BOD

COD

DO

Waste water

treatment

Submitted ToDr.(Mrs.) Poonam Syal

Associate Professor

Submitted byDIVYA SHAKTI

162511

OUTLINE

– Water

– Overview of photosynthesis and respiration

– Water pollution

– Oxygen Demand

– Biochemical oxygen demand (BOD)

– Typical values for BOD

– Methods of measurement of BOD

– Chemical oxygen demand(COD)

– Typical values for COD

– Methods of measurement of COD

– Dissolved oxygen(DO)

– Typical values for DO

– Methods of measurement of DO

– Nature of waste water

– Problems from different pollutants

– Waste water treatment

– Waste water treatment process

– Treatments

– When the treatment is done

– Ongoing work

Water?

– Water is a transparent and nearly colorless chemical substance that is the main

constituent of Earth's streams. Lakes, and oceans and the fluids of most living

organisms.

– Its chemical formula is H2O, meaning that its molecule contains one oxygen and

two hydrogen atoms, that are connected by covalent bonds.

– Safe drinking water is essential to humans and other life forms even though it

provides no calories or organic nutrients.

OVERVIEW OF

PHOTOSYNTHESIS

AND RESPIRATION

– Water(H2O), together with carbon

dioxide (CO2), form oxygen and

organic compounds, which can be

respired to water and carbon dioxide.

– Autotrophs can use carbon dioxide

and water to form oxygen and

complex organic compounds, mainly

through the process of

photosynthesis. All organisms can use

such compounds to again form CO2

and water through cellular respiration.

WATER POLLUTION

– Water pollution is the contamination of water bodies (e.g. lakes, rivers,

oceans, aquifers and groundwater).

– This form of environmental degradation occurs when pollutants are

directly or indirectly discharged into water bodies without adequate

treatment to remove harmful compounds.

– It has been suggested that water pollution is the leading worldwide

cause of deaths and diseases, and that it accounts for the deaths of more

than 14,000 people daily.

– The specific contaminants leading to pollution in water include a wide

spectrum of chemicals, pathogens, and physical changes such as

elevated temperature and discoloration.

Oxygen Demand

– It is a measure of the amount of “reduced” organic andinorganic matter in a water

– Relates to oxygen consumption in a river or lake as a result ofa pollution discharge

– Measured in several ways

BOD - Biochemical Oxygen Demand

COD - Chemical Oxygen Demand

Dissolved oxygen

BIOCHEMICAL OXYGEN

DEMAND (BOD)

– Most natural waters contain small quantities of organic compounds. Aquatic

microorganisms have evolved to use some of these compounds as food.

– Microorganisms living in oxygenated waters use dissolved oxygen to oxidative

degrade the organic compounds, releasing energy which is used for growth and

reproduction.

– Biochemical oxygen demand is the amount of oxygen required for microbial

metabolism of organic compounds in water.

Continued….

– It is used in water quality management and assessment, ecology and

environmental science.

– BOD is not an accurate quantitative test, although it is considered as an

indication of the quality of a water source.

– It is most commonly expressed in milligrams of oxygen consumed per liter of

sample during 5 days of incubation at 20 °C or 3 days of incubation at 27 °C.

TYPICAL VALUES

– Most pristine rivers will have a 5-day carbonaceous BOD below 1 mg/L.

– Moderately polluted rivers may have a BOD value in the range of 2 to 8 mg/L.

– Rivers may be considered severely polluted when BOD values exceed 8 mg/L.

– Municipal sewage that is efficiently treated would have a value of about

20 mg/L or less.

– Untreated sewage varies, but averages around 600 mg/L in Europe and as low

as 200 mg/L in the U.S..

METHODS

– There are two commonly recognized methods for the measurement of BOD.

– Dilution method

In order to obtain BOD, dissolved oxygen (DO) concentrations in a sample

must be measured before and after the incubation period, and appropriately

adjusted by the sample corresponding dilution factor.

This analysis is performed using 300 ml incubation bottles in which buffered

dilution water is dosed with seed microorganisms and stored for 5 days in the

dark room at 20 °C to prevent DO production via photosynthesis.

