What causes straggler floc? Excessive solids losses in the final clarifier can be the result of hydraulic overload or due to the type and characteristics of the biological solids present. (1) Straggler Floc is indicative of a young sludge which tends to settle slowly.
What is straggler floc?
( 1 ) Straggler Floc is indicative of a young sludge which tends to settle slowly. This type of floc consists of light, fluffy, buoyant particles. Click to see full answer. Also know, what causes pin floc?
What causes pin floc?
Pin floc occurs most commonly at starvation conditions -- a very low F/M and long sludge age. Chronic toxicity can also cause a pin floc condition. Free floating filaments can, at times, cause a dispersed growth problem.
What is floc forming bacteria?
Floc is a collection of smaller particles agglomerating into larger particles containing particulate matter, debris, bacteria and Bio-polymers. Some of the positive aspects of floc forming bacteria is that they settle out easily as solids, reduce the need for polymers in clarifiers and reduce consumption in dewatering applications.
What does it mean when floc turns black?
Black indicates the floc is turning anaerobic and running out of air or is older. Sometimes floc can be colored if the influent contains dyes. Usually this does not impact anything unless there are heavy metals or toxic compounds that will not pass a leach test when disposing of the solids.
What causes pin floc in clarifier?
Pin floc occurs most commonly at starvation conditions -- a very low F/M and long sludge age. Chronic toxicity can also cause a pin floc condition. Free floating filaments can, at times, cause a dispersed growth problem.
What causes sludge to rise?
Rising sludge occurs in the secondary clarifiers of activated sludge plants when the sludge settles to the bottom of the clarifier, is compacted, and then starts to rise to the surface, usually as a result of denitrification, or anaerobic biological activity that produces carbon dioxide or methane.
What does pin floc look like?
Pin floc can be described as small, weak flocs that are subject to flotation within the clarifier. Pin floc leads to a more turbid effluent. It is most commonly the result of exceedingly high sludge age. Reducing sludge age often minimizes the occurrences of pin floc.
What causes floating sludge in clarifier?
When entrapped in floc, excessive grease or oil can cause floating biomass. This appears as a scum blanket that can cover the entire clarifier. Viscous bulking or billowing sludge – viscous bulking can sometimes create floating sludge (more often it is just billowing over the weir versus floating).
How do I stop sludge bulking?
To avoid sludge bulking some of the flow that enters the reactor can be bypassed, recycle ratio can be increased, lime or soda can be added to the reactor or the re-aeration rate increased.
What causes bulking?
Abstract. Sludge bulking is the most common solids settling problem in wastewater treatment plants, which is caused by the excessive growth of filamentous bacteria extending outside the flocs, resulting in decreasing the wastewater treatment efficiency and deteriorating the water quality in the effluent.
What is pinpoint floc?
Very small floc (the size of a pin point) that does not settle out of the water in a sedimentation tank or clarifier.
How do I reduce SVI?
Raising the amount of MLSS (reducing waste rates) changes the density of the floc, creating a heavier sludge particle. The more dense the particle, the more likely it will settle faster. The higher milligram per liter MLSS reduces the SVI result.
How do you get rid of filamentous bacteria?
Filamentous bacteria can be controlled by treating the return sludge with chlorine or hydrogen peroxide to selectively kill filamentous microorganisms. Chlorine concentration should be 10-20 mg/L (concentrations greater than 20 mg/L may cause deflocculation and formation of pin-point flocs).
How do you remove sludge from clarifier?
0:143:47Clarifier sludge scraper mechanism - sludge removal from clarifiersYouTubeStart of suggested clipEnd of suggested clipAre available but the most common are sludge hoppers chain scraper rotary scraper mechanism vacuumMoreAre available but the most common are sludge hoppers chain scraper rotary scraper mechanism vacuum suction systems sludge hoppers are usually used for smaller round or square basins.
How do you stop denitrification in clarifier?
So what can you do to prevent denitrification in secondary clarifiers:Control bed depths to between 2 - 3 feet by adjusting recycle rates.Hydraulic residence time in clarifier 2 - 4 hours.Warm temperatures increase denitrification (high metabolic activity) so problem is usually more pronounced in summer months.More items...•
How do you reduce sludge age?
The easiest and most practical way to control sludge age is with hydraulic control by wasting a defined proportion of the reactor volume daily. In AS plants with reactor concentration control, nitrification fails first.
What are the factors that affect sludge settling?
Changes in temperature, pH, DO and sludge age, or even amounts of available nutrients such as nitrogen, phosphorus, oils and grease, can affect these bacteria. Dominance of filamentous bacteria in activated sludge can cause problems with sludge settling.
