB® software to predict biogas production, with readily available input data for an unheated, uninsulated, and partially buried biodigester. The results obtained showed that the temperatures and the average daily biogas productions were higher for the steel biodigester (1.5 ± 0.12 m3/day at 36 ± 2℃) than those produced from the PVC (1.3 ± 0.1 m3/day at 31 ± 1.5℃) and concrete (1.2 ± 0.05 m3/day at 27 ± 2℃) biodigesters. Moreover, the production of electricity for a steel biodigester (14.64 kWh) was found to be greater than that produced from the PVC (12.81 kWh) and concrete (10.98 kWh) biodigesters. The results showed that the properties of the construction materials of the digester had a significant influence on the temperature and production of biogas, and therefore on the production of electricity. On the other hand, among the three materials studied, steel was the material, which yielded the best results. The proposed model gave rRMSE values between 7.4 and 8.3% and R2 between 0.92 and 0.96.

Sustainable Valorization of Four Types of Fruit Peel Waste for Biogas Recovery and Use of Digestate for Radish (Raphanus sativus L. cv. Pusa Himani) Cultivation

Food waste has become a challenging global issue due to its inefficient management, particularly in low and middle-income countries. Among food waste items, fruit peel waste (FPW) is generated in enormous quantities, especially from juice vendors, resulting in arduous tasks for waste management personnel and authorities. However, considering the nutrient and digestible content of organic wastes, in this study four types of FPW (pineapple: PA; sweet lemon: SL; kinnow: KN; and pomegranate: PG) were investigated for their potential use within biogas production, using conventional and electro-assisted anaerobic reactors (CAR and EAR). In addition, the FPW digestate obtained after the biogas production experiments was considered as a soil bio-fertilizer under radish (Raphanussativus L. cv. Pusa Himani) cultivation. In the results, all four types of FPW had digestible organic fractions, as revealed from physicochemical and proximate analysis. However, PA-based FPW yielded the maximum biogas (1422.76 ± 3.10 mL/62.21 ± 0.13% CH4) using the EAR system, compared to all other FPW. Overall, the decreasing order of biogas yield obtained from FPW was observed as PA > PG > SL > KN. The kinetic analysis of the biogas production process showed that the modified Gompertz model best fitted in terms of coefficient of determination (R2 > 0.99) to predict cumulative biogas production (y), lag phase (λ), and specific biogas production rate (µm). Moreover, fertilizer application of spent FPW digestate obtained after biogas production significantly improved the arable soil properties (p < 0.05). Further, KN-based FPW digestate mixing showed maximum improvement in radish plant height (36.50 ± 0.82 cm), plant spread (70.80 ± 3.79 cm2), number of leaves (16.12 ± 0.05), fresh weight of leaves (158.08 ± 2.85 g/plant), fruit yield (140.10 ± 2.13 g/plant), and fruit length (25.05 ± 0.15 cm). Thus, this study suggests an efficient method of FPW management through biogas and crop production.

Performance and microbial community analysis of anaerobic sludge digestion enhanced by in-situ microaeration

The effectiveness of in-situ microaeration was investigated with varied air dosages [0–25 mL/(L·d)] to enhance mesophilic anaerobic digestion (AD) of sludge in semi-continuous systems in terms of specific biogas production and volatile solids (VS) removal rate, focusing on performance evaluation, microbial community analysis, and underlying mechanisms. The optimal dosage of 12.5 mL/(L·d) increased specific biogas production by 15.8 ± 7.3% and enhanced VS removal by 18.3 ± 1.6%. In-situ microaeration stimulated activity of hydrolytic enzymes, enlarged sludge particle size, and improved sludge dewaterability. MiSeq sequencing analysis showed that dominant bacterial and archaeal communities were remarkably different between in-situ microaeration and obligate AD process. The presence of oxygen enriched relative abundances of Deltaproteobacteria, Anaerolineae, Clostridia, Synergistia and Caldilineae, enabling the acid-producing process to metabolize more types of substrates. Due to the selective enrichment, in-situ microaeration significantly enriched aceticlastic methanogens rather than hydrogenotrophic methanogens in the AD reactor. Analysis of coupling microaeration pretreatment and in-situ microaeration for anaerobic digestion indicated that excessive microaeration decreased VS removal rate and methane yield owing to substrates consumption by facultative bacteria. In-situ microaeration-based AD could be a promising process for sludge treatment and bioenergy recovery.

An anaerobic dynamic membrane bioreactor for enhancing sludge digestion: Impact of solids retention time on digestion efficacy

An anaerobic dynamic membrane bioreactor (AnDMBR), which enabled the decoupling of hydraulic retention time (HRT) and solids retention time (SRT), was used for enhancing sludge digestion, with the associated mechanisms elucidated. With the increase of SRT, the biogas production and sludge reduction rate were both enhanced. The specific biogas production and volatile solids (VS) reduction rate were improved to 0.79 L/g VS and 55.9% under SRT 50 d, respectively. Microbial community analysis revealed that Chloroflexi, which is capable of degrading metabolites and dead cells, was enriched at longer SRT. Further analysis showed that both acetoclastic and hydrogenotrophic methanogenesis contributed to the enhanced biogas production under higher SRT compared to the dominance of acetoclastic methanogenesis under lower SRT. The enhanced utilization of organic matter and acetate at longer SRT further confirmed the mechanisms. The results highlighted the potential of AnDMBR for high-efficient sludge digestion.

Performance of a Full-Scale Biogas Plant Operation in Greece and Its Impact on the Circular Economy

Biogas plants have been started to expand recently in Greece and their positive contribution to the economy is evident. A typical case study is presented which focuses on the long-term monitoring (lasting for one year) of a 500 kW mesophilic biogas plant consisting of an one-stage digester. The main feedstock used was cow manure, supplemented occasionally with chicken manure, corn silage, wheat/ray silage, glycerine, cheese whey, molasses and olive mill wastewater. The mixture of the feedstocks was adjusted based on their availability, cost and biochemical methane potential. The organic loading rate (OLR) varied at 3.42 ± 0.23 kg COD m−3 day−1 (or 2.74 ± 0.18 kg VS m−3 day−1) and resulted in a stable performance in terms of specific biogas production rate (1.27 ± 0.12 m3 m−3 day−1), biogas yield (0.46 ± 0.05 m3 kg−1 VS, 55 ± 1.3% in methane) and electricity production rate (12687 ± 1140 kWh day−1). There were no problems of foaming, nor was there a need for trace metal addition. The digestate was used by the neighboring farmers who observed an improvement in their crop yield. The profit estimates per feedstock indicate that chicken manure is superior to the other feedstocks, while molasses, silages and glycerin result in less profit due to the long distance of the biogas plant from their production source. Finally, the greenhouse gas emissions due to the digestate storage in the open air seem to be minor (0.81% of the methane consumed).

Appraisal of methane production and anaerobic fermentation kinetics of livestock manures using artificial neural networks and sinusoidal growth functions

This study aimed to perform a comparative analysis of the performance of five models (Gompertz, logistic, Richards, the first-order, artificial neural networks) in predicting methane production rate from anaerobic digestion of livestock manures. The input variables were fermentation time, digestion temperature, biogas temperature, ambient temperature, pH, and specific biogas production rate. The physicochemical compositions of cow manure and sheep manure showed that volatile solid (VS) contents were close to each other in manure compositions (77.6% and 64.7%, respectively), while the potential of methane production from cow manure (673.44 mL CH4/g VS) was greater than that from sheep manure (320.32 mL CH4/g VS). The determination coefficients (R2) for logistic function, Gompertz, Richards, the first-order, and ANN models were obtained as 0.968, 0.967, 0.975, 0.825, and 0.995 for the cow manure, respectively. In case of the sheep manure, the R2 values obtained from these models were 0.976, 0.979, 0.981, 0.968 and 0.991, respectively. Although the determination coefficients of all models were in satisfactory agreement with the experimental data, the ANN model showed competitive lower RMSE values of 0.111 and 0.164 for cow and sheep manure data sets, respectively, indicating its superior performance than other models.

