Lesson Nine Flashcards
Primary Objectives of Wastewater Treatment
Protect the Public,
Preserve Aquatic Life,
Preserve the Receiving Water Environment,
Preserve Water Quality
Original Goal of Wastewater Treatment
Prevent the outbreak of communicable diseases transmitted in water (the relationship between water and disease).
Protect the Public - Focus
Prevent communicable diseases (typhoid, cholera, dysentery, polio, hepatitis) from untreated wastewater. Disease-causing organisms are called pathogens.
Preserve Aquatic Life
Maintaining sufficient dissolved oxygen (DO) in receiving waters for the fish and aquatic life respiration.
Preserve Aquatic Life - Impact of Organic Matter
Increased organic matter leads to increased bacteria, which consume DO during oxidation, potentially depleting it.
DO Levels & Aquatic Life
DO below 5 mg/L can seriously harm or kill fish. High organic loads reduce DO.
Preserve Receiving Water Environment - Concerns
Untreated wastewater can cause: loss of clarity/colour, floating scum, excessive algae/weed growth (due to added nutrients), reducing aesthetics and recreation.
Preserve Water Quality - Industrial Wastewater Issues
Can be highly acidic/alkaline and contain toxic substances, hazardous to aquatic life and public water supplies (taste/odour).
Sources of Wastewater - Smaller Communities
The majority is domestic (residential) wastewater (60-80% of per capita water consumption).
Sources of Wastewater - Commercial
From businesses frequented by the public (shopping centers, restaurants, hotels, etc.).
Sources of Wastewater - Industrial
May contain toxic compounds and heavy metals. Often requires pretreatment before discharge to municipal systems.
Sources of Wastewater - Institutional & Recreational
Essentially domestic. Hospitals may have high pathogen levels. Recreational flows are seasonal.
Sources of Wastewater - Infiltration
Groundwater and stormwater are entering the collection system, increasing volume. Depends on the soil, precipitation, and pipe condition.
Sources of Wastewater - Inflow
Surface water entering the collection system through sewers or access points. Influenced by system layout and drainage.
Wastewater Characteristics - Composition
Over 99.9% pure water, less than 0.1% solids (organic & inorganic).
Wastewater Characteristics - Fresh vs. Septic
cloudy, grey, musty odour. Septic (stale): black, foul smell, black solids (indicates blockage).
Total Solids in Wastewater - Categories
Organic solids (from plants/animals, decompose) and Inorganic solids (sand, gravel, silt, don’t decompose).
Types of Solids (Further Breakdown)
Suspended solids (small particles held in suspension) and Dissolved solids (in solution). Also Settleable solids (larger particles that settle).
Regulations - Provincial (Alberta Environment)
License to Operate or Code of Practice issued. Includes system classification (Class I-IV), operator requirements, volume allowed, sampling/testing/reporting, effluent standards.
Federal (Fisheries Act)
Illegal to discharge “deleterious” substances to fish-bearing waters (administered by DFO).
Regulations - WSER
Wastewater System Effluent Regulations may require reporting of effluent quality and quantity to the federal government.
Wastewater Collection - Sanitary Sewers
Gravity sewer pipes transport wastewater to treatment plants. Size/grade depends on flow and infiltration/inflow.
Wastewater Collection - Combined Sewers
Older systems carrying both wastewater and stormwater. Often lead to bypasses during storms.
Wastewater Collection - Trunk & Outfall Sewers
Trunk: collect from large areas. Outfall: major sewer to the treatment facility (carry combined flows).
Wastewater Collection - Lift Stations
Pump wastewater to higher elevations when gravity is uneconomical (wet well, sewage pumps, force main).
Wastewater Collection - Low Pressure Systems
Holding tanks & small pumps at each household, pumping to a low-pressure main. Solids removed periodically.
Class I Wastewater Treatment Facilities
Wastewater ponds and aerated lagoons. Basic treatment: solids removal and organic matter stabilization (bacterial breakdown).
Bacteria in Waste Stabilization Ponds (Types)
(use dissolved oxygen), Anaerobic (get oxygen from compounds), Facultative (can use both).
Waste Stabilization Ponds - Best Use
Smaller communities with lower land costs. Lower operating skill needed than mechanical plants.
Mechanical Plants - Best Use
Larger communities with higher land costs. Continuous discharge to receiving streams (requires sufficient flow).
Mechanical Plants - General Pretreatment
Screening (remove large debris)
Grit removal (remove sand/gravel)
Pre-aeration (freshens wastewater, adds DO)
Primary Treatment - Main Process
Sedimentation in primary clarifiers to remove settleable solid matter (sludge/biosolids) and floatable material (scum). Detention time ~1.5-2 hours.
Secondary Treatment - Main Goal
Remove dissolved and non-settleable organic material (biological process using microorganisms).
Secondary Treatment - Common Processes
Rotating Biological Contactors (RBC) and Activated Sludge processes.
Rotating Biological Contactors (RBC) - Key Feature
Rotating plastic discs are partially submerged in wastewater, developing a biological slime (aerobic bacteria) that consumes organic matter.
Activated Sludge - Key Feature
Forced aeration to introduce oxygen, mixing microorganisms with organic matter in aeration tanks. Sludge is recycled.
Secondary Clarifier - Purpose
Solids/liquids separation after secondary treatment, removing microorganisms and humus. Effluent then disinfected.
Dissolved Air Flotation (DAF) - Secondary Treatment
Alternative to secondary clarifiers. Fine air bubbles attach to solids, causing them to float and be removed from the top.
Suspended Biofilm Reactors (SBR)
Small plastic discs suspended in aerated tank, biofilm grows on discs, wastewater flows through screens to keep discs in tank.
Membrane Bio-Reactor (MBR)
Uses manufactured films with fixed pore sizes to filter solids. Requires effective pretreatment. High effluent quality possible.
