Biohydrogen production by anaerobic co-digestion of municipal food waste and sewage sludges

Food waste (FW), primary sludge (PS) and waste activated sludge (WAS) were characterized and found to be complementary in the concentrations of carbohydrates, total Kjeldahl nitrogen (TKN), PO₄–P and some metal for biological hydrogen production. Moreover, FW was found to have low pH buffering capacity while the values for PS and WAS were relatively higher. An anaerobic toxicity analysis (ATA) derived from a methanogenic ATA protocol showed that these waste materials had no toxicity to hydrogen production. Adding phosphate buffer to the FW significantly improved hydrogen production while initial pH was 7.0. Co-digestion of FW and sewage sludge was studied using a batch respirometric cultivation system. All combinations of the feedstocks (FW+PS, FW+WAS and FW+PS+WAS) showed enhanced hydrogen production potential as compared with the individual wastes. A mixing ratio of 1:1 was found to be the best among the ratios tested for all three co-digestion groups. A hydrogen yield of 112 mL/g volatile solid (VS) added was obtained from a combination of FW, PS and WAS. This yield was equivalent to 250 mL/g VS added if only FW contributed to hydrogen production. The reason for the enhancement of hydrogen production was postulated to be multifold in which the increase in buffer capacity in the co-digestion mixture was verified.     

Feasibility of biohydrogen production by anaerobic co-digestion of food waste and sewage sludge

Anaerobic co-digestion of food waste and sewage sludge for hydrogen production was performed in serum bottles under various volatile solids (VS) concentrations (0.5–5.0%) and mixing ratios of two substrates (0:100–100:0, VS basis). Through response surface methodology, empirical equations for hydrogen evolution were obtained. The specific hydrogen production potential of food waste was higher than that of sewage sludge. However, hydrogen production potential increased as sewage sludge composition increased up to 13–19% at all the VS concentrations. The maximum specific hydrogen production potential of 122.9 ml/g carbohydrate-COD was found at the waste composition of 87:13 (food waste:sewage sludge) and the VS concentration of 3.0%. The relationship between carbohydrate concentration, protein concentration, and hydrogen production potential indicated that enriched protein by adding sewage sludge might enhance hydrogen production potential. The maximum specific hydrogen production rate was 111.2 ml H₂/g VSS/h. Food waste and sewage sludge were, therefore, considered as a suitable main substrate and a useful auxiliary substrate, respectively, for hydrogen production. The metabolic results indicated that the fermentation of organic matters was successfully achieved and the characteristics of the heat-treated seed sludge were similar to those of anaerobic spore-forming bacteria, Clostridium sp.     

Biohydrogen production from waste glycerol and sludge by anaerobic mixed cultures

Key factors affecting biohydrogen production from waste glycerol and sludge by anaerobic mixed cultures were optimized using response surface methodology (RSM) with central composite design (CCD). Investigated parameters were waste glycerol concentration, sludge concentration, and the amount of Endo–nutrient addition. Concentrations of waste glycerol and sludge had a significant individual effect on hydrogen production rate (HPR) (p ≤ 0.05). The interactive effect on HPR (p ≤ 0.05) was found between waste glycerol concentration and sludge concentration. The optimal conditions for the maximum HPR were: waste glycerol concentration 22.19 g/L, sludge concentration 7.16 g-total solid (TS/L), and the amount of Endo–nutrient addition 2.89 mL/L in which the maximum HPR of 1.37 mmol H₂/L h was achieved. Using the optimal conditions, HPR from a co-digestion of waste glycerol and sludge (1.37 mmol H₂/L h) was two times greater than the control (waste glycerol without addition of sludge) (0.76 mmol H₂/L h), indicating a significant enhancement of HPR by sludge. Major metabolites of the fermentation process were ethanol, 1,3-propanediol (1,3-PD), lactate, and formate.     

