Inhibited microbial activity

If the pH is adjusted as part of an engineered remediation, the microbial balance may be upset and bioreactions slowed until the microbe cultures adjust to the new conditions. Alternatively, if the release of organic chemicals has altered the pH outside the natural range, it may be necessary to add certain chemicals (i.e., aluminum sulfate, carbon dioxide, sodium hydroxide, etc.) to return the pH to preexisting conditions. Changes of pH should be monitored since rapid changes of more than 1 to 2 pH units over a short period can inhibit microbial activity and may extend the acclimation period before the microbes adapt and renew activity. 

As with any bioremediation technology, high or low pH may inhibit microbial activity. Extreme temperatures also inhibit microbial activity, and high concentrations of contaminants may be toxic to microorganisms. 

Essential oils are known to inhibit microbial activity in ruminants and disrupt digestive processes (65). 

Coals are generated by burial of peats, which are formed in swamps and marshes. Geographic and tectonic requirements for formation of thick peat deposits include slow subsidence, protection of the swamp from erosion by marine inundation or fluvial flood waters and a restricted supply of fluvial sediment. These requirements are met on coastal plains where most Recent peat swamps are located. Microbial activity is capable of degrading great quantities of the plant material which is the ultimate source of peat. Therefore, conditions which inhibit microbial activity are favorable for the... 

A wide variety of organic and inorganic compounds inhibit microbial activity by interfering with the uptake of metabolites and enzymic reactions (Davis and Feingold, 1962 Pelczar and Reid, 1958). In particular, the heavy metals are extremely toxic to the heterotrophs but are tolerated at higher levels by Desulfovibrio spp. due to their precipitation as metal sulphides (see p. 343). Other factors affecting the activity of sulfate-reducers are discussed in Chapter 6.1. 

The leaves of the California bay laurel Umbellularia califomica, Lauraceae), sometimes used as a spice, contain 0.5-4% of an irritating oil of which 40-60% is umbellulone (53). The vapors of this compound produce severe headache, skin irritation, and, in some cases, unconsciousness. This plant is one of several avoided by deer. Essential oils inhibit microbial activity in mminants and dismpt digestive processes (MacGregor et al., 1974 Buttery et al., 1974). 

Consequently, it is necessary to add sufficient SO2 to obtain an adequate concentration in the molecular form to inhibit microbial activity, but not so much as to have an excess in the bisulphite form. The suggested concentration of free molecular SO2 for maximal antimicrobial activity is 0.8 mg/1 (Rankine, 1989 Margalit, 1990). The maximum permitted concentration of SO2 for wines produced in Australia is 300 mg/1 and 350 mg/1 in the USA, although most wines contain nowhere near this level. From Figure 9.5, 97% of 1280 Australian wines analysed at the Australian Wine Research Institute during 1991 contained less than 200 mg/1 of SO2. 

It is clear that such unphysiological levels of copper are not required as a nutrient and the idea seems to be to inhibit microbial activity in the digestive... 

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