Immobilization of Diatom Phaeodactylum tricornutum with Filamentous Fungi and Its Kinetics.

Immobilizing microalgae cells in a hyphal matrix can simplify harvest while producing novel mycoalgae products with potential food, feed, biomaterial, and renewable energy applications; however, limited quantitative information to describe the process and its applicability under various conditions leads to difficulties in comparing across studies and scaling-up. Here, we demonstrate the immobilization of both active and heat-deactivated marine diatom Phaeodactylum tricornutum (UTEX 466) using different loadings of fungal pellets (Aspergillus sp.) and model the process through kinetics and equilibrium models. Active P. tricornutum cells were not required for the fungal-assisted immobilization process and the fungal isolate was able to immobilize more than its original mass of microalgae. The Freundlich isotherm model adequately described the equilibrium immobilization characteristics and indicated increased normalized algae immobilization (g algae removed/g fungi loaded) under low fungal pellet loadings. The kinetics of algae immobilization by the fungal pellets were found to be adequately modeled using both a pseudo-second order model and a model previously developed for fungal-assisted algae immobilization. These results provide new insights into the behavior and potential applications of fungal-assisted algae immobilization.

Functions of bacteria and archaea participating in the bioconversion of organic waste for methane production.

Anaerobic digestion (AD) is a widely applied technology for treating organic wastes to generate renewable energy in the form of biogas. The effectiveness of AD process depends on many factors, among which the most important is the presence of active and healthy microbial community in the anaerobic digesters, which needs to be explored. However, the deciphering of microbial populations and their functions during the AD process of different materials is still incomplete, which restricts the understanding of its long-term performance under different operational conditions. This review describes the type, morphology, functions, and specific growth conditions of commonly found hydrolytic, acidogenic, acetogenic bacteria, and archaea during the AD process. The effects of microbes on the performance and stability of the digestion process are also presented. Furthermore, the article offers a deep understanding of the AD management strategies for the enhancement of methane production and the efficiency of the energy conversion process of various organic wastes.

Biorefining of rice straw by sequential fermentation and anaerobic digestion for bioethanol and/or biomethane production: Comparison of structural properties and energy output.

Three routes; namely R1 representing direct anaerobic digestion (AD), R2 representing enzymatic hydrolysis followed by fermentation, distillation, then AD, and R3 representing AD of fermentation broth without distillation; of alkali pretreated rice straw were investigated. Results showed that sequential fermentation and AD effectively enhanced fibers degradation with significant changes in the composition. Fermentation through R2 resulted in ethanol yield of 87.4 g kg-1 dry straw. Maximum biogas yields of 286.9, 233.3 and 372.4 L kg-1 VS were recorded by AD for R1, R2 and R3 after reaching the steady state at 36, 24 and 33 days, respectively. However, biogas produced through R3 showed the highest significant biomethane content (79.3%) which represented 15 and 8% higher than that of R1 and R2, respectively. Therefore, the highest bioenergy output and energy conversion efficiency of 10.58 GJ ton-1 and 75.6%, respectively, were obtained through R3 demonstrating the positive effect of fermentation prior to AD.

Kinetics of methane production from the codigestion of switchgrass and Spirulina platensis algae.

Anaerobic batch digestion of four feedstocks was conducted at 35 and 50 °C: switchgrass; Spirulina platensis algae; and two mixtures of both switchgrass and S. platensis. Mixture 1 was composed of 87% switchgrass (based on volatile solids) and 13% S. platensis. Mixture 2 was composed of 67% switchgrass and 33% S. platensis. The kinetics of methane production from these feedstocks was studied using four first order models: exponential, Gompertz, Fitzhugh, and Cone. The methane yields after 40days of digestion at 35 °C were 355, 127, 143 and 198 ml/g VS, respectively for S. platensis, switchgrass, and Mixtures 1 and 2, while the yields at 50 °C were 358, 167, 198, and 236 ml/g VS, respectively. Based on Akaike's information criterion, the Cone model best described the experimental data. The Cone model was validated with experimental data collected from the digestion of a third mixture that was composed of 83% switchgrass and 17% S. platensis.

