..Role Of Microbes In Sewage

Treatment..

..Microbes..o Are single celled organisms.o Are heterotrophic or autotrophic in nature.o Includes fungi, protists and bacteria. o Protists includes 1) Amoeba.2) Algae.3) Protozoa. 4) Slime molds.

..Types Of Microbes.. Heterotrophs are microorganisms that use organic carbon for the

formation of new biomass, depend on a readily available source of organic carbon for cellular synthesis and chemical energy.

Autotrophic microorganisms can create cellular material from simple forms of carbon (such as carbon dioxide), do not depend on other organisms for the creation of complex organic compounds.

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..Algae(protist).. Is normally involved in photosynthesis. Converts solar energy into useful biomass, thus incorporating nutrients such as

nitrogen and phosphorus. Used in treating 1. Human sewage.2. Livestock waste.3. Industrial waste.4. Piggery effluent .5. Removal of toxic materials.

….…..Continued….…..Also used in……1. Removal of coliform bacteria. 2. B.o.d and C.o.d removal.3. Offers a cost effective approach to remove nutrients

from waste water. (tertiary and quaternary treatment). 1.

4. Acc. to studies algae removes 50.2% nitrogen, 85.7% phosphorus in industrial waste water and 97.8% phosphorus in domestic waste water. 2

Water turning into green colour(indicates presence of algae).

..Factors affecting Algal growth..

ph.Light intensity.Temperature.Biotic factors.

..Disadvantages of Algae in

WWTP..3Continuous and good efficiency is not achieved.Costly to operate.Chemical process often lead to secondary pollution.Loss of valuable nutrients (N & P).

…Case studies…Presence or absence of certain species of Scenedesmus

can be used for evaluation of water quality.4

Euglena, oscillatoria, chlordla, etc can be used as indicator of water pollution.5

Also presence of lemanea, certain species of micrasterias, meridion etc. indicate that water sample will be considered unpolluted.5

..Conclusion..High concentration on N& P means, waste water may possibly

be used for cheap nutrient source for algal biomass production. This algal biomass could be used for

Methane production.Composting.Production of liquid fuel.Animal feed or aqua culture .Production of fine chemicals. .Home.

..Fungi..Recent studies have shown that 1. Filamentous fungi had a biochemical pathway to perform

denitrification.6

2. Fungi have significant advantages over bacterial denitrifiers including- 7

Higher rates of nitrification and Denitrification.Resistance to toxic compounds.

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Scientific visualization of a Fungal structure….

..Bacteria..A bacteria is a single cell life of form. Bacteria often grow into

colonies that appear as jelly-like masses, but each cell remains as independent. Under ideal conditions, bacteria can reproduce very rapidly, producing a new generation every 20 to 30 minutes.

The population explodes as the number of organisms increases logarithmically.

This population boom begins soon after the bacteria is introduced into a favorable environment, after a short lag time when the bacteria becomes acclimated to the new conditions. (155 billion/ounce).

..Types of Bacteria (on the basis of their food)..Aerobic types (which require oxygen to live) .

Anaerobic (which can live without oxygen )(eg-Ruminococcussp., Clostridiumsp) or (Eubacteriumsp).

Facultative (types can thrive under both aerobic and anaerobic conditions.).

..Types of bacteria (on the basis of their function)..Hydrolytic bacteria break down complex organic wastes

into sugars and amino acids. Fermentative bacteria then convert those products into

organic acids. Acidogenic microorganisms convert the acids into

hydrogen, carbon dioxide and acetate. Methanogenic bacteria produce biogas from acetic acid,

hydrogen and carbon dioxide. 

Acidogenic and Methanogenic bacteria used in Biogas Formation ….

Bacteria Fermenting Waste….

.. Bacteria should.. Consume (digest) a wide variety of organic material that

are present in wastes.  Digest waste quickly and completely, without producing

significant odors of noxious gas. Not cause any disease in man or animals - they must

be non-pathogenic.  Grow and reproduce quickly and readily in the

environmental conditions found in waste disposal systems.

Bacteria belonging to the Bacillus species have  these characteristics. They consume organic  waste thousands of times faster than the bacteria that are naturally present in the waste. They grow and reproduce easily, are non-pathogenic, and do not produce foul odors or gas as they digest waste.

These bacteria are cultured on liquid or dry nutrient medium. These cultured bacteria are then freeze dried to put them in a state of suspension. They remain alive, ready to swim, eat, and reproduce as soon as they are activated (rehydrated) and put into the proper environment.

..Environment needed for Bacterial growth..