Characteristics of Biohydrogen Production and Performance of Hydrogen-Producing Acetogen by Increasing Normal Molasses Wastewater Proportion in Anaerobic Baffled Reactor.

The biohydrogen production efficiency and performance of hydrogen-producing acetogen in a four-compartment anaerobic baffled reactor (ABR) were studied by gradually increasing the influent normal molasses wastewater (NMWW) proportion. When the influent NMWW proportion increased to 55%, ABR could develop microbial community with methanogenic function in 63 days and reach a stable operation. When the influent NMWW proportion increased to 80% and reached a stable state, ethanol fermentation was established from butyric acid fermentation in the first three compartments, whereas butyric acid fermentation in the fourth compartment was strengthened. The average biohydrogen production yield and biohydrogen production capacity by COD removal increased to as high as 12.85 L/day and 360.22 L/kg COD when the influent NMWW proportion increased from 55% to 80%, respectively. Although the biogas yield and the specific biogas production rate reached 61.54 L/day and 232 L/kg MLVSS·day, the biohydrogen production yield and specific biohydrogen production rate were only 12.85 L/day and 48 L/kg MLVSS·day, which results in hydrogen consumption by homoacetogenesis and methanogenesis.

Effect of Hydraulic Retention Time on Anaerobic Baffled Reactor Operation: Enhanced Biohydrogen Production and Enrichment of Hydrogen-producing Acetogens

Biohydrogen production by fermentation has become a promising technology developed in the world. In this study, diluted normal molasses wastewater is used as the raw material, and biohydrogen production efficiency and operation characteristics of an anaerobic baffled reactor (ABR) are studied. The effect of hydraulic retention time (HRT) on biohydrogen production efficiency and operating characteristics of ABR is extensively discussed. Experimental results showed that methanogen residuals were still observed in the last three compartments under HRT of 24 h and COD(Chemical oxygen demand) concentration of 8000 mg/L. Meanwhile, the first three compartments presented an ethanol fermentation type. The characteristics of butyric acid fermentation in Compartment IV were also enhanced. The average removal efficiency of COD was reduced to 15.4%. The average rates of biohydrogen production and specific biohydrogen production were 12.85 and 360.22 L/kg COD, respectively. The extension of HRT was beneficial to enrich hydrogen-producing acetogens and could increase the production rate of biohydrogen by a factor of 1.65. However, with the decrease in the bioactivity of acidogenic fermentation bacteria, the biohydrogen production efficiency of ABR was significantly reduced when HRT was longer than 30 h. The specific biogas production rate decreased from 191 to 92 L/(kg MLVSS·d). The specific biohydrogen production rate also decreased from 24.34 to 2.7 L/(kg MLVSS·d).

Influence of substrate to inoculum ratio (S/I) on the treatment performance of food processing wastewater containing high oil and grease (O&G) in batch mode

Anaerobic digestion is one of the promising methods for treating high strength organic waste liquid with the recovery of energy such as biogas. The current study reports the physical–chemical characteristic of the waste, its treatment performance and methane gas production from a liquid organic substrate high in oil and grease generated from a food processing industry in Malaysia. The substrate is suitable for energy recovery as it contains high organic matter ranging between 15 and 17 g/L chemical oxygen demand (COD). The batch biodegradability test assays were used in anaerobic digestion of the food processing wastewater (FPW) for its treatment performance and methane yield at different ratios of the substrate (FPW) to inoculum (anaerobic digester sludge) (S/I) of 1.0, 1.5 and 2.0 for 54 d. From the results, S/I 1.0 ratio performance is ideal for COD, biochemical oxygen demand, total solids and volatile solids (VS) removal at 96.9%, 96.6%, 75.8%, 65.2%, respectively, showing a balanced substrate/food and microorganism (F/M ratio) in the digester that is important for the degradation of complex organic material. The maximum amount of specific biogas production rate was 228.6 mL/gVS in S/I of 1.0 treatment, with a methane gas production yield of 200.5 mL/gVS. While the minimum methane gas production yield of 67.5 mL/gVS was produced for S/I of 2.0. The specific biogas production rate was found at 84.6 mL/gVS. The higher substrate to the inoculum ratio of S/I 1.5 and 2.0 has delayed the biogas and methane production by 20 d. The results indicate that FPW anaerobic digestion is promising to treat the effluent and produce biogas containing a moderate amount of methane.

