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1. Understanding Odour Sources

Primary Odour Compounds

Compound	Source	Characteristics	Threshold (ppm)
H₂S (Hydrogen Sulphide)	Anaerobic decomposition of sulphur-containing proteins	Rotten egg smell, highly toxic	0.0005
NH₃ (Ammonia)	Protein breakdown, urea decomposition	Pungent, irritating	5.0
Mercaptans	FOG decomposition, industrial waste	Skunk-like, cabbage	0.001
VFAs (Volatile Fatty Acids)	Incomplete anaerobic digestion	Sour, vinegar-like	0.001-1.0
Indoles/Skatoles	Protein fermentation	Fecal odour	0.001

Common Odour Generation Points

• Influent Collection Systems: Long retention times, anaerobic conditions in sewers
• Primary Treatment: Screens, grit chambers, primary clarifiers
• Aeration Basins: Under-aerated zones, dead spots, surfacing sludge
• Secondary Clarifiers: Septic sludge, poor sludge blanket management
• Sludge Handling: Thickening, digestion, dewatering operations
• Lagoons: Turnover events, stratification, anaerobic bottom layers

2. Diagnostic Protocol

3. Common Problems & Solutions

Problem: H₂S Generation in Clarifiers

Root Causes:

• Excessive sludge blanket depth (>1.5m)
• Low DO in return activated sludge (<0.5 mg/L)
• Long sludge retention in clarifier (>2 hours)
• High sulfate-containing industrial discharge

Solutions:

1. Immediate: Increase RAS rate to reduce sludge blanket, increase DO in aeration basin
2. Short-term: Apply bioaugmentation products to oxidize sulfides, add nitrate to clarifier
3. Long-term: Optimize sludge wasting schedule, implement DO setpoint control, work with industries on sulfate reduction

Problem: Lagoon Turnover Events

Root Causes:

• Thermal stratification breakdown (seasonal temperature change)
• Heavy rainfall causing rapid mixing
• Deep anaerobic sludge layer accumulation
• Wind-driven destratification

Solutions:

1. Prevention: Regular mechanical mixing/aeration, seasonal sludge surveys, controlled turnover scheduling
2. During Event: Maximize aeration, apply hydrogen peroxide or nitrate, deploy floating aerators
3. Recovery: Bioaugmentation to re-establish aerobic microbial community, monitor DO continuously for 2 weeks

Problem: Abattoir Wastewater Odours

Root Causes:

• High protein and FOG loads overwhelming treatment
• Anaerobic zones created by poor mixing
• Temperature spikes from hot wash-down water
• Inadequate nutrient balance (N:P deficiency)

Solutions:

1. Source Control: Install better FOG removal (dissolved air flotation), cool influent before treatment
2. Process Optimisation: Increase aeration capacity, add nutrients (urea, phosphoric acid)
3. Bioaugmentation: Apply specialised protein and FOG-degrading cultures, maintain stable microbial population
4. Monitoring: Daily protein testing, weekly microscopy to assess microbial health

4. Bioaugmentation Protocols

When to Use Bioaugmentation

• Persistent odour issues despite process optimisation
• After toxic shock or plant upset
• High-strength industrial waste events
• Startup or restart situations
• Seasonal loading changes

Application Guidelines

Parameter	Requirement	Notes
DO Level	>1.0 mg/L	Essential for aerobic culture survival
pH Range	6.5 - 8.5	Optimize to 7.0 - 7.5 for best results
Temperature	15 - 35°C	Activity doubles every 10°C rise
Mixing	Continuous	Prevent settling, ensure contact
Contact Time	>4 hours HRT	Longer is better for establishment

5. Operator Checklist

Daily Monitoring

• Visual inspection of all treatment units
• DO readings at aeration basin inlet, middle, and outlet
• Sludge blanket level in clarifiers
• Note any unusual odours (location, intensity, character)
• Check foam levels and color
• Review weather conditions and temperature

