WATER POLLUTION DEFINITION WASTE WATER POLLUTION OF RECEIVING WATER WASTEWATER COLLECTION
Water Pollution It is an imprecise term that reveals nothing about either the type of polluting material or its source Water pollution occurs when a body of water is adversely affected due to the addition of large amounts of materials to the water. When it is unfit for its intended use,water is considered polluted.
2 TYPES OF WATER POLLUTANTS • POINT SOURCES • pollution of our water resource can occur directly from sewer outfalls or industrial charges • occur when harmful substances are emitted directly into a body of water. • Ex: Oil spill best illustrates a point source water pollution.
NONPOINT SOURCES • indirectly from air pollution or agricultural or urban runoff. • delivers pollutants indirectly through environmental changes. Ex: when fertilizer from a field is carried into a stream by rain, in the form of run-off which in turn effects aquatic life
Waste Water • also called “sewage” • a complex mixture containing water (usually over 99%) together with organic and inorganic contaminants, both suspended and dissolved.
Microorganisms • Wastewater may contain microorganisms which may be either harmless or which can cause diseases • PATHOGENS (disease-causing organisms) .
WATERBORNE BACTERIAL DISEASES: • Cholera • Typhoid • Tuberculosis • VIRAL DISEASES: • Infectious hepatitis • Protozoan-caused dysentery
Solids • The total solids (organic plus inorganic) in wastewater.
Inorganic Constituents Chlorides and sulfates – normally present in water and in wastes from humans Nitrogen and phosphorus – forms in wastes from humans, with additional phosphorus detergents Carbonates and bicarbonates – normally present in water and wastes as calcium and magnesium salts Toxic substances – arsenic, cyanide, and heavy metals found in industrial wastes
Organic Matter • 90% are proteins and carbohydrates • sources of biodegradable contaminants are excreta and urine from humans, food wastes from sinks, soil and dirt from bathing, washing and laundering • various parameters are used as a measure of the organic strength of wastewater.
Measurement of organic strength of wastewater 1. TOC (total organic carbon) – determined by measuring the amount of CO2 produced when the organic carbon in the sample is oxidized by a strong oxidizing agent and comparing with the amount in a standard of known TOC 2. COD (chemical oxygen demand) – the measured amount of oxygen needed to chemically oxidize the organics present
The 6800 Series Total organic carbon analyzer
3. BOD (biochemical oxygen demand) – the measured amount of oxygen required by acclimated microorganisms to biologically degrade the organic matter in the wastewater
Lt = Lo e-kt CBODt = Lo ( 1-e-kt) Where: Lt = carbonaceous BOD remaining at time t=t (O2 needed to oxidize carbonaceous organic matter remaining) Lo = ultimate carbonaceous oxygen demand (ultimate BOD; O2 needed to oxidize carbonaceous organic matter initially present) CBODt= carbonaceous oxygen demand (BOD satisfied; O2 used to oxidize carbonaceous organic matter at t=t) t = time (days) k = rate constant (base 10) per day
BOD curve at 20oC • Carbonaceous + Nitrogenous Oxygen Demand • Lo Ultimate Carbonaceous Oxygen Demand • CBODt = Carbonaceous Oxygen Demand • L= Carbonaceous BOD Remaining • 2 4 6 8 10 12 16 20
kT = (T-20) k20 = 1.047 T = temperature (oC) k20 = reaction rate constant at the standard lab T kT = reaction rate at a different T
Source of organic contaminations Rate of change k in BOD/day (base 10) River water 0.10 Domestic sewage 0.17 Glucose solution 0.25 BOD Removal Rate Constants
DO (dissolved oxygen) – the amount of oxygen dissolved in surface waters ThOD (Theoretical oxygen demand) – the amount of oxygen needed to oxidize an organic matter to CO2 and H2O if the composition of the organic matter is known BOD5 – the total amount of O2 consumed by the microorganisms during the 1st 5 days of biodegradation
Conditions in Measuring BOD5 • light must be kept out of the bottle to keep algae from adding oxygen by photosynthesis • stopper is used to keep the air from replenishing DO that has been removed from biodegradation • sample must be diluted
BOD5 = DOi – DOf p where DOi = initial DO of the diluted waste water DOf = final DO of the diluted waste water P = dilution factor = vol waste water / vol wastewater + dilution water
Sample Problems: • A 10.0-mL sample of sewage was mixed with enough water to fill a 300-mL bottle has an initial DO of 9.0 mg/L and a final Do of 2.0 mg/L. What is the BOD5? • The dilution factor for an unseeded mixture of waste and water is 0.030. The DO of the mixture is initially 9.0 mg/L, and after five days it has dropped to 3.0 mg/L. The reaction constant k has been found to be 0.22/day. A. What is the five-day BOD of the waste? B. What would be the ultimate carbonaceous BOD? C.What would be the remaining oxygen demand after five days?
