Wastewater Treatment: Water & Wastewater

Course Outline • Wastewater

– Definition – Type/origin

• Wastewater treatment -In Brief

– Primary Treatment – Function – Significant

• Secondary treatment

– Function – Significant

• Tertiary Treatment

– Function – Significant

Wastewater -in details - Type and Origin/source Wastewater Treatment • Primary Treatment- In details

– Principle – Unit operations Involve – screening, grit channel, communitor, primary clarifier

• Secondary Treatment – Principle – Suspended growth

• Oxidation ponds • Activated Sludge • Oxidation ditch • Sequencing batch reactor

– Attached growth • Trickling Filter • Rotating biological Contactor

• Sludge management • Suspended growth vs film growth

• Tertiary/advance treatment – UV treatment – Ozonation

• Other treatment – Wetland

• WASTEWATER • What is wastewater

– Water that has been adversely affected in quality by anthropogenic source

• Why wastewater need to be treated

– It stinks • get smelly very fast, i.e Kitchen waste etc

– It contains harmful bacteria. • Human waste naturally contains coliform bacteria (E. coli) • Disease

– It contains suspended solids and chemicals. • Waste from industry, grey water etc

• For example, contains: • Nitrogen and phosphates

– encourage the growth of algae. – Aquatic life cannot breathe

• organic material – Reduce the oxygen level

• The suspended solids in wastewater

– Cloudy/turbid water – Less sunlight

Classification of wastewater classification based on origin: 1) Municipal Wastewater:

Is a direct result of the activities of the inhabitants of these areas.

The contributions:

•  Raw  sewage  or  fecal •  Water  from  the  domestic  washing •  Waters  stuff  out  of  the  drainage  system  of  streets  and  avenues •  Water  from  rain  and  leachate  

pollution load and composition generally uniform contributions are generally always the same. Volume depending on the population density

2) Industrial Wastewater: come from business activities,

i.e manufacturing or handling processes that use water • Extremely variable in its volume and its composition. ( from different as well as within same sector industries) • Characteristic of discharge varies influence by the processes of production and total

manufacturing process (production scheduling etc)

• Contamination, difficult to remove. -high concentration and its variability • require more complex treatment ( comparing to municipal

wastewater)

• Treatment stages- municipal or industrial wastewater

• Type of treatment

– depending on the origin of wastewater and its characteristic

• Basically 3 stages as follows: – primary – secondary – Tertiary/advanced

• Wastewater from either municipal or industrial undergoes the same treatment stages.

• However, the exact treatment process depend on the nature/characteristics of the wastewater

Ultimate objective of wastewater treatment -To produce a treated effluent and a

sludge suitable for discharge or reuse back into the environment.

Wastewater Treatment- overall process diagram

• Primary treatment • Is a Physical Treatment • Objective:

– To screens out, grinds up, or separates debris in the wastewater. • Sticks, rags, large food particles, sand, gravel, toys, plastics,

and other objects are removed at this stage

• Why needed – To protect pumping and other equipment from clogs, jams or

excessive wear

• Treatment unit – bar screens, – comminutors (a large version of a garbage disposal that shreds

material), – grit chambers

� Primary Treatment

�Bar Screen

- catches large objects that have gotten into sewer system such as bricks, bottles, pieces of wood, etc.

Shredding • devices reduce solids to a smaller size so that it can enter the plant without causing mechanical problems

or clogging. • comminutor -the most common shredder

• All of the wastewater flow passes through the grinder assembly. • The grinder consists of a screen or slotted basket, a rotating or

oscillating cutter and a stationary cutter

• Grit Removal • Purpose

– To remove the heavy inorganic solids -which could cause excessive mechanical wear

• Example of Grit: – sand, gravel, clay, egg shells, coffee grounds, metal filings,

seeds and other similar materials.

The processes use gravity/velocity, aeration or centrifugal force to separate the solids from the wastewater.

