Digestion of pre‐treated food waste in a hybrid anaerobic solid–liquid (HASL) system

The hybrid anaerobic solid–liquid (HASL) system was developed to be used in industrial‐scale operations to minimize the amount of food waste for disposal in Singapore. Thermal pre‐treatment of food waste at 70 °C for 2 h (experiment E1) or at 150 °C for 1 h (experiment E2) facilitated the hydrolytic and acidogenic processes in the acidogenic reactor and methanogenesis in the methanogenic reactor in the HASL system. The highest dissolved chemical oxygen demands in the effluents from the acidogenic reactors were 17 575, 19 980 and 24 235 mg dm^?3 in the control with food waste without thermal pre‐treatment and experiments E1 and E2, respectively. The maximum concentrations of methanogens in the methanogenic reactor were 2.3 × 10⁷, 3.8 × 10⁷, 4.3 × 10⁷ cells cm^?3 for the control and experiments E1 and E2, respectively. However, the performances of the methanogenic phase in terms of specific activity of methanogens did not differ significantly for the control and experiments E1 and E2. Use of thermally pre‐treated food waste halved the time to produce the same quantity of methane in comparison with anaerobic digestion of fresh food waste. The fluorescent measurements of co‐enzyme F₄₂₀ and oligonucleotide probe Arc915 specifically bound (hybridized) with 16S rRNA were used for monitoring of methanogens during anaerobic digestion of food waste. There was a linear correlation between these parameters and the concentration of methanogens in the effluent from the methanogenic reactor. Copyright © 2005 Society of Chemical Industry     

Mesophilic and Thermophilic Anaerobic Digestion of Model Kitchen Waste with Variation of Fat Content

Anaerobic digestion of model kitchen waste (MKW) produced on basis of real kitchen waste (KW) is studied in batch tests. The impact of fat content of three MKWs (14.7 %, 23 %, and 27.2 % rapeseed oil content) on the biogas production at mesophilic and thermophilic conditions and two loadings is examined. The loading of 5 g_VSL⁻¹ leads to fast degradation under both temperature modes and the volume of biogas produced is only weakly correlated to the oil content. For the loading of 25 g_VSL⁻¹ a strong retardation of biogas production, high concentration of volatile fatty acids and no correlation of oil content is observed.     

Kinetics of syntrophic acetogenesis in a saline medium

BACKGROUND: The anaerobic degradation kinetics of volatile fatty acids (VFA) in a saline (24 g NaCl dm^?3) and mesophilic (37 °C) medium was studied under batch test conditions. The acetate production kinetics without inhibition by propionic, butyric and valeric acids was determined. The inhibition of acetate production during syntrophic acetogenesis by VFA and pH was studied. The acetogenesis without inhibition was modelled using a Monod equation. The pH inhibition was represented by a Michaelis pH function, while the inhibition by acetic acid (HAc) was represented by a non‐competitive model. RESULTS: The specific maximum degradation rate and saturation constant (k_{max, VFA}, K_{S, max}) values were (5.89, 15.95), (7.97, 25.99) and (7.75 g VFA g^?1 volatile suspended solids day^?1, 11.52 mg VFA dm^?3) for propionic, butyric and valeric acids respectively, with maximum velocity at pH 7. The inhibition constants (K_{I, HAc}) were 1295, 671 and 572 mg HAc dm^?3 for propionic, butyric and valeric acids respectively. CONCLUSION: VFA and pH can be inhibitory for acetogenesis under these conditions. Copyright © 2008 Society of Chemical Industry     

Hydrogen production from sucrose using an anaerobic sequencing batch reactor process

Studies on hydrogen production in an anaerobic sequencing batch reactor (AnSBR) indicated that the anaerobic acidogenic conversion of sucrose could produce hydrogen. The hydrogen production of acclimated sewage sludge depended on hydraulic retention time (HRT) and reaction period/settling period (R/S) ratio. A short equivalent HRT, even up to 4 h, gave good hydrogen productivity and high hydrogen production rate (HPR) values. For each equivalent HRT, R/S ratio control also increased the hydrogen productivity and HPR. Reactor operation at an intimate control of HRT and R/S ratio was preferable for hydrogen production. At HRT 8 h, R/S ratio 5.6 and an organic loading rate of 0.23 mol‐sucrose dm^?3 day^?1, each mole of sucrose in the mesophilic hydrogenic reactor yielded 2.6 mole of hydrogen; each gram of biomass produced 0.069 mole of hydrogen per day. Copyright © 2003 Society of Chemical Industry     