An Experimental Study on Recovery of Energy from Biodegradable Waste with Eichhornia Crassipes in TKRCET, Hyderabad, Telangana

Objectives: The work is to recover the energy from food and vegetable waste with water hyacinth and cowdung. Methods: The present study focuses the lights to recover energy from organic waste and to adopt safe disposal and conserving natural resources. Laboratory scale batch digesters were set up to find the biogas production potential of Food waste and Vegetable waste with water hyacinth and cow dung. Food waste was collected from our TKR college mess similarly Vegetable waste was collected from the Hyderabad market and prepared for further analysis. Similarly water hyacinth was collected from a Meerpet lake in Hyderabad. Six digesters with varying Vegetable wastes and Food wastes were combined individually by increasing concentrations with fixed amount of water hyacinth and Cow dung by water displacement method. The effect of food waste and vegetable waste concentration on the biogas yield was investigated and the experiments were characterised before and after digestion. Findings: Modified Gompertz Equation (MGE) model was fitted to the experimental values and kinetic parameters such as maximum cumulative biogas potential Bmax (L/gVS), specific biogas production rate, Rb (L gVS-1d-1) and lag phase time, λ(d), were estimated. Experimental values were compared with MGE using MAT LAB. Applications/Improvements: From the experimental study observed that an aerobic degradation took place and the biogas produced was measured daily. Kinetic analysis of the biogas production was done and compared & conclusions were drawn. Keywords: Anaerobic Digestion, Food Waste, Modified Gompertz Equation (MGE), Vegetable Waste Kinetic Modelling, Water Hyacinth

Mesophilic and thermophilic anaerobic digestion of faecal sludge in a pilot plant digester

In many developing countries, the sewage consisting of faecal sludge is discharged untreated into rivers, lakes and coastal areas. This poses a health hazard and a risk to the ecosystem, and wastes a resource which could produce sustainable energy. This paper reports results from an anaerobic digester of 1000L used for digestion of faecal waste at mesophilic and thermophilic conditions. The specific biogas production rate from faecal sludge was in the range of 0.06–0.12 m3/(kg DM.d) at mesophilic conditions at NTP (Normal Temperature & Pressure i.e. 25 °C and 1 atm. Pressure) and 0.1–0.21 m3/(kg DM.d) at thermophilic conditions calculated at NTP. The number of toilet users affects the biogas production with changes in the organic loading rate. The results showed 97% reductionin chemical oxygen demand and 90% reduction in biological oxygen demand of anaerobic digester discharge water as compared to inlet substrate values.

Kinetics of biogas production and chemical oxygen demand removal from compost leachate in an anaerobic migrating blanket reactor

In this study, laboratory anaerobic migrating blanket reactor (AMBR) with four units was used to reduce and remove COD leachate of composting process; it was also used to determine the kinetic coefficients of COD removal and biogas and methane gas production in several different OLRs. The maximum concentration of organic matter entering the reactor was 100,000 mg/L and the reactor was under operation for 319 days. The results showed that the COD removal efficiency of AMBR in all concentrations of substrate entering the reactor was above 80%. First-order model and Stover-Kincannon were used to investigate the kinetics of COD removal via AMBR biological process; in addition, the two models of Modified Stover-Kincannon and Van der Meer and Heertjes were used to check the kinetic constants of biogas and methane gas production. The results obtained from the models showed that the experimental data on COD removal were more consistent with the results obtained from Stover-Kincannon model (R2 = 0.999) rather than with the First-order model (R2 = 0.926). Kinetic constants calculated via Stover-Kincannon model were as follows: saturation value constant (KB) and maximum utilization rate constants (Umax), respectively, were 208,600 mg/L d and 172,400 mg/L d. We investigated the linear relationship between the experimental data and the values predicted by the models; as compared with the values predicted by the First-order model, the values predicted by Stover-Kincannon model were closer to the values measured via experiments. Based on the results of the evaluation of kinetic coefficients of Stover-Kincannon model, with the migration of the leachate flow from unit 1 to unit 4, Umax value has fallen significantly. The values of maximum specific biogas production rate (Gmax) and proportionality constant (GB) obtained from the Stover-Kincannon model, respectively, were 35,714 ml/L d and 42.85 (dimensionless) and value of kinetic constant of Van der Meer and Heertjes (ksg) was 0.0473 ml CH4/mg COD.

