Microorganisms in Waste Management
Adebayo, F.O.*, Obiekezie, S.O.
Department of Microbiology, Nassarawa State University, Keffi, Nigeria.
*Corresponding Author E-mail: fattysocioscope@yahoo.com
Abstract:
Microorganisms play important roles in the maintenance of many natural and man-made phenomenon in the environment. They serve positive functions that make life easier and better for man. One of such areas that microorganisms are adopted is in waste management. The proper disposal of the voluminous waste that humans generate in their daily activities is a great challenge that government and environmental agencies are continuously seeking better ways of addressing. An important way of successfully combating this menace is through the use of microorganisms. Thus, this paper examines the various applications of microorganisms in the management of municipal waste. It reviews the various roles of microorganisms in the environment, such as in sewage and soil treatment, energy generation, oil spillage and radioactive contamination. It also discusses waste generation and management methods, and some specific use of microorganisms (bacteria, fungi, algae, virus and protozoa) in waste management. It concludes by highlighting some recent advances in microbiological waste management.
KEY WORDS: Microorganisms, waste management, composting, wastewater, bioreactor, anaerobic digestion.
Introduction
Microorganisms are ubiquitous in nature where they have a variety of essential functions. Many microbes are uniquely adapted to specific environmental niches, such as those that inhabit the Dead Sea (Halobacterium) and Chlamydomonas nivalis that causes pink snow.1 Microbes also play an essential role in the natural recycling of living materials. All naturally produced substances are biodegradable, that is, they can be broken down by living organisms such as bacteria or fungi.
Microorganisms have been invaluable in finding solutions for several problems mankind has encountered in maintaining the quality of the environment. They have, for example, been used to positive effect in human and animal health, genetic engineering, environmental protection, and municipal and industrial waste treatment. Microorganisms have enabled feasible and cost-effective responses which would have been impossible via chemical or physical engineering methods.2 More so, microbial technologies have successfully been applied to a wide range of environmental problems, especially waste management issues.
In Nigeria with a population of 182 million,3 waste generation and disposal is a problem with several challenges to be addressed. The municipal wastes in Nigeria are from domestic, agricultural and industrial sources, and may be grouped into liquid, solid, gaseous and hazardous. However, the most problematic are the liquid and solid wastes.4 The liquid wastes are wastewater arising from municipal and industrial sources, while the solid waste management is a complex major issue that requires technology, human resources and funding. A lot of harmonized effort must be put into the control of wastes at all stages of production, collection, transportation, treatment and ultimate disposal in order to achieve the desired results.
Amori et al.5 intimated that high composition of non-biodegradable wastes from residential areas bears implication of the requirement for alternative waste management solutions for attaining sustainable and environmental friendly system. Such sustainable waste management scheme should include the development of biological methods for reducing the biodegradable waste components and any other methods of recycling, incineration, pyrolysis and gasification system could be employed for reducing the non-biodegradable waste components.
One successful biological scheme that is increasingly being adopted in curtailing the many aesthetic and harmful effects of waste disposal in the environment is the use of microbiological techniques that has little or no adverse effect on the environment. Hence, this paper attempted to elucidate how microorganisms act as agent of waste management, by considering the various roles they play in the environment, waste generation and management in Nigeria, some specific use of microorganisms in waste management and recent advances in microbiological waste management.
Role of microorganisms in the environment:
The activities of man in his environment involve a lot of chemical synthesis in the process of converting natural resources in the environment into other convenient forms for consumption. In the process of creating products, man also creates problems of pollution. As a result, the most acceptable solution to the generated wastes in the environment is such that will conveniently integrate them back into the environment.6 That method involves the use of microorganisms (usually yeasts, bacteria, or fungi). These microorganisms or their products are integrated into the substrates that yield desired industrial products such as bioleaching (biomining), biodetergent, biotreatment of pulp, biotreatment of wastes (bioremediation), biofiltrations, aquaculture treatments, biotreatment of textiles, biocatalysts, biomass fuel production, biomonitoring, and so on.
Also, microorganisms are vital to humans and the environment, as they participate in the carbon and nitrogen cycles, as well as fulfilling other vital roles such as recycling other organisms' dead remains and waste products through decomposition. Microorganisms also have an important place in most higher-order multicellular organisms as symbionts.7
Some examples of the application of microorganisms in the environment are discussed as follows:
Sewage treatment
The majority of all oxidative sewage treatment processes rely on a large range of microorganisms to oxidise organic constituents which are not amenable to sedimentation or flotation. Anaerobic microorganisms are also used to reduce sludge solids producing methane gas (amongst other gases) and a sterile mineralized residue. In potable water treatment, one method, the slow sand filter, employs a complex gelatinous layer composed of a wide range of microorganisms to remove both dissolved and particulate material from raw water.8
The nitrogen cycle in soils depends on the fixation of atmospheric nitrogen. This is achieved by a number of diazotrophs. One way this can occur is in the nodules in the roots of legumes that contain symbiotic bacteria of the genera Rhizobium, Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Azorhizobium.9
Microbes can make nutrients and minerals in the soil available to plants, produce hormones that spur growth, stimulate the plant immune system and trigger or dampen stress responses. In general, a more diverse soil microbiome results in fewer plant diseases and higher yield.10
Microorganisms are used in fermentation to produce ethanol11 and in biogas reactors to produce methane.12 Scientists are researching the use of algae to produce liquid fuels,13 and bacteria to convert various forms of agricultural and urban waste into usable fuels.14 Bacteria with tiny wire-like appendages called nanowires digest toxic waste (including PCBs and chemical solvents) to produce electricity.15 One type in particular, called Shewanella, is a deep-sea bacteria that grows these oxygen-seeking nanowires when placed in low-oxygen environments. Researchers discovered that when the microbes’ nanowires are pricked with platinum electrodes, they can carry a current. If these capabilities can be harnessed effectively, they could one day be used in sewage treatment plants to simultaneously digest waste and power the facilities.
