Microbial activities

Microbial activities are by far the most difficult factor of instability when handling natural products. All products have an incurred microbial activity (e.g. soils, sediments, sludge) or represent perfect culture media for microbes (e.g. food, feed, human, animal or plant tissues). Bacteria, viruses, moulds, fungi, parasites etc. may also present a risk for the health of the producer or the end-user of the material. In order to eliminate or control microbial activity two possibilities exist kill the microbes 

In general, when preparing natural materials that present particular difficulties because of their microbial activity (degradation or contamination risk), it is better to consult food (industry) or biological specialists on the ways of preservation of materials. 

Antiseptics An easy way to destroy microbes is to add an antiseptic to the material. This can only be done if this antiseptic can be added in a sufficient amount and does not affect the analyte or the analytical behaviour of the material unduly. Such a stabiliser, butylated hydroxytoluene (BHT), has been used by BCR several times in the production of fish oil and fresh mussel tissue materials certified for PCBs [13-15]. 

DEGRADATION OF ORGANOCHLORINE PESTICIDES IN PORK FAT BY -IRRADIATION CO SOURCE IRRADIATION DOSE = 0, 2.5 AND 5.0 KGY). 

The data have been normalised to the content determined on five test portions which were not irradiated (base = 100). the data given are the normalised means of five determinations and the corresponding standard deviations (after [53]). up to 50% losses are noticed for one substance already at 2.5 kGy 

Sulfur-metabolising organisms have been monitored within the timbers of the Mary Rose by extraction and analysis of bacterial ribosomal RNA. The 

In addition to this study, timber samples previously examined by XANES and infused with acid salts have been treated with various biocides to inhibit continued bacterial oxidation of reduced sulfur species. This may also help prevent continuing production of acid. 

To prevent oxidation of reduced organosulfur in the wood cell walls, conservators are currently investigating antioxidants. Commercial antioxidants (ascorbic acid, anthocyanidins, proanthocyanins, flavon-3-ols, flavonones and flavonols) are being used to prevent oxidation of reduced species by mopping up free radicals. 

However, it is worth noting that while the Swedish warship Vasa is still contaminated with sulfur and generating acid, it is now apparent that during its treatment by spraying a considerable amount of acid was generated, as the pH of the spray solution kept falling. This was neutralised by the addition of borax/boric acid buffer. In the case of the Vasa, the major sulfur contaminant appears to be elemental sulfur that is essentially insoluble in water. However, 

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Are the levels of contaminant amenable to bioremediation Are they toxic to microorganisms Are they so abundant that even substantial microbial activity will take too long to clean the site ... 

In situations where conserved internal markers caimot be used, such as in spills of essentially pure compounds, the evidence for enhanced biodegradation may have to be more indirect. Oxygen consumption, increases in microbial activity or population, and carbon dioxide evolution have all been used with success. 

In basic soils mepiquat chloride is nonpersistent and is rapidly degraded. There is a half-life of two years in other soil types, but 86—93% is metabolized within 30 days (10). Breakdown does not appear to be a function of microbial activity. 

S-oxidation of sulfur-containing pesticides such as aldicarb, parathion, and malathion can be of importance in the absence of microbial activity (29). The products of chemical vs biological oxidation are generally identical (eq. 8). 

The diffusion process has not been designed to ensure sterility, although temperatures above 65°C significantly retard microbial activity. Sulfur dioxide, thiocarbamates, glutaraldehyde, sodium bisulfite, and chlorine dioxide are all used, occasionally disregarding their redox incompatibilities, to knock down or control infections. The most common addition point is to the water from the pulp presses as it is returned to the diffuser. Surfactants ate almost... 

Raw juice is heated, treated sequentially with lime (CaO) and carbon dioxide, and filtered. This accomplishes three objectives (/) microbial activity is terminated (2) the thin juice produced is clear and only lightly colored and (J) the juice is chemically stabilized so that subsequent processing steps of evaporation and crystalliza tion do not result in uncontrolled hydrolysis of sucrose, scaling of heating surfaces, or coprecipitation of material other than sucrose. 

Once in the soil solution, urea—formaldehyde reaction products are converted to plant available nitrogen through either microbial decomposition or hydrolysis. Microbial decomposition is the primary mechanism. The carbon in the methylene urea polymers is the site of microbial activity. Environmental factors that affect soil microbial activity also affect the nitrogen availabiUty of UF products. These factors include soil temperature, moisture, pH, and aeration or oxygen availabiUty. 