A water medium containing food (organic waste). Dissolved oxygen (for the aerobic types that require it) in

sufficient quantities. Proper pH not too acidic nor too alkaline -- between 6 and

9 on the pH scale. Moderate temperature, between 50°F and 110°F.

..How Bacteria Digest the

Organic Waste..    Enzymes are manufactured by bacteria.

An enzyme is a chemical catalyst that breaks up long, complex waste molecules (Hydrolytic Reaction) into smaller pieces, which can then be digested directly by the bacteria.

 When added to the organic waste, the enzymes immediately go to work breaking down the waste into water - soluble nutrients for the bacteria to digest. The enzymes break the large, complex molecules of starches, proteins, carbohydrates, and cellulose into smaller, simpler pieces. The growing bacteria will then start to produce more enzymes on their own, creating a continuing cycle of enzyme production.

How Bacteria digest the Organic Waste….

..Types of Enzymes..Lipase enzyme split fats, grease and oils for

rapid digestion.

Cellulase enzyme  convert the tough fibrous cellulosic structure into a soluble fluid state.

..Mechanism of Enzyme Action..Adsorb to biopolymers and hydrolyse them to monomers

or at least to oligomers .Only soluble low molecular weight compounds can be

taken up by microorganism and can be metabolized for energy production and cell multiplication.

.Mechanism of substrate

degradation. • Aerobic degradation ….1. Saturating substrate supply – high load conditions

1 unit substrate carbon=0.5 unit CO2 + 0.5 unit of cell carbon. 2. Limiting substrate supply – low load conditions

1 unit substrate carbon= 0.7 units CO2 + 0.3 unit of cell carbon.• Anaerobic degradation ….

1 unit substrate carbon = 0.95 times (CO2 + CH4) carbon + 0.05units of cell carbon

..Continued..Ammonia oxidizing bacteria (Nitrosomonas, Nitrosospiru) convert ammonia

to nitrite acc. to eq1. Nitrite oxidising bacteria (Nitrobactor) convert nitrite to nitrate consistent with eq2

15CO2+13NH4+ 3C5H7NO2 + 23H+ + 4H2O (eq1)

5CO2+NH4+ + 10NO2

- + 2H2O C5H7NO2 + H+ + 10NO3- (eq2)

Denitrification bacteria (Pseudomonas, Alcaligenes, Bacillus) use anoxic reaction5CH3COOH + 8NO3

- 8HCO3- +6H2O + 4N2 .

Conversion of Ammonia to nitrite and to nitrate..

..Activated sludge

process..The purpose of the process is to reduce amount of dissolved organic matter from wastewater, using microorganisms growing in aeration tanks.

The formed semi-liquid material (a community of microorganisms grouped in flocs) is than separated from treated supernatant.

Process flow diagram of an ASP..

..Flocs formation in Aeration tank..Separating individual bacterial cells from water would be

a very difficult process if they didn't have a very important property - a predisposition to gather together.

Microorganisms aggregate in flocs - flake-like structures that consist of alive and dead cells of microorganisms and products of their metabolism. Such structures are easy settled, enabling us to separate treated effluent from sludge. (poly-saccharides) .

Floc formation in ASP

..Role of Filamentous bacteria in floc formation..Filamentous bacteria serve as the backbone of floc

formation.The filamentous bacteria are analyzed in two ways: their

effect on floc structure and their abundance. In small amounts, they are quite good to a biomass, but in large amounts they can cause many problems.

Eg- Nocardia, Microthrix parvicella.

:Positive Aspects:

1. They are very good BOD removers.2. They add a backbone or rigid support network to the floc

structure.3. Helps the floc structure to filter out fine particulate

matter that will improve clarifier efficiency.4. They help the floc to settle if in small amounts.5. They reduce the amount of "pin" floc.

..Negative aspects..• They can interfere with separation and compaction of activated sludge

and cause bulking when predominant.• They can affect the sludge volume index (SVI) (Sludge Volume Index).• They can cause poor settling if dominant.• They can fill up a clarifier and make it hard to settle, causing TSS (Total

Suspended Solids) carryover.• They can increase polymer consumption.• They can increase solids production and cause solids handling costs to

increase significantly.

..Filamentous

Bulking..• Sludge bulking has been one of the major problems affecting biological waste treatment.

• Often in industrial and municipal activated sludge processes a nutrient deficiency may occur.

• The nutrients that are usually deficient in these processes are either nitrogen or phosphorus.

• This deficiency results in the production of nutrient deficient floc particles, loss of settleability, and possibly a billowy white or greasy gray foam on the surface of the aeration tank.

