Nitrogen Removal in STPs & EcoSBR Advantages
Nitrification is a two-step aerobic biological oxidation process where ammonia (NH₄⁺) is converted first into nitrite (NO₂⁻) by ammonia-oxidizing bacteria (AOB), and then nitrite is converted into nitrate (NO₃⁻) by nitrite-oxidizing bacteria (NOB). This conversion is crucial because ammonia cannot be denitrified directly. Full nitrogen removal requires both nitrification and denitrification.
Organic - N → NH4+ → NO2- → NO3- → N₂ gas
The microbial groups involved:
Ammonia-Oxidizing Bacteria (AOB): Nitrosomonas, Nitrosospira
Nitrite-Oxidizing Bacteria (NOB): Nitrobacter, Nitrospira (dominant)
These bacteria are autotrophic, slow-growing, and sensitive to dissolved oxygen, pH, temperature, and toxins.
Development Timeline of Autotrophs in a New STP
Autotrophs (AOB & NOB) grow extremely slowly. Typical timeline in a new plant:
Days 1–3: Heterotrophs dominate, BOD reduces
Days 4–10: AOB begin developing, nitrite appears
Days 10–20: Stronger ammonia oxidation
Days 20–30: NOB appear → nitrate formation
Days 30–45: Full nitrification stabilizes
Days 45–60: Robust and stable nitrifying community
High DO is essential for this development.
Impact of High Ammonia & C:N Ratio
High ammonia concentration, especially from urine-heavy wastewater, requires a strong nitrifying capacity. However, office wastewater often has very low COD (lack of kitchen waste), leading to very low C:N ratios (1:1 or 2:1). This limits denitrification and causes nitrate buildup unless an SBR cycle promotes endogenous carbon usage.
Case Studies: Office Buildings
Office buildings without kitchens produce high nitrogen and very low COD wastewater. Urine dominates pollutant load, and carbon deficiency makes denitrification difficult. Office buildings with kitchens have better C:N balance and achieve better nitrogen removal.
EcoSBR manages both scenarios by using endogenous respiration and granular sludge.
EcoSBR Granular Sludge Advantages
EcoSBR naturally forms granular sludge due to selective pressure from its sequencing phases.
Benefits include: