biological treatment of wastes and pollutants (part 1)

BIOLOGICAL TREATMENT OF WASTES AND

POLLUTANTSH.G.D.A.P. Jayasinghe

BSc. (undergraduate)

05/03/2023H.G.D.A.P.JAYASINGHE. BSc. (undergraduate)

WASTE, POLLUTANTS AND BIODEGRADATION

Section 1


MY FOCUS..

Wastes Classification of wastes

Wastes and Pollutants Wastewater Biodegradatio

n


WASTES• What is waste??

• Waste include all the items that people no longer have any use for, which they either intend to get rid of or have already discarded.

• “Wastes are substances or objects, which are disposed of or are intended to be disposed of or are required to be disposed of by the provisions of national law.” – Basel convention-

• Interestingly, if biologically originated, any waste will decompose in nature under natural low..


CLASSIFICATION OF WASTES

• Why classify wastes?• It is essential for the management of wastes in a proper way for the protection of

the environment and also for human health• Can be done according to;

• Physical state• Place of origin• Type of origin• Mode of degradation


WASTE AND POLLUTANTS

• Pollutant is a waste material that pollutes air, water or soil. • Severity of a pollutant depend on its;

• Chemical nature• Concentration • Persistence

• Damage done to environment can be long term or short term.• Some are biodegradable. Hence, persistence is very low.• But, some resultant chemicals of biodegradation of some wastes are themselves polluting.

• Example: DDE and DDD arise from the biodegradation of DDT


WASTE WATER

• Any water that has been adversely affected in quality by anthropogenic influence.

• Origin can be a combination of;• Domestic, industrial, commercial or agricultural activities or surface runoffs,

sewer inflow, storm runoffs etc.• Municipal wastewater is normally called sewage. But recently, the term

sewage is also used to mean any type of wastewater.• May contain various types of pollutants.


ADVERSE EFFECTS OF POLLUTED WATER

• When polluted water is discharged in to the environment;• Drinking water may taste bad• Eutrophication of water bodies• Floating oil blankets • Odor problems, aesthetic concerns• Increase of aquatic life forms etc.


BIODEGRADATION

• Is a natural system in an equilibrium which ensures the circulation of matter through the environment via recycling dead plant and animal matter.

• Done by environmental microorganisms.• Hence, is a complex process of decomposition carried out by various

microbial biochemical reactions.• Can occur aerobically and/or anaerobically.• Generalized procedure;

Complex substances Simple substances gases + minerals


BIODEGRADATION CONT.

• Depends on microbial enzymatic activities.• Microbial enzymes will degrade complex compounds in to simpler

compounds. • Hence, it’s a biological transformation of complex compounds in to simple

compounds.• Simple compounds will be absorbed and broken down to gases and minerals

and/or converted in to biomass within cells.


BIODEGRADABILITY

• Ability of decomposition of a pollutant via biological activities such as microbial metabolism in the environment.

• With respect to time it takes to be degraded, a pollutant can be;• Very easily degradable• Easily degradable• Potentially degradable• Very slowly degradable or;• Non-biodegradable


BIODEGRADABILITY Some waste materials and their approximate

times for biodegradation


AEROBIC BIODEGRADATION

• Biodegradation of waste materials by microorganisms in the presence of oxygen.

• A rapid process.• Heat energy is released.• Convert oxygen to water along with degradation of complex compounds in to

simple components.• Both Gram positive and Gram negative microbes get involved.


MICROBES INVOLVED IN AEROBIC BIODEGRADATION

Here, both Gram positives and Gram negatives play their part


ANAEROBIC BIODEGRADATION

• Decomposition of waste materials by microorganisms in the absence of oxygen.• Occurs when anaerobes are dominant over aerobes.• No heat energy is released.• Provides both volume and mass reduction. Hence, important in sludge and biodegradable

waste treatment.• Anaerobic digestion involves four biological and chemical stages;

• Hydrolysis• Acidogenesis• Acetogenesis• Methanogenesis


MICROBES INVOLVED IN ANAEROBIC BIODEGRADATION

• Acidogenesis -ClostridiumEubacteriumRuminococcus

• Acetogenesis -Syntrophobacter wolanii Syntrophomonas wolfii

• Methanogenesis -Methanothrix Methanosacenia

Here, different microbes are involved in different stages

of degradation


AEROBIC VS. ANAEROBIC WHO’S THE BEST?

