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Getting biotechnology books PDF free download and every other textbook you need is much easier now than it ever was. Biotechnology Books PDF. A short summary of this paper. Download Download PDF. Translate PDF. Patil Biotechnology and Bioinformatics Institute, Dr. Actinomycetes, one of the most diverse groups of filamentous is on par with commercial antimicrobials, clearly manifest- bacteria, are well recognized for their metabolic versatility.
Streptomyces lunal- multitude of primary and secondary metabolites produced by inharesii produces antimicrobial substances against sulfate- actinomycetes. At the same time, the reactor contents can be easily mixed, which permits controlled degassing and defined concentration equalization in the fermenter.
As a consequence, the degradation performance of the microorganisms is optimized. The mean substrate concentrations and thus also the related degradation rates are lower than in plug flow systems, since, for completely mixed systems, the concentrations in the system are equal to the outlet concentrations.
Mixing is limited by the shear-sensitivity of methane bacteria; however, too-low a degree of mixing may result in floating and sinking layers. Homogeneity and a fluid consistency permit easier process control. By fluidizing the biowaste, the mass to be treated increases until the 5-fold, depending on the total solids content of the substrate with the consequence that the aggregates and reactors have to be made much larger. Fluidization and dewatering of the fermentation suspension especially require considerable technical and energetic expenditures.
But if the degrees of degradation are the same, recycling the liquid phase from the dewatering step to the fluidization of the input material, makes it possible to reduce the wastewater quantity to an amount comparable to that used in dry fermentation and to keep a considerable part of the required thermal energy within the system.
Completely mixed and plug flow systems are available. Enough substrate is fed into the reactor to replace the putrefied material as it is discharged. Therefore, the substrate must be flowable and uniform. Steady provision of 14 Anaerobic Fermentation of Wet and Semidry Garbage Waste Fractions nutrients in the form of raw biodegradable waste enables stable process operation and constant biogas yield. Depending on the reactor design and the means of mixing, short circuits may occur, and the retention time therefore cannot be guaranteed for each part of the substrate in completely mixed systems.
In the discontinuous operation mode batch process , the fermentation vessel is completely filled with raw garbage mixed with inoculum e. Batch digesters are easy to design, comparatively low in cost, and suitable for all wet and dry organic wastes Table According to the experience gained with this way of operation, the process stability is high.
Minor temperature variations have only a small effect on mesophilic bacteria. The advantages of mesophilic process operation result from the lower amount of heat to be supplied and the related higher net energy yield.
In addition, higher process stability is achieved, since a broad spectrum of mesophilic methane bacteria that show low sensitivity to temperature changes exist. Under certain circumstances thermophilic process operation allows faster substrate turnover, so that the residence times can be shorter. The higher expenditure of energy to maintain the process temperature is a disadvantage. When the process is run under thermophilic conditions for a defined residence time, sanitation in the reactor is possible,; otherwise, sanitation has to be achieved in a separate treatment step or by aerobic after-composting.
On the other hand, the net energy yield is lower, due to the higher heat requirement, and the temperature sensitivity of the microorganisms reduces the process stability.
Simultaneously, the metabolic products Table Process Operation Continuous Discontinuous Retention time Technical equipment shorter complex longer simple These requirements can be met by mechanical mixing or other agitation of the reactor contents. Another possibility is to install a water recirculation system, by which the process water, which ensures nutrient provision and the removal of metabolic products, trickles through the biowaste in the reactor Rilling and Stegmann, Other processes use compressed biogas for total or partial mixing of the material.
Each has its own benefits. Currently, the European market offers at least 30 different processes or process variants. The number of dry fermentation processes is comparatively small. One primary reason for this situation is the higher technical effort required for dry fermentation. Although wet fermentation can be based on the well known and successful technology used in sewage sludge treatment and the digestion of manure, dry fermentation requires the employment of new, innovative technologies, especially in the field of gas-tight filling and emptying, as well as in conveyance systems.
This growth may be inhibited by an excess of organic volatile acids, which are toxic to methanogenic bacteria at concentrations of —16 mg L—1 Stegmann and Spendlin, The methane concentration in the gas increases, while hydrogen, carbon dioxide, and volatile fatty acids decrease.
Conversion of fatty acids causes an increase in pH values and alkalinity, with a consequent decrease in solubility of calcium, iron, manganese, and heavy metals. The latter are probably precipitated as sulfides. Ammonia is released and is not converted in the anaerobic environment. The third phase of anaerobic degradation Phase IV, Figure This confirms that solubilization of the majority of organic components has decreased at this stage of landfill operation, although the process of waste stabilization will continue for several decades.