Linkage of kinetic parameters with process parameters and operational conditions during anaerobic digestion

Kinetic characteristics play an important role in anaerobic digestion system for representing biogas production performance, however, its relationship with anaerobic digestion process parameters (i. e., volatile fatty acids, total ammonia nitrogen, pH and total alkalinity) and operational conditions remains poorly understood. To illustrate the linkage of kinetic parameters with process parameters and swine manure content and initial pH, and the effects of swine manure content and initial pH on anaerobic digestion performance, substrate properties, accumulative biogas production, specific biogas production rate and process parameters were analyzed under different treatments. Additionally, the effects of swine manure and initial pH on hydrolysis constant, lag phase, biogas production potential and the maximum biogas production rate were investigated. The results revealed that volatile solid and C:N ratio were significantly decreased with swine manure content increased which were considered as operational conditions with initial pH following the linkage illustration. Furthermore, accumulative biogas production, biogas production rate, final pH, total ammonia nitrogen and hydrolysis constant were increased with swine manure content and initial pH increased, while volatile fatty acids and lag phase showed the opposite trend. The results showed that these operational conditions significantly influenced process parameters and kinetic parameters, with close correlations were observed. Lag phase closely correlated with VFA which was closely correlated with C:N ratio. Therefore, C:N ratio impacted kinetic parameters via effecting VFA, while initial pH directly influenced kinetic parameters. Meanwhile, the correlation of kinetic parameters with C:N ratio was stronger than initial pH. Therefore, C:N ratio should be an indicator for estimating process performance, time the bacteria's acclimatization to the new environment and biogas production. Taken together, these findings provide a scientific theory for estimating anaerobic digestion performance.

Comparative evaluation of biogas production from dairy manure and co-digestion with maize silage by CSTR and new anaerobic hybrid reactor.

This study aimed to investigate potential methane production through anaerobic digestion of dairy manure and co-digestion with maize silage. Two different anaerobic reactor configurations (single-stage continuously stirred tank reactor [CSTR] and hybrid anaerobic digester) were used and biogas production performances for each reactor were compared. The HR was planned to enable phase separation in order to improve process stability and biogas production under higher total solids loadings (≥4%). The systems were tested under six different organic loading rates increased steadily from 1.1 to 5.4 g VS/L.d. The CSTR exhibited lower system stability and biomass conversion efficiency than the HR. The specific biogas production of the hybrid system was between 440 and 320 mL/gVS with 81-65% volatile solids (VS) destruction. The hybrid system provided 116% increase in specific biogas production and VS destruction improved by more than 14%. When MS was co-digested together with dairy manure, specific biogas production rates increased about 1.2-fold. Co-digestion was more beneficial than mono-material digestion. The hybrid system allowed for generating methane enriched biogas (>75% methane) by enabling phase separation in the reactor. It was observed that acidogenic conditions prevailed in the first two compartments and the following two segments as methanogenic conditions were observed. The pH of the acidogenic part ranged between 4.7 and 5.5 and the methanogenic part was between 6.8 and 7.2.

Effect of Hydrothermal Pretreatment for Enhanced Biogas Production Using Micro-algal Biomass

The filamentous algal biomass, Hydrodictyon reticulatum (H. reticuatum) was used to evaluate the biogas production after hydrothermal pretreatment in batch anaerobic digestion. The effect of hydrothermal pretreatment at range of 50 ~ 280 o C was tested with filamentous algal biomass. The solubilization by pretreatment showed a higher degree of disintegrated filamentous algal biomass and the soluble COD was increased 12.8 fold than untreated sample at 280 o C. Solubilization due to hydrothermal pretreatment increased the specific biogas production and volatile solids reduction rates. Using the hydrothermal treatment approach, the specific methane production were 161.8, 169.1, 178.4, 191.7, 274.9, 285.2 and 364.4 mL/g-VS of the pretreated at raw, 50, 100, 120, 180, 230, and 280 o C, respectively. The volatile solids reduction was greater with increased temperature applied, and the degradation increased 69.7% at 280 o C from 45.8 % VS reduction of raw filamentous algal biomass.

ANAEROBIC CO-CULTIVATION OF MULTI-ALGAL SPECIES WITH OIL PALM EMPTY FRUIT BUNCHES FOR MILL EFFLUENT TREATMENT AND BIOMETHANE PRODUCTION

This study investigated the optimization of anaerobic co-cultivation of multi-algal species with Oil Palm Empty Fruit Bunches (OPEFB) for Palm Oil Mill Effluent (POME) treatment and biomethane production. The highest removal of COD (95-98%), BOD (90-98%), TOC (81-86%) and TN (78-80%) were achieved after 7 days anaerobic treatment with the presence of microalgae. The highest biomethane (4,651.9 mL CH4/L POME/day) and the specific biogas production rate (0.124 m3/kg COD/day) with CO2 (2,265.9mL CO2/L POME/day) were achieved by co-cultivating N. oculata and Chlorella sp. (each at 1 mL/mL POME) with OPEFB (0.12 g/mL POME). The combination of N. oculata (2 mL/mL POME) with T. suecica or Chlorella sp. (each at 1 mL/mL POME), and OPEFB (0.12 g/mL POME) obtained high biomethane (4,018.9 mL CH4/L POME /day) but lower biogas (0.097 m3/kg COD/day) and CO2 (2,079.5mL CO2/L POME/day). Generally, low OPEFB and having all the three strains or increasing the level of any (2 mL/mL POME) especially T. suecica, could lower biomethane (870-953 mL CH4/L POME/day) and CO2 (803-854mL CO2/L POME/day), with the biogas around 0.08-0.09 m3/kg COD/day. The optimum conditions were predicted by Response Surface Methodology and the multiple coefficients of determination, r2, of 86% suggests good agreement between experimental and predicted values.

MODELING OF BATCH AND CONTINUOUS ANAEROBIC DIGESTION OF PALM OIL MILL EFFLUENT: THE EFFECT OF WASTEWATER-SLUDGE RATIO

In this work, both models for batch and continuous anaerobic digestion of palm oil mill effluent were developed based on Monod’s kinetics. Then the authors attempt to understand the effect of wastewater-sludge (WW:S) ratio on the biogas production efficiency in batch digesters. The experiments were carried out at a controlled temperature of 35±0.5 °C. Two series of the experiment were conducted. In the first series, the wastewater-sludge ratios covered 1:1 (add sodium bi-carbonate), 1:1, 1:2 and 2:1. It was found that the ratio of 1:2 gave the highest biogas producing efficiency followed by the ratio 1:1 (add sodium bi-carbonate). At 1:1 ratio, sodium bi-carbonate addition was required to start anaerobic digestion at a workable pH range whereas at 1:2 ratio the initial pH is in the workable range without the need of its addition. However, at the ratio of 2:1 the starting pH was too low to adjust pH economically by adding sodium bi-carbonate. The second series was to confine experiments to a narrower ratio range, namely: 1:1 (add sodium bi-carbonate), 1:1.5, 1:2, 1:2.5. In both sets of experiment, the ratio 1:2 gave the best biogas production potential of 76.62 and 78.52 ml of biogas/g COD removed respectively. In all treatments, the process was able to remove more than 80% of wastewater initial COD. The modified Gompertz equation was used to estimate the maximum specific biogas production rate (MBPR or Rm/S0). It was also found that the ratio of 1:2 gave the best MBPR in both experimental series (26.87 ml biogas/g COD-day). A modified Monod-type Model was also developed to describe the microbial growth, substrate consumption and biogas production in continuous operation. In general, sludge recycle provided active biomass which can use the substrate in the wastewater instantly without significant lag phase or delay. Furthermore, continuous-flow model developed, with parameters estimated from batch experiments, predicted the experimental kinetics of the actual continuous experiments satisfactory.

