Environmental Management Water resources and pollutants

Transcription

1 Università di Pisa Environmental Management Water resources and pollutants Prof. C. Nicolella Università di Pisa 1

2 Università di Pisa Technological water cycle ENVIRONMENT fresh water fresh water water treatment drinking water untreated discharge treated discharge use waste water wastewater treatment 2

3 Università di Pisa Water quality Selfpurification Water quality Freshwater Drinking water Wastewater Treated water 3

4 Università di Pisa Water Pollution Water Pollution = degradation of water quality (biological, chemical, or physical) Judged according to the use of the water Pollutant = any substance that in excess is known to be harmful to life Pollutants discharged by a source enter the environment where they undergo physical, chemical and physical processes which change their concentration and position in the receiving body. The rate at which the concentration and the position of the pollutants changes depends, among other factors, on: Physico-chemical properties of the pollutant. Type and conditions of receiving body. 4

5 Università di Pisa Point sources Domestic sewage and industrial wastes collected by a network of pipes and channels and conveyed to a single point of discharge into the receiving water. Municipal sewage: domestic sewage into which industrial wastes are also discharged. Point source pollution can be reduced through waste minimisation and wastewater treatment prior to discharge. 5

6 Università di Pisa Non-point sources Non-point Source = diffuse, intermittent pollution Influenced by: Land-use Hydrology Native vegetation Topography Geology Image: Lake SWCD Difficult to control, contains multiple pollutants 6

7 Università di Pisa Environmental Pollution: general mechanism transport transport Source Environment Target emission 1 st Level Impact Vector dispersion dilution transformation 2 Level Impact Vector effects 7

8 Università di Pisa Contents 1 Water resources 2 Water pollutants 3 Water quality 4 Wastewater treatment 8

9 Università di Pisa 2. Water pollutants 2.1 Physical characteristics 2.2 Chemical characteristics 2.3 Biological characteristics 9

10 Università di Pisa Water pollutants Suspended solids Biodegradabile organics Nutrients Pathogens Priority pollutants Refractory organics Heavy metals Dissolved inorganics May lead to sludge deposits and anaerobic conditions when untreated wastewater is discharged in the aquatic environment. Composed mainly of proteins, carbohydrates and fats. Commonly measured in terms of biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Their biological stabilisation can lead to the depletion of natural oxygen in water bodies and to the development of septic conditions Both nitrogen and posphorous, along with carbon, are essential nutrients for growth. When discharged to the aquatic environment, they can lead to the growth of undesirable aquatic life. They can also lead to groundwater pollution. Communicable diseases can be transmitted by pathogenic organisms in wastewaters. Organic and inorganc compounds selected on the basis of their toxicity, carcinogenicity, mutagenicity or teratogenicity. Tend to resist conventional methods of wastewater treatment, e.g. phenols, surfactants, pesticides. Added to wastewater from commercial and industrial activities. e.g. calcium, sodium, sulphate added to the original water supply as a result of water use 10

11 Università di Pisa Oxygen-Demanding Waste Bacteria in water consume organic matter and use oxygen in the process Too much bacteria in the water causes oxygen shortage so fish and other organisms die Urban sewage is prime breeding ground for bacteria 11

12 Università di Pisa Pathogenic Organisms Microscopic Disease-causing: cholera, typhoid, hepatitis, dysentery Monitor: E. coli Found in human or animal waste E. coli 12

13 Università di Pisa Nutrients Phosphorus & nitrogen used in fertilizers, detergents, sewagetreatment plants Results in rapid growth of algae which: covers water surface blocking light from reaching plants below consumes oxygen, killing off organisms The green color along the coast is an algal bloom- Fish die Image: The SeaWiFS Project, NASA/Goddard Space Flight Center, & ORBIMAGE 13

14 Università di Pisa Oil Image: Survivors of the Exxon Valdez Oil Spill Exxon Valdez, Alaska March 1989 Worst oil spill in U.S. history Ran aground >250,000 barrels of oil spilled area was one of most pristine and ecologically rich in world Short-term impacts: Many seabirds and mammals were killed Fishing and tourism disrupted Long-term impacts:??? 1999 High line of oil at Herring Bay Image: NOAA Office of Response & Restoration 14

15 Università di Pisa Heavy Metals Lead, mercury, zinc, and cadmium metals can dissolve and become incorporated into plants, crops, and thus animals and humans Sources: some natural, others burning fossil fuels, incinerating waste, processing metals It is believed that human activity has increased mercury levels in the atmosphere 2-3x and 1.5% per year Particles in the atmosphere get rained out and soak into soil 15