Anaerobic treatment of palm oil mill effluent by tank digesters

Palm oil mill effluent was treated anaerobically in 210 dm^?3 tank digesters in which inoculation with anaerobic seeding coupled with careful addition of lime could shorten the natural stabilisation process to about 30 days. The system was subsequently scaled up to 500 tonnes capacity. The characteristics of the anaerobically digested liquors were studied at 10 and 20 days hydraulic retention time (HRT) respectively, and close to 90% treatment efficiency could be achieved at 20 days HRT with complete microbial conversion of plant cell debris. However, the digested liquor still contained 0.325% (by wt) suspended solids. The kinetics of the anaerobic process show close resemblance to those treating other high strength organic wastes. Optimum gas production occurred only over a narrow pH range of 6.8–7.2 units. A methane content of 62–67% on gas production was noted about equivalent to 0.34 to 0.39 dm^?3 CH₄ g^?1 of BOD destroyed.     

Fuel ethanol production from concentrated food waste hydrolysates in immobilized cell reactors by Saccharomyces cerevisiae H058

BACKGROUND: Continuous ethanol fermentation of concentrated food waste hydrolysates has been studied. The process was carried out in an immobilized cell reactor with beads of calcium‐alginate containing immobilized Saccharomyces cerevisiae H058 at temperature 30 °C and pH 5.0. RESULTS: The total residual sugar decreased with increase of hydraulic retention time (HRT) under various reducing sugar concentrations. Ethanol production by immobilized cells increased with increase in HRT, regardless of the substrate concentrations employed. The highest ethanol concentration of 89.28 g L^?1 was achieved at an HRT of 5.87 h and reducing sugar concentration of 200 g L^?1. At an HRT of 1.47 h, the maximum volumetric ethanol productivity of 49.88 g L^?1 h^?1 and the highest ethanol yield of 0.48 g g^?1 were achieved at reducing sugar concentration of 160 and 200 g L^?1, respectively. The difference between the fresh and the 30‐day Ca–alginate immobilized cell was also shown by scanning electronic micrographs of beads taken from their outer and inner surfaces. CONCLUSIONS: Continuous ethanol production from concentrated food waste hydrolysates using immobilized yeast cells is promising in view of the high ethanol productivity obtained at relatively high conversion and excellent reactor stability. Copyright © 2011 Society of Chemical Industry     

Anaerobic acidogenesis of dairy wastewater: the effects of variations in hydraulic retention time with no pH control

The performance of a laboratory‐scale mesophilic acidogenic reactor was evaluated in this study, in terms of volatile fatty acid production and distribution, with respect to variations in hydraulic retention time (HRT). The continuous flow‐completely mixed anaerobic reactor, coupled with a conventional gravity settling tank and a continuous recycling system, was operated in a hydraulic retention time ranging between 24 and 12 h, and up to an organic loading rate of about 9.3 kg COD m^?3 d^?1, without pH control. The acid production gradually increased proportionally to the organic loading rate, with decrease in hydraulic retention time. The highest degree of acidification and the rate of acid production were 56% and 3.1 g dm^?3 d^?1 at 12 h of HRT. Variations in hydraulic retention time affected volatile fatty acid production and distribution substantially, for the range investigated. Acetic, propionic, butyric and valeric acids were commonly produced during acidogenesis of dairy wastewater. Copyright © 2004 Society of Chemical Industry     

Methanogenesis of black liquor in a two‐stage biphasic reactor system using an immobilized cell system

The methanogenesis of black liquor from pulp and paper mill was achieved using immobilized cell technology in a laboratory‐scale two‐stage reactor system run continuously for 340 days. The optimum organic loading rate for the anaerobic treatment of black liquor was 8.0 kgm^?3d^?1 at which the % COD removal, biogas production and methane content were 55%, 11 dm³d^?1 and 71%, respectively. Organic loading rates above 8.0 kgm^?3d^?1 were observed to be toxic to the methanogenic bacteria and resulted in decreased methane content, biogas and COD removal. The applicability of the system to the large‐scale processing and treatment of paper mill liquid waste is discussed. © 2001 Society of Chemical Industry     

Staged and non-staged anaerobic filters: Microbial activity segregation,hydrodynamic behaviour and performance

