Microbial film fermenters: Their present and future applications

Recycle in fermentation processes

Until recently, the recycle of the solid (microbial), liquid, or gaseous phases in microbiological processes has only been practiced rarely, with the notable exception of activated sludge processes for wastewater treatment, where recycling of a large fraction of the microbial phase is essential for process stability and performance. During the last decade, the economic impact of a number of politically motivated changes with respect to energy and feedstock costs and availability, and legislation directed towards markedly higher levels of environmental protection have encouraged the evaluation and subsequent development of recycle technology in the fermentation industry. Many of the developments have occurred in isolation and some have failed to result in either an improvement in process economics or any reduction in the quantity of pollutants discharged. This article seeks to review the present diversity of approaches to recycle technology in fermentation processes in order to provide a sensible basis for future developments.

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.

The enzymatic conversion of L-histidine to urocanic acid by whole cells of Micrococcus luteus immobilized on carbodiimide activated carboxymethylcellulose

Whole cells of Micrococcus luteus (formerly Sarcina lutea ATCC 9341) have been covalently linked to a carboxymethylcellulose support system, with the retention of histidine ammonia-lyase activity. The dependence of the rate of urocanic acid formation on pH, temperature, and added surfactant concentration was similar for the free and the immobilized cells. The immobilization procedure used is based on the carbodiimide activation of carboxymethylcellulose and has been optimized for the histidine ammonia-lyase activity of the immobilized cells on a given weight of cellulose. In a column reactor at 23 degrees C and superficial velocity of 0.044 cm/min, 5 g of cellulose with bound cells gave a 35% conversion of an L-histidine solution (0.25M, pH 9.0) to urocanic acid for 16 days of continuous operation. The scope of this carbodiimide assisted immobilization procedure has been investigated for a series of microorganisms and a variety of carboxylate functionalized supports.