Davide Dionisi

Production of ethanol, organic acids and hydrogen: an opportunity for mixed culture biotechnology?

Anaerobic fermentation of biodegradable organic materials is usually carried out to obtain the final product, methane, a valuable energy source. However, it is also well known that various intermediates are produced in this process, e.g. ethanol, volatile organic acids and hydrogen. All these species have applications and value as fuels or chemicals. This paper shows a critical analysis of the potential of using anaerobic fermentation by mixed cultures to produce intermediates, e.g. ethanol, acetic, lactic and butyric acid and hydrogen, rather than methane. This paper discusses the current processes to produce these chemicals and compares them with the alternative approach of using open mixed cultures to produce them simultaneously via fermentation from renewable resources. None of these chemicals is currently produced via mixed culture fermentation: ethanol and lactic acid are usually produced in pure culture fermentation using food crops, e.g. corn or sugar cane, as starting materials; hydrogen, acetic and butyric acids are mainly produced via chemical synthesis from fossil fuel derived starting materials. A possible flow-sheet for the production of these chemicals from organic waste using mixed culture fermentation is proposed and the advantages and disadvantages of this process compared to current processes are critically discussed. The paper also discusses the research challenges which need to be addressed to make this process feasible.

Quantification of hydrocarbon species on surfaces by combined microbalance-FTIR

Absorption coefficients for the asymmetric stretching modes of CH3 and CH2 groups formed by adsorbing alkyl chained species from the vapour phase onto two different adsorbents; a γ-alumina support material and a supported metal catalyst have been determined using a custom made thermogravimetric-infrared cell. Results show that despite variations in the individually calculated absorption coefficients (ca. ±20%), the ratio of the absorption coefficients (CH2:CH3) remained consistent despite employing adsorbates of varying chain length and functionality, and despite the choice of adsorbents which exhibited different surface areas and light scattering characteristics. The use of this absorption coefficient ratio has been shown to be applicable in the quantification of the average chain length of multiple adsorbed species of differing chain length. The potential for applying this to scenarios where reactions on surfaces are monitored is discussed.

Biorefinery with Open Mixed Cultures for Biofuels and Chemicals Production from Organic Waste: Biodegradation of Unpretreated Cellulose

This work fits in the general research area of organic waste conversion to chemicals and fuels using anaerobic digestion. In particular this study investigates the ability of undefined mixed microbial cultures to ferment cellulose to ethanol and organic acids without any chemical or physical pretreatment of the feed. The anaerobic conversion of microcrystalline cellulose was investigated in four batch experiments, carried out at 25 °C without any pretreatment of the cellulose. The mixed culture effectively fermented the substrates, however cellulose degradation only occurred after the microorganisms had been acclimated to cellulose in continuous runs, while cellulose was not degraded by unacclimated microorganisms. Acetic acid was the main metabolic product while ethanol, butyric acid and propionic acid were also present in low concentrations. Within 100 days from the start of the batch tests, the cellulose removal was in the range 40-50 %. The maximum concentration of acetic acid observed was 8.8 g/L while the maximum ethanol concentration was 0.6 g/L. The experimental results demonstrates the capability of open mixed microbial culture to ferment cellulose under mild conditions. Even though the rates observed in this study are still too low for industrial exploitation, they indicate the potential of mixed cultures to biodegrade cellulose even in the absence of any pretreatments. The next step of the study will be aimed at finding the conditions that increase the cellulose biodegradation rate.

Experimental investigation of a new process for treatment and valorisation of pot ale wastewaters

This study investigated an innovative process for the treatment and valorisation of pot ale wastewater. The first phase was to balance the pH to precipitate nitrogen, phosphorus and magnesium, recovering them as fertiliser; the second phase investigated the evaporation of water, reducing the volume of liquid to be transported to an anaerobic digester. In the pH balancing phase we investigated the effect of the final pH, in the range 8-11, on the removal of calcium, magnesium, ammonia, phosphorus and copper. We observed that, for all the species, most of the precipitation occurred when pH was increased from 8 to 9. By pH balancing, a removal from the liquid phase of up to 65% of ammonia and 60% of total phosphorus was obtained. Calcium and magnesium also precipitated from the liquid phase, giving solids with the following composition, calculated from liquid phase measurements: 24-27% magnesium, 4-5% nitrogen, 16-18% phosphorus. We investigated the evaporation process at pH 6 and 10 and at atmospheric pressure and under vacuum. The results showed that only a few % of the chemical oxygen demand (COD) evaporates, indicating very little loss of organic substance for anaerobic digestion. Mass balances for this process in a medium-size whisky distillery were also carried out.

Determining biokinetic coefficients for the upflow anaerobic sludge blanket reactor treating sugarcane wastewater in hot climate conditions

Sugar extraction from sugarcane is a process which contains high volume of effluent, high levels of biochemical oxygen demand (BOD) and organic matter. Thus, their discharge into the rivers and environmental systems endangers the aquatic life. This study investigates and determines the kinetic coefficients of anaerobic treatment system (upflow anaerobic sludge blanket) in sugarcane industrial wastewater treatment plant. COD, BOD5 and TSS parameters in the input and output effluent of reactor were measured, and the kinetic coefficients of Kd, KS, Kmax and µmax were calculated using modified Monod equations by determining the design and operating parameters of the system. The experimental results showed that rate of KS, Y, Kd, µmax and Kmax for the application of UASB process in wastewater treatment of sugarcane factories was 506.4xa0mg/L, 0.053xa0g VSS/g COD, 0.086, 0.0049 and 0.055xa0day−1, respectively. The kinetic coefficients obtained in this research can be used in management, operation and preparation of design principles of similar sugarcane treatment plants particularly in topical areas.

Anaerobic digestion of wheat grass under mesophilic and thermophilic conditions and different inoculum sources

Anaerobic digestion of lignocellulosic biomass can be used to produce in one single step different products with applications as fuels or as bulk chemicals such as methane, ethanol and other particular volatile fatty acids: acetic, propionic and butyric acids. This study aims to investigate the anaerobic digestion of lignocellulosic biomass (wheatgrass) in batch condition under mesophilic (40°C) and thermophilic (50°C) conditions, two inoculum concentrations and different microbial sources: anaerobic digester sludge and soil. Vials of wheatgrass powder (20 g/l) were inoculated and maintained under anaerobic condition in a water bath shaker with temperature control. The results showed that both inocula were able to hydrolyse lignocellulose biomass without physicochemical pre-treatment, but higher VSS and TC removals were achieved when anaerobic sludge inoculum was used. Acetic acid was the main product for the different batch conditions and corresponded to around 60% of the CODproducts. Butyric acid, propionic acid and ethanol were identified in lower concentration. The maximum volatile suspended solids (VSS) and total carbohydrates (TC) removal were (44 ± 5) % and (50 ± 11) % respectively. The maximum yield of products in the liquid phase was 37% in COD basis.