ENVIRONMENTAL ENGINEERING

343Lecture 9:

Wastewater treatment 1

Philadelphia UniversityFaculty of Engineering

Department of Civil EngineeringFirst Semester, 2013/2014

A -Nutrients: Two nutrients are essential for the growth of organisms: Nitrogen Phosphorus

SOME PHYSICAL AND CHEMICAL PROPERTIES OF WASTEWATER 1- INORGANIC SUBSTANCES

Nitrogen; Exist in a form of “inorganic”, and “organic nitrogen

Measured by TKN “total Kjeldahl Nitrogen; is a measure of the total organic and ammonia nitrogen.

Phosphorus ; Exist in a form of “inorganic”, and “organic phosphate

Total phosphorus (P)Nitrogen & Phosphorus are essential for building

cell

I- INORGANIC SUBSTANCES

DISSOLVED OXYGENOne of the most important measures of water quality is dissolved oxygen. Oxygen, although poorly soluble in water, is fundamental to aquatic life. Without free dissolved oxygen, streams and lakes become uninhabitable to aerobic organisms, including fish and most invertebrates. It is found that the concentration of DISSOLVED OXYGEN in water is SMALLDissolved oxygen is inversely proportional to temperature, andthe maximum amount of oxygen that can be dissolved in water at 0°C is 14.6 mg/L to 7.6 at 30C.

Dissolved oxygen in water is consumed by the oxidation of dissolved ammonia (NH3)and ammonium ion (NH4+)to form the nitrate ion (NO3 ).⎯ NH3(aq) + 2O2(aq) + OH-----NO3-(aq) + 2H2O(aq)

The most common substance oxidized by oxygen in water is ORGANIC MATTER OF BIOLOGICAL ORIGIN

Such organic matter (such as dead plant material like polymerized carbohydrate below), is oxidised by dissolved oxygen. e.g. CH2O+O2(aq) ------ CO2(g) + H2O(aq)

Various parameters are used as a measure of the organic strength of wastewater: BOD –Biochemical oxygen demand COD –Chemical oxygen demand  TOC –Total organic carbon VSS –Volatile suspended solid

SOME PHYSICAL AND CHEMICAL PROPERTIES OF WASTEWATER II- ORGANIC SUBSTANCES

II- ORGANIC SUBSTANCES1- BIOCHEMICAL OXYGEN DEMAND- BODThe quantity of oxygen utilized by a mixed

population of micro organisms to biologically degrade the organic matter in the wastewater under aerobic condition.

BOD is the most important parameter in water pollution control.

it is used a measure of organic pollution as a basis for estimating the oxygen

Needed for biological processes, as and indicator of process performance

Expressed in milligrams of oxygen required per liter of wastewater (mg/L).

BIOCHEMICAL OXYGEN DEMAND

BOD : BOD5: is the amount of dissolved oxygen used up from the water by microorganisms as they break down organic material at 20C over a 5-day periods. BOD5 for Rivers if > 5 mg/L, they considered

polluted BOD For MWW range 150-1000mg/L

- Determine the amount of oxygen needed to oxidize

the organics in a water or wastewater using a strong oxidizing chemical agent- Potassium dichromate rather than using micro-organisms as in BOD

It measures the total organic carbon with the exception of some aromatics such as benzene which are not oxidized in the reaction.

Indirectly measure amount of organic matter in the water sample

Faster determination of oxygen demand in a water sample, than BOD

It takes shorter time ( 2hrs) compared to 5 days for BOD5

The EU upper limit of 125mg/L for treated wastewaters prior to discharge to rivers

II- ORGANIC SUBSTANCES2- chemical oxygen demand -COD

RELATION BETWEEN COD AND BOD COD > BOD COD ~ ultimate BOD COD/BOD ~ 2, biodegradable organic COD >> BOD, non-biodegradable organic

II- ORGANIC SUBSTANCES3-TOTAL ORGANIC CARBON- TOC TOC- : measures all carbon as CO2 in mg/L Inorganic carbon ( HCO3, CO2, CO3, etc) must

be removed prior test by acidifying and aerating the sample.

Theoretically the COD is 2.66 times greater than TOC

Composition of WW

Suspended Solids

Biodegradable Organics Pathogens

Body waste, food waste rags, paper, biological cells

Soluble organics Bacteria, virus etc.

Protein (40-60%) – amino acids

Carbohydrates 25-50% - sugars starch, cellulose

Lipids (10%)- fats, oils and grease

Contain Carbon – exert an oxygen demand

The composition of municipal waste varies seasonally as well as daily.

Wastewater Characteristics –Industrial MunicipalIf Industrial waste characteristics are similar to municipal, the waste is discharged into the municipal sewers. If not, pre-treatment is requiredNote: although suspended organic materials are biodegradable, In wastewater we consider biodegradable materials to be of the Soluble type.

Note: Unit Operation – contaminants are removed via physical forcesUnit Process – contaminants are removed via chemical and or biological processes

Wastewater Treatment Plants

WASTEWATER TREATMENT PLANTS

Municipal treatment is divided into: Primary, Secondary and Tertiary

Primary Treatment – removes solid materials from stream-Large debris may be removed by screens or reduced in size by grinding device.

Inorganic solids are removed by the grit chamber

Much of the organic suspended solids are removed by sedimentation

Primary treatment removes 60% SS and 35% BOD

This treatment is still the only treatment for used by many cities around the world

WASTEWATER TREATMENT PLANTS Secondary Treatment: the major goal is to remove the

soluble BOD and SS that escape the primary treatment Consist of the biological conversion of colloidal organics

into biomass – this is then removed by sedimentation Designed to speed up these natural processes so that

the break down of degradable organic pollutants can be achieved in relatively short time periods May remove > 85% BOD & SS; Not removing N, P & heavy metals or pathogens

Contact is maintained between the MO and the organics by: Suspending biomass in a reactor – Activated Sludge System Passing the wastewater over a film of biomass attached to a

solid - Trickling Filter

WASTEWATER TREATMENT PLANTS

Trickling Filter Stones are used to increase the surface area

for biofilm growth.

Mature biofilms become dislodge due to friction and are washed out of the settling basin with the liquid flow.

Part of the liquid effluent may be recycled to the trickling filter for additional treatment or to maintain hydraulic flow rates

WASTEWATER TREATMENT PLANTS

TRICKLING FILTER

WASTEWATER TREATMENT PLANTS

Sludge Digestion Sludge from primary treatment as well as the

secondary clarifier are sent to the sludge digestion unit where it is undergoes anaerobic degradation.

The results are: • Methane – Used for power generation• CO2 • Liquid – contains high organic – recycled through

the plant• Inert solids – contains high minerals – soil

conditioner/ fertilizer on agricultural lands

CLARIFIER

SLUDGE DIGESTER