Domestic Wastewater Treatment PDF

DOMESTIC DOMESTIC WASTEWATER WASTEWATER TREATMENT...

DOMESTIC DOMESTIC WASTEWATER WASTEWATER TREATMENT TREATMENT 1.BACKGROUND INFORMATION SHEET SHEET Water resources are rapidly decreasing day by day in the world and are almost to be depleted. On the other hand, discharging the used water to environments without treatment also causes the pollution of the PREPARATION decreasing water resources. Considering that the rapidly decreasing water resources are very important for humanity, it is necessary to use the water resources more efficiently and to treat the wastewater in order not to pollute the existing water resources. Besides, after appropriate treatment of wastewater, it is possible to PREPARATION use it in various areas if the desired values are met. TREATMENT Industrial TREATMENT Wastewater WASTEWATER Domestic WASTEWATER Wastewater produced due to human activities in households (the kitchen, shower, washbasin, toilet, and laundry, etc.) is called domestic wastewater. It consists of the following water types (Boutin and Eme, 2016): DOMESTIC Black water: Human feces mixed with urine. Yellow water: Human urine, flush water. DOMESTIC Brown water: Human feces with flush water (can include paper). Others: Cleaning activities, spillage. Grey water: Water used in the kitchen, bathroom including sinks, baths, showers and laundry except water from toilets. The composition of typical domestic wastewater is shown in Table 1. 1 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT Table 1. The characterization of typical domestic wastewater (Metcalf and Eddy, 2003). Analysis parameters Unit Range of value 0 Biochemical Oxygen Demand-5d-(BOD5, 20 C) mg O2/L 110-350 Chemical Oxygen Demand (COD) mg O2/L 250-800 Total Organic Carbon (TOC) g C/cm3 80-260 Total Dissolved Solid (TDS) mg/L 270-860 DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET 3 Suspended Solid (SS) g SS/m 120-400 Alkalinity (as CaC03) mg/L 50-200 3 Total Nitrogen (TN) g N/m 20-70 3 Total Phosphorous (TP) g P/m 4-12 3 Fats, oil and grease g/m 50-100 Volatile Organic Compounds (VOCs) mg/L 100 Sulfate mg/L 20-50 Chlorides mg/L 30-90 Total coliform CFU (no./100 mL) 106-1010 Fecal coliform CFU (no./100 mL) 103-108 A typical conventional domestic WWTP and detailed information about the steps of its treatment are given in Figure 1 and Table 1, respectively. Figure 1. The flow diagram of typical domestic wastewater treatment plant. 2 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT Table 2. The information about the process in wastewater treatment plant (Richard and Reynolds, 1996; Metcalf and Eddy, 2003). Treatment Step Principles 1.Screening The wastewater coming to wastewater treatment plants first passes DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET through screening equipment. This equipment removes objects such as rags, paper, plastic, wood fragments, metal, and grease to prevent damage and clogging of downstream equipment, and piping. Typical opening sizes for Coarse screen: 6 mm or larger a)Coarse screen Fine screen: 1.5 to 6 mm The removed material is washed, pressed, and disposed of in a landfill. The screened wastewater is then pumped to the grit chamber. b)Fine screen 2.Grit chamber In this step, heavy but fine materials such as sand and gravel are removed from the wastewater. These materials are also disposed in a landfill. 3 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT 3.Primary clarifier These tanks provide about two hours of retention time for gravity settling to take place. Part of the solid materials, and BOI5 in the raw wastewater are removed in this step. Thus, the organic load to be treated in the aeration tank is reduced. As the wastewater flows through tanks slowly, the solids gradually DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET sink to the bottom. The settled solids known as raw or primary sludge are moved along the tank bottom by mechanical scrapers. Floating debris such as grease is skimmed off the top and sent with the settled material to digesters. 4.Aeration tank In this tank, the wastewater receives most of its treatment. This process is based on adding air into a tank which promotes the growth of microorganisms for biodegradation of organic materials in wastewater. The microorganisms consume the organic material forming flock which can easily settle out. Suspended growth (activated sludge, aerated lagoons, etc.) Attached growth (trickling filters, rotating biological contactors, etc.) 5.Secondary clarifier These tanks are used to remove the settleable suspended solids created in biological treatment processes such as the activated and trickling filter process. After settling in this clarifier tank, bacteria forming the activated sludge flocks are continually recirculated back to the aeration tank to increase the rate of decomposition. 4 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT 6. Disinfection Disinfection is the process designed to kill or inactivate most microorganisms in wastewater, including essentially all pathogenic organisms. Chlorination (the most common and inexpensive type of SHEET disinfection), Ultraviolet light, SHEET Ozonation. PREPARATION If chorine is used, it is important to test for free-chlorine levels to PREPARATION ensure they are acceptable levels before being released into the (UV disinfection) environment. 