Biogasification of green and food wastes using anaerobic-phased solids digester system.

The performance of a laboratory-scale anaerobic-phased solid (APS) digester system treating food and green wastes was evaluated at thermophilic condition. The APS system comprised of four hydrolysis digesters and one biogasification reactor. The hydrolysis reactors were operated batchwised at a 12-day retention time, while the biogasification reactor was continuously operated at different hydraulic retention times (HRT). The biogas and methane yields from green waste were determined to be 0.438 and 0.252 L/g volatile solid (VS), respectively, with VS removal of 78%. The biogas and methane yields from food waste were 0.596 and 0.379 L/g VS, respectively, with VS removal of 85%. Hydrogen was produced from hydrolysis reactors during the digestion of food waste. Its content was 30.1% and 8.5% of the biogas produced on the first and second day of digestion, respectively. Hydrogen yield from the whole system was determined to be 0.029 L/g VS representing about 4.9% of the total biogas production from the system. The ratio between the volumes of biogasification and hydrolysis reactors (BR/HR) was found to be a factor that affects the process performance and stability.

Biogas production from co-digestion of dairy manure and food waste.

The effect of manure-screening on the biogas yield of dairy manure was evaluated in batch digesters under mesophilic conditions (35 degrees C). Moreover, the study determined the biogas production potential of different mixtures of unscreened dairy manure and food waste and compared them with the yield from manure or food waste alone. A first-order kinetics model was developed to calculate the methane yield from different mixtures of food waste and unscreened dairy manure. The methane yields of fine and coarse fractions of screened manure and unscreened manure after 30days were 302, 228, and 241L/kgVS, respectively. Approximately 93%, 87%, and 90% of the biogas yields could be obtained, respectively, after 20days of digestion. Average methane content of the biogas was 69%, 57%, and 66%, respectively. Based on mass balance calculations, separation of the coarse fraction of manure would sacrifice about 32% of the energy potential. The methane yield of the food waste was 353L/kgVS after 30days of digestion. Two mixtures of unscreened manure and food waste, 68/32% and 52/48%, produced methane yields of 282 and 311L/kgVS, respectively after 30days of digestion. After 20days, approximately 90% and 95% of the final biogas yield could be obtained, respectively. Therefore, a hydraulic retention time (HRT) of 20days could be recommended for a continuous digester. The average methane content was 62% and 59% for the first and second mixtures, respectively. The predicted results from the model showed that adding the food waste into a manure digester at levels up to 60% of the initial volatile solids significantly increased the methane yield for 20days of digestion.

Effect of feed to inoculum ratios on biogas yields of food and green wastes.

Biogas and methane yields of food and green wastes and their mixture were determined using batch anaerobic digesters at mesophilic (35+/-2 degrees C) and thermophilic (50+/-2 degrees C) temperatures. The mixture was composed of 50% food waste and 50% green waste, based on the volatile solids (VS) initially added to the reactors. The thermophilic digestion tests were performed with four different feed to inoculum (F/I) ratios (i.e., 1.6, 3.1, 4.0 and 5.0) and the mesophilic digestion was conducted at one F/I (3.1). The results showed that the F/I significantly affected the biogas production rate. At four F/Is tested, after 25 days of thermophilic digestion, the biogas yield was determined to be 778, 742, 784 and 396 mL/g VS for food waste, respectively; 631, 529, 524 and 407 mL/g VS for green waste, respectively; and 716, 613, 671 and 555 mL/g VS for the mixture, respectively. About 80% of the biogas production was obtained during the first 10 days of digestion. At the F/I of 3.1, the biogas and methane yields from mesophilic digestion of food waste, green waste and their mixture were lower than the yields obtained at thermophilic temperature. The biogas yields were 430, 372 and 358 mL/g VS, respectively, and the methane yields were 245, 206, and 185 mL/g VS, respectively.

Anaerobic digestion of saline creeping wild ryegrass for biogas production and pretreatment of particleboard material.

