CE 132: Sanitary Engineering I and Wastewater Treatment Notes

Wastewater

• "Used water" discharged by households, commercial and industrial establishments, including stormwater runoff.
• Types:
  • Domestic
  • Industrial
  • Agricultural

Types of Wastewater

• Domestic wastewater: Liquid discharge from residences, business buildings, institutions.
• Industrial wastewater: Discharge from manufacturing plants, power plants, extractive industries.
• Agricultural wastewater: Discharge from animal farms (poultry and livestock), agricultural runoffs including organic wastes such as decayed plants, livestock manure, dead animals, pesticides, fertilizer residues.

Domestic Wastewater

• Blackwater: Sewage water; mixture of water with excrement and/or urine.
• Greywater: From sinks, showers, bathtubs, and washing machines.
• Sewage: Mixture of blackwater and greywater.

Wastewater Sources

• Point Source
  • Specific source (pipe).
  • Collected by a network of pipes or channels and conveyed to a single point of discharge into the receiving water.
  • Monitored and controlled by a permit system.
• Non-Point Source
  • Stormwater or runoff characterized by multiple discharge points.
  • Water flowing over the surface of the land or along natural drainage channels to the nearest water body.
  • Cannot be traced to a direct discharge point.

How to Reduce Water Pollution

• Point source pollution: Waste minimization; proper wastewater treatment prior to discharge in a water body.
• Nonpoint source pollution: Decrease in agricultural nonpoint source requires changes in land use practices and improved education.

Principal Constituents of Concern in Wastewater

• Suspended Solids
  • Organic and inorganic solids.
  • Organic substances exert oxygen demand.
  • Lead to the development of sludge and sediment deposits in water bodies, destroy habitats of benthic organisms, and create anaerobic conditions.
• Biodegradable Organics
  • Measured in terms of BOD and COD.
  • Biodegradable organic matter (human waste, food residue in domestic wastewater).
  • Cause depletion of natural oxygen resources and cause the development of septic conditions.
• Pathogens
  • Bacteria, viruses, and protozoa excreted by diseased persons and animals.
  • May transmit communicable diseases such as gastroenteritis, hepatitis A, typhoid, polio, cholera, dysentery.
• Nutrients
  • Detergents, fertilizers, food-processing wastes.
  • Cause the growth of undesirable aquatic life (eutrophication).
• Priority Pollutants
  • Carcinogenic, mutagenic, or highly toxic compounds depend on the type of industry/process that produces wastewater.
  • Pesticides: chlordane, dieldrin, heptachlor, DDT.
  • Industrial chemicals: polychlorinated biphenyls.
• Heavy Metals
  • Commercial and industrial activities (mining, electroplating, tanning, battery manufacturing, etc.).
  • Removed if the wastewater is to be reused.
• Dissolved Oxygen
  • Fish, other aquatic organisms require at least 5 mg/L to live.
  • Varies with temperature, salinity, elevation, turbulence.
  • Stream with good mixing will replenish DO quickly.

Typical Composition of Wastewater

• High strength WW – high pollutant loading

Effects of Water Pollution

• Effects on human health
  • Spread of disease-causing bacteria and viruses, which may cause gastroenteritis, diarrhea, typhoid, cholera, dysentery, hepatitis, SARS.
  • Diseases caused by inorganic and organic contaminants: Itai-Itai disease, black foot disease, liver damage, skin irritation.
• Effects on aquatic ecosystem
  • Depletion of oxygen leads to death of aquatic life.
  • Eutrophication.
  • “Red tide” phenomenon when there are toxic phytoplankton and algal blooms.
  • May 2011: Bangus and tilapia in Taal Lake was largely affected by a fish kill, estimated to have reached 800 MT.
  • June 2011: Fish kill in Bolinao and Anda waters in Pangasinan, where at least 10,000 MT bangus were affected, amounting to PhP 3 M worth of losses.
• Effects on aesthetics
  • Unsightly; sources of foul odors and gases.
  • August 2013: Makisig tanker at Cavite terminal when a leak from an underwater pipe caused a large oil spill to Manila Bay.

