There have been many searches for information on red worms in wastewater treatment plants over the past few weeks. The worms are a common problem in warm weather and when the treatment plant has sufficient D.O. and is running well.

The worms are not really worms but the larvae of the midge fly. You may notice the non-biting midge flying above the plant around the time the worms appear.

While their ecology is interesting - most people just want to know how to control this bloom that eats the MLVSS and can cause TSS issues in the effluent.

Option 1 - Strike
Strike is an EPA approved insect growth regulator (IGR) is applied in relatively low concentrations and preempts the midge fly life cycle and brings about control.
http://www.strikeproducts.com/

Option 2 - Aquabac XT
A Bacillus thuringensis based biological control agent that works for controlling midge larvae. The are killed when they consumer the spores in the Bt liquid. Aquabac XT is manufactured by Becker Microbial Products and is available from a number of vendors. I have included a link the label for Aquabac XT from one of the online vendors. http://www.allprovector.com/labels-msds/Aquabac_XT_Label.pdf

Dosing and application information for both products is included on the labels and websites. They are both effective at controlling the red worm/midge larvae. I have used both successfully in activated sludge and fixed film systems. Hope the information helps.

I have just finished a quick summary course on bioaugmentation. Every day I see bioaugmentation, nutrients, and other additives offered as a panacea for all sorts of problems in waste treatment. The course below covers the basics of bioaugmenation including how products are designed and what to expect if you use bioaugmentation including its limitations.

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.

Trickling Filters
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

• Simple, durable system
• Good efficiency at BOD and Ammonia removal
• Low power use
  
  

Cons of Trickling Filters

• Limited flexibility
• Not well buffered for shock loadings or spills
  
• Plugging or clogging of media
• Potential media fouling by substances such as oils & grease
• Odors
• Nuisance flies
  

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%             

I have  completed a new training document for operators doing microscopic exam of wastewater. The short course covers the basic bacteria type, protozoa, and other higher life-forms seen in biological waste treatment units. In addition to helping identify the organism, I have provide hints as to their ecology and what promotes their growth in the unit.

Take a look and tell me what you think.

The dissolved oxygen uptake rate, commonly referred to as DOUR or OUR, is simply the amount of oxygen consumed by either chemical or biological activity over a set period of time. This means the OUR tests have many similarities to the respirometer tests which have the ability to feed more oxygen into the samples and take multiple time-series measurements. The difference being the OUR test uses a stirred BOD type bottle and oxygen probe whereas the respirometer is a much more complex and expensive single use device. If want to review the basics of performing a OUR test, I detailed it fully in a previous post (DOUR Procedure).

What do changes in OUR mean?
OUR usually remains in a steady range so we become concerned when the OUR is significantly higher or lower than normal. A high OUR means there is increased soluble organics increasing microbial respiration or a chemical oxygen demand such as sulfide has created a chemical oxygen demand. A low OUR, can mean either very low organic loading rates where the biomass has moved further into decline phase growth or a toxic shock event that causes a biomass die-off. Examples of toxic shock include - phenol, cyanides, solvents, or biocides.

Can I screen influent for toxicity with a DOUR test?
Yes, you can screen influent to some extent with a DOUR. It requires taking standard influent and adding the correct percentage of the new waste stream. Add this to mixed liquor at the appropriate percentage. For a control, use the existing influent and mixed liquor at the same percentages. Add an aquarium air stone and allow to aerate/mix for at least 4 hours up to 12 hours. Run a standard DOUR and test different dilutions between influents and mixed liquor to get a uptake rate profile. (contact me if you have questions on using OUR as a toxicity screen).

We often do common wastewater tests daily and rarely think about how they are all related. In the next few posts, I am going to cover how biological unit tests are all data points that help operators get a picture of the unit's "biological health". While under good operating conditions, you do not need to run all the tests or do them on a daily basis; under changing conditions frequent tests help operators head-off problems before effluent quality is compromised.

Today, I am going to relate how settling rates and solids mass tests are related.

SV30
The SV30 is a settling rate test. When mixed liquor is poured into a graduated settling vessel (large graduated cylinder or single purposed SV30 container); it is allowed to settle, undisturbed, for 30 minutes. Some operators record the solids volumes at 5 minute intervals to give a settling rate plot. What we are trying to determine is how well the system is flocculating and what to expect from secondary clarification. In addition to the biomass volume, operators should also note supernatant turbidity and if fines or small floc are floating.

MLVSS or MLSS
Biological solids are measured in a lab procedure to determine the weight of solids. The difference is the MLSS is total solids weight and MLVSS is the volatile fraction of the total solids (usually just biological solids - but can also include fibers and other organic influent solids).

SVI
After getting both the SV30 and the MLVSS numbers, we can calculate the SVI. The purpose of the SVI is to get a standardized number for settling rates. For example a system with an MLVSS of 2,000 should have a lower SV30 than the same system run with a MLVSS of 4,000. To relate settling performance when running different MLVSS numbers, we divide the SV30 number by the MLVSS number (in grams rather than milligrams).

In most system we look for an SVI between <120 ml/g and consider the system bulking with SVI >150 ml/g. If settling happens too quickly as seen with longer sludge ages, you may have pin floc or high turbidity in the supernatant. This is why I like operators to note turbidity and pin floc in the SV30 test.

What do I need to run on a daily basis?
In systems with very uniform operations (little influent variation in flow or makeup), a daily SV30 test with weekly MLVSS checks may be enough for operations. Certain industrial system may require daily MLVSS and 2x daily SV30 tests as influent can change quickly and settling is often the first thing impacted during a spill or upset event. Base your frequency based on the variation that you have seen in the past and since the SV30 is a low cost, simple test - run it on a frequent basis.