What causes foaming in aeration basin?
Some filamentous microorganisms may cause foaming in the aeration basin and clarifiers. Algae and fungi are photosynthetic organisms and generally do not cause problems in activated sludge, their presence in the treatment system usually indicate the kinds of problems associated with pH changes and older sludge.
What is activated sludge?
Activated sludge isn’t a thing, it’s a process. As a sewage and industrial wastewater treatment, it makes use of air and a biological floc composed of bacteria and protozoa. The idea in controlling activated sludge is to keep the wastewater biomass-to-food ratio in balance. To control activated sludge, you need to "have a handle" ...
How to control activated sludge?
To control activated sludge, you need to "have a handle" either on aeration, sludge-wasting or return-sludge flow. Aeration-rate adjustment is probably the simplest way to go. It involves, however, more than measuring aeration-basin dissolved oxygen (DO) concentration once each day.
Why does my diffuser header boil?
The probable causes of equipment issues often include leaks in the aeration-system piping, plugged diffusers or air discharging from diffuser-header blow-off pipes, causing local boiling to occur on surfaces near the diffuser-header pipe or insufficient or inadequate oxygen transfer.
What happens when sludge is not wasted?
If sludge is not wasted, the secondary clarifier eventually fills up with solids.
What causes cloudy effluent?
For any conventional activated-sludge process , the probable causes of cloudy effluent include that mixed-liquor suspended solid ...
Why does my diffuser header boil?
The probable causes of equipment issues often include leaks in the aeration-system piping, plugged diffusers, air discharging from diffuser-header blow-off pipes, causing local boiling to occur on surfaces near the diffuser-header pipe or insufficient or inadequate oxygen transfer.
Why does sludge foam?
Old sludge conditions usually cause a dark brown, thick, scummy foam. It is usually caused by the growth of Nocardia or Microthrix parvicella, both of which grow at the high MCRT/low F/M condition associated with old sludge. A treatment pressure is required to decrease the total sludge units in the system. Thus, one must increase wasting and try to remove foam from the system. Once Nocardia has started to grow profusely, it is difficult to eliminate through increased wasting. Therefore, removal of foam from the system becomes more important. Foaming due to M. parvicella appears to occur more during colder temperature conditions while Nocardia can bloom profusely under higher temperature conditions. Both also appear to like oils and grease in their diets.
What causes high effluent suspended solids?
High effluent suspended solids are usually caused by one of two conditions: either individual particles that will not settle are discharged or the sludge blanket in the clarifier washes out. Either of these can cause conditions 6 through 24 to occur. Look first at clarifier blanket washout related to conditions 6 through 17. In this situation, the sludge blanket in the clarifier actually rises close enough to the surface so that it washes over the effluent weir. To learn the reason for the clarifier-blanket washout, the first thing to do is to look at the sludge settleability. If the problem is not a blanket wash-out, it is individualparticle washout. The individual particles may be tiny pin-floc, large straggler-floc or individual, dispersed cells. Physical observation of the effluent and microscopic observation of the mixed liquor or effluent will show which type or combination of types of individual particles is involved.
What bacteria grow well under low oxygen?
Type 1701, Sphaerotilus natans, and Haliscomenobacter hydrossis have all been known to grow profusely under low dissolved oxygen conditions. In recent years, it came to light that Microthrix parvicella also grew well under low DO conditions at high MCRT. Also, it was not known until recently that as the food-to-microorganism ratio increases, aeration basin dissolved oxygen also needs to increase, otherwise low DO bulking can occur. For instance, to protect a system with an F/M of approximately 1.0, almost 5 mg/L DO is required (watch potential denitrification problems). That F/M is defined as pounds of COD removed per pound of ML VSS in the aeration tank (Jenkins, et aI., 1993).
Why is white foam in aeration tanks?
White billowy foam is caused by high concentrations of surfactants such as detergents. It is not nearly the problem today that it was before biodegradable detergents were used. Condition 4 occurs at start-up of a system where a young sludge exists due to low mixed liquor suspended solids concentrations. In this condition there are just not enough solids present to break the surface tension of the surfactant bubbles that form. Thus, billowy white foam can accumulate on the aeration tank and can even be blown around by the wind. The condition is usually short-lived since at start-up the operator is usually applying oxidative pressure by increasing the total sludge units in the system. If the condition occurs due to previous excessive wasting, the solution is still to decrease wasting and increase the total sludge units in the system.
What causes slime bulking?