Filamentous Bulking in Wwtp…

..Continued..• During a nutrient deficiency, the bacteria within the floc

particles remove soluble BOD from the wastewater. • However, when nitrogen or phosphorous is deficient, the

soluble BOD is not degraded but it is stored within the floc particles as an exocellular polymer-like material.

• This slimy material interferes with settling and may cause foam upon aeration.

..Sludge Digester..

Large numbers of anaerobic bacteria convert organic matter into methane and carbon dioxide (a mixture called biogas) in the absence of air.

..Process divided into three

steps..• Hydrolysis: proteins, cellulose, lipids & other complex organics are

broken down into smaller molecules and become soluble by utilizing water to split the chemical bonds of the substances.

• Volatile acid fermentation: products of hydrolysis are converted into organic acids through the biochemical processes of acidogenesis (where monomers are converted to fatty acids) and acetogenesis (the fatty acids are converted to acetic acid, CO2 & H2)

• Methane formation: organic acids produced during the fermentation step are converted to CH4 and CO2.

..Process divided into three steps..

Efficiency of each step influenced by temperature and amount of time

process allowed to react. For e.g : Organisms performing hydrolysis and volatile acid fermentation

(acidogenic bacteria) are fast growing microorganisms that prefer a slightly acidic environment and higher temperatures than the organisms performing methane formation step (methanogenic bacteria).

Acidogenic bacteria are also less sensitive than the methanogenic bacteria to changes in organic strength and composition in the incoming feed stream.

Therefore, to optimize the various stages of the anaerobic digestion process, conventional single-stage anaerobic digestion performed at a constant temperature have been separated into multiple stages, by many waste water treatment plants by physically separating the stages or by controlling the process to separate the stages in time, or both.

Standard multi-stage anaerobic digestion system is a two-stage acid/gas (AG)-phased system → first stage, known as the primary or acid phase digester comprising acid-forming steps , physically separated from second stage, known as the secondary or methane stage.

• Alternative method is temperature-phased anaerobic

digestion, or TPAD for i.e. separate the stages over time by adding different levels of heating at different times. Hydrolysis and acidogenesis can be enhanced by increasing the operating temperature.8

• If the system is heated to enhance hydrolysis and acidogenesis, the resulting volatile acid production can overwhelm the ability of the slower-reacting acetogenic and methanogenic bacteria to convert the volatile acids, resulting in increased pH and inhibited acetogenesis and methanogenesis .8Therefore, controlling the temperature can be critical in optimizing system performance.

..Advantages..Gas Recovery and Storage: The gas produced from the anaerobic digestion

of biosolids comprises 55 to 70% CH4 and approximately 25 to 30 % CO2, with the remaining fraction composed primarily of N2, H2, H2S (USEPA 1979).

Multi-stage systems require less digester volume to handle the same amount of input volume because they have lower retention times and allow higher loading rates than single-stage systems.

Multi-stage systems have achieved VS reduction, which provides better odour control & configured to reduce foaming problems.

Biosolids Quality: Multi-stage anaerobic digestion systems that

use a thermophilic stage can produce biosolids that meet Class A pathogen reduction requirements.

For example, recent research by the City of Los Angeles indicates that their product resulting from systems operated at thermophilic temperatures achieved Class A status and had lower odour than the product produced by mesophilic processes. Their results indicated that the odour concentrations in solids digested using mesophilic temperatures continued to increase as the biosolids went through the digestion process and even after they were applied on farmland. In contrast, the odour content of material subjected to thermophilic digestion temperatures decreased by about 70 % by the time it reached the land application site.

..Case studies..Waterloo, Iowa..The City of Waterloo wanted to increase its biosolids treatment capacity and improve its VS destruction and gas production. In 2002 the city upgraded its anaerobic digestion process from a single-stage mesophilic process to a TPAD-TM system by converting two of its six digesters into thermophilic digesters. VS reduction improved from approximately 47% in the old system to approximately 60–64% in the new system. Gas production increased to 0.18–0.21 m3 per kg of VS destroyed (14–16 ft3/lb) (Wilson et al.)

Woodridge WWTP, DuPage County, IllinoisWWTP converted from its original single stage process to a two-

stage AG-MT anaerobic digestion system in the late 1980s in an attempt to control foaming problems in the old system.

For conversion, a mesophilic acid-stage digester was added to the existing digestion facility, which was converted to a thermophilic gas-phase digester.

The overall VS reduction averages approximately 65%. During the first 4 months of 2000, fecal coliforms were reduced by an avg. of 99.996%.

