Chapter 2.pdf

Characteristics of Wastewater Wastewater Characteristics Wastewater characteristics can be divided into 3 parts: ➢ Physical characteristics ➢ Chemical characteristics ➢ Biological characteristics Physical characteristicsThe physical characteristics of wastewater include those items that can be...

Characteristics of Wastewater Wastewater Characteristics Wastewater characteristics can be divided into 3 parts: ➢ Physical characteristics ➢ Chemical characteristics ➢ Biological characteristics Physical characteristicsThe physical characteristics of wastewater include those items that can be detected using the physical senses. They are ✓ Solids. ✓ Odor, ✓ Temperature, ✓ Color, Physical characteristics-Solids Wastewater is normally 99.9 percent water and 0.1 percent solids. The most common types are dissolved, suspended, settleable, floatable, colloidal, organic (volatile), and inorganic solids (fixed). Total solids All the matter that remains as residue upon evaporation at 103oC to 105oC. Suspended solids: Those solids that are not dissolved in wastewater are called suspended solids. Dissolved solids Dissolved solids pass through a fine mesh filter. Floatable solids When suspended solids float, they are called floatable solids. Settleable solids Those suspended solids that settle are called settleable solids, grit, or sludge. How to Measure Solids—TS Where M= Mass of residue (mg) V= Volume of sample (l) How to Measure Solids—TSS Where, A = mass of SS + filter B = mass of filter V = Volume of sample (l) How to Measure Solids—DS DS Can be determined by filtration as follows: DS = TS - TSS Where, TS = total solids V = total suspended solids Or by taking the filtrate and dry at 103- 105º C if, mDS : mass of residue (mg) How to Measure Solids—VS VS Can be determined as follows: Where, A = mass of residue + dish after drying at 105º C (total solids) B =mass of residue +dish after burring at 550º C V = Volume of sample (l) Suspended Solids (mg/L) 1000 mg Wt. of Solids (grams) X (mL) 1 gram Sample Volume 1000 mL X 1 Liter Wt. of Solids (grams) X 1,000,000 Sample Volume (mL) - Wt. of Cruc. & Solids Wt. of Cruc. (grams) Volume of Sample (mL) X 1,000,000 Volatile Suspended Solids (mg/L) 1000 mg Wt. of Volatile (grams) X (mL) 1 gram Sample Volume Wt. of Volatile (grams) Sample Volume (mL) - 1000 mL X 1 Liter X 1,000,000 Wt. of Cruc. & Solids Wt. of Cruc. & Ash (grams) X 1,000,000 Volume of Sample (mL) SUSPENDED SOLIDS EXAMPLE PROBLEM Calculate suspended and volatile suspended solids in mg/L given the following data: Sample Volume Weight of Crucible Weight of Crucible & Dry Solids Weight of Crucible & Ash Suspended Solids, mg/L = = = = = = Wt. Dry Solids, grams Sample Volume, mL 18.1482 g - 18.1450 g 25 mL = 25 mL 18.1450 grams 18.1482 grams 18.1456 grams 0.0032 g 25 mL = 128 mg/L X 1,000,000 X 1,000,000 X 1,000,000 SUSPENDED SOLIDS EXAMPLE PROBLEM Calculate suspended and volatile suspended solids in mg/L given the following data: Sample Volume Weight of Crucible Weight of Crucible & Dry Solids Weight of Crucible & Ash Volatile Sus. Solids, mg/L = = = = = = Wt. Volatile Solids, grams Sample Volume, mL 18.1482 g - 18.1456 g 25 mL = 25 mL 18.1450 grams 18.1482 grams 18.1456 grams 0.0026 g 25 mL = 104 mg/L X 1,000,000 X 1,000,000 X 1,000,000 SUSPENDED SOLIDS PRACTICE PROBLEM Calculate suspended and volatile suspended solids in mg/L given the following data: Weight of Crucible Weight of Crucible & Dry Solids Weight of Crucible & Ash Volume of Sample Filtered Suspended Solids, mg/L = = = = = = 21.0256 grams 21.0301 grams 21.0263 grams 50 mL Wt. Dry Solids, grams Sample Volume, mL 21.0301 g - 21.0256 g 50 mL = = X 1,000,000 0.0045 g 50 mL 90 mg/L X 1,000,000 X 1,000,000 SUSPENDED SOLIDS PRACTICE PROBLEM Calculate suspended and volatile suspended solids in mg/L given the following data: Weight of Crucible Weight of Crucible & Dry Solids Weight of Crucible & Ash Volume of Sample Filtered = = = = 21.0256 grams 21.0301 grams 21.0263 grams 50 mL Volatile Sus. Solids, mg/L = Wt. Volatile Solids, grams X 1,000,000 Sample Volume, mL 21.0301 g - 21.0263 g = X 1,000,000 50 mL = 0.0038 g X 1,000,000 50 mL = 76 mg/L SUSPENDED SOLIDS (mg/L) Wt. Of Dry Solids (grams) Volume of Sample (mL) X 1,000,000 VOLATILE SUSPENDED SOLIDS (mg/L) Wt. Of Vol. Sus. Solids (grams) Volume of Sample (mL) X 1,000,000 Physical characteristics-Odor Odor is produced by gas production due to the decomposition of organic matter or by substances added to the wastewater. Detection of odor: Odor is measured by special instruments such as the Portable H2S meter which is used for measuring the concentration of hydrogen sulfide. Physical characteristics-Temperature Temperature of wastewater is commonly higher than that of water supply. Depending on the geographic location the mean annual temperature varies in the range of 10 to 21oC with an average of 16oC Importance of temperature:-Affects chemical reactions during the wastewater treatment process. Affects aquatic life (Fish, ……). Oxygen solubility is less in worm water than cold water. Optimum temperature for bacterial activity is in the range of 25°C to 35 Aerobic digestion and nitrification stop when the temperature rises to 50 oC. When the temperature drops to about 15°c, methane producing bacteria become in active. Nitrifying bacteria stop activity at about 5°c. Density:Almost the same density of water when the wastewater doesn't include significant amount of industrial waste. Color:Fresh waste water light brownish gray. With time dark gray More time black (septic). Some times pink due to algae or due to industrial colors. Turbidity:- It's a measure of the light –transmitting properties of water. Chemical characteristics of wastewater:Points of concern regarding the chemical characteristics of wastewater are: -Organic matter -Measurements of organic matter -Inorganic matter –Gases -pH Organic matter: 75% SS organic. (Suspended Solids) 40% FS organic. (Filtered Solids) Organic mater is derived from animals & plants and man activities. Proteins (40-60%). Carbohydrates (25-50%). Fats, Oils, and Grease (10%). Measurements of organic matter:Many parameters have been used to measure the concentration of organic matter in wastewater. The following are the most common used methods: The Biological Oxygen Demand (BOD) is a measure of the quantity of dissolved organic pollutants that can be removed in biological oxidation by the bacteria. It is expressed in mg/l. Biological Oxygen Demand (BOD5) BOD determines the amount of dissolved oxygen needed by aerobic organisms in a water body to break the organic material present in the given water sample at certain temperature over a specific period of time, Usually time is taken is 5 days, The temperature is 20 0C. Chemical oxygen demand (COD) It is the oxygen equivalent of organic matter. It is determined by measuring the dissolved oxygen used during the chemical oxidation of organic matter in 3 hours. The Chemical Oxygen Demand (COD) measures the quantity of dissolved organic pollutants than can be removed in chemical oxidation, by adding strong acids. It is expressed in mg/l. The BOD/COD gives an indication of the fraction of pollutants in the wastewater that is biodegradable. Total organic carbon (TOC) This method measures the organic carbon existing in the wastewater by injecting a sample of the WW in special device in which the carbon is oxidized to carbon dioxide then carbon dioxide is measured and used to quantify the amount of organic matter in the WW. This method is only used for small concentration of organic matter. Theoretical oxygen (ThOD) If the chemical formula of the organic matter existing in the WW is known the ThOD may be computed as the amount of oxygen needed to oxidize the organic carbon to carbon dioxide and other end products. Inorganic Matter The following are the main inorganic materials of concern in wastewater treatment: 1. Chlorides:- • High concentrations indicate that the water body has been used for waste disposal. •It affects the biological process in high concentrations. 