Rhamnolipid induced deagglomeration of anaerobic granular biosolids for energetically feasible ultrasonic homogenization and profitable biohydrogen

The present study exposes the effect of deagglomeration using rhamnolipid on anaerobic granular biosolids (AGB) followed by ultrasonic homogenization for effective biohydrogen production. Rhamnolipid was used to remove the extracellular polymeric substance bound over the surface of AGB to increase the rate of biogranular lysis during ultrasonic homogenization. Extracellular polymeric substance (EPS) removal was achieved at an optimum rhamnolipid dosage of 0.04 g Rh/g SS. Ultrasonic homogenization (UH) of AGB demands 27016 kJ/kg TS of specific energy to achieve 16.8% and 13.9% of biogranular lysis and biosolids reduction, respectively. However, rhamnolipid-alkaline pH induced ultrasonic homogenization (RAUH) demand lesser (12607 kJ/kg TS) and achieves greater biogranular lysis (25.4%) and biosolids reduction (20.7%). RAUH significantly saves the net energy. Exponential first order kinetic analysis was done to evaluate and compare the biohydrogen production potential of RAUH with that of UH. The biohydrogen production was found to be 55.1 mL H₂/g COD and 36.7 mL H₂/g COD for RAUH and UH respectively. A higher positive net energy of 2.62 kWh/kg AGB was achieved by RAUH when compared to UH (−3.49 kWh/kg anaerobic granular biosolids).     

Biohydrogen production from rice straw: Effect of combinative pretreatment,modelling assessment and energy balance consideration

Biohydrogen production from agro waste biomass through combinative pretreatments is an emerging cost effective, alternative energy technology. The present study aimed to ascertain the extent to which the combinative dispersion thermochemical disintegration (DTCD) enhances the cost effective and energy efficient biohydrogen production from rice straw. The efficiency of the combinative pretreatment was evaluated in terms of degree of disintegration and biohydrogen generation. The optimal conditions for combinative pretreatments are pH 10, temperature 80 °C, rpm 12000 and disintegration time 30 mins. A higher degree of disintegration of about 20.9% was achieved through DTCD pretreatment when compared to dispersion thermal disintegration (DTD) (13.2%) and disperser disintegration (DD) (9.5%). The specific energy spent to achieve maximal degree of disintegration for the three pretreatments were in the following order: DD (1469 kJ/kg Rice Straw) > DTD (1044 kJ/kg Rice Straw) > DTCD (742 kJ/kg Rice Straw). Hence, a considerable amount of energy could be saved through this combinative pretreatment. First order kinetic model (exponential rise to maximum) of biohydrogen production is helpful in deriving the two parameters of uncertainty: substrate biodegradability and hydrolysis rate constant. These two parameters evaluate the maximal biohydrogen yield potential of rice straw through combinative pretreatments. As expected, a higher biohydrogen yield of about (129 mL/g COD) was observed in DTCD when compared to DTD (81 mL/g COD) DD (58 mL/g COD) and Control (8 mL/g COD). To gain insights into the feasibility of implementing the pretreatment at large scale, scalable studies are essential in terms of energy balance and cost. A higher positive net energy of about 0.39621 kWh/kg rice straw was achieved for DTCD when compared to others.     

Energetically feasible biohydrogen production from sea eelgrass via homogenization through a surfactant,sodium tripolyphosphate

The present work aimed to increase the liquefaction and biohydrogen recovery of sea eelgrass by combining the surfactant, sodium tripolyphosphate (STPP) with dispersion homogenization. Firstly, the dispersion homogenization (DH) of sea eelgrass was performed by varying the dispersion revolution speed (rpm) from 4000 to 16,000 and treatment time from 0 to 60 min. The conditions for STPP induced dispersion homogenization (SDH) pretreatment (10,000 rpm and 0.05 g/g TS of STPP dosage) was optimized based on the liquefaction (solubilization) of sea eelgrass biomass. A higher liquefaction of 25.6% was achieved through SDH pretreatment. Bioacidification result shows that the percentage increment of volatile fatty acids (VFA) in SDH was found to be 54% higher when compared to DH. SDH pretreated sea eelgrass, when subjected to biohydrogen production yielded a peak production of 23.2 mL H₂/g VS than DH (16 mL H₂/g VS) and control-untreated raw biomass (3.2 mL H₂/g VS). The preliminary energy analysis revealed that SDH was considered to be an energy efficient pretreatment process with energy ratio of 1.9 when compared to DH (0.75).     