7. Water analysis and effluent Testing for proper pH level, ammonia, nitrates, phosphates, TREATMENT disposal dissolved oxygen, and residual chlorine levels to conform to the discharge standards is critical to the plant’s performance. TREATMENT Although testing is continuous throughout the wastewater treatment process to ensure optimal water flow, clarification and WASTEWATER aeration, final testing is done to make sure the effluent leaving the plant meets permit specifications. After meeting all permit WASTEWATER specifications, clean water is reintroduced into the environment. 8. Sludge treatment The primary sludge pumped from the bottom of the primary clarifiers, along with the continuous flow of waste activated sludge DOMESTIC from the aeration/activated sludge process, must be treated to reduce volume and produce a usable end product. DOMESTIC Thickening, Anaerobic digestion Dewatering Sludge disposal After the treatment process, receiving media discharge standards for municipal wastewater according to The Water Pollution Control Regulation (2004) is given in Table 3. 5 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT Table 3.Output values of effluent after treatment procedure in a domestic wastewater treatment plant. DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET Analysis parameters Unit Value BOD5 mg O2/L 50 COD mg O2/L 100 SS g SS/m3 150 pH - 6-7 2. REUSE OF TREATED DOMESTIC WASTEWATER Water treated at appropriate levels can be used for specific purposes. Usage areas and applications of treated wastewater are given in Table 4. Table 4. Usage area and application of treated wastewater (WHO,2006). Reuse Applications Regulating stream flow, swamps and Agricultural field wetlands, recreational areas (parks, lakes), and fishing and aquaculture. garden irrigation Feed and seed crops, edible crops, basic feed water, grass and forests, nursery garden. Protection against salinity, recharge of The Environment potable aquifer, saltwater inlet control. recovering arid land. Fire protection, toilet flusher, street/car Urban washing dust control, air conditioning. Cooling, boiler feeding, construction, flue Industry gas cleaning. Drinking water Direct (possible) There are many benefits of wastewater reuse. Wastewater reuse causes a decrease in energy consumption, provides less consumption of clean water resources, 6 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT decreases surface water quality deterioration, reduces water supply costs. 3. ADDITIONAL INFORMATION DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET 3.1. General information related to the topic BOD: is the amount of the dissolved oxygen used by microorganisms in the biochemical oxidation of organic compounds at a certain temperature over a specific time period. COD: is the amount of the oxygen required to chemically oxidize the organic compounds in wastewater using dichromate in an acid solution. TOC: is the amount of carbon found in organic compounds or contaminants in the water sample. TDS: is the term used to describe inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates) and some small amounts of organic matter that are dissolved in water. SS: is the materials in wastewater which will not remain in suspension during a preselected settling period, such as one hour, but settles to the bottom. Alkalinity: is the buffering capacity of a water body; a measure of the ability of the water body to neutralize acids and bases and thus maintaining a fairly stable pH level. VOCs: are organic chemicals that have a high vapor pressure at room temperature. Total coliforms: are a large bacteria group that are naturally found on plants and in soil, water, and in the intestines of humans and warm-blooded animals. They can be used as one of the many operational tools to determine the efficacy of a drinking water treatment system. Fecal coliforms: are a group of total coliforms that are passed through the fecal excrement of humans, livestock and wildlife. 3.2. Example wastewater treatment plants https://www.youtube.com/watch?v=FvPakzqM3h8 https://www.youtube.com/watch?v=PCejLBRhR7o https://www.youtube.com/watch?v=XjEuWLr78b8 https://www.youtube.com/watch?v=lqzZ84FiUaA 7 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant  DOMESTIC WASTEWATER TREATMENT https://www.youtube.com/watch?v=GUBRRXzYXpI DOMESTIC WASTEWATER TREATMENT PREPARATION SHEET 4. REFERENCES Boutin, C. and Eme, C. 2016. “Domestic Wastewater Characterization by Emission Source”. hal.archives- ouvertes.fr. WHO, 2006. “Wastewater reuse”. https://www.who.int/water_sanitation_health/hygiene/plumbing19.pdf 5. ADDITIONAL SOURCES Virtual Fie Sources Description This book provides students with an Metcalf & Eddy, 2003. overview of wastewater treatment and “Wastewater Engineering: explains the fundamentals of process Treatment and Reuse”. McGraw design, based on technical advances in Hill, 4th Ed. environmental engineering over the past years. Additionally, it gives a detailed information on federal legislation regarding water quality control and sludge management. This book gives a detailed information on Reynolds & Richards, 1996. chemical concepts, biological concepts, “Unit Operations and Processes mass balances, flow models, basic in Environmental Engineering”, principles of reactors, quality and quantity PWS Publishing, 2nd Ed. of water/wastewater. Besides, it explains the basics of water treatment, wastewater treatment. atment 5 8 ENV-101 Introduction to Environmental Engineering Virtual Field Trip-2: Domestic Wastewater Treatment Plant