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?
Treatment Processes involved in the system. We will focus on the treatment processes within the system. This presentation will not discuss operation and maintenance but introduce how the treatment system works. We will discuss O&M later.
Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal
What is a Flow Equalization Tank? Allow the option to control the flow of the wastewater

3. Aerobic Treatment Unit System
The different components of an aerobic treatment unit:
Trash tank
Aeration tank with a clarifier
Chlorinator
Pump tanks
Spray Heads

4. Wastewater Treatment Processes
Oxygen state
Aerobic vs. Anaerobic
Processes
Physical
Chemical
Biological
Wastewater treatment is achieved by processing effluent in various treatment steps to remove contaminants. Several wastewater treatment processing methods fall into one of two main categories based upon their oxygen state: aerobic and anaerobic. Oxygen is needed for aerobic treatment to take place and aerobic bacteria need oxygen to grow and live. Anaerobic bacteria grow and live in the absence of oxygen. (NOTE: Another category of bacteria which can be supported in aerobic or anaerobic conditions is referred to as facultative. Facultative processes will not be covered.) The processing methods necessary for wastewater treatment depend on the constituents present in the effluent and the level of treatment desired.
Wastewater treatment processes are categorized as:
Physical
Chemical
Biological

5. Aerobic vs. Anaerobic Processes (???)
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
Specific organisms needed for specific treatment steps.
Aerobic:
Need free oxygen
Use aerobic microbes to break down the waste.
Common condition in soil treatment, media filters, MATUs
Anaerobic:
Common condition in septic tanks, processing tanks, and usually any saturated environment
Grow in limited to no oxygen environments
Give off oxidized compounds which have an odor

6. Juvenile Rotifers Feeding on Rod-Shaped Bacteria pH 7.04 DO 1.2 ppm
Wastewater sample under a microscope.
Early stage Rotifers feeding on a sea of rod-shaped Bacillus. pH DO 1.2ppm
Rod-shaped and free-swimmer bacteria are absorbing nutrients and are being consumed by fast moving higher micro-organisms
These are the organisms that you are growing in your system. Its important to keep them healthy.
Juvenile Rotifers Feeding on Rod-Shaped Bacteria pH 7.04 DO 1.2 ppm

7. Rotifers attached to aerobic media feeding on bacteria and organic matter.
Note rotary action of cilia and vacuum effect, also pulsing chewing mastax.
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
Aerobic mite from the biomass around the riser of a tank.
Mite on Aerobic Treatment Media pH 6.94, DO 4.54 8

9. Aerobic Treatment Unit System for a Residence
The components typically present in an aerobic treatment system for a residence. The next slides will discuss each component.

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
The aerobic treatment process can be generally broken down into five components.
You may have a trash tank for trash removal and/or anaerobic treatment,
the aerobic treatment, where we are mixing the food and the organisms together,
an air supply system,
clarification process, where we are removing the material from the water,
and lastly, we have the sludge return process where we are returning the material that has been clarified and put it back into the aeration chamber or the pretreatment device.
No matter what manufacturer’s technology you have, you should be able to find or identify these five components in the units.

11. Septic / Trash Tank
The first component is the septic or 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.
A septic tank uses gravity to move the effluent around as it is treated. Solids that are lighter than water float to form the scum layer and solids that are heavier than water sink to form the sludge layer. After we separate the solids, the anaerobic bacteria go to work and eat away at those solids, break them down and reduce the volume.
If there is a small anaerobic tank in front of an aerobic tank we call the first a trash tank. Typically a trash tank has about ¾ to 1 day detention time. A bigger tank is not used because the advanced treatment unit downstream needs more BOD and TSS in order to work as designed. Trash tanks target the big pieces – things that probably should not be going into the tank in the first place. They are typically used in conjunction with other advanced pretreatment units.
Some systems do not have a trash tank. This makes the aerobic tank also perform the duties of the trash tank. Its recommended to have a trash tank to remove the non-degradable items.

