We commonly do testing of hydrocarbon contaminated wastewater and find big differences in different types of treatments when it comes to microbial growth. We will compare control growth rates compared to treatments that are pH adjusted, micronutrient adjusted, CNP adjusted and differences in aerobic vs facultative anaerobic growth. In these types of studies, we can often find ways to get the microbes to a higher peak growth and obtain these peaks 2-3 days sooner. I guess at first glance as long as your holding times are more than 2-3 days, who cares about who gets their first. If you factor in microbe build up in the sludge, than possibly this doesn’t matter too much. However, we do see with wasting and microbial cell death that the dosage and amount of strains are very important. But this is really what I am writing about and we will leave this to another day.
I am really writing about how this liquid prescreen is in our mind a rapid indicator of what and how fast we expect soil remediation results. We don’t like doing field work until we have at least some indicator of success in the lab. So we will often using liquid studies, to provide this fast indicator of success or failure. Better to fail in the lab then in the field. As you know the doubling time of many of these rapid growing bacteria can be 20-30 MINUTES in the right media and conditions. In soil, doubling time is reported to be around 50-100 HOURS, yes that’s not a typo, 50-100 HOURS. Soil does not have ideal moisture/water activities, aeration, and often missing the right micronutrients and CNP ratio you would find in lab media. Doing some rough calculations and making adjustments for lag time. 16 hrs in the lab will be equivalent to 35-70 days in the soil (assuming all the nutrients are right) to reach peak numbers of breakdown. I’m not sure I am using the correct scientific calculation here, and should be considered a rough “what if” number. So if I see peak results in 16 hrs in ideal conditions, should I expect peak results (not final results) in 35-70 days in the soil? I guess that depends upon making sure the soil has the correct balance of moisture, nutrients, aeration and other amendments required to provide for proper growth. In fact these are absolutely essential so the PATTON system applies here as well similar to wastewater. How do these rough numbers match up with how long others say bioremediation should take? Some of our clients have told us as quickly as 3 weeks but tend to find 8-12 weeks is more realistic. That tracks with what I discuss above. From what I see online and in literature I see numbers ranging from 60-180 days which is comparable to what I discuss below. Most likely how well they apply their own PATTON system dictates the short or longer range time frames.
So why am I babbling on about this? Because I commonly find that different amendments in liquid can mean a difference between peak growth from 16 hrs with amendments to 70 hrs without amendments (micronutrients, macronutrients, bacteria, etc ;). Not only do the peaks vary in growth activity, but the timeframe in liquid is astounding with differences of 54 hrs. Big whoop, 54 hr difference in liquid. But remember our soil doubling times. So by my rough calculations a peak of 16 hrs would translate to 35-70 days in soil, whereas the control which is hitting the peak after 70 hrs translates to 153-306 days. These numbers fall right in line with what I see in the literature or what I have heard in the field. Further the control never reaches even half our amended highest yields so without the amendments I think they are looking at 306-712 days if double, and 712-1414 days if triple. That’s a long time to wait to see if it’s working or not. At that point we should stop talking in days, but rather in years.
These liquid screen methods we believe are a nice prescreen to possible lab soil studies. The prescreens give us the opportunity to look at a lot of different variables to save precious time, effort and money.
That brings me to my next topic which I would like to hear from you. What surfactants are best? I haven’t had much luck finding good results with these as shown in literature but we aren’t surfactant people. We do see some surfactant improvements but not as good as adding for instance micronutrients. We have screened 100’s of micronutrients and have seemed to separate the good from the bad, but surfactants we are still at a loss. I would love to hear your thoughts and opinions on this. Most importantly would want a sample and target testing concentrations so we can educate ourselves better in this area. Electron acceptors come next!
