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How OWTSs Using Aerobic Treatment Work

Learn about the treatment processes, components of an OWTS using aerobic treatment, the role of aerobic and anaerobic processes, and the functioning of an aerobic treatment unit system in Texas.

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How OWTSs Using Aerobic Treatment Work

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  1. How OWTSs Using Aerobic Treatment Work Texas AgriLife Extension Sevice

  2. Overview • Treatment Processes • Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal • What is a Flow Equalization Tank?

  3. Aerobic Treatment Unit System

  4. Wastewater Treatment Processes • Oxygen state • Aerobic vs. Anaerobic • Processes • Physical • Chemical • Biological

  5. Aerobic vs. Anaerobic Processes (???) • Aerobic • Aerobic bacteria require O2 to live and grow • Aerobic treatment processes require O2 to proceed • Common condition in soil treatment, media filters, MATUs • Anaerobic • Anaerobic bacteria grow in absence of free oxygen,O2 • Anaerobic treatment processes do not use oxygen, but consumption of items, breaks oxygen bonds Ex. SO4, NO3 • Common condition in septic tanks, processing tanks, and usually any saturated environment

  6. Juvenile Rotifers Feeding on Rod-Shaped Bacteria pH 7.04 DO 1.2 ppm

  7. Large Rotifers Attached to Aerobic Treatment Media Feeding on Bacteria & Organic Nutrients pH 6.94, DO 4.54 ppm

  8. Mite on Aerobic Treatment Media pH 6.94, DO 4.54

  9. Aerobic Treatment Unit System for a Residence

  10. ATU, Disinfection and Spray Distribution System Components • Septic/Trash tank • Aerobic Treatment • Air Supply • Clarification • Sludge Return • Disinfection • Pump tank with pump and controls • Spray field

  11. Septic / Trash Tank

  12. Septic/Trash Tanks • Most common treatment system: • Water tight tanks. • Anaerobic Treatment. • Most common treatment device. • Septic tank: Minimum of two compartments • Trash tank: Typically smaller with one compartment • Some systems do not have a trash tank.

  13. Two-Compartment Septic Tank

  14. Septic Tank Treatment Process • Physical separation processes – • Settling of heavy materials – sludge layer • Floating of lighter materials – scum layer • Clear zone (clear layer) • Effluent screen to assist in trapping solids (septic tank) • Time is the main requirement to allow separation to occur • Detention time: • Septic tank - 2-3 days • Trash tank – 1 day • Distance between inlet/outlet baffles is critical • Calm conditions to prevent mixing in the tank • Anaerobic digestion and storage of materials until the tank is pumped

  15. Aerobic Treatment Aeration Chamber

  16. Aerobic Treatment Process • Aerobic microbes digest solids • Organic matter + O2 = CO2 + H2O + new cells • Sludge accumulates in tank • Extended aeration • High DO, Long detention, Low Food/Microorganisms ratio • Organic matter to microbes, microbes eat each other, result in sludge

  17. Suspended Growth • Aerobic microbes free swimming in the aeration chamber • Mixing in the chamber mixes the microbes and the wastewater contaminants • Extended aeration to limit biomass wasting

  18. Submerged Attached Growth/Fixed Film Media • Media is submerged in the aeration chamber • Microbes are attached to the media • Effluent is circulated through the media thus passing contaminants by the microbes • Extended aeration to limit biomass wasting

  19. Suspended Growth Configurations • Should be three chambers/tanks. • Single tank with three compartments. • Multiple tanks. • May combine aeration and clarification chamber with divider

  20. Attached Growth Configurations • Most have three chambers • May be a separate media filled insert • May have media placed in the aeration chamber • Check manufacturer literature

  21. Air Supply

  22. Aeration of Wastewater • Air is 21% oxygen • Oxygen must transfer to wastewater for DO • Quantity of oxygen transferred directly related to BOD removal • Mixing of sewage

  23. Aspirator/Aerator • Vacuum pulls air into the water • Spinning shaft or impeller causes the vacuum • Limited resistance

  24. Compressors • Greater pressure • Lower air flow • Two distinct types of compressors • Rotary • Linear • Air inlet • Housing - cover Rotary Linear

  25. Compressor Air Flow Rotary • Rotary compressor - Relatively straight increase in flow with a decrease in pressure • Linear compressor – rapid decrease with increasing pressure • Flow drops with resistance to air flow • Must have the correct compressor to have the correct air flow Linear

  26. Blowers • Greater air flow • Lower pressure • Air inlet screens/filters • Air flow discharge from unit • Larger pipe • Air flow stops sharply • Cannot operate under higher pressure

  27. Air Distribution Lines • Minimize friction loss in the distribution lines: • Proper pipe diameter • Reasonable distance between aerator and aeration chamber • Minimize number of fittings (changes in direction) in the line.