Evaluation of different supplementary nutrients for enhanced biohydrogen production by Enterobacter aerogenes NRRL B 407 using waste derived crude glycerol

Crude glycerol (CG) has several advantages over a range of conventional substrates used for biohydrogen production by Enterobacter aerogenes NRRL B 407. Meanwhile, high process cost due to requirement of expensive supplementary media component is a concern. Therefore, different less expensive (or wastes) materials have been evaluated as supplementary nutrient for H₂ production by CG (meat processing and restaurant waste based biodiesel derived) bioconversion. Among the materials selected, slaughterhouse liquid waste (SL), brewery waste biomass (BWB) and urea was found to improve the production by 18.81 ± 3.56, 27.30 ± 3.54 and 38.57 ± 3.66%, respectively. Further, in the case of urea (10 mg/L), cumulative production as high as 116.41 ± 3.72 mmol H₂/L media has been achieved; which is comparable to other reports available on CG bioconversion. Thus, present study demonstrates successful replacement of large amount (∼5–6 g/L) of expensive nutrients/buffering agents by negligible amount (∼10 mg/L) of different waste materials, without compromising the cumulative H₂ yield. Further, the strain used in the present study was found to grow at an acidic pH as low as 3.3, indicating its prospective application for dark fermentative H₂ production.     

Hydrogen production from crude glycerol in an alkaline microbial electrolysis cell

Crude glycerol is an undesired by-product of biodiesel production with a low commercial value (i.e. a ton of biodiesel results in around 110 kg of crude glycerol) and, thus, glycerol needs valorization. In particular, there is a need of providing a benefit to alkaline wastewaters from biodiesel production with excess of glycerol. Bioelectrochemical systems (BES) are an emerging technique to recover the energy contained in a substrate either as electricity or as other added-value products such as hydrogen. Moreover, promising results have been reported with alkaline BES showing higher current intensities than neutral pH conditions. This study is the first experimental evaluation of alkaline bioelectrochemical production of hydrogen from real crude glycerol as sole carbon source. The results show that alkaline glycerol degradation is feasible under both microbial fuel cell mode (2 mA, 71.4 A/m³ and 55% of CE) and microbial electrolysis mode (maximum of 0.46 L_H2/L/d and 85% of r_CAT). The values obtained are promising since they are in the range of those obtained with other simpler carbon sources such acetate. A complex consortium involving fermentative bacteria (such as Enterococcaceae), alkaline exoelectrogens (such as Geoalkalibacter) and homoacetogens (such as Acetobacterium) was naturally developed in the anode of the MEC.     

Effect of inoculum pre-treatment on mesophilic hydrogen and methane production from food waste using two-stage anaerobic digestion

Two-stage anaerobic digestion of food waste was performed using four different inoculum pre-treatment methods to enrich hydrogen (H₂) producing bacteria from sludge. The pretreatments used in this study included heat shock, alkaline treatment, aeration, and a novel pretreatment using waste frying oil (WFO). Alkaline pretreatment and aeration did not completely inhibit methanogens in the first stage while no methane (CH₄) was detected in the reactors cultivated either with heat shock or WFO-pretreated inocula. The highest H₂ and CH₄ yields (76.1 and 598.2 mL/gVS, respectively) were obtained using the inoculum pretreated with WFO. The highest total energy yield (21.96 kJ/gVS) and total organic carbon (TOC) removal efficiencies (95.77%) were obtained using inoculum pretreatment with WFO. The total energy yield trend obtained using the different pretreatments was as follows: WFO > alkaline > heat > aeration > control.     

