Table of Contents
Reducing BOD means that the sewage will support the growth of less bacteria and therefore the effluent will be better able to infiltrate tight soils. Many enhanced treatment technologies that remove BOD were designed specifically to enhance disposal of effluent in tight silt or clay soils.
How is BOD associated with secondary sewage treatment?
Secondary treatment is the portion of a sewage treatment sequence removing dissolved and colloidal compounds measured as biochemical oxygen demand (BOD). Secondary treatment is traditionally applied to the liquid portion of sewage after primary treatment has removed settleable solids and floating material.
How is BOD reduced?
These are the best practices for reducing BOD and TSS that facility managers should know: Focus on removing TSS from wastewater first. Get a properly sized EQ tank. Control the pH of the waste stream. Install a modern plate pack DAF made of stainless steel or plastic. Use a regenerative turbine air dissolution pump.
In which way sewage can be treated?
Four common ways to treat wastewater include physical water treatment, biological water treatment, chemical treatment, and sludge treatment.
Why is BOD done for 5 days?
The standard oxidation (or incubation) test period for BOD is 5 days at 20 degrees Celsius (°C) (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 (see TECHNICAL NOTE).
What are the 3 types of sewage treatment?
There are three main stages of the wastewater treatment process, aptly known as primary, secondary and tertiary water treatment.
Do we drink sewage water?
But while this may be so, treated sewage water is not widely accepted as a drinking water source, largely due to the ‘gross’ factor. But the fact of the matter is that anyone who lives downstream from a wastewater treatment discharge point effectively drinks treated wastewater in some form or another.
What is the difference between primary and secondary sewage treatment class 12?
The main difference is the way each respective treatment is processed. Primary treatment works on sedimentation, where solids separate from the water through several different tanks. In contrast, secondary treatment uses aeration, biofiltration and the interaction of waste throughout its process.
What is the average COD in sewage?
Is My Wastewater “High-Strength”? Table 1. Typical concentrations of organics in untreated domestic wastewater. BOD (biochemical oxygen demand) mg/L 110 COD (chemical oxygen demand) mg/L 250 TOC (total organic carbon) mg/L 80 O&G (oil and grease) mg/L 50.
What happens if BOD is high?
The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.
Why secondary treatment is called biological treatment?
Secondary treatment of wastewater works on a deeper level than primary level. It is called as biological treatment because it is designed to substantially degrade the biological content of the waste through aerobic biological processes. This step removes the dissolved organic matter by the use of biological agents.
What are the 5 stages of wastewater treatment?
Treatment Steps Step 1: Screening and Pumping. Step 2: Grit Removal. Step 3: Primary Settling. Step 4: Aeration / Activated Sludge. Step 5: Secondary Settling. Step 6: Filtration. Step 7: Disinfection. Step 8: Oxygen Uptake.
What is the primary treatment of wastewater?
Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation.
What is needed for the secondary treatment of sewage?
Secondary wastewater treatment processes use microorganisms to biologically remove contaminants from wastewater. In an aerobic system, the organic contaminants are converted to carbon dioxide, water, additional microorganisms, and other end products.
What happens in the secondary treatment stage of sewage treatment?
The secondary stage uses biological processes to further purify wastewater. Sometimes, these stages are combined into one operation. As sewage enters a plant for treatment, it flows through a screen, which removes large floating objects such as rags and sticks that might clog pipes or damage equipment.
Why secondary treatment is important?
The objective of secondary treatment is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. The microorganisms must be separated from the treated wastewater by sedimentation to produce clarified secondary effluent.
Is high BOD in water good?
Higher BOD indicates more oxygen is required, which is less for oxygen-demanding species to feed on, and signifies lower water quality. Inversely, low BOD means less oxygen is being removed from water, so water is generally purer.
What does secondary treatment not remove?
Secondary treatment removes the soluble organic matter that escapes primary treatment. It also removes more of the suspended solids. Removal is usually accomplished by biological processes in which microbes consume the organic impurities as food, converting them into carbon dioxide, water, and energy…
Why is BOD important in wastewater treatment?
BOD has traditionally been used to measure of the strength of effluent released from conventional sewage treatment plants to surface waters or streams. This is because sewage high in BOD can deplete oxygen in receiving waters, causing fish kills and ecosystem changes.
Why is secondary water treatment sewage treatment considered a biological process?
Secondary treatment uses biological processes to further reduce solids in the effluent. Bacteria feed on organic matter; the excess sludge is removed to be made into biosolids and the water goes through secondary clarification, followed by disinfection.
Why is COD higher than BOD?
COD is normally higher than BOD because more organic compounds can be chemically oxidised than biologically oxidised. This includes chemicals toxic to biological life, which can make COD tests very useful when testing industrial sewage as they will not be captured by BOD testing.
What is a good BOD level?
A BOD level of 1-2 ppm is considered very good. There will not be much organic waste present in the water supply. A water supply with a BOD level of 3-5 ppm is considered moderately clean.
What is BOD in sewage treatment?
Biological Oxygen Demand (BOD) is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms “bio-bugs” in a body of water to break down organic material present in a given water sample at a certain temperature over a specific time period.
What is BOD limit?
For drinking water BOD has to be less than 5 mg/L and for treated wastewater to be disposed of in the water bodies it is 30 mg/L, 100 mg/L if treated waste water is discharged into the sewerage system in India.
What causes BOD to increase?
High biochemical oxygen demand can be caused by: high levels of organic pollution, caused usually by poorly treated wastewater; high nitrate levels, which trigger high plant growth.
