ErgoPlanner

Appearance

CSTR-Sidestream - Sidestream Treatment Reactor ​

Specialized continuously stirred reactor for high-strength sidestream treatment, particularly reject water from dewatering operations with elevated ammonia concentrations.

Overview ​

The CSTR-Sidestream reactor is designed to treat high-ammonia sidestreams (reject water, centrate, filtrate) that would otherwise impose significant recycle loads on the mainstream treatment process. These reactors often employ deammonification (anammox-based) processes for energy-efficient nitrogen removal.

When to Use ​

  • Dewatering reject water treatment (500-2000 mg/L NH4-N)
  • Reducing nitrogen recycle loads (15-30% plant load)
  • Plants with limited mainstream capacity
  • Energy optimization through deammonification
  • New construction or retrofit applications

Key Characteristics ​

  • High ammonia concentrations (10-50x mainstream)
  • Elevated temperature (25-35C from digestion)
  • Low carbon-to-nitrogen ratio
  • Suitable for shortcut nitrogen removal
  • Significant energy savings vs. conventional treatment

Process Options ​

Conventional Nitrification-Denitrification ​

Traditional approach requiring external carbon:

  • Full nitrification (NH4 to NO3)
  • Denitrification with methanol/acetate
  • High energy and chemical costs
  • Complete nitrogen removal possible

Nitritation-Denitritation ​

Shortcut via nitrite:

  • Partial nitrification (NH4 to NO2 only)
  • Denitritation from nitrite
  • 25% less oxygen, 40% less carbon
  • Requires NOB suppression

Deammonification (Anammox) ​

Most energy-efficient approach:

  • Partial nitritation (55% NH4 to NO2)
  • Anammox (NH4 + NO2 to N2)
  • 60% less oxygen, no carbon required
  • 90% less sludge production

Deammonification Process ​

Stoichiometry ​

Partial Nitritation (AOB): $$NH_4^+ + 1.5O_2 \rightarrow NO_2^- + H_2O + 2H^+$$

Anammox Reaction: $$NH_4^+ + 1.32NO_2^- + 0.066HCO_3^- + 0.13H^+ \rightarrow$$ $$1.02N_2 + 0.26NO_3^- + 0.066CH_{2}O_{0.5}N_{0.15} + 2.03H_2O$$

Overall (combined): $$NH_4^+ + 0.85O_2 \rightarrow 0.44N_2 + 0.11NO_3^- + 1.14H_2O + 1.43H^+$$

Oxygen Comparison ​

ProcessO2/N RemovedRelative
Conventional N/DN4.6 kg O2/kg N100%
Nitritation-Denitritation3.4 kg O2/kg N75%
Deammonification1.9 kg O2/kg N40%

Biokinetics ​

AOB Kinetics (Ammonia Oxidizers) ​

$$\mu_{AOB} = \mu_{AOB,max} \times \frac{S_{NH}}{K_{NH,AOB} + S_{NH}} \times \frac{S_O}{K_{O,AOB} + S_O}$$

NOB Kinetics (Nitrite Oxidizers) ​

$$\mu_{NOB} = \mu_{NOB,max} \times \frac{S_{NO2}}{K_{NO2,NOB} + S_{NO2}} \times \frac{S_O}{K_{O,NOB} + S_O}$$

Anammox Kinetics ​

$$\mu_{AMX} = \mu_{AMX,max} \times \frac{S_{NH}}{K_{NH,AMX} + S_{NH}} \times \frac{S_{NO2}}{K_{NO2,AMX} + S_{NO2}} \times \frac{K_{O,inh}}{K_{O,inh} + S_O}$$

NOB Suppression Strategies ​

StrategyMechanismImplementation
Low DOAOB outcompetes NOBDO = 0.2-0.8 mg/L
High temperatureHigher AOB/NOB ratioT > 30C
Free ammoniaNOB inhibitionFA > 1-5 mg/L
Intermittent aerationAnammox selectionOn/off cycling
SRT controlWashout NOBSRT < NOB doubling time

Design Equations ​

Nitrogen Mass Balance ​

$$Q_{centrate} \times NH_{4,in} = Q_{eff} \times NH_{4,out} + r_N \times V$$

Required Volume ​

For deammonification: $$V = \frac{Q \times \Delta NH_4}{NRR}$$

Where NRR = Nitrogen Removal Rate (kg N/m3/d)

Typical NRR Values ​

Process ConfigurationNRR (kg N/m3/d)Notes
Suspended growth (startup)0.2-0.5Anammox buildup
Suspended growth (mature)0.5-1.0Stable operation
Granular sludge1.0-3.0Enhanced retention
MBBR/biofilm0.5-2.0Media dependent

HRT Calculation ​

$$HRT = \frac{V}{Q}$$

Typical: 1-3 days for suspended growth deammonification

SRT Requirements ​

OrganismMinimum SRT (days)Design SRT (days)
AOB1-23-5
NOB1.5-3(suppress)
Anammox10-1520-40

Parameters ​

Influent Characteristics ​

ParameterUnitDefaultRangeDescription
NH4-Nmg/L800400-2000Ammonia concentration
TKNmg/L900500-2200Total Kjeldahl N
CODmg/L500200-1500Low C:N ratio
TSSmg/L500100-2000Suspended solids
TemperatureC3025-35From digestion
pH-7.87.2-8.5Alkaline

Process Parameters ​

ParameterUnitDefaultRangeDescription
Volumem3calculated-Reactor volume
HRTdays21-4Hydraulic retention
SRTdays3020-60Anammox retention
DO setpointmg/L0.50.2-1.0Low for NOB suppression
TemperatureC3028-35Optimal range
pH-7.57.0-8.0Controlled