13. Two-Compartment Septic Tank
Components of the septic tank are:
the inlet, which is higher than the outlet
an inlet baffle or sanitary tee to dissipate the energy coming from the toilet flush or washing machine that could disturb the settling solids
An outlet baffle or tee to keep the scum in the tank and to draw the effluent from the clearest part of the tank.
The outlet pipe
the risers coming all the way to the surface.
The critical difference is the distance between the inlet and outlet baffles. This distance determines that amount of settling that will occur.

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 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
The main purpose of the tank is to separate the solids and let the ‘clear’ liquid go through, and there are a variety of things we can do to optimize that separation. To help with solids retention, we can use a two compartment tank or a bigger tank. We also use of an effluent screen at the outlet to increase solids retention. An effluent screen traps solids that find their way to the outlet tee. When the solids accumulated within the screen get heavy enough they should slough to the bottom.
Septic tanks need a nice calm environment to prevent mixing. The size of the tank determines the speed of the water movement.

15. Aerobic Treatment Aeration Chamber
The next component is the 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
Aerobic microbes digest solids.
Microorganisms take the organic matter, add oxygen and convert it into carbon dioxide, water and new cells.
Aerobic microbes generate sludge that will need to be pumped out. The quantity of sludge directly relates to its operation as an extended aeration system.
Extended aeration to limit biomass wasting - The system is also operated in a condition where there is excess oxygen to promote microbial growth. The food supply is limited. Therefore, the microbes are not only eating the waste in the water but are also eating the other microbes. This process limits the amount of biomass that is generated in the treatment process and thus the amount of residuals that need to be pumped from the system.

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
The diagram shows a trash/septic tank to collect the wastewater. Wastewater then flows into the aeration tank where air is introduced. The treated wastewater passes into the clarifier. The settled solids /effluent can be returned to either the aeration chamber or the septic/trash tank depending on the treatment arrangement.
Suspended growth systems generally have the following components:
Aerobic microbes are free swimming in the aeration chamber – The suspended growth system has the microbes free swimming and moving around in the system.
Mixing in the chamber mixes the microbes and the wastewater contaminants – The air entering the system or the aerator can assist in mixing the microbes with the food entering the aeration chamber.
Extended aeration to limit biomass wasting – The system is operated in a condition where there is excess oxygen to promote microbial growth. Also, the food supply is limiting. Therefore, the microbes are not only eating the waste in the water but are also eating the other microbes. This process limits the amount of biomass that is generated in the treatment process and thus the amount of residuals that need to be pumped from the system.

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
The diagram shows a trash/septic tank to collect the wastewater. Wastewater then flows into the aeration tank where air is introduced. The aeration tank also contains the media which serve as the home for the microbes. The treated wastewater passes into the clarifier. The use of a clarifier may be limited in some of the attached growth systems. The settled solids /effluent can be returned to either the aeration chamber or the septic/trash tank depending on the treatment arrangement.
Submerged Attached Growth / Fixed film Media systems generally have the following components:
Media is submerged in the aeration chamber - The submerged media allows the microbes to be attached in the saturated condition. These medias are generally made of plastic and must allow water and sloughing biomass to pass through the media.
Microbes are attached to the media - The microbes grow on the surface of the media. The microbes will remove the food (waste) from the wastewater as it flows past.
Effluent is circulated through the media thus passing contaminants by the microbes – Rising air or a mechanically induced circulation moves the effluent through the media.
Extended aeration to limit biomass wasting - The system is also operated in a condition where there is excess oxygen to promote microbial growth. The food supply is limited. Therefore, the microbes are not only eating the waste in the water but are also eating the other microbes. This process limits the amount of biomass that is generated in the treatment process and thus the amount of residuals that need to be pumped from the system.

