Oh no my nitrifiers are dead!!! What happened?

One of the most difficult problems in the waste treatment area refineries have to face is dealing with hard to degrade compounds, amines and nitrogen residuals. It is hard for the biomass sometimes to degrade organic hydrocarbons with large ring structures. A significant amount of time, as well as the right bacteria, is required to break down these large, complex compounds. An even harder challenge is the breakdown of amine compounds and conversion of ammonia to nitrate. This is done by a completely different mechanism and with a different set of nitrifying bacteria.

Ammonia -nitrogen is one of the main pollutants contained in wastewater from petroleum refineries and petrochemical wastewater treatment plants that can cause serious discharge final effluent permit violations. Ammonia is toxic even at very low concentrations to fish in receiving waters. Also the autotrophic conversion of ammonia to nitrite and subsequently to nitrate requires large amounts of oxygen for energy transfer.
 
To treat the many sources of wastewater from plant operations, normally an activated sludge treatment system is used. The different sources of influent making up the waste streams includes cooling tower blowdown, boiler blowdown, steam traps, vent gas wash towers, sour water strip effluent, overhead condensate streams etc. Refineries also have in addition to that cokers, Benzene reduction units, cat crackers, etc. These can sometimes create quite a mixture of difficult to treat compounds, if not slightly toxic to nitrifiers. Biocides are used in cooling towers and too much of these can cause a high load of amines, or a toxic load of biocides, depending upon the chemical make-up of the product used.

The Activated sludge system contains two types of bacteria. Carbonaceous bacteria primarily remove the BOD. Nitrogen elimination via nitrification/denitrification with nitrosomonas and nitrobacter has proven to be a successful way to solve the excess ammonia that is leftover after all nutrient requirements are met by the carbonaceous bacteria. This is where many times problems in wastewater treatment occur.

With stringent discharge limits imposed by the EPA, refineries are looking for potential modifications including stream isolations, equipment additions and operational changes that may help improve ammonia removal rates and ensure compliance with future permit limitations.

In the past several years, the Environmental Leverage® Lab has developed technology including products, testing procedures and programs that have successfully helped our Refinery customers meet their discharge limits via biological removal.

Products
Bioaugmentation is the application of specifically selected bacteria into a wastewater treatment system to increase the biological activity and overall health of the biomass thereby enhancing the performance of the system. These bioaugmentation products, when used correctly can help a system to recover from an upset, increase biomass capabilities to degrade compounds that take too much time for the current system, increase floc structure for easier settleability and dewatering or increase the ability to nitrify.

Some of the bioaugmentation products used are a liquid nitrification product, which contains specific bacteria that are able to convert nitrogen to Nitrate. Nitrosomonas and Nitrobacter

Another bioaugmentation product sometimes used is a specially formulated bacterial blend to help break down hard to degrade compounds, amines, rings, etc. thereby allowing the nitrifiers (Nitrosomonas and Nitrobacter) an easier environment to grow in and allowing them a faster rate of nitrification. Most problems occur because amines are not broken down fast enough in a system, make it to the clarifier, finally are broken down, but by then the nitrifiers are not able to break it down fast enough before it bleeds out the final effluent and causes permit violations. Either that, or the amines are present in the final effluent and are not noticed, and when BOD or toxicity samples are performed, they then cause problems.

Testing Procedures
The general health, diversity and nitrification capabilities of the wastewater treatment system biomass can be determined using numerous tests developed by our Environmental Bioengineering lab.

Wastewater Biomass Analysis

A microscopic examination of the wastewater sample is documented by photomicrographs. Biological floc structures, higher life forms, polysaccharide coating in floc structures, presence and identification of filaments, etc. are carefully examined and documented in this analysis. By routinely doing these biomass analyses under all operating conditions, baseline information can be obtained and monitored, thereby enabling incremental system changes to be measured and implemented.

Shake Flask Toxicity Study- Shake flask studies are the bioengineering version of jar testing. This testing can be used as a screening method to determine if existing biomass can be enhanced by bioaugmentation along with the treatability/toxicity of the wastewater to improve COD/BOD removal. Testing can also be done with additives such as nutrients or chemicals to determine their impact on the sample treatability. Toxicity can also be checked on.

Nitrification Inhibition Testing-Composite samples from individual wastewater streams contributing to the total nitrogen in the system can be analyzed for nitrification inhibition testing. The samples are spiked with a known amount of ammonia, pH stabilized with buffers and inoculated with a nitrifying population with known ammonia removal capabilities. A flask with DI water and ammonia serves as the Control. The ammonia readings are recorded and monitored hourly. Ammonia degradation in the sample is compared to the Control and reported as % inhibition. The capacity of the MLSS to achieve nitrification can also be measured.

By a combination of the above lab testing methods along with a review of the wastewater treatment plant data, it is possible to determine if there is any correlation between wastewater plant operating conditions and nitrification or if it is a lack of sufficient nitrifying population in the system. Are there sufficient Nitrosomonas and Nitrobacter present. Is alkalinity an issue? Are amines not completely broken down? Is there sufficient oxygen?

The Critical 5 plus one- Alkalinity is critical for nitrification

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