Enhancing anaerobic hydrolysis of cattle manure in leachbed reactors

In this study, it is hypothesized that anaerobic hydrolysis of organic solid wastes (OSWs) in leachbed reactors can be enhanced by two approaches: (1) by increasing the porosity of the leachbed; and (2) by seeding the bed with brown-rot fungi or anaerobically digested residues. The hypothesis is verified using cattle manure as a model OSW and pistachios-half-shell as an inert additive to increase the porosity of the leachbed. The enhancement was quantified in terms of volatile fatty acid (VFA) generation and soluble COD generation. Results of this study showed that 15% more VFAs and 8% more soluble COD can be obtained at higher bed porosities and with brown-rot fungi or digested residues as the seed. Compared to a leachbed without any recirculation, porosity enhancement, nor seed addition, the VFA yield (g VFA/g manure) in a leachbed with pistachios-half-shell as porosity enhancers was 193% higher; that in a leachbed with leachate recirculation (of 4 L/day), pistachios-half-shell as porosity enhancers, and brown-rot fungi or digested sludge as seed was 230% higher.     

Energetic evaluation of an internally illuminated photobioreactor for algal cultivation

An annular internally illuminated photobioreatcor (IIPBR) configuration based on the airlift/bubble column principles was developed and validated at an 18 l prototype scale using Scenedemus sp. and Nannochloropsis salina in batch and semi-continuous modes, at constant light supply and constant gas-to-culture volume ratio, but at varying CO₂-to-air ratios. Highest biomass production was recorded at CO₂-to-air ratio of 4% with Scenedesmus sp. and at 1% with Nannochloropsis salina. The energetic performance of this IIPBR was quantified in terms of biomass productivity per unit energy input, P/E (g W^?1 day^?1), considering energy input for illumination and for pneumatic mixing and circulation. Under optimal conditions, the IIPBR evaluated in this study achieved P/E of 1.42 g W^?1 day^?1 for Scenedesmus sp. and P/E of 0.34 g W^?1 day^?1 for Nannochloropsis salina. These P/E values are better than those estimated for airlift and bubble column photobioreactor configurations reported in the literature.     

Optimization of microwave-assisted transesterification of dry algal biomass using response surface methodology

The effect of microwave irradiation on the simultaneous extraction and transesterification (in situ transesterification) of dry algal biomass to biodiesel was investigated. A high degree of oil/lipid extraction from dry algal biomass and an efficient conversion of the oils/lipids to biodiesel were demonstrated in a set of well-designed experimental runs. A response surface methodology (RSM) was used to analyze the influence of the process variables (dry algae to methanol (wt/vol) ratio, catalyst concentration, and reaction time) on the fatty acid methyl ester conversion. Based on the experimental results and RSM analysis, the optimal conditions for this process were determined as: dry algae to methanol (wt/vol) ratio of around 1:12, catalyst concentration about 2 wt.%, and reaction time of 4 min. The algal biodiesel samples were analyzed with GC-MS and thin layer chromatography (TLC) methods. Transmission electron microscopy (TEM) images of the algal biomass samples before and after the extraction/transesterification reaction are also presented.     

Evaluation of dairy cattle manure as a supplement to improve net energy gain in fermentative hydrogen production from sucrose

This study evaluated fermentative biohydrogen production from sucrose supplemented with dairy cattle manure at different sucrose:manure ratios. Hydrogen yields found in this study (2.9-5.3 M hydrogen/M sucrose) at ambient temperature are higher than literature results obtained at mesophilic temperatures. This study demonstrated that dairy cattle manure could serve as a buffering agent to maintain recommended pH levels; as a nutrient source to provide the required nutrients for hydrogen production; as a seed to produce hydrogen from sucrose; and as a co-substrate to improve the hydrogen yield. Based on an analysis of the net energy gain, it is concluded that positive net energy gains can be realized with non-thermal pretreatment and/or by combining dark fermentation with anaerobic digestion or microbial fuel cells to extract additional energy from the aqueous products of dark fermentation.     

Cattle wastes as substrates for bioelectricity production via microbial fuel cells

A new 2 l scale microbial fuel cell (MFC) configuration was developed to generate bioelectricity from particulate substrates. Voltage and power densities generated in this MFC fed with sucrose, particulate cattle manure, and manure wash-water as the substrates were evaluated in batch mode, with and without external mediators. Voltages averaged 0.5 V in open circuit, and 0.4 V under a resistive load of 470 Ω. Power densities (67 to 215 mW/m²) were comparable to previous work that had used liquid wastes as substrates. Based on the energy yield per unit mass of feedstock (~10 kJ/kg wet manure), cattle manure has limited potential to serve as a feedstock for electricity production via MFCs.     

Optimization of direct conversion of wet algae to biodiesel under supercritical methanol conditions

This study demonstrated a one-step process for direct liquefaction and conversion of wet algal biomass containing about 90% of water to biodiesel under supercritical methanol conditions. This one-step process enables simultaneous extraction and transesterification of wet algal biomass. The process conditions are milder than those required for pyrolysis and prevent the formation of by-products. In the proposed process, fatty acid methyl esters (FAMEs) can be produced from polar phospholipids, free fatty acids, and triglycerides. A response surface methodology (RSM) was used to analyze the influence of the three process variables, namely, the wet algae to methanol (wt./vol.) ratio, the reaction temperature, and the reaction time, on the FAMEs conversion. Algal biodiesel samples were analyzed by ATR-FTIR and GC-MS. Based on the experimental analysis and RSM study, optimal conditions for this process are reported as: wet algae to methanol (wt./vol.) ratio of around 1:9, reaction temperature and time of about 255 °C, and 25 min respectively. This single-step process can potentially be an energy efficient and economical route for algal biodiesel production.     

Electricity production in membrane-less microbial fuel cell fed with livestock organic solid waste

Two different MFC configurations designed for handling solid wastes as a feedstock were evaluated in batch mode: a single compartment combined membrane-electrodes (SCME) design; and a twin-compartment brush-type anode electrodes (TBE) design (reversed T-shape MFC with two-air cathode) without a proton exchange membrane (PEM). Cattle manure was tested as a model livestock organic solid waste feedstock. Under steady conditions, voltage of 0.38 V was recorded with an external resistance of 470 Ω. When digested anaerobic sludge was used as the seed in the SCME design, a maximum power density of 36.6 mW/m² was recorded. When hydrogen-generating bacteria (HGB) were used as the seed used in the TBE design, a higher power density of 67 mW/m² was recorded.