Pretreatment Processes of Biomass for Biorefineries: Current Status and Prospects

This article seeks to be a handy document for the academy and the industry to get quickly up to speed on the current status and prospects of biomass pretreatment for biorefineries. It is divided into two biomass sources: vegetal and animal. Vegetal biomass is the material produced by plants on land or in water (algae), consuming sunlight, CO2, water, and soil nutrients. This includes residues or main products from, for example, intensive grass crops, forestry, and industrial and agricultural activities. Animal biomass is the residual biomass generated from the production of food from animals (e.g., manure and whey). This review does not mean to include every technology in the area, but it does evaluate physical pretreatments, microwave-assisted extraction, and water treatments for vegetal biomass. A general review is given for animal biomass based in physical, chemical, and biological pretreatments.

Nitrogen removal in domestic wastewater. Effect of nitrate recycling and COD/N ratio

A denitrification/nitrification pilot plant was designed, built and put into operation, treating the effluent of an anaerobic reactor. The operation of the plant examined the effect of the nitrate recycling and the COD/N ratio on the nitrogen and the remaining organic matter removal at 18 °C. The system consisted of a two-stage treatment process: anoxic and aerobic. The hydraulic retention time (HRT) of the system was 1 h for the anoxic bioreactor and 2 h for the aerobic one. The increase in the nitrate recycling ratio did not cause a significant improvement in the nitrogen removal due to the insufficient carbon source. The wastewater to be treated had a C/N ratio of 1.1 showing a lack of organic carbon. The addition of methanol was a key point in the denitrification process used as a model for the traditional wastewater by-pass in the WWTP. The maximum nitrogen and organic matter removal (87.1% and 96%, respectively) was achieved with a nitrate recycling ratio of 600% and a C/N of 8.25, adjusted by methanol addition.

Sequencing batch reactor process for the removal of nitrogen from anaerobically treated domestic wastewater

This work presents the performance of a sequencing batch reactor (SBR) system used as a means of removing nitrogen from domestic wastewater containing a low chemical oxygen demand (COD) to nitrogen ratio due to pre-treatment with an anaerobic reactor. The aim of the work was to determine the feasibility of this system for the removal of nitrogen from the domestic wastewater. An SBR with a working volume of 5 L was investigated at different cycle times of 12, 8 and 6 h, at 18 °C. The efficiency of the SBR varied together with the duration of the cycle, where the optimum performance was seen in the 6 h cycle with the anoxic-aerobic-anoxic sequence. Due to the low quantity of organic matter present in the domestic wastewater after the anaerobic treatment, an additional supply of external carbon was necessary before the second anoxic stage. The removal efficiencies obtained were: 98% for total Kjeldahl nitrogen, 84% for total nitrogen and 77% for soluble COD. The reactor was thus shown to be viable, and it was concluded that this process may be successfully applied as a post-treatment for the removal of nitrogen from anaerobically treated domestic wastewater.

Recirculation of gas emissions to achieve advanced denitrification of the effluent from the anaerobic treatment of domestic wastewater

A denitrifying pilot plant was designed, constructed and operated for more than five months. The plant treated domestic wastewater with high ammonium nitrogen concentration, which had previously undergone an anaerobic process at 18 °C. The process consisted of one biofilter with 2 h of hydraulic retention time for denitritation. Different synthetic nitrite concentrations were supplied to the anoxic reactor to simulate the effluent of a nitritation process. This work investigates the advanced denitritation of wastewater using the organic matter and other alternative electron donors present in an anaerobic treatment process effluent: methane and sulfide. The denitrifying bacteria were able to treat wastewater at an inlet nitrite concentration of 75 mg NO₂^--N/L with a removal efficiency of 92.9%. When the inlet nitrite concentration was higher, the recirculation of the gas from the top of the anoxic reactor was successful to enhance the nitrite removal, achieving a NO₂^- elimination efficiency of 98.3%.

Ultrafast Generation of Unconventional {001} Loops in Si

Ultrafast laser annealing of ion implanted Si has led to thermodynamically unexpected large {001} self-interstitial loops, and the failure of Ostwald ripening models for describing self-interstitial cluster growth. We have carried out molecular dynamics simulations in combination with focused experiments in order to demonstrate that at temperatures close to the melting point, self-interstitial rich Si is driven into dense liquidlike droplets that are highly mobile within the solid crystalline Si matrix. These liquid droplets grow by a coalescence mechanism and eventually transform into {001} loops through a liquid-to-solid phase transition in the nanosecond time scale.

Denitrification of the anaerobic membrane bioreactor (AnMBR) effluent with alternative electron donors in domestic wastewater treatment

A fixed film bioreactor for the denitrification of the effluent from an anaerobic membrane bioreactor (AnMBR) treating domestic wastewater was designed, built and investigated. After anaerobic treatment, the wastewater usually has a low C/N ratio (∼1.3), and a remaining chemical oxygen demand of around 117mg O₂/L, which is not enough to make conventional heterotrophic denitrification possible. That effluent also holds methane and sulfide dissolved and oversaturated after leaving the AnMBR. This paper demonstrates the feasibility of using these reduced compounds as electron donors in order to remove 80mg NO_x^--N/L at 18°C and 2h of hydraulic retention time. In addition, the influence of the NO₂^-/NO₃^- ratios in the feed was studied. Total nitrogen removal was achieved in all the cases studied, except for a feed with 100% NO₃^-. Methane was the main electron donor used to remove the nitrites and nitrates, with a participation rate of over 70%.

Kinetic Monte Carlo simulations for transient thermal fields: Computational methodology and application to the submicrosecond laser processes in implanted silicon

Pulsed laser irradiation of damaged solids promotes ultrafast nonequilibrium kinetics, on the submicrosecond scale, leading to microscopic modifications of the material state. Reliable theoretical predictions of this evolution can be achieved only by simulating particle interactions in the presence of large and transient gradients of the thermal field. We propose a kinetic Monte Carlo (KMC) method for the simulation of damaged systems in the extremely far-from-equilibrium conditions caused by the laser irradiation. The reference systems are nonideal crystals containing point defect excesses, an order of magnitude larger than the equilibrium density, due to a preirradiation ion implantation process. The thermal and, eventual, melting problem is solved within the phase-field methodology, and the numerical solutions for the space- and time-dependent thermal field were then dynamically coupled to the KMC code. The formalism, implementation, and related tests of our computational code are discussed in detail. As an application example we analyze the evolution of the defect system caused by P ion implantation in Si under nanosecond pulsed irradiation. The simulation results suggest a significant annihilation of the implantation damage which can be well controlled by the laser fluence.

Microscopic description of the irradiation-induced amorphization in silicon

We have investigated the atomistic mechanism behind the irradiation-induced amorphization in Si using molecular dynamics simulation techniques. The microscopic description of the process is based on the defect known as bond defect or IV pair. IV pairs recombine very fast when isolated, but if they interact to each other they survive longer times and thus accumulate giving rise to amorphization. This fact accounts for the superlinear behavior of the accumulated damage with dose and the different activation energies for recrystallization observed in the experiments. The molecular dynamics results have been used to define an atomistic model for amorphization and recrystallization which has been implemented in a kinetic Monte Carlo code. The model is able to reproduce quantitatively the dependence of the critical crystal-amorphous transition on the irradiation parameters.