Denitrification unit
Anaerobic nitrate reduction stage with carbon dosing and automatic control of ORP/NO₃⁻. Work without water discharge and without stress for the fish.
−50…+50 mV ORP (reference)
HRT: 6–12 h
Efficiency: up to −70% NO₃⁻
- Efficiency
- up to −70% NO₃⁻
- Hold time
- 6–12 h
- Control
- ORP, NO₃⁻
Replace denitrification-unit.jpg in the photo of your block.
Nitrate control without water discharge
What does the equipment solve?
- Reduces NO₃⁻ in circulation without large changes, stabilizes conditions in pools.
- Anaerobic chamber with agitators/recirculation for uniform loading of biofilm.
- Carbon dosing according to the ORP/NO₃⁻ algorithm, protection against “overdose”.
- Safe degassing (N₂/CO₂) and removal of possible traces of H₂S.
Equipment
- Sealed PP/PE reactor with insulation, inspection and drainage.
- Agitator/recirculation pump with VFD, maintenance bypass.
- Dosing stations (methanol/ethanol/acetate/carbohydrates), flow meters, check valves.
- Gas collector, degassing column, H₂S sensor (optional).
- Automation: ORP, NO₃⁻ (online option), event log, remote access.
How it works and what are the options
Principle
In low oxygen conditions, bacteria use nitrate as an electron acceptor and reduce it to N₂. A carbon source is supplied as an electron donor. Management is carried out using ORP and/or online NO₃⁻ to keep the process within the denitrification “window”.
- ORP reference: −50…+50 mV. Below ~−100 mV, the risk of sulfate reduction and H₂S increases.
- HRT (Hydraulic Hold Time): Typically 6-12 hours, under nitrogen load.
- Alkalinity: denitrification partially returns alkalinity - we take into account the pH balance.
Types of executions
- Heterotrophic (standard): external carbon (methanol/ethanol/vinegar/syrup). High speed, flexible configuration.
- Gray-autotrophic (optional): without organics, on sulfur/sulfide; relevant for sea water, requires special safety.
- Reactor: stirred stirrer (CSTR) or fixed/suspended biofilm feed reactor.
Selection and dosing
- Initial data: kg of feed/day, % protein, NO₃⁻ (in/out), temperature, pH.
- Stoichiometry (guidelines per 1 g of NO₃-N): methanol ~2.5 g, ethanol ~4.3 g, acetic acid ~3.5–4.0 g eq. according to COD. Setting - based on analysis.
- Anti-overdose circuit: upper limit ORP/NO₃⁻, cut-off when water flow drops.
- Start: inoculation, “soft” dose acceleration and smooth approach to target NO₃⁻.
Options and integration
- Online NO₃⁻ analyzer, SCADA integration, trend log.
- Permeate polishing: UV/ozone in trace doses, degassing.
- Redundancy of dosing pumps and power supply, GSM/Push alarms.
- Materials for sea water, spark-proof gas ventilation.