Possible causes of sludge flotation are classified into intrinsic and extrinsic ones. Extrinsic causes include substrate overloading, inappropriate carbon source, overloading of proteins or oils, insufficient reactor mixing, a low temperature, and a low pH.
How do you get rid of floating sludge?
Floating-sludge clumping due to septicity may be remedied by maintaining dissolved oxygen at a minimum level of 1.0 Mg/L, along with making sure adequate mixing is occurring in the aeration tank.
What causes rising sludge?
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.
Why does sludge float in aeration tank?
And more importantly, what can be done to control it. First floating sludge is most often caused by: Denitrification – small nitrogen gas bubbles float the sludge in the clarifier creating floating sludge chunks with small bubbles entrapped. Fats, Oils & Grease – simply put, FOG floats on water.
Where does activated sludge come from?
Activated sludge refers to a flocculent culture of organisms developed in aeration tanks under controlled conditions.
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.
Does old sludge settle faster?
Old sludge tends to settle very rapidly but leaves pin floc in the supernatant and a surface material known as “ashing”. Ashing appears just as though ashes were scattered on the surface of a settleometer test or secondary clarifier.
What percentage should sludge be removed?
Primary treatment typically removes about one-third of the BOD and one-half of the suspended solids in domestic wastewaters. Combined primary and secondary treatment is required to achieve 85 percent reduction in both BOD and suspended solids concentration to meet the regulatory definition of secondary treatment.
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 sources of sludge?
Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Some sewage plants also receive septage or septic tank solids from household on-site wastewater treatment systems.
What happens if MLSS is too low?
However, an MLSS concentration that is too low can reduce BOD removal rates and disrupt settling during secondary clarification as a critical mass is essential in order to form a dense, uniform sludge blanket.
How do you stabilize sludge?
Chemical stabilization is almost always performed with lime. Thus lime stabilization is the process where the sludge is mixed with lime to raise the pH to greater than 12. The high pH and a rise in temperature reduces pathogens (hygienization effect) and reduces offensive odors (via stopping the fermentation).
What happens if MLSS is high?
If the MLSS concentration is above the desired concentration, the wasting of the excess solids will have to be started or increased. If the MLSS concentration is below the desired concentration level, wasting should be decreased or stopped.
What is the difference between sludge and activated sludge?
Solution : Activated sludge possesses flocs of decomposer microbes, whereas, primary sludge does not possess flocs. Unlike primary sludge a lot of decomposition occurs during formation of activated sludge.
What is the common problem with activated sludge?
Filamentous bulking and foaming are common and serious problems in activated sludge operation, affecting most activated sludge plants at one time or another. Filamentous bulking is the number one cause of effluent noncompliance today in the U.S.
Is activated sludge toxic?
Activated sludge was used to analyse the effect of those pollutants in a biological reactor of a sewage treatment plant (STP). The results demonstrate that none of the compounds is toxic to activated sludge, except ofloxacin to P. putida.
What are the three methods of treating sludge?
The most common treatment options include anaerobic digestion, aerobic digestion, and composting. Sludge digestion offers significant cost advantages by reducing sludge quantity by nearly 50% and providing biogas as a valuable energy source.
Where does sludge go after treatment?
Once treated, sewage sludge is then dried and added to a landfill, applied to agricultural cropland as fertilizer, or bagged with other materials and marketed as “biosolid compost” for use in agriculture and landscaping.
How long does it take for sludge to settle?
The common range for sludge age for a conventional activated sludge plant is between 3 and 15 days. For extended aeration activated sludge plants the range is between about 15 and 30 days.
How do you know a sludge is healthy?
Good sludge
It will smell earthy. In the 30-minute sedimentation test, the volume of sediment will be 200-300 mL / L. The SVI will be 80-150. The sludge age for conventional systems will be 3-10 days and 15-30 days for extended aeration systems.
What is the liquid removed from a settled sludge called?
SUPERNATANT: Liquid removed from settling sludge. Supernatant commonly refers to the liquid between the sludge on the bottom and the scum on the surface of an anaerobic digester. The liquid is usually returned to the influent wet well or to the primary clarifier.