Oil spill in New Orleans

• Economic Effects
  • Health (PhP 3B).
  • Fishery production (PhP 17B).
  • Tourism (PhP 47B).

Sanitation

• Hygienic and proper management, collection, disposal or reuse of human excreta (feces and urine) and community liquid wastes to safeguard the health of individuals and communities.
• Objectives:
  • Improving health conditions.
  • Promoting dignity of living or enhanced quality of life.
  • Protecting the environment.

Components of a Sanitation Infrastructure

• Toilet

  • Stationary area for urination and defecation.
  • Flush toilets, dry toilets.
  • 76.8 % of families in the Philippines have sanitary toilet facilities.

• Collection

  • Sewers can either be separate or combined system.

• Wastewater Treatment System

  • On site
    • Found near the source of wastewater
    • For generation of small volume of wastewater
    • Septic system, constructed wetland, stabilization pond
    • Septic System – decentralized wastewater treatment system consists of a septic tank and a trench or bed subsurface wastewater infiltration system (drainfield)
  • Septic Tanks
    • Buried, watertight tank designated and constructed to receive and partially treat domestic sanitary wastewater; detention time 1-2 days
      • Three purpose:
        • Sedimentation tank for removal of incoming solids while allowing liquid fraction to pass
        • Biochemical reactor for anaerobic decomposition of the retained solids
        • Storage tank in which nondegradable residual solids accumulate
      • 30-60% BOD removal, 80-85% SS removal, 50% coliform removal
      • Advantages:
        • Flexible and adaptable to a wide variety of individual household waste disposal requirements
        • No maintenance needed except for periodic desludging
      • Disadvantages:
        • More expensive than other on-site waste treatment.
        • Drinking water sources must be set away from septic tanks (about 25 m).
        • Permeable subsoil structure so effluent can be distributed.
      • Septic Tank Design Considerations
        • Retention time at least 24 h
        • 2/3 of tank reserved for sludge and scum storage
        • WW inflow – 120 L/person·day
        • Sludge accumulation rate – 40 L/person·year
        • Max. filled volume of tank = 50%
        • Desludging – 4-5 years (sludge and scum occupy 2/3 of the tank)
        • Ventilation pipe to permit gas produced in the tank to escape
        • Do not disinfect the tank – small residual of sludge should remain in it for seeding purposes
        • Sludge from tank can be disposed of by burial; do not place in empty open fields or water bodies
  • Constructed Wetland
    • Treats municipal or industrial WW, grey water, stormwater runoff
    • Employs plants for treatment (canna lily, bulrush, reeds, cattail, phragmites, duckweeds, canna lily)
    • Term: Engineered Reed Bed
      • Treatment: biological, physical filtration, chemical adsorption
      • Basin containing microbes, media, and plants that provide treatment of incoming effluent; Philippines – used for treatment for industrial WW
      • Factors affecting efficiency: soil, aerobic and anaerobic microbes, type of plant
      • Vertical flow wetland occupies 0.5 land area when compared to horizontal wetland
      • Square bed is often used
      • Removes heavy metals, inorganic chemicals, pathogens via adsorption to roots of the plants
  • Lagoon/waste stabilization ponds
    • Use relatively shallow earthen basins that allows physical, chemical and biological processes to treat WW in the presence or absence of oxygen
    • Suitable for 260 to 3,200 $m^3$/day of sewage
      • Use natural and energy-efficient processes to provide low-cost wastewater treatment in homes and rural areas
      • Anaerobic pond (>=3m depth), facultative pond (1.5-2 m), maturation pond (1 m or less)
      • Anaerobic pond for organic matter removal, facultative pond for organic matter removal, maturation pond for pathogen and suspended solids removal; requires large land area

• Off-site Wastewater treatment plants

  • Secondary treatment: Maynilad uses sequencing batch reactors (SBR), moving bed biofilm reactors, conventional activated sludge systems
  • Maynilad: 5 WWTPs – Dagat-Dagatan, Alabang, Central Manila, Makati Isolated System, San Juan River

• Effluent Disposal

  • Discharge into body of water (DAO 2016-08, DAO 2021-19)
  • Aquaculture - controlled process of cultivating aquatic organisms, especially for human consumption

• What is Sludge and its Treatment?