Continued….

The dilution water blank is used to confirm the quality of the dilution water that

is used to dilute the other samples.

This is necessary because impurities in the dilution water may cause significant

alterations in the results. The GGA control is a standardized solution to

determine the quality of the seed, where its recommended BOD concentration

is 198 mg/l ± 30.5 mg/l.

Continued….

– Manometric method

This method is limited to the measurement of the oxygen consumption due only

to carbonaceous oxidation. Ammonia oxidation is inhibited.

The sample is kept in a sealed container fitted with a pressure sensor. A substance

that absorbs carbon dioxide (typically lithium hydroxide) is added in the container

above the sample level. The sample is stored in conditions identical to the dilution

method. Oxygen is consumed and, as ammonia oxidation is inhibited, carbon

dioxide is released.

The total amount of gas, and thus the pressure, decreases because carbon dioxide

is absorbed. From the drop of pressure, the sensor electronics computes and

displays the consumed quantity of oxygen.

Continued….

– The main advantages of this method compared to the dilution method are:

Simplicity: no dilution of sample required,

Direct reading of BOD value.

Continuous display of BOD value at the current incubation time.

CHEMICAL OXYGEN DEMAND

(COD)

– In environmental chemistry, the chemical oxygen demand (COD) is an indicativemeasure of the amount of oxygen that can be consumed by reactions in ameasured solution.

– COD gives the oxygen required for the complete oxidation of bothbiodegradable and non-biodegradable matter.

– COD is a measure of the oxygen equivalent of the organic matter content of asample that is susceptible to oxidation by a strong chemical oxidant.

– It is an indirect method to measure the amount of organic compounds in water.

– It is expressed in milligrams per liter (mg/L), which indicates the mass ofoxygen consumed per liter of solution.

Typical Value

– Many governments impose strict regulations regarding the maximum chemical

oxygen demand allowed in waste water before they can be returned to the

environment.

– For example, in Switzerland, a maximum oxygen demand between 200 and

1000 mg/L must be reached before waste water or industrial water can be

returned to the environment.

Method

– COD measurements are commonly made on samples of waste waters or ofnatural waters contaminated by domestic or industrial wastes.

Chemical oxygen demand is measured as a standardized laboratory assay inwhich a closed water sample is incubated with a strong chemical oxidant underspecific conditions of temperature and for a particular period of time.

A commonly used oxidant in COD assays is potassium dichromate (K2Cr2O7)which is used in combination with boiling sulphuric acid (H2SO4). Because thischemical oxidant is not specific to oxygen-consuming chemicals that are organicor inorganic, both of these sources of oxygen demand are measured in a CODassay.

Dissolved oxygen

– Dissolved oxygen (DO) analysis measures the amount of gaseous oxygen (O2)dissolved in an aqueous solution. Oxygen gets into water by diffusion from thesurrounding air, by aeration (rapid movement), and as a product of photosynthesis.

– Fish and other aquatic animals depend on dissolved oxygen (the oxygen present inwater) to live. The amount of dissolved oxygen in streams is dependent on the watertemperature, the quantity of sediment in the stream, the amount of oxygen takenout of the system by respiring and decaying organisms, and the amount of oxygenput back into the system by photosynthesizing plants, stream flow, and aeration.

– DO is measured in standard solution units such as milligrams O2 per liter (mg/L),milliliters O2 per liter (ml/L), mill moles O2 per liter (mmol/L), and moles O2 per cubicmeter (mol/m3).

– DO is measured by way of its oxidation potential with a probe that allows diffusionof oxygen into it.

Typical Values

– Trout need DO levels in excess of 8 mg/liter,

– Striped bass prefer DO levels above 5 mg/l,

– And most warm water fish need DO in excess of 2 mg/l.

Methods

– There are three methods available for measuring dissolved oxygen

concentrations.

Continued…

– Colorimetric method

The colorimetric method offers a basic approximation of dissolved oxygenconcentrations in a sample. This method is quick and inexpensive for basicprojects, but limited in scope and subject to error due to other redoxing agentsthat may be present in the water.