Microbiauy induced corrosion (MIC) probes. Devices are available to measure the amount of microbial activity in some environments. MicrobiaUy induced corrosion is known to be an actor in many corrosion-related problems in processing plants. The monitoring devices for MIC are limited in their range and, at present, are available only for a few specific environments. This is an exciting area for development of corrosion probes and monitoring systems. 

Sandy Soils. The particles in sandy soils are relatively large, with correspondingly large spaces between them. Because these soils are also fairly homogeneous, water moves freely through much of the soil matrix. Any nitrate that is in the soil, whether from fertilizer or from microbial activity, is likely to be carried through the soil slowly but surely with little impediment. A sandy soil above an aquifer is usually seen as a threat to the quality of the water in the aquifer. 

Pesticides vary widely in their chemical and physical characteristics and it is their solubility, mobility and rate of degradation which govern their potential to contaminate Controlled Waters. This, however, is not easy to predict under differing environmental conditions. Many modern pesticides are known to break down quickly in sunlight or in soil, but are more likely to persist if they reach groundwater because of reduced microbial activity, absence of light, and lower temperatures in the sub-surface zone. 

While stable under normal conditions of storage and use, the polymer degrades when deposited in microbially active environments. 

Anaerobic reactor A bioreactor in which no dissolved oxygen or nitrate is present and microbial activity is due to anaerobic bacteria. 

If the pH level of drilling fluid drops and the hydrogen sulfide test result is negative, there is a good possibility that carbon dioxide will be present. Positive results of microbial activity tests (described later) also indicate the possibility of carbon dioxide presence. Carbon dioxide meters are also available commercially and can be used. 

As mentioned earlier, microorganisms can attack drilling fluid additives and introduce corrosive agents to the system. Therefore, it is very important to monitor their activity and detect any source of problem as early as possible. API RP 38 is probably the most widely used testing procedure in the industry [201]. The methods that can be used to monitor the microbial activity can include the following [201,208] ... 

MIcrobiocldes. There are several microbiocides available commercially that can perform an effective function in controlling microbial activity. Some of these chemicals are inorganic, such as chlorine, sodium hypochlorite, calcium hypochlorite, hydrogen peroxide, chromates and compounds of mercury and silver. However, the organic chemicals find the highest use as microbiocides. Some examples of these organic compounds are peracetic acid, paraformaldehyde, polychlorophenols and quaternary ammonium derivatives, to name a few [208]. 

Mlcrobiocidal Treatment. Once the microbial activity reaches a high enough level to cause problems, physical and chemical methods may be used to control the problem. In drilling operations, the most effective method is chemical treatment—the use of microbiocides [184,208]. 

This is one of the most important factors in alleviating microbial problems. A decrease in microbial activity after treatment indicates a positive response to the microbiocidal treatment. Continuous monitoring is imperative for effective control. 

Soil reaction (pH) The relationship between the environment and development of acid or alkaline conditions in soil has been discussed with respect to formation of soils from the parent rock materials. Soil acidity comes in part by the formation of carbonic acid from carbon dioxide of biological origin and water. Other acidic development may come from acid residues of weathering, shifts in mineral types, loss of alkaline or basic earth elements by leaching, formation of organic or inorganic acids by microbial activity, plant root secretions, and man-made pollution of the soil, especially by industrial wastes. 

Soil resistivity The role of soil in the electrical circuitry of corrosion is now apparent. Thus the conductivity of the soil represents an important parameter. Soil resistivity has probably been more widely used than any other test procedure. Opinions of experts vary somewhat as to the actual values in terms of ohm centimetres which relate to metal-loss rates. The extended study of the US Bureau of Standards presents a mass of data with soil-resistivity values given. A weakness of the resistivity procedure is that it neither indicates variations in aeration and pH of the soil, nor microbial activity in terms of coating deterioration or corrosion under anaerobic conditions. Furthermore, as shown by Costanzo rainfall fluctuations markedly affect readings. Despite its short comings, however, this procedure represents a valuable survey method. Scott points out the value of multiple data and the statistical nature of the resistivity readings as related to corrosion rates (see also Chapter 10). 

In biochemical engineering processes, measurement of dissolved oxygen (DO) is essential. The production of SCP may reach a steady-state condition by keeping the DO level constant, while the viable protein is continuously harvested. The concentration of protein is proportional to oxygen uptake rate. Control of DO would lead us to achieve steady SCP production. Variation of DO may affect retention time and other process variables such as substrate and product concentrations, retention time, dilution rate and aeration rate. Microbial activities are monitored by the oxygen uptake rate from the supplied ah or oxygen. 

In reality, oxygen concentration never reaches the concentration defined in the proposed model, since the microbial activities at optimal and maximum cell density would reach the point where oxygen depletion takes place.5... 

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