This work describes a comparative study of staged and non-staged anaerobic filters for treating a synthetic dairy waste under similar operating conditions. The effect of increasing the substrate concentration from 3 to 12 g COD dm⁻³ at a constant hydraulic residence time (HRT) of 2 days was evaluated with respect to overall reactor performance, biogas production, volatile fatty acids profiles along the height, methanogenic and acidogenic activity distribution, and hydrodynamic behaviour. The potential maximum specific methanogenic activity against acetate, hydrogen, propionate and butyrate and the lactose specific activity were determined for sludge sampled from three different points in each reactor, under two operating conditions (influent COD of 3 and 9 g COD dm⁻³). Although all trophic groups involved in the anaerobic process were found throughout the reactors, it was possible to identify different specific sludges at different heights in both reactors. Performances of the two configurations were very similar under the operating conditions tested and the plug flow behaviour of the staged reactor was clearly reduced when the influent concentration increased from 3 to 9 g COD dm⁻³. © 1998 Society of Chemical Industry     

Production of L‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor

Production of L ‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor was investigated. Based on the determination of relative enzymatic activity in the immobilized pellets, the optimum pH and temperature for the resolution reaction were 8.0 and 60 °C, respectively. The effects of substrate concentration on the resolution reaction were also investigated and the kinetic constants (K_m and V_m) of immobilized pellets were found to be 7.99 mmol dm^?3 and 1.38 mmol dm^?3 h^?1, respectively. The maximum substrate concentration for the resolution reaction without inhibition was 0.2 mol dm^?3. The L ‐methionine conversion rate reached 94% and 78% when substrate concentrations were 0.2 and 0.4 mol dm^?3, respectively, at a flow rate of 7.5 cm³ h^?1 using the small‐scale packed bed reactor developed. The half‐life of the L ‐aminoacylase in immobilized pellets was 70 days in continuous operation. All the results obtained in this paper exhibit a practical potential of using immobilized pellets of Aspergillus oryzae in the production of L ‐methionine. © 2002 Society of Chemical Industry     

Graft copolymerization of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid onto carboxymethylcellulose (sodium salt) by H2O2/Fe+2 redox pair

The effect of the reaction conditions on the grafting parameters during grafting of 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid onto sodium carboxymethylcellulose using H₂O₂/Fe⁺² redox pair are studied at 30°C. The grafting ratio, add on, and conversion initially increase with the H₂O₂ concentration in the range of (10.0–15.0) × 10^?2 mol dm^?3. Thereafter, these parameters decrease with the H₂O₂ concentration. The grafting ratio, add on, and conversion increase when increasing the ferrous ion concentration from (0.5 to 4.0) × 10^?2 mol dm^?3 and decrease with a further increase in the concentration. It is observed that the grafting ratio and add on increase with the monomer concentration, whereas the conversion decrease. The hydrogen ions seem to be facilitating the grafting reaction up to a certain concentration and after this concentration seem to be retarding the process. The grafting ratio, add on, and conversion decrease with the sodium carboxymethylcellulose concentration. When increasing the time period from 60 to 90 min, the grafting parameters increase but decrease thereafter. Similarly, when increasing the temperature from 25 to 30°C, the grafting parameters increase and decrease thereafter. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4819–4825, 2006     

Kinetics and thermodynamics of glucoamylase inhibition by lactate during fermentable sugar production from food waste

BACKGROUND: Glucoamylase hydrolysis is a key step in the bioconversion of food waste with complicated composition. This work investigated the effect of lactate on glucoamylase from Aspergillus niger UV‐60, and inhibition mechanisms of glucoamylase by lactate during food waste hydrolysis. RESULTS: For 125 min hydrolysis of food waste (10%, dry basis), reducing sugars produced in the absence of lactate were 15%, 26% and 56% more than those produced in the presence of 24 g L^?1 lactate at 60, 50 and 40 °C, respectively. Kinetic study showed that the type of glucoamylase inhibition by lactate was competitive, and K_m (Michaelis‐Menten constent), V_max (maximum initial velocity), K_I (inhibition constant) were 103.2 g L^?1, 5.0 g L^?1 min^?1, 100.6 g L^?1, respectively, for food waste hydrolysis at 60 °C and pH 4.6. Lactate also accelerated glucoamylase denaturation significantly. Activation energy of denaturation without inhibitor was 61% greater than that of denaturation with inhibitor (24 g L^?1 lactate). Half‐lives (t_1/2) without inhibitor were 7.6, 2.7, 2.6, 1.7 and 1.2 times longer than those with inhibitor at temperature 40, 45, 50, 55 and 60 °C, respectively. CONCLUSION: These results are helpful to process optimization of saccharification and bioconversion of food waste. Copyright © 2010 Society of Chemical Industry     

Synthesis and characterization of polysaccharide based graft copolymer by using potassium peroxymonosulphate/ascorbic acid as an efficient redox initiator in inert atmosphere

