Co-digestion of waste glycerol and glucose to enhance biogas production

Co-digestion in anaerobic fermentation has been widely used to improve biogas production. The biogas production from co-digestion of glucose and glycerol was studied in laboratory-scale batch reactors under mesophilic temperatures, pH 7. The batch experiments involved a variation of glycerol/glucose ratios with initial chemical oxygen demand (COD) for all conditions was fixed at 5,200 mg L⁻¹. The highest yield of biogas production was obtained from glycerol/glucose with 5:5 ratio. The cumulative biogas production was 298.2 mL, and the maximum production rate was 8 mL hr⁻¹. The findings suggested that co-digestion is a potential method to achieve glycerol waste treatment and energy recovery at the same time.     

Biofuel production from spent coffee grounds via lipase catalysis

Lipases namely Mucor miehei, Pseudomonas cepacia, Rhizopus delemar, Geotrichum candidum, Candida rugosa, Porcine pancreas-II, Pseudomonas fluorescence, and Candida antarctica lipase-B (Novozyme-435) were employed for biodiesel synthesis from spent coffee oil. Around 96% oil-to-biodiesel conversion was obtained using Novozyme-435 as a catalyst at 1:5 oil-to-methanol molar ratio and 40ºC. Total spent coffee grounds generated at the North-West University, Potchefstroom Campus (NWU PC) was estimated which could be used to produce 162 L of biodiesel. A waste valorization strategy was devised for converting organic wastes produced at the NWU PC to bioenergy.     

Co-digestion of cassava starch wastewater with buffalo dung for bio-hydrogen production

Batch and continuous modes for bio-hydrogen production by co-digesting cassava starch wastewater with buffalo dung were investigated. Response surface methodology with central composite design was used to optimize the bio-hydrogen production conditions. A hydrogen production potential of 1787 mL H₂/L was achieved under optimal conditions of 2.84 g/L of NaHCO₃, an initial pH of 6.77 and a total chemical oxygen demand (tCOD)/total nitrogen ratio of 42.36. A continuous stirred tank reactor was operated under the optimum conditions from batch mode to investigate the effects of hydraulic retention time (HRT) of 72, 60 and 48 h on hydrogen production. The highest hydrogen content, hydrogen production rate and hydrogen yield of 33%, 839 mL H₂/L.d and 16.90 mL H₂/g-COD_added, respectively, were achieved at a HRT of 60 h. The predominant hydrogen producer under the optimal conditions in batch mode was Clostridium sp. while Clostridium sp., Megasphaera sp. and Chloroflexi sp. were observed in the continuous hydrogen production mode at an optimal HRT.     

Co-digestion of oil palm trunk hydrolysate with slaughterhouse wastewater for thermophilic bio-hydrogen production by Thermoanaerobacterium thermosaccharolyticm KKU19

The key factors influencing a co-digestion of the oil palm trunk (OPT) hydrolysate with a slaughterhouse wastewater (SHW) to produce hydrogen by Thermoanaerobacterium thermosaccharolyticum KKU19 were investigated. The OPT hydrolysate was obtained by the hydrolysis of OPT by microwave-H₂SO₄ method using 1.56% (w/v) H₂SO₄ and 7.50 min reaction time at 450 W. The Plackett–Burman method was used to screen the key factors that influenced the hydrogen production potential (P_s). Results indicated that initial cell concentration, tCOD/TN (total COD/total nitrogen) ratio and CuSO₄ concentration influenced the P_s. These factors were further optimized using response surface methodology (RSM) with central composite design (CCD). A maximum P_s of 2604 ± 86 mL H₂/L substrate was achieved at an initial cell concentration of 224 mg dry cell/L, tCOD/TN ratio of 49.87 and CuSO₄ concentration of 13.33 mg/L. The main soluble metabolite products were butyric and acetic acids. The P_s obtained when the hydrolysate was supplemented with SHW (2604mL ± 86 mL H₂/L substrate) was comparable to the P_s obtained when it was supplemented with yeast extract at the same tCOD/TN (2802 ± 87 mL H₂/L substrate). This result suggests that SHW can be used to replace the costly nitrogen source.     

