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Questions and Answers

What is the combination of human feces, urine, and "gray water" called?

Domestic wastewater

The term "gray water" refers to what kind of water?

Water from washing, bathing, and meal preparation

What does BOD stand for?

Biological Oxygen Demand

BOD test measures the amount of oxygen consumed by bacteria over a period of 10 days.

<p>False</p> Signup and view all the answers

What is the formula to calculate BOD?

<p>BOD (mg/L) = D1-D5/P</p> Signup and view all the answers

What are two main purposes of the BOD test?

<p>Determines the amount of oxygen needed for biological treatment and determines the required size of treatment facilities</p> Signup and view all the answers

What is the primary goal of wastewater treatment?

<p>To remove and degrade organic matter under controlled conditions.</p> Signup and view all the answers

Name the three major steps in wastewater treatment.

<p>Primary, secondary, and tertiary treatment</p> Signup and view all the answers

What are the three methods used in secondary treatment?

<p>(1) aeration tanks, (2) trickling filter beds, (3) sewage lagoon</p> Signup and view all the answers

Disinfection is usually accomplished before secondary treatment.

<p>False</p> Signup and view all the answers

What is the primary objective of primary treatment?

<p>Physical separation of large solids from the waste stream.</p> Signup and view all the answers

Which of these are methods used in primary treatment?

<p>Metal grating</p> Signup and view all the answers

What does "sludge" refer to in wastewater treatment?

<p>The settled organic solid in the settling tank during primary treatment</p> Signup and view all the answers

What is the purpose of secondary treatment in terms of organic matter and pathogens?

<p>Biological degradation of organic matter and reduction in pathogen numbers.</p> Signup and view all the answers

Which of the following is NOT a method used in secondary treatment?

<p>Sand or mixed media filter</p> Signup and view all the answers

What type of film is formed during secondary treatment and what is it made of?

<p>A zoogleal film, composed of bacteria, fungi, algae, and protozoa</p> Signup and view all the answers

What is the approximate BOD removal efficiency of trickling filters?

<p>~85%</p> Signup and view all the answers

What is the process called where effluent is mixed with bacterial-rich slurry in aeration tanks?

<p>Activated sludge process</p> Signup and view all the answers

Aeration tanks solely rely on natural air for bacterial growth and decomposition.

<p>False</p> Signup and view all the answers

What is the final product of anaerobic digestion of secondary sludge?

<p>Biosolids</p> Signup and view all the answers

How are pathogens removed during the activated sludge process?

<p>All of the above</p> Signup and view all the answers

What is the typical detention time for wastewater in aeration tanks?

<p>4-8 hours</p> Signup and view all the answers

What is the term used to describe the contents of an aeration tank?

<p>Mixed liquor suspended solids (MLSS)</p> Signup and view all the answers

What is the organic component of MLSS called?

<p>Mixed-liquor volatile suspended solids (MLVSS)</p> Signup and view all the answers

What is the ratio of substrate to microorganisms in activated sludge called?

<p>Food-to-microorganism ratio, or F/M</p> Signup and view all the answers

What does "F/M" stand for in the context of wastewater treatment?

<p>Food-to-microorganism ratio</p> Signup and view all the answers

What is the recommended F/M ratio for effective wastewater treatment?

<p>0.2 to 0.5 lb BOD5/day/lb MLSS</p> Signup and view all the answers

High F/M ratio is desirable because it allows for faster decomposition of organic matter.

<p>False</p> Signup and view all the answers

What are the two key modifications that can be made to the activated sludge process to improve nutrient removal?

<p>Nitrogen removal and Phosphorous removal</p> Signup and view all the answers

How is nitrogen removal achieved in activated sludge?

<p>By encouraging nitrification followed by denitrification</p> Signup and view all the answers

How can the activated sludge process be modified to facilitate phosphorous removal?

<p>By introducing an anaerobic/oxic process with an anaerobic zone added upstream of the aeration tank</p> Signup and view all the answers

What is the main purpose of tertiary treatment?

<p>To further reduce organics, turbidity, nutrients (nitrogen and phosphorous), metals, and pathogens.</p> Signup and view all the answers

Which of these is NOT a typical method used in tertiary treatment?

<p>Aerobic Digestion</p> Signup and view all the answers

Tertiary treatment is always required for safe discharge of wastewater into the environment.

<p>False</p> Signup and view all the answers

Why is pathogen removal so important even after primary and secondary treatment?

<p>To ensure the safe reuse of treated wastewater or its discharge into the environment.</p> Signup and view all the answers

What is the primary method of pathogen removal in secondary treatment?

<p>Activated sludge process</p> Signup and view all the answers

What percentage of enteric bacteria is typically removed by activated sludge treatment?

