Control of the FOG in lift-stations is often done using a combination of physical and chemical approaches. Water jets and vacuum trucks can loosen and collect grease deposits. Often surfactants/solvents are added to liquefy the grease for easier removal. Solvents, even natural ones such as d-limonene, emulsify grease and allow any FOG not removed by vacuum truck to pass down to the treatment plant.
Since the 1990s, many municipalities have used microbial blends for grease control in lift-stations. The microbial products are found in liquid, solid block, or dry powder form. Here is a quick run-down on what they contain:
- Liquid - spore forming microbes + surfactants. The spore forming microbes do have the needed beta-oxdiation pathways and can control grease. The surfactants improve results by increasing the oil/water interface where the bacteria degrade the FOG. Generally, the surfactant dose does not push the grease to the treatment plant and only enhances FOG biodegradation. Liquid are usually fed via a metering pump.
- Solid - contains microbes (usually spore formers but some manufacturers include higher activity vegetative strains) and surfactants in an organic solid base. The solid block is designed to release bacteria over time. The idea is not need for electricity or manual product addition. All blocks have problems with dissolving time not being uniform - it all depends upon temperature, mixing, and flows. If they work in a lift-station, a block can be the easiest method to control grease.
- Dry Powder - the oldest, lowest cost per unit of microbe dosed product. In addition to spore forming microbes, dry powders may contain vegetative strains (such as Pseudomonas) that are more efficient in degrading grease. The biggest challenge with powders is the requirement for manual dosing between 3- 5x per week.
Over the past several years, we have been evaluating ways to improve biological activity in the lift-station. We looked at using various blowers and mixers to determine:
- Could the lift-station FOG be controlled by only adding aeration and mixing
- Would combining microbes and aeration/mixing be better than either technology alone.
With over a year of testing, we have noted the best approach is to combine the aeration/mixing with the microbes. The aeration/mixer can be in almost any form. The key is to mix and increase the bacteria/oil/water interface - with mixing we have enough oxygen for beta oxidation pathways. With treatment, grease does not build up into a solid cap. Any grease that accumulates is easily washed off with water spray. FOG to the treatment plant does not increase as seen with using surfactant/solvent treatments - as the fatty acids are being converted from FOG into soluble organics (BOD5) which is not a problem for most treatment plants.