We all know the best way to prevent grease accumulation in collection systems is to "keep grease out". Even with well maintained grease traps and public education, collection systems tend to suffer from grease accumulation in problem areas such as bends, bellies, slower flow zones, and lift-stations.

As I biological treatment person, I was involved in multiple field tests that used biological maintenance options. Of course some worked better than others, this post will detail some of the things that we found when going from lab to the field.

As an insoluble organic, grease (usually long chain insoluble fatty acids) causes problems in the following ways:

• Sticks to pipe walls which restricts flows. In severe cases, this can cause SSO.
• Harmful to lift station equipment and anaerobic zones under grease film produce H2S
• In wastewater plant the FOG is slow to degrade and can cause floating sludge/scum
• Can promote hydrophobic microbe growth - the most seen is Nocardia

So what did we learn from numerous field tests

​Grease traps
Grease traps are not checked enough - often restaurant managers barely know they exist. Inspecting the trap can lead to timely pumping. Biological additives, when used in a maintenance program, can reduce BOD5 and FOG entering the colletion system. The best biological products in testing were metered liquid formulations containing fatty-acid degrading cultures. Side benefits to stress to restaurant managers include - fewer mystery odors in parking lot and reducing emergency plumber call outs for drain line clogs. 

Gravity mains
We looked at manual dry product dosing and adding liquid cultures with a metering pump. The liquid by virtue of more frequen dosing fequency was more effective. Grease accumulation rates decreased and the grease that accumulated was partially degraded and easily jetted from pipe walls. Camera guys noted the grease was "fluffy" versus the normal hard grease seen in problem lines. Keys for success in treating gravity mains included dosing upstream of the problem. It is best to do a survey and find sources of the grease and dose at a point where grease degrading biofilm can be established upstream of the problematic site. This is where experience comes into play and we can use tools to find the best dosing point.
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Lift Stations
Having worked with time-release blocks, manual dry products, and metered liquid blends; I have found that the best product depends on lift-station size, amount of grease, and access issues. Often if we treat grease traps and gravity mains upstream, the lift-station grease is controlled. This is because bacteria are able to grow on pipe surfaces forming a grease degrading biofilm. This biofilm contains aerobic and microaerophilic organisms that are the same ones seen in healthy wastewater treatment plants. So by treating collection systems, you are moving biological wastewater treatment upstream. We have used this to lower loading to WWTP that are undersized for increased influent loadings while waiting on new treatment plant construction.

Here are a few take-home messages from the trials:

• Grease degrading microbes come in many forms - it is not just Nocardia. You can favor specific ones to prevent Noardia foams on aeration basins by doing upstream  pretreatment.
• It is best to keep grease out of a system via education. However some still enters the collection system. Treating upstream is most efficient. 
• Treatment is not as simple as ordering something out of a catalog and hoping for the best. A collection system treatment program should involve investigation, selecting proper product for the location, and finding proper addition points. 
• Collection system programs behave by natural laws. There are no bug steroids, super bugs, or anything that has a mystery. We know that controlling the environment, promoting the right organisms, and seletively modifying microbial populations can achieve treatment goals. 

I often hear that ammonia removal across a system is low based only on influent and effluent ammonia numbers. I often ask what is influent and hear that the system does not run TKN. TKN is more difficult to run than ammonia, but is very useful for systems with significant influent organic nitrogen. 

For dicussion purposes, TKN = Ammonia + Total Organic Nitrogen. It does not include nitrite or nitrate. 

Influent TKN takes into account the generation of ammonia from biologial waste degradation by heterotrophic organisms. While some of the nitrogen is used in cell division and other metabolic processes, excess is converted biologically into ammonia. It is this ammonia that is used by your nitrifiers (ammonia oxidizing bacteria & nitrite oxidizing bacteria). 

So when you are looking at ammonia removal effiency across a system, you should look at influent TKN as a better indicator of efficiency than using influent ammonia. Now in some systems influent TKN is 90% ammonia. In that case, influent ammonia is fine. If your TKN:Ammonia ratio is consistent, you can just run influent ammonia. Others with inconsistent organic nitrogen loads should run TKN daily.

If I ask people about their problems with low temperatures, the most common problem is maintaining ammonia oxidation (AKA Nitrification) during winter months. So why can we see decent BOD/COD removal with low temperatures and not ammonia/nitrite oxidation to nitrate? 

It all has to do with AOB & NOB having slow growth rates under all conditions that become more exagerated under low temperature conditions. Secondly, genera that oxidize ammonia/nitrite are mesophilic organisms that don't do well at temperatures under 10 - 12 Deg C.

Nitrifier Growth Rates
Ammonia Oxidizing Bacteria (AOB) - often a mix of Nitrosomonas, Nitrospira (the COMAMMOX subset), Nitrosococcus - are the slowest growing of the chemotrophic nitrifiers. That means the initial conversioni of ammonia into nitrite is usually the rate limiting step. The AOB growth under ideal conditions (D.O. > 2 at cell level, pH 7.2 - 8.2, sufficient alkalinity, and no inhibition) maxes out at 10 - 12 hours versus 30 - 60 minutes for many heterotrophic (BOD removing) organisms. AOB ideal growth happens between 25 - 30 deg C.  As you decrease temperature below 20 Deg C, time required for cell replication increases and if operating at a low MCRT, you may see the AOB population "washout".

More on Temperature Impact on Nitrifier Population
Nitrifiers growth slows as you drop below 20 deg C and is so slow that by 10 Deg C that we consider the cultures dormant. Unlike the heterotrophic populations that can adjust to lower temperatures with low range mesophiles and some psychrophiles that thrive at temperatures between 3 - 15 deg C. The increase in lower temperature heterotrophic organisms is the reason that you can keep BOD removal even with low temperature wastewater. In fact, I have worked with cultures that grow well at 5 deg C. 

Ways to keep nitrification at low temperatures
Now that you know why nitrification is a problem at lower temperatures, what can you do to keep ammonia from reaching the effluent? Here are some suggestions:

• Increase MCRT to avoid washout
• Keep pH, Alkalinity, and D.O. at ideal levels 
• Try to keep inhibitory compounds amines, sulfides, phenol, solvents, and other inhibitory compounds out of the biological unit as much as possible
• Moving from surface aeration to diffusers can help "insulate" and reduce temperature drop across the biological unit