Sewage Water Treatment- Anaerobic Bacterial Digestion

Basma Sarfraz06.12.2013

Content…IntroductionProcess overview of sewage treatment:• Pre-treatment• Primary Treatment• Secondary treatment• Tertiary treatmentTypes of Bacteria used in water treatment:• Aerobic bacteria • Anaerobic bacteria Anaerobic Digestion Process:• Advantages• Production and purification of by productsFurther ResearchesConclusion

Sewage water treatment…

Objectives:1. To reduce the volume by eliminating the liquid portion of the sludge. 2. To alter the highly putrescible organic matter into relatively stable or

inert organic and inorganic compounds; thus allowing water to separate more effortlessly.

Sewage water treatment is basically the process of removing contaminants from wastewater either from residential or commercial establishments. These contaminants

could be biological, chemical and physical.

• Nutrient availability high• Activated Sludge is more

Untreated water

DischargeEnironment

• Will pollute the receiving water

Distributionwater-borne

diseases

Colonies of bacteria are factories for the automatic production of the right enzyme

for the biological reduction of any waste material, provided the selection of right bacteria to start with.

Enzymes

Degradation of organic matter and many chemical

reactions.

Precise design of the treatment plant:• Maximum advantage of the bacterial activity• Equate to lower costs• Amplified capacity• Enhanced quality of effluent• Freedom from bad odors

Inoculation of specifically cultured bacteria

• Using anaerobic digestion:

1. Minimizes the amount of final sludge disposal- easy handling

2. Although many sludge stabilization methods exist- remove hazardous by products.

3. And it also furnishes a considerable power supply in the form of methane gas – cost effective.

BOD v/s COD• BOD = Biochemical Oxygen Demand • COD = Chemical Oxygen Demand BOD means the amount of oxygen (in mg/l) microorganisms like bacteria need to 'eat' the organic pollution (sugars, fat, proteins, ...). Note that not all pollution can be removed (eaten) by bacteria. COD is the amount of oxygen required to degenerate all pollution in a chemical way (by adding oxidizing agents and heating). In general with chemical destruction you can remove more pollution than with the biological way. BOD is actually the parameter to measure the amount of biodegradable organic matter in the treated water which is commonly determined by measuring the amount of oxygen necessary to degrade the organic matter in water. The stable primary sludge signifies suspended solids up to 40% to 60% present in the treated water signals the presence of 25% to 35% of BOD in the sewage.

BOD uses and limitations: BOD testing has its widest application in measuring waste loadings of treatment plants, and in evaluating the efficiency of treatment processes. It is of limited use in industrial wastewaters containing heavy metal ions, cyanides, and other substances that may be toxic to the microorganisms.

Process Overview…

• Centralized System

• Decentralized System

1. Pre-treatment…

• Removal of easily eliminated waste. i.e. large material•It consists of two portions:

Coarse screening: In which large materials are filtered e.g. rags, trash, bottles and log etc. To optimize solid waste removal,

mesh screens or bar screens of various sizes may be used.

Grid removal: Based on the velocity of the incoming waste water

which is adjusted in such a way that the stones, sand, grit and broken glass are settled down.

before they would clog or damage the pumps and

pipes of primary treatment plant.

2. Primary Treatment…

Schematic Diagram of Primary Treatment

Quiescent basin

Oils / Grease

Heavy Solids

Air Blowers

Skimmers

Secondary Treatment

Compact

Landfills

Sewage

Treated water comprises dissolved organic and inorganic solids.

3. Secondary treatment…

Secondary Clarifiers

Fixed film systems: in it the bacteria grow on the filters, through which the

treated water passes.

Suspended growth system: In it the activated sludge is inoculated directly into

water.

Biogas

CondensingHeating

Incinerate

Fertilizer

Primary Treatment

Disinfectant

4. Tertiary treatment…

Treated water may comprises- organic materials- should be remove chemically or physically before discharging it.