<p>90%</p> Signup and view all the answers

What is the genus of eukaryotic parasites that causes respiratory and gastrointestinal illness?

<p>Cryptosporidium</p> Signup and view all the answers

Cryptosporidium is transmitted through waste from only human sources.

<p>False</p> Signup and view all the answers

What form of Cryptosporidium is excreted from the host?

<p>Oocysts</p> Signup and view all the answers

What happens when oocysts enter a new host?

<p>They release sporozoites which then parasitize epithelial cells</p> Signup and view all the answers

Cryptosporidium oocysts are easily disinfected.

<p>False</p> Signup and view all the answers

What type of tertiary treatment is effective in removing Cryptosporidium?

<p>Mixed-sand media filtration</p> Signup and view all the answers

What is the primary purpose of septic tanks in wastewater management?

<p>To treat wastewater from individual homes, typically in rural or suburban areas with limited access to centralized sewage systems.</p> Signup and view all the answers

How does wastewater enter a septic tank?

<p>Through a pipe connected to the home's plumbing system.</p> Signup and view all the answers

What happens to wastewater inside a septic tank?

<p>Oil and grease rise to the top, solids settle to the bottom, and organic matter undergoes anaerobic decomposition.</p> Signup and view all the answers

After how long does the wastewater typically remain in the septic tank?

<p>24-72 hours</p> Signup and view all the answers

What happens to the treated wastewater from the septic tank?

<p>It is typically discharged into a drainage field, where it is further filtered and released into the environment.</p> Signup and view all the answers

Septic tank sludge is typically not a concern and never needs to be removed.

<p>False</p> Signup and view all the answers

Why are contaminants from septic tanks a potential threat to groundwater?

<p>Leaky septic tanks can release untreated wastewater into the surrounding soil, contaminating groundwater sources.</p> Signup and view all the answers

For what types of populations are septic tanks typically the most suitable option?

<p>Rural or suburban populations with low densities.</p> Signup and view all the answers

What is the main purpose of constructed wetlands in wastewater treatment?

<p>To provide an additional treatment step, particularly for secondary effluents.</p> Signup and view all the answers

How do plants contribute to the effectiveness of constructed wetlands?

<p>They provide increased surface area for microorganisms, filter contaminants, and contribute to the overall health of the wetland ecosystem.</p> Signup and view all the answers

Which of the following are types of constructed wetlands?

<p>Free water surface systems (FWS)</p> Signup and view all the answers

Study Notes

Wastewater Treatment

  • Wastewater is a mixture of human waste, washing water, and food preparation water
  • Wastewater treatment aims to remove and break down organic matter under controlled conditions
  • The main steps of wastewater treatment are primary, secondary, and tertiary treatment

Nature of Wastewater

  • Domestic wastewater combines human waste (feces and urine) and "graywater" (water from washing, bathing, and food preparation)
  • Graywater is water used for washing, bathing, and food prep
  • The BOD (Biological Oxygen Demand) is a key metric to measure the oxygen consumed by microbes during the organic matter breakdown in the wastewater

Biological Oxygen Demand (BOD)

  • BOD is a measure of the oxygen consumed by microbes during the oxidation of organic and inorganic matter in wastewater
  • The BOD test measures oxygen consumption by microorganisms in dark conditions over 5 days at room temperature
  • The test is performed on a series of wastewater dilutions
  • The BOD formula: BOD (mg/L) = (D1 - D5) / P
    • D1 is the initial dissolved oxygen (mg/L)
    • D5 is the final dissolved oxygen (mg/L)
    • P is a decimal volumetric fraction of the sample used
  • Typical BOD ranges of wastewater are 110 – 440 mg/L and often reduced to 95%

Wastewater Treatment Process

  • The main goal of the wastewater treatment process is to remove and break down organic matter
  • Three main steps include: primary treatment, secondary treatment, and tertiary treatment

Primary Treatment

  • Primary treatment physically separates solids from wastewater
  • Removes large solids (metal grating, bar screens, grit tanks)
  • Approximately 50% of suspended organic matter settles out as primary sludge in settling tanks

Secondary Treatment

  • Secondary treatment involves the biological degradation of organic matter by microorganisms
  • Other benefits include reduced pathogen numbers.
  • Performed in aeration tanks, trickling filter beds, or sewage lagoons.
  • Pathogens are removed through microbial competition, or adsorption
  • Detention time for aeration tanks ranges from 4-8 hours

Trickling Filters

  • Trickling filters use plastic or stone units for older facilities and are a form of secondary treatment.
  • Effluent is pumped over a filter bed.
  • Microorganisms within the biofilm intercept and degrade organic matter via aerobic decomposition
  • Biofilm maintenance allows organic matter to be converted to biomass.
  • BOD removal efficiency is about 85%

