Routine Analysis of Waste Water

Quality Parameter

NAMRATA JARIWALA, Lecturer

CIVIL ENGINEERING DEPARTMENT

S. V. NATIONAL INSTITUTE OF TECHNOLOGY, SURAT

Objective

• Essential for an effective and economical waste management programme.

• Helps in the choice of waste treatment methods• Helps in deciding the self purification capacity of

natural bodies.• Helps in deciding the efficiency of various

treatment units.• Monitoring the treatment plant.

Types of Analysis• Physical Analysis: Determine aesthetic quality.• Chemical Analysis: Determine the amount of

chemical substances.

Points to be considered

• Methods of examination

• Expression of result

• Sampling points

• Sampling equipment and recording the reading

Significant Parameters for

Physical Characteristics Chemical Characteristics Biological Characteristics

Solids –

Total, Suspended and Dissolved, Volatile and Fixed or mineral solids

Organic contents –

BOD,COD, Fats, phenols

surfactants, oil and grease, etc.

Animals

Colour Inorganic contents-

alkalinity, chlorides,

nitrogen, sulfur, phosphorous, heavy metals,

pH, carbohydrates etc.

Plants

Odour Gases – oxygen, methane, hydrogen sulfide

Protista

Temperature & Turbidity Pathogenic organisms, Viruses

CHARACTERISTICS OF WASTEWATER

Physical Characteristic(1) COLOUR

• Fresh sewages is grey in colour:- like soap solution.

• As time passes it begins to get black.

• The colour of industrial waste water depends upon the chemical processes used in the industries.

(2) ODOUR

• Normally fresh sewage is not offensive.

• It starts to gets stale it begins to give offensive odour.

• Elimination of odour has become major consideration in the design and operation of waste water collection, treatment and disposal facilities.

(3) TEMPERATURE:

• Generally higher than water supply.

• As the temperature increases the viscosity and bacterial activity increases.

• Solubility of gases in waste water decreases as increases in temperature.

• D.O. content decreases which affects the aquatic life.

• High temperature results the growth of the undesirable water plants in the receiving water.

Physical Characteristic(4) TURBIDITY

• It is a measure of light emitting property of waste water.

• The stronger or more concentrated sewage, the higher is its turbidity.

• Turbidity can be determine either by turbidity rod or by jackson’s turbidity meter.

(5) TOTAL SOLIDS

• Sewage contains 99.9% of water and 0.1% of solids.

• The total solid contains of waste water is define as all the matter that remains as a residue upon evaporation to 103 to 105 degree centigrade.

• Total solids are of three types (i) Suspended solids (ii) Colloidal solids and (iii) Dissolved solids.

• S.S. are those which can be filtered out on a filter paper. i.e. Non-filterable solids.

• S.S. can be divided as settleable solid and Non-settleable solids.

• The T.S. can be classified as fixed solids and volatile solids.

Chemical Characteristic(1) pH Value:

• Generally fresh sewage is alkaline in nature.

• The determination of pH is important since certain treatment methods depends on proper pH value.

(2) Chlorides contents:

• Chlorides are mineral salts and therefore are not affect biological action of sewage.

• The chlorides contents can be measured by titrating the sample of waste water with standard AgNo3 using potassium chromate as a indicator.

(3) Nitrogen Contents:

• The presence of nitrogen in waste water indicates the presence of organic matter.

• Nitrogen is essential for the growth of plants and animals.

• Nitrogen data is require to evaluate the treatability of waste water by biological process.

Chemical CharacteristicNitrogen appears in the following different forms(i) Ammonia nitrogen or free nitrogen.- Indicate old sewage.(ii) Organic nitrogen(iii) Albuminoid nitrogen – Indicates easily decomposable nitrogen presents.(iv) Nitrites nitrogen – Partially decomposed organic matter.(v) Nitrate nitrogen – Indices presence of fully oxidize organic matter.

(4) Oil and Grease:• Clogged pipes and filters in winter.• Interfere with biological action.• Not easily decomposed by bacteria so necessary to remove from waste

water.

(5) Surfactants:• Primary from synthetic detergent.• The contents is determine by measuring the colour change in standard

solution of Methylene Bule dye.• This interference in aeration of waste water.• Now-a-days ABS is replace with LAS which is biodegradable

Chemical Characteristic(6) Toxic compounds:- Bio-assay test

(7) Sulphates concentration:- Turbidity method

(8) D.O. Test:-

• D.O. is the amount of oxygen in the dissolve state.

• D.O. can be determine by Wrinker’s methods.

• The presence of D.O. in waste water is desirable for aquatic life and to prevent from odour problem.

Biochemical Oxygen Demand:

Biochemical oxygen demand has been defined as the amount of oxygen required by the microorganisms (mainly bacteria) to stabilize the biodegradable organic matter under aerobic conditions.

NOTE : As the oxygen consumed by the microorganisms is directly proportional to the amount of biodegradable organic content, the BOD parameter indirectly measures the organic content of the liquid.

NOTE : BOD parameter does not provide information about the amount of non-biodegradable organic contents of the liquid waste.

Based on the first order kinetics of oxygen consumption by the microorganisms for carbonaceous organic matter present in the wastewater, following equations are used to compute the values of ultimate BOD (L0) and BOD at any time t (Lt).