16 Università di Pisa Priority pollutants The U.S. Environmental Protection Agency has identified approximately 129 priority pollutants, both organic and inorganic. Priority pollutants are selected on the basis of their known or suspected Carcinogenity Mutagenicicty Teratogenicity High acute toxicity 16

17 Università di Pisa Thermal Pollution Thermal pollution = artificial heating of water Caused primarily by hot-water emissions from industrial operations and power plants Problems: Contains less oxygen Favors different species May increase growth rates of undesirable species May benefit some desirable species especially in winter 17

18 Università di Pisa Classification Water quality is determined by: physical chemical biological characteristics, which define the suitability for discharge in a water body or for treatment in a treatment plant. 18

19 Università di Pisa Physical chracteristics solids temperature odor color turbidity 19

20 Università di Pisa Solids Solids: matter remaining upon evaporation at C. Settleable solids: those settling to the bottom of a coneshaped container (Imhoff cone) in a 60 min period. Suspended solids: those remaining upon filtration at 0.45 mm. Dissolved solids: those passing a 0.45 mm filter. They consist of colloidal and dissolved solids. Solids may be further classified on the basis of their volatility: Fixed solids: the fraction remaing upon oxidation at C. Volatile solids: the fraction oxidised at C. 20

21 Università di Pisa Classification of solids settleable solids Imhoff cone sample evaporation total solids filtration evaporation evaporation suspended solids dissolved solids muffle oven muffle oven VSS FSS VDS FDS VSS VSS 21

22 Università di Pisa Chemical characteristics organic matter oxygen demand oils and fats priority pollutants inorganic matter ph Nutrients gases dissolved oxygen 22

23 Università di Pisa Organic matter proteins carbohydrates fats oils and greases surfactants volatile organic compounds pesticides and agricultural chemicals 23

24 Università di Pisa Oxygen demand One of the most important water quality parameters is the amount of dissolve oxygen (DO) present. Saturation values: 8-15 mg L -1, depending on temperature and salinity. Minimum required for a healthy fish population: 5-8 mg L -1. Oxygen demanding-wastes are oxidised in the receiving body of water, reducing the amount of DO. As DO drops: Fish and other aquatic life are threatened. Undesirable odors, tastes and colors reduce the acceptability of water as a domestic supply and/or for recreational uses. Oxygen demanding wastes are: Biodegradable organic substances. Biodegradable inorganic compounds. Oxygen demand in a wastewater is measured as: COD: the amount of oxygen required to chemically oxidise the waste. BOD: the amount of oxygen required to chemically oxidise the waste. 24

25 Università di Pisa COD Oxygen required to oxidise all organic compounds in (waste)water. Relatively rapid test (3 h) based on the measurement of the oxygen equivalent of organic matter that can be oxidised by a strong oxidising agent (potassium dichromate). COD tests are performed at high temperature and it may result inaccurate for the determination of volatile organic compounds. 25

26 Università di Pisa 10 Recalcitrant 60 Readily biodegradable soluble 100 Readily hydrolysed COD in wastewater 110 Slowly hydrolysed 20 Heterotrophs 60 Nitrifiers suspended 40 Recalcitrant COD = 400 mg L -1 26

27 Università di Pisa BOD Oxygen required by aerobic microorganisms in the wastewater for the degradation of the organic substrate. While COD is a measure of the total carbon, BOD tests determine the biodegradable fraction of organic carbon in a wastewater. COD= BOD (ultimate) COD= BOD 5 Higher values of these ratios (up to 4-6) characterise industrial wastes containing scarcely biodegradable organic compounds, which may not suitable for biological treatment The BOD test has the following limitations: A high concentration of active, acclimatised bacteria is required; Preatreatment is needed when dealing with toxic substances; The effects of nitrifying organisms must be reduced; Only the biodegradable organics are measured The test does not have stoichiometric validity after the soluble organic matter has been used; An arbitrary, long period of time is required to obtain result: a five-day period may or may not correspond to the complete degradation of soluble organic matter. 27

28 Università di Pisa BOD 5 BOD 20 C 10 C days Biochemical oxidation is a slow process and theoretically takes an infinite time to go to completion (ultimate BOD). The incubation period is usually 5 days at 20 C (BOD 5 ). The ultimate BOD is estimate from the measurement of the BOD 5 assuming a first order kinetics (with rate contant of 0.23 d -1 ) 28

29 Università di Pisa Fats and oils Fats: contributed to domestic wastes by foodstuff residues, they are among the more stable of organic compounds and are not easily decomposed by bacteria. Oils: tend to float on water and coat surfaces, causing problems to biological action and maintenance of equipments. 29

30 Università di Pisa Surfactants Large organic molecules that are slightly soluble in water and cause foaming in wastewater treatment plants and in the receiving waters into which effluents are discharged. During aeration of wastewater, surfactants collect on the surface of air bubbles and create a stable foam. 30