Activated Sludge

  • Activated sludge is a biological process involving effluent mixing with bacterial-rich slurry and adding air to encourage aerobic decomposition
  • Secondary sludge is removed, combined with primary sludge, and anaerobically digested
  • Pathogen removal occurs through competition and adsorption
  • Detention time for aeration tanks is 4-8 hours

Aeration Tank Contents

  • Mixed liquor suspended solids (MLSS) contains organic matter, including volatile suspended solids (MLVSS).
  • Proper food-to-microorganism ratio is important (F/M)
  • MLSS must maintain proper load with substrate (organic matter) and microbes to allow adequate F/M
    • F/M is often 0.2-0.5 lb BOD5/day/lb MLSS
  • A lower F/M is desirable, enabling microbes to efficiently break down wastewater

More on Activated Sludge

  • Treatment processes can modify for nitrogen and phosphorus removal
  • Nitrogen removal often requires encouraging nitrification, followed by denitrification to encourage nitrifying bacteria.
  • Sludge ages need to be determined to encourage growth of nitrifying bacteria over heterotrophic bacteria for optimum denitrification
  • Phosphorous modifications can include A/O process

Tertiary Treatment

  • Tertiary treatment further reduces organics, turbidity, nitrogen, phosphorus, metals, and pathogens
  • Common physiochemical methods are coagulation, filtration, activated carbon adsorption, reverse osmosis, and disinfection

Pathogen Removal

  • Processes before tertiary treatment remove most pathogens
  • Activated sludge removes 90% of enteric bacteria, up to 99% of enteroviruses, and rotaviruses, up to 90% of Giardia, and Cryptosporidium
  • Pathogens are difficult to remove, so multiple steps might be needed
  • "Crypto" is a genus of eukaryotic parasites causing respiratory issues

Septic Tanks

  • Wastewater enters tank and oils rise to the top, with solids sinking to the bottom
  • Anaerobic decomposition results in septic tank sludge
  • Wastewater stays in tanks for 24-72 hours
  • Residual sludge may need to be pumped
  • Significant contaminants can be present and possibly pollute groundwater

Wetlands

  • Constructed wetlands offer secondary effluent treatment
  • Vegetation increases surface area for microbes, filtering out contaminants
  • Two types: free water surface (FWS) and subsurface flow (SFS) systems

Drinking Water Treatment

  • Past treatment was basic, primarily slow sand filtration.
  • Germ theory was developed in the 1870s, demonstrating chlorine's effectiveness in killing bacteria (1880s)
  • Drinking water disinfection reduced typhoid fever outbreaks

Process Train

  • Simple treatment is chlorination to disinfect water
  • Filtration using sand or coal may be included to reduce turbidity
  • In-line filtration involves a coagulant to flocculate suspended particles, improving filtration efficiency

Coagulation

  • Chemicals are added to remove dissolved and suspended solids via sedimentation and filtration
  • Common chemicals include hydrolyzing metal salts ("alum") or organic molecules (polyelectrolytes)

Flocculation

  • Flocculation is a physical process of stirring the water
  • Encourages particle collision, promotes larger particles
  • Particles come together, and this process makes filtration easier
  • Microorganisms in the water are trapped in the "flocs" and removed

Sedimentation and Filtration

  • Sedimentation allows particles to settle out
  • Filtration filters out particles
  • Combined, these processes remove 99.99% of microorganisms, including viruses

Filtration

  • Filtration is important in removing protozoan parasites.
  • Cysts and oocysts are resistant to disinfection, requiring additional procedures to prevent illness

Drinking Water Distribution Systems

  • Treated water is transported to consumers over long distances
  • Quality can degrade due to factors like reduced disinfectant residual, biofilm buildup, pipe breaks, and microbial regrowth

Microbial Growth

  • Bacterial concentrations in distribution systems range from low to high
  • Pipe biofilms can contain high concentrations of microorganisms
  • Biofilms can tolerate chlorine residuals
  • E. coli is 2400x more resilient when attached to a biofilm

Legionella in Distribution Systems

  • Legionella is more resistant to chlorine compared to E. coli
  • Legionella thrives in hot water tanks and hospitals
  • Thrives at 50°C and can grow at 42°C

Organic Matter

  • Organic matter growth is influenced by retention time and temperature
  • Examples of organic matter affecting wastewater are Pseudomonas, and amino acids (acetate, lactate)
  • Amount of biodegradable organic matter analysis is complex.
  • Assimilable organic carbon (AOC) is a significant factor, about 0.1 – 9% of total organic carbon

Course Information (Monday)

  • Quiz on the week's lecture material
  • Review of previous exam materials (Exam 2)
  • Topic review on Organic Pollutants and emerging topics

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Wastewater Treatment Lecture 14 PDF

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