Microbial pretreatments

Keller, F. A., Hamilton, J. E., Nguyen, Q. A. (2003). Microbial pretreatment of biomass potential for reducing severity of thermochemical biomass pretreatment. Applied Biochemistry and Biotechnology 105,27-41. 

To facilitate biodegradation, the leachate may require modification through pH adjustment, removal or addition of oxygen, amendment with nutrients, or dilution or removal of toxic species. Microbial nutrition is complex and is better understood for aerobes than for anaerobes.34 Biological processes typically favor a pH near 7. Pretreatment processes to remove inhibitory components include coagulation and precipitation, carbon adsorption, and possibly ozonation. 

PMN infiltration also occurs following exposure to some common microbial cotton contaminants (Enterobacter aerogenes (44), Klebsiella pneumoniae or Escherichia coll), but not others (. subtills) (45). Cotton dust extracts pretreated at 80 C and 100 C for 20 minutes cause successively higher leucocyte responses, indicating that the chemotactlc effect is not solely affected by viable bacteria (46). Thus, while the increase seen in PMNs may not, by itself, represent a pathological alteration, it could be of importance in the later development of pathological effects. 

Another key factor that determines the lability of ambient DOM is exposure to light and UV (see Chapter 10). The majority of the bioassays reported here were conducted in the dark, and, in this sense, they do not mimic the ambient conditions, because the surface water DOM pool is exposed to at least some light through mixing in the water column as it is being degraded by microbes. Even in cases where the DOM was pretreated with UV (Moran et al., 2000), the actual microbial consumption proceeds in the dark with no further exposure. 

Pretreatment of contaminants with various reagents to produce degradates more amenable to microbial mineralization (Leeson et al, 1993) and treatment of soil slurries with microbial enzymes (Nelson and Jones, 1994) have been successful in remediation. 

Comparison of Microbial Inhibition and Enzymatic Hydrolysis Rates of Liquid and Solid Fractions Produced from Pretreatment of Biomass with Carbonic Acid and Liquid Hot Water... 

This research quantified the enzymatic digestibility of the solid component and the microbial inhibition of the liquid component of pretreated aspen wood and com stover hydrolysates. Products of liquid hot water and carbonic acid pretreatment were compared. Pretreatment temperatures tested ranged from 180 to 220°C/ and reaction times were varied between 4 and 64 min. Both microbial inhibition rates and enzymatic hydrolysis rates showed no difference between pretreatments containing carbonic acid and those not containing no carbonic acid. Microbial inhibition increased as the reaction severity increased, but only above a midpoint severity parameter of 200°C for 16 min. Both the rates and yields of enzymatic hydrolysis displayed an increase from the lowest tested reaction severity to the highest tested reaction severity. 

The midpoint pretreatment condition of 200°C forl6 min could be an optimal condition for reduced microbial inhibition. For severities around... 

Both microbial inhibition rates and enzymatic hydrolysis rates showed no differences between pretreatments containing carbonic acid and those not containing carbonic acid. Additionally, when the microbial inhibition and enzymatic hydrolysis rates were tested at varying reaction severities and between different substrates, this remained true. 

Although there are reports of improved biodegradation with Fenton pretreatment, there are also reports indicating limitations of Fenton pretreatment. Acid conditions often used for Fenton treatment are usually incompatible with microbial activity, and measures to overcome this incompatibility must be taken. For example, the use of iron chelators and higher pFi values is one approach that has been taken [61]. 

Microbial fouling is best dealt with before biofilm becomes mature. Biofilm protects the microorganisms from the action of shear forces and biocidal chemicals used to attack them. Microbes can be destroyed using chlorine, ozone, ultraviolet radiation, or some non-oxidizing biocides (see Chapters 8.2.1,8.2.2, 8.1.8, and 8.2.5, respectively). An effective method to control bacteria and biofilm growth usually involves a combination of these measures. Specifically, chlorination or ozonation of the pretreatment system, followed by dechlorination to protect the membranes, or UV distraction followed by periodic sanitation with a non-oxidizing biocide used directly on the membranes. 

Membrane pretreatment includes microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF). Microfiltration and UF membrane processes can remove microbes and algae. However, the pores of MF and UF membranes are too large to remove the smaller, low-molecular weight organics that provide nutrients for microbes. As a result, MF and UF can remove microbes in the source water, but any microbes that are introduced downstream of these membranes will have nutrients to metabolize. Therefore, chlorination along with MF and UF is often recommended to minimize the potential for microbial fouling of RO membranes. The MF or UF membranes used should be chlorine resistant to tolerate chlorine treatment. It is suggested that chlorine be fed prior to the MF or UF membrane and then after the membrane (into the clearwell), with dechlorination just prior to the RO membranes. See Chapter 16.1 for additional discussion about MF and UF membranes for RO pretreatment. 

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