Optimization of biogas production by co-digesting whey with diluted poultry manure

A series of laboratory experiments were performed in continuously stirred tank reactors at mesophilic conditions, fed semi-continuously with various mixtures of diluted poultry manure and whey. Co-digestion of whey with manure was proved to be possible without any need of chemical addition up to 50% participation of whey (by volume) to the daily feed mixture. Up to this point, specific biogas production (L/kg VS_in) remained roughly unchanged at the various whey fractions added in the feed mixture, mainly due to the lower chemical oxygen demand (COD) of whey compared to that of manure. At whey fractions above 50%, the reactor turned to be unstable, as shown by the considerable decrease in pH and biogas production. The experiments were scaled up to a continuously stirred pilot tank reactor, which had previously been acclimated to poultry manure digestion. Whey was gradually introduced in the feed, at increasing rates, replacing equivalent volumes of manure, in such a way, that total COD of the feed remained constant. For an hydraulic retention time of 18 days at 35 °C and organic loading rate of 4.9 g COD/L_R d, it was found that biogas production increased from 1.5 to 2.2 L/L_R d (almost 40%). This could be mainly attributed to the higher biodegradability of carbohydrates (main constituent of whey) compared to lipids (main constituent of manure) and to the correction (increase) of C:N ratio.     

Optimization of key factors affecting hydrogen production from coffee waste using factorial design and metagenomic analysis of the microbial community

The objective of this study was to evaluate the fermentation conditions that led to the optimization of H₂ production from coffee waste (wastewater, pulp and husk) and the taxonomic and functional characterization of autochthonous microorganisms. Assays in batch reactors with microbial consortium bioaugmentation (bacteria and fungi) evaluated the pH (4.82–8.18), pulp and husk concentration (6.95–17.05 g/L) and headspace factor (33.18–66.82%) by means of rotational central composite design and response surface. Operating conditions in the reactor optimized for 3.04 LH₂/Ld were at pH 7.0, 7 g/L pulp and husk and 30% headspace. The main metabolites observed were butyric acid (3838 mg/L), isobutyric acid (506 mg/L), methanol (226 mg/L) and butanol (156 mg/L). Clostridium sp. (87.9%), Lactobacillus sp. (1.7%), Kazachstania sp. (18.6%) and Saccharomyces sp. (16.3%) were the main genera identified in the optimized reactor, which had functional gene diversity for H₂ production, alcoholic fermentation, cellulose degradation, lignin, hemicellulose and phenol.     

Enhanced biogas production from anaerobic co-digestion of municipal wastewater treatment sludge and fat,oil and grease (FOG) by a modified two-stage thermophilic digester system with selected thermo-chemical pre-treatment

Anaerobic co-digestions with fat, oil and grease (FOG) were investigated in two-stage thermophilic (55 °C) semi-continuous flow co-digestion systems. One two-stage co-digestion system (System I) was modified to incorporate a thermo-chemical pre-treatment of pH = 10 at 55 °C, which was the best pre-treatment condition for FOG co-digestion identified during laboratory-scale biochemical methane potential (BMP) testing. The other two-stage co-digestion system (System II) was operated without a pre-treatment process. The anaerobic digester of each digestion system had a hydraulic retention time (HRT) of 24 days. An organic loading rate (OLR) of 1.83 ± 0.09 g TVS/L·d was applied to each digestion system. It was found that System I effectively enhanced biogas production as the thermo-chemical pre-treatment improved the substrate hydrolysis including increased COD solubilization and VFA concentrations. Overall, the modified System I yielded a 25.14 ± 2.14 L/d biogas production rate, which was substantially higher than the 18.73 ± 1.11 L/d obtained in the System II.     

Improvement of biohythane production from Chlorella sp. TISTR 8411 biomass by co-digestion with organic wastes in a two-stage fermentation

The suitability of molasses, Napier grass (Pennisetum purpureum), empty fruit bunches (EFB), palm oil mill effluent (POME), and glycerol waste as a co-substrate with Chlorella sp. TISTR 8411 biomass for biohythane production was investigated. Mono-digestion of Chlorella biomass had hydrogen and methane yield of 23–35 and 164–177 mL gVS⁻¹, respectively. Co-digestion of Chlorella biomass with 2–6% TS of organic wastes was optimized for biohythane production with hydrogen and methane yield of 17–75 and 214–577 mL gVS⁻¹, respectively. The hydrogen and methane yield from co-digestion of Chlorella biomass with molasses, POME, and glycerol waste was increased by 8–100% and 80–264%, respectively. The biohythane production of co-digestion of Chlorella was 6–11 L L-mixed waste⁻¹ with an optimal C/N ratio range of 19–41 and H₂/CH₄ ratio range of 0.06–0.3. Co-digestion of Chlorella biomass was significantly improved biohythane production in term of yield, production rate, and kinetics.     