2. Nitrogen:- This element is essential for the growth of microorganisms, plant and animals. Nitrogen and phosphorus are, in most cases, the major nutrients of importance. 3. Phosphorus:Phosphorous is also essential for the growth of algae and other biological organisms. •Municipal waste contains (4-15 mg/l). 5. Sulfur:Sulfate exists in waste and necessary for synthesis of proteins. 5. Toxic inorganic Compounds:Copper, lead, silver, chromium, arsenic, boron. 6. Heavy metals:Nickels, Mn, Lead, chromium, cadmium, zinc, copper, iron, mercury. pH:-The hydrogen-ion concentration is an important quality parameter in both natural waters and wastewaters. It is a very important factor in the biological and chemical wastewater treatment. Water and wastewater can be classified as neutral, alkaline or acidic according to the following ranges: PH = 7 neutral. PH > 7 Alkaline. PH < 7 Acidic. For treated effluents discharged to the environment the allowable pH range usually varies from 6.5 to 8.5 Typical meter used for the measurement of pH Biological Characteristics:The environmental engineer must have considerable knowledge of the biological of waste water because it is a very important characteristics factor in wastewater treatment. The Engineer should know:1.The principal groups of microorganisms found in wastewater. 2.The pathogenic organisms. 3.Indicator organisms (indicate the –presence of pathogens). 4.The methods used to amount the microorganisms. 5.The methods to evaluate the toxicity of treated wastewater Main groups of Microorganisms:The main microorganisms of concern in wastewater treatment are Bacteria, Fungi, Algae, Protozoa, Viruses, and pathogenic microorganisms groups. Bacteria:Types: Spheroid, curved rod, spiral, filamentous. Some important bacteria:- Zoogloea:helps through its slime production in the formation of flocs in the aeration tanks. Sphaerotilus natuns: Causes sludge bulking in the aeration tanks. Acinetobacter: Store large amounts of phosphate under aerobic conditions and release it under an –anaerobic condition so, they are useful in phosphate removal. Nitrosomonas: transform NH4 into NO2 Nitrobacter: transform NO2-to NO3- Pseudomonas:reduce NO3 to N2, So it is very important in biological nitrate removal in treatment works. Coliform bacteria:The most common type is E-Coli or Echerichia Coli, (indicator for the presence of pathogens). E-Coli is measured in (No/100mL) Fungi: •Important in decomposing organic matter to simple forms. Algae: • Useful in oxidation ponds. (positive effect) •. (negative effect) Cause taste and problems when decayed Protozoa: •Feed on bacteria so they help in the purification of treated waste water. •Some of them are pathogenic. Viruses: Viruses are a major hazard to public health. Some viruses can live as long as 41 days in water and wastewater at 20 oC. They cause lots of dangerous diseases. Pathogenic organisms: The main categories of pathogens are:Bacteria, Viruses, protozoa, helminthes Wastewater treatment standards The most common WWT standards are set for the secondary treatment effluent. The main effluent parameters are: BOD5, TSS, pH and CBOD5.: (Carbonaceous BOD, from organic compounds and oxidation of inorganic compounds such as ferrous iron) The standards for the removal of nitrogen and phosphorus (N,P) are not included in this table because (N) and (P) need tertiary treatment. Removal of the coliform bacteria is also regulated according to reuse purpose: -Fecal coliforms < 500/100 ml (disposed into recreational waters) < 1000/100 ml (for irrigations) Interrelationships of Constituents Type of wastewater Untreated After primary settling Final effluent BOD/COD 0.3 – 0.8 0.4 – 0.6 0.1 -0.3 BOD/COD > 0.5 - wastewater easily treated by biological processes. 0.3 < BOD/COD < 0.5 - biological treatment possible; probable presence of inhibitors; need for biomass acclimatizatio BOD/COD < 0.3 – biological treatment difficult without pre-treatment Characteristics of Municipal Wastewater