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 objects 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 of 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 of 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 occurs when oxygen levels are depleted and nitrate becomes the primary oxygen 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 of 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 over 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 of microorganisms which feed on the organic waste products contained in the process flow. As the liquid passes over 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.

 Facility staff increased the concentration of sludge solids in the digester (from 7000 mg/L to 19,000 mg/L) to enhance the endogenous  Sludge removal has two stages, respiration phase and reduce the belt press Aerobic digestion and belt pressing. operational hours.  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 .

 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.

Trophy Club MUD 1 Wastewater Treatment Facility Incoming Wastewater from Raw Water Lift Station Bar screen Grit screen Bio-selector Collection System Return Water from BP Activated Sludge (RAS) Line Belt Press Water from Lift Station Aeration Basins Water from Drying Beds In Plant Lift Station Drying Beds Dumpsters Waste Activated Sludge (WAS) Line Clarifiers Decanted water from Digesters Digester Sludge to Landfill Washwater from Filters ABW Sand Filter & 5 star disc filter Discharge to Lake Grapevine Parshall Flume U.V. Disinfection Marshall Creek Contaminated water Sludge 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.