Slime bulking (Jenkins, et al., 1993) is usually caused by a nutrient deficiency. As in Condition 2, ammonia or nitrate must be added if the ammonia plus nitrite plus nitrate is less than 1 mg/L. Phosphate must be added if the phosphate is less than 0.5 mgIL in the effluent. Slime bulking is usually associated with industrial waste, but may be found in municipal systems that have high concentrations of industrial wastes discharged to them. Even higher concentrations of N & P may be required with certain industrial wastes. This is true if the organic loading comes from easily metabolized materials, such as simple sugars, short-chain organic acids, or alcohols. These may be metabolized so rapidly that excess N and P are required in the system to ensure that the local concentrations are high enough. Complete mixing may also help in this situation.
Why is my slime thick?
A grayish slimy foam that is very thick is commonly caused by nutrient deficiencies. It is often noted with a slime bulking condition. Those deficiencies may be either nitrogen or phosphorus. The solution usually involves addition of the limiting nutrient, such as ammonia to provide nitrogen, or phosphoric acid to provide phosphorus. There is usually enough nutrient if the ammonia plus nitrate in filtered (0.45 μm) effluent is greater than 1 mg/L and the soluble orthophosphate is greater than 0.5 mg/L (Jenkins, et al., 1993). However, in certain cases where easily degradable, soluble BOD is available, higher N and P concentrations may be necessary.
Does 0041 grow well on aeration?
Types 0041, 0675, and 0092 along with M. parvicellaare known to grow well on slowly metabolized food. There are no real answers to controlling this growth to date, but it appears that maintaining good mixing and proper dissolved oxygen throughout the aeration process helps. These are also associated with older sludges. Therefore, reducing MCRT often reduces their growth.
What is floc in sludge?
Basic floc formation, required for activated sludge operation due to the use of gravity clarifiers, is due to a growth form of many species of natural bacteria. Floc-forming species share the characteristic of the formation of an extracellular polysaccharide ("slime") layer, also termed a glycocalyx. This material, which consists of polysaccharide, protein and sometimes cellulose fibrils, "cements" the bacteria together to form a floc. Floc formation occurs at lower growth rates and at lower nutrient levels, essentially starvation or stationary growth conditions.
What causes activated sludge?
Most activated sludge upsets and loss of process control are caused by one of several microbiological problems which include poor floc formation, pin floc, dispersed growth, filamentous and slime bulking, filamentous foaming, zoogloeal bulking, nitrification and denitrification problems and toxicity. Use of the microscopic examination and the OUR test are invaluable tools in troubleshooting the activated sludge process. Once the cause of the problem or upset is known, specific remedies appropriate for the problem can be used. Short term control methods such as chlorination are often used to quickly stop a bulking problem. However, the best approach is to investigate the long-term control methods suitable for the problem that is occurring to achieve trouble free operation.
What causes foaming in wastewater?
Three filaments cause foaming: Nocardia, M. parvicella and type 1863. All of these filaments grow on grease and oil, and these can become a problem when grease and oil are high in amount in the influent wastewater. Systems that lack primary clarification (the main grease and oil removal mechanism) appear to suffer more foaming problems. Communities with enforced grease and fat ordinances appear to suffer less from foaming problems. Also, disposal of septage, which contains substantial grease and oil content, to small activated sludge systems has been associated with foaming problems.
What are the short term measures of sludge juggling?
Short term measures include: "sludge juggling" - changes in return activated sludge (RAS) rates and in waste feeding points; polymer and coagulant addition to aid sludge settling; and chlorination.
How to improve activated sludge settling?
There exist several methods of chemical addition to enhance activated sludge settling. Most used are synthetic, high molecular weight, anionic polymers alone or in combination with cationic polymers that serve to overcome the physical effects of filaments on sludge settling. These are usually added to the MLSS as it leaves the aeration basin or to the secondary clarifier center well. Use of polymer does not significantly increase waste sludge production but can be quite expensive, up to $450. per million gallons treated (obviously this is only used if absolutely necessary). A polymer supply company should be consulted for advice on selection of a polymer and its dosage (the chemical composition of most polymers is a trade secret). Jar testing should be performed to determine the type of polymer needed and its dosage, which is quite plant specific. Further, this jar testing needs to be repeated often, as the needed polymer and its dosage can change, particularly if the filament type(s) change.
What are some methods of intermittent bulking?
Several methods useful for intermittent bulking problems, but which will not solve a chronic problem, are manipulation of RAS flow rate and manipulation of waste feed points to the aeration basin to minimize the adverse effects of a bulking sludge.
