Wastewater Treatment Basics
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Questions and Answers

What is the purpose of sewage treatment?

The purpose of sewage treatment is to manage wastewater discharged from homes, businesses, and industries to reduce the threat of water pollution, remove pollutants from wastewater for its recycling, promote health concern and public hygiene, and preserve aquatic life and wildlife habitat.

What are the three main types of sewage treatment?

  • Preliminary, Primary, Secondary
  • Preliminary, Secondary, Tertiary
  • Primary, Tertiary, Quaternary
  • Primary, Secondary, Tertiary (correct)

What is the main purpose of pretreatment in sewage treatment?

The main purpose of pretreatment is to protect the wastewater treatment plant (WWTP) equipment.

What does primary treatment remove from wastewater?

<p>Primary treatment removes pollutants that either settle or float. It removes 50% of suspended solids (SS) and 35% BOD.</p> Signup and view all the answers

What does secondary treatment not remove from wastewater?

<p>Nitrogen, Phosphorus, Heavy Metals (A)</p> Signup and view all the answers

What is the primary solid byproduct of sewage treatment?

<p>Sludge</p> Signup and view all the answers

What is the main factor that differentiates animal/vegetable oil and grease from petrochemical oil and grease?

<p>Biodegradability</p> Signup and view all the answers

Biodegradable oil and grease are often emulsified.

<p>False (B)</p> Signup and view all the answers

What is the acronym used for oil and grease in sewage systems?

<p>FOG</p> Signup and view all the answers

What is the primary method for separating free oil from water?

<p>Stokes' Law</p> Signup and view all the answers

What is the primary function of a grit chamber in sewage treatment?

<p>To remove inorganic solids like pebbles, sand, silt, eggshells, glass, and metal fragments.</p> Signup and view all the answers

What is the typical water velocity in a horizontal flow rectangular grit chamber?

<p>0.3 m/s</p> Signup and view all the answers

What is the typical detention time in an aerated grit chamber?

<p>2 to 5 minutes</p> Signup and view all the answers

Describe the structure of a vortex-type grit chamber.

<p>A vortex-type grit chamber consists of a cylindrical or conical tank where flow enters tangentially, creating a vortex flow pattern. Grit settles by gravity at the bottom of the tank, while effluent exits at the top.</p> Signup and view all the answers

What is the typical water velocity in a vortex-type grit chamber?

<p>0.3 m/s (A)</p> Signup and view all the answers

What is the typical minimum water velocity in a grit chamber?

<p>30 cm/sec</p> Signup and view all the answers

What is the typical detention time in a grit chamber?

<p>60 seconds</p> Signup and view all the answers

What is the typical total depth of a grit chamber?

<p>Y + 0.50m</p> Signup and view all the answers

What is the typical over flow rate (OFR) for a grit chamber?

<p>1200 m³/m²/d</p> Signup and view all the answers

What is the primary goal of anaerobic processes in biological treatment?

<p>To convert nitrate nitrogen into nitrogen gas in the absence of oxygen.</p> Signup and view all the answers

What is the primary goal of facultative processes?

<p>To allow organisms to function in the presence or absence of molecular oxygen.</p> Signup and view all the answers

What is the primary goal of carbonaceous BOD removal?

<p>To convert carbonaceous organic matter into cell tissue and gaseous end products, while converting nitrogen into ammonia.</p> Signup and view all the answers

What does COD stand for and what does it measure?

<p>COD stands for Chemical Oxygen Demand, and it measures the oxygen required to oxidize all compounds in water, both organic and inorganic.</p> Signup and view all the answers

Flashcards

Purpose of Sewage Treatment

Wastewater treatment aims to reduce water pollution by removing contaminants from wastewater discharged by homes, businesses, and industries, allowing for recycling and reuse.

Oxygen Demand

The amount of oxygen required to break down organic compounds in a unit volume of wastewater. It's a measure of wastewater strength.

BOD

Biochemical Oxygen Demand, a measure of the oxygen consumed by microorganisms to oxidize organic matter in water over 5 days at 20°C.

COD

Chemical Oxygen Demand, a measure of the total oxygen required to oxidize all organic and inorganic compounds in water using a strong chemical oxidant.

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Wastewater Quality Indicators

The five key indicators for assessing wastewater quality are BOD, COD, total phosphorus (TP), total nitrogen(TN), and suspended solids (SS).

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BOD & COD and Water Pollution

BOD and COD are measures of organic matter content in wastewater. Higher values indicate more severe water pollution.

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Degradable vs. Non-Degradable Organic Matter

Degradable organic matter in wastewater can be utilized by microorganisms, while non-degradable matter cannot.

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Primary Treatment

A preliminary treatment step in wastewater treatment that removes pollutants that settle or float, reducing suspended solids and BOD.

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Secondary Treatment

Biological treatment process that effectively removes BOD and suspended solids, reaching up to 85% removal efficiency.

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Tertiary Treatment

Advanced treatment stage that aims to remove remaining pollutants like nutrients (nitrogen and phosphorus), suspended solids, bacteria, and viruses.

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Sludge

Solid material removed from wastewater during treatment. It requires proper handling and disposal to ensure effective pollution control.

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Grit

Small inorganic particles like sand, pebbles, silt, and metal fragments present in wastewater. They can cause wear and tear on equipment and obstruct flow.

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Grit Chamber

A component of wastewater treatment plants, designed to remove grit from wastewater, protecting equipment and preventing blockages.