The objective of this research was to develop an integrated process to produce biogas and high-quality particleboard using saline creeping wild ryegrass (CWR), Leymus triticoides through anaerobic digestion (AD). Besides producing biogas, AD also serves as a pretreatment method to remove the wax layer of CWR for improving binding capability and then the residue is used to produce high-quality particleboard. CWR was digested for three time periods, 15, 22, and 33 days with the volatile solid (VS) loading of 10 g-VS/L-sludge and the food to microorganism (F/M) ratio of 1.41. The highest biogas yield after digestion for 33 days was 251 mL/g-VS, which is corresponded to energy of 8419BTU/kg-dry CWR. The highest methane content of biogas was 63%. Compared with particleboards manufactured from urea formaldehyde (UF) and untreated CWR, the mechanical and long-term (24 h) water resistance properties of particleboards made from UF and 33-day AD CWR residue were statistically significantly improved, except for modulus of elasticity (MOE). For example, the modulus of rupture (MOR) was increased by 39%. The results indicated that the integrated process could be a cost-effective and environmentally friendly method for producing bioenergy and particleboard with agricultural residues.

Characterization of food waste as feedstock for anaerobic digestion.

Food waste collected in the City of San Francisco, California, was characterized for its potential for use as a feedstock for anaerobic digestion processes. The daily and weekly variations of food waste composition over a two-month period were measured. The anaerobic digestibility and biogas and methane yields of the food waste were evaluated using batch anaerobic digestion tests performed at 50 degrees C. The daily average moisture content (MC) and the ratio of volatile solids to total solids (VS/TS) determined from a week-long sampling were 70% and 83%, respectively, while the weekly average MC and VS/TS were 74% and 87%, respectively. The nutrient content analysis showed that the food waste contained well balanced nutrients for anaerobic microorganisms. The methane yield was determined to be 348 and 435 mL/gVS, respectively, after 10 and 28 days of digestion. The average methane content of biogas was 73%. The average VS destruction was 81% at the end of the 28-day digestion test. The results of this study indicate that the food waste is a highly desirable substrate for anaerobic digesters with regards to its high biodegradability and methane yield.

Rheological properties of dairy cattle manure.

Rheological properties are important for the design and modelling of handling and treating fluids. In the present study, the viscosity of liquid manure (about 10% total solids) was measured at different shear rates (2.38-238 s(-1)). The effect of temperature on the viscosity at different shear rates was also studied. The results showed that manure has non-Newtonian flow properties, because the viscosity strongly depended on the applied shear rate. The results showed also that manure behaves like real plastic materials. The power-law model of the shear stress and the rate of shear showed that the magnitude of the consistency coefficient decreased while increasing the temperature, with high values of the determination coefficient. Moreover, the results showed that the Arrhenius-type model fitted the temperature effect on manure viscosity very well (R2 at least 0.95) with calculated activation energy of 17.0+/-0.3 kJ mol(-1).

Effect of temperature and temperature fluctuation on thermophilic anaerobic digestion of cattle manure.

The influence of temperature, 50 and 60 degrees C, at hydraulic retention times (HRTs) of 20 and 10 days, on the performance of anaerobic digestion of cow manure has been investigated in completely stirred tank reactors (CSTRs). Furthermore, the effect of both daily downward and daily upward temperature fluctuations has been studied. In the daily downward temperature fluctuation regime the temperatures of each reactor was reduced by 10 degrees C for 10 h while in the daily upward fluctuation regime the temperature of each reactor was increased 10 degrees C for 5 h. The results show that the methane production rate at 60 degrees C is lower than that at 50 degrees C at all experimental conditions of imposed HRT except when downward temperature fluctuations were applied at an HRT of 10 days. It also was found that the free ammonia concentration not only affects the acetate-utilising bacteria but also the hydrolysis and acidification process. The upward temperature fluctuation affects the maximum specific methanogenesis activity more severely as compared to imposed downward temperature fluctuations. The results clearly reveal the possibility of using available solar energy at daytime to heat up the reactor(s) without the need of heat storage during nights, especially at an operational temperature of 50 degrees C and at a 20 days HRT, and without the jeopardising of the overheating.