Microbial hydrogen production by bioconversion of crude glycerol: A review

Hydrogen is a clean source of energy with no harmful byproducts produced during its combustion. Bioconversion of different organic waste materials to hydrogen is a sustainable technology for hydrogen production and it has been investigated by several researchers. Crude glycerol generated during biodiesel manufacturing process can also be used as a feedstock for hydrogen production using microbial processes. The possibility of using crude glycerol as a feedstock for biohydrogen production has been reviewed in this article. A review of recent global biodiesel and crude glycerol production and their future market potential has also been carried out. Similarly, different technical constraints of crude glycerol bioconversion have been elaborately discussed and some strategies for improved hydrogen yield have also been proposed. It has been underlined that use of crude glycerol from biodiesel processing plants for hydrogen production has many advantages over the use of other organic wastes as substrate. Most importantly, it will give direct economic benefit to biodiesel manufacturing industries, which in turn will help in increasing biofuel production and it will partially replace harmful fossil fuels with biofuels. However, different impurities present in crude glycerol are known to inhibit microbial growth. Hence, suitable pretreatment of crude glycerol is recommended for maximum hydrogen yield. Similarly, by using suitable bioreactor system and adopting continuous mode of operation, further investigation of hydrogen production using crude glycerol as a substrate should be undertaken. Furthermore, isolation of more productive strains as well as development of engineered microorganism with enhanced hydrogen production potential is recommended. Strategies for application of co-culture of suitable microorganisms as inoculum for crude glycerol bioconversion and improved hydrogen production have also been proposed.     

Anaerobic mesophilic co-digestion of sewage sludge with glycerol: Enhanced biohydrogen production

Anaerobic mesophilic co-digestion of mixed sewage sludge from wastewater treatment plants, WWTP, with crude glycerol, the major byproduct of the biodiesel industry, has been examined using a two-phase digestion process in a semi-continuous CSTR at laboratory scale. The objective was to determine the operational conditions that enhanced biohydrogen and methane production and to evaluate the effect of the organic loading rate (OLR) applied to the process. It was concluded that the Hydraulic Retention Time HRT of the methanogenic stage did not have an important influence on the operational process of co-digestion of sewage sludge and glycerol in terms of efficiency of organic removal and biogas yield. Hence, the results obtained were 73–77% organic matter removal (as CODr) with 0.032 LH₂/gCODr and 0.16 LCH₄/gCODr when the system operated at OLRs in the range of 15.33–17.90 gCODs/L d with HRTs of 3 days in the acidogenic digester and 6, 8, and 10 days in the methanogenic digester. In terms of volatile solids, the results obtained were 92–88% organic matter removal (as VSr) with 0.20 LH₂/gVSr and 1.27 LCH₄/gVSr when the system operated at OLRs in the range of 1.94–2.79 gVS/L d.     

Effect of food to microorganism ratio on biohydrogen production from food waste via anaerobic fermentation

The effect of different food to microorganism ratios (F/M) (1–10) on the hydrogen production from the anaerobic batch fermentation of mixed food waste was studied at two temperatures, 35 ± 2 °C and 50 ± 2 °C. Anaerobic sludge taken from anaerobic reactors was used as inoculum. It was found that hydrogen was produced mainly during the first 44 h of fermentation. The F/M between 7 and 10 was found to be appropriate for hydrogen production via thermophilic fermentation with the highest yield of 57 ml-H₂/g VS at an F/M of 7. Under mesophilic conditions, hydrogen was produced at a lower level and in a narrower range of F/Ms, with the highest yield of 39 ml-H₂/g VS at the F/M of 6. A modified Gompertz equation adequately (R² > 0.946) described the cumulative hydrogen production yields. This study provides a novel strategy for controlling the conditions for production of hydrogen from food waste via anaerobic fermentation.     

Thermodynamic study of hydrogen production from crude glycerol autothermal reforming for fuel cell applications

This study presents a thermodynamic analysis of hydrogen production from an autothermal reforming of crude glycerol derived from a biodiesel production process. As a composition of crude glycerol depends on feedstock and processes used in biodiesel production, a mixture of glycerol and methanol, major components in crude glycerol, at different ratios was used to investigate its effect on the autothermal reforming process. Equilibrium compositions of reforming gas obtained were determined as a function of temperature, steam to crude glycerol ratio, and oxygen to crude glycerol ratio. The results showed that at isothermal condition, raising operating temperature increases hydrogen yield, whereas increasing steam to crude glycerol and oxygen to crude glycerol ratios causes a reduction of hydrogen concentration. However, high temperature operation also promotes CO formation which would hinder the performance of low-temperature fuel cells. The steam to crude glycerol ratio is a key factor to reduce the extent of CO but a dilution effect of steam should be considered if reforming gas is fed to fuel cells. An increase in the ratio of glycerol to methanol in crude glycerol can increase the amount of hydrogen produced. In addition, an optimal operating condition of glycerol autothermal reforming at a thermoneutral condition that no external heat to sustain the reformer operation is required, was investigated.     

