Learning Module: Environmental Engineering (Week 11) PDF

TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES VISAYAS Capt. Sabi St., City of Talisay, Negros Occidental College of Automation and Control LEARNING MODULE Subject: (ENVIRONMENTAL ENGINEERING) (Week 11) COMPILED BY:...

TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES VISAYAS Capt. Sabi St., City of Talisay, Negros Occidental College of Automation and Control LEARNING MODULE Subject: (ENVIRONMENTAL ENGINEERING) (Week 11) COMPILED BY: ARON J. LEONORAS 2022  2 LEARNING GUIDE Week No.: 11 TOPICS: INDUSTRIAL AIR EMISSIONS CONTROL, AGRICULTURAL POLLUTION CONTROL LEARNING OUTCOMES 1. Introduction to Industrial Air Emission Control 2. Characterizing the Air Stream 3. Equipment Selection 4. Equipment Design 5. Special Topics in Industrial Air Emission Control 6. Introduction to Agricultural Pollution Control 7. Obstacles to Agricultural Pollution Control 8. Agricultural Water Pollution Control Principles 9. Point Source Controls 10. Non-point Source (NPS) Controls 11. Land Application of Wastes 12. Codes of Practice for Land Application of Animal and Other Wastes 13. Agricultural Air Pollution Control EXPECTED COMPETENCIES The students will be able to learn the basic knowledge of gaseous pollutants and particulate contaminants in the air stream brought about by burning fossil fuels in power plants and manufacturing plants; especially the physical and chemical characteristics of this air stream; the type and design of equipment needed to reduce the effects of air pollution under specific applications, with important discussions on handling and control of harmful pollutants such as sulphur and NOx. Also, agricultural pollution control is importantly summarized with emphasis on understanding the obstacles and conditions of control mitigation, and the nature of this pollution itself in order to handle and properly dispose of this agricultural water and air pollution. A. INDUSTRIAL AIR EMISSIONS CONTROL Introduction Industrial air emissions are regulated, so as to keep the air quality acceptable to national and international standards. Industry achieves these standards by utilizing a variety of air emission abatement technologies. The waste stream is often ‘air’ which may contain a variety of gaseous and particulate contaminants of different densities, particle sizes and volatility, etc. For instance, coal-fired power plants generate a waste gas stream containing gases such as oxides of nitrogen and sulphur and particulates such as fly ash from the burnt coal.  3 The design of air emissions abatement equipment is a difficult and complex task. It requires not only a knowledge of the physical and chemical properties of the stream but also an appreciation of the vast array of equipment available and how this equipment operates. The equipment itself must, in operation, consistently comply with very tight performance criteria. There are three general options in air emissions abatement: ⚫ Waste minimization (of raw materials, a product or a by-product) ⚫ Recovery and recycling ⚫ Destruction or disposal Characterizing the Air Stream Wastewater treatment relies on the microbiological treatability or chemical composition of the liquid waste stream to effect purification. Water purification manipulates the chemistry of a waste stream to purify it. However, the purification of a gaseous stream involves manipulating the physical, chemical and, sometimes, the biological properties of the stream. The reason for this is because a vast choice of abatement equipment exists today, each manipulating a different property of the gas stream. For example, condensers utilize the relationship between a liquid and its vapor. It is well known that if an air stream, saturated with steam at a temperature of, say, 60oC, is cooled down, the steam will then condense. The principle of operation of an industrial condenser is the same. Cyclones, on the other hand, separate particles from a gas by utilizing the fact that their densities are different. To choose and design the most cost-effective equipment the engineer must therefore characterize the stream fully. The most important measurable properties of a stream include: ⚫ The stream composition ⚫ The stream flowrate ⚫ The stream temperature ⚫ The stream pressure Based on this information the choice of abatement equipment can be short listed. Further information which is required to make the final choice is: 1. The variability in the composition, flowrate, temperature and pressure of the stream (i.e. due to start-up, shutdown). 2. The explosivity of the stream. This is especially important where VOCs are concerned, e.g. petrol. Properties such as the flash point, auto-ignition temperature and the concentration at which it forms an explosive mixture with air, known as the lower explosive limit (LEL), should be known. 