Advanced Treatment

Question 1

Required for proper operation of “rapid sand” filters.

Answer 1

Filter aid polymer

Question 2

“Rapid sand” gravity filters.

Answer 2

• Mixed media
  anthracite
  medium silica sand
  fine garnet sand
• Dual media
  anthracite
  silica sand
• Deep bed mono-media
  anthracite or medium silica sand

Question 3

Media sorting during filter backwash is due to this characteristic.

Answer 3

As the filter expands and is fluidized during backwash, the specific gravity of the media allows the formation of distinct layers.
TOP anthracite 1.4 spec gravity
MIDDLE silica sand 2.6 spec gravity
BOTTOM garnet 4.0 spec gravity

Question 4

Indications of adequate filter backwash.

Answer 4

*20- 25% expansion of media
*media become fluidized

Question 5

Typical backwash rate for rapid sand filters

Answer 5

□ 15-20 gpm/sq ft filter surface or
□ 2-2.7 ft/min backwash rise rate

Question 6

Continuous backwash occurs in these filters.

Answer 6

□ Moving bridge filter
□ Continuous backwash upflow “clarifier

Question 7

Problems associated with inadequate filter backwash.

Answer 7

□ Mudballs
□ Debris on filter surface
□ Filter surface cracking

Question 8

Filter status is determined by continuously monitoring these.

Answer 8

□ Effluent turbidity
□ Headloss

Question 9

This initiates filter backwash.

Answer 9

□ Turbidity breakthrough or
□ Filter reaches “terminal” headloss (6-8 ft) or
□ Filter run time has been reached

Question 10

Bacteria associated with the nitrification process.

Answer 10

• Nitrosomonas sp. (Converts ammonia to nitrite)
• Nitrobacter sp. (Converts nitrite to nitrate)

Question 11

Characteristics of the nitrification process:
Overall reaction
Oxygen requirements
Aerator requirements
Optimum pH range ■ J
Alkalinity and pH ]relationship
Solids retention time required
Source of nitrifying bacteria

Answer 11

Characteristics of the nitrification process:
* NH, — NO, (NH,+202 -HNO,+H,0)
* Nitrification is an acrobic process: 4.5 lb 02 consumed per lb of ammonia nitrified
* 40- 60% additional aeration is needed to support nitrification
* 7.5-8.5
* Nitrification consumes alkalinity (natural buffer in water) and can drive the pH below 6.0
* SRT necessary for nitrification isdependant on the aeration basin temperature.
~5 days if the temp is 16 °C
~12 days if temp is 10 °C
* A population of nitrifying bacteria must be “grown” in the treatment plant (aerator MLSS, TF, RBC, etc)

Question 12

Nitrite “lock”

Answer 12

• Nitrification stuck in the intermediate step allowing nitrite to accumulate
• Low pH is typically the cause of incomplete nitrification
• Nitrite in the effluent interferes with disinfection by reacting with and destroying chlorine residual

Question 13

Characteristics of denitrification:
Overall reaction
Conditions required
Byproducts

Answer 13

• Nitrate or nitrite is converted to nitrogen gas
  
  • Respiring (food eating) bacteria and anoxic (oxygen depleted) conditions. Adding readily available food like
    sucrose or methanol can stimulate denitrification.
  • In addition to N2 gas, alkalinity is produced and the pH is raised

Question 14

Treatment processes that can accomplish nitrogen removal by BNR.

Answer 14

• Treatment processes that promote nitrification and denitrification of wastewater
• Activated sludge aeration basin partitioned to provide aerobic nitrification zone and anoxic denitrification zone
• Extended aeration oxidation ditch operated to produce alternating aerobic and anoxic zones
• Sequencing batch reactor (SBR) operated to provide time periods of aerobic and anoxic treatment

Question 15

PAOs

Answer 15

phosphate accumulating organisms

Question 16

Most treatment plants achieve phosphorus removal by this method.

Answer 16

Chemical precipitation using alum, ferric sulfate or lime

Question 17

Summary of phosphorus removal by BNR

Answer 17

Exposing MLSS to a continuous cycle of anaerobic and aerobic conditions stimulates the growth of PAOs and the “luxury” uptake of 80 - 90% of the soluble phosphate in wastewater.

Question 18

Process overviewof phosphorus removal by BNR

Answer 18

• Influent wastewater and RAS are fed to an anaerobic phase basin:
  PAOs multiply and accumulate in MLSS over time
  Under anaerobic conditions PAOs actually release phosphorus into the MLSS\
• MLSS then enters the aerobic phase (aeration basin):
  PAOs take up, remove 80 - 90% of soluble phosphate in the MLSS
• After settling in the clarifier, the settled sludge is returned to the anaerobic phase:
  Settled sludge must not beallowed to become anoxic in the clarifier - phosphate is released back into the
  wastewater
• Wasting of the high-phosphate activated sludge provides actual removal of phosphorus

Question 19

Why N and P are removed from wastewater.

Answer 19

• Nitrogen and phosphorus are plant nutrients - they stimulate algae blooms which choke waterways.
• Algae blooms contribute to “aging,” the long-term decline in lakes called eutrophication.
• Algae bloom die-off produces high oxygen demand and low D.O. in receiving streams.
• Ammonia is toxic to some fish and exerts oxygen demand on the receiving stream

Question 20

How constructed wetlands accomplish BNR.

Answer 20

As wastewater flows through beds planted with bulrushes and cattails, Nitrogen and phosphorus are taken up by wetlands plants. The N and P nutrients become part of the plant material and must be periodically harvested from the beds.

Question 21

Percent of filtered water needed to provide filter backwash

Answer 21

About 3% is normal

Question 22

Odor control methods.

Answer 22

• Wet air scrubbing
  Foul air is piped to one or more scrubbers where chemical sprays (NaOH and hypochlorite) strip out and
  neutralize odor compounds
• Biofiltration
  Foul air flows upward through moist media (compost, mulch or peat).
  Microorganisms grow on moist media and utilize odor compounds for food
• Activated carbon adsorption
  Foul air is piped through vessels filled with activated carbon. Odor molecules are adsorbed into highly
  porous carbon surfaces.

Question 23

Odor compounds removed by odor control methods

Answer 23

• Hydrogen sulfide
• Organic sulfides like mercaptan and dimethyl sulfide
• Ammonia