• Several devices to remove grit i.e Grit Chamber

Grit Chamber The removal principle based on Gravity/Velocity Heavy grit will settled while light suspended organic solid will move to the primary clarifier

• Secondary Treatment

• Basically, is a biological treatment process *However, In some cases, chemical treatment I,e coagulation may apply. • microorganism use organics matter as food and convert it to

biological cells, or Biomass • Aerobic decomposition equation: the decomposition of organic matter in the presence of oxygen. 6 (CH2O)x + 5O2 Æ (CH2O)x + 5CO2 + 5H2O + Energy Organic matter Bacteria cells

• Oxygen assisting micro-organisms to grow and eat small bits of

organics. • Same process that nature uses to get rid of waste (we just speed it up).

Biological Treatment

Wastewater contain

-various type of pollutant and

-Mixture of microorganism (mixed culture)

Each (type) of microorganism, utilized food source ( organic pollutant) that most suitable for it metabolism

Due to that, reactors should be engineered to optimize both rate (cell growth and food utilization)

Biomass growth and food utilization in secondary treatment

• This growth pattern consists of the following four phases:

• 1. The lag phase. – Acclimation period of microbes to food supply. – Length is varied and depend on the seed organisms – The microbes cell start to divide/ multiply/growth in number in this

stages

• 2. The log-growth phase/exponential phase. – Cell divide rapidly in this stage – Maximum growth occur at this stage – Growing/multiply rate determined by their generation time and their

ability to process food.

• 3. The stationary phase. – Here the population remains stationary. – Rate of production new cells = rate of dyeing old cells (due to the

depleted food source) – No net increase in the biomass/cell population

• 4. Endogenous phase. – During this phase, the bacteria death rate exceeds the production of

new cells. – Rate production of cells << rate of dyeing of old cells ( due to low food

supplies)

Kinetic of metabolism of biomass growth vs food utilization will be discussed in Activated sludge section

• Suspended Growth Biological treatment – Stabilization pond/ oxidation pond – Activated sludge – Sequential Batch Reactor (SBR) – Oxidation ditch

Stabilization pond/ oxidation pond

• Suspended growth biological treatment

• Stabilization ponds – open flow through basins – specifically designed to treat sewage and biodegradable industrial

wastes. – provide long detention periods – Lightly loaded ponds used as tertiary step in waste treatment for

polishing of secondary effluents and removal of bacteria are called maturation ponds.

• Classification of Stabilization Ponds based on the type of processes occurring within the pond. 1. Aerobic Ponds and Aerated Ponds

• Aerobic pond

– is a pond in which oxygen is present throughout the pond. – Biogical activity in the pond is aerobic decomposition. – shallow ponds with depth less than 0.5 m to maximize penetration of

light – This ponds develop intense algal growth – Not widely used because, due to lack of oxygen at the lower portions of

a pond, – pond need to be very shallow

• Aerated pond – Alternatively, oxygen is introduced-to maintain oxygen level – Oxygen added using mechanical or diffused air systems

• Ponds which add oxygen to the water in this way are known as

aerated ponds. – Aerated ponds allow the depth of the pond and/or the acceptable

loading levels to be increased. – The mechanical or diffused aeration systems used to supply oxygen

2. Facultative Pond • Most common type of pond.

– upper portion is aerobic, while the bottom layer is anaerobic, which promotes nitrogen removal

– often about 1 to 2 m in depth. – aerobic layer prevent odour evolution from the pond. – must have a balance between photosynthesis and aerobic

decomposition

• Oxygen is added to the water in two ways. – Wind diffuse oxygen to the surface. – Algae also produce oxygen during photosynthesis

• These bacteria use oxygen to break down organic matter suspended in the water

• In turn, the bacteria produce the carbon dioxide which the algae use in photosynthesis.

• Some of the solids settle to the bottom of the pond. • These solids are broken down by anaerobic bacteria which produce

methane or hydrogen sulfide.

• Factors Affecting Pond Reactions Various factors affect pond design: – wastewater characteristics and fluctuations. – environmental factors (solar radiation, light, temperature) – algal growth patterns – bacterial growth patterns and decay rates. – solids settlement, gasification, upward diffusion, sludge

accumulation.