  28. Air Diffusion Perforated Pipe Porous Stone Diffuser

  29. Clarification

  30. Clarification • Process occurs in a “clarifier” • Clarification is the process were the microbes, cell waste and biomass settle out of the water. • Sludge blanket in the bottom and a clear zone below the discharge point

  31. Vertical Settling Chamber • Calm Environment • Particles of Sufficient size and mass to settle • Flow dependent • Upward flow rate must be less than the settling rate V = Q/ A

  32. Configurations • Separate chamber with no extra filtration • Cone inserted into aeration chamber • Many have sloped walls • Added tertiary filter or screen in clarifier • Filtration through socks placed in the aeration chamber • Added filtration improves quality but increases maintenance

  33. Flow Equalization Tank

  34. Controlling Flow from a Residence • Owner controls water usage to match clarifier capacity • No large water using devices • 500 gpd ATU has a max of 42 gph without flow equalization • Or Install larger capacity system

  35. Flow Equalization/Surge Tank Concepts • Moderate Flow • Daily fluctuations • Weekly fluctuations • Down stream components • Function more effectively • May allow decrease size • Timer controls dosing to ATU

  36. Flow Equalization/Surge Tank Sized based on Peak Flow

  37. Incorporating Flow Equalization • Modify the treatment train by adding components • Add an additional tank between the trash tank and aeration chamber • Upsize trash tank to full size septic tank, add pump with timer controls to dose ATU

  38. Sludge Return

  39. Sludge return • Settled solids passing into a previous treatment chamber • Passive system • Settled solids passing through the bottom opening • Most common method • Active system • Settled solids blanket below the outlet baffle

  40. Disinfection

  41. Disinfection, not Sterilization The goal of disinfection is to rid the wastewater stream of organisms capable of causing infection Sterilization is freeing the wastewater stream of ALL LIFE.

  42. Chlorine • Destroys target organisms by chemical oxidation of cellular material. • Some organisms are resistant to low doses of chlorine • Oocysts of Chrytosporidium parvum • Cysts of Endamoeba histolytica • Cysts of Giardia lamblia • Eggs of parasitic worms

  43. Chlorination Considerations • Chlorine is an oxidizer. • Need clean water (low BOD, low TSS): chlorine is not “stolen” to oxidize organic matter. • Chlorine reacts with ammonia to form chloramines. • Chloramines are not as effective as hypochlorous acid and hypochlorite ion for disinfection. • Interferences: BOD, TSS, Humic Materials, Nitrite, pH, Iron, manganese and hydrogen sulfide

  44. Dosing Dose = Concentration x Time • Increasing either dosage or contact time, while decreasing the other, can achieve the same degree of disinfection. • Breakpoint- the process where sufficient chlorine is added to the system to obtain a free chlorine residual

  45. Caution • People should be trained to properly handle and work with chlorine products • High risk • Exposure • Handling • Corrosive • Unstable • Be careful where stored!!!!!!

  46. Tablet Chlorination • Tablet chlorinators generally have four components: • Chlorine Tablets. • A tube that holds the tablets. • A contact device, which puts the chlorine tablets into contact with the wastewater. • A storage reservoir, usually a pump tank where the water is stored before it is distributed.

  47. Typical Chlorine Tablets • Wastewater tablets- Calcium Hypochlorite • Basic compound – high pH • Swimming pool – Trichlorocyanuric acid • Acidic compound – low pH • Hazard to mix acids and bases • Must use products in accordance with label

  48. Residential Liquid Bleach Chlorinator • Reservoir • Delivery of chlorine • Vacuum/suction • Pump • Dose volume • Mixing with effluent

  49. Residential Liquid Chlorination • Flow passes through aspirator developing a vacuum or through a pump to draw a dose of chlorine. • Tubing delivers chlorine dose to aspirator or pump • Control volume of chlorine • Mixing of chlorine with effluent in pump tank

  50. Ultraviolet Light Disinfection Units • UV light destroys microorganisms by altering their genetic material and / or retarding their ability to reproduce

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