Secondary effluent provides essential nutrients that support microbial activity.
Biological odor control systems rely on microbial activity to degrade odor-causing compounds such as hydrogen sulfide (H2S), ammonia (NH3), and volatile organic compounds (VOCs). Properly maintaining these systems requires a consistent and controlled supply of make-up water to sustain microbial communities and ensure system longevity.
Secondary effluent, a byproduct of wastewater treatment, presents a viable alternative to potable water, offering cost savings and additional nutrients that enhance microbial metabolism. However, its implementation requires a strategic approach to manage potential drawbacks, such as fouling and variable water quality.
Secondary Effluent vs. Tertiary Effluent
- Secondary effluent is the preferred make-up water source over potable water due to its residual nutrients that support biological processes.
- Tertiary effluent is more suitable for humidification applications, as it contains minimal residual nutrients and BOD, limiting biomass growth in the humidification chamber.
- When using secondary effluent in the humidification chamber, biomass accumulation on the humidification packing may occur, leading to excessive fouling. Regular maintenance and monitoring are recommended.
Water Quality Specifications for Secondary Effluent Usage
The following table outlines optimal water quality parameters necessary for effective system performance:
| Parameter | Optimal Range | Notes |
|---|---|---|
| Free Chlorine | <0.1–0.5 ppm (ideal) <5 ppm (maximum) |
Even low levels can be toxic to biofilm-forming bacteria. |
| Total Suspended Solids (TSS) | <10–15 ppm | Prevents clogging and maintains media porosity. |
| Total Nitrogen (TN) | 20–40 ppm | Ensures sufficient nitrogen for microbial growth. |
| Ammonia (NH4+-N) | 20–30 ppm | Supports nitrification; higher levels (<50 ppm) can inhibit microbial activity if oxygen is low. |
| Nitrate (NO3–-N) | 5–15 ppm | Indicates active nitrification; ensures proper nitrogen cycling. |
| Phosphorus (P) | 10–20 ppm | Avoids excess microbial overgrowth while supplying nutrients. |
| Magnesium (Mg2+) | 5–15 ppm | Supports microbial enzyme function and biofilm stability. |
| Water Hardness (as CaCO3) | 50–150 ppm | Prevents excessive scaling while providing essential calcium / magnesium. |
| Biochemical Oxygen Demand (BOD) | 5–15 mg/L | Ensures sufficient organic carbon for microbial metabolism without overwhelming the system. |
| Chemical Oxygen Demand (COD) | ≤50 mg/L | Keeps organic load manageable and prevents excessive fouling. |
Key Considerations for Optimization
- Alkalinity: Maintain 50–150 mg/L as CaCO3 to support nitrification and pH stability.
- Dissolved Oxygen (DO): Keep levels ≥2 mg/L to sustain aerobic microbial processes.
- pH Stability: Maintain within 6.5–8.5 to support diverse microbial communities.
System-Specific Adjustments
- High Ammonia Levels: Increase aeration and alkalinity to promote nitrification.
- Slow Biofilm Growth: Adjust phosphorus and magnesium levels to support microbial development.
- Clogging Issues: Monitor TSS, hardness, and COD/BOD ratios to prevent excessive accumulation.
Monitoring & Adjusting Biological Odor Control Water Quality in Real-Time
To maintain optimal performance, regular monitoring and proactive adjustments are key. Here is how to track and fine-tune your biological odor control parameters:
1. Routine Monitoring Schedule
| Parameter | Testing Frequency | Monitoring Method |
|---|---|---|
| Free Chlorine (<0.1–0.5 ppm) | Daily | DPD Colorimetric Test / ORP Meter |
| TSS (<15 ppm) | Weekly | Gravimetric Filtration |
| Total Nitrogen (20–40 ppm) | Bi-Weekly | Kjeldahl or Spectrophotometer |
| Ammonia (20–30 ppm) | Weekly | Ion-Selective Electrode / Test Kits |
| Nitrate (5–15 ppm) | Weekly | Ion Chromatography / Test Strips |
| Phosphorus (10–20 ppm) | Weekly | ICP-OES / Colorimetric Tests |
| Magnesium (5–15 ppm) | Monthly | ICP-OES / Atomic Absorption Spectroscopy |
| Hardness (50–150 ppm) | Monthly | Titration Test Kit |
| BOD (5–15 mg/L) | Bi-Weekly | Standard BOD Test (5-day incubation) |
| COD (≤50 mg/L) | Weekly | Spectrophotometric COD Test |
| pH (6.5–8.5) | Continuous | Inline pH Probe |
| Dissolved Oxygen (≥2 mg/L) | Continuous | DO Probe with Online Sensor |
2. Adjustments Based on Monitoring Results
- If Free Chlorine is Detected (<0.1 [Ideal] – 0.5 ppm [Maximum]):
- Action: Add sodium thiosulfate or activated carbon filter to neutralize chlorine.
- Goal: Protect beneficial microbial communities.
- If TSS is too high (>15 ppm):
- Action: Increase backwashing frequency or add pre-filtration.
- Goal: Prevent clogging and maintain airflow.
- If Ammonium (NH4+) is Too High (>30 ppm):
- Action: Increase aeration to promote nitrification.
- Goal: Convert NH4+ to NO3– to prevent toxicity.
- If Nitrate (NO3–) is Too Low (<5 ppm):
- Action: Check for insufficient ammonia oxidation (possible oxygen limitation).
- Goal: Ensure a complete nitrogen cycle.
- If Phosphorus is Too High (>20 ppm):
- Action: Increase biomass removal or dilution with lower-phosphorus water.
- Goal: Prevent microbial overgrowth and excessive biofilm formation.
- If Hardness is Too High (>150 ppm):
- Action: Install a water softener or adjust alkalinity.
- Goal: Prevent scaling in the media.
- If Dissolved Oxygen is Too Low (<2 mg/L):
- Action: Increase aeration or backwashing to prevent anaerobic zones.
- Goal: Maintain aerobic microbial processes.
- If COD/BOD Ratio is Too High (>3:1):
- Action: Check for non-biodegradable organics; adjust media or retention time.
- Goal: Maintain efficient microbial breakdown of organics.
Alternative Nutrient Supplementation
Secondary effluent serves as a viable and sustainable make-up water source for biological odor control systems, providing essential nutrients that support microbial activity. However, successful implementation requires diligent monitoring and proactive adjustments to prevent operational challenges such as biomass accumulation and clogging. By adhering to the outlined optimization strategies and monitoring protocols, facilities can maximize the benefits of secondary effluent while maintaining system efficiency and longevity.
When secondary effluent water is not available, an alternative solution may be needed. GES 1578 nutrients, as manufactured by GES Biotek, LLC, are formulated as a supplement to enhance the growth of Acidthiobacillus Thiooxidans and Ferroxidans microorganisms in a biological odor control ecosystem, where the primary food source is H2S in the foul air stream. The formula is in a concentrated liquid form, requiring only one-part nutrient to 3,500 parts of water (3,500:1 ratio).