Evaluation of biohydrogen production potential of fragmented sugar industry biosludge using ultrasonication coupled with egtazic acid

In this study, the influence of ultrasonication (USN) combined with egtazic acid fragmentation method on sugar industry waste (SWS) sludge was studied for improving biohydrogen production. Initially, USN method was proceeded by varying power and fragmentation time. At an optimal power (115 W) and fragmentation time (30 min), USN method demanded 23,000 kJ/kg TS specific energy for achieving 15.2% complex organics solubilization rate (COR). To further upsurge of SWS sludge solubilization, USN assisted with egtazic acid (USNEG) method was performed by varying fragmentation time and egtazic acid dosage at an optimal power (115 W). USNEG method has achieved more COR (23%) at minimum specific energy of 11,500 kJ/kg TS (fragmentation time: 15 min and EGTA dosage: 0.03 g/g TS). Then, biohydrogen potential (BHP) assay was investigated in which USNEG method has obtained higher biohydrogen production. Also, energy analysis revealed that USNEG method exhibited an energy ratio of 1.78.     

Studies on evaluation of pretreatment efficiency of surfactant mediated ultrasonic pretreatment of Sargassum tennerimum (marine macroalgae) for achieving profitable biohydrogen production

Growing energy demand is inevitable in the future, due to increased commercialization and industrialization. Biohydrogen production from renewable biomass is considered as clean energy technology and, in this study, the feasibility of using Sargassum tennerimum as a renewable energy source has been attempted. Pretreatment using sonication pretreatment (ST) and surfactant Dioctyl sodium sulphosuccinate (DOSS) mediated ultrasonic pretreatment (DOSSSP) were investigated and the optimized pretreatment time and sonication power, respectively, were 30 and 200W for ST. DOSS dosage of 0.005 g/g TS was found to be optimum for DOSSSP with the corresponding maximum of 2600 mg/L and 27.36% respectively for sCOD (Soluble chemical oxygen demand) release and COD (Chemical oxygen demand) solubilization percentage. Biohydrogen assay analysis of the pretreated algal biomass was carried out and 86 mL/g COD of maximum biohydrogen production was achieved for DOSSSP pretreated sample than ST and control owing to higher COD solubilization percentage, carbohydrate and protein release. Energy analysis was performed to test the economic viability of the pretreatment process. This analysis showed that the maximum net positive energy of 0.0407 and energy ratio of 2.43 was obtained for DOSSSP revealing its economic viability. This study also reveals that macroalgae Sargassum tennerimum could be a sustainable renewable energy source for biohydrogen production as it is abundant throughout the year.     

Fermentative hydrogen production from wastewaters: A review and prognosis

Biohydrogen is a promising candidate which can replace a part of our fossil fuels need in day-to-day life due its perceived environmental benefits and availability through dark fermentation of organic substrates. Moreover, advances in biohydrogen production technologies based on organic wastewater conversion could solve the issues related to food security, climate change, energy security and clean development in the future. An evaluation of studies reported on biohydrogen production from different wastewaters will be of immense importance in economizing production technologies. Here we have reviewed biohydrogen production yields and rates from different wastewaters using sludges and microbial consortiums and evaluated the feasibility of biohydrogen production from unexplored wastewaters and development of integrated bioenergy process. Biohydrogen production has been observed in the range of substrate concentration 0.25–160 g COD/L, pH 4–8, temperature 23–60 °C, HRT 0.5–72 h with various types of reactor configuration. The most efficient hydrogen production has been obtained at an organic loading rate (OLR) 320 g COD/L/d, substrate concentration 40 g COD/L, HRT 3 h, pH 5.5–6.0, temperature 35 °C in a continuously-stirred tank reactor system using mixed cultures and fed with condensed molasses fermentation soluble wastewater. The net energy efficiency analysis showed vinasse wastewater has the highest positive net energy gain followed by glycerin wastewater and domestic sewage as 140.39, 68.65, 51.84 kJ/g COD feedstock with the hydrogen yield (HY) of 10 mmol/g COD respectively.     

