Michael J. Dempsey

Marine bacterial fouling: A scanning electron microscope study

A range of substrates has been examined in order to determine the types of attachment mechanism employed by marine bacteria. Use of the scanning electron microscope (SEM) has also allowed an investigation of the initimate relationship between an antifouling paint matrix and its attached bacterial community. Plastic (Thermanox) and glass coverslips, together with Cu2O-based and TPTF-based antifouling paints and their respective empty-matrix analogues have been used in this study. Observations over periods of up to 4 wk have shown that extensive bacterial communities can develop. A variety of bacteria have been found: cocci; various rods; stalked forms; and prosthecate types. These bacteria also exhibit a range of attachment mechanisms. Initial attachment is by simple stickiness of cell walls, flagella, pili (fimbriae) or stalks. This stickiness can be attributed to an actual adhesive, electrostatic forces, electrical double-layer phenomena or to London/van der Waals forces. Often, attachment is subsequently improved by the secretion of insoluble, high molecular weight, polysaccharidic material. This material is found in the form of strands, pads, sheets or capsules and acts to bridge the space between the cell wall and substrate or adjacent cells. Thus, stalked forms are found attached by basal pads of mucilage whilst cocci and rods are often found enmeshed in mucilage strands and sheets, but less often attached by pads and capsules. Initially, single bacterial cells attach and give rise to colonies by cell division. Continuing growth of adjacent colonies leads to the development of confluent films over the substrate surface. Further growth results in thickening until eventually the entire surface is coated with a dense community of mixed bacteria together with their adhesive mucilage. In the case of antifouling paints, the porous nature of the matrix allows invasion by bacteria and the possibility of pore blockage by adhesive polysaccharides. This problem is discussed with reference to the paints loss of antifouling efficiency.

Optimization of biobleaching of paper pulp in an expanded bed bioreactor with immobilized alkali stable xylanase by using response surface methodology.

Purified alkali stable xylanase from Aspergillus fischeri was immobilized on polystyrene beads using diazotization method. An expanded bed bioreactor was developed with these immobilized beads to biobleach the paper pulp in continuous mode. Response surface methodology was applied to optimize the biobleaching conditions. Temperature (degrees C), flow rate of pulp (ml/min) and concentration of the pulp (%) were selected as variables in this study. Optimal conditions for biobleaching process were reaction temperature 60 degrees C, flow rate of 2 ml/min and 5% (w/v) of pulp. The kappa number reduced from 66 in the unbleached pulp to 20 (reduction of 87%). This system proves to be a better option for the conventional chlorine based pulp bleaching.

Detection of cellulolytic actinomycetes using cellulose-azure

Abstract A rapid method is described for the detection of cellulolytic, thermophilic actinomycetes involving the use of a dyed cellulose substrate (cellulose-azure) in an agar medium. The test was performed in test tubes in which agar containing cellulose-azure was layered on top of a basal medium (mineral salts agar) resulting in two distinct layers. After inoculation, and incubation at 50°C, strains which were cellulolytic caused release substrates for such a test.

Biofilms and fluidized bed fermentation

The exploitation of biofilms in industrial processes such as wastewater treatment and metabolite production is described. In this way it is intended to highlight the positive aspects of biofilms, and provide a contrast with the negative associations which these microbial aggregations normally have. In particular, the exploitation of adhesive microbes in fluidized bed operation is discussed. A range of processes is outlined, from wastewater treatment to the production of ethanol, enzymes, and antibiotics. These various processes use a range of cell types; which has required the modification of the basic design of FB bioreactor, e.g. for anaerobic or aerobic operation; and for bacteria, actinomycetes, or plant cells. One basic design is illustrated, and reference made to how this is modified for different fermentations.

Natural Immobilization and Fluidized Bed Fermentation

Immobilization of biomass within a fermenter produces a large increase in cell concentration, which results in a substantial increase in volumetric productivity (rp, mass of product per unit volume of fermenter per unit time). For primary metabolites, immobilization allows continuous culture operation at dilution rates in excess of μmax; whilst for secondary metabolites, immobilization allows continuous culture operation at dilution rates which support the maximum rate of product synthesis. If naturally adhesive cells are immobilized on small (1mm) support particles, it is possible to operate the fermenter as a fluidized bed (FBF) and thereby benefit from the efficient mass transfer which characterises this mode of operation. For example, the biomass concentration of Zymomonas mobilis in the FBF was up to 12 times that expected in conventional chemostat culture and rp for ethanol was up to 10 times higher; with Streptomyces coelicolor, the volumetric productivity of actinorhodin (an antibiotic) was over 20 times higher than that obtained in the best batch culture.

The Effect of a Dynamical Layer in Neural Network Prediction of Biomass in a Fermentation Process

In this paper, computational intelligence has been considered as a tool (software sensor) for state-estimation and prediction of biomass concentration in a simulated fermentation process. Two different paradigms of an artificial neural networks have been introduced as possible computational engines. Inclusion of process dynamics is inherent within the second paradigm, as a pre-processing layer. The constructed computational engines ‘infer’ the production of biomass from easily measured on-line variables. First and second-order non-linear optimisation methods are used to train the neural networks. It is shown that the use of the pre-processing layer which contains dynamical elements, produces better results and shows significant improvement in the convergence rate of the neural networks.

Nitrification at Low Temperature for Purification of Used Water

Prokaryotes that can oxidize ammonia and/or nitrite are known as nitrifiers and are common in terrestrial, freshwater and marine environments. Where the temperature is commonly in the range 0–20 °C, psychrophilic strains or species can be isolated or identified using molecular techniques. It is therefore no surprise to also find psychrophilic nitrifiers in engineered systems used, for example, to remove ammonia from raw, used or wastewater or from contaminated air. In temperate regions, we have been using psychrophilic nitrifiers without most people realizing, and this chapter attempts to put their importance into context by comparing and contrasting their presence in natural and engineered systems. It concludes by describing a biofilm-based process technology, the expanded bed biofilm reactor, which the author has improved with several inventions that make this technology cost-effective for wider adoption.

Nitrification of raw or used water using expanded bed biofilm reactor technology.

Excessive ammonia in raw water increases the consumption of chlorine for disinfection during production of potable water, through oxidation to produce chloramines. Excessive ammonia in used water results in pollution of the aquatic environment, where it is particularly toxic to fish. Furthermore, nitrifying prokaryotes in the receiving water will consume dissolved oxygen equivalent to 4.6 g oxygen per g ammonia-nitrogen oxidized to nitrate. This places a considerable oxygen demand on the receiving water and can result in anoxic conditions. One solution to these problems is to nitrify the ammonia in a dedicated biological process. As nitrifiers are particularly slow growing, they are easily washed out of conventional water and wastewater treatment processes; hence, the use of immobilized biomass in an expanded bed biofilm reactor. This solution typically allows at least 10-times the biomass concentration of conventional systems, with a similar decrease in bioreactor size or increase in bioreactor productivity. This chapter describes expanded bed technology for nitrification of water, and methods for studying biomass and process performance.