Using Environmental Genomics - 16s rDNA testing - to identify key microbial genera in petrochemical wastewater treatment plants

The wastewater treatment plant microorganisms, often called biofilm, MLSS or MLVSS, depend upon influent composition, biological treatment unit environmental conditions and treatment plant operations. Aster Bio’s research suggests that a core microbial group is present in most designs for extended aeration treatment systems. Via routine monitoring for key microbial genera, Aster Bio can detect the impact of new influents and operational changes at the microbial level. By closely monitoring changes in biomass microbial composition, WWTP do not rely on trailing indicators for tracking biomass health.

At Aster Bio, we have been working hard to understand what these different communities look like by harnessing our Environmental GenomicsTM platform for microbial community analysis using high- throughput 16S rRNA gene sequencing. Petroleum refining and organic chemical industries have quite variable influent compositions. While many wastewater plants treat both petroleum refining and organic chemical wastewaters, we break the group into two segments:

• Petrochemical Refinery – hydrocarbons, aromatics, phenol, and amines at mesophilic temperatures and relatively neutral pH. Process units centered around producing fuels, lubricants, and high-volume intermediate organic chemicals.
• Organic chemical Production – hydrocarbons, aromatics, amines at mesophilic temperatures and relatively neutral pH. Process units commonly include olefins, specialty organic compounds, and finished marketable products.

In these systems, we have found a group of "core four" microbial genera:

• Thauera
• Hyphomicrobium
• Nitrospira
• Nitrosomonas

​The first two are facultative organisms that use dissolved oxygen and nitrate/nitrite as electron acceptors while degrading influent organic compounds. As petrochemical and organic chemical plants often require ammonia oxidation, we note consistent populations of AOB/NOB composed of Nitrosomonas and Nitrospira. These genera convert ammonia via nitrite to nitrate – while using carbonates and carbon dioxide as the primary carbon source for cellular materials. These four microbial genera make up a very significant portion of the biomass in MLSS, often 25% or more. We also find significant quantities of Achromobacter, Bacillus, Burkholderia, and Pseudomonas genera present.
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But beyond this core group, the source influent and operating conditions impact the MLSS microbial composition. Systems with lower MCRT select against slower growing organisms such as Nitrosomonas and Nitrospira. Petrochemical facilities including olefin wastewater encourages the growth of Methyloversatilis, a group that thrives on C1 and other common hydrocarbon compounds. Other significant microbial genera found inside WWTP treating integrated petrochemical wastewater include Variovorax, Candidatus symbiobacter, Edwardsiella, Ottowia, Massilia, Aromatoleum, Immundisobacter, Limnohabitans, Rododbacter, Azoarcus, Azospirillum, and Cupriavidus.
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Interestingly, even with samples taken from aeration basins with dissolved oxygen above 2.0 mg/L, we find microorganisms that are either strict anaerobes like Clostridia, or require anoxic conditions to denitrify, like Thauera and Hyphomicrobium. Longer sludge ages, lower F/M, and high biological solids tend to increase the number of anaerobic and facultative anaerobic cultures. Both groups are favored by the internal floc or lower levels of the biofilm where the microbes are not exposed to the dissolved oxygen found in the surrounding water. Additionally, as the amount of inorganics and insoluble organics increase as a fraction of the MLSS, we see a shift to anaerobic and facultative anaerobic cultures as oxygen transfer efficiency into the floc decreases.