Ultrasonic pretreatment for an enhancement of biohydrogen production from complex food waste

The efficacy of ultrasonication pretreatment method for complex food waste prior to anaerobic digestion is evaluated for enhancement of H₂ yield (HY) and rate (R). The RSM results showed that the ultimate H₂ production increased with increasing TS content and ultrasonication time (UT). Desirability function integrated with RSM predicted an optimum condition of TS and UT as: 8% TS and 12 min, for maximization of HY and R. The highest HY, 149 mL/g VS_added, and R, 5.23 mL/h, were achieved during the verification test at optimized conditions. Furthermore, a significant decreased lag phase followed by highest molar HBu/HAc ratio (2.2) was also achieved at optimized conditions with lowest specific energy input (13,500 kJ/kg TS). The significant relative enhancement of HY, 75%, and R, 104%, implies that ultrasonically pretreated complex food waste with higher TS loading is about 1.7–2.1 times more effective for enhanced bioH₂ production compared to unsonicated food waste.     

Evaluation of ultrasonication as a treatment strategy for enhancement of biohydrogen production from complex distillery wastewater and process optimization

Dark fermentation of distillery wastewater (DWW) gives a lower hydrogen yield (HY) and hydrogen production rate (R), owing to the complexity and a recalcitrant nature of effluent. Therefore, an effective pretreatment of DWW becomes imperative for the improvement of biohydrogen production. In the present study, the efficacy of ultrasonic pretreatment for enhancement of biohydrogen production from DWW was evaluated in batch test. Several variables, such as COD input, ultrasonic density (UD), and ultrasonication time (UT) were studied for optimization using response surface methodology integrated with desirability function. The highest HY, 10.95 mmol/g COD, and R, 6.67 mmol/L h, were obtained for batch test of ultrasonically pretreated DWW under optimal conditions for COD, UD and UT at 56 g/L, 0.12 W/mL, and 17 min, respectively. The significant relative enhancement of HY, 101%, and R, 103%, implies that ultrasonically treated DWW is about 1.2–1.4 times more effective for enhanced biohydrogen production from complex DWW compared to unsonicated DWW.     

Integrated process to produce biohydrogen from wheat straw by enzymatic saccharification and dark fermentation

In this study, different pretreatment methods, including lyophilization, hydrothermal pretreatment, and ultrasound combined with dilute alkali post-cooking, were investigated to enhance the efficiency of enzymatic saccharification and biohydrogen production of the wheat straw. All pretreatment methods could effectively remove lignin and hemicellulose while retaining cellulose, further enhancing the biomass accessibility for subsequently enzymatic saccharification and biohydrogen production. A reducing sugar concentration of 13.18 g/L was acquired when wheat straw was treated with ultrasound and dilute alkali cooking (R_U). The sequential fermentative hydrogen yield of the substrate R_U was 133.6 mL/g total solids (TS), which was 5.6-fold larger than that of the raw material (23.9 mL/g TS). The study confirmed that ultrasound combined with dilute alkali cooking was an effective method, which not only provided significant guideline for improving biohydrogen production but also presented helpful direction for the efficient pretreatment of other lignocellulosic biomass.     