  • Sludge – solid or semisolid residue generated during the municipal wastewater and sewage treatment process
  • Before disposal – sludge will be treated
    • Treatment includes pathogen inactivation, dewatering, stabilization and nutrient management
  • Composting - organic material undergoes degradation into a stable, end product (stabilization, pathogen inactivation, nutrient management)

• Sludge Disposal

  • Land application - spread biosolids onto agricultural lands, forests, designated disposal sites
  • Agricultural Reuse - beneficial since it contains macronutrients (N, P) and micronutrients (Fe, Mn, Cu, Zn)

Sewerage and Sanitation Statistics (Philippines)

• 92.5% of families in the Philippines have access to sanitary toilet facilities (2012).
• 10% of wastewater is treated.
• 5% have access to piped sewerage systems.
• 58% of the groundwater is contaminated.
• 95% of the wastewater from urban households flows into groundwater, public canals, drainage systems, rivers, and other water bodies.
• Diarrhea ranked 4th among the leading causes of morbidity.
• 4,200 die each year in Philippines due to contaminated drinking water.
• 80% of water in households becomes wastewater.

Metro Manila Sanitation

• 43 sewage treatment plants and septage treatment plants that provide service to 11% of NCR's population.
• 7 new septage treatment plants in Sarangani and Davao Del Sur.
• 85% are served by septic tanks; 4% of the population has no toilet.

Wastewater Flowrate and Constituent Loading

Wastewater Generators

• Infiltration: Water that enters the collection system through leaking joints, cracks and breaks, or porous walls ($m^3/d \, mm-km$, flow per area, percentage of sewage flow).
• Inflow: Stormwater (runoff) that enters the collection system.

Typical Wastewater Flowrates

• Wastewater generated is about 70-80% of the water consumption of each household.
• For BOD: 77 to 91 g BOD/person·day.

Wastewater Reduction Strategies

• Reduction in interior water use from domestic sources.

Infiltration/Inflow (I/I) Into Sewer Lines

• High groundwater levels result in leakage into the sewer lines.

• Infiltration may range between 0.2 to 28 $m^3/ha \cdot day$

  • Factors affecting infiltration:
    • Quality of material and workmanship in constructing the sewer lines.
    • Age of collection systems.
    • Sewer line maintenance.
    • Elevation of groundwater relative to the sewer line.
  • Factors affecting rate and quantity of infiltration:
    • Length of collection system.
    • Size of area served.
    • Soil and topographic condition.
    • Population density (affects size and length of sewer line).
  • Infiltration - water entering a collection system from a variety of entry points
  • Steady Inflow - water discharged from cellar and foundation drains, cooling water discharges, direct connections from springs and swampy areas; usually reported with infiltration
  • Direct Inflow - result from direct stormwater runoff connections to the sanitary or combined collection system
  • Delayed Inflow - slowed entry of surface water through access ports

Example: Determining I/I from Flow Records

A large city has measured high flowrates during the wet season of the year. The flow during the dry period of the year, when rainfall is rare and groundwater infiltration is negligible, averages 120,000 $m^3/d$. During the wet period when groundwater levels are elevated, the flowrate averaged 230,000 $m^3/d$ excluding those days during and following any significant rainfall events. During a recent storm, hourly flowrates were recorded during the peak flow period, as well as several days following the storm.

Compute I/I and determine if the infiltration is excessive. Excessive infiltration is defined by the local regulatory agency as rates over 0.75 $m^3 /(d \cdot mm \cdot km)$ of collection system. The composite diameter length of the collection system is 270,000 mm·km.

Solution:

• $Infiltration = 230,000 - 120,000 = 110,000 \, m^3/d$

• To compute for inflow - obtain "peak flow"

• $Inflow = 606,000 - 340,000 = 266,000 \, m^3/d$

• Determine if infiltration is excessive:

  • (110,000 \, m^3/d) / (270,000 \, mm \cdot km) = 0.407 \, m^3/(d \cdot mm \cdot km) < 0.75
  • Therefore, infiltration is not excessive.

