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In the light of microalgae rich in proteins, carbohydrates, and lipids, development of multi-product biorefinery from microalgae has become a promising approach towards commercialization of microalgae-based products. This review discusses an integrated algal biorefinery (IABR) based on a combination of four microalgae-to-products chains for the production of biofuels, biopower, and byproducts. Two systematic analytical approaches by life cycle assessment (LCA) and techno-economic assessment (TEA) are used to quantify the economic and environmental benefits. From process systems engineering (PSE) aspects, the approach procedures include that (i) the engineering process model serves as the foundation for assessment, (ii) an IABR is generated via process design, simulation, and integration, and (iii) the multi-objective optimization of an IABR with respect to economic and environmental issues is addressed.

Anaerobic co-digestion of a mixture of industrial animal by-products (ABP) from meat-processing in conjunction with dairy cattle slurry (mixed in a ratio of 1:3; w.w.) was evaluated at 35 °C focusing on methane production and stabilization. Three pre-treatments were applied (1) digestion with no pre-treatment (control), (2) ultrasound, and (3) thermal hygienization (70 °C, 60 min). Methane production potentials (MPP) of the untreated, ultrasound pre-treated and hygienized feed mixtures were 300, 340, and 360 m(3) CH(4)/t volatile solids (VS) added, as determined in the batch experiments. However, the specific methane productions (SMP) achieved in reactor experiments (hydraulic retention time HRT 21 d, organic loading rate OLR 3.0±0.1 kg VS/m(3) d) were 11±2% (untreated and ultrasound pre-treated) and 22±3% (hygienized) lower than the potentials. Ultrasound with the energy input of 1000 kJ/kg total solids (TS) and hygienization of the ready-made feed were the most suitable pre-treatment modes studied.

The on-going annual increase in global methane (CH4) emissions can be largely attributed to anthropogenic activities. However, as more than half of these emissions are diffuse and possess a concentration less than 3% (v/v), physical-chemical treatments are inefficient as an abatement technology. In this regard, biotechnologies, such as biofiltration using methane-oxidizing bacteria, or methanotrophs, are a cost-effective and efficient means of combating diffuse CH4 emissions. In this review, a number of abiotic factors including temperature, pH, water content, packing material, empty-bed residence time, inlet gas flow rate, CH4 concentration, as well biotic factors, such as biomass development, are reviewed based on empirical findings on CH4 biofiltration studies that have been performed in the last decades.

In this study, nitrogen-containing chemicals and nitrogen-rich biochar were prepared using ammonia (NH3) torrefaction pretreatment technology. The effects of temperature and duration of torrefaction on the characteristics of torrefaction and pyrolysis products were evaluated. The results indicated that when the torrefaction temperature was increased to 290 °C, the nitrogen content increased significantly from 0.98% to 6.85%. XPS analysis showed that the raw biomass mainly contained amide-N and pyrrole-N. As the torrefaction temperature and duration increased, quaternary-N formation was promoted, while amide-N, pyrrole-N, and pyridine-N were consumed. Potential nitrogen doping and transformation pathways during the ammonia torrefaction process were proposed. GC-MS analysis showed that ammonia torrefaction promoted the formation of pyridines, while reducing the content of oxygen-containing species. In addition, torrefaction duration had positive effects on the yield of nitrogen-containing chemicals.

A central composition design was developed to study the influence of process variables (temperature, pulping time and ethanol concentration) on the properties of the pulp produced (yield and holocellulose, alpha-cellulose and lignin contents) and the pH of the resulting wastewater, in the ethanol pulping of olive tree trimmings. The proposed equations reproduce the experimental results for the dependent variables with errors less than 5% for the holocellulose and alpha-cellulose contents, yield and wastewater pH, and less than 15% for the lignin content. Obtaining pulp with acceptably high yield (37.6%), high holocellulose and alpha-cellulose contents (above 88.8% and 46.9%, respectively), and low lignin contents (below 7.2%), entails operating at a pulping temperature of 200 degrees C, using an ethanol concentration of 75% and a pulping time of 60 min.

The conversion of tamarind seed into bio-oil by pyrolysis has been taken into consideration in the present work. The major components of the system were fixed bed fire-tube heating reactor, liquid condenser and collector. The crushed tamarind seed in particle form was pyrolyzed in an electrically heated fixed bed reactor. The products were liquid, char and gasses. The parameters varied were reactor temperature, running time, gas flow rate and feed particle size. The maximum liquid yield was 45 wt% at 400°C for a feed size of 3200 μm diameter at a gas flow rate of 6l/min with a running time of 30 min. The obtained pyrolysis liquid at these optimum process conditions were analyzed for physical and chemical properties to be used as an alternative fuel. The results show the potential of tamarind seed as an important source of alternative fuel and chemicals as well.

Conversion of Cladophora glomerata (C. glomerata) as a Caspian Sea's green macroalgae into gaseous, liquid and solid products was carried out via pyrolysis at different temperatures to determine its potential for bio-oil and hydrogen-rich gas production for further industrial utilization. Non-catalytic tests were performed to determine the optimum condition for bio-oil production. The highest portion of bio-oil was retrieved at 500°C. The catalytic test was performed using the bio-char derived at 500°C as a catalyst. Effect of the addition of the algal bio-char on the composition of the bio-oil and also gaseous products was investigated. Pyrolysis derived bio-char was characterized by BET, FESEM and ICP method to show its surface area, porosity, and presence of inorganic metals on its surface, respectively. Phenols were increased from 8.5 to 20.76area% by the addition of bio-char. Moreover, the hydrogen concentration and hydrogen selectivity were also enhanced by the factors of 1.37, 1.59 respectively.

A novel volute aerator was proposed to generate shear force and break gas flow through water centrifugation to promote mass transfer for CO2 fixation with microalgae. The bubble evolution and gas-liquid mixing processes in volute aerator were numerically simulated. The bubble generation time and diameter were measured on a high-speed camera and assessed with level-set method. By optimizing gas inletpipe angle and water/gas inlet velocities of volute aerator, the bubble generation time decreased by 60.1% to 3.3 ms and outlet bubble diameter decreased by 50.7% to 1.8 mm, compared with traditional strip aerator. The corresponding gas-liquid mixing time reduced by 15.6% and mass transfer coefficient increased by 42.2%. The volute aerator was used as an alternative to traditional strip aerator to culture microalgae under high-purity CO2 condition, which promoted average growth rate and biomass production by 26.6% and 50.7%, respectively.

Microbial degradation of phenol was studied using batch and fedbatch cultures of acclimatized activated sludge under a wide range of phenol (0-793 mg l(-1)) and biomass (0.74-6.7 g l(-1)) initial concentrations. As cell growth continued after total phenol removal, the production and later consumption of a main metabolic intermediate was considered the step governing the biodegradation kinetics. A model that takes explicitly into account the kinetics of the intermediate was developed by introducing a specific growth rate model associated with its consumption and the incorporation of a dual-substrate inhibitory effect on phenol degradation. Biomass growth and phenol removal were adequately predicted in all the cultures. Moreover, the model-based design of the fedbatch feeding strategies allowed driving separately the phenol degradation under substrate-limitation and substrate-inhibition modes. A sensitivity analysis was also performed in order to establish the importance of the parameters in the accuracy of model predictions.