3. The corrosiveness of the stream in both liquids and gases, e.g. if SO2 combines with water vapor and condenses, it forms corrosive sulphuric acid (H2SO4). With regard to each constituent of the stream, some, or all, of the following information may be required: ⚫ Molecular formula and weight  4 ⚫ Freezing and boiling point ⚫ Solubility ⚫ Adsorptive and absorptive properties ⚫ Chemical behavior/reactivity ⚫ Heats of condensation, adsorption and solution ⚫ Particle size distribution and densities of any solids ⚫ Odor threshold ⚫ Health Effects ⚫ pH ⚫ Vapor pressure curve Equipment Selection Equipment selection first considers the type of compounds which are required to be removed. These may be considered under three broad categories: ⚫ VOCs, defined as ‘Any organic substance or mixture which can release vapor to the atmosphere and with the potential to cause environmental effects at low atmospheric levels’, (Chemical Industries Association - CIA, 1992). ⚫ Inorganic compounds ⚫ Particulate matter The stream contents will determine the type of equipment which may be used in any application. Below are the major types of equipment in use today. Figures 1 and 2 show typical air pollution control devices. ⚫ Incinerators ⚫ Adsorbers ⚫ Condensers ⚫ Filters ⚫ Scrubbers ⚫ Absorbers ⚫ Various particle collection devices Figure 1 Scrubbers for Air Pollution Control  5 Figure 2 Air Pollution Control Cyclone Separator Equipment Design Condensation Condensers transfer heat from a vapor stream to a cooling stream. This removal of heat cools the gases present and condenses some, or all, of the vapor. They can be of the direct or indirect contact type. In the former, the cooling stream is contacted directly with the vapor stream while in the latter, contact is effected through a solid barrier. It is the latter type that is most commonly used today. They are traditionally of the shell and tube variety but other designs such as spiral condensers are becoming very popular. A schematic of a shell and tube exchanger is shown in Figure 3. The schematic shows a horizontal condenser with the coolant on the tube side. Figure 3 Schematic diagram of a condenser  6 Absorption In an absorber, the gas, rich in the compound which it is required to remove, enters the bottom of a tall narrow column down through which liquid is poured. The liquid selectively absorbs the compound, thereby producing a purer gas stream from the top of the column, while liquid rich in the substance removed from the gas is removed from the bottom of the column. This is known as simple absorption and its main disadvantage is that it generates a liquid waste stream. An example of this is flue gas desulphurization (FGD) which is discussed in succeeding topics. Adsorption Adsorption is most commonly used to recover compounds from very dilute streams. It can be used in a number of different ways including fluidizing the adsorbent, rotating it through the vapor or passing the gas stream through a fixed bed of carbon. The latter is by far the most common method employed and is examined here. It consists of two units, through one of which the gas stream is passed while the other is being regenerated. Filtration A filter comprises a solid porous media which allows only gas and very small particles to pass through it. Gas filters normally consists of either bags or cartridges through which the gas passes. The construction of a typical gas filter is shown in Figure 4. The performance of a filter is characterized by two parameters: ⚫ Particle collection efficiency ⚫ Pressure drop Both are a function of the filter media, through the latter is also a function of the filtration velocity. Figure 4 Construction of a typical bag filter unit  7 Impingement Separators Because of the density difference between solids and gases, in laminar flow their streamlines are different if the direction of flow is changed. This fact is frequently exploited to separate a solid particle from a gas stream, usually by suddenly changing the direction of flow of the gas stream. Scrubbers Scrubbers, also known as wet collectors, employ a liquid to remove particles from a gas stream. In use it is either the liquid droplets which collect the particles or liquid that is poured continuously on to a porous packing and the particles collected by both the liquid droplets and adhesion to the liquid on the packing. Figure 5 shows the construction of a basic scrubber. The use of packing allows a smaller tower to be used but the pressure drop is higher (thereby increasing inefficiency). The pressure drop through a spray tower is typically between 0.25 and 0.5 kPa. For a packed bed it is between 0.25 and 2.0 kPa. The liquid to gas ratio in a spray tower is typically between 1.3 and 2.7 L/m3. In a packed tower it is normally between 0.1 and 0.5 L/m3 (Corbitt, 1989). Figure 5 A typical spray tower Electrostatic Precipitators These are used to remove very small liquid and solid particles from a gas stream and are used mainly in the utility industries. They operate by generating a corona between a high- voltage electrode, usually a fine wire, and a passive earthed electrode, such as a plate or pipe. Particles passing through such an electric field are ionized by ions migrating from the discharge to the collector electrode, with whom they collide. These particles then drift towards the collector electrode to which they are held by electrostatic attraction. The particles are removed from the collector by either