1. Sand filtration2. Phosphorus elimination: Bioaccumulation by specific polyphosphate accumulating bacteria.

3. Nitrogen elimination:LagooningAmmonia - highly toxic to aquatic biota. Biologically, ammonia can be eliminated through two processes:Nitrification Process: Ammonia is oxidized into nitrate. ( e.g. Brocadia anammoxidans )

Denitrification Process: Nitrate is converted into the nitrogen gas. ( e.g. Thiobacillus denitrificans )

4. Chemical treatment:

5. Ultraviolet radiations: Kill bacteria- damage its genetic material. Kill endospores of bacteria- higher dosage.

6. Chlorination: More effective in killing bacteria than viruses.

7. Ozone treatment: More effective and environment friendly method to destroy viruses. And readily decomposes into oxygen without producing harmful byproducts.

8. Carbon Adsorption: Elimination of resistance showing organic materials. Comprises a bed of activated carbon granules through which the treated water is passed. This process removes 98

percent of the remaining organic material.

9. Odor control: Emission of hydrogen sulfide. Such water can process through carbon reactors, comprises chlorine, bio-slimes, or bioactive fluids which

biologically trends to metabolize the noxious gases. Other methods include addition of calcium nitrate, iron salts and hydrogen peroxide.

Alum, ferric chloride or limeAllow the clotting of the

smaller particles to cluster into larger masses

Remove via sedimentation

Types of Bacteria used in sewage treatment

Bacteria categorize by the way they obtain energy

Aerobic Anaerobic Facultative

• Aerobic bacteria:Use the free oxygen present in the waste water.

1. For the production of energy which they can use for growth and reproduction.

2. To degrade the pollutants in the wastewater.

They are used in most new treatment plants where the oxygen has to be added mechanically to the wastewater through the use of aerators in the aerated section of the treatment plant. The range of the dissolved oxygen content should be kept between 3 and 5 MG/L, with a normal influent load of pollutants.

• Anaerobic bacteria:Proliferate in the absence of oxygen or without any dissolved oxygen.

For the sake of respiration, anaerobic bacteria normally get the oxygen from their food source.

Such process/digestion could be thermophilic (55 °C) or mesophilic (36 °C).

Anaerobic Digestion ProcessMost common process to deal with the sewage sludge.

• Advantages of Anaerobic Systems:1. Low yield of sludge – to be dewatered.

2. Low energy requirement – high power blowers or aerators are excluded.

3. Higher organic loading – give significant treatment efficiencies in both BOD and COD concentrations removal.

4. Alternative energy source – methane rich biogas.

5. High stability – show great resistance under highly variable organic, thermal and hydraulic conditions.

6. Less nutrient requirement – far less.

7. Lower functional costs

The anaerobic process is bases on two main categories of bacteria:• Acid formers: (Harsh)

• Methane formers: (Sensitive)

anaerobic and facultative bacteria

solubilize organic figureshydrolysis alcohols and acidsFermentation

strict anaerobic

alcohols, acids, carbon dioxide and hydrogen Transform MethaneAct

Biogas- the rich source of energy:

Uses :1. Directly burn within a gas engine and for cooking purposes.2. As fuel for blowers, electric generators, hot water boilers and pump engines. 3. During pretreatment, it can serve as fire incinerators to heat the influent sludge.4. To heat the digester influent on the site of its production.

Solid Sludge: Fertilizer or soil conditioner:

1. For the elevation of organic content in the soil. 2. Such liquor cost-effective3. Serve as alternative of chemical fertilizers to

provide essential nutrients to the soil.

Purification:Separated from other biogas constituents such as carbon dioxide, hydrogen sulfide, and excess moisture and purified.• Removal of Hydrogen sulfide: By metal oxides-

converting into insoluble salts.• Removal of Carbon dioxide: By absorption via the

chemicals- to reduce gas volume.

Production:1. Most sensitive and slowest step. 2. Requires specific conditions i.e. pH of 6.6-

7.6 , pre-heating of the sewage waste .