Oil spillage and radioactive contamination:
Certain types of bacteria can clean up troublesome environmental pollutants like spilled petroleum. According to Steph,15 a specific strain called Alcanivorax drastically increases in population when an oil spill provides them with large amounts their nutrients, such that they are able to remove much of the oil (for instance, at Deepwater Horizon spill in the Gulf of Mexico).
The nanowires grown by certain types of bacteria can also be used to immobilize harmful materials – like uranium – and keep them from spreading. A research team at Michigan State University has learned that Geobacter bacteria, which is found naturally in soil, essentially electroplates uranium, rendering it insoluble so it cannot dissolve and contaminate groundwater.15 These bacteria can be brought into uranium contamination sites like mines and nuclear plants in order to contain the radiation, potentially limiting the disastrous consequences of these types of spills.
Waste generation and management in Nigeria:
Solid wastes could be defined as non-liquid and nongaseous products of human activities, regarded as being useless.16 It could take the forms of refuse, garbage and sludge.17 The quantity and rate of solid waste generation in an area depends on the population, socio-economic status of the citizens and the kinds of commercial activities predominant in the area.5 Table 1 shows the distribution of waste generation and density in some major cities in Nigeria, while figure 1 shows the municipal waste generation in some African countries, including Nigeria.
In developing countries, open dumping of solid wastes into wetlands, watercourses, drains and burrow pit is a prevalent form of disposal. This practice has sometimes resulted in the littering of the surroundings, creates eyesore and odour nuisance.18 Sangodoyin19 stated that open dumping of wastes serves as breeding place for flies, insects and rats.
Also, commercial areas like market places commonly exhibits mountains of open refuse by the roadside and other open location. The heaps of refuse provide excellent breeding grounds for vectors of communicable diseases including rodents, insects, which increases the potential for the spread of infectious diseases. It is also acknowledged that many of the diseases that affect Nigerians, including malaria, tuberculosis and diarrhea are due to unhealthy environmental conditions.22 They may also pose fire hazards apart from being eyesores and sources of unpleasant odors. Very frequently, refuse is dumped in drainages or canals and along watercourses with impunity. The unsanitary mode of wastes disposal, such as open urination, defecation in streams and the dumping of refuse in pits, rivers and drainage channels are widespread and the resultant contamination of the environment contributes to environmental degradation.23,24
Table 1: Waste generation and density in major cities in Nigeria.20 Lagos, Kano and Port-harcout are the three densely populated and most active commercial cities in the South-western, Northern and Eastern Nigeria respectively. It is therefore expected that the quantity of waste generation in these cities would be high. Ibadan is another commercial city in the south-western Nigeria, ranking after Lagos.
|
City |
Tons per month |
Density (Kg/m3 ) |
Volume/capita/day (m3) |
|
Lagos |
255,556 |
294 |
0.63 |
|
Kano |
156,676 |
290 |
0.56 |
|
Ibadan |
135,391 |
330 |
0.51 |
|
Kaduna |
114, 433 |
320 |
0.58 |
|
Portharcout |
117, 825 |
300 |
0.60 |
|
Makurdi |
24,242 |
340 |
0.48 |
|
Onitsha |
84,137 |
370 |
0.53 |
|
Nsukka |
12,000 |
310 |
0.44 |
|
Abuja |
14,785 |
280 |
0.66 |
Figure 1: Municipal solid waste generation in some African countries .21 Nigeria and South-Africa are both known to be the largest economies in Africa, while Nigeria is said to be the most populated nation in Africa. Egypt is a more populated country than South-Africa. It is therefore not surprising that municipal waste generation in these African countries is high.
Additionally, the volume of solid waste being generated continues to increase at a faster rate than the ability of the agencies to improve on the financial and technical resources needed to parallel this growth. Solid waste management in Nigeria is characterized by inefficient collection methods, insufficient coverage of the collection system and improper disposal of solid waste. The quantity of solid waste generated in urban areas in industrialized countries is higher than in developing countries;20 though municipal solid waste management remains inadequate in the latter. Solid waste in developing countries differs from developed countries. Most developing countries have solid waste management problems different from those found in industrialized countries in areas of composition, density, political, and economic framework, waste amount, access to waste for collection, awareness and attitude.
On the other hand, wastewater is generated from domestic sewage, agricultural processes and industrial effluent. Trivedi et al.25 stated that out of the total wastewater generated, 90.62% find its destination into the coastal waters without any treatment. The average domestic sewage contains organic matter, nitrogen and phosphorus, suspended solids, dissolved oxygen and bacterial parameter (fecal coliform).