A pilot study of biohythane production from cornstalk via two-stage anaerobic fermentation

This study aimed to study the feasibility and stability of biohythane production from cornstalk via two-stage anaerobic fermentation without hydrolysis step in a semi-continuous pilot scale system. The present study applied a 1 m³ continuous stirred tank reactor for biohydrogen production and a 0.5 m³ up-flow anaerobic sludge bed for biomethane production. During the entire operation, a hydrogen production yield of 25.02 L/kg TS and hydrogen production rate of 0.46 L/L/d was achieved in first-stage. In addition, a methane yield of 95.38 L/kg TS and methane production rate of 4.06 L/L/d was achieved in second-stage by using the liquid effluent after first-stage. The percentage of hydrogen in the biohythane gas was 18.47% which suitable for vehicle fuel. Moreover, it was feasible to use the solid residue as a growth medium in seedlings to improve energy and carbon recovery. The results suggest that biohythane production from cornstalk could be a promising biofuel avenue.     

Delignification of rapeseed straw using innovative chemo-physical pretreatments

Rapeseed straws are recoverable lignocellulosic biomass for second generation bioethanol production. Therefore, a pretreatment step is recommended in order to increase accessibility of enzymes to sugars. As a pretreatment step in this study, several innovative technologies have been performed in order to investigate their efficiency for delignification and enzymatic hydrolysis purposes: microwaves (MW), high voltage electrical discharges (HVED) and ultrasounds (US). As a key processing parameter, different levels of energy input were studied MW (1832–7328 kJ/kg), US (916–3664 kJ/kg) and HVED (204–814 kJ/kg) corresponding to a treatment duration range of 10–40 min. Treatment temperature (60–90 °C) and medium alkalinity (0.125–0.5 M) impact was also investigated and optimized based on sugar and soluble lignin contents in black liquor, and lignin removal yields. Delignification yields increased from 28.3%, 28.6% and 31.2% for 10 min of treatment to 38.4%, 41.5% and 42.3% for 40 min of treatment, respectively for MW, US and HVED. However, in order to achieve the same efficiency the energy required by HVED is 9 times and 4.5 times less than that required by MW and US respectively. Treatment temperature also revealed to be important as sugars yields increased by 41.6% when temperature increased from 60 °C to 90 °C for HVED and the optimal medium alkalinity was found to be 0.3 M. Finally, better enzymatic hydrolysis yields were obtained and correlated to better delignification performances improving material accessibility.     

Adaptation of biohydrogen producing reactor to higher substrate load: Redox controlled process integration strategy to overcome limitations

Adaptation of acidogenic sequencing batch biofilm reactor (AcSBBR) to higher loading conditions of vegetable waste extract was studied during biohydrogen production at pH 6.0 under ambient conditions. H₂ production rate (HPR) and cumulative H₂ production (CHP) were found to improve with increase in organic load from 4.50 to 26.44 kg COD/m³ and later at 35.25 kg COD/m³ stabilization was observed. Acid metabolic intermediates production tends to lower the system pH which limits the substrate degradation and H₂ production at higher loading conditions. To overcome these limitations, redox controlled strategy (pH 7.0) was applied by integrating another AcSBBR. Upon redox controlled integration, CHP and substrate degradation were found to improve by 42.81% and 36.82% respectively. This approach helped to maintain the favorable redox microenvironment for fermentation at higher VFA concentrations. This process integration methodology will help to overcome some persistent limitation observed during biohydrogen production and make the process sustainable especially with high strength waste/wastewaters.     

Two-stage anaerobic process for bio-hydrogen and bio-methane combined production from biodegradable solid wastes

