Does adding sludge from a nearby plant help?

Activated Sludge Unit

I often get this question. If you believe that a microbe is a microbe - then it should work perfectly. You could truck in sludge from a municipal plant and it would work perfectly for building biomass in a refinery. Of course we all know it is not that simple. To answer the title question, adding sludge can help but it all depends on  your expectations and treatment needs.

​To more fully answer the question, we need to look at wastewater microbiology and the nature of Mixed Liquor Suspended Solids (MLSS). As I like bullet points, here it is:

• ​The microbial composition depends upon the influent makeup including organics present, waste concentration, inorganics including TDS/chlorides, toxic and quasi toxic compounds.
• Another factor in microbial makeup is the system's environment - pH, macronutrient (N,P) concentrations, temperature, dissolved oxygen, and sludge age.
• MLSS contains a mixture of active bacteria, dead cells, extracellular polymeric substances (EPS), and adsorbed particles. In most systems the active bacteria portion is less than 15% with longer sludge ages having a lower active fraction.

​Now, when you add sludge from a plant without the same influent or operating conditions the MLSS experiences a shock which can kill many of the active microbes. This die off is seen with increased turbidity and floating solids often seen when adding off-site MLSS to a system. While some of the surviving bacteria will grow and potentially flourish, the most common benefit from adding sludge is the increase in adsorptive capacity (in effect adding a sponge). If the system can handle the solids even requiring adding polymer, the added mass can give you time for a sufficient microbial population to develop. This is where bioaugmentation can prove valuable.

​Bioaugmentation includes adding cultures screened for growth in the system. The resulting product is highly concentrated with respect to active microbial fraction. How we use it with adding MLSS from nearby plants is based on evaluation and experience. Here are the situations:

• If a similar wastewater facility is nearby - trucking in sludge can be highly beneficial using MLSS alone.
• Long distance transport can add substantial cost and long storage time can result in septic sludge being added with associated problems.
• If a system is experiencing moderate upset and has sufficient MLSS but low microbial activity, the best option is often adding bioaugmentation product as it can restore the active portion quickly without adding inert solids.
• In cases where the MLSS is depleted (lost) - adding sludge for mass purposes along with active bioaugmentation cultures is the most rapid option to restore full treatment efficiency.

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