19. Suspended Growth Configurations
Should be three chambers/tanks.
Single tank with three compartments.
Multiple tanks.
May combine aeration and clarification chamber with divider
The homeowner must be able to envision what is below the ground. This slide should help them understand what is below the ground surface.
Key is to have three chambers, compartments or tanks. You must spend time on this slide to help the class participants understand how the riser lid relates to what is below the ground surface. Additionally, they need to understand that some tanks may be buried.
One tank configuration has the cone inserted into the aeration tank.

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
Again, the homeowner must be able to envision what is below the ground. This slide should help them understand what is below the ground surface.
Key is to have three chambers, compartments or tanks. You must spend time on this slide to help the class participants understand how the riser lid relates to what is below the ground surface. Additionally, they need to understand that some tanks may be buried.
Most have three chambers
May be a separate media filled insert
May have media placed in the aeration chamber
Check the manufacturer literature to determine the style of system they have. They must be able to relate the literature picture to what is in the ground at their specific location.

21. Air Supply
The next series of slides will cover the aeration of wastewater.

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
Air is 21% oxygen.
Oxygen must transfer to wastewater for DO
The goal is to get the oxygen out of the bubble and into the water
Aerobic microbes need DO to function
Biochemical Oxygen Demand (BOD) is the amount of oxygen needed to break down the waste.
Mixing in the aeration chamber helps microbes get in contact with waste.

23. Aspirator/Aerator Vacuum pulls air into the water
Spinning shaft or impeller causes the vacuum
Limited resistance
An aspirator uses a vacuum to pull air into the unit.
Most aspirators will use a motor with a spinning shaft or impeller on the end that develops a vacuum as it’s spinning within the fluid.
The air is drawn down through the system and out the hole into the water.
It is important to check the air flow to ensure it hasn’t shut off.
Each visit the aerator should be removed and the shaft needs to be cleaned.

24. Compressors Greater pressure Lower air flow
Two distinct types of compressors
Rotary
Linear
Air inlet
Housing - cover
Rotary
Compressors operate at greater pressure and lower airflow.
As we just mentioned an aspirator is functioning under a vacuum. Well, compressors do just what the name implies, it is compressing the air, and sends it into the fluid.
There’s two types of compressors. There’s linear and there’s rotary. Each type of compressor operates differently.
The rotary compressor is a friction-based system. Inside the housing there is a carbon vanes that rotate around an off center shaft. As it rotates the air is compressed and is forced out of the exit. Because it is friction-based, it’ll tend to generate more heat. It also has the ability to move air under a higher pressure.
The linear operates using a diaphragm system. Electromagnets control a shuttle that flies back and forth in between two pumps that are basically a rubber diaphragm that moves back and forth. Since the linear is not friction based, it will run cooler. Because there isn’t a shaft or motor but uses electromagnet forces to keep things moving, it will tend to be a little easier to shut off the flow of air.
With either type of compressor you can introduce air at a deeper depth in the unit. Units that use compressors tend to aerate down lower and have mixing in a lower zone.
From a maintenance standpoint, the operating pressure needs to be checked and the filters need to be cleaned.
And a lot of maintenance providers rebuild these compressors as a part of their business. Some opt to dispose of them properly when they aren’t functioning.
Linear

25. Compressor Air Flow Rotary Linear
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
This is a flow rate curve just like a pump has a curve. This liner compressor provides a greater pressure variation over the flow range.
Different sized compressors for different flow rates. Therefore, you must have the correct compressor for your treatment system.

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
Blowers are different in the aspect that they move a large volume of air, at a lower pressure. When using a blower, you are going to generally aerate in a fairly shallow depth in the unit.
Inlet screens/filters. Blowers have fairly coarse screens that will need to be checked and possibly cleaned.
The blowers have a fan that is trying to move a large volume of air in there. You’ve got to watch the inlet stream so that it doesn’t plug up. Air that goes in has got to come out so you need to have good air flow discharge from the unit.
Blowers require larger pipe size because they move a much larger volume of air.