Recently, an increasing category of waste stream in the world (including Nigeria) is the Waste Electrical and Electronic Equipment or E-waste.26 It is a term for electronic products that have become unwanted, non-working or obsolete, and have essentially reached the end of their useful life. In developed countries, it equals 1% of total solid waste on an average, while in developing countries, it ranges from 0.01% to 1% of the total municipal solid waste generation. In Nigeria though annual generation per capita is less than 1 kg, it is growing at an exponential pace in addition to the ever-growing hazardous waste stream. Heavy metals such as silicon, lead, mercury, and other related items had been found in rivers, lakes and water with adverse effects on human cells, which had been traced to illegal and indiscriminate dumping of e-waste into water bodies thereby percolating into soil.27 An estimated 53,600 metric tonnes of e- waste are dumped annually at Lagos state landfills which include 860,000computers, 530,000 printers, 900,000 monitors and 480,000 television sets.28
Waste management methods:
Waste management is the collection, transport, processing or disposal, managing and monitoring of waste materials to minimize its consequences on humans and environment. Solid waste treatment techniques act to reduce the volume and toxicity of solid waste, transforming it into a more convenient and/or beneficial form. In Awosusi,29 waste management is viewed as a process of source reduction, refuse recycling, controlled combustion and controlled landfill; energy generation from waste (energy recovery) and lastly, solid waste disposal, if the aforementioned do not offer appropriate solution. A number of processes are involved in effectively managing solid waste. These include monitoring, collection, transport, processing, recycling, incineration, landfilling and composting.30
This include different types of methods such as follows thermal treatment (whereby the process use heat to treat waste materials) such as incineration, gasification and pyrolysis, and open burning; dumps and landfills such as sanitary landfills, controlled dumps and bioreactor landfills; biological waste treatment such as composting and anaerobic digestion.31
Use of microorganisms in waste management:
The microorganisms which inhabit the aerobic biological treatment systems include bacteria, fungi, algae, protozoa, rotifers, and other higher animals. The growth of any or all types of microorganisms in a given industrial waste disposal system will depend upon the chemical characteristics of the industrial waste, the environmental limitations of the particular waste system and the biochemical characteristics of the microorganisms. All of the microorganisms which grow in a given industrial waste disposal system contribute to its over-all characteristics, both good and bad. It is important to recognize the contributions made by each type of organism to the over-all stabilization of the organic wastes if the waste treatment system is to be properly designed and operated for maximum efficiency.
Bacteria:
The bacteria are the basic biological units in aerobic waste treatment systems. The diverse biochemical nature of bacteria makes it possible for them to metabolize most, if not all, organic compounds found in industrial wastes. Obligate aerobes. and facultative bacteria are found in all aerobic waste treatment systems. Growth of any particular species is dependent upon its competitive ability to obtain a share of the available organic material in the system. Bacterial predomination will normally divide itself into two major groups: the bacteria utilizing the organic compounds in the waste, and the bacteria utilizing the lysed products of the first group of bacteria.32 The bacteria utilizing the organic compounds in the waste are the most important group and will determine the characteristics of the treatment system. The species with the fastest growing rate and the ability to utilize the majority of the organic matter will predominate. The extent of secondary predomination will depend upon the length of starvation. Depletion of the organic substrate is followed-by death and lysis of the predominate bacteria. Release of the cellular components of the bacteria permits other bacteria to grow up. Since all biological treatment systems are normally overdesigned as a safety factor, secondary predomination will occur. Aside from the metabolic characteristics of the bacteria, the most important characteristic is their ability to flocculate. All of the aerobic biological waste treatment systems depend upon the flocculation of the microorganisms and their separation from the liquid phase for complete stabilization.
It was first thought that flocculation was caused by a single bacterial species, Zoogloea ramigeria, but recent studies have shown that there are many different bacteria which have the ability to flocculate.32 It has been postulated that all bacteria have the ability to flocculate under certain environmental conditions. The prime factors affecting flocculation are the surface charges of the bacteria and their energy level. The electrical surface charge on bacteria grown in dilute organic waste systems has been shown to be below the critical charge for auto-agglutination, 0.020 volts. This means that Brownian movement provides sufficient energy to overcome the repelling electrical forces when two bacteria approach each other and to permit the Van der Waal forces of attraction to predominate and hold the two bacteria together. Autoagglutination does not take place if the energy level of the system is sufficiently high to permit the bacteria to multiply and to be rapidly motile. Autoagglutination, or flocculation, occurs only after the bacteria lack the energy of motility to overcome the Van der Waal forces. Once floc has started to form, some of the bacteria die and lyse. An insoluble fraction of the bacterial cell is left which is primarily polysaccharide. The older the floc becomes, the more polysaccharide builds up and the less active bacteria are entrained in it.
Fungi:
Fungi play an important role in the stabilization of organic wastes. Like the bacteria, the fungi can metabolize almost every type of organic compound found in industrial wastes. The fungi have the potential ability to predominate over the bacteria but they do not except under unusual environmental conditions. The filamentous nature of most of the fungi found in industrial wastes makes them undesirable since they do not form a tight compact floc and settle easily. For this latter reason, considerable efforts are expended to make the environmental conditions more favorable for bacteria predomination than for filamentous fungi predomination. The filamentous fungi predominate over the bacteria at low oxygen tensions, at low pH, and at low nitrogen. Low oxygen tension results from a low oxygen supply or from a high organic load causing the demand to exceed the supply. Under reduced oxygen levels, metabolism does not proceed to carbon dioxide and water but stops with the formation of organic alcohols, aldehydes, and acids. If the system lacks sufficient buffer, the organic acids depress the pH to the more favorable range for fungi. Thus, it can be seen that low oxygen tension and pH can be interrelated. Many of the fungi grow well at pH 4 to 5 while few bacteria are able to grow well enough to compete. Fungi require less nitrogen than bacteria per unit mass of protoplasm.32 In nitrogen deficient wastes, the fungi are able to synthesize more active masses of protoplasm from the wastes than are the bacteria and predominate. Bacteria average approximately 10 to 12% nitrogen while fungi range from 5 to 6% nitrogen. Under normal environmental conditions fungi will be present and will aid in the stabilization of the organic matter. But the fungi are of secondary importance and will not predominate.