a water spray or ‘rapping’ it periodically. The collectors can either be flat plates or tubular units. Usually, a number of discharge electrodes will hang.  8 Odor Abatement Odors are not easily characterized or quantified and therefore represent a particular design problem. Control of odors is best achieved at source. This involves identifying the cause of the odor instead of the odor itself and then changing the operating conditions, methods, design, or raw materials to eliminate or minimize the odor. Failing this, a number of options exist, such as: ⚫ Adsorption, usually onto activated carbon ⚫ Incineration ⚫ Absorption/Scrubbing ⚫ Use of masking agents (all too common) ⚫ Biofiltration (soil, peat beds, biological scrubbers) Special Topics Flue Gas Desulphurization There are two main types of flue gas desulphurization (FGD) systems. One generates a residue which must be disposed. The other converts the sulphur dioxide (and sulphur trioxide) to a marketable product. Approximately 95 to 97 % of the world’s FGD systems are of the former type, i.e. non-regenerable. The limestone-gypsum process is the more economical to run and accounts for 40 % of the installed systems. In the longer term it is most likely that regenerable and catalytic processes will emerge as the desirable method of desulphurization. This is for two reasons. Firstly, the quantities of sludge that are required to be landfilled are growing with the increasing numbers of FGD plants. This is combined with the fact that the cost of landfilling is likely to increase substantially with increased monitoring and control requirements. Secondly, the public are unlikely to accept that a non-regenerable waste is the best practicable environmental option where a number of regenerable stream options also exist. Most flue gas desulphurization processes center around an absorption tower in which the sulphur dioxides are chemically absorbed into an alkaline liquid stream. They are further classified as either wet or dry, depending on the phase in which the reaction occurs. Most FGD systems in use today are wet non-regenerable processes. NOx Removal The term NOx implies two major oxides, nitrogen oxide (NO) and nitrogen dioxide (NO2). In combustion, NO is the dominant of the two, NO2 mainly a downstream derivative of NO. There are three main mechanisms of NOx production from combustion processes: ⚫ From the reaction of N2 in the fuel air with oxygen at the high temperatures of a burner chamber ⚫ From nitrogen existing in the fuel ⚫ From reactions of fuel-derived radicals with N2 ultimately leading to NO To control NOx emissions effectively, the dominant formation mechanism must be known. There are a number of ways of then controlling the NOx emissions.  9 B. AGRICULTURAL POLLUTION CONTROL Introduction The primary objective of agricultural enterprise is the optimization of profit. In the past, maximizing output has been the most expedient way of achieving this objective; farmers have accomplished this by modifying the agro-ecosystem. Modifications over recent decades include increased use of inorganic fertilizers and greater use of chemicals for controlling weeds and other pests, both resulting in improved plant yields and quality. Other changes include larger animal herds, higher stocking rates, increased use of feed concentrates and improved animal performance from breeding programs. Modified animal housing designs and the use of high-density, confined animal production practices are other changes in agricultural practice. The results of these changes have been higher concentrations of nutrients, organic matter and chemicals on modern farms compared to those operating a few decades ago. Consequently, the pollution potential of modern farms is significantly greater than that of the more extensive farming systems of previous decades. In addition, agricultural land is now used as a receptor of non-farm organic wastes, such as food processing wastes and municipal wastewater sludges. The need to control pollution from agriculture is more obvious, now that efforts begun in the 1970s to reduce pollution from industries and municipalities have taken effect. This topic introduces concepts for developing and evaluating effective agricultural pollution control strategies. The primary emphasis is on controlling water pollution. Obstacles to Agricultural Pollution Control Several unique characteristics of the agricultural industry make pollution control difficult. Agricultural production occurs under circumstances that are quite different from those common to most industries required to control pollution. Firstly, the basic medium for almost all agricultural production (i.e. the soil) is a non-homogeneous biological system, with physical, chemical and biological characteristics that may vary widely, even within a few meters. Other industries take elaborate quality control precautions to minimize variability in their production base (e.g. machinery, raw products and facilities). Secondly, unlike manufacturing industries that are based in confined areas under controlled conditions (inside factories, for example), land-based agricultural production systems involve