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.
ATUs using a compressor or blower must convey air to the treatment unit. The friction loss in the piping must be minimized to not restrict air flow. Therefore, the following items must be considered:
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
ATUs use different approaches to introducing air into the wastewater. You must refer to the manufacturer literature for your particular unit to determine the approach used in your system.
Some have drop pipe holes, slots – stores diffusers, plastic diffuser.
The object is to disperse the air into the water.
There are many types of diffusers ranging from open PVC to line plastic.
Each diffuser will have different bubble sizes and head loss.
Porous Stone Diffuser

29. Clarification
The next component is the clarifier.

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
The clarification process occurs using a clarifier.
The goal of clarification is to separate out the solids from the clear liquid. This is done by allowing the microbes, cell waste and biomass to settle out of the water.
The solids will collect at the bottom of the clarifier as a sludge blanket allowing a clear zone of liquid to form above it that can be decanted from.

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
Water flows up vertically through the chamber. It is important that the water flow rate is less than the settling rate so the settling materials are not re-suspended
The velocity exiting is equal to the flow rate divided by surface area that is connected hydraulically.
A rule of thumb is to compare how the ATU is tested to verify performance.
1 gal/minute is the flow rate for NSF standard 40 testing.
NSF – flow equal – tested under 60 gal/hr – 1 gal/min
Velocity = Flow rate / Area
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
The clarification step can be achieved with several different configurations:
Separate chamber with no extra filtration –
Cone inserted into aeration chamber.
Sloped walls for controlled settling
Tertiary filter or screen filters the water leaving the clarifier. Reduces solids accumulation in the pump tank.
Filtration socks will need to be removed and cleaned.
Added filtration improves quality but increases maintenance
Again, the homeowner must review their manufacturers literature to learn about the approach used in their treatment unit.

33. Flow Equalization Tank
Flow equalization prevents water surges from forcing solids or organic matter out of the treatment components.

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
If you are on a non flow equalized house you are the flow equalization. The homeowner can control the water flow by monitoring their water usage. Water usage exceeding the flow rate of the clarifier will affect the clear zone.
Washing machines or high capacity bathtubs can create a hydraulic surge.

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
A flow equalization tank keeps components within their designed hydraulic load.
Compensates for usage fluctuation.
Prevents the movement of solids or organic material to the next component.
The volume of water moving forward through the flow equalization tank is timed.

36. Flow Equalization/Surge Tank
The flow equalization tank is located after the septic/trash tank. Floats and a pump in the flow equalization tank control the dosing if the aerobic chamber.
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
The flow equalization tank is located between the trash tank and the aeration chamber.
The trash tank is upsized because it is not flow equalized. Upsizing the trash tank keeps the materials from moving down stream.

38. Sludge Return
Sludge return is the process of settling out the biomass and returning it to the previous component.

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
Sludge return can be achieved with either a passive or active operation.
Passive – operations have the solids automatically returning to the previous component. Mainly they use gravity to move the solids into the previous component.
Active solids return systems are generally in a separate tank and use a pump to convey the settled solids to the previous component. This Pump must be operational to pump the solids to the previous components. These pumps are generally on the bottom of the pump tank and will draw the solids into the pump inlet. Appropriate operation of the pumped return system can be checked by measuring the depth of solids in the clarifier tank.

40. Disinfection
Disinfection is what we are trying to achieve.

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.
Some pretreatment devices employ a disinfection unit as part of their treatment system. Disinfection is the destruction or inactivation of disease-causing organisms. Disinfection rids the wastewater stream of organisms that are capable of causing infection. It is not to be confused with sterilization, which rids the wastewater stream of all life.
Approved disinfection methods include chlorination, ozonation, and ultraviolet radiation.

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
Chlorine is often used for disinfection in residential systems. It works by oxidizing the cellular material of the targeted organisms.
Chlorine appears to react strongly with lipids in the cell membrane and membranes having high lipid concentrations appear to be more susceptible to destruction. For this reason, viruses, cysts, and ova are more resistant to disinfectants than bacteria.
Chlorination is an effective process, but it may be ineffective on some of the protozoa and helminths that can cause disease.

