Wastewater fermentation

Cuevas-Rodriguez, G., O. Gonzalez-Barcelo, and S. Gonzalez-Martinez (1998). Wastewater fermentation and nntrient removal in seqnencing batch reactors. Water Science Technol., Wastewater Nutrient Removal, Proc. 1998 19th Biennial Conf. Int. Assoc, on Water Quality. Part 1, June 21-26, Vancouver, Canada, 38, 1, 255-264. Elsevier Science Ltd., Exeter, England. 

Although the biosynthesis of PHA from wastewater offers an interesting alternative to the pure culture, high-cost sugar-based PHA production, the PHA yields reported are not yet comparable to the petrochemical counterparts. Integration and optimisation need to be considered further to improve the performance of wastewater fermentability in PHA production [6]. 

Low-cost PHAs would not only benefit the PHA material application as bioplastics, but promote the application of PHAs as biofuels as well. There is a large potential for compromise in this area, as low-cost PHAs could also be obtained from activated sludge and wastewater fermentation, so it will not run into the controversy of food versus fuel or fuel versus arable land. Plant production of PHAs could become a reality, as indicated by some promising results, in the foreseeable future. 

Low cost PHA will not only benefit the application of PHA material as bioplastics, but will also promote the application of PHA as biofuel. This is an area full of promise, since low cost PHA could also be obtained from aetivated sludge and wastewater fermentation. 

Bruggink (1996) has given an account of how the production of cefalexin, which is the largest cephalosporin in the market, can be converted from a ten-step process based on benzaldehyde and penicillin into a six-step process where biocatalysis is involved in three steps. The wastewater stream, containing 30-40 kg of unwanted materials in the conventional process, has been substantially reduced. Similarly, Van Loon et al. (1996) have given details of fermentation processes for cleaner and cheaper compared to the process practised so far. 

In the manufacture of absolute alcohol by fermentation, the product is separated and purified using several stages of distillation. In the first stage, a mixture of 5 mol per cent ethanol in water, with traces of acetaldehyde and fusel oil, is concentrated to 50 mol per cent. The concentration of alcohol in the wastewater is reduced to less than 0.1 mol per cent. 

The 1980 s and the early 1990 s have seen the blossoming development of the biotechnology field. Three-phase fluidized bed bioreactors have become an essential element in the commercialization of processes to yield products and treat wastewater via biological mechanisms. Fluidized bed bioreactors have been applied in the areas of wastewater treatment, discussed previously, fermentation, and cell culture. The large scale application of three-phase fluidized bed or slurry bubble column fermen-tors are represented by ethanol production in a 10,000 liter fermentor (Samejima et al., 1984), penicillin production in a 200 liter fermentor (Endo et al., 1986), and the production of monoclonal antibodies in a 1,000 liter slurry bubble column bioreactor (Birch et al., 1985). Fan (1989) provides a complete review of biological applications of three-phase fluidized beds up to 1989. Part II of this chapter covers the recent developments in three-phase fluidized bed bioreactor technology. 

The most widespread biological application of three-phase fluidization at a commercial scale is in wastewater treatment. Several large scale applications exist for fermentation processes, as well, and, recently, applications in cell culture have been developed. Each of these areas have particular features that make three-phase fluidization particularly well-suited for them Wastewater Treatment. As can be seen in Tables 14a to 14d, numerous examples of the application of three-phase fluidization to waste-water treatment exist. Laboratory studies in the 1970 s were followed by large scale commercial units in the early 1980 s, with aerobic applications preceding anaerobic systems (Heijnen et al., 1989). The technique is well accepted as a viable tool for wastewater treatment for municipal sewage, food process waste streams, and other industrial effluents. Though pure cultures known to degrade a particular waste component are occasionally used (Sreekrishnan et al., 1991 Austermann-Haun et al., 1994 Lazarova et al., 1994), most applications use a mixed culture enriched from a similar waste stream or treatment facility or no inoculation at all (Sanz and Fdez-Polanco, 1990). 

Gas logging, the adherence of small bubbles to particles, causing them to rise to the surface in the reactor and form an inefficient packed bed with poor mass transfer properties, can be a problem in various fermentations and in wastewater treatment. A double entry fluidized bed reactor has been developed with simultaneous top (inverse) and bottom (conventional) inlets to overcome this problem (Gilson and Thomas, 1993). 

For waste treatment rather than fermentation for product formation, again few examples of process economics exist in the literature. Those that do, favor fluidization. Badot et al. (1994) described an industrial prototype fluidized bed reactor that competed favorably on an economical basis with activated sludge processes for treating carbon pollution and was estimated to be economically comparable to fixed bed processes for denitrification. Schneeberg (1994) described the successful and economically-sound implementation of fluidization as an upgrade to an existing wastewater treatment plant. The restricted space available for extension of the wastewater plant made fluidization particularly advantageous in this case. 

Single-strand conformation polymorphism (SSCP) Wastewater bioreactors (including denitrifying and phosphate-removal system, Chinese traditional medicine wastewater treatment system, beer wastewater treatment system, fermentative biohydrogen producing system, and sulfate-reduction system) Microbial community structures, diversity and distribution in different wastewater treatment processes, and relationship between the structures and the status of processes [157]... 

Fermentation may take place in the three major microbial subsystems of a sewer, i.e., the wastewater, the biofilm and the sediments (Figure 3.2). Sulfate-reducing bacteria are slow growing and are therefore primarily present in the biofilm and in the sediments, where sulfate from the wastewater may penetrate (Nielsen and Hvitved-Jacobsen, 1988 Hvitved-Jacobsen et al., 1998 Bjerre et al., 1998). However, as a result of biofilm detachment, sulfate reduction may, to some minor extent, take place in the wastewater. Methanogenic microbial activity normally requires absence of sulfate — or at least a low... 

TABLE 4.2. Examples of Volatile Organic Compounds (VOCs) Associated with Odors and Produced by Fermentation Processes in Wastewater (Dague 1972 Vincent and Hobson 1998). 

Sulfate is needed as an electron acceptor for the sulfate reduction process, but normally, it is available in unlimited concentrations in wastewater. If this is not the case, iron sulfate may support the process. The anaerobic fermentation processes still proceed, and the odorous organic substances produced are generally not affected by the addition of iron salts. 

The VFAs, primarily formate, acetate, propionate, n-butyrate and isobutyrate, can be determined analytically on an ion chromatograph (Standard Methods for the Examination of Water and Wastewater, 1998). Determination of fermentable, readily biodegradable substrate, SF, and fermentation products, SA, in units of COD requires that the VFA components be converted to this unit. The following example using formate demonstrates this ... 

C02 exists under anaerobic conditions in wastewater. They also found that typically 50% of the C02 was produced by the sulfate-reducing bacteria, the other half by the fermenting biomass. However, the net production rate of Ss was typically about 70% of the total produced Ss by anaerobic hydrolysis [Equation (7.10)]. Hence, this equation may, even in a reduced form, be valuable for the estimation of the production of readily biodegradable substrate under anaerobic conditions. 

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