Trophy Club MUD No. 1 August 15, 2012 Overview of WWTP Operations - - PowerPoint PPT Presentation

Trophy Club MUD No. 1 August 15, 2012

 Overview of WWTP Operations  TPDES Permit Requirements & Compliance Status  Enforcement Order  Options Available  Board Discussion and Decisions

The Wastewater Treatment Facility involves three stages of treatment:

 Preliminary Treatment

The removal of large objects (cans, rags, sticks etc.) from the wastewater coming into the facility.

 Secondary Treatment

Designed to substantially degrade the biological content of the sewage, which is derived from human waste, food waste, soaps and detergents.

 Tertiary Treatment

Provides a final treatment stage to raise the effluent quality before it is discharged to the receiving stream (Marshall Creek).



The facility has two mechanically raked bar screens and one grit chamber.



As the influent passes through the bar screen, objects larger than ½” are trapped on the screen. The

• bjects accumulate on the screen

and restrict the influent flow increasing the influent level in the chamber, this causes a bar screen float switch to turn on and removes the larger debris.



As the influent continues through the facility, the next stage of preliminary treatment is the grit

• chamber. The velocity of the

incoming sewage is adjusted and aeration is added to allow the settling

• f

heavier inorganic material like sand & grit. After the inorganic material settles, they are pumped out and disposed.



Secondary treatment consists of two processes, the biological stabilization of the sewage and collection of the stable sewage.



Raw influent enters the Bio-selector where return activated sludge (RAS) is introduced, thus causing a reaction with the raw influent, and allowing the immediate break down of contaminates (NH3, CBOD, & Nitrates).



In June 2012, facility staff implemented changes in operation of the Bio-selector to increase RAS delivery to ensure proper removal

• f

contaminates. Additionally, Dissolved Oxygen (DO) levels where reduced from 2.0 mg/L to 0.2 mg/L causing the bacteria to start the denitrification process earlier to remove the nitrates.

Denitrification

• ccurs

when

• xygen levels are depleted and

nitrate becomes the primary

• xygen

source for

• microorganisms. The process is

performed under anoxic conditions; that is, when the dissolved oxygen concentration is less than 0.5 mg/L, ideally less than 0.2 mg/L. When bacteria break apart nitrate (NO3) to gain the oxygen (O2), the nitrate is reduced to nitrous oxide (N2O), and, in turn, becomes nitrogen gas (N2) the stable form of Nitrogen.



Aeration Basins (AB) are basic bioreactors that create an environment that allows microorganisms to grow, to work (consume/break down CBOD & NH3) and to reproduce.



In June 2012, facility staff reduced the free DO (from 6.0 mg/L to 0.2 mg/L) at the inlet of the AB to increase the time needed for denitrification of microorganisms.



Staff is now performing essential calculations (Food to Mass ratio, Sludge Volume Index, Sludge Age, Detention Times, etc.) with a better understanding

• f

their necessity for controlled and improved operations.

After Mixed Liquor Suspended Solids (MLSS consisting of RAW & RAS) are stabilized in the AB, the MLSS enters the

• Clarifiers. Gravity allows the

MLSS to separate into solids that settle to the bottom of the Clarifier & liquids that flow

• ver the top of the Clarifier.

This is the process that removes the Total Suspended Solids (TSS).



Tertiary Treatment uses filtration to remove CBOD & TSS.



TSS is removed through filtration through cloth filters on the 5 Star Filter and through sand for the Automatic Backwash Filters (ABS).



CBOD is removed on the ABS by passing through the sand. A biological growth called zoogleal mass, forms a slime layer or jelly- like mass over the surface of the sand media. This mass consists

• f

microorganisms which feed on the

• rganic waste products contained in

the process flow. As the liquid passes

• ver the surface of the biomass, the

bacteria feed on and digest these wastes, transforming and breaking them down into more treatable and less polluting forms of matter.



Sludge removal has two stages, Aerobic digestion and belt pressing.



Aerobic digestion is an extension of the activated sludge aeration process, whereby wasted sludge is continually aerated for long periods of time. In this process the microorganisms extend into the endogenous respiration phase, which is where materials previously stored by the cell are oxidized, because of a reduction in the biologically degradable organic

• matter. The organic matter from the

sludge cells is oxidized to carbon dioxide, water and ammonia. The ammonia is further converted to nitrates as the digestion process proceeds.



Eventually, the oxygen uptake rate levels off and the sludge matter is reduced to inorganic matter and relatively stable volatile solids.



Facility staff increased the concentration of sludge solids in the digester (from 7000 mg/L to 19,000 mg/L) to enhance the endogenous respiration phase and reduce the belt press

• perational hours.



The Belt Press is used to further thicken the wasted sludge through the use of zones.



The first zone is a gravity zone where the water is removed from the sludge by water passing through the belt.



