《环境化学》课程PPT教学课件讲稿（英文版）Unit 14 Water Pollution-Oxygen Consuming Wastes

Water Pollution-Oxygen Consuming Wastes

Water Pollution-Oxygen Consuming Wastes

General types of water pollutants Disease-causing agents(Pathogens) .Oxvgen-consuming agents Suspended solids and sediments e Oil Radioactive substances( radionuclides) Heat(thermal pollution)

General types of water pollutants • Disease-causing agents (Pathogens) • Oxygen-consuming agents • Plant nutrients • Toxic substances – Heavy metals – Pesticides • Dissolved solids • Acids • Suspended solids and sediments • Oil • Radioactive substances (Radionuclides) • Heat (thermal pollution)

Oxygen and aquatic life Animals and plants living in an aquatic habitat depend on oxygen dissolved in the water for their survival The availability of o2 in water sets the boundary between aerobic and anaerobic life. this has implications on: Water quality Health of ecosystem Oxygen in water comes from dissolution of atmospheric 02

Oxygen and aquatic life • Animals and plants living in an aquatic habitat depend on oxygen dissolved in the water for their survival. • The availability of O2 in water sets the boundary between aerobic and anaerobic life. This has implications on: – Water quality – Health of ecosystem • Oxygen in water comes from dissolution of atmospheric O2

Dissolved oxygen 15 The amount of dissolved 14 (6600ft) oxygen(Do)depends on 1000m the temperature and the (3300ft) 12 altitude of the water level Relates to atmospheric pressure 8 6 010203040 Temperature(°C)

Dissolved oxygen The amount of dissolved oxygen (DO) depends on the temperature and the altitude of the water. Relates to atmospheric pressure

Biological oXygen demand Energy is acquired by oxidation of organic material. In his process, oXygen is required CH2O 十 02= C02+H20 12 mgC 32mg mgc 2. 7mg o2 At 20C, Do=9 mg/, therefore, only N3 4mg of CH20 can be oxidized by the o2 in a liter of water. When the concentration of organic material is high water can be easily depleted of DO Biological oxygen demand boD) is the amount of 02 in milligram) required by microorganisms to carry out the oxidation of organic carbon in one liter of water. BOD5: the oxygen consumed by microorganisms in five days

Biological oxygen demand • Energy is acquired by oxidation of organic material. In this process, oxygen is required. CH2O + O2 = CO2 + H2O 12 mgC 32mg 1mgC 2.7mg O2 • At 20oC, DO=9 mg/l, therefore, only ~3.4mg of CH2O can be oxidized by the O2 in a liter of water. • When the concentration of organic material is high, water can be easily depleted of DO. • Biological oxygen demand (BOD) is the amount of O2 (in milligram) required by microorganisms to carry out the oxidation of organic carbon in one liter of water. – BOD5 : the oxygen consumed by microorganisms in five days

BOD: example problem What is the bod of water in which 10 mg of sugar is dissolved in a liter How does this compare with the o2 solubility at 20C?

BOD: example problem What is the BOD of water in which 10 mg of sugar is dissolved in a liter? How does this compare with the O2 solubility at 20oC?

Oxygen-consuming wastes Organic waste materials released into the water can rapidly deplete dissolved oxygen When water is overloaded with organic materials, oxygen-consuming(aerobic) bacteria proliferate As a result, Do is consumed more rapidly than it can be replaced from the atmosphere When Do< 5ppm, fish start to die If do drops further invertebrates and aerobic bacteria will be unable to survive In the absence of do, anaerobic bacteria take over to decompose organic material The water begins to smell unpleasant

Oxygen-consuming wastes • Organic waste materials released into the water can rapidly deplete dissolved oxygen. • When water is overloaded with organic materials, oxygen-consuming (aerobic) bacteria proliferate. • As a result, DO is consumed more rapidly than it can be replaced from the atmosphere. • When DO<5ppm, fish start to die. • If DO drops further, invertebrates and aerobic bacteria will be unable to survive. • In the absence of DO, anaerobic bacteria take over to decompose organic material → The water begins to smell unpleasant

organIc waste 是器 Direction of flow 12 Clean water: Decomposition: Anaerobic Clean water: Clean water Low oxygen decomposition Low oxygen tolerant fish Clean water tolerant fish: Anaerobic Gar, Carp organisms. Bass, Perch.Gar, Carp ediment-dwelling worms Bass. Perch Crayfish, Clam Sediment Bacteria fungi Crayfish, Clan dwelling Sediment-dwelling Distance downstream DO variation with the distance from organic waste charge point

DO variation with the distance from organic waste charge point

Sources for organic wastes Human and animal sewage Industrial waste from paper mills, tanneries, and food-processing plants

Sources for organic wastes • Human and animal sewage • Industrial waste from paper mills, tanneries, and food-processing plants

Typical BODs for wastes from various processes Type of discharge BOD (mg O2/iter waste water) Domestic sewage 165 All manufacturing 200 Chemicals and allied 314 products Paper 372 Food 747 Metals 13

Typical BODs for wastes from various processes Type of discharge BOD (mg O2/liter waste water) Domestic sewage 165 All manufacturing 200 Chemicals and allied products 314 Paper 372 Food 747 Metals 13