3. Anaerobic Pond • used to treat high strength industrial wastes • ponds depth ranging from 2.5-5m as light penetration is

unimportant. • No oxygen is present in this type of pond, so all biological activity

within an anaerobic pond is anaerobic decomposition.

• Anaerobic digestion mechanism to be discussed at later stage

Activated sludge process

Consist of two main units -Aeration tank -Secondary / final clarifier/settling tank

• Aeration Tank Where the organic waste, microorganism and air come into contact M/organism stick/adsorb to organic matter hence break down it (with

presence of O2) This produce CO2, H20 and multiply the microorganism. Mixture of wastewater and suspended solids (with microorganism) in

aeration tank is known as Mixed Liquor. The suspended solids in aeration tank is known as Mixed Liquor

Suspended Solids (MLSS). The volatile portion of suspended solids in aeration tank is known as

Mixed Liquor Volatile Suspended Solids (MLVSS).

• Once the organic matter has been broken down, the mixed Liquor then transfer to secondary clarifier where the separates suspended solid from the liquid.

• The sludge will settle at the bottom. Because the sludge rich with hungry microorganism, it is known as

Activated Sludge • Portion of the Activated sludge will later recycle back to the aeration tank • Why not all recycle back to aeration tank??

Two types of Activated sludge process - Plug flow characterized by orderly flow of mixed liquor in the aeration tank Not thoroughly mixed

- Completely mixed (CSTR) aeration tank are well stirred and uniform throughout. at steady state, composition of the effluent from the aeration tank

= the aeration tank contents.

• The type of mixing regime is very important as it affects: – oxygen transfer requirements in the aeration tank, – susceptibility of biomass to shock loads, – local environmental conditions in the aeration tank, – the kinetics governing the treatment process.

• Terminology Sludge age/sludge retention time (SRT) duration of microorganism in aeration tank Hydraulic retention time ( ) duration of wastewater contacted with m/o in aeration tank F/M ratio-define Ratio of food (wastewater) to microorganism in aeration tank

Influent Flow Rate Qo m3/d

Influent BOD So g/m3

Effluent or desired BOD Se g/m3

Aeration tank MLSS X g/m3

Effluent SS concentration Xw g/m3

Design Volumetric Loading VL (kg BOD/day/m3)

Influent TSS concentration Xo g/m3

Waste/recycle activated sludge SS concentration

Xw g/m3

Aeration tank volume V m3

Sludge retention time SRT days

Recycle Activated Sludge Flow Rate Qr m3/d

Waste Activated Sludge Flow Rate Qw m3/d

V = (So x Qo) / VL m3

HRT = V/Qo day

F:M = (So x Qo) / (X x V) (kg BOD/day/kg MLSS)

Qr = Qo(X - Xo) / (Xw - X) m3/d

Qw = (V x X) / (SRT x Xw) m3/d

Inputs Influent Flow Rate, Qo = 36,000 m3/day Influent BOD, So = 150 g/m3 Aeration tank MLSS, X = 1800 g/m3 Design Vol. Loading, VL = 0.5 (kg BOD/day/m3)

Calculate Aeration tank volume, V ??? m3 Aeration tank, HRT ??? hr F:M ??? (kg BOD/day/kg MLSS)

Input Influent Flow Rate, Qo 38,000 m3/d

Influent BOD, So 150 g/m3 Influent TSS, Xo 200 g/m3 Waste/recycle activated sludge SS conc., Xw 7,000 g/m3 Aeration tank vol., V = 11,400 m3 Aeration tank MLSS, X = 2000 g/m3 Sludge ret. time, SRT = 12 days

Calculate

Recycle Activated Sludge Flow Rate, Qr 13680 m3/d

Waste Activated Sludge Flow Rate, Qw 271.43 m3/d

Aeration tank, F:M 0.250 (kg BOD/day/kg MLSS)

• Variation of activated sludge – Step aeration

• settled sewage is introduced at several points along the tank length

• produces more uniform oxygen demand

– Tapered aeration • attempts to supply air to match oxygen demand

along the length of the tank

– Contact stabilization • provides for reaeration of return activated sludge

from the final clarifier, which allows a smaller aeration or contact tank.