Aerobic biodegradation• Most rapid and fast• No pungent gas production• Expensive• Large amounts of disposable wastes

generated

Anaerobic biodegradation• Time consuming and slow• Pungent gas produced• Less expensive• Less waste generated


NON-BIODEGRADABLE COMPOUNDS

• Compounds that cannot be digested via biological means.• Some scientists believe that “nothing is non-biodegradable”• Even if so, some compounds take too long to be degraded in the

environment and by the time, damage done to environment may be severe. • Xenobiotic compounds are also falls under non-biodegradable compounds.


XENOBIOTIC COMPOUNDS

• A foreign chemical found within an organism, but is not normally naturally produced by or expected to be present within that particular organism. • Example: Antibiotics within human body

• Chemical compounds which are present in much higher concentrations than usual within an organism also falls under this class.

• Term often used in context of pollutants.• Dioxins and polychlorinated biphenyls. (xenobiotic to whole biota, not existed

before human synthesis) • Alkyl Benzene Sulfonates


ALKYL BENZENE SULFONATES

• A major component in some anionic detergents.• Two classes;

• Branched alkyl benzene sulfonates• Linear alkyl benzene sulfonates

• Widely used in the formulation of house hold detergent and industrial cleaning products.• Has a very slow rate of biodegradation.• Discharge to the environment can cause un-restorable damages;

• Poisoning water life• Pollution of ground water• Foam formation in revers


BIO-MAGNIFICATION

• Increase in concentration of a substance within an organism exceeding the background concentration of that substance in its diet.

• Is a combine result of three individual reasons;• Persistence of the compound• Food chain energetics• Low or non-existent rate of internal degradation or excretion of the substance

• Many xenobiotic chemicals such as pesticides are biomagnified. Many are chlorobenzene compounds

• Examples:• DDT - Persistence over 15 years• Malathion


RECALCITRANT COMPOUNDS

• Xenobiotic compounds that are completely resistant to biodegradation.• Simple structural changes can lead these to be biodegradable.• A xenobiotic may become recalcitrant due to followings;

• They may not be recognized by the existing bio-degradative enzymes• They may be highly stable, i.e., chemically and biologically inert due to the presence of substitution

groups like halogens, nitro-, sulfonate, amino-, methoxy- and carbamyl groups• Insolubility in water or absorbance in to external matrices like soil• highly toxic or give rise to toxic products due to microbial activity• large molecular size prevents entry into microbial cells• Inability of the compounds to induce the synthesis of degrading enzymes• Lack of the permease needed for their transport into the microbial cells.


WASTEWATER TREATMENTSection 2


WHAT IS WASTEWATER TREATMENT?

• Conversion of wastewater (water that is no longer needed nor suitable for its most recent use), in an effluent that can either be returned to the water cycle with minimum environmental issues or be reused.

• The physical infrastructure used is called;• Waste Water Treatment Plant - WWTP• Sewage Treatment Plant - STP• Effluent Treatment Plant - ETP


SELF-PURIFICATION OF WATER BODIES

• Is complex process in natural water systems that often involves simultaneous working of;• Physical processes• Chemical processes• Biological processes

• Returns DO back to the level required by the aquatic life• Only better when rate of waste production is lower than the rate of biodegradation.• Self purification will be affected by;

• Dilution• Water current• Temperature• Sunlight • Rate of oxidation


WASTEWATER TREATMENT PLANT


WASTEWATER TREATMENT PLANT

• Man made physical infrastructures to purify wastewater.• Involves basic principles of self-purification of natural water bodies. And uses its three steps of water

purification with slight modifications.• Physical purification• Chemical purification • Biological purification

• Objectives;• To remove all toxic chemicals• To remove all pathogens• To remove all dissolved nutrients

• It is expected that the final end product (clean water/clear water) of a wastewater treatment plant should be able to be used as portable water.


