I recently got a question on why bloodworms (midge fly larvae) seem to impact the AOB population more than the standard BOD removing or heterotrophic bacterial population. Given you only see worms when you have low BOD, high oxygen - why is ammonia the first effluent quality problem following a midge infestation.

Well it all goes back to how fast bacteria reproduce. The heterotrophic (carbonaceous) or just simply BOD removing microbes in wastewater tend to grow very quickly. In making bioaugmentation products, you can have a bioreactor reach maximum population density within 24 hours with many Bacillus and Pseudomonas cultures that can double every 30 - 60 minutes depending upon substrate and environmental conditions. The fastest reproduction time is called µ(max) or maximum growth rate. For AOB, nitrifiers, growth rate is measured in hours - 7 - 8 hours in laboratory environments. In wastewater facilities you are looking at 10 - 12 hours as maximum growth rate.
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Now how does this lead back to midge larvae causing more problems with effluent ammonia numbers? Simply, the midge larvae consume bacteria in the form of floc. They eat all microbes present including heterotrophic and ammonia oxidizing bacteria. Since the AOB reproduce as a slower rate, the percentage of AOB drops more than for the faster growing heterotrophic bacteria. Therefore, while we lose total MLSS (biological solids) to the larvae’s consumption, the AOB bacteria a disproportionately impacted.

Over the past month, I read about two Texas area water treatment workers, while working on a pump, were overcome by hydrogen sulfde exposure. One of the workers died and the other required hospitalization. This reminds us of how deadly hydrogen sulfide can become when working in wastewater. 

Hydrogen sulfide forms when a collection system has soluble organics, anaerobic conditions, and the presence of sulfate. All of this happens to occur to a limited extent in gravity lines but can become critical in the confines of force mains. We often think of H2S gas a a nuisance due to it causing odor complaints at 1 - 10 ppm, monitoring areas where H2S forms in collection systems can also save lives by limiting potential worker exposure. Even at low levels long term H2S exposure can be a problem. OSHA has limits set at 10 ppm for workers.

How can H2S be controlled in the collection system? Keys methods are:

• Avoid creating anaerobic zones by adding peroxides, nitrate, oxygen, etc
• Keep reduce sulfides in water phase by increasing the pH (avoid acid conditions that create the H2S (gaseous) form of sulfide (S=)
• Adding Fe or other chemicals that bind to reduced sulfur (S=)
• Adjusting pumping frequencies to prevent long residence time in force mains

This is the time of year that I start getting calls about blooms of midge larvae in wastewater treatment plants. These larvae feed on biological solids and can actually deplete system biomass during large outbreaks. While the larvae cause problems, they only flourish in systems with low BOD, good D.O., and otherwise excellent quality effluent. 

You can foresee and outbreak if you notice an abundance of tiny flying midge (look like small flies) near the biological treatment unit. The rapid life cycle of midge, ensures you have flying insects and larvae in conjunction with each other.

What can you do to prevent the biomass loss? Use EPA approved control methods such as Strike, an insect growth regulator, or Aquabac XT, a Bacillus thuringiensis spore solution that kills larvae by damaging the digestive tract. Using either product has given great results within a 2 - 5 days (another product of the rapid life cycle in midge flies). If the outbreak causes extreme loss of biomass, we often see ammonia removal efficiency drop (nitrifiers are very slow growers and susceptible to washout). In this case, you may want to add a floc forming bacterial inoculum such as Aster Bio's AB Munizyme that helps build MLVSS and prevents nitrifier washout. Adding, the more delicate (refrigerated/shipped overnight) and expensive nitrifier cultures is usually not needed as you can restore the population rapidly by just building good biomass.

While reading the WE&T Journal from the WEF, I found the following report from the US EPA. While we have removed a number of pollutants from our surface waters, much needs to be done to correct storm water, accidental releases, and non-point source pollution. The impact is clear:

"The U.S. Environmental Protection Agency (EPA) surveyed 1.9 million km (1.2 million mi) of rivers and streams and in March released its findings in the National Rivers and Streams Assessment (NRSA) 2008/2009: A Collaborative Survey. The survey found that 46% of rivers and streams are in poor biological condition, and 25% are in fair condition.