– Extended aeration • Long retention time • Low F/M to maintain culture

• Operational problems in activated sludge process

• Unsettled sludge in the sedimentation

tank/secondary clarifier • This is due to uncopius growth of less desirable

microorganism

Bulking sludge Sludge with poor settling properties Occurs due to the Filamentous bacteria long strand, high volume so cause

reduction in density

Bulking sludge at settling tank

Bulking sludge under microscope

Causes the growth of filamentous bacteria: – high organic loadings, – pH changes, – inputs of industrial wastes, – Low dissolved oxygen levels, – improper balance between carbon, nitrogen

and phosphorous in the waste

• To control: – Add chlorine to return activated sludge – Greatly reduce the recycle sludge

• Rising sludge Poor settling ability, float to surface after

short while

• Causes:

• The growth of actinomycetes and certain other filamentous organisms, which have a *hydrophobic cell surface. – adsorbs air and nitrogen gas bubbles and

causes the sludge to rise upwards.

• To control – Increase sludge recycling rate – Decrease flowrate to clarifier – Increase wasted sludge from clarifier – Decrease sludge age

• Nocardia Foam Viscous brown foam that covers aeration tank

and clarifier Normally occurred at plants that receive a lot of

fat, oil, grease and surfactants Cause: Low F/M Build up of MLSS-long sludge age Fast air flow rate

• Overcome: – Reduce sludge age – Reduce air flowrate – Chlorinating a selector compartment

• Sludge settles ability • Good settleability:

– clear supernatant and low SS in effluent.

• Happened when: – Low F/M ratio

• usually occurs in extended aeration *** • high F/M ratio cause poor sludge settleability • usually occur in high rate reactor at exponential growth

• To measure sludge settleability

SVI-sludge volume index

• Sludge Volume Index (SVI) • To indicate the sludge settleability in the secondary/final

clarifier.

• Describe the changes in the sludge settling characteristics and quality.

• SVI - the volume of settled sludge in millliliters occupied by 1 gram of dry sludge solids after 30 minutes of settling in a 1000 ml graduated cylinder

• A liter of mix liquor sample is collected at or near the outlet of the aeration tank, settled for 30 minutes in a 1 liter graduated cylinder, and the volume occupied by the sludge is reported in milliliters.

Work example : refer LKK note

The accepted range for an SVI at a conventional activated sludge plant should be between 50 and 150.

• Sludge management etc

• Sludge management • To reduce the volume of sludge

– Reduce storage space – Reduce transportation cost – Reduce disposal charge

• Commonly use technique

DEWATERING

remove water from sludge

Water will add to the sludge weight, indirectly increase the sludge disposable cost

• Dewatering methods – Drying bed

• dry the sludge under the sun in an open space

– Thickening the sludge • Dissolved air flotation-fine sludge separated by air

bubble • Belt filter-water is removed by suction under

vacuum(mechanical method)

• Filter press – separated the water by filter frame

• Centrifuging

sludge is place into a spin bowl to settle sludge under centrifugal force

Sequential Batch Reactor

• Variation of an activated sludge process

• designed to operate under non-steady state conditions.

• Is a fill and draw or batch process.

• All biological treatment phases occur in a single tank

• This differs from the conventional flow through activated sludge

process (required separate tanks for aeration and sedimentation/clarifier)

• contain either two or more reactor tanks that are operated in parallel, or one equalization tank and one reactor tank.

• The type of tank used depends on the wastewater flow characteristics

• installed where there is no public sewer and a septic tank is not environmentally acceptable.

• treats the effluents to a very high standard

• There are normally five phases in the SBR treatment cycle: – Fill (with wastewater) – React (the ww with m/organism), – Settle (the sludge produce), – Decant ( the treated water), – and idle (ready for the next cycle as well as removing

some sludge).

• The following are the processes taking place in different phases:

• In the fill phase, raw wastewater enters the basin, Some aeration may occur during this phase. • Then, in the react phase, the basin is aerated, allowing oxidation

and nitrification to occur.

• At settling phase, aeration and mixing are stopped and the solids are allowed to settle.