THE PROCEDURE

• Have designed to achieve improvement in water quality.• It is closely related to the standards set for the effluent quality and ensures

reaching to them. • Removes or should remove;

• Suspended solids• Biodegradable organics• Pathogenic microorganisms• Dissolved nutrients


THE PROCEDURE CONT.

• In a general sewage treatment plant, there are three basic steps of water treatment.• Primary treatment - Physical or mechanical purification• Secondary treatment - Biological purification• Tertiary treatment - Chemical purification


PRIMARY TREATMENT

• Designed to remove gross, suspended and floating solids from raw sewage.• Involves mechanical purification techniques such as screening and sedimentation.• Can reduce BOD from 20-30% and total suspended solids from 50-60%.• There several operational units in primary treatment. Including;

• Screening• Flow equalizing• Neutralization• Gravity separation• Chemical aids• Floatation


SCREENING

• First operational unit in primary treatment.• Involves the operation of a screen filter.• A screen is a device with openings, generally of uniform size that is used to

retain the coarse solids found in wastewater.• Two classes; according to the size of openings.

• Coarse screens - openings ¼ inch or more• Fine screens - openings less than ¼ inch.

• Can be mechanically cleaned or manually/hand cleaned.


FLOW EQUALIZING

• Also known as flow balancing.• Waste water is collected in to a tank, mixed and discharged to downstream processes in a

constant rate.• Can also be used as an emergency tank in case of any process failure. • One of the important operational units to maintain a consistent flow rate.• Inconsistent flow rates?

• Can cause sludge settling problems in activated sludge process etc. • Flow balancing system must provide;

• Sufficient mixing - To create a homogenous mixture and to prevent solid deposition.• Sufficient aeration - To prevent odor problems due to anaerobic decomposition


NEUTRALIZATION

• Wastewater entering biological treatment must have a pH around 6.5-9 for optimum microbial growth.

• Industrial wastes mostly contain acidic or alkaline components and hence, require neutralization.

• Acidic wastes are commonly neutralized with waste alkaline streams, lime, dolomite, ammonia, caustic soda, or soda ash

• Alkaline wastes usually require treatment with a waste acidic stream, sulfuric acid or hydrochloric acid.


GRAVITY SEPARATION

• Separation of suspended particles that are heavier than water via gravity settling.

• In WWTP, sedimentation may be used in several steps. • During primary treatment, it is mainly used to remove grit and particulate

matter.• Done in a primary settling basin.• After settling, primary sludge is collected from the bottom and sent in to

anaerobic digestion.• Clarifier liquid is sent to further treatments downstream.


CHEMICAL AIDS

• Addition of chemicals (coagulants) to alter the physical state of dissolved and suspended solids and facilitate their removal via sedimentation.

• Takes place in rapid mixed or flash mixed basins.• Mixing is essential to disperse the coagulant so that it contacts all of the wastewater.• Few most common coagulants;

• Alum - Al2(SO4)3.18H2O• Ferrous Sulfate - FeSO4.7H2O• Lime - Ca(OH)2

• Ferric Chloride - FeCl3• Ferric Sulfate - Fe2(SO4)3


CHEMICAL AIDS CONT.

• Coagulation will remove;• Total suspended solids - 80-90%• BOD5 - 50-80%• Bacteria - 80-90%

• In contrast, plain sedimentation will only remove;• Total suspended solids - 50-70%• BOD5 - 25-40%• Bacteria - 25-75%


FLOATATION

• Separation is brought by introducing fine gas (usually air bubbles) into the liquid phase.• The bubbles attach to the particulate matter, and the buoyant force of the

combined particle and gas bubble is great enough to cause the particle to rise to the surface to form a scum blanket, which is removed by a skimming mechanism.

• Grit and other heavy solids that settle to the bottom are raked to a central sludge for removal.