The facility experiences no foaming, and the digested sludge is highly desirable as a soil enhancer for agricultural purposes. The digester gas is recirculated to power the digesters, and excess gas is used to produce electricity.

• Inland Empire Regional Water Recycling Plant 1 (RP-1),

Ontario, California ….• The anaerobic digestion system was upgraded from thermophilic

single-stage system in 2000 & turned to three-stage AG-MTM process in 2001. The system had experienced odour problems, therefore acid and gas phases separated using both a semi-batch and a continuous approach.

• Overall, VS reduction improved from approximately 55 % to 60–65 % with the AG-MTM process. Both processes showed non-detects for helminth ova, enteric viruses, and Salmonella. 9

• The semi-batch process qualified through time and temperature as Class A biosolids under alternative 1 of 40 CFR Part 503, while the continuous process received site specific EPA approval as Class A was granted under alternative 3 of 40 CFR Part 503.9

..OPERATION AND MAINTENANCE..The optimum pH range for anaerobic digestion is 6.8–7.2. A reduction in pH, which can be caused by overloading the digester, inhibits methane formation. Methane formation is further inhibited as the acid fermentation stage of digestion continues, possibly leading to digester upset and failure. Temperature control is also important to ensure satisfactory operation of the digestion system. Fluctuations in temperature can result in the die-off of microorganisms and process inefficiency. Chemical addition to anaerobic digesters might occasionally become necessary for pH/alkalinity control and to control the potential for metals and other chemicals to inhibit the process (WEF 1995). NaHCO3, Na2CO3 & Ca(OH)2 can be used to provide alkalinity. FeCl2, FeSO4, and alum can be added to precipitate or coagulate inhibitive chemicals or to control digester gas H2S content.

o A common operational problem is foaming i.e. trapping of fine bubbles

of gas in the semi-liquid digestion contents. Foam forms primarily when CO2 to CH4 ratio is higher than normal. This occurs during start-up operations or when a fresh food supply suddenly contacts active microorganisms. A common bacterium, Nocardia, has a filamentous structure that traps gas, leading to foaming. These bacteria should be eliminated in aeration basins before the solids are fed to the digesters. The first stage (acid phase) digester has low gas production and low pH, along with higher volatile acid concentrations, which together are detrimental to foam-causing microorganisms.

o Another operational concern is odour control at the plant during the anaerobic digestion process. Use covers to control odour from digestion system.

o Periodic clean-out of the digesters is necessary for all digestion systems. Typically systems require cleaning approximately every 5 years.

..Aerated lagoons..Working Principle

Aerated ponds or lagoons are similar to facultative ponds, with the difference that natural oxygenation is enhanced by mechanical air injection. As the oxygenation does not depend on algae activity and photosynthesis, ponds can be deeper (thus smaller in surface) and are also suited for colder climates. Mechanical aeration enhances the treatment efficiency due to more intense bacterial aerobic degradation and increases pathogen removal.

Capacity/Adequacy

Adapted for almost all wastewater (also industrial) in rural or urban areas. However, electricity supply needs to be continuous and a foul odour might be a problem in urban areas.

Performance

Aerated facultative ponds: 70 to 90 % BOD HRT: 4 to 10 dayCompletely mixed aerated ponds: 70 to 90 % BOD HRT: 2 to 4 day; high phosphorus, nitrogen and ammonia removal.

Advantages

• Can treat high loads• High reduction in BOD and pathogens• No real problems with insects or odours if designed

correctly• The treated water reused or discharged if a secondary

maturation/settling pond follows the aerated lagoon/completely mixed aerated pond

Disadvantages

• Sludge requires secondary treatment and/or appropriate discharge

• Requires a constant energy/electricity source for continuous aeration; the technique does not work in cases of power failure

Despite the knowledge that microbial communities evolving in WWTP play

a key role on treatment processes, there are few reports concerning the study of bacterial communities in aerated lagoons .Until now, studies were carried out using mainly traditional microbiological methods such as 16S rDNA clone libraries , ribosomal intergenic spacer analyses (RISA) , 16S-restriction fragment length polymorphism (16S-RFLP), repetitive extra genic palindrome PCR (REP-PCR) and fluorescent in situ hybridization have already been applied to the study of waste- water associated microbial communities.10

The combination of PCR amplification of 16S rRNA genes with denaturing gradient gel electrophoresis(DGGE) analysis has also provided a useful means to directly characterize bacterial populations within many samples. PCR–DGGE has been successfully used in many fields of microbial ecology to assess the diversity of microbial communities and to determine the community dynamics in response to environmental variations.

Image of an aerated lagoon