31 Università di Pisa Volatile organic compounds (VOCs) Organic compounds with boiling point < 100 C and/or saturation pressure > 1 mmhg at 25 C. Often used as solvents in industrial processes. VOCs are of great concern because: A number of them are listed as priority pollutants. In spite of their low water solubility, they tend to accumulate in aquifers as oil phase. Due to their high volatility, they are very mobile in the environment. 31

32 Università di Pisa Pesticides (VOCs) A range of complex organic chemicals that kill organisms that humans consider undesirable: Insecticides Herbicides Rodenditicides Fungicides Pesticides are toxic to most life forms (priority pollutants). They result mainly from agricultural runoff. 32

33 Università di Pisa Nitrogen Total nitrogen includes: Organic nitrogen; Ammonia; Nitrites; Nitrates. Ammonia Bacterial oxidation and reduction Nitrites Hydrolysis and bacterial decomposition Ammonia manufacture Bacterial oxidation and reduction Death Fecal matter Urine (urea) Fertilisers for plants Atmospheric N 2 Bacteria and algae Fertiliser manufacture Nitrates Organic N (animal proteins) Animal food Organic N (plant proteins) Fertilisers for plants 33

34 Università di Pisa Nitrogen in municipal wastewater Total N 100 Ammonia 75 Organic N 25 Biodegradable organic N 75 Recalcitrant Organic N 75 34

35 Università di Pisa Phosphorus - 1 As nitrogen, phosphorus is also essential to the growth of plants and organisms. Because of noxious algal blooms that occur in surface waters, phosphorus compounds in domestic and industrial wastes discharges (and natural run off) must be controlled. The usual forms of phosphorus found in aqueous solutions include: Orthophosphate, available for biological metabolism without further breakdown. Polyphosphate, reverting to orthophosphate through hydrolysis. Organic phosphate, of minor importance in domestic wastes, can be an important constituent of industrial wastes. O O O Orthophosphate OH P OH Pyrophosphate OH P O P OH Tripolyphosphate OH O P O OH O P O O P OH OH OH O O P OH O OH OH OH Trimetaphosphate O P P O OH O OH 35

36 Università di Pisa Phosphorus - 2 Inorganic soluble phosporous results from disgregation and solubilsation of phosphatic minerals. Polyphosphates mainly derive from use of synthetic surfactants and from metabolism of living organisms. Phosphorous in municipal wastewater: Orthophosphate: 50 %. Polyphosphate: 40%. Organic phosphate: 10%. Typical phosphorous concentrations (mg/l) Municipal wastewater 3 6 Agricultural drainage water Superificial water

37 Università di Pisa Heavy metals Trace quantities of many metals (Ni, Mn, Pb, Cr, Cd, Zn, Cu, Fe, Hg) are important consituents of most waters. Many of them are classified as priority pollutants. Some of them are necessary for growth of biological life. The presence of any of these metals in excessive quantities will interfere with many beneficial use of water because of their toxicity. 37

38 Università di Pisa Growth inhibition by heavy metals Pollutants Inhibiting concentration, mg/l Carbon removal Nitrification Alluminum Ammonia 480 Silver 5 Arsenic 0.1 Boron Cadmium Calcium 2500 Cresol 4 16 Cromium VI Cromium V 50 Cyanides ,4 - dinitrophenol 150 Phenol Iron 1000 Manganese 10 Magnesium 50 Mercury Nichel Copper Sulphates 500 Zinc

39 Università di Pisa Biological characteristics Bacteria Contaminated water is responsible for the spread of many contagious diseases. Pathogens are diseases-producing organisms that grow and multiply within the host: Bacteria: cholera, bacillary disentery, typhoid and paratyphoid fever. Viruses: hepatitis and polomelytis. Protozoa: amebic disentery. Non-pathogenic bacteria are natural catalysts for oxidation of organic and inorganic compounds in surface water, groundwater and wastewater Cocci (Stafilococcus aureus) Bacilli (Escherichia coli) Spirilli Filamentous (Microtrix parvicella) 39

40 Università di Pisa Microorganisms in municipal wastewater Organism Concentration, n /ml Coliforms, total Coliforms, fecal Streptococci Enterococci Shigella present Salmonella Pseudomonas aeroginosa Clostridium perfringens Mycobacterium Present tubercolosis Protozoa Viruses

41 Università di Pisa Municipal wastewater composition Concentration Contaminants Units Weak Medium Strong Solids, total mg L Volatile mg L Dissolved mg L Suspended mg L BOD 5 mg L COD mg L TOC mg L Nitrogen mg L Phosphorous mg L Total coliforms N o L VOCs µg L -1 < >400 41