Principal Design Parameters for Flowrate and Mass Loading

• Mass Loading: Total mass of one or more organic or inorganic effluent constituents delivered to the wastewater system over a specified period.
• Average Daily: Average flow occurring over a 24 h period based on total annual flowrate data.
• Peak Hourly: Peak sustained hourly flowrate occurring during a 24 h period based on annual operating data.
• Maximum Day: Maximum flow occurring over a 24 h period based on annual operating data.
• Minimum Hour: The minimum sustained hourly flowrate occurring over a 24 h period based on annual operating data.
• Minimum Month: The minimum daily flow that occurs over a period of 1 month based on annual operating data.

Absence of Measured Flowrate Data

• Minimum daily flowrate is assumed to range from 30 to 90% of the average flowrates for communities.

Estimating the Peak Flowrate (PFR) from Existing Data

1. Step 1: Arrange the dataset in increasing order.
2. Step 2: Compute the percentile rank of each data point: $P\% = (m / (n + 1)) \times 100$
3. Step 3: Check if the distribution of dataset is normal or lognormal by graphing Q vs. P%. Fit a line through the points.
4. Step 4: Compute the P% of peak flowrate: $P\% = (N / (N + 1)) \times 100$
5. Step 5: Using the fitted line through Q vs P%, estimate Q corresponding to the P% of peak flow from graph.Use this method for short-term data (less than 1 year)

Example: Determining the Peak Wastewater Flow

Using the following weekly flowrate data obtained from an industrial discharger for the dry (May - October) and wet (November - April) periods, estimate the probable annual maximum weekly flowrate that will occur during each period.

Solution

$P\% = m / (n + 1) = 1 / (26 + 1) \times 100 = 3.7037\%$, where m=1

$Peak \, flow \, rate = N / (N + 1) = 26 / (26 + 1) \times 100 = 96.2963\%$

Percentage for the peak flow rate for both dry and wet season

• Peak flow rate Wet season: 45,000 $m^3/d$
• Dry season: 36,000 $m^3/d$
• %P = 96.2963%

Estimating PFR Using Peaking Factors

• $PF = (183 \, m^3/d) / (106.1 \, m^3/d) = 1.72$

• $Peaking \, Factor = (peak \, daily, \, hourly, \, monthly \, Q) / (long-term \, Q)$

• $PFR = Q_{avg} \times PF$

Example: Determining the Design Flowrate

A residential community with a current population of 15,000 is planning to expand its wastewater treatment plant. In 20 years, the population is estimated to increase to 25,000.

Given the following information, estimate the future average, peak, and minimum design flowrate after (a) 10 years and (b) 20 years

Current:

1. Population is 15,000 people
2. Average daily wastewater flowrate is 7500 $m^3/d$
3. Infiltration/inflow has been determined to be non excessive. Infiltration is estimated to be 100 L/cap/d at average flowrate and 150 L/cap/d at peak flowrate.
4. Municipal use is estimated to be 40 L/cap/d at average flowrate and 60 L/cap/d at peak flowrate.
5. An industry contributes an average flowrate of 1000 $m^3 /d$ with a peak flowrate of 1500 $m^3 /d$.

Future:

• Population is estimated to increase linearly to 25,000 in 20 years.
• Residential water use in new homes is expected to be 20% less than the existing residences because of the installation of water saving appliances and fixtures as new homes are built and old homes are renovated.
• The per capita wastewater from existing homes will decrease by 20% linearly over 20 years.

Other assumptions:

• Current wastewater peaking factor is 3.0, which is expected to decrease linearly to 2.0 in 20 years.
• Current ratio of minimum to average flowrate is 0.35, which is expected to increase to 0.45 in 20 years.