• Further Researches:• New Method Monitors Critical Bacteria in Wastewater Treatment:

New technique has establish for the constant monitoring of the health of bacteria involved in the sewage treatment by using various sensors. The minor changes in chemistry regarding to bacterial health is detectable and produces results instantaneously without disrupting the biofilm, whereas conventional techniques time-consuming and required laborious analyses. Such method alarmed workers before bacteria are weaken or about to cease processing the sewage waste. So, this may fix the problem before the release of toxins into waterways. From the sewage, how well the bacteria are absorbing charged atoms, ions, or molecules is revealed by the sensor data. For example, in the case of nitrosomonas europaea

As an early warning signals, the sick, poisoned and stressed bacterial biofilms start to release ions especially calcium and potassium. The problem regarding the uncontrolled flushing of untreated sewage into waterways is eliminated by the self-referencing procedure comprises the sensor which after every three seconds moves mechanically back and forth enabling the device to gather data from two locations instantaneously. The rapid and minor changes in the concentrations can also be easily detected by it by comparing the data derived from the same sensor from two different sites.

• The "superbug" methicillin-resistant Staphylococcus aureus (MRSA) :

MRSA is highly known for causing potentially fatal bacterial infections whom presence is detected in the treated water. But its presence can highly decreased. As MRSA strains exhibit a high level of resistance towards most antibiotics and comprises many virulence associated genes which remain alive unless they are subjected to the tertiary chlorination treatment, which eradicates almost all MRSA (up to 93%). This proposes that while from influent to effluent as sewage processing successfully eradicate MRSA and MSSA, but on the other perspective this could be the factor behind the boosted resistance towards antibiotics and enhanced virulence, chiefly where the chlorination treatment is not applied.

• Sewage Treatment Plants May Contribute to Antibiotic Resistance Problem:

Possible public health alarms for sewage treatment plants are elevated as further researches are done. Because the chlorination treatment is widely used now, so further findings are also needed side by side to estimate the possibilities of presence of antibiotic-resistant bacteria in treated sewage water. Hazardous of all is the fact that even the most high-tech water treatment center would be a significant source of antibiotic resistance genes in the water channels.

• Using Recycled Waste Sewage Treatment Plant Water for Irrigating Purposes- enhanced resistance towards bacteria :

It is now becoming the common practice in the world, to do irrigation by the treated water from the sewage treatment plants. Due to which rapid evolution of antibiotic-resistant bacteria occurs responsible of the outburst of thousands of harmful diseases each year. A fairly large section of antibiotics taken by a person, does not metabolize properly and through urine or feaces, pass out in the sewage from the body, where it to the sewage treatment plant. These plants are not capable enough to completely eliminate such antibiotics like ciprofloxacin, tetracycline and sulfonamide and probably becoming the source of lavishness of such bacteria and their genes.

• Fighting Antibiotic-Resistant Bacteria by Treating Municipal Wastewater at Higher Temperatures:

Frequently, mutated genome of bacteria is responsible for causing rapid decrease in the effect and efficiency of antibiotics by the high evolution of antibiotic-resistant bacteria. The latest approach to overcome this problem is the anaerobic digestion occurs at high temperature to inhibit the growth of antibiotic resistant bacteria, which may prove as an effective tool. Heating the water up to about 55 degrees Celsius approximately 99.9 percent of numerous virulent and resistance genes are destroyed. As during this process the bio gas is also evolved which may use in reactors to maintaining such temperature, so this process is cost-effective too. This approach can be supported by reducing the frequency to antibiotic uptake etc. to extend the effective life of precious drugs.

Conclusion…

Thus the use of anaerobic players for municipal water treatment renders many qualitiescost efficiencyenvironment friendly conditions. final volume of the sludge to discard is highly reducedbio gas yield, which could serve as rich energy source, to even cater

the whole treatment plant.

Thank you…

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