Sanitary Engineering Notes

Sanitary Engineering - 6th Semester

Course Structure

• Course Code: BEG 364 CI
• Year: III, Semester: II
• Teaching Schedule:
  • Theory: 3 hours/week
  • Tutorial: 1 hour/week
  • Practical: 2/2 hours/week
• Examination Scheme:
  • Final Theory: Duration 3 hours, Marks 80
  • Internal Assessments Theory: Marks 20
  • Practical: Duration --, Marks 25
• Total Marks: 125
• Course Objective: To provide students with advanced knowledge of sewerage systems, sludge treatment, and disposal.

Course Contents

1.0 Introduction (2 hrs)

• 1.1 Importance of wastewater and solid waste management
• 1.2 Objectives of sewage disposal
• 1.3 Sanitation systems: conservancy system and water carriage system
• 1.4 Types of sewerage systems: combined, separate, and partially separate systems

2.0 Quantity of Wastewater (3 hrs)

• 2.1 Sources of sanitary sewage
• 2.2 Factors affecting sanitary sewage
• 2.3 Determination of quantity of sanitary sewage
• 2.4 Methods for determining storm water quantity: tangent method; limitation of rational method

3.0 Characteristics and Examination of Sewage (5 hrs)

• 3.1 Sewage sampling
• 3.2 Different characteristics of sewage: physical, chemical, and biological
• 3.3 Decomposition of sewage, aerobic and anaerobic reactions
• 3.4 Biochemical oxygen demand (BOD) and chemical oxygen demand (COD)
• 3.5 Tests of solids, DO, pH-value, brief review of water supply, BOD, COD, Nitrogen, chloride demand

4.0 Design and Construction of Sewers (5 hrs)

• 4.1 Typical design periods, flow velocity, flow diagrams, hydraulic formulae and gradients
• 4.2 Shape of sewers
• 4.3 Sewer materials: requirements, salt glazed stoneware, C.I. and cement concrete pipes
• 4.4 Design of the sewer for separate and combined systems
• 4.5 Construction of sewer: excavation, laying, joining, testing: water test, air-test

5.0 Sewer Appurtenances (4 hrs)

• 5.1 Manholes, drop-manholes and lamp-holes
• 5.2 Street inlets
• 5.3 Catch basins
• 5.4 Flushing devices
• 5.5 Sand, Grease and oil traps
• 5.6 Inverted siphons
• 5.7 Sewer outlets
• 5.8 Ventilating shaft

6.0 Sewage Disposal (6 hrs)

• 6.1 Meaning and objects of sewage disposal
• 6.2 Disposal of sewage by dilution: Process, essential conditions for dilution, Self-purification of streams, factors affecting self-purification, oxygen sag curve, Streeter-Phelps equation
• 6.3 Disposal of sewage by land treatment: process, suitability of land treatment, methods of land treatment irrigation, over land flow and rapid filtration

7.0 Sewage Treatment (10 hrs)

• 7.1 Objects of treatment and different treatment methods: physical, chemical, biological
• 7.2 Preliminary treatment processes: racks or screens, skimming tanks, grit chamber, sedimentation, and chemical precipitation
• 7.3 Secondary treatment processes and their types
• 7.4 Principles of biological treatment, principal of suspended and attached growth process
• 7.5 Sewage filtration, intermittent sand filler, contact bed tricking filters, bio filters and design of trickling and bio-filters.
• 7.6 Activated sludge process: theory, design and aeration, advantages and disadvantages of the activated sludge process
• 7.7 Oxidation ponds: functions, theory and design

8.0 Sludge Treatment and Disposal (4 hrs)

• 8.1 Sources of sludge and need of treatment
• 8.2 Aerobic and anaerobic digestion
• 8.3 Methods of sludge treatment: grinding and blending, thickening, stabilization, dewatering, drying, composting and incineration
• 8.4 Methods of sludge disposal: spreading on land, lagooning, dumping, and land filling

9.0 Disposal of Sewage from Isolated Buildings (4 hrs)

• 9.1 Privies: Pit privy, ventilation improved pit latrine, and pour-flush latrine
• 9.2 Septic Tank: design, construction, working and maintenance
• 9.3 Disposal of septic tank effluent: drain field, soak pits, watching, Evapotranspiration mounds

10.0 Solid Waste (2 hrs)

• 10.1 Types and characteristics of solid waste
• 10.2 Collection and disposal
• 10.3 Methods of solid waste disposal: dumping, sanitary landfill, incineration and composting

Field Visit

• Field visit of a sewerage treatment plant, group presentation and submission of individual report to the respective teacher.

Chapter 1: Introduction

• Carries 4-8 marks in exams (Theory Only)

Objectives of Sewage Disposal

• a) To achieve sanitary condition by proper disposal of human excreta to a safe place before it starts decomposition.
• b) To evacuate waste water as soon as possible from the point of generation, so that mosquitoes, flies, bacteria etc. may not breed in it and cause nuisance.
• c) To maintain hygiene condition and increase aesthetic appearance of the city.
• d) To prevent from sporadic outbreak of diseases.
• e) To prevent land and water pollution.
• f) To use sewage as fertilizer by sewage farming.

Sanitation Systems / Sewage Collection System

• Mainly divided into two systems:
  • 1. Conservancy system or dry System
  • 2. Water carriage System

Water Conservancy System

• In this system, the collection, conveyance, and disposal of various types of waste are carried out with the help of water.
• Water is used as a medium to convey the waste from its point of production to the point of its final disposal.
• Sufficient quantity of water is required to be mixed with the wastes so that the dilution ratio is so great that the mixture may flow just like water.
• The sewerage is so formed that 99% is water & 1% is solid waste.

