What Is Environmental Microbiology?

The study of how microorganisms affect the earth and its atmosphere is called environmental microbiology or microbial ecology.

Environmental microbiology is the study of microbes in the environment and their interactions with each other. Microbes are the tiniest creatures on Earth, yet despite their small size, they have a have a huge impact on us and on our environment.

Most types of microbes remain unknown. It is estimated that we know fewer than 1% of the microbial species on Earth. Yet microbes surround us everywhere -- air, water, soil. An average gram of soil contains one billion (1,000,000,000) microbes representing probably several thousand species.

Environmental microbiology is the study of the relationships that exist between microorganisms and the environment.

Environmental microbiology is the relationship of microorganisms with themselves and with their surroundings. Microorganisms have special impact on the whole biosphere. They are the backbone of ecosystems of the zones where light cannot approach. In such zones, chemosynthetic bacteria are present which provide energy and carbon to the other organisms there. Some microbes are decomposers which have ability to recycle the nutrients. So, microbes have a special role in biogeochemical cycles. Microbes, especially bacteria, are of great importance in the sense that their symbiotic relationship (either positive or negative) have special effects on the ecosystem.

Bacteria and their enzymes, along with some fungi and critical nutrient additives are cost effective agents for in-situ remediation of hazardous wastes and subsurface pollution in soils, sediments and wastewaters. The ability of each bacteria strain to degrade toxic waste depends on the nature of each contaminant. Since most sites are typically comprised of multiple pollutant types, the most effective approach to bioremediation is to use a mixture of bacterial species/strains, each specific to the degradation of one or more types of contaminants. It is critical to monitor the composition of the indigenous and added bacterial consortium in order to evaluate the activity level of the bacteria, and to permit modifications of the nutrients and other conditions for optimizing the bioremediation process.

Environmental Microbiology - overview: The pervasive and manifold positive and negative impacts of microbial activities on human and environmental health, and human activities, require that efforts to improve the human condition include efforts to modulate microbial activities. Attainment of this goal will be greatly facilitated by acquisition of a fundamental understanding of microbial functioning in their natural settings, and of parameters that regulate such activities. Our current fragmentary knowledge of microbial processes is based largely on information obtained from individual strains of microbes studied in the laboratory as pure, exponentially-growing cultures in nutrient-rich, homogeneous aqueous solutions.

Sewage treatment is the process that removes the majority of the contaminants from waste-water or sewage and produces both a liquid effluent suitable for disposal to the natural environment and a sludge. To be effective, sewage must be conveyed to a treatment plant by appropriate pipes and infrastructure and the process itself must be subject to regulation and controls.

Sewage is the liquid waste from toilets, baths, showers, kitchens, etc. that is disposed of via sewers. In many areas sewage also includes some liquid waste from industry and commerce. In the UK, the waste from toilets is termed foul waste, the waste from items such as basins, baths, kitchens is termed sullage water, and the industrial and commercial waste is termed trade waste.

The division of household water drains into Greywater and Black water is becoming more common in the United States, with greywater being permitted to be used for watering plants or recycled for flushing toilets. Much sewage also includes some surface water from roofs or hard-standing areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste discharges, and may include stormwater runoff.

Sewerage systems that transport liquid waste discharges and stormwater together to a common treatment facility are called combined sewer systems. The construction of combined sewers is a less common practice in the U.S. and Canada than in the past and is no longer accepted within Building Regulations in the UK. Instead, liquid waste and stormwater are collected and conveyed in separate sewer systems, referred to as sanitary sewers and storm sewers in the U.S. and as foul sewers and surface water sewers in the UK. Overflows from foul sewers designed to relieve pressure from heavy rainfall are termed storm sewers or combined sewer overflows.

As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants including soil particles (sediment), metals, organic compounds, animal waste, and oil and grease. Some jurisdictions, such as certain communities located in southern California, require stormwater to receive some level of treatment before being discharged to the environment. Examples of treatment processes used for stormwater include sedimentation basins, wetlands, and vortex separators (to remove coarse solids).