The second zone is the S-Curl. This is where the water is squeezed out of the sludge.



Polymer is added to the sludge to assist in the removal of water.



With a thicker solid content being pumped to the belt press, the press runs more efficiently.



After leaving the filters, the treated water goes through an Ultra Violet (UV) chamber.



This chamber uses UV light to sterilize the pathogens, ensuring they can not reproduce. For example, Escherichia coli (E.coli) live approximately 24 hours. Stopping the reproductive cycle of harmful bacteria ensures that the treated effluent is safe and complies with the Texas Commission on Environmental Quality (TCEQ) & The Environmental Protection Agency (EPA) discharge requirements.



Policies & Procedures have been developed and implemented that address frequency of cleaning UV bulbs and proper sampling and testing preparation techniques for

• E. coli.

Incoming Wastewater from Collection System Raw Water Lift Station Grit screen Bar screen Clarifiers Aeration Basins ABW Sand Filter & 5 star disc filter U.V. Disinfection Parshall Flume Discharge to Marshall Creek Lake Grapevine Return Activated Sludge (RAS) Line Waste Activated Sludge (WAS) Line Digester Belt Press Dumpsters Sludge to Landfill Decanted water from Digesters Water from BP

Trophy Club MUD 1 Wastewater Treatment Facility

Contaminated water Sludge

In Plant Lift Station Drying Beds Bio-selector Water from Drying Beds Washwater from Filters Water from Lift Station

Treated water

 Received July 26, 2012  Violation for failure to meet effluent limitation of 5 mg/L for

CBOD March, April, June, August, October, November, and December 2011 and January and February 2012.

 Violation for failure to meet daily max effluent limitation of 394

CPU/100 mL for E. coli during December 2011 and February 2012.

 Violation for failure to meet monthly minimum concentration

effluent limitation of 5 mg/L for DO during January and February 2012.

 Violation for failure to meet minimum effluent limitation of 6

SU for pH during January 2012.

 Violation for failure to meet daily average concentration effluent

limitation of 12 mg/L for TSS during February 2012

 Violation for failure to meet daily maximum concentration

effluent limitation of 40 mg/L for TSS during January 2012.

 Violations for failure to collect a sample and analyze for copper

during December 2011, January and February 2012 (after new permit was issued in December).

 Order assesses a penalty of $50,500  Complying with TCEQ requirements will reduce the

penalty by $10,100 to an amount of $40,400

 Allows for payment of fine or participation in a

Supplemental Environmental Project (SEP)

 SEP must be in same category of violation. In our case

this means a water quality project.

 Pre-approved SEP: Denton County low income septic

rehabilitation project.

 Custom SEP: Participate with Town of Trophy Club.

Town of Trophy Club would be responsible for the project and TCMUD would pay up to amount of fine towards project. Suggested project is recycled water line to Harmony Park.

 Compliance SEP: Most difficult to get approved.

Allows funds to be invested into a project at the WWTP to achieve compliance. Suggested project is upgraded in-plant lift station.

 Purpose

The Town of Trophy Club’s Harmony Park is adjacent to the District’s wastewater treatment plant. The park currently uses treated potable water for irrigation purposes. A recycled water line will allow for treated wastewater to be used at the park for irrigation instead of potable water.

 Benefits

Using recycled wastewater for irrigation purposes at the park will reduce water system and distribution demand and will reduce effluent discharged to the receiving stream. The park uses an average of 417,000 gallons per month. This potable water can be redirected for domestic use. At the current average monthly usage for District customers, this would allow the District to serve an approximately 25 additional homes with no impact to the water system

• infrastructure. Additionally, because recycled wastewater can be sold at a lower

cost, residents of Trophy Club would benefit from lower costs to the Town for water service to the park.

 Estimated Cost

Staff estimates the project cost to be $60,000. Additional funds (over the fine amount of $40,400) would be provided by the Town of Trophy Club.



Purpose The operational capacity of the existing in-plant lift station is undersized. The insufficient capacity results in system backups throughout the plant and high water levels in the wet well for extended periods of time. Additionally, the insufficient capacity causes the lift station pumps to fail to cycle efficiently which increases wear on the pumps and decreases the electrical efficiency. Finally, the undersized capacity of the lift station hinders the ability to operate other plant components as designed for optimum performance.



Benefits Addition of a new in-plant lift station will result in greatly improved plant performance, reduced wear on pumps, reduced potential overflows within the plant site, and allow for additional plant capacity during an emergency power outage and/or wet weather events.



Estimated Cost Staff estimates the project cost to be $43,000. Pumps (2) $14,000 Lift Station Construction $23,000 Engineering Design $ 6,000 Total: $43,000

 Approve Agreed Order and submit to TCEQ by August

26, 2012.

 Pay fine or perform SEP.  Protest Agreed Order and request enforcement

hearing.