MODELING OF ANAEROBIC CO-DIGESTION OF PIG MANURE AND DOMESTIC ORGANIC WASTE

The normal practice in Thailand is that the wastes from pig-farms and households are treated separately. Nutrient imbalance as well as other physico-chemical characteristics of each waste cause the anaerobic digestion process to work at suboptimal rates. This work is an attempt to describe the kinetics of anaerobic co-digestion of wastewater mixture from a pig-farm and domestic organic waste to understand the effect of their ratio on the biogas production efficiency in batch digesters which mimic a similar industrial practice. The batch experiments were carried out at three different temperatures (28 oC, 32oC and 35oC ), with and without initial pH adjustment (pH 7), and four levels of total solid (8%,12%,16% and 20% TS). It was found that the best operating condition was 35 oC, 16% TS and the pig-manure-to-domestic-waste ratio of 75:25. The modified Gompertz equation was used to estimate some Monod parameters and biomethane potential. Then modified two-substrate Monod equation was used to estimate the maximum specific biogas production rate (MBPR). It was also used to describe the microbial growth, substrate consumption and biogas production satisfactorily.

Production of Biogas Using Maize Silage Supplemented with Residual Glycerine from Biodiesel Manufacturing

Abstract The aim of this study was to investigate the influence of residual glycerine (5 and 10% w/w) from the biodiesel industry, used as a co-substrate, on biogas production from maize silage. The experiments were conducted in a laboratory-scale, single-stage anaerobic digester at 39ºC and hydraulic retention time (HRT) of 60 d. Addition of 5% residual glycerine caused organic load rate (OLR) to increase to 1.82 compared with 1.31 g organic dry matter (ODM) L-1d-1 for maize silage alone. The specific biogas production rate and biogas yield were 1.34 L L-1d-1 and 0.71 L g ODM-1 respectively, i.e. 86% and 30% higher than for maize alone. Increasing the residual glycerine content to 10% increased OLR (2.01 g ODM L-1d-1), but clearly decreased the specific biogas production rate and biogas yield to 0.50 L L-1d-1 and 0.13 L g ODM-1 respectively. This suggested that 10% glycerine content inhibited methanogenic bacteria and organics conversion into biogas. As a result, there was accumulation of propionic and valeric acids throughout the experiment.

Aerobic and anaerobic co-cultivation of Nannochloropsis oculata with oil palm empty fruit bunch for enhanced biomethane production and palm oil mill effluent treatment

This study explored co-cultivation of Nannochloropsis oculata microalgae with oil palm empty fruit bunch (OPEFB) for anaerobic biomethane production and palm oil mill effluent (POME) treatment. The highest specific biogas production rate (1.13–1.14 m3 kg−1 COD d−1) and methane yield (4606–5018 mL CH4 L−1 POME d−1) were achieved with co-cultivation of N. oculata (2 mL/mL POME) and OPEFB (0.12 g/mL POME), as similarly predicted by response surface methodology for optimum conditions. Without microalgae and OPEFB co-cultivation, the biomethane yield was 1.3-fold lower, although the specific biogas production rate remained constant at 1.13–1.16 m3 kg−1 COD d−1. Aerobic and anaerobic treatment of POME after 7 d with microalgae achieved higher removal efficiency of COD (90–97%), BOD (84–98%) and TOC (65–80%) as compared to without microalgae with COD (58–68%), BOD (77–86%) and TOC (58–68%).