Polysaccharide based graft copolymer (xanthan gum‐g‐4‐vinyl pyridine) was synthesized using potassium peroxymonosulphate/ascorbic acid redox initiator in inert atmosphere at 40°C. By studying the effect of the concentration of monomer, peroxymonosulphate (PMS), ascorbic acid (AA), xanthan gum (XOH), hydrogen ion along with effect of time and temperature on grafting characteristics: grafting ratio (%G), add on (%A), conversion (%C), efficiency (%E), homopolymer (%H), and rate of grafting (Rg), the reaction conditions for optimum grafting were determined. The optimum concentration of AA, H⁺ ion, 4‐VP for maximum grafting were found to be 10.0 × 10^?3 mol dm^?3, 2.5 × 10^?2 mol dm^?3, 10.0 × 10^?3 mol dm^?3, respectively. Maximum %G was obtained at minimum concentration of xanthan gum i.e., at 40.0 × 10^?2 g dm^?3 and at maximum concentration of PMS i.e., at 10.0 × 10^?3 mol dm^?3. The optimum temperature and time duration of reaction for maximum % of grafting were found to be 45°C and 120 min respectively. The synthesized graft copolymer was characterized by FTIR analysis. Thermogravimetric analysis showed that the xanthan gum‐g‐4‐vinyl pyridine is thermally more stable than pure gum. A probable mechanism was suggested for the graft copolymerization. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of sodium dodecyl benzene sulfonate (SDBS) on the performance of anaerobic co-digestion with sewage sludge,food waste,and green waste

Abstract

The anionic detergent sodium dodecyl benzene sulfonate (SDBS) inhibits anaerobic solid waste fermentation process in mesophilic anaerobic digesters. In this study, the effect SDBS on the performance of anaerobic digestion (AD) of mixture of sewage sludge, food waste, and green waste serving as substrate was investigated. The batch experiments were conducted with five SDBS concentrations namely 0, 0.01, 0.02, 0.05, 0.1, and 0.2?g/g (SDBS/dry sludge) under mesophilic condition (37?±?1?°C) and lasted for 63?days. The results showed that the presence of SDBS remarkably increased the release of protein and carbohydrate, and resulting in the serious accumulation of volatile fatty acids (VFAs), especially for propionate accumulation. Likewise, the observed variations in enzyme activities associated with different stage of AD revealed that methanogenesis was quite sensitive to SDBS and inhibited by the increase of SDBS addition. Meanwhile, the presence of SDBS decreased the pH value and the concentration of free ammonia, but increased the concentration of NH₄⁺-N. Furthermore, the production of biogas was reduced by SDBS. In conclusion, SDBS addition has a negative impact on anaerobic co-digestion. On the one hand, methanogens were severely inhibited and biogas yield decreased remarkably, on the other hand, the accumulation of VFAs was excessive. Thus, the presence of surfactant (SDBS) in the municipal organic waste should be concerned during the waste disposal via anaerobic digestion process.     

Lactic acid production from dining‐hall food waste by Lactobacillus plantarum using response surface methodology

BACKGROUND: Food waste generally has a high starch content and is rich in nutritional compounds, including lipids and proteins. It therefore represents a potential renewable resource. In this study, dining‐hall food waste was used as a substrate for lactic acid production, and response surface methodology was employed to optimise the fermentation conditions. RESULTS: Lactic acid biosynthesis was significantly affected by the interaction of protease and temperature. Protease, temperature and CaCO₃ had significant linear effects on lactic acid production, while α‐amylase and yeast extract had insignificant effects. The optimal conditions were found to be an α‐amylase activity of 13.86 U g^?1 dried food waste, a protease activity of 2.12 U g^?1 dried food waste, a temperature of 29.31 °C and a CaCO₃ concentration of 62.67 g L^?1, which resulted in a maximum lactic acid concentration of 98.51 g L^?1 (88.75% yield). An increase in inoculum size would be appropriate for accelerating the depletion of initial soluble carbohydrate to enhance the efficiency of α‐amylase in dining‐hall food waste fermentation. CONCLUSION: A suitable regression model for lactic acid production was developed based on the experimental results. Dining‐hall food waste was found to be a good substrate for lactic acid fermentation with high product yield and without nutrient supplementation. Copyright © 2008 Society of Chemical Industry     

Electrochemical conversion of phenolic wastewater on carbon electrodes in the presence of NaCl