Ammonia continues to be released by the firststage acetogenic process. Ehrig compiled leachate concentrations from German landfills from the s and s. Kruse investigated 33 landfills in Northern Germany, the leachate concentrations mainly derive from the late s and early s. This can be explained by developments in the technology of waste landfilling.
In many younger landfills waste deposition and compaction in thin layers, in combination with an aerobic pretreated bottom layer, were carried out. This led to a reduction in the period for the acid phase and to an accelerated conversion of organic leachate components into the gaseous phase, as well as the degradation of organics to methane and carbon dioxide. Of the former. The inorganic content of the leachate depends on the contact between waste and leaching water, as well as on the pH and the chemical balance at the solid—liquid interface.
In particular, the majority of metals are released from the waste mass under acid conditions. Landfill age obviously plays an important role in the determination of leachate characteristics governed by the type of waste stabilization processes.
We should emphasize that variations in composition of leachate do not depend exclusively on landfill age but also on the degree of waste stabilization and the volume of water that infiltrates the landfill. The pollutant load in leachate generally reaches maximum values during the first years of operation of a landfill 2—3 years and then gradually decreases in the following years.
Thus more attention was focused on studying the hydrogeology of the area so as to identify the best siting of the landfill. Containment, however, poses the problem of leachate treatment. Discharge of leachate into the environment is today considered under more restrictive views.
Therefore, leachate management facilities should also last and their effectiveness be ensured over a long period of time. State-of-the-art technology is required and, with the so-called multibarrier concept, it is the waste to be dumped itself that forms the most important barrier.
The other barriers are the geological barrier of the landfill site, base sealing with an effective drainage system, and surface sealing after a landfill section has been completely filled. This can be achieved by waste avoidance, separate collection activities, recycling centers for recyclables, incineration, and mechanical—biological pretreatment of residual municipal solid waste MSW or composting of biowaste.
With regard to its properties, the waste can be separated into different fractions: a light fraction of high calorific value, in some instances also a mineral fraction and a fraction rich in organics can be gained. Some of these fractions also have reutilization potential.
The mechanical—biological pretreatment of MSW can be used within a waste management concept as a sole process or in combination with thermal pretreatment Fig. For nonbiodegradable waste and according to its potential hazard to the environment, prevention of water infiltration can be used as the main option usually by means of top sealing.
In contrast, for biodegradable waste, water input must Here, water input should be limited to the strictly necessary amount and minimization techniques should be used. The most important parameters in this regard are Stegmann et al. Quality control of materials and construction should be improved to ensure higher safety and durability. The main problems of drainage systems are proper choice of materials, clogging, durability, and maintenance.
In Figure The sealing For landfill class II, the geological barrier should comprise naturally arranged, slightly permeable bedrock several meters thick. The surface of the base sealing system must be formed in the manner of a roof profile.
Perforated pipes collectors , additionally capable of being rinsed and monitored, must be provided for the collection and discharge of leachate. The leachate must be channeled by means of free flow into drainage shafts that must be installed outside the dumping area. Today, according to the increasingly restrictive limits for wastewater discharge, complicated and costly treatment facilities are required.
The first Table Anhang Rahmen-AbwasserV, Current treatment facilities for the treatment of leachate mainly consist of several treatment methods to meet the limiting concentrations for the effluent. Typical combinations are shown in Figure Methods and combinations of methods often used for leachate treatment Ehrig et al. On the other hand, little is known about the leachate composition of later phases of the landfill, and the basis for making good estimates is rather weak.
The purpose was to describe the present stage of stability of landfills of different ages, their corresponding emissions, and the future development of emissions.
The main focus of the research program included long-term experiments in test lysimeters that were carried out to predict emissions that the solid waste in old landfills will release in the future. The test system ensured that the typical landfill phases, such as the acid phase and the stable methane phase, took place in sequence in the reactor. Choosing appropriate milieu conditions enabled the researchers to achieve an enhanced biologic degradation process.
By this means, the maximum emission potential represented by gas production and leachate load were determined within reasonable periods of time Heyer et al.
The range of emissions in the water phase that can occur in the landfill in the future was based on experiments in four LSR lysimeters. The BOD5 concentrations were very low as expected, because almost all waste samples were in the stabilized methane phase when the tests began. However, the decline of nitrogen in the leachate occurred more slowly, because a higher portion of organic compounds became hydrolyzed during the LSR test period. One reason was the specific conditions of each landfill site, e.
