As the most common cause of blockages and sanitary sewer overflows, grease (usually a combination of insoluble fatty acids) creates headaches for collection system operators. Grease from restaurants and households enters the sewer as fats or oils. With microbial activity, the grease is split into fatty acids which the longer chain forms are not readily soluble in water. The long chain fatty acids tend to deposit in areas of reduced flow velocity - in bends, larger pipes, or on lift-station walls. 

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It is this solid form of grease that must be removed by operators. In collection system grease control there are three main options:

• Physical removal - using mechanical or water jets to dislodge the clogs and move the grease as smaller chunks. This simply moves the grease down stream for further collection/capture.
• Microbial approach - adding microbes with fatty acid degrading capabilities will shorten the fatty acid chain length (making the grease convert first to soluble BOD then new cells, carbon dioxide and water). This is the same activity that occurs at the wastewater treatment plant - resulting in the final mineralization of grease. Micrbial modified grease will not redeposit as hard grease which is key to avoiding SSO and lift station problems. However, microbes must be introduced correctly and have time to form the biofilm that protects pipes from grease accumulation.
• d-limonene or solvents - a common chemical approach to grease removal is to use d-limonene (that strong orange odor) or other solvents such as butyl-cellosolve to solubilize the fatty acids. The problem here is the solvents rapidly emulsify the grease allowing for the slug to arrive at the treatment plant in a form that is difficult to separate in primary treatment. The long chain fatty acids that read as FOG and high COD/BOD remain in solution and enter secondary biological treatment. In high concentrations this can cause problems with effluent grease permits, floating solids/scum on clarifiers, and foam on the aeration basin. Additionally, fatty acids also make wasted biological solids entrap more water making disposal more difficult.

The potential for a slug of solubilized or emulsified grease to hit the biological treatment unit is why I do not often recommend the use of solvents in collection systems. While in a few cases they are needed to remove heavy buildup, it should not be the first treatment option. If problem areas of a collection system are identified - steps can be taken to reduce maintenance costs and prevent SSOs. Most of  the actions include the installation and maintenance of grease traps at restaurants and high density developments. If problems still exist, the use of a microbial dose with periodic physical monitoring/jetting often can keep the line free flowing and the lift-station clear.

Treatment of wastewater results in the removal of organic components measured as BOD/COD/TOC and the final conversion of organics into carbon dioxide, water, and new microbial cells. The new cells form the mixed liquor suspended solids in activated sludge or the biofilm in fixed film systems. In any case, normal operation includes keeping a fixed amount of microbial biomass to treat influent loading. So some of the cells must be wasted (keep a stable food/microorganism (F/M) or sludge age (MCRT).

How must wasting needs to be done is calculated based on cell yield per unit of organic treated. Using BOD5 or soluble BOD as the influent loading, we often plug in 0.5 g of new cells per gram of BOD5. However, this is not a constant or fixed number and can easily vary from 0.3 - 0.7.  What causes variation in cell yield? I will list a few:

• Composition of the influent - more complex/difficult organics result in less cell yield
• F/M ratio - lower F/M ratios result in less growth
• MCRT - works the same way as F/M
• Dissolved Oxygen - aerobic has much higher cell yield than facultative or anaerobic metabolism
• Environmental factors - temperature, pH, metals, etc in the water

The greatest impact on cell yield in aerobic systems comes from manipulating the F/M or MCRT to an "older sludge". However too old a sludge can start to cause problems with water clarification (biosolids start to become pin floc) and there is also a utility costs to maintaining oxygen with excess solids (much harder to quantify) - so I usually leave the proper MCRT question at keeping strong floc or biofilm in the system.

At Aster Bio, we are often asked about startup of new waste treatment systems and the impact of new industrial process streams on biomass. While toxicity tests such as Tox-Bac or Tox-N are useful in screening for toxicity to existing biomass, we often have cases where the customer has no existing biomass (new systems) or wants to know more about cell yield and kinetic rates than is given in quick toxicity testing.