• The treated wastewater is then discharged from the basin in the decant phase.

• In the final phase, the basin is idle as it waits for the start of the next cycle.

• During this time, part of the solids are removed from the basin and disposed of as waste sludge.

• Advantages of SBR :

• High effluent quality;

• operates on a storage and batching system – Batch system eliminates peak surges

• There are no moving parts or electrical components within the tank.

• Process is simplified. Since all the unit processes are operated in a single tank

• The system allows for automatic and positive control of mixed liquor suspended solids (MLSS) concentration and solids retention time (SRT) through the use of sludge wasting.

• Disadvantages :

• High peakflow can disrupt operation unless accounted for in design

• Batch discharge may require equalization prior to disinfection,

• Higher maintenance skills required for instruments, monitoring devices, and automatic valves

• It is hard to adjust the cycle times for small communities.

• Sludge must be disposed frequently.

• Specific energy consumption is high

• Oxidation Ditch

• Oxidation ditch is an extended aeration activated sludge process.

• Is a large holding tank in a continuous ditch with oval shape similar to that of a racetrack.

• The ditch is built on the surface of the ground and is lined with an impermeable lining.

• This increase the exposure wastewater to the open air for the diffusion of oxygen.

• The liquid depth in the ditches is very shallow, 0.9 to 1.5 m, (to prevent anaerobic conditions from occurring at the bottom of the

ditch).

• Oxidation ditch -Ammonia Removal

• Can be set up to remove ammonia very effectively

• Wastewater through two sets of ditches, each of which has a different pH.

• The different pH in the two ditches creates a niche for certain microorganisms.

• Oxidation ditches are much more efficient at ammonia removal than

packaged plants are.

• Nitrification & Denitrification • Bacteria remove nitrogen from wastewater by a two step biological

processes:

1) nitrification followed by 2) denitrification. . • Nitrification. • The biological conversion of ammonium to nitrate nitrogen • Nitrification is a two-step process.

• 1) Nitrosomonas convert ammonia and ammonium to nitrite.

• 2) Nitrobacter finish the conversion of nitrite to nitrate.

• These bacteria(Nitrosomonas + Nitrobacter) known  as  “nitrifiers”  are  

strict  “aerobes”  

• Nitrification occurs only under aerobic conditions at dissolved oxygen levels of 1.0 mg/L or more.

• The optimum pH for Nitrosomonas and Nitrobacter is between 7.5 and 8.5 – Most treatment plants are able to effectively nitrify with a pH of

6.5 to 7.0. – Nitrification stops at a pH below 6.0.

• The Water temperature also affects the rate of nitrification.

– Nitrification reaches a maximum rate at temperatures between 30 and 35 C .

– > 40 C, nitrification rates fall to near zero. – <20 degrees C, nitrification proceeds at a slower rate

• The following equations describe the nitrification process. Biological nitrification • 1) NH3 + CO2 + 1.5 O2 + Nitrosomonas →  NO2

- + H2O + H+

• 2) NO2- + CO2 + 0.5 O2 + Nitrobacter →  NO3

-

Denitrification. • The biological reduction of nitrate (NO3) to nitrogen gas (N2) by

facultative heterotrophic

• “Heterotrophic”  bacteria  need  a  carbon  source  as  food  to  live.

• “Facultative”  bacteria  can  get  their  oxygen  by  taking  dissolved  oxygen out of the water or by taking it off of nitrate molecules.

• Denitrification occurs when oxygen levels are depleted and nitrate

becomes the primary oxygen source for microorganisms • Most treatment plants are able to effectively denitrify with a pH of 7

to 9.0.

• The process is performed under anoxic conditions, when the dissolved oxygen concentration is less than 0.5 mg/L, ideally less than 0.2 mg/L.

• When bacteria break apart nitrate (NO3) to gain the oxygen (O2), the nitrate is reduced to nitrous oxide (N2O), and, in turn, nitrogen gas (N2).

• Since nitrogen gas has low water solubility, it escapes into the

atmosphere as gas bubbles. •

• The equation describing the nitrification reaction follows:

• 6NO3 + 5CH3OH Æ 3N2 + 5CO2 + 7H2O + 6OH

• A carbon source (shown in the above equation as CH3OH) is required for denitrification to occur.

• Denitrification occurs only under anaerobic or anoxic conditions.

• Requirement for carbon;

• Sufficient organic matter needed to drive denitrification reaction • Organic matter may be in the form of

– 1) raw wastewater, or 2) supplemental carbon

• The highest growth rate can be found when using methanol or acetic acid.

• A slightly lower rate using raw wastewater

• Conditions that affect the efficiency of denitrification include – nitrate concentration, – anoxic conditions, – presence of organic matter, – pH, – temperature, – alkalinity and the effects of trace metals.

• Denitrifying organisms are generally less sensitive to toxic • Denitrification can occur between 5 and 30 C (increasing with temperature) and type of organic source present.

• Wastewater cannot be denitrified unless it is first nitrified.

• Example of facultative heterotrophic bacteria=aerobacter, lactobacillus, micrococcus, pseudomonas

• ATTACHED GROWTH

-Trickling Filter - Rotational Biological Contactor

EM (effective micro-organism) mudballs

Trickling Filter

Trickling Filter

• comprises a bed of highly permeable medium to which micro-organisms are attached.

• Sewage is percolated or trickled through this media which is made from rocks (2cm to 10cm in size) or specially designed plastic.

• Rock beds are typically 2 meters deep and are circular.

• Plastic media varies in design with depths ranging from 4 to 12 meters depending upon the organic load.

• A revolving arm is used to distribute the sewage over the media.

• Filters under the media drain the effluent and biological solids, which have become detached from the media.

• Air is circulated back through the drainage system to the media.

• The effluent from the drain is settled before discharge to the receiving environment.

• Some effluent from the drain is recycled to dilute the strength of the incoming sewage and to ensure the media remain moist.

• As the effluent passes through the media organic material is absorbed onto the biological film or slime layer covering the media.

• It then degraded by aerobic micro-organisms.

• As the slime layer grows an anaerobic environment is created near the media interface.

• Eventually the micro-organisms at the media interface loose their ability to cling to the media and the slime is washed off.

• A slime layer begins to grow again and the cycle is repeated.

• Filters are classified by hydraulic or organic loading rates.

• Classifications are low rate, intermediate rate, high rate, super high

rate and roughing.

• Re-circulation of filter effluent permits higher organic loadings in high rate filters.

Typical figures for high rate trickling filter are as follows:-

(mg/L) Raw Sewage Effluent DOE Standard A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

• Advantages – Low operating cost – Can sustain variation in hydraulic or organic load.

• Disadvantages

– Huge area needed – Clogging of media – Suitable for small community

Rotational biological contactor

• robust and capable of withstanding surges in organic load.

• comprises a series of closely spaced "circular disks" normally made from a plastic material.

• The disks are partially submerged in the sewage and are slowly rotated through it.

• The rotating disks support the growth of bacteria and micro-organisms present in the sewage, which breakdown and stabilise organic pollutants.

• micro-organisms need both oxygen to live and food grow.

• Oxygen is obtained from the atmosphere as the disks rotate.

• As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage.

• Effluent from the RBC is then passed through final clarifiers where the micro-organisms in suspension settle as a sludge.

• The sludge is withdrawn from the clarifier for further treatment.

• There are currently approximately 40 RBC plants in Malaysia

Typical values for RBC's are as follows

(mg/L) Raw Sewage Effluent DOE Standard A

Biological Oxygen Demand 200-400 10-30 20

Suspended Solids 200-350 15-40 50

• Advantages • RBC units are suitable where land is restricted.

• They are quite and consistently produce a high quality effluent.

• Due to modular they are also suitable for a staged development.

• Operations and maintenance costs are lower than for other forms of

mechanical treatment.

• Large biomass on surface drum-shorter contact time

• Disadvantages

• High Capital cost • Sensitive to temperature • Need to cover drum surface to prevent algae growrth

• Anaerobic

• Anaerobic Digestion

• the most suitable option for the treatment of high strength organic effluents (BOD> 8000 mg/L)

• series of processes – microorganisms break down biodegradable material in the absence of oxygen.