Dark fermentation of starch factory wastewater with acid- and base-treated mixed microorganisms for biohydrogen production

Biohydrogen (Bio-H₂) can be produced from starch factory wastewater and mixed microorganisms using dark fermentation. Acidic and basic chemicals were used to treat the microorganisms to select the hydrogen (H₂)-producing culture. The experiment used a 120 mL bioreactor at 35 °C and the operation commenced with the initial pH level of wastewater in the pH range 4–7 in batch mode. The bacteria:chemical oxygen demand (COD) ratio was 0.2. The initial pH level of the wastewater in the fermentation process affected the H₂ yield and the specific hydrogen production rate (SHPR). For acid-treated bacteria, the maximum H₂ yield and SHPR were produced at an initial pH of 6.5. The maximum H₂ yield and SHPR were 138 mL/g COD degraded and 7.42 mL/g cells?h, respectively. For the base-treated bacteria, the maximum H₂ yield and SHPR were produced at initial pH of 6.5 and pH 7, respectively. The maximum H₂ yield and SHPR were 182 mL/g COD degraded and 25.60 mL/g cells?h, respectively. The COD degradation efficiency levels were 16 and 20% for acid- and base-treated bacteria, respectively. The digested wastewater remained acidic at pH 4.79–4.83. Throughout the study, no methane gas was observed in the gas mixture produced.     

Biogas production from the sludge of the municipal wastewater treatment plant of Adrar city (southwest of Algeria)

This study deals with the treatment and valorization of sludge issued from the municipal wastewater treatment plant of Adrar city (southwest of Algeria). The sludge considered was a complex mixture of substances, essentially organic matters with a rate of 54%. An acute biological activity of the crude substrate was noted (1.67 10⁶ germs/1 ml). The diluted sludge with a content of 16 g/l of total solids (TS) was fermented in a digester of one litter capacity under anaerobic conditions during 33 days. The quantity of biogas produced was 280.31 Nml with a yield of 30 Nml of biogas/mg of COD removed. The COD, BOD and TS reduction yields were 88, 90 and 81% respectively, followed by a complete destruction of the pathogenic flora particularly Escherichia coli. This study presented an important energetic opportunity by producing 30,950 KWh.     

Enhancement of biohythane production from solid waste by co-digestion with palm oil mill effluent in two-stage thermophilic fermentation

Improvement of biohythane production from oil palm industry solid waste residues by co-digestion with palm oil mill effluent (POME) in two-stage thermophilic fermentation was investigated. A two-stage co-digestion of solid waste with POME has biohythane production of 26.5–34 m³/ton waste. The co-digestion of solid waste with POME increased biohythane production of 67–114% compared to digestion POME alone. Co-digestion of solid waste with POME enhanced hydrolysis constant (k_h) from 0.07 to 0.113 to 0.120–0.223 d⁻¹. The hydrolysis constant (k_h) of co-digestion was 10 times higher than the single digestion of solid waste. Clostridium sp. was predominated in the hydrogen stage, while Methanosphaera sp. was predominant in methane stage. The co-digestion of solid waste with readily biodegradable organic matter (POME) could significantly increase biohythane production with achieving the significant cost reduction for pretreatment of solid wastes.     

Improvement of photofermentative biohydrogen production using pre-treated brewery wastewater with banana peels waste

In this study, the impacts of banana peels pre-treatment stage on photofermentative hydrogen production of Rhodobacter sphaeroides 158 DSM using brewery wastewater (BWW) were investigated in a batch bioreactor. The experimental results indicate that banana peels pre-treatments can significantly enhance the cumulative hydrogen production. The maximum hydrogen production yield (408.33 mL H₂ L⁻¹_wastewater) was achieved from the substrate, which was composed of 50% BWW pretreated with 1 g L⁻¹ of banana peels for 2 h and 50% standard medium. This highest amount of hydrogen production was 2.7-folds higher than those that applied the same percentage of raw BWW as the substrate source.     

