Waste Water Treatment

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Waste Water Treatment by Mind Map: Waste Water Treatment

1. Efficiency of treatment

1.1. Biochemical Oxygen Demand (BOD)

1.1.1. Old and rather inaccurate test

1.1.2. Biologically relevant

1.1.3. Determined by taking a water sample and diluting and aerating it well to saturate the water with dissolved oxygen (DO). Placing it in a sealed bottle and incubating in the dark at 20 degrees

1.1.4. BOD value is determined by measuring the residual oxygen (BOD= amount of oxygen consumed by microbes in the space of time)

1.1.5. Measures sewage strength because amount of oxygen consumed is ~ proportional to the amount of biodegradable matter present

1.1.6. takes too long so more a retrospective analysis

1.1.7. Incubated in the dark to minimize contribution of photosynthetic bacteria

1.2. Chemical Oxygen Demand

1.2.1. involves the oxidation of sewage with strong chemical oxidising agents in an acidic solution and heat

1.2.2. carrying out titrations/colormetrics to determine how much of the oxidising agent has been used

1.2.3. Two chemicals can be used

1.2.3.1. Potassium dichromate made up in concnetrated H2SO4. Mixture is boiled for 2 hrs. Chemical titration is then executed with ferrous ammonium sulphate to determine how much potassium dichromate remains

1.2.3.2. Permanganate Value (PV)

1.2.3.2.1. known amount of sewage is added to known amount of potassium permanganate in diluate H2SO4. Sample stands for 4hrs at room temp. Followed by titration

2. Activated sluge

2.1. Biological flocs

2.1.1. Biological flocs -suspended biofilms which are made up of complex population of living an dead microorganisms, their debris, extracellular polymeric substances and organic material

2.1.2. Flocs are heterogeneous, diverse in microbes in high cell density which are naturally selected and considered as catalysts of the process

2.1.3. aerobically respire C compounds

2.1.4. Filamentous microorganisms form a backbone within the floc

2.1.5. too much filamentous fungi and yeast form bulking sluge which doesn't want to settle in the clarifier

2.1.6. too much filamentous fungi and yeast form bulking sluge which doesn't want to settle in the clarifier

2.2. Formation of activated sluge

2.2.1. 1. Food (biodegradable C) to Microorganism ratio is high

2.2.2. 2. Short initial lag phase followed by exponential phase

2.2.3. 3. Saprophytic organisms grow most rapidly. They are most dominant (mixture of aerobes and facultative anaerobes)

2.2.4. 4. As the number of saprophytic microorganisms increase hey provide food for predatory protozoa (free-swimming ciliates)

2.2.5. 5. Lots of activity. Large quantities of C removed and Oxygen consumed. Poor quality effluent and sluge won't settle

2.2.6. 6. C becomes limiting for the large numbers of cells. Low F/M ratio

2.2.7. 7. Growth rates decline and numbers are reduced by predator protozoa

2.2.8. 8. Energy in the system becomes less so organisms that bump into each other clump together

2.2.9. 9. C removal has slowed down and Oxygen consumption too. Effluent quality improves though due to clumping

2.2.10. 10. Size of flocs increase as less energy and C is available.

2.2.11. 11. Microbes continue to grow at a slow rate using lipids, stored materials, cell walls and organisms that lyse to live off. Effluent quality improves

2.2.12. 12. Free swimming ciliates get replaced by stalked ciliates which attach to the large flocs

2.2.13. 13. Eventually, the sluge itself is eaten by rotifers and other higher organisms

2.2.14. 10. Size of flocs increase as less ergy and C is available.

2.2.15. 10. Size of flocs increase as less ergy and C is available.