Effect of ammonia on biohydrogen production from food waste via anaerobic fermentation

The effect of different additive ammonia (0–10 g/l as nitrogen) on hydrogen production from the anaerobic batch mesophilic fermentation of food waste was studied at two feed-to-microorganism ratios (F/M), 3.9 and 8.0. Anaerobic sludge taken from an anaerobic digester was used as inoculum. The hydrogen yield at F/M 3.9 and 8.0 without additive ammonia was 77.2 and 51.0 ml-H₂/gVS, respectively. At F/M 3.9, the hydrogen production was enhanced by adding additive ammonia in the system when the total ammonia nitrogen (TAN) concentration was no higher than 6.0 g/l. A maximum hydrogen yield of 121.4 ml-H₂/gVS was obtained at a TAN concentration of 3.5 g/l. At F/M 8.0, the enhancement of hydrogen production was found in a narrower range of additive TAN concentrations, with a highest yield of 60.9 ml-H₂/gVS at the TAN of 1.5 g/l. Hydrogen production was inhibited at higher additive TAN concentrations for both F/M ratios. This study provides a novel strategy for controlling ammonia for production of hydrogen from food waste via anaerobic fermentation.     

Enrichment of activated sludge for enhanced hydrogen production from crude glycerol

Enriched activated sludge that can effectively convert crude glycerol into bio-hydrogen was selected by an eco-biotechnological approach, in very strict conditions, using biodiesel-derived glycerol as the only carbon source. The thus obtained functional consortium was characterized by the genera Klebsiella, Escherichia/Shigella and Cupriavidus. During enrichment, the dominant metabolic end-product shifted from a 1,3 propanediol to ethanol, with a concomitant increase of the hydrogen yield from 0.18 ± 0.003 to 0.66 ± 0.06 mol/mol and an almost five-fold increase of the hydrogen production. Glycerol degradation efficiency showed an increase of around 50%. In optimized and upscaled conditions it was possible to obtain a hydrogen production rate of 2960 mL H₂/L/day ± 185 at a near stoichiometric yield (of 0.90 mol/mol ± 0.01), with a carbon recovery of almost 90%, both in sterile and non-sterile conditions. Glycerol was almost totally degraded (degradation efficiency of 97.42% ± 0.98), independently of the glycerol type used.     

Biogas production from sewage sludge and microalgae co-digestion under mesophilic and thermophilic conditions

Isochrysis galbana and Selenastrum capricornutum, marine and freshwater microalgae species respectively, were co-digested with sewage sludge under mesophilic and thermophilic conditions. The substrates and the temperatures significantly influenced biogas production.Under mesophilic conditions, the sewage sludge digestion produced 451 ± 12 mL_Biogas/g_SV. Furthermore, all digesters were fed with I. galbana, or mixed with sludge, resulting in an average of 440 ± 25 mL_Biogas/g_SV. On the contrary, S. capricornutum produced 271 ± 6 mL_Biogas/g_SV and in the mixtures containing sludge produced intermediate values between sludge and microalgae production.Under thermophilic conditions, the sewage sludge digestion achieved yet the highest biogas yield, 566 ± 5 mL_Biogas/g_SV. During co-digestion, biogas production decreased when the microalgae content increased, and for I. galbana and for S. capricornutum it reached minimum values, 261 ± 11 and 185 ± 7 mL_Biogas/g_SV, respectively. However, no evidence of inhibition was found and the low yields were attributed to microalgae species characteristics.The methane content in biogas showed similar values, independently from the digested substrate, although this increased by approximately 5% under thermophilic condition.     