Biochemical Oxygen Demand (BOD) of Pasig River • BOD levels from 1999 to 2000 have decreased in nearly all stations. Station 7 (downstream San Juan River), however, was still beyond the BOD standard of 1mg/L for class C waters.
MUNICIPAL WASTEWATER SANITARY SEWAGE DOMESTIC SEWAGE kitchen wastes Excreted wastes bath wastes laundry wastes floor drain wastes Municipal Wastewater
Industrial Wastewater • includes employee’s sanitary wastes, process wastes from manufacturing, wash waters, and relatively uncontaminated water from heating and cooling operations.
Stormwater • less contaminated compared to municipal wastewater. Quantity of storm water runoff from a municipality varies widely with the time of year, type of terrain, and intensity and duration of the storms that occur.
Pollution of Receiving Waters POLLUTANTS in RECEIVING WATERS • Pathogens • Organic matter • Solids • Nutrients • Toxic and hazardous substances • Other Pollutants
Primary Treatment - during primary treatment, a large percentage of the suspended solids and inorganic material is removed from the sewage. Secondary Treatment - the focus of secondary treatment is reducing organic material by accelerating natural biological processes. Tertiary Treatment - is necessary when the water will be reused; 99 percent of solids are removed and various chemical processes are used to ensure the water is as free from impurity as possible.
Wastewater Collection EARLY SYSTEMS • Roman Times – widespread use of sewers occurred • Pipes were installed to carry away storm water from the streets • Problems with combines sewers led to the concept of separate sewers: one system for storm water and one for sanitary wastes. PRESENT SYSTEMS • sewage collection today normally consists of separate storm and sanitary sewers in the newer areas and combined sewers in the older sections of cities.
Sanitary Sewers • Sanitary sewers are underground pipes that collect domestic and industrial wastewater and convey them to a treatment facility. • Sanitary Sewers • provide service for domestic and industrial wastewater • do not provide drainage for roof leaders or yard drains • In older areas, drain weeping tile systems (now prohibited) • convey peak dry weather flow plus groundwater to treatment plant • must now also consider infiltration/inflow which can be significant. Sanitary sewers must be designed to handle the peak rate of flow.
Storm Sewers • Storm sewers are underground pipes that collect street and yard drainage and discharge the collected water to a surface watercourse, lake or ravine. • Storm Sewers • provide convenience drainage for roads and adjacent properties • are designed for a specific storm event (e.g. 1 in 5 year rain storm) • provide an economic balance between flooding and construction costs • in conjunction with major drainage systems, provide greater protection in newer areas.
building with basements are protected against high groundwater levels by installation of perforated or open jointed drainage pipes laid in a gravel trench around the basement footings. • The uncontaminated water collected by these foundation drains may then discharge to: • a storm or combined sewer if sewer backup is unlikely • (2) A sanitary sewer or basement sump • (3) A separate foundation drain collector
Combined Sewers • Combined sewers are underground pipes that collect domestic sewage, industrial wastewater and storm water. • Perform the functions of sanitary and storm sewers. • In dry weather all flows collected by combined sewers are delivered to a wastewater treatment facility. • In wet weather some flow collected by combined sewers is delivered to the treatment facility through the interceptor sewers and the rest is spilled to the surface through combined sewer overflows.
Combined Sewers • provide basic sanitary service for domestic and industrial wastewater • provide convenience drainage for roads and adjacent properties • exist in over 1200 communities across North America • provided economical servicing • made sense in “horse & buggy” days • are not good modern practice • eliminating is expensive. • Combined Sewer Overflows (CSO's) • protect homes and streets from flooding during storms • spill diluted sewage to the river during storms • are not environmentally friendly • quantity of flows spilled and frequency of spillage are expensive to reduce.