Hydrogen production from the tannery wastewater treatment by using agriculture supports membrane/adsorbents electrochemical system

The tannery is one of the oldest and most popular industries in the world. It is also characterized as pollutants generated industries which discharge toxic chemical output effluents to the environment. The process of tannery included a wide variety of chemical and inorganic constituents. This work focused on the removal of Chromium heavy metals as well as producing clean energy from the treatment of tannery wastewater. Accordingly, the analysis result on the input effluents appeared to have a brown color with a very high COD value, a high concentration of Chromium heavy metals as well as other organic compounds. After collected from the source, the effluents were settling and applied a simple subsequent filtration with lab scale cloth filter, the filtered effluents then were treated in an electrochemical system. Throughout many experiments, we introduce an electrochemical system with 5 × 5 cm electrodes (Platinum coated panel anode and carbon fiber cloth cathode), the low input voltage (10 V), easy setup and the support of separator membrane/adsorbents placed in the middle of the system to enhance the removal rates of heavy metals.It was found that the performance of the electrochemical system is under the influence of various factors such as temperature, pH value, adsorbents dose, and apply voltage. During 48 h of treatment, almost 80% of Chromium metals were treated by means of adsorption and electrical reduction process. The generation rate of hydrogen gases during the electrolysis process was also notable (45–65 cc/min). Furthermore, the adsorbent materials were still intact and seem to be ready for a longer run. The study also observed the adsorbent membrane of bagasse and straw showed their best removal efficiencies over other candidates. In that manner, we successfully provide an effective method for heavy metals removal and also capable of generating clean energy. The analysis results clarify that most of the parameters of the physical and chemical result were found well below the prescribed permissible limits of discharged effluents follows the standard of industrial waste management in Vietnam.     

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.     

Hydrogen gas production from olive mill wastewater by electrohydrolysis with simultaneous COD removal

Diluted olive mill wastewater (OMW) was subjected to direct current (DC) voltages (0.5-4.0 V) for hydrogen gas production with simultaneous chemical oxygen demand (COD) removal by electrohydrolysis. The highest cumulative hydrogen production (3020 ml) and hydrogen yield (2500 ml H₂ g⁻¹ COD) were obtained with 3 V DC voltage while the highest current intensity (80 mA), percent hydrogen (95%) in the gas phase, hydrogen gas formation rate (614 ml d⁻¹), percent COD removal (44%) and energy conversion efficiency (95%) were realized with 2 V. Hydrogen gas production by electrolysis of water was negligible for all voltages. COD removal from OMW with no DC voltage application was usually lower than that obtained with DC power application. Hydrogen gas production by electrohydrolysis of OMW was proven to be a fast and effective method with simultaneous COD removal.     

Improvement of hydrogen production with thermophilic mixed culture from rice spent wash of distillery industry

Biohydrogen production processes were investigated using thermophilic bacterial consortia enriched from sludge of the anaerobic digester. A multiple parameter optimization viz. temperature, pH and substrate concentration was performed for maximization of hydrogen production. Heat shock pre-treatment followed by BES (2-bromo ethane sulfonate) treatment was done for the enrichment of hydrogen producing bacteria. Box–Behnken design and response surface methodology were adopted to investigate the mutual interaction among the process parameters. Experimental optimization of process parameters (60 °C, pH 6.5 and 10 g/L) gave the maximum hydrogen production and yield of 3985 mL/L and 2.7 mol/mol glucose respectively in the batch system which is higher than the reported value on UASB. These experimental parameters found concurrent with the values obtained from the theoretical model i.e. 58.4 °C, pH 6.6, 10.8 g/L and yield of 2.71 mol/mol glucose. At optimized conditions, maximum hydrogen production rate (R_m) of 850 mL/h, gas production potential (P) of 4551 mL/L and lag time (λ) of 1.98 h were determined using modified Gompertz equation. Using the optimum conditions, hydrogen production from rice spent wash was conducted in which hydrogen yield of 464 mL/g carbohydrate and hydrogen production rate of 168 mL/L h were obtained. PCR-DGGE profile showed that the thermophilic mixed culture was predominated with species closely affiliated to Thermoanaerobacterium sp.     