Algae:
The algae are the third form of biological plants which play a part in the over-all stabilization of organic wastes. Since the algae obtain their energy for synthesis from sunlight, they do not have to metabolize the organic compounds like the bacteria and the fungi. To form protoplasm the algae primarily utilize the inorganic components of the wastes, for example, ammonia, carbon dioxide, phosphate, magnesium, potassium, iron, calcium, sulfate, sodium and other ions. It is possible to have algae and the bacteria predominate together since they do not utilize the same waste components. The bacteria metabolize the organic components of the waste and release some of the inorganic components utilized by the algae. During protoplasm synthesis the algae release oxygen which is taken by the bacteria to bring about complete aerobic stabilization of the organic matter. In the absence of sunlight the algae must obtain the energy required to stay alive from the metabolism of organic matter in the same manner as bacteria and fungi. This organic matter normally comes from stored food within the cell but in some algal species it can come from the organic material in the wastes.
Viruses:
These are particles assembled from the biopolymers, which are capable of multiplying and assembling as new virus particles inside living prokaryotic or eukaryotic cells.33 In the environment, viruses are important for the following reasons: pathogenic viruses must be removed, retained or destroyed during water and wastewater treatment; viruses of bacteria (bacteriophages) can infect and degrade the bacterial cultures in the environment; and bacteriophages can be used for the detection of specific microbial pollution of waste in the environment.
Protozoa:
The protozoa are the simplest animals found in waste disposal systems. The role that the protozoa play in stabilizing organic wastes has only recently been clarified by combining a study of pure culture protozoa (Gram, 1953, unpublished observations) with the natural observations in various biological treatment systems. This study showed that rather than being the primary mechanism of purification, the protozoa were responsible for reducing the number of free-swimming bacteria, thus aiding in producing a clarified effluent. The succession of protozoa had long been observed in biological waste disposal systems32 but there was no explanation of the reasons for this succession. The succession of protozoa is affected by the same factors which affect the predomination of any biological species. The type of food and the competition for food are the major factors which determine the predomination of the protozoa. The Sarcodina are only briefly found in aerobic waste treatment systems since they do not find sufficient food to compete with the bacteria and other biological forms. The Phyto-Mastigophora survive a little longer than the Sarcodina as they take in soluble organics for their food but they are unable to compete against the bacteria and are soon displaced. The Zoo-Mastigophora predominates over the Phyto-Mastigophora in that they are able to utilize the bacteria for food rather than compete with the bacteria for food. But the Zoo-Mastigophora give way to the free-swimming Ciliata which have a better mechanism for obtaining the bacteria and other food components. As the system becomes more stable, there are less and less free-swimming Ciliata. The low-energy-requiring stalked Ciliata displace the high-energy-requiring free-swimming Ciliata. But soon the system becomes so stable that the stalked Ciliata cannot obtain enough energy and die out of the system.
The succession of protozoa offers a good index of stability of the biological waste treatment system. Efforts have been made to relate the numbers of protozoa to the degree of stabilization but they have not been successful since the same numerical population exists at two separate and distinct levels of purification. Low numbers of free-swimming Ciliata occur at both a low degree of purification, 20 to 40%, and at high purification, 75 to 95%. The relative types of protozoa and relative numbers can be used for any particular system to estimate the rough efficiency, ±10%, of any biological treatment system.32 The protozoa have more complex metabolic systems than do bacteria or fungi which make the protozoa more sensitive to toxic organic compounds. In systems containing toxic organic compounds, regular observations of the protozoa can be used as an indicator of the toxic concentration and to warn of potential toxicity to the bacteria which are responsible for stabilization of the wastes. The protozoa can also be used to indicate deficiencies of certain essential elements such as nitrogen or phosphorus. Nutrient deficiencies will reduce both number of species and number of any particular species.
Microbial waste management:
Generally, solid waste can broadly be categorized into biodegradable and non-biodegradable. The biodegradables (biowastes) are those solid wastes generated, which could be decomposed by microorganisms and does not constitute major sources of pollution for a long period of time.6 They include paper products and wastes of plant origin, wastes of animal origin (faecal matter, carcass, droppings, and poultry waste products).
These groups of solid waste even though they are easily degraded by microorganism in minimal time, give off offensive odour and constitute nuisance to the aesthetic environment more than the non-biodegradable solid wastes. They can also constitute a good habitat for the thriving of pathogenic microorganisms which could easily pollute fresh food product and sources of fresh water in the urban cities in Nigeria.
On the other hand, non-biodegradable solid wastes are not degradable by microorganisms. This implies that other means of treatment such as incineration, landfill, and recycling are employed as ways of disposing them. Examples of this group of solid wastes are solid wastes of metallurgical and smelting industries (abandoned vehicles, motor cycles, vehicle part and scrap metals, iron, zinc, aluminium sheets and other metals, machine parts); solids wastes of construction industries (sand, gravel, bitumen wastes, concrete and waste building materials); solid waste of plastic industries (plastic buckets, cable insulators, tyres, chairs, tables, cellophane bags, plastic bottles, cutleries, sachet water containments, etc.) and glass products.6
Solid waste management:
Management
of solid waste reduces or eliminates adverse impacts on the environment and
human health and supports economic development and improved quality of life. Composting is the
most frequently used biological solid waste treatment method which is the
controlled aerobic decomposition of organic waste materials by the action of
small invertebrates and microorganisms. Composting is a technique in which
organic waste materials (food, plants, paper) are decomposed and then recycled
as compost for use
in agriculture and landscaping applications.34 The most common
composting techniques include static pile composting, vermin-composting,
windrow composting and in-vessel composting.