A two-stage anaerobic digestion process intended for biohydrogen and bio-methane combined production from organic fraction of municipal solid wastes was investigated. In thermophilic conditions blocking of methanogenesis at the first stage of the anaerobic fermentation was achieved at pH 9.0. Cumulative hydrogen production made 82.5 l/kg volatile solids. Pretreatment of organic fraction of municipal solid wastes and exploitation of mixed cultures of anaerobic thermophilic cellulolytic and saccharolytic bacteria of Clostridia sp resulted in the increase of hydrogen cumulative production up to 104 l/kg volatile solids. Content of methane in biohydrogen didn’t exceed 0.1%. Cumulative bio-methane production made 520 l/kg volatile solids. Methane percentage in produced biogas was 78.6%. Comparison of energy data for two-stage anaerobic digestion with those for solely methane production shows the increase in energy recovery from biodegradable fraction of municipal solid wastes. Results obtained make a foolproof basis for the development of cost-effective technological process providing hydrogen and methane combined production from solid organic wastes. Technology can be implemented at large scale biogas plants improving economical and ecological characteristics of the overall process.     

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.     

Biological hydrogen production via dark fermentation: A holistic approach from lab-scale to pilot-scale

Biohydrogen is considered as fuel of future owing to its distinctive attribute for clean energy generation, waste management and high energy content. Suitable feedstock play important role for achieving high rate hydrogen production via dark fermentation process. In this regard, different organic wastes such as cane molasses, distillery effluent and starchy wastewater were examined as potential substrates for biohydrogen production by Enterobacter cloacae IIT-BT 08. Groundnut deoiled cake (GDOC) was considered as additional nutritional supplement to enhance biohydrogen yields. The maximum hydrogen yield of 12.2 mol H₂ kg⁻¹ COD_removed was obtained using cane molasses and GDOC as co-substrates. To further ensure reliability of the process, bench (50 L) and pilot scale (10000 L) bioreactors were customized and operated. The pilot scale study achieved 76.2 m³ hydrogen with a COD removal and energy conversion efficiency of 18.1 kg m⁻³ and 37.9%, respectively. This study provides an extensive strategy in moving from lab to pilot scale biohydrogen production thereby, providing further opportunity for commercial exploitation.     

Effects of pretreatment in a vortex layer apparatus on the properties of confectionery wastewater and its dark fermentation

Pretreatment prior to anaerobic digestion is an effective option for increasing the biodegradability of organic waste. Vortex layer apparatus (VLA) is considered one of the promising types of equipment for pretreatment. In this work, confectionery wastewater (CW) was pretreated in VLA for 1 and 3 min before dark fermentative hydrogen production in anaerobic upflow biofilters. The pretreatment resulted in a slight increase in soluble chemical oxygen demand (COD), soluble sugars and acetic acid, and a decrease in the concentration of propionic, butyric and caproic acids. Due to the abrasion of steel needles in VLA, the concentration of iron in the pretreated CW increased by 2.57 times. Hydraulic retention time in anaerobic upflow biofilters was gradually reduced from 5.6 to 1.8 and 1.3 days, which corresponded to organic loading rate of 2.0, 6.3 and 8.8 kg COD/(m³ day). Although the highest hydrogen yield (96.2 ± 8.1 ml/g COD) was obtained for non-pretreated CW, the pretreatment contributed to a significant increase in methane yield (39.2 ± 2.5 ml/g COD), possibly due to higher iron content (1.8 ± 0.3 mg/L). The highest energy production rate (4407 J/(L day)) was achieved after 3 min CW pretreatment. Thus, pretreatment in VLA can be a promising method for improving the biohythane production process.     

Biohydrogen production from acid hydrolyzed wastewater treatment sludge by dark fermentation