"Conventional wastewater treatment" is the process used in modern wastewater treatment plants that removes the majority of the contaminants from wastewater. This produces a liquid effluent suitable for disposal to the natural environment and also produces a sludge.

The treatment process typically involves the following three stages:

Primary treatment Primary treatment is to reduce oils, grease, fats, sand, grit, and coarse (settleable) solids.

Grit removal This stage typically includes a grit channel where the velocity of the incoming wastewater is carefully controlled to allow grit and stones to settle but still maintain all organic material within the flow. Grit and stones need to be removed early in the process to avoid damage to pumps and equipment in the remaining treatment stages.

Screening or maceration The grit free liquid is then passed through fixed or rotating screens to remove larger material such as rags. Screenings are collected and may be returned to the sludge treatment plant or may be disposed of off site by landfilling or incineration. Maceration, in which solids are cut into small particles through the use of rotating knife edges mounted on a revolving cylinder, is used in plants that are able to process this particulate waste. Macerators are, however, more expensive to maintain and are less reliable than physical screens.

Sedimentation

Primary sedimentation tank at a rural treatment plantIn almost all plants there is a sedimentation stage where the sewage is allowed to stand in large tanks so that faecal solids can settle and floating material such as grease and plastics can rise to the surface and be skimmed off. The main purpose of the primary stage is to produce a generally homogeneous liquid capable of being treated biologically together with a sludge that can be separately treated or processed. Primary settlement tanks are usually equipped with mechanically driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank from where it can be pumped to further sludge treatment stages.

Secondary treatment Secondary treatment is designed to substantially degrade the biological content of the sewage. The majority of municipal and industrial plants treat the settled sewage liquor using aerobic biological processes. For this to be effective, the biota require both oxygen and a substrate on which to live. There are number of ways in which this is done. In all these methods, the bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc particles.

Roughing Filters Roughing filters are intended to treat particularly strong or variable organic loads. They are typically tall, columnar filters filled with open synthetic filter media to which sewage is applied at a relatively high rate. The design of the filters allows high hydraulic loading and a high flow-through of air. The resultant liquor is usually within the normal range for conventional treatment processes.

Activated sludge Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen to generate a biological floc that substantially removes organic material. It also traps particulate material and can, under ideal conditions, convert ammonia to nitrite or nitrate.

Filter Beds

Trickling filter bed using plastic mediaIn older plants and plants receiving more variable loads, trickling filter beds are used where the settled sewage liquor is spread onto the surface of a deep bed made up of coke (carbonised coal), rocks or specially fabricated plastic media with high surface areas. The liquor is distributed through perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this bed and is collected in drains at the base. These drains also provide a source of air which percolates up through the bed, keeping it aerobic. Biological film comprising of bacteria, protozoa and fungi forms on all the available surfaces and this provides the required biological treatment capability to effect the reduction in organic content.

Rotating Plates and Spirals In some smaller plants slowly revolving plates or spirals are used which are partially submerged in the liquor. A biotic floc is created which provides the required substrate.

Secondary sedimentation The final step in the secondary treatment stage is to settle out the biological floc or filter material and produce an effluent with very low levels of organic material and suspended matter.

Secondary Sedimentation tank at a rural treatment plantTertiary treatment Tertiary treatment provides a final stage to raise the effluent quality to the standard required before it is discharged to the receiving environment (sea, river, lake, ground, etc.) More than one tertiary treatment process may be used at any treament plant. If disinfection is practiced, it is always the final process.

Effluent polishing Sand filtration Sand filtration removes much of the residual suspended matter.

Lagooning Lagoons provides settlement and further biological improvement through storage in large man-made ponds or lagoons.

Constructed wetlands These include engineered reed beds and a range of similar methodologies, all of which provide a high degree of aerobic biological improvement and can often be used instead of secondary treatment for small communities.