Wastewater treatment: activated sludge and trickling filter:
Microorganisms are particularly important in wastewater treatment, which utilizes the metabolic activities of diverse mixed microbial populations capable of degrading any compound that may be presented to them. According to Waites et al.,35 the two main objectives are to destroy all pathogenic microbes present in the sewage, particularly the causal organisms of the water-borne diseases cholera, dysentery and typhoid. The second objective is to break down the organic matter in waste-water to mostly methane and carbon dioxide, thereby producing a final effluent (outflow) that can be safely discharged into the environment. Microbial activities can also be employed in the degradation of man-made xenobiotic compounds within waste streams and in the bioremediation of environments contaminated by these materials.
Meanwhile, the ultimate goal in wastewater treatment is to convert both the carbon and the energy in the wastewater into microorganisms, and remove microorganisms from the water by settling. The relationship between the source of the carbon and the source of the energy for microorganisms is important. Carbon is the basic building block for cell synthesis while energy must be obtained from outside of the cell to enable synthesis to proceed. Microorganisms require certain nutrients for growth. The basic nutrients of abundance in normal raw sewage are carbon (C), nitrogen (N), phosphorus (P), with the ratio of C:N:P ratio approximately equal to 100:10:1.36 In addition to C,N,and P, trace amounts of sodium (Na), Potassium (K), magnesium (Mg), iron (Fe), and many others are required. In normal municipal sewage, most of these nutrients are provided. Most problems with nutrient deficiency occur when there are a lot of industrial wastes present. When proper nutrients are not available, the metabolism fails and a kind of bacterial fat (slime) will begin to accumulate around the cell. The cell slows down in activity because it cannot produce enough enzymes and because needed nutrients cannot penetrate the slime layer as they should. The sludge will not settle and BOD removal slows down.
According to Semerci,36 activated sludge can be defined as a mixture of microorganisms which contact and digest biodegradable materials (food) from wastewater. Thus, activated sludge process is a biological process. To properly control the activated sludge process, the growth of microorganism must be properly controlled. This involves controlling the conditions that affect those microorganisms. It is noted that bacteria make up about 95% of the activated sludge biomass. These single-celled organisms grow in the wastewater by consuming biodegradable materials such as proteins, carbohydrates, fats and many other compounds. Activated sludge utilizes compressed air for its oxygen source and for mixing. The basic process depends upon diffused air at 6 to 8 psi to supply oxygen to the microorganisms and to supply the necessary force to keep the microorganisms, waste, and oxygen well mixed at all times. The microorganisms after stabilizing the organic wastes flocculate and settle, leaving a clear supernatant containing 10 to 15 ppm BOD.32 The settled microorganisms are partially returned to the head end of the aeration tank as seed to maintain a high microorganism population in the aeration tank and the remainder is wasted to anaerobic digestion for further stabilization
On the other hand, trickling filter is a commonly used method of secondary wastewater treatment. It is made up of a filter bed that contains a highly permeable media (gravel or plastic material etc), which has a layer of microorganisms on the surface that leads to the formation of a slime layer. In a trickling filter system, the microorganisms are attached to the media in the bed and form a biofilm over it. As the wastewater passes through the media, the microorganisms consume and remove contaminants from the wastewater.37 In a trickling filter, the sewage is sprayed over the permeable media (bed of rocks, molded plastic, gravel and ceramics etc). The media must be large enough so that air will be able to pass through to the bottom but small enough to maximize the surface area available for microbial activity. A biofilm of aerobic microorganisms grows on the media because air passes through the media, the aerobic microorganisms in the slime layer can oxidize the organic matter trickling over the surface into carbon dioxide and water. This treatment system removes 80 - 85% of the BOD so they are less efficient than activated sludge systems. They are easier to operate and do not have problem with toxic sewage.
Recent advances in microbial waste management:
The review of recent scientific progress in usefully applying microbes to both environmental management and biotechnology is informed by acknowledgement of the polluting effects on the world around man of soil erosion, the unwanted migration of sediments, chemical fertilizers and pesticides, and the improper treatment of human and animal wastes. These harmful phenomena have resulted in serious environmental and social problems around the world, problems which require us to look for solutions elsewhere than in established physical and chemical technologies.2
Notably, biological methods including biotechnological tools are advances in sustainable environmental clean-up strategies that are increasingly adaptable to waste management systems. Among such biotechnological tools are biodegradation procedures such as bioremediation, biostimulation, bioaugmentation, phytoremediation, and so on. Biodegradation is breaking down organic matter into nutrients that can be used by other organisms. Chahal38 indicated that such breakdown (decay) is carried out by many bacteria, fungi, insects, worms, and other saprophytic organisms that consume dead material and recycle it into new forms. Bioremediation uses microorganisms and their products in the presence of optimum environmental conditions and sufficient nutrients to breakdown contaminants including hazardous substances. Bioremediation technology uses microorganisms to reduce, eliminate, contain, or transform to benign contaminants present in soils, sediments, water, and air.39 Biostimulation involves the modification of the environment to stimulate existing bacteria capable of bioremediation. This can be done by addition of various forms of limiting nutrients and electron acceptors, such as phosphorus, nitrogen, oxygen, or carbon (e.g. in the form of molasses), which are otherwise available in quantities low enough to constrain microbial activity.39 Bioaugmentation is the addition of living microbial cells capable of degradation to supplement the indigenous populations in the environment. The microorganisms used are known as bioremediators. It may take months or years for microbes to clean up a site, depending on several factors like high contaminant concentrations, contaminants trapped areas, or the contaminated site.38 Another type of bioremediation is mycoremediaiton. It involve use of fungi to decontaminate an area. Its mycelium secretes an extracellular enzyme and acids that break down lignin and cellulose.
