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Grease and Lift Stations. . .The Impact on Filaments in a Municipality

With all the new growth in a village or city, many changes are happening that impact the ability of the POTW to handle the incoming wastewater.

High growth spurts in new developments have not only impacted the flow rates to the wastewater treatment plant, but the loading has increased also. Why, it should be proportional to the changes in the houses and developments. While that should be true, it is often not the case. Many of the old tried and true engineering statistics calculated flow, and loading based upon population and growth.

What they did not account for is the change in society, the new housing developments that all have garbage disposals built in and now send many things that used to be scraped off into the garbage cans at homes. Many food particles and grease wind up in the drains that never used to be there before.

There are tons of new multi-family housing establishments, from assisted living, condo's to retirement centers that did not exist in the past. The loading from these can significantly increase the changes in flow and loading.

The largest impact on flow and loading and the most significant contributor to loading problems is fast food restaurants! And not to point the blame, actually they are required to have grease traps, the problem is that the government increased the temperatures on their cleaning and sanitation requirements. Temperatures for dishwasher's increased from 180-210 F, which means that even though they have a grease trap, most of the grease is still soluble in the water and flushed through the system and down the drain until it hits the lift stations or pipes and then cools down and hardens.

This winds up causing problems in the lift stations, increase grease in pipes, increases in maintenance, wear and tear on pumps, and increased jetting out of the lines. A grease ledge or solids build-up in the lift station can interfere with floats, pumps, etc.

Go one step beyond the lift stations and collections systems, now you have all that grease loading up the wastewater treatment plant. Some plants have primary clarifiers, which if optimized, can pull out some of the grease. Often times, this grease is sent to a digestor though, and additional loading is then put on the digestor.

If there is no primary, then the aeration basin or lagoon sees all this additional loading.

Dead floating solids in a primary or floating grease can often be seen and indicate a problem. Check the beds in the primary, watch the rake speeds or conveyers, depending upon the type of primary that you have and be sure to try to remove as much of the solids prior to the secondary biological system.

What happens when all this grease hits my aeration basin?

Nocardia and Microthrix Parvicella are often the result when high grease loading enters the municipality.

Nocardia Gram stain 1000x Microthrix parvicella gram stain 1000x

Imaging trying to dewater this, it would be like a sponge and hold a ton of water, not to mention trap air in all the pockets and float in the aeration basin or clarifier.

Microthrix foaming in an aeration basin Nocardia bulking in an activated sludge plant

Here there is so much foaming that it has clogged up the sprayer

Foaming in an aeration basin

Clarifier carry-over and problems:

If all the grease does not get digested in the aeration system, then it can carryover to the clarifier. Below is a picture of grease scum floating on the top of a clarifier.

Worse that the grease carrying through, is the problems with floating solids generated by Microthrix or Nocardia. These filaments tend to create a sponge like mass of floc and trap gasses. This tends to want to float. Solids floating in a clarifier a clarifier can increase polymer demand if any is used, increase dewatering solids problems, increase chemical consumption for dewatering, and increase solids handling costs by increasing the amount of solids generated. Filaments take up 3-5 times as much area or more depending upon the type of filament present and create bulking sludge.

Floating solids from filamentous problems

Grease scum on a clarifier

Solutions:

Bioaugmentation in the lift stations, upstream in the pipes, or directly in the restaurants and food plants is the easiest and cheapest way to solve the problems. The bacteria actually eat the grease as a food source, as opposed to manual cleaning which can be costly and require some safety issues with manpower. Chemicals and degreasers may dissolve the grease in the lift station, but basically they just send it through the pipes, which may cause blockage or directly down to the POTW, which causes overload on the plant.

This is a manhole 20 feet from a small restaurant. Look at how much crease and solids are built up in this small area. This restricts the flow and eventually may cause problems in the restaurant with back-ups. The solution- a small amount of bacteria were mixed in a bucket of water and poured directly on the surface of the grease to clean out this manhole. It worked! Continual dosage will be required weekly, though since there is no source for recirculation an it gets washed out periodically. Ongoing maintenance kept the manhole from ever building up so many solids again though!

Here is a municipality that had problems with Microthrix:

Before and after a bioaugmentation program was implemented to help control grease