– Titration

The traditional method is the Winkler titration. While this method wasconsidered the most accurate and precise for many years, it is also subject tohuman error and is more difficult to execute than the other methods,particularly in the field.

Continued….

– Meter and sensor

The most popular method for dissolved oxygen measurements is with a

dissolved oxygen meter and sensor. While the general categories of dissolved

oxygen sensors are optical and electrochemical, electrochemical sensors can be

further broken down into polarographic, pulsed polarographic and galvanic

sensors. In addition to the standard analog output, several of these dissolved

oxygen sensor technologies are available in a smart sensor platforms with a

digital output.

Nature of Wastewater

What’s in wastewater?

Human feces and urine

Food from sinks

Soaps and other cleaning agents

Runoff from streets and lawns

Industrial discharges

Problems from different Pollutant

Pollutant Problem

Solids Aesthetics

Pathogens Disease

Organic matter Oxygen

Nutrients Plant growth

Organics/Metals Toxicity

Waste water treatment

– Large quantity of biodegradable waste can affect living organism in the water

bodies in which waste are discharged .It is necessary to treat effluent or waste

water before discharging in water body. The treatment procedure are generally

divided into three groups-

Primary Treatment or Mechanical Treatment

Secondary Treatment or Biological Treatment

Tertiary Treatment or Advance Biological or Chemical Treatment

Treatments

– Primary Treatment- In primary treatment suspended solid and floating material

is removed. Effluent is passes through a screen which is used to remove certain

material like wood pieces, plastic , paper, floating debris. Then effluent is

passed through chamber which is known as grit chamber.-Fatty and oily

substance can be removed by flotation method. In order to trap fatty and oily

substance a instrument called Centrifugal Separator is used in this process fatty

substance are reached to outside and clean water remain in the center of

cyclone.- The water is passed in Settling Tank in which water remain for a long

time in which suspended particles are settled down this process is known as

Sedimentation.

Continued…

– Secondary Treatment or Biological Treatment It is the process in which

microorganism play a very important role for the treatment of effluent.

Microorganism like bacteria, fungi decompose the organic waste and convert

into simpler form. The main function of secondary treatment is to convert the

reaming organic matter of sewage into stable form by oxidation and nitrification.

Biological Treatment Can be classified into

1. Aerobic Treatment

a) Activated Sludge Process

b) b) Trickling Filter

2. Anaerobic Treatment

Continued…

– Tertiary Treatment (Advance waste water treatment)The main function of

tertiary treatment is to decrease the load of nitrogen and phosphorous

compound present in the effluent by the following process.

a) Precipitation

b) Nitrogen Stripping

c) Chlorination

When the treatment is done…

– Effluent back to stream after

A final carbon filtration and

Chlorination/de chlorination

– Sludge – very nutrient rich

Applied directly to land as fertilizer

Incinerated (good fuel after drying)

Composted

ONGOING WORK-A review on emerging contaminants in wastewaters and the environment:

Current knowledge, understudied areas and recommendations for future

monitoring.

– It is anticipated that environmental legislation will be widened to cover a range ofmunicipal derived emerging contaminant (EC). However, sound knowledge of their fateduring wastewater treatment and within the environment is currently lacking. Due to thelimitations of previously used sampling methods, reported removals of ECs by wastewatertreatment works (WwTWs) have uncertainties. Therefore, removal performance ofdifferent WwTW process types at various operational conditions needs re-evaluated withsuitable sampling protocols. This will help establish steps required for EC amelioration.The growing trend of improving sustainability and reducing energy demand of wastewatertreatment will see an increase in the application of novel treatment methods. Forexample, algae ponds for secondary effluent polishing are a promising treatment methodwhich can indirectly produce energy through the production of biogas.

– For example, measuring bio-solids and amended soils for their occurrence is needed aswell as supporting analysis. Detailed case studies of amended soils in field conditionswhich investigate leaching and runoff, impact to surrounding surface water quality, in soildegradation, toxicity to terrestrial organisms and the potential uptake by plants and entryinto the human food chain are needed