large land areas. Land-based agricultural production systems are open to the effects of uncontrollable and largely unpredictable climatic events, which add variability to production conditions. In contrast, other production industries strive for closely monitored and regulated production environments (e.g. ventilation, relative humidity and lighting levels) and predictable, if not controllable, supplies of raw inputs. Finally, but importantly, production of basic (not processed) agricultural products involves small profit margins. Increased production costs associated with pollution control are very difficult to transfer to consumers, partly because of farm price support mechanisms often operated by national governments and international trading blocks. From an environmental management perspective, the intensification of agricultural production and its conduct in the open and variable environment present many difficulties. Production inputs, which may become pollutants, such as nitrogen (N) and phosphorous (P), cannot be collected and removed once they are added to the production system. Instead, these  10 inputs become integrated into the production system and follow through natural cycles. This situation is dramatically different from that posted by, for example, a manufacturing facility where there is greater control over the flow of inputs if production (or pollution) problems arise. From a waste treatment perspective, the agricultural scenario is also quite different from that encountered at manufacturing plants and most urbanized areas. Wastes can be collected from these sources and diverted to a common location (wastewater treatment plant) where highly trained individuals can manage the unit treatment operations under controlled conditions to yield an effluent of a given quality. The ‘collection and treatment’ approach of pollution control is neither economically nor technologically feasible for land-based agricultural systems because collection often is not practical (e.g. runoff from farm fields) and their occurrence often is unpredictable (i.e. weather dependent). Finally, although farmers are highly trained and experienced in agricultural production, they are not experts in pollution control. Agricultural Water Pollution Control Principles Controlling agricultural pollution requires an interdisciplinary approach that combines the expertise of engineers, agronomists, soil scientists and, in some situations, biologists. Pollutants of primary concern from agriculture include nutrients (N and P), organic matter (BOD5), pathogens (bacteria), synthetic organic chemicals (pesticides) and, in arable areas, eroded soil (TSS). Agricultural pollution derives both from point (i.e. well-defined) sources around the farmyard, such as slurry tanks, and from non-point (i.e. ill-defined or diffuse) sources, such as fields or portions of fields. The same physical, chemical and biological principles used to control industrial and municipal sources of pollution are applicable to agricultural sources but must be applied in the context of an open, uncontrolled and variable environment instead of a controlled treatment system. Further, the techniques used to minimize pollution risk from the two types of agricultural pollution sources are different, although a total quality management (TQM) approach or systems approach is a basic requirement for the success of all methods. Point Sources Key point sources of pollution in agricultural systems are the farmyard itself (uncovered exercise or feeding areas, soiled water storage tanks), facilities used to store animal wastes (slurry pits and tanks, dungsteads), facilities for collecting and storing silage effluent (pads and tanks) and facilities used for storing and handling pesticides (storage sheds, filling and rinseate collection areas). These sources pose threats to the environment because they concentrate large amounts of potential pollutants in a relatively compact volume and area. Minimizing pollution risks from point sources depends on properly designing, constructing, and managing the facilities. From an engineering perspective, ‘properly designed and constructed’ facilities are those that satisfy their intended purpose at minimum cost consistent with accepted factors of safety. The intended purposes of controls for most agricultural point sources of pollution are to contain pollutants and prevent their uncontrolled release to the environment. The basic requirement for such facilities is adequate waste storage capacities, structural integrity and careful site locations. Many countries have research-based design criteria for these facilities, which are specified by appropriate government agencies. Accepted construction practices must be followed to guarantee that the facilities will perform as designed. Just as important, however, operators (farmers) must utilize, or manage, these facilities properly to achieve design objectives, i.e. follow a TQM approach to pollution control.  