Weekly Assessment

• BOD/COD testing of influent and effluent
• Suspended solids analysis
• Microscopic examination of mixed liquor
• Sludge volume index (SVI) testing
• Review community complaint log
• Check chemical inventory and dosing equipment

Monthly Review

• Comprehensive process performance analysis
• Trend analysis of key parameters
• Equipment maintenance verification
• Lagoon bathymetry (if applicable)
• Bioaugmentation effectiveness assessment
• Update odour management plan as needed

6. Emergency Response

Safety Considerations

7. Key Performance Indicators

Parameter	Target Range	Action Required If Outside Range
Aeration Basin DO	2.0 - 4.0 mg/L	Adjust blower output, check diffusers
RAS DO	>0.5 mg/L	Increase aeration, reduce RAS rate temporarily
H₂S (headspace)	<5 ppm	Investigate source, implement bioaugmentation
pH	6.8 - 7.5	Adjust with lime or acid, investigate cause
ORP	>0 mV (aerobic zones)	Increase aeration, check for anaerobic pockets
Sludge Blanket	<1.0 m	Increase RAS, optimise wasting
F/M Ratio	0.2 - 0.5 kg BOD/kg MLSS/day	Adjust wasting rate or influent flow

8. Resources & Contacts

Recommended Testing Schedule

Critical Parameters (Daily): DO, pH, temperature, visual inspection

Process Control (Weekly): BOD/COD, TSS, MLSS, SVI, microscopy

Comprehensive (Monthly): Nutrients, metals, full suite analysis

Technical Support

Additional Resources

• Water Environment Federation (WEF) Manual of Practice No. 25: Odor Control
• Australian Water Association (AWA) technical papers
• WWTP Operator Certification programs
• Micro-Genix online knowledge base and video tutorials

9. Case Studies

Case Study 1: Municipal WWTP - Clarifier H₂S Control

Facility: 5 ML/day municipal plant, oxidation ditch + clarifiers

Problem: Persistent H₂S odours from secondary clarifiers, complaints from nearby residential area

Root Cause: Excessive sludge blanket (2.3m avg), low RAS DO (0.2 mg/L), long clarifier retention (>3 hrs)

Solution Implemented:

1. Increased RAS rate from 60% to 85% of influent flow
2. Applied sulfide-oxidizing bioaugmentation product
3. Optimized DO setpoint to 2.5 mg/L in oxidation ditch

Results:

• H₂S reduced from 45 ppm to 3 ppm within 3 weeks
• Zero odour complaints after 4 weeks
• Maintained control with maintenance dosing (2x/week)

Case Study 2: Red Meat Processing - FOG & Protein Odours

Facility: Abattoir with 800 m³/day high-strength waste, DAF + lagoon system

Problem: Intense putrefaction odours, frequent foam events, regulatory complaints

Root Cause: BOD spikes (3,000-8,000 mg/L), FOG overloading (>500 mg/L), insufficient biological activity

Solution Implemented:

1. Improved FOG removal efficiency in DAF (recovery from 75% to 92%)
2. Applied specialised protein/lipid-degrading culture
3. Added supplemental aeration in lagoon cells 1-2
4. Established nutrient addition protocol (N:P balance)

Results:

• Odour intensity reduced by 85% within 6 weeks
• Foam events eliminated
• BOD removal efficiency improved from 65% to 88%
• Regulatory compliance achieved and maintained

10. Troubleshooting Quick Reference

Odour Character	Likely Cause	First Action
Rotten eggs	H₂S from anaerobic conditions	Increase aeration, check DO levels
Ammonia/urine	Protein breakdown, pH issues	Check pH, improve nitrification
Musty/earthy	Actinomycetes overgrowth	Review sludge age, consider wasting
Septic/sewage	Long HRT, insufficient treatment	Increase flow-through, add aeration
Chemical/solvent	Industrial discharge	Trace source, implement pretreatment
Rancid fat	FOG decomposition	Improve grease removal, bioaugmentation