wastewater treatment general steps
- used water from industrial and residential sources
physical (primary treatment) - screening and sedimentation
biological (secondary treatment) - anaerobic digestion
- aerobic digestion -> activated sludge/aeration, trickling filter
tertiary treatment - digested sludge, drying, incineration, use as fertilizer or burial
- disinfection -> treated effluent to discharge
what are the goals of wastewater treatment
- remove nutrient (nitrogen) to prevent algae bloom
- prevent disease (remove pathogens)
- remove organic carbon (pharmaceuticals, harmful compounds)
- remove phosphorus
- too much of these nutrients is harmful for fish and other organisms - creates chemoheterotrophs
wastewater parameters
TOC - total organic carbon, total amount of carbon in an organic form
COD - chemical oxygen demand, measurement of the chemically oxidizable carbon
BOD - biochemical oxygen demand - measurement of the biologically oxidizable carbon - used as a regulatory value to manage nutrient discharge
TN, TP - total nitrogen and phosphorus
-> urea and phosphorus are abundant in municipal wastewater and their discharge leads to eutrophication
TSS, VSS - total and volatile suspended solids
- VSS consists mainly of biomass aka microbial cells
how are TOC and COD different, what types of compounds might be present in COD but not TOC, which compounds might be present in TOC but not COD
- COD includes things TOC does not, like chemically oxidizable inorganic species.
-TOC may include compounds microbes cannot oxidize → so COD and TOC can differ.
which is larger BOD or COD
- COD is always larger because it measures all oxidizable carbon, including carbon microbes can’t access
primary treatment
- removal of large particles solids
-> screening
-> precipitation
-> settling - can be hampered by items that should not be flushed down the toilet
-> wipes, menstrual products, condoms, floss
secondary treatment (biological)
- aerobic and anerobic biological processes
- activated sludge - aerobic/anaerobic
- biomass is used to remove organic carbon, nitrogen, and often phosphorus
- aerobic removal of organics
- nitrification/denitrification
- anammox
anaerobic digestion (syntrophic process)
- often used for treatment of sludge
-> can also be used to treat food waste, farm waste, and on small to large scale
aerobic BOD removal
- aerobic chemoheterotrophic microbes oxidize diverse organic carbon compounds to make energy and for growth
-> converts waste material into energy that fuels microbial growth
other benefits
- competitive exclusion -> degrader bacteria outcompete many of the enteric bacteria in sewage that may be pathogenic
- 50-80% of the energy used for WWT goes into aeration
nitrification/denitrification
- simultaneously removes organic compounds and nitrogen
- requires switching between aeration and no aeration to support nitrifiers (aerobes) and denitrifies (anerobic process)
- results in the removal of N and organic carbon
- switches between adding and removing oxygen
NH3 -> NO2 -> NO3- -> N2
activated sludge - reducing energy costs and sludge protection
- anammox can also be used for N removal
- ## reduces the need for aeration, reducing energy needs -> results in less sludge
what is needed for anammox to work for WWT (what’s different between nitrification/denitrification and partial nitritation/anammox)
partial
- produces nitrite instead of nitrate
- only nitrogen get removed
- works if organic carbon is already removed (no external carbon source is needed)
- anaerobic = grow slower (less growth to remove the same amount of nitrogen) -> less sludge
- AOB able to grow NOB suppressed
anaerobic digestion
complex polymers -> monomers -> methanogenesis
- solids digest = end up with soil material used for fertilizer
- syntrophic process
how microbial metabolism treats wastewater
Aerobic Chemoorganoheterotrophs (Activated Sludge)
Role:Oxidize organic carbon → CO₂
- Convert waste organics into microbial biomass (VSS)
Benefits:
- Remove BOD
- Outcompete pathogens (competitive exclusion)
Downside:
- Aeration costs = 50–80% of all energy used in wastewater treatment.
Nitrifiers (Aerobic Lithoautotrophs)
-These remove ammonia during nitrification:
-Ammonia-oxidizing bacteria/archaea (AOB/AOA): NH₃ → NO₂⁻
-Nitrite-oxidizing bacteria (NOB): NO₂⁻ → NO₃⁻
- Requires lots of oxygen — it is energy intensive.
- Used in both conventional plants and Blue Plains.
Denitrifying Chemoorganoheterotrophs (Anoxic)
- Convert nitrate → N₂ gas, removing nitrogen permanently.
Requirements:
-No oxygen present
-Carbon source (Blue Plains adds methanol as carbon for denitrifiers)
Fermentative Bacteria & Syntrophs (Anaerobic Digestion)
During sludge treatment:
-Complex polymers → monomers → VFAs, H₂, CO₂.
-Syntrophs degrade fatty acids and alcohols into substrates methanogens can use (acetate, H₂).
-Complex polymers → fermentation → acetate/H₂/CO₂.
Methanogens (Archaea)
-Perform the final step of anaerobic digestion:
-Use acetate or H₂ + CO₂ → CH₄ (methane)
Benefits:
-Produces biogas → renewable energy
- Blue Plains generates 10 MW of electricity from methane
