Control of Water Pollution - Assignment Example

1(a). Outline the type of water pollutants likely to be found in surface runoff and wastewater from a livestock farm and discuss the likely impacts of uncontrolled prolonged discharge of these pollutants into a stream. Globally, the livestock sector consisting of swine, poultry, dairy cattle and beef cattle farming is growing more rapidly than any other agricultural sub-sector. Many developed countries have concentrated industrial cattle farms to minimise land use. Several densely-populated developing countries in Asia e.g., China, where meat production is rising faster than any other region over the past decade, are similarly instituting factory farming (FAO Food and Agriculture Organisation of U.N., Report, 2008). A major byproduct of livestock farming is animal waste. Thus, animal husbandry leads to point source pollution. One of the major problems associated with animal farming involves the movement of excessive nutrients from manure and other byproducts to soil, water and air causing significant environmental problems. In the U.S., the production of livestock and their feedcrops transports about one-third of the nitrogen and phosphorous discharged (from all sources) into freshwater. Besides the nutrients, the other major polluting agents resulting from livestock farming are pathogens and antibiotics and hormones, fertilisers, and the pesticides used to spray feed crops. Elements present in animal waste such as nitrogen, phosphorus, potassium, and other minerals are essential nutrients for plant growth. However, the manure may run-off during rainfall and pollute the waterways if inadequately contained. Uncontrolled and prolonged discharge of animal waste into waterways can add excessive amounts of nutrients to the waterways causing excessive growth of algae or algal blooms which may be toxic and consume large amounts of oxygen when decaying, thereby reducing the dissolved oxygen concentration in water, and killing fish and other organisms through the process of eutrophication. Pathogens including protozoan parasites such as Cryptosporidium parvum and Giardia duodenalis, bacteria such as Salmonella, Campylobacter, Escherichia coli, and Listeria monocytogenes and viruses are commonly present in manure and may runoff to surface waters with the possibility of  their eventual transmission to animals and humans (USDA, United States Department of Agriculture, 2008). Animal wastes including wastewater and manure can have large concentrations of pharmaceutically active compounds such as hormones and antibiotics which could be disseminated in the aquatic environment. A build-up of these compounds on account of uncontrolled and prolonged discharge via animal waste into waterways is potentially damaging to the marine and other biota, including the human beings. Among the other major environmental impacts caused by animal husbandry are accumulation of heavy metals in high concentrations in surface and ground waters that poses a threat to the health of human beings and animals such as from pig manure which is known to contain significant quantities of copper (FAO, 1996). Acidification of the environment in the areas with intensive livestock farming due to ammonia emission is another major form of surface water pollution 1 (b). Explain how the impacts outlined in Question 1(a) can be affected by the characteristics of the stream. Stream characteristics can influence the pollutant effects to a great extent. For instance, the streamflow volumes and the rate of water movement affect both concentrations and total loads. While increased streamflow would lead to increased nutrient loadings, a reduction in streamflow can lead to increases in peak concentrations of certain nutrients (IPCC, Intergovernmental Panel on Climate Change, 2010). Temperature of the water e.g., high temperatures combined with lower summer flows produces substantial reductions in dissolved oxygen concentrations, while the amount of suspended solids and floating matter, stream bed characteristics (e.g., whether rocky/sandy/silty) will affect the impact of the pollutants mainly by influencing the residence times or chemical adsorption of the pollutants to the substrata. 1 (c). Explain how the answers to Question 1(b) above can be affected by climatic conditions. The impact of the pollutants is determined by the load applied to the waterbody, water temperature, and the volume of stream flow. The stream characteristics, in particular the physical characteristics such as flow volume and rate, temperature and suspended solids are greatly influenced by climatic conditions. For instance rain and storm events can lead to increased runoff thereby increasing the transport of nutrients while warmer and drier conditions promote mineralization of organic nitrogen and thus increase the potential supply of nitrate to the river or groundwater. Nitrates are, thus, frequently flushed into rivers under stormy conditions following prolonged dry periods (IPCC, 2010). The over-abundance of nutrients results in eutrophication of the receiving waters. Both wind and solar radiation affect the temperature of river waters. Water quality is hampered with increase in temperature since higher water temperatures cause a rise in oxygen-consuming biological activities and a fall in the saturation concentration of dissolved oxygen. 