Kinetic Parameters ​

ParameterSymbolUnitDefaultRangeDescription
AOB max growthmu_AOB1/d0.90.6-1.5At 30C
Anammox max growthmu_AMX1/d0.080.05-0.15At 30C
AOB decayb_AOB1/d0.150.1-0.2Endogenous
Anammox decayb_AMX1/d0.010.005-0.02Very low
NH4 half-sat (AOB)K_NH,AOBmg/L1.00.5-2.0Monod
O2 half-sat (AOB)K_O,AOBmg/L0.30.1-0.5Monod
O2 inhibition (AMX)K_O,inhmg/L0.50.2-1.0Inhibition

Process Configurations ​

Single-Stage Suspended Growth ​

  • Both AOB and anammox in same reactor
  • DO controlled at 0.3-0.8 mg/L
  • Intermittent aeration optional
  • Simplest configuration

Two-Stage Process ​

  • Stage 1: Partial nitritation (SHARON)
  • Stage 2: Anammox
  • Better process control
  • More complex operation

Granular Sludge (One-Stage) ​

  • Self-granulating biomass
  • AOB in outer layer, anammox in core
  • High biomass retention
  • Compact footprint

MBBR Deammonification ​

  • Biofilm on carrier media
  • Layered biofilm structure
  • Good for retrofit
  • Lower biomass concentration

Configuration ​

Example Configuration ​

json
{
  "type": "cstrSidestream",
  "id": "deammonification-1",
  "parameters": {
    "volume": 500,
    "processType": "deammonification",
    "configuration": "singleStage",
    "hrt": 2.0,
    "srt": 30,
    "targetNH4": 50,
    "doSetpoint": 0.5,
    "temperature": 30,
    "aerationControl": {
      "mode": "intermittent",
      "onTime": 15,
      "offTime": 15,
      "doMin": 0.2,
      "doMax": 0.8
    },
    "biokinetics": {
      "model": "deammonification",
      "muAOB": 0.9,
      "muAMX": 0.08,
      "bAOB": 0.15,
      "bAMX": 0.01,
      "kNH_AOB": 1.0,
      "kO_AOB": 0.3,
      "kO_inh": 0.5
    },
    "nobSuppression": {
      "lowDO": true,
      "freeAmmonia": true,
      "faTarget": 2.0
    }
  }
}

Worked Example ​

Given ​

  • Centrate flow: 200 m3/d
  • NH4-N: 900 mg/L
  • Temperature: 32C
  • Target: <100 mg/L NH4-N (90% removal)

Design (Deammonification) ​

Step 1: Nitrogen Load $$Load = 200 \times 900 \times 10^{-3} = 180 \text{ kg N/d}$$

Step 2: Required Removal $$\Delta N = 900 - 100 = 800 \text{ mg/L}$$ $$N_{removed} = 200 \times 800 \times 10^{-3} = 160 \text{ kg N/d}$$

Step 3: Select NRR For suspended growth (mature): NRR = 0.7 kg N/m3/d

Step 4: Required Volume $$V = \frac{160}{0.7} = 229 \text{ m}^3$$

Design with safety factor: V = 300 m3

Step 5: HRT Check $$HRT = 300/200 = 1.5 \text{ days}$$ (within 1-3 days)

Step 6: Oxygen Demand $$O_2 = 1.9 \times 160 = 304 \text{ kg O}_2\text{/d}$$

Compare to conventional: 4.6 x 160 = 736 kg O2/d Savings: 59%

Step 7: Alkalinity Requirement Deammonification consumes less alkalinity: $$Alk_{consumed} = 3.57 \times 800 \times 0.5 = 1,428 \text{ mg/L as CaCO}_3$$

Influent typically sufficient (digester effluent high in alkalinity).

Startup and Seeding ​

Anammox Startup ​

PhaseDurationActivity
SeedingDay 0Inoculate with anammox sludge
Acclimation1-4 weeksLow loading, build population
Ramp-up1-3 monthsGradual load increase
StableOngoingFull capacity operation

Seed Sources ​

  • Existing anammox plants
  • Partial nitritation sludge
  • Granular sludge from other plants
  • Commercial anammox cultures

Troubleshooting ​

IssueCauseSolution
Low N removalNOB competitionLower DO, increase FA
Anammox inhibitionCheck for toxics
Low temperatureHeat reactor
Nitrite accumulationAOB/anammox imbalanceReduce aeration
High effluent NH4Insufficient AOBIncrease DO slightly
OverloadingReduce flow
Nitrate in effluentNOB breakthroughSRT control, lower DO
FoamHigh proteinDefoaming, SRT adjust
Poor settleabilityFilamentsSelector conditions

Integration with Mainstream ​

Load Reduction ​

Mainstream load reduction: $$\text{Reduction} = \frac{Q_{side} \times \Delta N_{side}}{Q_{main} \times N_{main}} \times 100%$$

Typical reduction: 15-30% of plant N load

Return Flow Timing ​

  • Equalize flow over 24 hours
  • Avoid peak mainstream loading
  • Consider storage tank
  • CSTR - Continuously Stirred Tank Reactor
  • Anoxic-Zone - Anoxic Zone
  • SBR - Sequencing Batch Reactor
  • MBBR - Moving Bed Biofilm Reactor
  • Deammonification

References ​

  1. Lackner, S. et al. (2014). "Full-scale partial nitritation/anammox experiences". Water Research, 55, 292-303.
  2. Siegrist, H. et al. (2008). "Anammox brings WWTP closer to energy autarky". Water Science & Technology, 57(3), 383-388.
  3. Wett, B. (2007). "Development and implementation of a robust deammonification process". Water Science & Technology, 56(7), 81-88.
  4. WEF (2018). Design of Municipal Wastewater Treatment Plants, MOP 8.