Often when dealing with questions on a system, I am given a trade name for a system which is thought to be unique. Well, in most cases the trademarked or patented system is just a variation on one of the time tested formats that have proven effective for years. In the past decade, many fixed film type systems have been installed - no matter if you call them fluidized bed, IFAS, FAST, RBC (Rotating Biological Contact), or even a tricking filter - all of these systems work on the principal of a biofilm attaching to a surface to support a high population of microbes that are not as susceptible to washout as a suspended growth (standard activated sludge or lagoon) system. We are now seeing retrofits where media is being added to increase aeration basin capacity by increasing the M in the F/M ratio. Today, I want to break down the various types of fixed film systems so comparisons of various "new" technologies is more easily accomplished.
All fixed film system rely on a "host" surface for a microbial colony that forms a biofilm. The standard film is represented in the graph below and is found in all variations of fixed film systems.
I am going to do a series of posts on each of the fixed film system technologies with the goal being to give a general overview of the technology and most importantly the pros and cons of each. Today I am going to start with the oldest of the fixed film technologies - the trickling filter.
The oldest of the fixed film system is the trickling filter. The most basic systems spray influent over rocks or other media contained in a tower. Treatment capacity and efficiency can be mproved by adding blowers to provide additional oxygen to the lower levels of the tower. Existing trickling filters can also be improved by utilizing newer, higher surface area plastic media rather than rock or other traditional media. Other mostly industrial trickling filters, recycle biologial solids from the secondary clarifier to "re-seed" biomass to the front of the system.
Pros of Trickling Filters
Expected Treatment Efficiency
Loading (kg BOD/100 m3/day) BOD Removal %
Low Rate Filters 40 80 - 90%
Intermediate Rate 64 65 - 85%
High Rate 160 50 - 75%
Roughing Filters 480 40 - 65%
Grease enters municipal wastewater treatment plants from multiple sources including restaurants, households, and light industrial customers. The fats, oils & grease (FOG) cause problems from the source point all the way down to the outfall of the sewage treatment plant. Each impact is detailed below
Upon allowing grease to enter a drain, the grease begins to accumulate on drain lines. With severe buildup, grease can clog the line causing backups and slow drains. Even with moderate grease accumulation, the restaurants will have problems with odors and drain flies which breed on the grease in the lines. Without proper grease trap maintenance, go the store will have exterior odors and experience excessive grease carryover into municipal sewer lines.
Grease can accumulate in sewer lines restricting flow and eventually blocking the pipe. The blockage can cause untreated sewage to discharge into the surrounding area in an event called a "sanitary sewer overflow (SSO)." A major number of these SSO events are caused by grease released into the sewer system from houses, restaurants, and local businesses. Small quantities of grease come out of solution in the sewers and begin to coat pipes and begin a buildup that starts to restrict flow. Most cities utilize camera inspection and physical cleaning to remove grease in troublesome sections of the sewer lines. In many cities, increased population density and older sewer lines have created a need for frequent cleaning and educational programs to keep people from dumping grease into the sewers.
Since the 1980s, people have been using microbial cultures to initiate grease degradation in the sewers. This process relies on the ability of select microbes to convert the grease into ever smaller particles that do not buildup in the sewer system. At Aster Bio we have several options to keep the grease from causing blockages while preventing free grease from entering the sewage treatment plant where it is more difficult to treat than other components of wastewater. Over the next three blog posts, we will discuss the treatment options that exist for grease control, odor control, and lower loadings hitting the treatment plant. The next topics are going to be:
Restaurant Grease Control - Treating lines in the restaurant helps prevent plumber emergencies caused by grease in drain lines. It also helps keep the grease trap from producing substantial foul odors and helps lower the amount of grease entering into the sewer system. Additional benefits include the reduction in "drain flies" that rapidly breed on grease found in floor drains.
Gravity Sewer Lines - Treatment can be established that allows for a beneficial grease degrading biofilm to establish on the pipe walls. This reduces grease accumulation and associated odors/corrosion caused by hydrogen sulfide (H2S).
Lift Stations/Force Mains - Lift stations often have grease accumulating on walls, pumps and floats. This grease causes damage to equipment and causes odors that can create complaints from local residents. Aster Bio can use a combination of microbes and equipment to convert the station into a working biological treatment system node that does not accumulate grease or produce odors.
Industrial facilities often discharge wastewater into municipal treatment systems and pay a surcharge based on loadings (pollutants) sent to the municipal facility. Often target components are BOD/COD, TSS, & ammonia. Surcharges are often high enough that the industrial facility will consider pretreatment to lower pollutants being transferred. The problem is most pretreatment systems tend to have either a high upfront equipment costs or have expensive chemical requirements.
Aster Bio has recently worked with an customer with high strength BOD (highly degradable organic acids majority of BOD) average of 3,500 - 4,800 mg/L with a flow of 20,000 gallons per day. Proposed pre-treatment systems were all priced $250,000 - 750,000 which was too high for the facility. Given a budget of $70,000, Aster Bio and the facility designed a pretreatment system using existing tanks with a total volume of 100,000 gallons. Adding a coarse bubble diffuser and eductor aeration/mixing system and associated piping resulted the facility meeting budgeted costs with room to spare. Since the system is simply an aerated series of tanks with no biosolids recycle, Aster Bio developed a microbial blend to inoculate active cultures at the front of the system. Testing runs resulted in 5 day decreases in influent BOD to <200 mg/L with a low of 75 mg/L. The ongoing Aster biological seed cultures used are a minor cost for the facility and run approximately $15 - 20/day depending upon charge and waste strength.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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