Bioreactor landfills are recent technological research that are better than the traditional sanitary landfills and controlled dumps. These landfills use superior microbiological processes to transform and stabilize the readily and moderately decomposable organic waste constituents in a short period of time.40 The controlling feature is the continuous addition of liquid to sustain optimal moisture for microbial digestion. The liquid is added by re-circulating the landfill leachate. When the amount of leachate is not adequate, liquid waste such as sewage sludge is used. There are three types of bioreactor: aerobic, anaerobic and a hybrid (using both aerobic and anaerobic method). All three mechanisms involve the reintroduction of collected leachate supplemented with water to maintain moisture levels in the landfill. The micro-organisms responsible for decomposition are thus stimulated to decompose at an increased rate with an attempt to minimize harmful emissions.41
In aerobic bioreactors air is pumped into the landfill using either vertical or horizontal system of pipes. The aerobic environment decomposition is accelerated and amount of volatile organic compounds, toxicity of leachate and methane are minimized.42 In anaerobic bioreactors with leachate being circulated the landfill produces methane at a rate much faster and earlier than traditional landfills. The high concentration and quantity of methane allows it to be used more efficiently for commercial purposes while reducing the time that the landfill needs to be monitored for methane production. Hybrid bioreactors subject the upper portions of the landfill through aerobic-anaerobic cycles to increase decomposition rate while methane is produced by the lower portions of the landfill.43 Bioreactor landfills produce lower quantities of volatile organic compounds than traditional landfills, except H2S. Bioreactor landfills produce higher quantities of H2S.
Anaerobic digestion is the latest and greatest process of in-vessel treatment of waste, and is generally considered to be one of the most innovative and useful technologies developed by our industry in recent years.44 Not only does it give a large-scale solution to organic waste but it allows the resulting gases to be turned into energy. By definition, anaerobic digestion is the multi-step biological process in which anaerobic microorganisms convert organic materials or waste to biogas and biofertilizer in the absence of oxygen. It involves a series of metabolic interactions among various groups of microorganisms, and occurs in four stages of hydrolysis/liquefaction, acidogenesis, acetogenesis and methanogenesis.45 Figure 2 shows the process of biogas generation from food waste. Anaerobic digestion can be used to treat organic solid waste and wastewater of almost any kind. The process works quickly and the remainder can be used as fertilizer while the biogas produced is converted into energy.
Figure 2: The process of biogas generation from food waste.
Source: http://www.biogen.co.uk/Anaerobic-Digestion/What-is-Anaerobic-Digestion
More so, an effective technology for large scale recycling of organic waste is by the application of biodung composting followed by vermiculture technology. Vermiculture technology is a system harnessing earthworms for bioconversion of organic waste into vermicompost which has extensive application in waste management and sustainable organic farming and has proved to be one of the efficient methods of managing organic wastes with least complexity and economic viability. This method was adopted in a research by Ansari.46 The combination of grass clippings, water hyacinth and cattle dung was used as organic waste for the process of biodung and vermicomposting. The results obtained indicated that the organic wastes were successfully processed through partial biodung composting and vermicomposting during a period of 60 days. This contributes to the supply of essential micro-nutrients and contains growth promoting substances like auxins and cytokinins.
According to Sneha,47 the steps involved in the formation of vermicompost include digging a pit about half a meter square and one meter deep, lining it with straw or dried leaves and grass, organizing the disposal of organic waste into the pit as and when generated, introducing a culture of worms (which are available commercially), ensuring that the contents are covered with a sprinkling of dried leaves and soil daily, watering the pit once or twice a week to keep it moist and turning over the contents of the pit every 15 days. In about 45 days the waste shall then be de-composed by the action of the microorganisms. The soil derived from this process is fertile and rich in nutrients.
CONCLUSION AND RECOMMENDATION:
Waste is any material, which have little or no value to producer or consumer. Humans with nearly all activities produce waste. The major component of municipal solid waste represent organic fraction, mostly from domestic, agricultural and industrial sources. There are many different methods of managing municipal waste streams. These include physical, chemical and biological methods. Conventional waste management practices usually involve one negative consequence or the other. This necessitated the search for and development of biological techniques, including the use of microorganisms that produce environmental-friendly outcomes.
Biological methods include the use of microorganisms such as bacteria, fungi, algae, virus and protozoa in techniques like composting, activated sludge, trickling filters and oxidation ponds. Recent scientific progress in applying microorganisms to environmental management includes hybrid applications that combine microbial methods with physical and chemical ones; these include bioreactor landfills, anaerobic digestion and vermiculture technology.
In view of the environmental-friendly and cost-effective benefits of using microorganisms in waste management, and considering the biodegradable nature of the voluminous waste generated in countries like Nigeria, the following are viable recommendation from this discuss:
· Relevant government parastatals should consolidate on their programs and projects like of the Integrated Solid Waste Management System (ISWM) project that educate residents on proper ways to manage waste, and management of waste collection
· Waste separation at the source should be done to allow for more effective and efficient waste collection and management
· Microbiological methods of waste management should be developed and utilized, not only for environmental clean-up but also for the value-added benefits of such methods
· Lastly, waste collection systems should be enhanced for sustainable and more hygienic environmental conditions especially around populated areas of the municipalities.
CONFLICT OF INTEREST:
The authors declare that there is no conflict of interest.