• widely used as a renewable energy source

– the process produces a methane and carbon dioxide rich biogas suitable for energy production

• As a fertilizer – nutrient-rich digestate

• The digestion process begins with :

• bacterial hydrolysis of the input materials – break it down insoluble organic polymers , i.e carbohydrates and make them

available for other bacteria.

• Acidogenic bacteria

– convert the sugars and amino acids into carbon dioxide, hydrogen, ammonia, and organic acids.

• Acetogenic bacteria – convert these resulting organic acids into acetic acid, along with additional

ammonia, hydrogen, and carbon dioxide.

• Methanogens bacteria – convert these products to methane and carbon dioxide.

• Summary: • Four key biological and chemical stages of

anaerobic digestion: • Hydrolysis • Acidogenesis • Acetogenesis • Methanogenesis

• Factors effecting anaerobic digestion

• Nutrients • C:N:P ratio = 100:1.25: 0.25

• pH • Optimun pH for anaerobic digestion: 7.0-7.2

• Temperature

• Can be operated at three levels of temperature • Cryophilic ( in a landfill): 16 C • Mesophilic ( in a digester) : 35-40 C • Thermophilic ( in a digester) : 55 – 60 C

• Toxic substances – High concentration of volatile fatty acids – High concentration of metal ions – Aromatic compounds – free ammonia – Sulfide

• Indication of failure or sick digester

– Low pH in digester system – Low production of methane gas

• Advantages – sludge is reduced – Low power consumptoion – Produce methane gas (recycled to produce power) – Low nutrient requirement

• Disadvantages

– Slow process (due to slow growh rate of methanogens) – Long retention time – May required heating – Sensitive nature of methanogens

WETLAND

Natural wetland

• Definition

• Convention of wetland of International Importance (the Ramsar Convention 1971) as;

"Land inundated with temporary or permanent water that is usually slow moving or stationary, shallow, fresh, brackish or saline, where the inundation determines the type and productivity of soils and the plant and animal communities".

• Functions of wetland

• Natural filter – the 'kidneys' of the catchment- trapping intercepting water flow, removing toxic

substances (pesticides, herbicides, metals) and assimilating nutrients and energy derived from the upstream catchment area.

• breeding grounds,

– nurseries and homes to numerous plants, invertebrates, frogs, reptiles, fish and waterbirds.

• Erosion control – Wetland vegetation reduce erosion along lakes and stream

banks by mitigating forces associated with wave action

• Ground water recharge and discharge – By detaining surface water(from quickly run off to lake), more

can percolate into the ground. – Some wetland are ground water discharge area

• Recreational area – Their biodiversity, open space, aesthetics make and attractive

recreational activities and social pursuit.

Constructed/Artificial wetland

• constructed wetlands: combination of sewage treatment with phytotechnology

• Application of proper phytotechnologies (fast gowning

plants: willows, reeds, or other native species for a region)

• Advantages of using constructed wetlands? – Utilize solar energy driven purification processes – Relatively easy to constructed – if available land is not a limitation, the longevity of

large systems is calculated to be 50 -100 years;

• Problems can be solved by constructed wetlands? • Denitrification

– nitrate is denitrified under anaerobic conditions in a wetland – organic matter accumulated in the wetland provides a carbon source – oxygen conditions can be regulated by water flow rates

• decomposition of biodegradable organic matter,

– either aerobically or anaerobically,

• uptake of heavy metals and other toxic substances

– proper selection of plants

• decomposition of toxic organic compounds

– anaerobic processes in wetlands

Natural wetland/ mangrove

Paya Indah wetland, Putrajaya

Artificial/constructed wetland

Artificial  wetland…one  for  many

• Treatment of Boiler Water

• Cooling tower and boiler water What is cooling tower and boiler What is cooling tower and boiler water Effect/problems of using untreated water How to overcome the effect/problems

- THE END -

Quiz Describe your understanding on: 1-Primary treatment 2-Secondary Treatment 3-Tertiary treatment Test 2 Water treatment 17th May @ Friday