The way we determine cell yield and kinetic rates is through the use of a bioreactor or chemostat. This unit can be adjusted to meet the anticipated environmental values of the system. In most cases we run a complete mix with excess dissolved oxygen when simulating aerobic treatment systems. 

What do you learn from running this type test?

• Cell yield per unit chemical or COD/BOD
• Degradation rates of individual chemicals
• Impact on microbial makes up of MLSS using Environmental Genomics 16S screening
• Evaluate floc and EPS formation on the new influent
• And determine which microbes are the best fit for treating the waste.

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When looking at influent data, I often ask customers having nitrification issues about their inlet TKN. Often they only run ammonia test on the influent. However, the biological treatment unit uses more alkalinity and has chronic DO even through the aeration system should provide more than enough oxygen for the full oxidation of influent ammonia and COD/BOD. 

The situation above is why I recommend any system with ammonia permits run both ammonia and TKN on the influent. To understand my reasoning, let's look at the tests.

First, ammonia testing is run by one of several methods. A common method is to use an ion selective electrode (ISE) to measure ammonia gas from a water sample to which sodium hydroxide is added to facilitate the conversion of water soluble ammonium (NH4+) into ammonia gas (NH3). This and other EPA approved methods, read only the ammonia/ammonium portion of total nitrogen in the water.

Now the TKN, also called Total Kjeldahl Nitrogen - after Mr. Kjeldahl the inventor. This test has more steps than the ammonia procedure as it relies on an acid digestion step that converts organic nitrogen into ammonia. Organic nitrogen includes proteins, amino acids, amines and other nitrogenous compounds that during biological treatment will tend to produce ammonium/ammonia.  After digestion, the amount of ammonia is measured. Therefore, for any sample: TKN > Ammonia. TON or Total Organic Nitrogen is simply:  TKN - Ammonia = TON
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For the wastewater system mentioned in the first part of this post, the influent TKN was significantly greater than influent ammonia. Alkalinity and aeration while sufficient for influent ammonia was insufficient for the ammonia derived from influent TKN. 

Researchers at the Cary Institute recently published a study on amphetamines (from both legal and illegal types) found in urban streams. More importantly, the researchers observed the following impacts at 1 ppb (part per billion) concentrations of amphetamine:

• Growth of biofilms were suppressed
• Bacterial and diatom communities changed
• Aquatic insects emerged earlier

While none of these impacts on the surface seem great, the changes are at the base of the food web which can make for major problems as you move to more apex creatures including humans. After reading the article, I am convinced that we will find significant impacts from many of our common pharmaceuticals that will eventually make wastewater treatment permits include removal of trace amounts. Key is what technology will prove most effective in removing xenobiotics at ppb levels.

Here is a link to a news release by the Cary Institute. 
http://www.caryinstitute.org/newsroom/ecological-consequences-amphetamine-pollution-urban-streams

Here is the link to the full article in Environmental Science & Technology.
Occurrence and Potential Biological Effects of Amphetamine on Stream Communities
Sylvia S. Lee, Alexis M. Paspalof, Daniel D. Snow, Erinn K. Richmond, Emma J. Rosi-Marshall, and John J. Kelly. Environmental Science & Technology . DOI: 10.1021/acs.est.6b03717http://pubs.acs.org/doi/full/10.1021/acs.est.6b03717

Concrete is great building material, but is subject to failure once cracks and fissures develop. Once a crack develops, water begins the process that results in overall failure and the need to replace or repair the concrete. Besides the potential to extend the life of concrete, it is also interesting to use bacteria to "build" things. Normally, we use bacteria to transform or degrade items into harmless building blocks.

Researches at the Delft Institute of Technology have created a way to use naturally occurring bacteria to in effect heal micro-fissures in concrete. Using alkaline resistant spores that can remain dormant for years in the harsh conditions found in concrete, researchers incorporated water soluble capsules containing calcium lactate and spores that only activate when moisture intrudes into the concrete. Once active, the bacteria consume the lactate as "food" and the calcium released binds with carbonates to create limestone which seals the fissure.

Here is a summary of the process with pictures from CNN. ​http://www.cnn.com/2015/05/14/tech/bioconcrete-delft-jonkers/