11 Non-point Sources Non-point sources of agricultural pollution are the land areas on which agricultural production is accomplished. Although these ‘fields’ can be identified by physical dimensions, the precise origin of pollutants from these areas cannot be clearly identified, especially within the context of an entire catchment. The diffuse nature of this type of pollution gives rise to its definition as ‘non-point source’ (NPS) pollution. Precipitation excess and snowmelt (creating surface runoff and interflow) are the transport agents of non-point source pollutants to surface waters; drainage water through the soil profile is the transporting agent for pollutants to groundwater. Wind can also transport non-point source pollutants to surface waters, but, except in special circumstances, the relative importance is small compared to water. In general, it is not feasible to collect runoff, interflow or drainage water so that entrained pollutants can be removed. Thus, controlling agricultural non-point source pollution depends largely on preventing pollutants from leaving the production system (i.e. the soil). The edges of fields and bottom of the root zone are convenient demarcations for land-based agricultural systems. Since most agricultural pollutants are initially production inputs (e.g. nutrients), keeping these constituents within the confines of the root zone and field edge is economically, as well as environmentally, sound. Point Source Controls Site Selection The proximity of any source of pollution to receiving waters is a major determinant in the relative pollution risk posed by the source. Site selection is thus the primary step in designing facilities that will contain agricultural pollutants. Codes of good agricultural practice typically give guidance for sitting point source pollution controls. As a rule, these facilities should be located as far as practicable from surface waters and down gradient from nearby (50 to 75 m) groundwater wells. In addition, facilities should be placed where surface and subsurface soil conditions are suitable (low organic matter, low shrink-swell potential, good compactability and adequate bearing capacity, deep water table, etc.), as determined by soil borings or test pits. The number and depth to which borings are made should be consistent with providing enough information on which to base a safe structural design. Where animal waste lagoons are proposed, a site investigation should confirm that subsurface soil conditions will prevent excessive leakage of the lagoon contents or that unsuitable conditions can be ameliorated by site modification (such as incorporation of low-permeability soils) or by the use of synthetic liners. Sites with creviced bedrock, karst limestone, shallow or garvelly soils, and soils with high water tables pose special challenges for a safe design of any facility that is to contain agricultural pollutants. Sizing of Structural Facilities The underlying purpose of agricultural point source pollution control facilities is to contain potential pollutants (e.g. dirty or soiled water, animal wastes, pesticide rinseate). Achieving this objective is dependent on providing structurally sound facilities with adequate capacities  12 to hold the pollutants (and rainwater in the case of uncovered structures) until they can be further managed, typically by application to land. Design capacities are determined by the rate at which the pollutants are generated and the required storage period. The duration of required storage periods are often specified by local regulations and typically are related to the availability of suitable periods during which wastes can be applied to land. If the facilities are to afford some degree of pollutant treatment, such as anaerobic lagoons, sizing of the facilities also depends on biochemical principles. While design principles are similar to those used for wastewater treatment facilities, the characteristics of agricultural wastes dictate that a somewhat different application for these design procedures be used (Barth, 1985; Merkel, 1981). Design and Construction Most agricultural point source pollution control facilities are reinforced concrete or steel structures that must be designed according to accepted engineering standards and procedures. The corrosive nature of many agricultural pollutants (such as animal wastes and silage effluent) requires that special precautions be taken to select resistant construction materials and follow accepted construction practices. Construction of most facilities should be supervised by a construction engineer or other competent inspector. Care must be exercised to ensure that foundations are sufficient to prevent differential settling of facilities that would weaken structural integrity or cause leakage. Design guidelines for most types of agricultural point source pollution control facilities are widely available (Midwest Plan Service, 1985; ASAE, 1990; Department of Agriculture, 1985; MAFF, 1991). Design and construction specifications typically are available from local or national government agricultural agencies for facilities constructed using government financial assistance. Information about climatic factors (predominant wind speed and direction, air and soil temperatures, precipitation amounts and patterns) can be obtained from national