Bioaugmentation on hydrogen production from food waste

The aim of this work was to evaluate the effect of two hydrolytic (Paenibacillus polymyxa and Bacillus subtilis) and two fermentative (Clostridium saccharobutylicum and Clostridium beijerinckii) strains on hydrogen (H₂) production in dark fermentation by batch testing. Food waste was used as a substrate, pretreated anaerobic sludge was used as the inoculum, and different concentrations of the evaluated microorganisms were used. Bioaugmentation with 3.5 × 10⁹ CFU/mL/L_reactor B. subtilis showed the best performance, obtaining a production of 84.5 mL H₂/g SV and a reduction in the lag phase (from 7.9 h in control to 3.5 h). Bioaugmentation with B. subtilis in an anaerobic sequencing batch reactor exhibited a significant effect on volumetric productivity, reaching a maximal increase of 344% of H₂ production in comparison with that obtained without the addition of the strain. The increase in H₂ was observed in a short period of time (4 cycles), after which H₂ production returned to the original H₂ production baseline. During all reactor operations, the main volatile fatty acids produced were acetic acid and butyric acid. Microbial community analysis when bioaugmentation was applied showed an importance of lactic acid bacteria abundance, such as that of Bifidobacterium and Lactobacillus, whose metabolic activity was crucial in reactor performance. The added concentration of microorganisms is a critical parameter for the bioaugmentation process.     

不同条件下餐厨垃圾厌氧发酵产沼气状况分析

餐厨垃圾具有水的质量分数高、易腐烂、富含油脂和有机质等特点,对餐厨垃圾处理不当会对人类生产生活造成极大危害.结合餐厨垃圾的特点提出高温厌氧发酵处理,对不同条件下(温度、水的质量分数、接种率)餐厨垃圾厌氧发酵产沼气过程进行了实验研究.通过对实验数据的分析,得出:不同条件下餐厨垃圾中水的质量分数对其厌氧发酵产沼气过程的日产气量、产气速率、产气稳定性等指标的影响较大,接种率的影响次之,温度的影响最小.     

Selective adaptation of an anaerobic microbial community: Biohydrogen production by co-digestion of cheese whey and vegetables fruit waste

The co-digestion process of crude cheese whey (CCW) with fruit vegetable waste (FVW) for biohydrogen production was investigated in this study. Five different C/N ratios (7, 17, 21, 31, and 46) were tested in 2 L batch systems at a pH of 5.5 and 37 °C. The highest specific biohydrogen production rate of 10.68 mmol H₂/Lh and biohydrogen yield of 449.84 mL H₂/g COD were determined at a C/N ratio of 21. A pyrosequencing analysis showed that the main microbial population at the initial stage of the co-digestion consisted of Bifidobacterium, with 85.4% of predominance. Hydrogen producing bacteria such as Klebsiella (9.1%), Lactobacillus (0.97%), Citrobacter (0.21%), Enterobacter (0.27%), and Clostridium (0.18%) were less abundant at this culture period. The microbial population structure was correlated with the lactate, acetate, and butyrate profiles obtained. Results demonstrated that the co-digestion of CCW with FVW improves biohydrogen production due to a better nutrient balance and improvement of the system's buffering capacity.     