2 (a) Coagulation and flocculation The main purpose of the coagulation/flocculation process is the removal of turbidity causing suspended particles from water. Essentially, coagulation and flocculation comprise a three step process, consisting of flash mixing, coagulation, and flocculation. In practice, though, the coagulation/flocculation process as applied in the treatment plant, has only two steps i.e., the water first flows into the flash mix chamber, and then enters the flocculation basin. In the flash mixer, coagulant chemicals including primary coagulants such as alum, ferric sulfate, or synthetic organic polymer compounds that neutralise the electrical charges of particles in the water causing them to clump together, and coagulant aids (e.g., lime, bentonite etc.) that increase the density to slow-settling flocs and enhance their toughness to prevent their degradation, are added to the water followed by quick and violent mixing to facilitate even distribution of the chemicals in the water. Flash mixing typically lasts only a minute or so. If the mixing time is less than thirty seconds, the mixing of the chemicals with water will not be proper, whereas if mixed for more than sixty seconds, there is the possibility of the mixer blades shearing the newly formed floc back into small particles. Coagulation occurs following flash mixing. In the next step that is, flocculation, a gentle mixing for about thirty to forty-five minutes causes the fine particles formed by coagulation to come into contact with each other and form floc. The flocculation chamber consists of a number of compartments with decreasing mixing speeds as the water advances through thechamber to allow the formation of increasingly large floc. Much of the turbidity collects as clumps of bacteria and particulate impurities that have come together and formed a cluster or floc.  The floc will then settle down in the sedimentation basin, while the remaining floc collects in the filter. The ideal floc size is 0.1 to 3 mm.  Smaller floc will not settle, while floc of a larger size may not settle as well and may be subject to breakup in the flocculation chamber.  Turbidity is a more common problem in surface water as compared to ground water. In addition to being aesthetically unacceptable, turbidity in water contributes to difficulties of disinfection of water. Hence, treatment involving coagulation and flocculation is applied typically to surface water. Coagulation/flocculation will remove colloidal and suspended solids from water. The process also removes suspended bacteria in the water and is useful for decolourising water. 2(b). Slow sand filtration Filtration is the last process of water treatment that is used to remove any particulate matter left over after flocculation and settling, before disinfection. The sand filtration process, in general, is based on two principles, mechanical straining and physical adsorption. It is, therefore, very important to effectively carry out this step since the presence of particles in the water can hinder eradication of germs by the disinfectant. Furthermore, the large protozoan parasites (e.g., Cryptosporidium) that cannot be killed by chlorine have to be physically removed. Since the mid-19th century, slow sand filtration (SSF) has been widely employed in treatment of municipal water supplies in developing countries against water-borne disease. The efficiency of SSF depends on the particle size distribution of the sand, the ratio of surface area of the filter to depth and the flow rate of water through the filter. The finest grade sand fractions( size 0.15-0.35 mm is usually recommended) and granulated rockwool have been shown to make the most efficient media. SSF relies on both physical and biological activity in controlling the pathogens. In a slow sand filter, the filter bed consists of a medium with high surface area. The fine medium not only presents a physical barrier to the passage of suspended particles and pathogens, the medium itself can be made to be colonized by helpful, suppressive microorganisms. The advantages of SSF over other methods of water disinfestation include the low energy consumption of the process, the great adaptability in components, minimal maintenance, simple systems that can be built and installed by laymen, and economical as compared to other disinfestation methods. The SSF roughly consists of the filter bed (depth 1-1.5 m or more) consisting of a uniform fine particle sand mixture and provided with a gravel drainage system at the bottom of the filter to prevent movement of the fine sand into the filter outlet. The flow rate is controlled by a regulating tap that is connected to the filter outlet. The flow rate through the filter is maintained less than gravitational fall and monitored with the help of a flow meter. 2(c). Rapid sand filtration In contrast to SSF, Rapid sand filtration (RSF) method of cleaning the filter bed involves an increased flow rate. A rapid sand filter functions up to 40 times faster than a slow sand filter. The rapid sand filters are cleaned more often by reversing the flow of water through the entire filter bed, that is, backwashing. The filter bed in RSF consists of two layers of coarse sand (size 0.4 to 8mm) and a bottom gravel layer composed of multiple layers of successively coarser gravel (size 5 - 60mm). The gravel layer helps to maintain a consistent and diffused flow during filtration and prevents disruption of the sand layer during backwash. Apart from the gravity fed type of rapid sand filters, Upflow filters employing filtration from the bottom up and backwashing also in the same direction but with increased flow velocity, Biflow filters that employ a divided flow - upflow from the bottom and downflow from the top permitting filtration in opposite directions simultaneously, and Pressure filters in which the filter bed (sand) is enclosed in a cylindrical shell of steel or iron and the water is passed through at a pre-determined pressure. This type of filter is most useful for smaller quantities of water. 2 (d). Activated carbon adsorption Adsorption is the process by which a chemical species adheres to the surface of a solid. Activated carbon is a very good adsorbing agent because of its high surface to mass ratio. Factors that affect the rate of adsorption are particle size, surface area, pore structure, acidity (pH), temperature, and the nature of the material to be absorbed. Activated charcoal is used to remove undesirable odour and taste in drinking water, besides many carcinogenic or toxic organic compounds that are likely to be present in untreated drinking water. In water treatment, particles of the same size as the pores are adsorbed and retained by the carbon. Volatile organic chemicals, metals, and some non-polar inorganic chemicals are held strongly by the carbon. Activated carbon is generally used in two forms for water treatment, as granular activated carbon (GAC) and powdered activated carbon (PAC). PAC is more commonly used than GAC to control taste and odour in drinking water treatment. It is added directly to the water prior to coagulation and until just before the rapid sand filter. The PAC adsorbs contaminants after which it is separated by sedimentation or filtration. On the other hand, GAC can be added after coagulation and sedimentation as a layer in sand filters to remove organics from the water. Activated carbon that is exhausted after all the adsorptive sites are filled, can be regenerated by heating it at a temperature of 820 to 930o C. The main advantage of the activated charcoal adsorption is that it is very successful in the removal of Class I compounds (organic compounds that cause taste, odour and/or colour problems according to EPA classification). The disadvantages are that activated carbon is expensive, and it can become a breeding ground for microorganisms. 