8a-Advanced Waste Water Treatment

Advanced Wastewater Treatment

Removal Capacity of Conventional Treatment Processes

BOD & SS = 85 – 95 % RemovalCOD = 65% Removal

Remaining organic matter needs to be removed further

Advanced Wastewater Treatment

Remove constituents not adequately removed by secondary treatmentNitrogen, phosphorus, other soluble organic and inorganic compoundsAccelerate plant growth, toxic, concentrate in food chain, increase chlorine demand, taste and odour problem

Limit for Sewage Treatment Plants (> 10,000 pe) in the EU Countries

Effluent concentration Minimum elimination rate

Total nitrogen

Total phosphorus

15 mg/l for plants < 100,000 pe10 mg/l for plants >100,000 pe

2 mg/l for plants < 100,000 pe1 mg/l for plants >100,000 pe

70 – 80%

80%

Nitrogen level in treated effluent in EU Countries

Total N NH4-N Source

German - Ruhr new old

8.9*14

2.36.3

Bode and Klopp (2001)

Italy 2** 6+ Carucci et al (1999)

Denmark 8 2 Rindel (2002)

Netherland 9 - Van der Graaf (2001)

note: * inorganic N ** as NH4+ + NO3-N nitrate nitrogen

Common Processes

Biological nutrient removalChemical coagulation and precipitation of phosphorusAmmonia strippingBreakpoint chlorinationFiltrationCarbon adsorptionIon exchangeMembrane separationOzonation

Biological Nutrient Removal BNR

Integrated with conventional biological process used for BOD and TSS removalAnaerobic, anoxic and aerobic zones for phosphorus release and uptake and nitrification and denitrificationEffluent quality; BOD5/TSS/TP/TN = 5/5/1/5 mg/l

Package constructed wetlands = 1 mg/l P

Enhanced Nitrogen Removal

High sludge ageLong detention timeBOD/TKN = not less than 3 for biological nitrification

Nitrified Effluent

Nitrifiers are slow growth microorganisms as compared with heterotropic bacteria (in carbonaceous oxidation)

Nitrogen Removal - Nitrification

Organic Matter + O2 NH3 + Microorganisms + CO2

NH3 + 2O2

NO3- + H2O + Microorganisms

Organic Matter + NO3-

N2 + Microorganisms

Bacteria

Nitrosomonas (the rate limiting bacteria) converts ammonia to nitrite and Nitrobacter converts nitrite to nitrate

NH4+ + 2O2 NO3

- + 2H+ + H2O

Alkalinity

Nitrification consumes alkalinityNH3 + 2O2

NO3- + H+ + H2O + Microorganisms

Need buffering capacity; maintain pH at 6.5 – 8.0Abrupt drop in rate of nitrification beyond pH 6.5

Denitrification

Anaerobic & Anoxic condition required 3 – 4 g methanol per gram of nitrate to be

removed Denitrifiers are sensitive to temperature variation pH 6-8 2 – 3 h retention time Minimum 1 – 2.5 d sludge age to produce

flocculating sludge

How much methanol is consumed by oxidation of 30 mg/l NO3- ?

Methanol demand for oxidation of nitrate =Half reaction for methanol

- [ 1/6 CO2 + H+ + e- = 1/6CH3OH + 1/6H2O ]

Half reaction for nitrate

+ [ 1/5 NO3- + 6/5 H+ + e- = 1/10 N2 (g) + 3/5 H2O]

+

1/6CH3OH + 1/5 NO3- + 1/5 H+ 1/10N2 + 1/6 CO2 + 13/30 H2O

Molecular Wt NO3 = 48Molecular Wt CH3OH = 32

Amount of methanol consumed, M = 5.33/9.6 x 30 mg/l = 16.7 mg/l

Nitrification & Denitrification

Carbonaceous Oxidation and Nitrification

(in the same tank)

Carbonaceous Oxidation

Nitrification

DenitrificationDenitrification

Add methanol, ethanol, acetate, molasses

Biodenipho process

Process works using Anoxic-oxic cycle

Denitrification(Nitrate decrease)

Nitrification(Nitrate increase)

Lynetten, Copenhagen 750,000 pe - Biodenipho

Lynetten STP is Biodenipho (Nitrification-denitrification) that produce Total Nitrogen in effluent below 8 mg/l

Capacity Lynetton STP - Biodenipho 750,000 PEFlowrate max Dry weather

m3/hrm3/hr

23,0007,083

Flowrate storm m3/hr 41,500

Waste Characteristic Raw effluent treated

BOD 150 15

(all in mg/l) COD 400 75

TSS 200

NH4-N 40 8 (TN)

TP 9 1.5

Retention time (hr) in cubic metres:

Primary settling tanks 2.7 19,200

BioP tanks 3.4 24,000

Aeration tanks 20.8 147,000

Final settling tanks 8.3 59,100

Thickeners 1.4 10,000

Digesters 22 days based on SRT 18,000

Biogas production 12,863 m3/d 0.7 m3/m3/day

Sludge incineration 7 tonnes/hr

Case study:

http://www.princeton-indiana.com/wastewater/index.html

BNR at Princeton, Indiana USA

Phosphorus Removal

Biological uptake by sludge Chemical precipitation = lime and iron &

aluminium salts Luxury uptake = Sludge being treated

anaerobically before returning the phosphorus deficient sludge to the reaction tank. The sludge would then assimilate greater quantity of phosphate than usual.