Solution

Solve for current average design flow rate:

• Solve for municipal flow:
  • $MF = 40 \, (L/(cap \cdot d)) \times 15,000 = 600,000 \, L/d$
• Solve for industrial flow:
  • $IF = 1000 \, m^3/d \times 1000 \, L/m^3 = 1,000,000 \, L/d$
• Solve for I/I flow:
  • $I/I = 100 \, (L/(cap \cdot d)) \times 15,000 = 1,500,000 \, L/d$
• Solve for total flow:
  `* ```$total \, average \, flow = 7500 \, m^3/d \times 1000 \, L/m^3 = 7,500,000 \, L/d$
• Solve for residential flow:
  • $RF = Total - MF - IF - I/I = 4,400,000 \, L/d$

Solve for average design flow rate after 10 yrs:

• Solve for municipal flow:
  • $MF = 40 \, (L/(cap \cdot d)) \times 20,000 = 800,000 \, L/d$
• Solve for industrial flow:
  • $IF = 1000 \, m^3/d \times 1000 \, L/m^3 = 1,000,000 \, L/d$
• Solve for I/I flow:
  • $I/I = 100 \, (L/(cap \cdot d)) \times 20,000 = 2,000,000 \, L/d$
• Solve for unit water use (UWU) in current year:
  • $UWU = RF/population = 4,400,000 / 15,000 = 293$
• Solve for water use in after 10 years:
  • $UWU_{new} = 293 \times 0.8 = 235$
• Solve for residential flow (new residents):
  • $RF = 5,000 \times 235 = 1,173,333 \, L/d$
• Solve for residential flow (old residents):
  • $RF = 4,400,000 \times 0.9 = 3,960,000 \, L/d$
  • $Total \, RF = Old + New = 5,133,333 \, L/d$
• Solve for total flow:
  • $Total = RF + MF + IF + I/I$
  • $Total \, average \, flow = 8,933,333 \, L/d$

Solve for current peak design flow rate:

• Solve for residential flow:
  • $RF = 4,400,000 \times 3 = 13,200,000 \, L/d$
• Solve for municipal flow:
  • $MF = 60 \, (L/(cap \cdot d)) \times 15,000 = 900,000 \, L/d$
• Solve for industrial flow:
  • $IF = 1500 \, m^3/d \times 1000 \, L/m^3 = 1,500,000 \, L/d$
• Solve for I/I flow:
  • $I/I = 150 \, (L/(cap \cdot d)) \times 15,000 = 2,250,000 \, L/d$
• Solve for total flow:
  • $total \, current \, peak \, flow = RF + MF + IF + I/I = 17,850,000 \, L/d$

Solve for peak design flow rate after 10 yrs:

• Solve for residential flow:
  • $RF = 5,133,333 \times 2.5 = 12,833,333 \, L/d$
• Solve for municipal flow:
  • $MF = 60 \, (L/(cap \cdot d)) \times 20,000 = 1,200,000 \, L/d$
• Solve for industrial flow:
  • $IF = 1500 \, m^3/d \times 1000 \, L/m^3 = 1,500,000 \, L/d$
• Solve for I/I flow:
  • $I/I = 150 \, (L/(cap \cdot d)) \times 20,000 = 3,000,000 \, L/d$
• Solve for total flow:
  • $total \, peak \, flow = RF + MF + IF + I/I = 18,533,333 \, L/d$

Solve for current minimum design flow rate:

• Solve for residential flow:
  • $RF = 4,400,000 \times 0.35 = 1,540,000 \, L/d$
• Solve for municipal flow:
  • $MF = 600,000 \times 0.35 = 210,000 \, L/d$
• Solve for industrial flow:
  • Assume no plant operations at night.
• Solve for I/I flow:
  • $I/I = 100 \, (L/(cap \cdot d)) \times 15,000 = 1,500,000 \, L/d$
• Solve for total flow:
  • $total \, minimum \, flow = RF + MF + IF + I/I = 3,250,000 \, L/d$

Solve for minimum design flow rate after 10 yrs:

• Solve for residential flow:
  • $RF = 5,133,333 \times 0.4 = 2,053,333 \, L/d$
• Solve for municipal flow:
  • $MF = 800,000 \times 0.4 = 320,000 \, L/d$
• Solve for industrial flow:
  • Assume no plant operations at night.
• Solve for I/I flow:
  • $I/I = 100 \, (L/(cap \cdot d)) \times 20,000 = 2,000,000 \, L/d$
• Solve for total flow:
  • $total \, minimum \, flow = RF + MF + IF + I/I = 4,373,333 \, L/d$