3(a). Identify the potential sources of pollutants from the river catchment. The potential sources of pollutants are domestic sewage, household pesticides, fertilizers and pesticides including fungicides and herbicides used in the city’s gardens and lawns, silt in surface runoff due to construction or land clearing activities, petroleum products, lead and other toxic metals from automobile discharges, and industrial wastes. 3(b). Recommend, with justification, the water quality parameters to be tested in order to determine the degree of pollution. The water quality parameters that should normally be tested include pH, dissolved oxygen, biological oxygen demand (BOD), temperature, conductivity, total dissolved solids turbidity, and discharge or flow measurements, and microbiological assays especially for faecal coliform. pH is a measure of the concentration of hydrogen ions in the water and the naturally occurring fresh waters have a pH range of 6 to 8. Testing the pH of the water is important because it affects the solubility and availability of nutrients, and how they can be utilised by aquatic organisms. Dissolved oxygen which is the amount of oxygen dissolved in water is critical to the survival of various aquatic life in streams, such as fish. Hence it is an important parameter that needs to be measured. Biological Oxygen Demand is a measure of how much oxygen is used by microorganisms in the aerobic oxidation of organic matter in the stream water. The higher the amount of organic material found in the stream, the more oxygen it uses for its breakdown, thereby depleting the amount of dissolved oxygen available to other aquatic life. Temperature is a critical water quality parameter as it directly determines the amount of dissolved oxygen that is available to aquatic organisms. E.g., water temperatures exceeding 18oC have a deleterious effect on several fish species. Conductivity measurements based on the ability of the water to conduct an electrical current, measure indirectly the ion concentration. The measurement is directly proportional to the amount of ions present. The concentration of total dissolved solids indicates the presence of nonpoint source pollution and the presence of faecal coliform bacteria in water is an indicator of the presence of disease carrying organisms in water. 3(c). Discuss any possible factors that you might have to take into consideration whilst undertaking the investigation. Physical factors such as flow velocity, volume of water, bottom contour, currents, depth, light penetration, and temperature govern the ability of a system to receive and assimilate pollution. Therefore, establishing the physical status of the river catchment in respect of the above mentioned physical parameters would be essential. 4 (a). Explain the main differences in setting effluent discharge standards for discharges to river and to ground. In-stream effluent discharge standards for rivers have to mainly reflect the assimilative capacity of the water body receiving the effluent. The purpose of the set standard is to preserve the aquatic environment at a certain specified minimum quality. The standards apply to the material being discharged to the receiving water through consideration of the dilution of the effluent inflow by the receiving water. They stipulate the quality of the effluent to be discharged as also restrict the quantity of pollutants in the effluent or recommend the desired degree of treatment. The standards for effluent discharges into the ground are set based on the properties of the soakage medium, the type of infiltration system (i.e., whether a soak pit or a drainage field), the proximity of other discharges to groundwater, the properties and structure of saturated and unsaturated aquifer pathways, the level of treatment applied to the effluent etc. 4 (b) A 75-person capacity new development is proposed with the wastewater discharged into a lowland river. The river quality is BOD 2.9 mg/l, ammonia 0.18 mg/l and phosphorus 17 µg/l. The Q95 river flow is 1500 m3/d. Suggest suitable numeric limits for the quality of the proposed discharge. The river classification scheme shown in Table Q4 is applicable to the site of the new development. On the basis of the water quality parameters provided, the lowland river quality could be described as ’high’ in accordance with the Simplified EU Water Frame Directive (WFD) Classification Standards shown in Table Q4. According to available general guidelines (UNEP, 2000), per capita production of sanitary sewage in Europe is assumed to be 200 litres per day, per capita BOD contribution to residential wastewater is 60 g/d, per capita phosphorus added to residential wastewater is 1.8 g/d, and per capita ammonia added is 0.6 g/d (all mean values). Based on these values, the total wastewater produced by the community of 75 persons would be 15000 L/d; total BOD would be 4500 g/d; total phosphorus 135 g/d; and total ammonia 45 g/d. Given that the Q95 river flow =1500 m3/d or 1500000 L/d, discharging 15000 L/d of wastewater without treatment would result in BOD = (2.9 + 2.7) = 5.6 mg/L; phosphorus = (17 + 80) = 97 μg/L; and ammonia = (0.18 + 0.069) = 0.249 mg/L. While the resulting river quality after discharge of raw wastewater would still be ‘good’ with reference to phosphorus and ammonia values, BOD value needs to be brought down further from 5.6 mg/L to Read More