REFERENCES:
1. Gallo M and Ventresca S. The Role of Microorganisms in the Ecosystem. American Society for Microbiology Education Department. 2016. Available from URL: https://www.asm.org/images/Education/K-12/mdamicroorganismsbwpdf.final.pdf
2. Satyanarayana T, Bhavdish-Narain J and Prakash A. Microorganisms in Environmental Management: Microbes and Environment. Springer Publishers, Netherlands. 2012.
3. National Population Commission (2017). Homepage. Available from URL: http://www.population.gov.ng/index.php/80-publications/216-nigeria-s-population-now-182-million-dg-npopc
4. Sridhar, M. K. C. (2013). The Challenge of Waste Management in Nigeria: Recommendations towards a Functional National Policy. National Conference on the Environment. Available from URL: http://tandice-bsolutions.com/rokdownloads/National_Conference_on_the_Environment/Prof_Sridhar_Abuja_presentation1.pdf
5. Amori, A. A , Fatile B. O, Ihuoma, S. O and Omoregbee, H.O. (2013). Waste Generation and Management Practices in Residential Areas of Nigerian Tertiary Institutions. Journal of Educational and Social Research, 3 (4). Available from URL: www.mcser.org/journal/index.php/jesr/article/download/422/439
6. Ezeonu, C. S., Tagbo, R., Anike, E. N., Oje, O. A. and Onwurah, I. N. E. (2012). Biotechnological Tools for Environmental Sustainability: Prospects and Challenges for Environments in Nigeria—A Standard Review. Biotechnology Research International. Vol 2012.
7. Wikipedia. Microorganisms. Wikimedia Homepage. 2017a. Available from URL: https://en.wikipedia.org/wiki/Microorganism
8. Gray NF. Biology of Wastewater Treatment. Imperial College Press. 2004. Available from URL: https://www.researchgate.net/publication/278036604_Biology_of_Wastewater_Treatment
9. Barea JM, Pozo M, Azcón R and Azcón-Aguilar C. "Microbial co-operation in the rhizosphere". J Exp Bot. 2005, 56 (417): 1761–78. Available from URL: https://academic.oup.com/jxb/article-lookup/doi/10.1093/jxb/eri197.
10. Vrieze J. "The littlest farmhands". Science. 2015, 349 (6249): 680–683. Available from URL: https://www.ncbi.nlm.nih.gov/pubmed/26273035
11. Kitani O and Hall CW. Biomass Handbook. Taylor and Francis US. 1989: 256.
12. Pimental D. Food, Energy, and Society. CRC Press. 2007: 289.
13. Tickell J. From the Fryer to the Fuel Tank: The Complete Guide to Using Vegetable Oil as an Alternative Fuel. Biodiesel America. 2000: 53.
14. Inslee J. Apollo's Fire: Igniting America's Clean Energy Economy. Island Press. 2008: 157.
15. Steph. Beneficial Bacteria: 12 Ways Microbes Help the Environment. Homepage of Momtastic Webecoist. 2017. Available from URL: http://webecoist.momtastic.com/2011/09/26/beneficial-bacteria-12-ways-microbes-help-the-environment/#Ui0eMCypLJvobdGf.99
16. Babayemi JO and Dauda KT. Evaluation of Solid Waste Generation, Categories and Disposal Options in Developing Countries: A Case Study of Nigeria. Journal of Applied Science and Environmental Management, 2009, 13(3): 83 – 88.
17. Leton TG and Omotosho O. Landfill Operations in the Niger Delta Region of Nigeria. Engineering Geology. 2004, 73(1-2): 171-177.
18. Ihuoma SO. Characterization and Quantification of Solid and Liquid Wastes Generated at the University of Ibadan, Ibadan, Nigeria. MSc. Thesis Presented to the Department of Agricultural and Environmental Engineering, University of Ibadan, Nigeria. 2012.
19. Sangodoyin AY. Consideration on Contamination of Groundwater by Waste Disposal System in Nigeria: Environmental Technology. 1993, 14 (10): 957-964.
20. Ogwueleka TC. Municipal Solid Waste Characteristics and Management in Nigeria. Iran. J. Environ. Health. Sci. Eng. 2009, 6(3) 173-180. Available from URL: http://resourcedat.com/wp-content/uploads/2013/02/municipal-solid-waste-and-xteristics.pdf
21. Adelana O. Life of scavengers inside Abuja's biggest dumpsite. 2016. Available from URL: https://www.naij.com/780541-feature-inside-abuja-dump-site-scavengers-make-n637-500-month.html
22. Nigerian National Planning Commission (2004): National Economic and Development Strategy. Nigerian National Planning Commission, Abuja.
23. Abejegah C, Abah SO, Awunor NS, Duru CB, Eluromma E, Aigbiremolen AO, Okoh EC. Market Sanitation: A Case Study of Oregbeni Market Benin - City Edo State, Nigeria. International Journal of Basic, Applied and Innovative Research. 2013, 2(2). Available from URL: http://www.arpjournals.com/docs/IJBAIR/IJBAIR%20volume%202%20issue%202/Paper%203.%20Abejegah%20et%20al.,%202(2)%202013.pdf
24. Sangodoyin AY. Ground and Surface Water Pollution by Open Dump in Ibadan, Nigeria. Discovery and Innovation. 1991, 2 (1): 37-43.