Forecasting the Peak Constituent Loading

• Step 1: Compute the average constituent loading based on available (comparable) data
  • $C<em>{avg} = (\sum q</em>iC<em>i) / (\sum q</em>i)$
  • Where:
    • $C_w$ = average constituent concentration
    • $C_i$ = average concentration during the ith period
    • $q_i$ = average flow rate during the ith period
    • n = number of observations
  • When data is NOT available, get available data from literature
• Step 2: Determine the Peaking Factor from available data
  • $PF = (peak \, daily, hourly, monthly \, C) / C_{avg}$
• Step 3: Compute the design constituent loading
  • $Design \, Loading = C_{avg} \times PF$

Example: Determining the Design BOD and TSS Concentration

Determine the design BOD and TSS values using the data provided for a community of about 5000 people. Use PF of 3.70

Solution

$C<em>W = (\sum (C</em>i q<em>i)) / (\sum q</em>i)$

$(\sum q_i) = sum \, of \, all \, flow \, rate= 3.3405 \, m^3/s$

Solve for q-BOD at M-1:

$q<em>{M-1} \times Q</em>{M-1} = 157.5 \, g/m^3 \, \times 0.1175 \, m^3/s = 18.5063$

Solve for q-TSS at M-1:

$q<em>{M-1} \times Q</em>{M-1} = 165 \, g/m^3 \, \times 0.1175 \, m^3/s = 19.3875$

Solve for BOD:

$(\sum C<em>iq</em>i) = 711.00$

$C_W = 711 / 3.3405 = 212.842 \, g/m^3$

$Design \, BOD \, Loading:DL = C_W \times PF$

$DL = 212.842 \times 3.7 = 787.517$

Solve for TSS:

$(\sum C<em>i q</em>i) = 693.26$

$C_W = 693.26 / 3.3405 = 207.53 \, g/m^3$

$Design TSS Loading:DL = 207.53 \times 3.7 = 767.862$

BOD, TSS variation depends on population size

I/I tend to decrease BOD, TSS variation (reduce strength of WW)

Wastewater Constituents Variations

The damping of flow rate variations so that a constant or nearly constant flow rate is achieved

Used for the following reasons:

1. To overcome the operational problems caused by flow rate variations
2. To improve the performance of the downstream process
3. To reduce the size and cost of downstream treatment facilities

Flow Equalization

Process of mitigating changes in flow rate and pollutant loading through a portion of a system by providing storage to hold water

Treatment processes work more efficiently if the flow rate through them is steady

Factors to consider in the design:

• Location and configuration
• Volume
• Basin geometry
• Mixing and air requirements
• Appurtenances
• Pumping facilities

Equalization Basin or Tank

• Inline Flow Equalization: All flows pass through the equalization basin to achieve a considerable amount of flow rate and constituent concentration damping.
• Offline Flow Equalization: Only the flow rate above some predetermined flow rate is diverted into the equalization basin.
  • Pumping requirements are minimized
  • Amount of constituent concentration damping is reduced.

Physical Unit Processes

Levels of Wastewater Treatment

Headworks

• Unit operations that are placed at the upstream end of the wastewater treatment plant (WWTP).
• Pumping station, flow measurement, unit operations commonly referred to as preliminary treatment.

Pump/Lift Station

• Responsible for pumping wastewater or sewage material from a lower elevation to a higher elevation.
• Equipped with sensors.

Screening

• First unit operation in WWTPs, under preliminary stage.
• Screen - device with openings, generally of uniform size, used to retain solids found in the influent wastewater to the treatment plant or in combined wastewater collection systems.

Types of Screens

• Consist of parallel bars, rods or wires, grating, wire mesh, or perforated plate.
• Process removes larger materials in order to:
  • Protect process equipment
  • Prevent interference with treatment
  • Prevent discharge to waterways
• Coarse Screen
  • Known as Bar Racks.
  • Composed of parallel bars or rods.
  • Clear openings of 5/8 in. (6 mm)