Another reason was the high water exchange rate in the LSR tests that was used to simulate accelerated conversion, mobilization. However, the possible future development of emissions is discussed below. The time course of emissions can be described with an exponential function. With the idealized conditions in the LSR test devices and the setting of a water balance, which was approximately times higher than at the landfill, periods TE can be estimated, until a limiting value CE is reached.
According to German standards for COD in the leachate, the estimation results in a period of 80— years, with a mean of years, until the limiting concentration of mg O2 L—1 is reached. Chloride shows similar periods. All investigations and tests point to nitrogen as the component with the longest period of release of relevant concentrations into the leachate phase: years on average may be necessary until a concentration of 70 mg L—1 is reached Heyer, The plausibility of these estimates is difficult to judge.
Each landfill has a different water balance, which can vary with the seasons or change because of surface covers, lining systems, or damage to these technical barriers. Then the question arises of how to positively influence the emission behavior of municipal solid waste deposits in such a way that the duration and extent of aftercare measures can be reduced.
For this purpose, two principal in situ stabilization methods can be used, depending on the boundary conditions of landfills and old deposits Fig. Likewise, short circuit currents and preferred seepage paths must be avoided by using suitable measures. Various technical methods are available for use with regard to water infiltration into the landfill body. At the same time, the effect of the infiltration plants on existing surface sealing systems or on systems that are yet to be installed is of great importance.
The choice of infiltration system is additionally determined by the quality of the infiltration medium see above and the quantity to be infiltrated. Common to all sites is the ultimate target: the controlled reduction of emissions and of the resultant risk potential of leachate within a relatively short period of time with the goal of economical site closure, aftercare, and securing measures Heyer et al.
The basic technical concept of aeration consists of a system of gas wells, through which atmospheric oxygen is fed into the landfill body via active aeration in such a way that aerobic stabilization of deposited waste is accelerated.
Simultaneously, the low-contaminated waste gas is collected and treated in a controlled manner by means of other gas wells. The increased carbon conversion during in situ aeration therefore leads to faster stabilization of organic substances. The aftercare phase is not considered complete after aeration has been terminated, but aftercare expenses are significantly reduced, since costly leachate purification measures can be terminated earlier.
If leachate percolates directly into the underground, as sometimes occurs in old deposits lacking sealing and drainage systems for the collection of leachate, the polluting effects would be considerably lower. In situ aeration is planned to operate for a period of 2—4 years under average landfill conditions. Meanwhile, results and experience concerning the operation of stabilization measures are available for several sites for a period of 2—3 years Heyer et al.
From the outset of aeration in April , a considerable decrease in the nitrogen contamination can be seen after one year of stabilization, in spite of several deviations. Barber, C. Belevi, H. Christensen, T. Statusseminar, Wuppertal , pp. Ehrig, H. Heyer K. Heyer, K. Proceedings Sardinia , Christensen, T. Proceedings Sardinia Symposium , Christensen, T.
Robinson, H. Stegmann, R. According to Tchobanoglous et al. Municipal solid waste is usually assumed to include all community wastes residential, commercial, institutional, construction and demolition, and municipal services and does not include industrial and agricultural sources.
Although municipal solid waste is only a relatively small fraction of the total amount of solid waste generated, proper management is essential for the control of disease vectors and for protection of the environment. In the United States, about 1.
The per capita generation rate is about 2 kg 4. EPA, b. These rates have vastly increased over the past 30—40 years, but are now starting to level off or even slightly decrease Fig. Generation rates in the United States are considerably higher than generation rates in European countries. EPA, a. Environmental Biotechnology. Because of recycling efforts, the net generation rate has been decreasing Fig. Net generation is the amount of solid waste remaining from the total amount generated after materials such as newspaper, glass, and aluminum have been recovered by recycling activities.
Municipal solid waste is a heterogeneous mixture of the materials that society uses. The standard unit for reporting waste generation is mass. However, mass data are of limited value for certain applications such as landfill design, since average landfill requirements depend on the volume of waste. In addition to the original density of any materials making up the solid waste mixture, the volume also depends on how much the waste has been compacted Table The comparative percentages of various components of the waste stream are variable.
Composition varies geographically and is also influenced by efforts in source reduction and recycling Table In summary, large amounts of municipal solid waste are generated, and the waste is diverse in nature.
These wastes must be managed for the control of disease vectors and for protection of the environment. Component Density kg m—3 Residential In compactor truck In landfill normal In landfill well compacted Baled Integrated solid waste management, according to Tchobanoglous et al.