Enhanced hydrogen gas production from mixture of beer spent grains (BSG) and distiller's grains (DG) with glycerol by Escherichia coli

Escherichia coli perform mixed acid fermentation and produce hydrogen gas (H₂) as one of the fermentation end products. E. coli can ferment sugars like glucose, xylose and alcohols like glycerol. It has been shown that E. coli has the ability to utilize pretreated organic waste (BSG or DG) or mixtures of it with glycerol and H₂ can be produced. H₂ evolution was maximum when the concentration of BSG was 4% and DG - 10% yielding 1.4 mmol L⁻¹ H₂. H₂ evolution was prolonged to ~24–120 h when mixtures of glycerol and DG or BSG wastes were applied. Moreover, in hycE (lacking large subunit of Hyd-3) or hyfG (lacking large subunit of Hyd-4) single mutants H₂ production was absent compared to wild type suggesting that Hyd-3 and Hyd-4 are responsible for H₂ generation. In addition, multiple mutant enhanced cumulative H₂ production ~3–4 fold. Taken together it can be proposed that BSG or DG wastes either together or in mixture with glycerol can be applied to obtain E. coli biomass and produce bio-H₂. The novel data can be used to further control effectively the application of organic waste resources as a feedstock for developing bio-H₂ production technology.     

Hydrogen,alcohols and volatile fatty acids from the co-digestion of coffee waste (coffee pulp,husk, and processing wastewater) by applying autochthonous microorganisms

The objective of this study was to screen the factors that affect H₂, organic acids and alcohols production from coffee waste pretreated in a hydrothermal reactor applying consortium of bacteria and fungi (indigenous from coffee waste) with hydrolytic and fermentative activity. The effects of pH (4.0–7.0), temperature (30–50 °C), agitation (0–180 rpm), headspace (50–70%), percentage of bioaugmentation (without microbial consortium to 20%), concentration of coffee pulp and husk (2–6 g/L), coffee processing wastewater (7-30 gCOD/L) and yeast extract (0–2 g/L) were evaluated using a Plackett-Burman design. The highest H₂ production potential (82 ml H₂) was obtained under the following conditions: 30 °C, 180 rpm, 50% headspace, without bioaugmentation, 2 g/L pulp and husk coffee, 30 gCOD/L coffee processing wastewater and 2 g/L yeast extract. The main soluble products were acetic acid (1956 mg/L), lactic acid (786 mg/L) and ethanol (816 mg/L). Lactobacillus sp., Clostridium sp., Saccharomyces sp. and Kazachstania sp. were the main autochthonous microorganisms identified. Through metagenome functional analysis, enzymes related to lignin, phenol, cellulose, lignocellulose, and pectin degradation were identified, as well as acidogenesis, and H₂ production.     

Hydrogen gas production from vinegar fermentation wastewater by electro-hydrolysis: Effects of initial COD content

Vinegar fermentation wastewater with different initial COD contents (9.66–48.6 g L⁻¹) were used for hydrogen gas production with simultaneous COD removal by electro-hydrolysis. The applied DC voltage was constant at 4 V. The highest cumulative hydrogen production (3197 ml), hydrogen yield (2766 ml H₂ g⁻¹ COD), hydrogen formation rate (799 ml d⁻¹), and percent hydrogen (99.5%) in the gas phase were obtained with the highest initial COD of 48.6 g COD L⁻¹. The highest energy efficiency (48%) was obtained with the lowest COD content of 9.66 g L⁻¹. Hydrogen gas production by water electrolysis was less than 250 ml and wastewater control resulted in less than 25 ml H₂ in 96 h. The highest (12%) percent COD removal was obtained with the lowest COD content. Hydrogen gas was produced by reaction of (H⁺) ions present in raw WW ( pH = 3.0) and protons released from acetic acid with electrons provided by electrical current. Electro-hydrolysis of vinegar wastewater was proven to be an effective method of H₂ gas production with some COD removal.