• Very small or light particles that settle slowly can be removed more completely and in a shorter time.


FLOATATION CONT.AIR FLOATATION

• In this system, air bubbles are formed by introducing the gas phase directly into the liquid phase through a revolving impeller through diffusers.


EFFICIENCY OF OPERATIONAL UNITS


SECONDARY TREATMENT

• Primary treatment removes most of the rubbish and solid wastes. • Secondary treatment removes dissolved nutrients and remaining solids

via bacterial decomposition.• Uses naturally occurring biological processes.• Steps followed in secondary treatment can be classified depending on

different parameters.• According to oxygen requirement• According to rate of biodegradation


ACCORDING TO OXYGEN REQUIREMENT

1. Aerobic methods - require oxygen for commencement• Activated sludge system - suspended growth system• Tickling filters - attached growth system• Aerobic lagoons and ponds- suspended growth system

Activated sludge is the system with highest rate and highest cost.

2. Anaerobic methods – no need of oxygen and presence of oxygen is inhibitory

• Anaerobic digester - high rate• Anaerobic ponds - low rate

From all on this slide, anaerobic digester has the highest rate.


ACTIVATED SLUDGE SYSTEMAerobic, high rate biological treatment of sewage


ACTIVATED SLUDGE PROCESS

• The conventional activated sludge system contains;• A tank for wastewater aeration - bioreactor/aeration tank• A settling tank - clarifier• Solid recycle line - Return Activated Sludge (RAS) line

• In an aeration tank, water is constantly aerated using bottom aeration systems and mixed using large impeller systems in order to establish a uniform oxygen concentration. • Aeration should be maintained at 1-2 mg/L. • Aeration above 2 mg/L is considered as a waste of energy.


ACTIVATED SLUDGE PROCESS CONT.

• Oxygen concentration• Maximum concentration of oxygen in pure water is around 8 mg/L (20%). But as dissolved organic

matter content rises, maximum oxygen content that can be retained within water drops gradually. As activated sludge system depends on aerobic decomposition, any lowering of oxygen below to the level required by associated microbes is not favorable. Therefore, aeration is a must

• In the aeration tank, aerobic microbial decomposition of organic particles take place. • Generally, the wastewater flows through under constant aeration in the presence of activated

sludge and exits at the end of the tank after 4-8 hours of residence/retention time. • During the retention time; aerobic microbes aggregate together and form small particles known

as floc. • These flocs carryout decomposition of organic matter.


MICROBIAL CONSORTIUM IN FLOCS

• Generally and essentially dominated by bacteria.• But may also include protozoa, fungi, nematodes, rotifers etc.• Dominant non-filamentous bacterial species include;

Zooglea spp. Achromobacter spp.Pseudomonas spp. Corynebacterium spp.Flavobacterium spp. Comamonas spp.Alcaligenes spp. Brevibacterium spp.Bacillus spp. Acenitobacter spp.


MICROBIAL CONSORTIUM IN FLOCS CONT.

• Dominant filamentous bacterial species include;• Sphaeriolitus (sheathed bacteria)• Beggiotoa• Actinomycetes• Norcardia spp.

• All these heterotrophic bacteria are primary consumers of organic matter present in incoming wastewater.

• All other heterotrophs such as protozoa and fungi are secondary consumers.


FUNGI AS INDICATORS

• In activated sludge, fungal growth is not very common.• Sludge system is not very favorable for them.• Accidental fungal growth can occur due to;

• Low pH• Toxic waste• Nitrogen deficient waste etc.

• Hence, fungal growth in an activated sludge system is considered to be an indication of a system error.• Predominant fungal species grow on activated sludge includes;

• Penicillium,• Cephalosporium, • Cladosporium, • Alternaria and Geotrichum.


FLOC FORMATION AND IMPORTANCE

• Formation of flocs with correct structure is important for both;• Biodegradation• Sludge settling

• In the aeration tank, aerobic microbes feed on dissolved organics and convert them in to;• Carbon dioxide• Water and;• Biomass

• These microbes then aggregate together in to structures called flocs.• Flocs contain live and dead microorganisms and products of microbial metabolism.• Correctly structured flocs are easily settled and hence, enable the separation of treated effluent

from sludge.