Nutrient removal Wastewater may also contain high levels of nutrients (nitrogen and phosphorus) that in certain forms may be toxic to fish and invertebrates at very low concentrations(e.g. ammonia) or that can create nuisance conditions in the receiving environment (e.g. weed or algal growth). Although the growth of weeds and algae may seem to be primarily an aesthetic issue, algae can produce toxins, and in dying their decay and consumption by bacteria in the environment can result in the depletion of oxygen in the water and the possible consequential suffocation of fish. Where receiving rivers discharge to lakes or shallow seas, the added nutrients can cause severe and sometimes irreversible eutrophication with the loss of many sensitive clean water species. The removal of nitrogen and/or phosphorus from wastewater can be achieved either biologically or by chemical precipitation treatment processes.

Nitrogen removal Biological treatment of nitrogen generally involves creating conditions within the treatment process for bacteria to convert the ammonia to nitrate, and then allowing other bacteria to reducing the nitrate to nitrogen gas, which is released to the atmosphere. Sand filters, lagooning and the use of reed beds can all be used to reduce nitrogen. Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.

Phosphorous removal The biological treatment of wastewater to remove phosphorus also involves the design and creation of specific environmental conditions within a treatment plant to enable specific bacteria to bio-accumulate large quantities of phosphorus. When the bacteria containing the phosphorus are removed, the resulting bacterial biosolids often have a high fertilizer value. Phosphorus can also be removed by chemical precipitation using (commonly) salts of iron (i.e. ferric chloride) or aluminum (i.e. alum). The resulting chemical sludge, however, is difficult to dispose of, and the use of chemicals in the treatment process is expensive and makes operation difficult and often messy.

Disinfection Disinfecting substantially reduces the numbers of living organisms in the water to be discharged. The effectiveness of disinfection depends on the quality of the water being treated, the type of disinfection being used, the application rate, the contact time and environmental variables. Turbid water will be treated less successfully since solid matter can shield organisms, especially from Ultraviolet light or if contact times are low. Generally, short contact times, low doses and high flows all mitigate against effective disinfection. Common methods of disinfection include ozone, chlorine, or UV light. Chloramine, which is used for drinking water, is not used in waste water treatment because of its persistence.

Chlorination remains the most common form of wastewater disinfection in North America due to its low cost and long-term history of effectiveness. One disadvantage is that chlorination of residual organic material can generate chlorinated-organic compounds that may be carcinogenic or harmful to the environment. Residual chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent must also be chemically dechlorinated, adding to the complexity and cost of treatment. Ultraviolet Light is becoming the most common means of disinfection in the UK because of the concerns about the impacts of chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the receiving water. Ultraviolet radiation is used to damage the genetic structure of bacteria, viruses, and parasites, making them incapable of reproducing. The key disadvantages of ultraviolet disinfection is the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that the ultraviolet radiation can get through to any microorganisms present (i.e. solids present in the treated effluent may protect microorganisms from the U.V. radiation). Ozone O3 is generated by passing oxygen O2 through a high voltage potential resulting in a third oxygen atom becoming attached and forming O3. Ozone is very unstable and reactive and oxidizes most organic material it comes in contact with, destroying many disease-causing microorganisms. It has the added bonus of removing other wastewater components such as colour. Ozone is considered to be safer than chlorine because, unlike chlorine which has to be stored on site, ozone is generated as it is required. Sludge treatment The coarse primary solids and secondary biosolids (bacteria) accumulated in a wastewater treatment process must be treated and disposed of in a safe and effective manner. This material is often inadvertently contaminated with toxic organic and inorganic compounds (e.g. heavy metals). The purpose of digestion is to reduce the amount of organic matter and the number of disease-causing microorganisms present in the solids. The most common treatment options include anaerobic digestion, aerobic digestion, and composting.