3. Operational Variables

3.1. Sluge age

3.1.1. Average length of time activated sluge spends in the aeration tank = sluge resistance time (SRT)

3.1.2. HIGH SRT

3.1.2.1. High sluge age favours the slow growers

3.1.2.2. lower F/M ratio

3.1.2.3. more in the stationary phase

3.1.2.4. Generally have larger flocs

3.1.2.5. Oxidize a larger fraction of the organic matter all the way to CO2 and H2O. -> less cell matter

3.1.2.6. Require more O2 (higher oxygen demand)

3.1.2.7. Older systems are less responsive to changes in influent conditions

3.1.2.8. lower F/M ratio

3.1.3. LOW SRT

3.1.3.1. Low sluge age (SRT) may result in wash-out of the slow growers

3.1.3.2. higher F/M ratio

3.1.3.3. tend to be in the log phase

3.1.3.4. more active bacteria

3.1.3.5. able to adapt to change faster

3.1.4. How can sluge age be contolled?

3.1.4.1. Recycling of activated sluge

3.1.5. How can sluge age be contolled?

3.1.6. HIgh sluge age (SRT) may result in wash-out of the slow growers

3.2. Hydraulic retention time

3.2.1. Retention time= Volume of vessel / flow rate

3.3. Aerobic and anerobic phases

4. Carbon Removal

4.1. Main component of sweage

4.2. Most common strategy is to supply the sewage with Oxygen to encourage the growth of aerobic microbes

4.3. Polysaccharidases, proteases and lipases digest the suspended solids and large macromolecules into soluable C compounds

4.4. This is then used as C and enregy sources

4.5. Some C is respired into the atmosphere and the rest will be converted into cell mass.

4.6. Most common strategy is to supply the sewage with Oxygen to encourage the growth of aerobic microbes

5. Nitrogen removal

5.1. Bacterial Nitrification

5.1.1. Nitrosomonas

5.1.2. Nitrobacter

5.1.3. Slow growers -sluge age

5.1.4. do not remove C

5.1.5. consume oxygen - AEROBIC

5.1.6. If nitirc acid is produced due to there being a lot of NH3 in the effluent then it can be neutralized with carbonate since nitrifying bacteria need a pH above 6

5.2. Bacterial Denitrification

5.2.1. Uses NO3 (produced by nitrification) as final e- acceptor

5.2.2. Dissimilative nitrate reduction

5.2.2.1. Nitrate reductase A

5.2.2.2. membrane bound enzyme

5.2.2.3. allows NO3 to be used in the terminal step of ETC in place of O2

5.2.3. Assimilative nitrate reduction

5.2.3.1. Nitrate reductase B

5.2.3.2. cytoplasmic enzyme

5.2.4. Requirements

5.2.4.1. An organic e- donor

5.2.4.1.1. can be sewage or other

5.2.4.2. absence of oxygen - ANAEROBIC

6. Phosphate Removal

6.1. Certain organisms accumulate poly-P storage polymer when stressed

6.2. poly-P can serve as an energy source

6.3. Removal is dependent on the subjection of the activated sluge to first anaerobic followed bu aerobic conditions

6.4. orthophophate is released during anaerobic stage and then taken up WITH the influent organic phosphate during the aerobic stage

7. Trickling filters

7.1. One system with specific zones within the biofilm

7.2. diffusion-limited

7.3. Nitrification (aerobic) so outer layer

8. Introduction

8.1. What is waste water?

8.1.1. Includes domestic sewage, grey water and liquid industrial waste

8.1.2. undefined composition

8.1.3. contains large amounts of biodegradable organic matter

8.2. Problem with untreated waste water?

8.2.1. It is able to serve as a C and energy source which can support the growth of many organisms

8.3. Products of aerobic metabolism

8.3.1. cell mass

8.3.2. organic C (CO2)

8.3.3. Organic or inorganic N (NO3-)

8.3.4. Organic or inorganic S (SO4-)

8.4. What happens during a sewage outfall?

8.4.1. Oxygen demand will exceed natural aeration capacity and water becomes anaerobic

8.4.2. Lack of oxygen- fish and plants die

8.4.3. Increased turbidity from microbial growth prevents light penetration in water - plants die

8.4.4. Lack of oxygen- fish and plants die

8.4.5. Lack of oxygen- fish and plants die

8.5. Products of anaerobic metabolism

8.5.1. more toxic and offensive

8.5.2. gasses such as H2

8.5.3. Organic C (organic acids, CO2 and CH4

8.5.4. Organic and inoganic N (NH4)

8.5.5. Organic and inorganic S (H2S)

8.6. Goal of waste water treatment

8.6.1. reduce organic and inorganic materials to a level that no longer supports microbial growth and to eliminate other potentially toxic materials