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
When choosing a disinfection process for your onsite system- it is important to look at your wastewater stream and how it will interact with a disinfection process. Chlorine is an oxidizer. Now, for those of you who have forgotten your chemistry (don't worry- I blocked that horrible class from my memory too) To oxidize is to add oxygen and oxidizers are any elements that react with oxygen.
Organic matter in the wastewater stream uses chlorine as an oxidizer, and can make it unavailable for killing pathogenic organisms.
In clean water (and by clean water I mean low BOD and Low TSS) – it is more effective as a disinfectant. BOD and Organic matter exert a chlorine demand and create precipitates that can clog the system and effect treatment. Suspended solids in the wastewater provide places for the pathogenic organisms to hide and make it more difficult for the chlorine to penetrate and reach the organisms.
Ammonia in the water reacts with chorine to form chloramines. Although chloramines can disinfect wastewater, they are not as effective as hypochlorous acid.
This is why advanced pretreatment is desired. The ammonia will have been converted to nitrite and will thus not be available to produce choramines.
All of these things will influence the effectiveness of the disinfectant.
BOD - Can exert chlorine demand
TSS - Shield organisms and exert chlorine demand
Humic Materials (possibly from peat filtration systems) - Exert chlorine demand
Nitrite - Oxidized by chlorine
pH - Affects distribution between hypochlorus and hypochlorite ions. pH also affects distribution among chloramine species.
Since chlorine is an oxidizer, if iron manganese and hydrogen sulfide are in the wastewater, they can be oxidized and precipitate downstream in the process. This may be an important consideration, particularly if Water Reuse is planned where the aesthetic quality of the water is important.
As previously mentioned, chlorinated organics or “trihalomethanes” are suspected carcinogens, so organic matter (BOD) in the wastewater stream not only interferes with the disinfection but also creates an undesirable chemical compound.

44. Dose = Concentration x Time
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
Dosing is a factor of concentration and time. Increasing either dosage or contact time, while decreasing the other can achieve the same degree of disinfection.
It is important to have an appropriate holding time to allow the chlorine to react with the microorganisms. The length of contact time necessary for proper treatment decreases as the chlorine concentration increases. Generally, 30 to 60 minutes of contact time is required for typical wastewater strengths and chlorine concentrations.
Breakpoint- the process where sufficient chlorine is added to the system to obtain a free chlorine residual
When chlorine is added to wastewater- it first reacts with organics, ammonia, BOD chloramines (which remember are not as effective for treatment) and other chlorine compounds.
As more chlorine is added, the residual chloramines and chloro-organic compounds are reduced to a minimum value and free chlorine residuals result.

45. Caution
People should be trained to properly handle and work with chlorine products
High risk
Exposure
Handling
Corrosive
Unstable
Be careful where stored!!!!!!
People should be trained to properly handle and work with chlorine products
High risk
Exposure
Handling
Corrosive - The gases leaving the container are corrosive to metal object.
Unstable
Chlorine can break down and off-gas.
Do not store chlorine inside. Chlorine stored in a garage may corrode tools and equipment.

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.
Tablet chlorinators generally have four components:
Chlorine tablets
Tube(s) that hold(s) the tablets
Basin where chlorine tablets come into contact with the wastewater
Contact chamber where the chlorinated wastewater is stored to allow sufficient contact time before it is distributed
The device usually consists of a basin, where the tubes containing a stack of chlorine tablets is placed. The top of the tubes should extend above ground surface and be protected by a cap. The bottom tablet in the tube is in contact with the wastewater flowing through the basin. As that tablet dissolves and/or erodes, the tablet above falls by gravity to replace it.