Enhanced Phosphorus Uptake

CAS = 1 – 2 % PEnhanced system = 3% PDetention time = 0.5 – 2 h

Anaerobic Aerobic

Produce short chain fatty acid & P released

Acid utilised & P taken up

Layout

Anoxic Aerobic

AerobicAnoxicAnaerobic

Nitrified recycle

Anoxic recycle

Nitrified recycle

Anaerobic > Anoxic > Aerobic system ensures denitrification & P removal

Membrane Separation

What is a membraneWhat drives the separationPore sizes, RO, UF, MF

Schematic Diagram of Membrane Separation

MEMBRANE MEMBRANE

MEMBRANE

Water

Salt Macromolecules

Selected Macromolecules

ULTRAFILTRATION

MICROFILTRATION

REVERSEOSMOSIS

Membrane Filtration Spectrum

0.001 0.01 0.1 1 10 100 1000m (log scale)

Reverse Osmosis

Microfiltration

Particle FiltrationUltrafiltration

Different Blocking Mechanisms

Complete blocking Intermediate blocking

Cake filtration Standard blocking

Crossflow and Dead-end Filtration

MEMBRANE

Feed Reject

FiltrateFilter Cake

Flux

Time

MEMBRANE

Feed

FiltrateFilter Cake

Flux

Time

Solute Rejection & Breakthrough

Functional groups present in the membraneNature of membrane surfaceSize of solute moleculeDissociation of solute molecule (pH dependent)Operation time

Ideal Membrane

High flux rateTolerant to chlorineResistant to biological attackResistant to foulingMechanically strongInexpensiveChemically stableExcellent filtrate quality

Ozonation

Ozone is the triatomic form of oxygen (composed of three oxygen atoms), O3. Under normal conditions ozone is unstable and quickly decomposed to the more stable gaseous oxygen, O2. Because ozone is unstable and cannot be stored successfully, it must be generated at the point of application.

Ozonation

Ozone can be generated by passing oxygen, or air containing oxygen, through an area having an electrical discharge or spark. (A clean smell in the air after a thunder and lightning storm was most likely caused by ozone formed by lightning bolts passing through the atmosphere).

Ozonation

Typical ozonators have two large area metal electrodes separated by a dielectric and an air gap. An alternating electric current is applied to the electrodes creating an electrical discharge. At the same time air or oxygen is passed through the air gap. As the air or oxygen flows through the air gap, and the electrical discharge, a portion of the oxygen is converted to ozone. The dielectric is necessary to spread the electric discharge over the entire electrode area and avoid producing an intensive single arc.

Ozonation

The concentration of the ozone leaving the ozonator is approximately 1 to 2% by weightAs with chlorination, the effectiveness of disinfection using ozone is depended on the concentration of the disinfectant, thorough mixing and contact time. To satisfy the mixing and contact time requirements, three general types of contactors are usually used: (1) packed bed, (2) sparged column, and (3) sparged column with mixing.

Advantages of Ozonation 1. eliminates odours 2. reduces oxygen demanding matter, turbidity and

surfactants 3. removes most colours, phenolics and cyanides 4. increases dissolved oxygen 5. production of no significant toxic side products6. increases suspended solids reduction

Disadvantages of Ozonation

1. high capital cost 2. high electric consumption3. highly corrosive, especially with steel or iron

and even oxidizes Neoprene

Disinfection Using Ozone

Ozone is thirteen times more soluble in water than oxygen. When first introduced into wastewater, very little disinfection occurs. The ozone is rapidly consumed, satisfying the ozone demand of inorganic salts and organic matter dissolved in the wastewater. The disinfecting properties of the ozone come into play only after the ozone demand is satisfied. When the demand is satisfied, research studies indicate, ozone brings about disinfection 3100 times faster than chlorine.

Disinfection Using Ozone

It has also been found that disinfection occurs within contact times of 3 to 8 seconds. Typical ozone dosages needed to reach the disinfection stage vary with the quality of the effluent. Dosages between 5 to 15 mg/L are commonly cited for disinfection of secondary wastewater effluents. Ozone also exhibits excellent virocidal properties at these dosages but with longer contact time of about 5 minutes needed. It has also been found that any residual ozone in the effluent of the contactor disappears in a matter of seconds outside the contactor.

Other Uses of Ozone in Wastewater Treatment

Ozone has the ability to remove solids from wastewater by oxidation and physical floatation. A foam develops when wastewater is ozonated. It has been found that this foam traps a significant amount of solids and nutrient material such as phosphates and nitrates.

pH has been found to increase very slightly because of ozonation. This is probably the affect of carbon dioxide being driven out of the solution by the gas feed in the ozone contactor.

Other Uses of Ozone in Wastewater Treatment

Colour and turbidity are reduced by addition of ozone. This is brought about by chemical oxidation of the substance causing the colour or turbidity.

Some minor nitrification occurs, but not at levels high enough to consider ozonation as an effective nitrification process.

Safety of Ozone

The Maximum Allowable Concentration (MAC) of ozone in air, as established by the American Council of Governmental Industrial Hygienists is 0.1 ppm by volume for continuous human exposure. The threshold odor of ozone is 0.01 ppm. This means a person working near an ozone-handling area should be able to detect the presence of ozone at levels far below the MAC.

Other Uses of Ozone in Wastewater Treatment

The odor of ozone has been described as similar to that of cloves, new mown hay, nitric acid, etc., depending on the concentration. Concentrations greater than 1 ppm are extremely pungent and are considered unsafe for prolonged human exposure, and therefore should be avoided.