Anaerobic digestion Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process can either be thermophilic digestion (in which sludge is fermented in tanks heated to about 380°C) or mesophilic digestion (cold digestion of sludge where sludge is maintained in large tanks for weeks to allow natural mineralisation of the sludge). Thermophilic digestion generates biogas with a high proportion of methane that may be used to both heat the tank and run engines for other on-site processes. In large treatment plants sufficient energy can be generated in this way to produce electricity for sale. The methane generation is a key advantage of the anaerobic process. Its key disadvantage is the long time required for the process (up to 30 days) and the high capital cost.

Aerobic digestion Aerobic digestion is a bacterial process that runs in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it into carbon dioxide. Because the aerobic digestion occurs much faster than anaerobic digestion, the capital costs of aerobic digestion are lower. However, the operating costs are characteristically much greater for aerobic digestion because of the need to add oxygen to the process.

Composting Composting is also an aerobic process that involves mixing the wastewater solids with sources of carbon such as sawdust or wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added carbon source and, in doing so, produce a large amount of heat. Properly designed and controlled, the heat generated can be sufficient to significantly destroy a sufficient number of the disease-causing microorganisms to enable the resulting composted product to be safely used as a soil amendment material (with similar benefits to peat) for agricultural use.

Both anaerobic and aerobic digestion processes can result in the destruction of disease-causing microorganisms to a sufficient level to allow the resulting digested solids to be safely applied to land or used for agriculture as a fertilizer provided that levels of toxic constituents are sufficiently low.

The choice of a wastewater solid treatment method depends on the amount of solids generated and other site-specific conditions. However, in general, composting is most often applied to smaller-scale applications followed by aerobic digestion and then lastly anaerobic digestion for the larger-scale municipal applications.

Sludge Disposal When a liquid sludge is produced, further treatment may be required to make it suitable for final disposal. This includes lagooning in drying beds to produce a cake that can be applied to land or incinerated; pressing, where sludge is mechanically filtered, often through cloth screens to produce a firm cake; or liquid injection to land or liquid disposal to landfill. There are concerns about sludge Incineration because of the contents of the emmissions to air, along with the high cost of supplemental fuel, making this a less attractive and less commonly constructed means of sludge treatment and disposal.

Treatment in the receiving Environment Many processes in a wastewater treatment plant are designed to mimic the natural treatment processes that occur in the environment, whether that environment is a natural water body or the ground. If not overloaded, bacteria in the environment will consume organic contaminants, although this will reduce the levels of oxygen in the water and may significantly change the overall ecology of the receiving water. Native bacteria feed on the organic contaminants, and disease-causing microorganisms are reduced by natural environmental conditions that are hostile to these organisms (microbial predation, ultraviolet radiation, etc.) Consequently in cases where the receiving environment provides a high level of dilution, a high degree of wastewater treatment is not necessarily required. However, recent evidence has demonstrated that very low levels of certain contaminants in waste water, including hormones (especially from animal husbandry) and synthetic materials such as pthalates that mimic hormones in their action, can have an unpredictable adverse impact on the natural biota and potentially on humans if the water is re-used for drinking water.

However, in nature, microbes live in complex structured communities of diverse, metabolically redundant interacting species, mostly growing as biofilms on surfaces in nutrient-poor, heterogeneous matrices. Most microbes cannot yet be cultivated in the laboratory. The challenge, then, is to exploit cultivation-independent methods to gain a mechanistic understanding of functional relationships in microbial biofilm communities in natural or near-natural settings, to elucidate the rules of microbial behaviour and interactions, and to understand the functional/evolutionary basis of microbial diversity. Genomics has proven to be a powerful, cultivation-independent approach for the characterization of cellular functions and metabolic potential.

What is Food Microbiology?, What Is Nitrification?, What Is Antibiotic?, What Is Genetic Engineering?, What Is Genetics?, e, Microbe, e, Bacteriology, n, Microorganisms, n, Microorganism, r, Microbiology, e, Citrobacter, o, Microbial, o, Lactobacillus, a, Cell suspensions, r, Cell cultures, o, Candida albicans, c, Escherichia coli




 

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Last modified: May 25, 2005