Statistical optimization of biohydrogen and ethanol production from crude glycerol by microbial mixed culture

Design of Experiments (DoE) was applied to improve the ability of enriched activity sludge to efficiently convert crude glycerol from biodiesel industry into hydrogen and ethanol, using a very simple synthetic medium. Based on Plackett–Burman screening design, glycerol concentration, temperature and initial pH were identified as significant variables. Box–Behnken design and Response Surface Method (RSM) were then used for optimization. The maximum hydrogen yield of 0.96 mol H₂/mol glycerol was estimated at the temperature of 37.0 °C, initial pH of 7.9 and glycerol concentration of 15.0 g/L. Maximum hydrogen production rate of 2191 mL/L/d was estimated at the temperature of 37.3 °C, initial pH of 8.0 and glycerol concentration of 15.2 g/L. Finally maximum ethanol production of 7.92 g/L was estimated at an initial pH of 8.0 and glycerol concentration of 15.0 g/L (temperature had no significant effect). These results show that it is possible to obtain both, high yield and production of hydrogen and ethanol together, using a very simple synthetic medium, without trace element- and vitamin solution, tryptone or yeast extract.     

Bioconversion of crude glycerol from biodiesel production to hydrogen

This study evaluates the potential of bioconversion of crude glycerol, discharged from biodiesel production plant, to hydrogen (H₂) by an enriched microbial community. Microbial community was enriched from activated sludge in a medium amended with 2.5 g/L of crude glycerol. Optimal cultivation parameters for H₂ production such as initial pH, cultivation temperature and substrate concentration were investigated. H₂ yields from raw glycerol at optimal conditions (pH 6.5; 40 °C and 1 g/L raw glycerol) were 1.1 ± 0.1 mol-H₂/mol-glycerol_consumed. H₂ production was associated with acetate-butyrate type fermentation, along with ethanol as one of the end products. Kinetic experiments on H₂ production from pure and crude glycerol indicated the absence of any inhibitory effects from the impurities present in crude glycerol. The community analysis revealed that the enriched microbial consortium was dominated mainly by Clostridium species.     

Effect of biochar in enhancing hydrogen production by mesophilic anaerobic digestion of food wastes: The role of minerals

The role of minerals in biochar in promoting hydrogen (H₂) production by anaerobic digestion of food waste was investigated. The cultures with the addition of biochar, leached biochar, metal sulphate solution and leached biochar combined with metal sulphate solution, respectively, were placed in bench-scale reactors and incubated at incubator at 32 °C. Daily H₂ production and volatile fatty acids (VFAs) were measured and the cumulative H₂ yield (Y_H) and maximum H₂ production rate (R_H) were calculated. The microbial analysis was performed using Illumina MiSeq sequencing. Biochar addition significantly increased the maximum Y_H by 107% and R_H by 54%. However, the addition of leached biochar only increased the maximum Y_H by 39% and R_H by 45% than control. The primary elements in biochars that contribute to H₂ production (Fe, K and Ca) were shown to increase the acetic acid, butyric acid and prevalence of the H₂ producing bacteria Clostridium butyricum.     

The ability of macroalgae to stabilise and optimise the anaerobic digestion of household food waste

This study investigated the potential of seaweed waste (SW) as a sustainable feedstock for anaerobic co-digestion with food waste (FW). The study was conducted at laboratory scale using a batch test approach run over 34 days. Methane (CH₄) potential assays were conducted at the following FW to SW dry mass ratios: 100:0, 90:10, 75:25, 50:50 and 0:100. Results indicated that anaerobic co-digestion of FW and SW at a mixture ratio of 90:10 produced the highest methane yield (252 cm³ g⁻¹ of volatile solids (VS)), rates of reaction (0.08 d⁻¹) and resulted in a better stability of the process. Predictions based on the Buswell formula suggested that all reactors were performing below the theoretical (maximum) with a greater disparity at increasing levels of seaweed in the feed, likely due to high levels of sulphur in the SW (1.73% mass fraction). The analysis of heavy metals in SW and final digestate indicated that using SW for anaerobic co-digestion with FW enhanced the process by providing trace nutrients without impacting the heavy metal content of the digestate. The analysis of carbon (C) and nitrogen (N) indicated that by using SW for co-digestion with FW, C:N optimal mass ratios were achieved. It was concluded that the addition of SW for anaerobic co-digestion of FW can be used to accelerate the bioenergy production from FW. An additional benefit will be the abatement of the negative impacts of SW in coastal areas, making the overall process more sustainable.