or local meteorological offices and agricultural research/advisory agencies. Non-Point Source (NPS) Controls Agricultural non-point source pollution controls are managerial, structural or vegetative practices. Regardless of type, the objective of all techniques is to prevent or reduce the availability, release or transport of agricultural pollutants to receiving waters. Agricultural NPS pollution control practices can be viewed as on-site controls. The term ‘best management practices’ (BMPs) is often used collectively for these pollution control techniques. ‘Best’ implies that an individual practice or combination of practices is the most effective and practicable control technique for a particular combination of farm characteristics and pollution problems. Practicability is an absolutely essential component of BMPs to control agricultural non- point source pollution. Agricultural production practices at any given geographic location are the result of evolution and adaption over centuries to the interactive influences of climate, soils and topography. NPS pollution control techniques must be suited to these same influences and be economically viable as well. Designing BMPs for a given farm requires a field-by-field examination of soils, slope lengths, steepness and proximity to groundwater or surface waters, as well as whole-farm evaluation of the type of enterprise, financial resources available and  13 level of managerial expertise. The techniques for making such evaluations are given elsewhere (Hudson, 1981; Novotny and Chesters, 1981; Schwab, et al., 1993). Land Application of Wastes Land application of wastes is the most economical, practical and environmentally sustainable method for managing agricultural wastes, especially animal wastes. Application of agricultural wastes to the land recycles valuable nutrients and organic matter into the system from which they originated. Land application can also be an effective component of management strategies for other organic wastes, such as wastewater treatment sludges and food processing wastes. When designed and managed ‘properly’, systems for the land application of wastes do not pose undue threats to environmental quality. One aspect of proper design and management involves applying wastes at the correct rates, at the correct time, using the correct methodology. Hydrologic and agronomic principles govern the design of land application systems. Rate of Application - Organic From a waste treatment perspective, the soil system can be viewed as a fixed film biological reactor which, due to an immense microbial population, has a large - although finite - waste assimilative capacity. For the soil system to function effectively, wastes must be applied to land at rates that do not exceed either the instantaneous or long-term assimilative capacity of the soil system. The instantaneous assimilative capacity of a soil system is related most closely to an ability to degrade organic matter aerobically, thereby avoiding problems resulting from septic soil conditions (odors and plant damage). This in turn is dependent on the aeration status of the soil (a function of soil texture and structure and moisture content), temperature and the organic strength of the waste. Organic strength of wastes is measured by BOD5, BODult, and/or COD, as appropriate for a specific waste. Rate of Application - Other Parameters Hydraulic Hydraulic loading influences the instantaneous assimilative capacity of soil when liquid or semi-solid wastes are applied. Application rates that exceed the infiltration rate of the soil will result in surface ponding, surface runoff and the consequent transport of pollutants. Likewise, application rates that exceed the storage capacity of the soil profile will result in leaching and, potentially, the transport of dissolved pollutants downwards and out of the root zone. Infiltration rates decrease with time, approaching as a limit the saturated hydraulic conductivity of the soil. Characteristics of the applied liquid, the tendency of the soil surface to crust or seal, soil moisture content and the presence and type of vegetation all influence the infiltration rate. Infiltration capacity, sometimes referred to as the final infiltration rate, is the rate at which liquid will enter the soil surface and is limited only by soil factors (soil structure and pore size distribution). As with all soil characteristics, actual values for infiltration capacities can vary widely making on-site soil investigations imperative for a complete design.  