Lt = L0e-k’t or Lt = L0 x 10-kt

and yt = L0(1 - e-k’t) or yt = L0(1 - 10-kt)

where Lt = BOD at any time t, mg/L L0 = ultimate BOD at time t = 0, mg/L

K’ = BOD rate constant to the base e, d-1

K = BOD rate constant to the base 10, d-1

= k’/e =k’/2.3 (normally assumed as 0.1 at 20°C)

yt = BOD exerted or used at any time t, mg/L

The temperature correction for BOD rate constant is done by using the following equation.

KT = K20 θ(T – 20) Where KT = BOD rate constant at any temperature T°

K20 = BOD rate constant at temperature 20° C

θ = temperature coefficient factor (varies from 1.056 to 1.135)

= 1.047 (normally assumed for temperature range of 20 to 30°C)

The presence of a sufficient concentration of dissolved oxygen is critical to maintaining the aquatic life and aesthetic quality of streams and lakes. Determining how organic matter affects the concentration of dissolved oxygen (DO) in a stream or lake is integral to water-quality management.

The decay of organic matter in water is measured as biochemical oxygen demand. Oxygen demand is a measure of the amount of oxidizable substances in a water sample that can lower DO concentrations.

The test for biochemical oxygen demand (BOD) is a bioassay procedure that measures the oxygen consumed by bacteria from the decomposition of organic matter (Sawyer and McCarty, 1978). The change in DO concentration is measured over a given period of time in water samples at a specified temperature

There are two stages of decomposition of organic matter in the BOD test: a carbonaceous stage and a nitrogenous stage.

Figure : Biochemical oxygen demand curves: (A) typical carbonaceous-demand curve showing the oxidation of organic matter, and (B) typical carbonaceous- plus nitrogeneous-demand curve showing the oxidation of ammonia and nitrite. (Modified from Sawyer and McCarty, 1978.)

The carbonaceous stage, or first stage, represents that portion of oxygen demand involved in the conversion of organic carbon - to carbon dioxide.

The nitrogenous stage, or second stage, represents a combined carbonaceous plus nitrogenous demand, when organic nitrogen, ammonia, and nitrite are converted to nitrate. Nitrogenous oxygen demand generally begins after about 6 days.

For some sewage, especially discharge from wastewater treatment plants utilizing biological treatment processes, nitrification can occur in less than 5 days if ammonia, nitrite, and nitrifying bacteria are present.

The standard oxidation (or incubation) test period for BOD is 5 days at 20 degrees Celsius (BOD5). The BOD5 value has been used and reported for many applications,

most commonly to indicate the effects of sewage and other organic wastes on dissolved oxygen in surface waters.

The 5-day value, however, represents only a portion of the total biochemical oxygen demand. Twenty days is considered, by convention, adequate time for a complete biochemical oxidation of organic matter in a water sample, but a 20-day test often is impractical when data are needed to address an immediate concern.

BOD TEST APPARATUS

Note that BOD results represent approximate stream oxygen demands because the laboratory environment does not reproduce ambient stream conditions such as temperature, sunlight, biological populations, and water movement.

Chemical Oxygen Demand

Chemical oxygen demand (COD) is a measure of the ability of chemical reactions to oxidize matter in an aqueous system. The results are expressed in terms of oxygen so that they can be compared directly to the results of biochemical oxygen demand (BOD) testing.

The test is performed by adding a strong oxidizing solution of a dichromate salt (e.g. potassium dichromate, K2Cr2O7) to a sample, boiling the mixture on a refluxing apparatus

for two hours, and then titrating the amount of dichromate remaining after the refluxing period, with ferrous ammonium sulfate (FAS), at a known normality, to reduce the remaining dichromate.

Generally, the COD is larger than the BOD exerted over a five-day period (BOD5), but there

are exceptions in which microbes of the BOD test can oxidize materials that the COD reagents cannot.

For a raw, domestic wastewater, the COD/BOD5 ratio is in the area of 1.5-3.0.

Higher ratios would indicate the presence of toxic, non- biodegradable or less readily biodegradable materials.

The COD test is commonly used because it is a relatively short-term, precise test with little interference. However, the spent solutions generated by the test are hazardous. The liquids are acidic, and contain chromium, silver, mercury, and perhaps other toxic materials in the sample tested. For this reason laboratories are doing fewer or smaller COD tests in which smaller amounts of the same reagents are used.

COD/BOD ratio The ratio of COD to BOD can give an indication of the biodegradability of a wastewater.  i) In domestic sewage which is known to be readily biodegradable and treated successfully world-wide using a variety of biological treatment methods, the COD/BOD ratio varies typically from 1.5: 2. Thus if the COD/BOD ratio of industrial wastewater is also < 2, this provides a good indication that the wastewater can be treated biologically. ii) If the COD/BOD ratio is high and generally >5:1 , this indicates that the wastewater is non biodegradable , toxicity or nutrient imbalance is present and thus will present problems if biological treatment selected. iii) If COD/BOD falls between 2 – 5 :1 then this is a gray area. A lot of industrial wastewaters fall into this category. Therefore, further studies are needed.