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Horizontal Flow Grit Chamber

Removes grit from wastewater by slowing down the water flow, allowing grit to settle at the bottom of the chamber.

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Aerated Grit Chamber

A grit chamber that uses aeration to keep organic material suspended, allowing grit to settle out while organics remain suspended.

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Vortex Grit Chamber

A cylindrical or conical tank that creates a vortex flow pattern. Grit is removed from wastewater as it settles to the bottom.

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Grit Chamber Design Criteria

The design of grit chambers must incorporate specific criteria to ensure effective grit removal.

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Settling Velocity

The rate at which a substance settles to the bottom of a water column. It's influenced by size, shape, and density of the particle.

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Aerobic Processes

Biological treatment processes that occur in the presence of oxygen, where microorganisms use oxygen to break down organic matter.

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Anaerobic Processes

Biological treatment processes that occur in the absence of oxygen, where microorganisms break down organic matter without requiring oxygen.

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Anoxic Denitrification

A biological process where nitrate nitrogen is converted to nitrogen gas in the absence of oxygen. It's a crucial step for nitrogen removal in wastewater.

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Facultative Processes

Biological processes where microorganisms can function in both the presence or absence of oxygen.

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Carbonaceous BOD Removal

The process of removing carbonaceous organic matter in wastewater biologically, converting it to cell tissue and gases.

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TDS (Total Dissolved Solids)

The total amount of dissolved solid materials present in an aqueous solution, indicating the overall dissolved matter content.

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TOC (Total Organic Carbon)

A measure of the amount of carbon in a sample originating only from organic matter, indicating the amount of organic carbon present.

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TSS (Total Suspended Solids)

A measure of the suspended solids in water, indicating the amount of particles that are not dissolved in the water.

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Pathogens

Microbial organisms that can cause disease in humans, animals, or plants, found in wastewater, requiring removal during treatment.

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DO (Dissolved Oxygen)

The measure of the amount of oxygen present in a water sample, essential for aquatic life.

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BOD (Biochemical Oxygen Demand)

A measure of the oxygen required for the biological oxidation of organic matter in water.

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Study Notes

Wastewater Treatment

  • Wastewater or sewage treatment is used to manage wastewater from homes, businesses, and industries to reduce water pollution.
  • The purpose of sewage treatment includes removing pollutants for recycling, promoting health concerns and public hygiene, and preserving aquatic life and wildlife habitats. Untreated sewage can spread diseases.
  • Untreated sewage in water bodies can cause depletion of oxygen resources, turbidity, and toxicity for aquatic life.

Wastewater Characteristics

  • Sewage is primarily water (99.94%) with a small amount of dissolved and suspended solids (0.06%).
  • Wastewater's strength is expressed by oxygen demand, which is the amount of oxygen needed to break down organic compounds. BOD is a measure of the amount of oxygen required by bacteria to oxidize organic matter in 5 days at 20°C. COD measures all organic matter.
  • Domestic untreated sewage has a BOD ranging from 100 to 300 mg/l.
  • Sewage also contains nutrients like ammonia (12-50 mg/l) and phosphorus (6-20 mg/l), along with other minerals.

Wastewater Treatment Plant Components

  • Municipal wastewater treatment has four stages: Preliminary, Primary, Secondary, and Tertiary treatment.
  • Preliminary treatment protects the treatment plant equipment.
  • Primary treatment removes settleable and floatable pollutants, removing 50% of suspended solids and 35% BOD.
  • Secondary treatment removes 85% of suspended solids and BOD, but not all nitrogen, phosphorus, or pathogenic bacteria.
  • Tertiary treatment removes most remaining BOD, phosphorus, suspended solids, and bacteria, along with 95% of nitrogen.

Grit Chamber

  • Grit removal is a physical process to remove small inorganic solids (pebbles, sand, silt, eggshells, glass, and metal) from wastewater.
  • Grit is abrasive and causes wear on pumps, and can also absorb grease and solidify in pipes, sumps, and clarifiers.
  • The grit chamber helps protect moving mechanical equipment and reduce the need for digester cleaning.
  • Grit chambers are often located after bar racks and before sedimentation tanks.
  • Several types exist, including horizontal flow rectangular, aerated, vortex, and detritus tanks.

Design Criteria for Grit Chambers

  • Water velocity should be at least 30 cm/sec.
  • Overflow rate (OFR) is typically 1200 m³/m²/day.
  • Detention time should be 60 seconds.
  • Total depth is often Y + 0.5 meters.

Oil and Grease

  • Animal/vegetable, meat packing, food processing, and restaurant wastewaters often contain biodegradable oil and grease that usually float.
  • Petrochemical, cutting/grinding, and automotive wastewaters frequently contain toxic oil and grease that frequently form emulsions.
  • Oil and grease can cause problems in collection systems and wastewater treatment plants.

Factors Affecting Oil Separation

  • Density differences (specific gravity) between oil and water are significant, with lower specific gravity oil rising faster.
  • Viscosity of the oil affects separation rate. Lower viscosity oil rises faster in water.
  • Droplet size affects the rate at which oil particles separate from water.

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Related Documents

Lecture 11 Grit Removal - CVLE 453 Sanitary Engineering PDF

Description

Explore the crucial processes involved in wastewater treatment and the characteristics of sewage. This quiz covers the importance of removing pollutants to ensure public health and protecting aquatic life. Delve into concepts like BOD and COD to understand wastewater strength.

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