14 In addition, wastewaters usually behave differently to clear water, resulting in infiltration capacities that may in some cases be as little as 10 % of clear water values. Nutrients Whereas the short-term or instantaneous assimilative capacity of the soil system is most closely related to organic and hydraulic loadings, the long-term assimilative capacity of a waste application site is more aligned with nutrient application rates. (For wastewater treatment sludges, heavy metals may determine long-term loading rates). For environmental sustainability, wastes should be applied at rates that supply the nutrient needs of the crop produced (and, where appropriate, the buildup of soil fertility). Unfortunately, organic wastes rarely contain the major plant nutrients (N, P and K) in the relative proportions that are required by plants. In addition, the N content of organic wastes (especially animal wastes and sewage sludges) tends to be ‘unreliable’ because it must be mineralized from organic form to be useful to plants. Mineralization rates are variable and dependent on uncontrollable factors such as weather. For these reasons, inorganic fertilizers are often used in combination with organic wastes to meet the nutrient needs of crops. Analysis of both the soil (to determine fertility status) and the organic wastes (to determine nutrient contents) is imperative to minimize pollution potential and the need for inorganic fertilizers. Limiting Factor Successful land application of wastes depends on many factors as described above. One limiting factor will, however, ultimately govern the utilization of wastes on land. Designs may be limited hydraulic loading, organic loading, nutrient loading or, in the case of wastewater sludges, metal loadings. If nutrient loading is the limiting design criterion, local circumstances will dictate whether the design must be based on nitrogen or phosphorous application rates. Generally, where surface waters must be protected, nutrient loadings should be based on phosphorous, especially if catchment soils are prone to runoff. Conversely, if groundwater aquifers are to be protected, nutrient loadings should be based on achieving nitrogen balances. Application methodology The techniques by which wastes are applied to land are dictated by the waste characteristics, the production system and sometimes by regulatory considerations. Wastes that are 15 % or more in dry matter content are considered solid wastes and are land applied by flail-type application machinery. Wastes with between 4 and 15 % dry matter are considered to be slurries and can be land applied as liquids using specialized application equipment. Wastes with less than 4 % dry matter are dilute liquids and can be satisfactorily land applied using irrigation equipment. Whatever the application technique, care must be exercised to assure that the application equipment is calibrated and operated to give the target application rate. Codes of Practice for Land Application of Animal and Other Wastes Animal wastes have been applied to the land as a source of nutrients and organic matter for all of recorded history. Not surprisingly, codes of practice have been developed to guide the utilization of these wastes to meet agronomic and environmental goals. These codes also offer appropriate guidance for the land application of other organic wastes. A concise summary of a typical code of practice is given in Table 17.8. Other codes of practice are available elsewhere (e.g. MAFF, 1991; MAFF, 1992).  15 Table 17.8 Typical code of good practice for slurry spreading 1. Apply slurry at rates that take account of crop nutrient requirements and soil fertility levels. 2. Use a regular program of soil and slurry testing to determine nutrient needs and supplies. 3. Apply slurry earlier rather than later in any crop growing season. 4. Avoid applying slurry on wet or waterlogged soils, on frozen or snow-covered soils, and on areas near surface waters and groundwater wells. 5. Always check weather forecasts before applying slurry; avoid spreading if precipitation predicted likely to produce runoff within 48 hours. 6. Use calibrated application equipment and operate it according to specification for achieving desired waste application rates. 7. Avoid direct contamination of surface waters and groundwater by maintaining sufficient safety margin (buffer zones or unsaturated soil respectively) between these resources and the slurry application site. 8. Where possible, avoid leaving bare soil over winter. 9. Take all reasonable steps to minimize odor emissions (incorporate wastes immediately, if possible; do not apply slurry when prevailing winds are in the direction of nearby residences; use low-trajectory instead of high-trajectory splash plates). ‘ Agricultural Air Pollution Control As discussed in the previous topic, the major air pollutants from agriculture are odorous emissions related to the storage and handling of animal wastes. There are three main areas on farms with which odors are generally associated: the housing/yard area, the waste treatment/holding area and the waste utilization area. Odors in the housing and yard areas originate from animals themselves (body odors), from feed materials, and from decomposition of wastes excreted by the animals. Odors from the waste treatment/storage area are compounds derived from the incomplete anaerobic, microbial breakdown of organic matter in the wastes (carbohydrates, proteins and fats). At the waste utilization area, odorous compounds that developed during waste storage/treatment and handling escape to the atmosphere as the wastes are applied to the land. Most odor complaints from the public are associated with the land application portion of the waste management process. Controlling Odors from Housing/Yard