FLOC FORMATION CONT.

• Flocs with correct structure have two parts;• Core• Filamentous mesh

• Some non-filamentous bacteria (e.g. Zoogloea ramigera) which produce EPS are responsible for forming the core structure.

• EPS will enable such bacteria to aggregate together forming a sticky center.• The core will then get covered by several species of filamentous bacteria

forming a filamentous mesh around them.


FAVORABLE CONDITIONS

• Activated sludge process is more or less completely dependent upon correctly structured flocs.• Formation of such flocs require;

• Presence of right microbes• High oxygen concentration (for both formation & survival. Hence, continuous aeration is a must.)• Good phosphorous content and C: N ratio.• Correct pH (around 6.5-7.5)

• Apart from that, for proper biodegradation and sludge settlement sludge age is important.• Eukaryotes such as protozoa feed on flocs and act as a biological control system.• Bacteriophages are problematic as they attack floc formers destroying floc structures.• Fungal growth is an indication of lowering of pH, presence of toxic waste or low nutrient waste.


MONITORING ACTIVATED SLUDGE SYSTEMS

• Is a complex procedure. Includes several parameters that must be closely studied.

• Important to maintain the correct operation of the plant in order to achieve objectives.

• Parameters include;• Mixed Liquor Suspended Solids - MLSS• Food-to-Microorganism ratio - F/M ratio• Hydraulic Retention Time - HRT• Sludge Volume Index - SVI


MIXED LIQUOR SUSPENDED SOLIDS

• Concentration of total suspended solids in the aeration tank.• Includes all the suspended organic material and microbial biomass and

minerals.• Determined experimentally using gravimetric methods mainly which include

filtrations et. at a temperature of 105 Celsius.• Units – mg/L• The typical control band for the concentration of MLSS in wastewater is 2,000

to 4,000 mg/L for conventional activated sludge


WHAT IF..

MLSS is too high• Process is prone to bulking and over

loading.• DO will drop.• Reduced nitrification efficiency and

sludge settleability.• Requirement of excessive aeration.

• This will be a will be a waste of energy

MLSS is too low• Process may not remove sufficient

amount of organic matter.• The sludge age may be too low to

enable nitrification


FOOD-TO-MICROORGANISM RATIO

• An indication of the biomass available to consume the applied quantity of organic pollutant at any time.• Helps to have a balance between substrate consumption and biomass generation to keep the system

at an equilibrium.• Calculated using the equation;

Where;Q - influent flow rate - m3 per dayBOD5 - five-day biological oxygen demandMLSS - mixed liquor suspended solids - mg/LV - volume of the biological reactor - m3


HYDRAULIC RETENTION TIME

• The average resident time of wastewater in the aeration tank.• Average HRT usually ranges from 3 to 8 hours but can be higher with high BOD5

wastewaters.• Calculated using the equation;

Where;D - dilution factorV - volume of the biological reactorQ - flow rate of the wastewater influent


SLUDGE VOLUME INDEX

• The volume (in ml) occupied by 1 gram of activated sludge after settling the aerated liquor for 30 minutes.

• Used to describe the settling characteristics of sludge.• Good settling sludge - SVI below 100 mg/L• Poor settling sludge - SVI above 150 mg/L

• A process control parameter to determine the recycle rate of sludge.• Equation;

• For a 1 liter of sludge, minimum of 1/3 of its volume must settle. If not, the system is not working at all.


SLUDGE SETTLING PROBLEMS

• Due to poor settling sludge formation;• Suspended solids pass to the effluent in concentrations that often exceed regulatory

standards.• Desired SRT cannot be maintained.• Effluent BOD limitations are often exceeded

• Such settling problems may be due to;• Sludge bulking• Rising sludge• Foam formation etc.


SLUDGE BULKING

biological treatment of wastes and pollutants (part 1)

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