Waste generation, waste management, sustainable energy production, and global warming are interrelated environmental issues to be considered together. Wastewater treatment sludge is an organic substance rich waste which causes significant environmental problems. However, these wastes can be used as raw material in biofuel generation. This study was designed to investigate the possible utilization of waste sludge in biohydrogen production by taking these facts into consideration. For this purpose, the sludge was first pre-treated with acid and then, the solid (sludge) and liquid (filtrate) phases of acid pre-treated sludge were used as the substrates for biohydrogen generation dark fermentation. Two-factor factorial experimental design method was used in acid hydrolysis of sludge to determine the effect of pH (pH = 2–6) and reaction period (time, min) elution of chemical oxygen demand (COD), total organic carbon (TOC) and total sugar (TS), NH₄N and PO₄P. Statistical evaluation of the results indicated that pH significantly affects the elution of organic carbon and nutrient content of sludge while the reaction time is significant for only organic carbon content. The optimum pretreatment conditions for maximum organic and nutrient elution were determined as pH = 2 and t = 1440 min. The pretreated products, named as filtrate sludge and sludge, conducted to dark fermentation under mesophilic conditions for biohydrogen generation showed that pretreatment of waste sludge at pH = 6 is the best condition giving the maximum yields (Y_H2) as Y_H2 = 24 mmol g⁻¹ Total Sugar _consumed and Y_H2 = 41 mmol g⁻¹ Total sugar consumed, for filtrate and sludge, respectively.     

Start up study of UASB reactor treating press mud for biohydrogen production

Anaerobic digestion of press mud mixed with water for biohydrogen production was performed in continuous fed UASB bioreactor for 120 days. Experiment was conducted by maintaining constant HRT of 30 h and the volume of biohydrogen evolved daily was monitored. Various parameters like COD, VFA, Alkalinity, EC, Volatile solids, pH with respect to biohydrogen production were monitored at regular interval of time. SBPR was 10.98 ml g⁻¹ COD reduced d⁻¹ and 12.77 ml g⁻¹ VS reduced d⁻¹ on peak yield of biohydrogen. COD reduction was above 70 ± 7%. Maximum gas yield was on the 78th day to 2240 ml d⁻¹. The aim of the experiment is to study the startup process of UASB reactor for biohydrogen production by anaerobic fermentation of press mud. The inoculum for the process is cow dung and water digested in anaerobic condition for 30 days with municipal sewage sludge. The study explores the viability of biohydrogen production from press mud which is a renewable form of energy to supplement the global energy crisis.     

Effect of microwave pretreatment of mixed culture on biohydrogen production from waste of sweet produced from Benincasa hispida

To enhance the production of biohydrogen from biomass, various pretreatment methods play important role. In this study, effect of microwave irradiation on the culture was studied on biohydrogen production from Benincasa hispida (Petha) solid waste at different powers for a fixed interval of time. The highest power studied was 800 W with a frequency of 2450 MHz. The amount of soluble sugars found in the waste was 13.9 mg/L having the chemical oxygen demand (COD) of 3000 mg/L. Studies have been performed in batch reactors using mixed consortia and results were also compared with the reactor operated at the normal conditions i.e. without any inoculum pretreatment. Maximum hydrogen produced was 14 mmol H₂ per mol of soluble sugar consumed in the reactor in which the inoculum was exposed to 320 W of microwave for 5 min. SEM analysis of this microwave pretreated culture was done.     

Sugar industry waste-derived anode for enhanced biohydrogen production from rice mill wastewater using artificial photo-assisted microbial electrolysis cell

Microbial Electrolysis Cell (MEC) is a promising green technology for energy production from wastewater. This study attempts to investigate the biohydrogen production from rice mill wastewater using artificial photo-assisted microbial electrolysis cell (APAMEC) with an inexpensive anode prepared from carbonaceous material disposed by sugar industry. The X-ray diffraction (XRD) and scanning electron microscopic (SEM) analyses confirmed the presence of carbon on the electrode surface. Cyclic Voltammogram analysis indicated that the carbonaceous anode has higher reduction peak at 0.7 V compared to control (plain carbon cloth) electrode. The experimental results showed a maximum hydrogen production of 220 mL on 5th day of fermentation and the production rate observed was 3.6 ± 0.4 mL/l/h. The effect of pH and acid concentration used in the acid hydrolysis of rice mill wastewater and the effect of artificial light on biohydrogen production were investigated. The optimum pH and acid concentration of 6 and 1.5%, respectively, gave better biohydrogen production and COD removal. The results demonstrated that the development of inexpensive anode from the waste disposed by sugar industry would pave the path to scale-up MECs.