To maintain pH stability (around 6–7) during liquid biofertilizer fermentation with bacterial consortia, several strategies have been explored. Studies show that while common buffering agents like CaCO₃, NaHCO₃, and phosphate buffers provide some pH control, their effectiveness diminishes over extended fermentation as organic acid production by bacteria (like lactic or fumaric acids) lowers the pH again. Recent findings recommend incorporating protective agents such as polyvinylpyrrolidone (PVP), glycerol, and dimethyl sulfoxide (DMSO) into formulations. These compounds not only help stabilize microbial viability but also buffer pH by binding water, reducing salt stress, and slowing acidification. Using combinations of thickeners and protective polymers — like carboxymethyl cellulose, gum arabic, or sodium alginate — improves water retention and aeration, creating a more stable microenvironment for bacterial growth. Additionally, maintaining fermentation at cooler temperatures (like 4°C) has been shown to better preserve pH and cell viability over time compared to room or high temperatures. Ultimately, achieving long-term pH stability requires a combined approach: selecting the right protective agents, optimizing nutrient medium composition, and carefully controlling fermentation conditions.

Sharing two articles below:

• Allouzi, M. M. A., Allouzi, S. M. A., Keng, Z. X., Supramaniam, C. V., Singh, A., & Chong, S. (2022). Liquid biofertilizers as a sustainable solution for agriculture. Heliyon, 8(12), e12609. https://doi.org/10.1016/j.heliyon.2022.e12609

• Jaiswal, A., Kumari, G., Upadhyay, V. K., Pradhan, J., & Pramanik, H. S. K. (2023). A methodology to develop liquid formulation of biofertilizer technology. The Pharma Innovation Journal, 12, 875-881.

I want to know the difference between consortia and composite culture of bacteria. Can anybody specify me whether all bacteria growing in the same media ( consortia) or grown individually in their respective selective media with different carbon source and finally mixed ( composite culture). Because the carbon source of Azotobacter is different from Azospirillum. Similarly for othe microbes. All have their own choices. Some use penthouses some use hexose. Sometime I get puzzled. Can anybody clarify this dout?

I used to add MOPs to maintain pH of liquid broth during fermentation.

In Sokra Thank you for the suggestion! MOPS is a great buffer, especially for lab-scale fermentation due to its stability and good pH control. However, since we are working on an industrial-scale biofertilizer production, cost becomes a major consideration. Unfortunately, MOPS is too expensive for large-scale use, so we are looking for something more affordable and scalable.

Curious - why 6-7?

Suggest caution regarding pumping up buffer concentration re. impact direct /indirect on consortium and its metabolism.

Hi Phil Geis , thanks for your response!

The reason i'm aiming to maintain the pH between 6-7 is to support a balanced environment for the microbial consortium, and also targeting this pH range to help maintain the stability of the final product during storage, as overly acidic conditions can shift the microbial balance and reduce shelf life. it includes Lactobacillus, Bacillus, Pseudomonas, Saccharomyces, Actinomycetes, phosphate solubilizing bacteria (PSB), nitrogen-fixing bacteria and cellulolytic microbes

From my observation :

- The pH tends to drop due to acid production, especially from Lactobacillus and Saccharomyces. However, after testing. I've confirmed that both these strains remain viable and active at pH 6-7, so maintaining this range won't compromise their function.

- a pH below 4 doesn't provide the best environment for Bacillus, NFB, PSB to thrive or function optimally, and over time i've noticed their viability tends to decrease under these conditions.

I've been cautious about buffer concentration s for exactly the reason you mentioned- excessive buffering (especially phosphate) seems to interfere with microbial metabolism. That's why i'm exploring combination of mild buffer and controlled pH adjustments, aiming to stabilize without inhibiting any key players

looking forward to hearing your thoughts any guidance or ideas based on your experience would be truly appreciated as i continue refining this formulation

It is a challenge.

Perhaps consider the function rather than the formula pH. Is the material less effective as a biofertilizer at 4 than 6?

Phil Geis Based on early tests, the formulation is more effective as a biofertilizer at pH 6—better microbial viability and nutrient availability compared to pH 4.

Viability and nutrient availability. Anything in terms of actual yield?

What happens to pH in application?