Integrated solid waste management refers to the complimentary use of a variety of waste management practices to safely and effectively handle the municipal solid waste stream with the least adverse impact on human health and the environment. The United States Environmental Protection Agency has adapted a hierarchy in waste management, which can be used to rank management actions U. EPA, The hierarchy Fig. Source reduction is at the highest level, and landfilling is at the lowest level.
Certain materials cannot be reduced at the source, recycled or transformed and are therefore landfilled. However, the percentage is decreasing Table Unfortunately, land disposal was often not properly conducted. Rather than disposal into well-engineered and operated landfills, solid waste was merely buried in uncontrolled dumps. In addition, there was no distinction between municipal solid waste and hazardous waste — both were placed in these dumps. This often resulted in an adverse impact on the environment.
In fact, many of the sites listed on the National Priority List of the United States Environmental Protection Agency are abandoned dumps or orphaned landfills. A diagram of the potential impacts of improperly constructed dumps Fig. As of result of the problems from improperly constructed dumps, new federal regulations were promulgated. A summary of the U.
The cost of landfilling has greatly increased because of the new federal regulations Fig. Average tipping fees increased greatly after passage of the RCRA. At the same time, many old landfills have been closed, often because they were causing environmental damage. Although the number of landfills has decreased, the trend is to build larger landfills often regional , which are often owned by private businesses Denison et al.
In landfills, solid waste is disposed of in thin layers that are compacted to minimize volume and then covered usually daily with a thin layer of material usually soil to minimize environmental problems. Intermediate cover is usually placed on the top and exposed sides of the compacted solid waste. The covered compacted material is called a cell.
A series of adjacent Fig. Item Applicability Requirement — all active landfills that receive MSW after October 9, — certain requirements also apply to landfills that received MSW after October 9, , but were closed within 2 years — certain exemptions for very small landfills — some requirements are waived for existing landfills — new landfills and landfill cells must comply with all requirements Location — airport separation distances of 1.
A lift is usually 3—3. The bottom lift is placed on the bottom liner usually a composite of clay and a flexible membrane and a leachate collection and removal system. A landfill eventually consists of several vertical lifts and is 15—30 m tall. The landfill cap is placed on top of the top lift and is a combination of soil and synthetic materials. A schematic diagram of selected engineering features of a modern sanitary landfill is shown in Figure The design of a modern sanitary landfill focuses on the prevention of leachate and gas migration.
Vents and collection systems ensure that any gas produced is captured and then recovered, flared, or dissipated in the atmosphere. The landfill cap is designed to prevent precipitation from entering the landfill.
Liners prevent contamination of the subsurface. Leachate collection and removal systems prevent a buildup of hydraulic head on the liner. Note, however, that the strategy of complete entombment of municipal solid waste is somewhat controversial. Many believe that, even though landfills may be carefully designed and operated, all landfills will eventually leak. Subtitle D require- Fig.
Wet-cell design and operation also increased the methane yield in earlier years, which made gas recovery more feasible and presented the potential for reuse of the physical property of the landfill Dension et al. The three common configurations for landfills are area, ramp, and trench.
The area configuration involves constructing a landfill above ground, and the trench configuration involves excavation. The ramp configuration is a variant of the area configuration, as it is built above ground, but on a slope.
The rate and extent of gas generation are influenced by numerous factors but are controlled primarily by the products of microbial reactors in the landfills. Typical constituents of MSW landfill gas are shown in Table Methane and carbon dioxide are the principal gaseous products.
Smaller amounts of nitrogen, oxygen, hydrogen and trace compounds many of which are volatile organic compounds; VOC can also be found in landfill gas. Some of the trace gases, although present in small amounts, can be toxic and may present risks to public health Tchobanoglous et al. The occurrence of significant quantities of VOC is associated with older landfills, which accepted industrial and commercial wastes containing VOC.
In newer landfills, the disposal of hazardous wastes is not allowed, and thus the concentrations of VOC in the landfill gas are low. Gas migration is controlled by landfill caps, vents, and recovery systems or flaring systems. Leachate is formed when water passes through the landfilled waste materials. Leachate is a mixture of organic and inorganic, soluble and colloidal solids. It includes the products from decomposition of materials, as well as soluble constituents leached from the landfilled materials.
Leachate generation rates are determined from the amount of water contained in the original material and the amount of precipitation that enters the landfill. Other factors include climate, site topography, final cover material, vegetative cover, site operating procedures and type of waste in the landfill.
Landfill leachate characteristics vary widely from season to season and from year to year, as well as from one landfill to another.
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