Waterways with high levels of phosphorus, nitrogen, and sediments are about twice as likely to have poor macroinvertebrate (aquatic insect) communities. In every 8 km (5 mi) surveyed, levels of excess nutrients were found in more than 3 km (2 mi) and high levels of riparian disturbance, such as nearby roads, buildings, and parking lots, were found in about 1.6 km (1 mi). In addition, about 1.6 km (1 mi) in 6 km (4 mi) did not have healthy shoreline vegetation, and 1.6 km (1 mi) in 10 km (6 mi) had excess streambed sediments.
The survey also found that 23% of waterways had enterococci bacteria levels exceeding thresholds set to protect human health, and more than 20,900 km (13,000 mi) had mercury in fish tissues exceeding these thresholds, the fact sheet says.

When compared to the 2004 Wadeable Streams Assessment, the survey found that while riparian vegetation cover had improved by 10%, there was a 9% decline in biological quality, a 14% decline in phosphorus conditions, and a 12% increase in riparian disturbance, the fact sheet says.

Reducing nutrients and improving habitat would improve biological health of these waterways. Potential solutions include completing state nutrient management strategies, adopting stream and shoreline buffers, supporting farmers’ efforts to manage nutrients and prevent pollution, and improving nutrient removal in wastewater treatment, the fact sheet says."

​https://www.epa.gov/national-aquatic-resource-surveys

At Aster Bio, we receive many samples from new processes that may impact the existing wastewater unit biomass. We wanted to develop a rapid test for screening purposes that could identify percent inhibition to standard wastewater organisms. In many instances, you use a spiked oxygen uptake rate (OUR) or perform a respirometery study to see if microbial respiration is inhibited by the compound.

Background information on the Tox-Bac test
While we have used OUR to test biomass respiration as an indicator of high loadings or other biomass stress, we found the spiked OUR subject to variation from the MLSS sample and often the lack of fresh MLSS when doing extensive lab toxicity testing.

Key to our needs was a reproducible biomass for consistent inhibition reporting results. So, our R&D group developed a known preserved biomass from various vegetative microbes. The resulting preserved biomass was similar to that found in municipal and light industrial wastewaters. This "known" biomass contains a uniform mix of microbes that gives a narrow range of oxygen uptake when hydrated on chlorine free or DI water. The DI water respiration rate serves as the control as it has no inhibition to the microbes. The test influent is evaluated at pre-set dilutions for determining toxicity.

We also designed the test for use with existing BOD bottles & DO meters - so the test could be run in any standard wastewater facility without needed any unusual equipment or reagents. The resulting test takes approximately 25 minutes per sample with most of the time being inactive as the microbial respiration is measured only between minutes 19 and 21 (near maximum activity is reached and no reproduction has occurred).

Example Application using Tox-Bac™
A customer was introducing a new process unit that was going to add a completely new influent to the wastewater treatment system. The environmental staff wanted to know the potential impact from the new influent on the biomass. The waste stream was adjusted to a pH of 7.2 for purposes of testing and allowed to aerate for 1 hour to ensure oxygen saturation. The test was performed using a DI water control with the influent being added at 16% and 33% by volume for the tested inhibition samples.

​Results

Conclusions
The testing found significant inhibition at both 16 and 33 percent concentrations. Moreover, the toxicity appeared linear in nature with a near doubling of inhibition with increased concentration. Given the test results, the new influent could cause significant upset to the biological treatment system.​

Contact me if you would like more information on Tox-Bac™ testing and kit availability. Aster Bio will be making them available for sale in August 2016. 

I thought this was a good exhibit of how the choice of cylinder for measuring SV30 can impact settleometer results.  Key point is to use the same type vessel for running the tests every day.