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
Use only chlorine tablets that are approved for use in wastewater. They are made of calcium hypochlorite. These tablets dissolve in the wastewater and release the hypochlorite, which then becomes hypochlorous acid, the primary disinfectant.
Do not use swimming pool chlorine tablets. They are often made from trichloroisocyanuric acid, which is not approved for use in wastewater treatment systems. These tablets make the chlorine available too slow for it to be effective. If wetted repeatedly, they also can produce nitrogen chloride, which can explode.
Do not combine tablets of trichloroisocyanuric acid with calcium hypochlorite. The combination will form the explosive compound nitrogen chloride. Read the list of active ingredients on the tablet label to make sure you are using calcium hypochlorite. Petroleum products mixed with chlorine are also explosive.
Additionally, it is technically breaking the law to use unapproved chemicals.

48. Residential Liquid Bleach Chlorinator
Reservoir
Delivery of chlorine
Vacuum/suction
Pump
Dose volume
Mixing with effluent
Liquid chlorination is simple, inexpensive, and can be safe if proper precaution is used. The chlorine solution may be made from liquid chlorine bleach or from chlorine powder in water. The liquid chlorination system generally consists of a tank, mixer, and chemical metering pump.
Once the dosage is determined and the concentration of the solution in the mixing tank is determined, the chemical metering pump may be set to deliver the required dose.
The chemical metering pump may be a peristaltic pump or a diaphragm pump. The pump should have the flexibility to adjust the speed of the peristaltic mechanism or the stroke rate to allow the dosing rate to be adjusted.
Also, in the arrangement shown above, some precaution must be used to prevent siphoning of the chlorine solution from the mixing tank into the wastewater flow piping if the wastewater pipe is not under pressure. If the wastewater pipe is under pressure, the metering pump must be selected to provide adequate pressure to deliver the chlorine at the correct dosing rate against the head in the wastewater pipe.

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
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
Ultraviolet light is also an approved disinfection method
UV disinfection destroys DNA, breaking genetic
make-up of pathogens, so they no longer live/reproduce.

51. Ultraviolet Light Disinfection Units
Electromagnetic energy (UV light) from source lamp is emitted into a chamber through which effluent passes
Electromagnetic energy (UV light) from source lamp is emitted into a chamber through which effluent passes.

52. Middle: dry chamber (direct inlet and outlet)
Right: Chamber, lamp is in inside a sleeve, and the wastewater flows on either side of it
The system has a pee trap where solids can settle. Solids need to be washed out.

53. Other Interferences to Effective UV Disinfection
Dissolved organic compounds (BOD, TOC, COD)
Organic iron compounds
Humic compounds (tannins)
Inorganic coatings on protective tubes
Dissolved organic compounds (BOD, TOC, COD) inhibit the passage of UV light to the organisms.
Organic iron compounds can absorb UV light, precipitate, and build up on the sleeve, inhibiting the passage of UV light into the water to the organisms.
Inorganic coatings on protective sleeves may be a result of source water (hard).
Teflon sleeve resists buildup a bit better than quartz.

54. Pump Tank with Pumps and Controls

55. Pump Tank & Pump Stores water until time for dosing effluent
Acts as storage for disinfection
Storage capacity when system breaks
Pump
Type: effluent or sewage
Not a grinder or sump
Specific flow & pressure
Stores water until time for dosing effluent.
Acts as storage for disinfection
Provides a limited storage capacity when system breaks – many minimum sized tanks will only have one-third of the daily flow or about 80 gallons of capacity after the alarm is activated.
The type of pump is critical to long-term performance. Pump selection is based on three parameters: flow, pressure and solids handling capability.
Effluent pump is designed for clarified water
Sewage pump can handle solids.
Solids in the pump tank will shorten pump life.
Sump pumps are for moving clear water and will not handle solids.
Grinder pumps are typically not needed in residential systems. Grinder pumps have cutting blades to cut items into small pieces for moving them through the system.
The type and size of pump is directly related to the number of spray heads and flow rate.