Conservancy (Dry) System

• In the conservancy (dry) system, refuse is collected separately and disposed of.
• Garbage is collected separately in dustbins and conveyed by covered carts or trucks or tractors to a suitable place.
• The combustible and non-combustible garbage is sorted out. The combustible is burnt, and the non-combustible and inorganic is buried in low-lying areas.
• Human and animal waste (feces and urine) are collected in pans and is then carried by labors in carts or trucks or tractors for disposal outside where it is buried for manure.
• Stormwater is conveyed separately by closed or open drains and discharged into natural streams.
• This system is obsolete now and can be used in rural areas.

Advantages of Conservancy System

• Environment friendly:
  • No fear of surface as well as ground water contamination so that storm water is disposed of separately.
  • There is no water requirement for flushing.
• Cost: Initial investment and maintenance cost is low.
• No Treatment requirement: Night soil and urine are collected separately. Hence, no treatment requirement.

Disadvantages of Conservancy System

• Less Hygiene and sanitary aspect
• Transportation is difficult
• Labour aspect/health issue
• Building aspect
• Risk epidemic
• Pollution problem
• Cost consideration
• Disposal land requirement

Water Carriage System

• In this system, water is used as a medium to carry wastes to the point of final disposal.
• The quantity of water is so high (99.9%) that wastes become liquid which is carried by the sewers.
• Specially designed latrines called water-closets are used to flush after its use.
• The garbage is collected separately as in the conservancy system.
• The sullage is also led to the sewers. The storm water may be disposed of separately or combined with sanitary sewage.

Advantages of Water Carriage System

• Hygiene and sanitary aspect: The system is very hygienic since the night soil and other wastewater is conveyed through closed conduits which are not directly exposed to the atmosphere. There is no bad smell because of continuous flow.
• Epidemic aspect: There are no chances of outbreak of epidemic because flies and other insects do not have direct access to the sewage.
• Pollution aspect: The liquid wastes etc. are directly conveyed through the sewers, and therefore there are no changes of the wastewater being soaked in the ground thus contaminating the soil. The waste water does not percolate down to join the ground water. There are no chances of pollution of water of wells in individual houses if any.
• In design: Since the latrines are flushed after every use, excreta does not remain and there are no foul smells. The latrines can therefore be attached to the living and bed rooms. This permits a compact design. The lavatories can be accommodated in any part of the house.
• Labor Aspect: This system does not depend on manual labour at any time except when sewers get choked.
• Treatment Aspect: The sewage collected through the sewers can be conveyed directly to a treatment plant, and proper treatment can be done to safely dispose it to nearby water bodies.

Types of Sewerage Systems

The sewerage system can be classified as:

• 1. Separate System
• 2. Combined System
• 3. Partially Separate System

Separate System

• In this system, two sets of sewers are provided.
• When the sanitary sewage is taken in one set of sewers, whereas storm and surface water are taken in another set of sewers, it is called a separate system.
• The storm water may be carried in open drains or closed conduits.
• The sewage from the first system of sewers should be led to treatment works while the flow from the second system of sewers can be discharged directly into natural streams without any treatment.

Merits of Separate System

• The quantity of sewage to be treated is small as sewage flows in a separate conduit.
• The cost of installation is low as storm water can be conveyed through open channels.
• Storm water can be discharged into natural streams without any treatment.
• Sewers of small sections can be easily ventilated than those of large sections.
• During disposal, if sewage is to be pumped, this system is cheaper.
• There is no fear of stream pollution.

Demerits of Separate System

• Sewer lines are difficult to clean because of their small size.
• They are likely to be clogged.
• Two sets Of sewers may ultimately prove to be costly.
• As two sets of sewers are laid, their maintenance cost is more.
• Generally, self-cleansing velocity is not available due to a small quantity of sewage.
• Storm water sewers come in use only during rainy seasons. During other parts of the year, these may serve as dumping places for garbage and may get clogged.

Combined System

• When only one set of sewers is laid for carrying both sanitary sewage and storm water, it is called a combined system.
• The sewage and storm water are carried to sewage treatment plants before their disposal.

Merits of Combined System

• Maintenance cost is low as the system uses only one set of sewers.
• Self-cleansing velocity is available at every place due to more quantity of sewage.
• The strength of sewage is reduced by dilution with rainwater
• The sewers are of larger size and thus the chances of their choking are rare. Also, it is easy to clean them.
• Sewer gas that may be formed in the sewer gets diluted as more air is present in larger sewers than small sewers.

Demerits of Combined System

• The cost of construction is high because of large dimensions of sewers.
• Because of the large size of sewers, their handling and transportation are difficult.
• Due to the inclusion of storm water, the load on the treatment plant increases.
• It is uneconomical if whole sewage is to be disposed of by pumping.
• During heavy rains, the sewer many overflow and thus create unhygienic conditions.

Partially Separate System

• In the separate system, a part of storm water, especially originating from the roofs or paved courtyards of buildings, is allowed to enter in the sewers carrying sewage, and the remaining storm water flows into a separate set of sewers, it is called a partially separate system.

Merits of Partially Separate System

• As sewers are a reasonable size, their cleansing is relatively easier.
• It possesses the advantage of both the separate as well as combined systems.
• The storm water permitted in the sewers eliminates the chances of chocking.
• The problem of disposing of storm water from homes is simplified.

Demerits of Partially Separate System

• Self-cleansing velocity may not be available during dry weather as the velocity of flow is low.
• The addition of storm water on sewage increases the loads on treatment units.
• If sewage is to be disposed of by pumping, the cost will be more than the separate system.
• There are possibilities of overflow during the rainy season.

Difference Between Separate and Combined Systems