Areas Practices associated with good animal husbandry facilitate odor control from housing and yard areas. For facilities designed for continuous waste removal, maintenance of the mechanical apparatus to assure efficient waste removal is essential. Providing adequate ventilation for humidity and temperature control in buildings that house animals should disperse odors at non-objectionable levels in the outside atmosphere. Keeping yards clean of animal wastes and spilled feeds will not only minimize odor generation but will also control flies and other pests, as well as contribute to the appearance of an efficiently operated enterprise. Controlling Odors from Waste Treatment/Holding Areas For aerobic lagoons, maintaining sufficient oxygen in the lagoons to assure aerobic conditions at all times is essential for odor control, as well as effective waste treatment. Likewise, maintaining anaerobic conditions in anaerobic lagoons is equally important, as is achieving environmental conditions in the lagoon that facilitate acid-forming and methane- forming bacteria to work in tandem. Assuming lagoons of either type are designed (i.e. sized) correctly (Barth, 1985; Merkel, 1981), loading the lagoons with wastes at rates that avoid ‘shocks’ to the bacterial populations and provide sufficient energy supplies to the bacteria results in near-odor-free operation.  16 Controlling Odors from Waste Utilization Areas Reductions in odor emissions associated with land spreading are achieved by reducing the concentrations of odorous compounds in the air following land-spreading. This can be accomplished readily by changing the method of waste application. Only approximately 1 % of the odorous emissions emanate from the actual spreading of wastes; 99 % of the odors are emitted after the wastes are applied. Consequently, incorporating wastes immediately after application normally controls odors to non-objectionable levels. For grassland systems where waste incorporation is not feasible, odor reductions can be achieved by using band-spreading or shallow injection application equipment. In addition, codes of good practice should be followed when applying wastes to land. Recommended practices include avoiding spreading at times when the risk of causing odor nuisance to the public is high (e.g. on weekends and holidays), avoiding spreading when prevailing winds are in the direction of neighboring housing and population centers and avoiding the use of application techniques that tend to atomize wastes or otherwise disperse them into the atmosphere. PROGRESS CHECK Essay. Total: 100 points. Write your answers clearly. 1. What is the difference between organic and inorganic compounds? (10 points) 2. Classify the following compounds as either organic, inorganic, or particulate: (20 points) a. Dry cleaning agents, b. Petrol, c. Ammonia, d. Boiler flue gases. 3. Under what circumstances should incineration be considered as a method of air emissions control? (10 points) 4. Why would urea be preferable to ammonia as a method of controlling NOx emissions? (10 points) 4. Explain why sulphur and NOx are present and are harmful pollutants in industrial air emission. (15 points) 5. Discuss the obstacles to agricultural pollution control. (15 points) 7. An activated sludge effluent treatment plant is experiencing complaints from surrounding area. The plant is a secondary treatment plant. Discuss the possible sources of odors and the ways to control them. (20 points) REFERENCES American Society of Agricultural Engineers (ASAE) (1990). Standards, Engineering Practices and Data, 37th Edition. American Society of Agricultural Engineers.  17 Barth, C. L. (1985). ‘The national design standard for anaerobic livestock lagoons’, in Agricultural Waste Utilization and Management: Proceedings of the 5th International Symposium on Agricultural Wastes, American Society of Agricultural Engineers. Chemical Industries Association (CIA) (1992). Guidance on the Management of VOC emissions. Chemical Industries Association. Corbit, R. A. (1990). Standard Handbook of Environmental Engineering, 1st Edition. McGraw-Hill. Davis, M. L. and S. J. Masten (2009). Principles of Environmental Engineering and Science, 2nd Edition. McGraw-Hill. Department of Agriculture (1985). Guidelines and Recommendations on Control of Pollution from Farmyad Wastes (revised). Department of Agriculture and Food. Hudson, N. (1981). Soil Conservation, 2nd Edition. Cornell University. Kiely, G. K. (1997). Environmental Engineering. McGraw – Hill. MAFF (1991). Code of Good Agricultural Practice for the Protection of Water. Ministry of Agriculture, Fisheries and Food. MAFF (1992). Code of Good Agricultural Practice for the Protection of Air. Ministry of Agriculture, Fisheries and Food. Merkel, J. A. (1981). Managing Livestock Wastes. AVI Publishing. Midwest Plan Service (1985). Livestock Waste Facilities Handbook, 2nd Edition (MWPS- 18), Midwest Plan Service. Novotny, V. and G. Chesters (1981). Handbook of Nonpoint Pollution. Van Nostrand Reinhold Co. Schwab, G. O., D. D. Fangmeier, W. J. Elliot, and R. K. Frevert (1993). Soil and Water Conservation Engineering, 4th Edition. J. Wiley.