FOS/TAC Ratio Analysis Service

Comprehensive FOS/TAC Analysis Service at Creative Biolabs

Anaerobic Digestion is a process that degrades organic matter in an oxygen-free environment to produce biogas (mainly methane and carbon dioxide). This process is usually used to treat organic waste such as sludge, agricultural waste, etc. To keep the efficiency and stability of anaerobic digestion, it is very important to monitor and control some key parameters within the system. FOS stands for volatile fatty acids (VFA), such as propionic acid, acetic acid, butyric acid, etc, which are intermediate products in the anaerobic digestion process, and the concentration of these acids reflects the degree of accumulation of organic acids in the system. If VFA accumulates too much, it will affect the activity of microorganisms and inhibit the anaerobic digestion process. TAC stands for total alkalinity in the digestion system, which can neutralize acidic substances and act as a buffer during the anaerobic digestion process, thereby maintaining the stable operation of the digestion system. Creative Biolabs has high-precision analytical instruments. Our team of experts evaluates the stability of the anaerobic digestion system by measuring the FOS/TAC ratio. By monitoring this ratio, it can be determined whether the digestion system is balanced and whether adjustments need to be made.

• Step 1: Sample preparation

We take out the sample to be analyzed, filter it to remove large suspended particles, and ensure that the sample is uniform.

• Step 2: FOS analysis
  • Prepare for titration: We pour the sample solution (about 20 mL) into a beaker and place it on a magnetic stirrer. Then insert the pH meter electrode and make sure that the electrode is submerged below the liquid surface but not touching the bottom or side of the beaker.
  • Titration: We titrate the sample solution with 0.1 N sulfuric acid solution and record the change in pH during the titration. When the pH drops to 5.0, record the volume of acid consumed at this time (V1, mL). Then continue to titrate the sample solution until the pH drops to 4.4, and record the volume of acid consumed at this time (V2, mL).
  • Calculation: We calculate the difference ΔV between V1 and V2, and then calculate FOS using the following formula: FOS = (ΔV × 1.66-0.15) × 500
• Step 3: TAC analysis
  • Prepare for titration: We pour another sample solution (about 20 mL) into a beaker, place it on a magnetic stirrer, and insert the pH meter electrode.
  • Titration: We titrate the sample solution with 0.1 N sulfuric acid solution and record the change in pH during the titration. When the pH drops to 5, record the acid consumption volume (V3, mL).
  • Calculation: TAC=V3*250

• Step 4: FOS/TAC ratio analysis

We calculate the FOS/TAC ratio according to the value obtained in step 3. Usually, a FOS/TAC ratio between 0.3 and 0.4 indicates that the anaerobic digestion system is stable, but it needs to be monitored. A ratio of less than 0.3 indicates that the anaerobic digestion system is stable. A ratio greater than 0.4 indicates that the system may be unstable and measures such as adding alkaline substances or reducing the feed amount are needed to restore balance.

The FOS/TAC ratio is a critical monitoring indicator in the anaerobic digestion process. Creative Biolabs provides comprehensive FOS/TAC analysis services in the digestion system to help clients scientifically monitor and adjust system stability, ensure the smooth operation of the digestion system, and efficient organic matter degradation. Please contact us if you would like to obtain detailed analysis details.

Published data

Anaerobic digestion is an effective process for recovering high-value components from olive mill wastewater (OMW). The authors studied OMW in a large-scale anaerobic digestion unit and collected digestate and biogas samples at irregular intervals. They measured the biomethane content in the digestion system using gas chromatography and tested the FOS/TAC ratio in the system by sulfuric acid titration, which was a practical indicator of the biochemical state of the digester, with an ideal value between 0.2 and 0.3. As shown in the figure below, to avoid excessive acidification of the digestion system, the authors adjusted the pH of the reaction system to 6 with 20% NaOH solution during the first 70 days of the experiment. After the pH adjustment of the feedstock was stopped, the FOS/TAC ratio increased. By the 96th day of the experiment, the FOS/TAC ratio was 0.38, slightly higher than the ideal value. The results showed that the FOS/TAC ratio maintained a stable biochemical balance inside the digestion reactor even after the pH adjustment of the feedstock was stopped after 70 days of the experiment. In addition, the microbial population in the digestion system could remain stable and was able to process acidic OMW without pH adjustment, producing a digestate with a pH between 7.0 and 7.8, and the pH of the effluent was relatively stable.

Fig.1 Test results of FOS/TAC of OMW.^{1, 2}

FAQs

Q1: How often should the FOS/TAC ratio be measured during anaerobic digestion?

A1: The FOS/TAC ratio should be measured at least weekly, but more frequently when changes occur in the system or abnormal conditions are observed. For efficiently operating digesters, we recommend more frequent monitoring of the FOS/TAC ratio to respond quickly to any potential issues.

Q2: What should I do if my FOS/TAC ratio is above the recommended range?

A2: A high FOS/TAC ratio indicates organic acid accumulation and the feed rate and composition should be checked immediately. In addition, measures such as reducing feed rates, improving pretreatment steps, and increasing pH or alkalinity can help reduce organic acid levels and restore system stability.

Q3: How does the FOS/TAC ratio work with other parameters to optimize the anaerobic digestion process?

A3: In addition to the FOS/TAC ratio, monitoring parameters such as VFA, alkalinity, gas production and quality, and pH are necessary. Multi-parameter monitoring provides comprehensive information to optimize feeding strategies, adjust operating conditions, and respond promptly to any abnormal conditions that may arise.

Customer Review

References

1. Pluschke, Jonas, et al. "Anaerobic digestion of olive mill wastewater and process derivatives—Biomethane potential, operation of a continuous fixed bed digester, and germination index." Applied Sciences 13.17 (2023): 9613.
2. Under Open Access license CC BY 4.0, without modification.

Related Services:

1. BMP Assessment
2. Biological & Chemical Analysis
3. Chemical Oxygen Demand Detection
4. Biological Oxygen Demand Detection
5. VFA Profiling
6. Digestate Solid Impurities Determination
7. Ammoniacal Nitrogen Profiling
8. Nitrates Profiling
9. Viable Weed Seed Analysis
10. Organic Matter Profiling
11. SHA Determination
12. SAdA Determination
13. SMA Determination
14. Microbiological Activity Assessment
15. Sludge Granule Size Analysis
16. Sludge Activity Analysis
17. Toxicity Assessment in Microbial Digestion Processes
18. Persistent Digestion Process Profiling