The electrochemical conversion of highly concentrated synthetic phenolic wastewater was studied on carbon electrodes in a batch electrochemical reactor. The effects of reaction temperature, electrolyte concentration, current density and initial phenol concentration on phenol conversion were elucidated. The wastewater was synthetically prepared and used in reactions carried out generally at 25 °C with an initial phenol concentration of 3500 mg dm^?3. Although current density increased, phenol conversion% and initial phenol conversion rate did not increase correspondingly above 35 °C and an electrolyte concentration of 90 g dm^?3. As the voltage values applied were increased, the increasing current density resulted in fast phenol conversion. Kinetic investigations denoted that overall phenol destruction kinetics was of zero order with an activation energy of 10.9 kJ mol^?1. Under appropriate conditions, phenol was completely converted within 15 min for an initial phenol concentration of 98 mg dm^?3 while 8 h was required to gain 95% conversion using 4698 mg dm^?3. Solid polymeric materials were produced at initial phenol concentrations above 500 mg dm^?3 using the appropriate current density. In the reaction medium, only mono‐, di‐ and tri‐substituted chlorophenols were formed and 100% of all species were either oxidised or contributed to the formation of a polymeric structure. Almost all of the phenol loaded to the reactor was converted into non‐passivating polymeric products, denoting a safe and easy method for the separation of phenol. © 2001 Society of Chemical Industry     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Mesophilic anaerobic digestion of corn thin stillage: a technical and energetic assessment of the corn‐to‐ethanol industry integrated with anaerobic digestion

BACKGROUND: The purpose of this study was to reduce the VS (volatile solid) and recover energy (methane) from thin stillage through mesophilic anaerobic digestion in corn–ethanol plants. The performance of a continuously stirred tank reactor (CSTR) with different hydraulic retention times (HRTs) was evaluated in this study. RESULTS: The results show no differences in volatile solid (VS) destruction (82–83%) in the reactor with HRTs ranging from 25 to 40 days. The maximum volumetric methane production rate of 1.41 L L^?1 day^?1 was produced at 25‐day HRT, whereas the maximum methane yield of approximately 0.63 L CH₄ g^?1 VS_fed (0.77 L g^?1 VS_removed) was achieved with HRTs between 30 and 40 days. Simulation results using a kinetic model indicate that the reactor needs to be operated for longer than 23 days in order to achieve 80% of maximum methane yield. The techno‐economic potential of a corn–ethanol facility to produce an estimated 57% energy recovery using mesophilic anaerobic digestion has long been overlooked. A corn–ethanol plant integrated with mesophilic anaerobic digestion increases the net energy balance ratio from 1.26 to 1.80. CONCLUSION: Mesophilic anaerobic digestion complements the corn–ethanol business so that the sustainable energy obtained from corn recovery is made more lucrative and renewable. Copyright © 2011 Society of Chemical Industry     

D‐Lactic acid production from waste cardboard

The effects caused by alkaline treatment on the susceptibility of waste cardboard to enzymatic hydrolysis have been studied. Optimised conditions leading to extensive saccharification of both cellulose (870 g kg^?1 conversion) and hemicelluloses (845 g kg^?1 conversion) were identified. Samples treated under selected operational conditions were employed for producing D ‐lactic acid by simultaneous saccharification and fermentation (SSF) in media containing cellulases, β‐glucosidase and Lactobacillus coryniformis ssp torquens cells. SSF fed‐batch experiments led to D ‐lactic acid concentrations up to 23.4 g dm^?3 at a product yield of 514 g lactic acid kg^?1 of potential glucose and a volumetric productivity of 0.48 g dm^?3 h^?1. Copyright © 2004 Society of Chemical Industry     

Advanced oxidation processes for the degradation of p‐hydroxybenzoic acid 2: Photo‐assisted Fenton oxidation

Oxidation of p‐hydroxybenzoic acid in aqueous solution by the photo‐assisted Fenton reaction (Fe²⁺ + H₂O₂ + UV) has been studied. The effects of ferrous ion concentration (0.05, 0.14 and 0.29 mmol dm^?3), temperature (10, 20, 30 and 40 °C), and initial hydrogen peroxide concentration (0.7, 1.4, 2.2 and 2.9 mmol dm^?3) on the p‐hydroxybenzoic acid conversion were established. Experimental results indicate that the kinetics of this oxidation process fits pseudo‐first‐order kinetics well. The overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH·) generated in the system. The importance of these two reaction paths for each specific value of ferrous ion concentration, temperature and initial hydrogen peroxide concentration was evaluated. A semi‐empirical expression is proposed for the overall reaction rate which takes into account both oxidation pathways and is a function of operating variables. © 2001 Society of Chemical Industry