56. Panel & Electrical Control Circuits
Panel is a housing for components needed to control a system.
Record valuable operational information
Provide a means to collect operational data on the system
Timer for night spray
Timer for flow equalization
Audio and visual alarms
Power must be ON!
Most panels have limited operation controls except for a timer. However additional controls will help collect valuable data.
A Cycle counter and Elapsed time meter – allows the calculation of flow rate
A timer is included in systems with night spray or flow equalization.
Audio and visual alarms
The power must remain on to the system to allow correct operation. The power should not be turned off when you leave the residence.

57. Spray Field

58. Spray Field Lawn Sprinkler systems? --- NO!!!
Spray treated wastewater over the surface of a yard
Requires greatest level of treatment
High risk system!!!!
Spray distribution systems for wastewater are much like a lawn sprinkler. They spray treated wastewater over the surface of a yard. Unlike a subsurface dispersal system, a spray distribution system requires the greatest level of wastewater treatment because of the risk of human contact. This in turn increases the cost of a complete treatment and land application system. Spray systems may incorporate an element of landscape irrigation.

59. No Playing in Sprinklers
Water Quality
High potential for human contact with water
Secondary- Quality Effluent
Remove 85-98% of solids and organic matter
Remove pathogens?
Nutrients (nitrogen and phosphorus) are not required to be removed
Soil for Final Treatment
Because of the potential for human contact with wastewater, a spray system must treat the wastewater to a very high quality before spraying it onto the landscape. This system must treat the wastewater to a “secondary-quality effluent,” which means that it must remove 85 to 98 percent of the solids and organic matter. It also must disinfect the wastewater to remove pathogens.
Wastewater must be treated to lower its BOD to less than 20 parts per million (ppm) and its total suspended solids (TSS) concentration to less than 30 ppm (depending on local and state regulations). To make sure the pathogens are destroyed, the chlorine level in the pump tank must be at least 0.1 ppm, or a fecal coliform test must find concentrations of these organisms below detection levels. Although the wastewater is relatively clean when it meets these standards, it still contains nutrients such as nitrogen and phosphorus. Some advanced treatment systems may also remove these nutrients.
Spray distribution systems rely on the soil for final wastewater treatment. The soil must be able to support vegetation that uses the nutrients in the wastewater. Plants use the nitrogen and phosphorus in the wastewater, preventing those nutrients from leaching to groundwater or flowing into surface water supplies.
No Playing in Sprinklers

60. Role of vegetative cover in treatment system
A healthy cover crop is essential for the system to function properly. Plants will:
Take up nutrients
Take up water
Stabilize the soil and prevent erosion
Provide food and habitat for beneficial soil organisms
Soil microbes are the final treatment!!!!
This is effluent – NOT DRINKING WATER!!!!
The vegetative cover is an essential part of the system. Vegetation will take up water and nutrients. The intake of water allows for good aerobic soil for the final treatment.
Vegetation growing for water and nutrient removal.
Clear area around spray head – 10 feet in the direction of spray from the head.
Dead vegetation should be reseeded to establish vegetation.

61. Connecting Distribution Heads to Laterals
The distribution heads are connected to the lateral using a riser. The riser can be a solid rigid pipe extending from the lateral to the distribution head located above grade. The riser can also be constructed in a flexible manner to allow greater ability to set the distribution head location and ease of repair.
A swing joint uses rigid PVC piping and connections to set the location of the head.
A flexible nipple has multiple threaded sections that can be selected and cut to the appropriate length which places the distribution head at the soil surface.
A flexible pipe connection utilizes flexible pipe as a riser. This flexible pipe can assist in locating the distribution head at the ground surface and at a good location with respect to the lateral.

62. Summary Treatment requirements
Components of an OWTS using Aerobic Treatment, Disinfection and Spray Dispersal
What is a Flow Equalization Tank?
The wastewater treatment system is installed to remove the constituents from the wastewater. If the components are not working properly, the wastewater will not be treated.
The components work together to achieve proper treatment. It is important for all components to be working.
Flow equalization is a technique used to collect water used in the residence and then time dose the wastewater to down stream components.