25. Trivedi RC, Bhardwaj SRM, Agrawal S, Nazimuddin Sh, Malhotra K and Pandey M. Wastewater Generation and Treatment: Domestic Sewage. 2005. Available from URL: http://cpcbenvis.nic.in/cpcb_newsletter/sewagepollution.pdf
26. Ogungbuyi O, Nnorom IC, Osibanjo O and Schluep M. E-Waste Country Assessment Nigeria: e-Waste Africa project of the Secretariat of the Basel Convention. 2012. Available from URL: http://ewasteguide.info/files/Ogungbuyi_2012_BCCC-Empa.pdf
27. Okenwa S. Nigeria: Lasepa Deploys Experts to Rid Lagos of E-Waste. 2010. Available from URL: http://ewasteguide.info/nigeria-lasepa
28. LASEPA. E-Waste Management Policy (Final Draft). 2015. Available from URL: http://www.lasepa.gov.ng/pdf/E_waste_policy_final_draft_LASG.pdf
29. Awosusi AO. Assessment of Environmental Problems and Methods of Waste Management in Ado-Ekiti, Nigeria. African Research Review, 2010, 4(3): 331-343. Available from URL: https://www.ajol.info/index.php/afrrev/article/download/60273/48517
30. Atalia KR, Buha DM, Joshi JJ and Shah NK. Microbial Biodiversity of Municipal Solid Waste of Ahmedabad. J. Mater. Environ. Sci., 2015, 6 (7): 1914-1923. Available from URL: https://www.jmaterenvironsci.com/Document/vol6/vol6_N7/231-JMES-1353-2015-Atalia.pdf
31. LeBlanc R. Waste Treatment and Disposal Methods. 2016. Available from URL: https://www.thebalance.com/g00/waste-treatment-and-disposal-methods-2878113?i10c.referrer=
32. McKinney RE. Activity of Microorganisms in Organic Waste Disposal. 1957. Available from URL: http://pubmedcentralcanada.ca/pmcc/articles/PMC1057284/pdf/applmicro00311-0033.pdf
33. Ivanov V. Microbiology of Environmental Engineering Systems. In: Handbook of Environmental Engineering, Vol 10: Environmental Biotechnology. Wang et al. (Eds), Springer Science and Business Media Publishers. 2010.
34 Both D. Waste Management for a Modern World. 2017. Available from URL: https://www.experience.com/alumnus/article?article_id=article_1175017543375andchannel_id=energy_utilitiesandsource_page=additional_articles
35. Waites MJ, Morgan NL, Rockey JS and Higton G. Industrial Microbiology: An Introduction. Blackwell Science Ltd., Oxford. 2001. Available from URL: https://4lfonsina.files.wordpress.com/2012/11/industrial-microbiology-an-introduction-0632053070-wiley.pdf
36. Semerci N. Introductıon to Envıronmental Engıneerıng. 2012. Available from URL: http://mimoza.marmara.edu.tr/~neslihan.semerci/ENVE100/ENVE100Ch5.pdf
37. Akpor OB, Ogundeji MD, Olaolu TD and Aderiye BI. Microbial Roles and Dynamics in Wastewater Treatment Systems: An Overview. International Journal of Pure and Applied Bioscience, 2014, 2 (1): 156-168. Available from URL: www.ijpab.com/form/2014%20Volume%202.../IJPAB-2014-2-1-156-168.pdf
38. Chahal K. Bioremediation, Bioaugmentation and Phytoremediation. 2015. Available from URL: https://hubpages.com/education/BIOREMEDIATION-BIOAUGMENTATION-PHYTOREMEDIATION
39. Adams GO, Fufeyin PT, Okoro SE and Ehinomen I. Bioremediation, Biostimulation and Bioaugmention: A Review. International Journal of Environmental Bioremediation and Biodegradation, 2015, 3(1): 28-39. Available from URL: http://www.sciepub.com/journal/IJEBB
40. Townsend T, Kumar D and Ko J. Bioreactor Landfill Operation: A Guide for Development, Implementation and Monitoring. Prepared for the Hinkley Center for Solid and Hazardous Waste Management, Gainesville, FL. 2008. Available from URL: http://www.bioreactorlandfill.org/BioreactorFinalReport/FinalReportVOLUME1_10AttachmentforVOLUME8/Bioreactor_Landfill_OperationV10.pdf
41. Wikipedia. Bioreactor landfills. Wikimedia Homepage. 2017b. Available from URL: https://en.wikipedia.org/wiki/Bioreactor_landfill
42. Murphy SR. A Lysimeter Study of the Aerobic Landfill Concept. Waste Management and Research, 1992: 485-503. Available from URL: http://journals.sagepub.com/doi/abs/10.1177/0734242X9201000603
43. Hinkley Center for Solid and Hazardous Waste Management. Bioreactor.org - General Info. 2006. Available from URL: https://www.hinkleycenter.org/pubs.html
44. Capel C. Innovations in Waste. 2010. Available from URL: https://waste-management-world.com/a/1-innovations-in-waste
45. Kangle KM, Kore SV, Kore VS and Kulkarni GS. Recent Trends in Anaerobic Codigestion: A Review. Universal Journal of Environmental Research and Technology, 2012, 2(4): 210-219. Available from URL: www.environmentaljournal.org
46. Ansari AA. Vermitech: An Innovation in Organic Solid Waste Management. Journal of Sustainable Development and Environmental Protection, 2011, 1(1): 107
47. Sneha AG. Environmental Pollution. 2015. Available from URL: https://www.slideshare.net/AbhinitiGarg23/environmental-pollution-54311488
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Received on 12.10.2017 Modified on 20.11.2017 Accepted on 30.12.2017 ©A&V Publications All right reserved Research J. Science and Tech. 2018; 10(1): 28-39 DOI: 10.5958/2349-2988.2018.00005.0 |
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