Lesson Ten Flashcards
Waste Stabilization Ponds - Definition
Economical alternative to mechanical treatment. Uses natural processes to stabilize wastewater. Lower cost, simpler operation, high-quality effluent (if managed well).
Stabilization Ponds - Natural Treatment Processes
Heavy solids settle (anaerobic bacteria decompose).
Suspended solids/organic matter stabilized by bacteria in suspension.
Dissolved N & P are used by algae for growth (algae use CO2/bicarbonates).
Stabilization Ponds - Typical Use
Smaller communities, often located outside municipal boundaries. Can be single or multiple ponds.
Benefits of Waste Stabilization Ponds (List - 8)
Limited expensive equipment.
Lesser operator skill needed.
More economical (construction & operation) vs. mechanical.
Effluent quality equal to or better than mechanical. Adaptable to changing hydraulic/organic loads.
Effluent can be used for land application (if suitable).
Less energy required.
Fewer possible problems than other processes.
Limitations of Waste Stabilization Ponds (List - 5)
Seasonal/overload odours.
Requires large land areas.
Potential groundwater contamination (if not careful).
Treatment efficiency depends on climate.
May have high suspended solids in effluent.
Bacteria & Algae in Stabilization Ponds - Role
Microorganisms use organic matter/nutrients for growth/respiration (needs oxygen). Bacteria decompose, algae photosynthesize (release O2, use CO2).
Aerobic Ponds - Characteristics
Shallow, good oxygen distribution. Oxygen from wind action and algal photosynthesis. Primarily aerobic bacteria.
Anaerobic Ponds - Characteristics
Deeper, less surface area. Anaerobic bacteria at the bottom consume settled organic matter (produce CO2, N2, organic acids).
Facultative Ponds - Characteristics
Aerobic near surface, anaerobic at bottom (3-8 feet deep). Aerobic, anaerobic, and facultative bacteria present. Oxygen from photosynthesis and aeration. Most common type.
Algae in Ponds - Function
Uses sunlight/CO2 for growth, releases O2 (photosynthesis). Present in upper layers. O2 used by bacteria.
Bacteria in Ponds - Function
Release CO2, methane, nutrients, ammonia. CO2 used by algae. Interdependent relationship with algae for stabilization.
Pond Aeration - Natural
Surface winds create turbulence, adding air/oxygen. Oxygen transfer depends on turbulence and oxygen solubility (higher in colder water).
Dissolved Oxygen in Ponds - Daily Variation
Lowest in early morning (bacteria used it overnight). Increases during day (algae produce O2), highest midafternoon (if sunny). Lower on cloudy days.
Dissolved Oxygen in Ponds - Winter
Ice cover can lead to extremely low DO levels. Ponds kept at max depth to prevent freezing.
Biological Zones - Photosynthetic/Aerobic Zone
Upper layer, dominant algae and aerobic bacteria. Depth depends on water clarity and sunlight penetration
Biological Zones - Facultative Zone
Below photosynthetic zone, dominant facultative bacteria. Oxygen mainly from pond aeration.
Biological Zones - Anaerobic Zone
Bottom layer, no sunlight penetration. Anaerobic bacteria digest organic matter (produce volatile acids, methane, CO2, ammonia, H2S).
Treatment Factors - Physical (Examples)
Type of soil (containment), surface area, depth, wind action, sunlight, temperature, short circuiting, inflow variations.
Treatment Factors - Chemical (Examples)
Organic material (loading), pH, solids (type/concentration), concentration/nature of waste.
Treatment Factors - Biological (Examples)
Type of bacteria (heterotrophic important), type/quantity of algae, activity of organisms, nutrient deficiencies (N, P), toxic substances.
Pond Colour - Warm Weather Indicators
lear dark green: Well-balanced facultative pond (high algae).
Clear light green: Facultative storage ponds (less algae).
Dark “pea soup”/blackish green: Blue-green algae.
Pond Colour - Other Conditions
Dark green to black: Anaerobic wastewater.
Brown: Anaerobic wastewater, low DO.
Grey: Dead algae.
Red or pink: Purple sulfur bacteria (anaerobic) or red algae (aerobic).
Disinfection of Pond Effluent - When Necessary
Discharge to water course leading to public water supplies and/or recreational use.
Accepted Disinfection Methods for Pond Effluent
Chlorination or complex ultraviolet (UV) light system.
Chlorination Requirements for Pond Effluent
Minimum 2.0 mg/L residual chlorine after a 20-minute contact time.
Discharge of Chlorinated Water
Prohibited into fish-bearing streams under federal law. Dechlorination required before discharge.
Aerated Waste Stabilization Ponds - Definition
Economical alternative to regular stabilization ponds and mechanical treatment. Less land needed. Uses mechanical aeration for oxygen.
Aerated Ponds - Bacteria & Algae
Bacteria are similar to activated sludge. Algae are less significant due to high mixing from aeration.
Aerated Ponds - Oxygen Supply
Primarily from mechanical aeration equipment (less from algae compared to stabilization ponds).
Aerobic Aerated Ponds - Mixing
Complete mix, particles do not settle to the bottom.
Aerobic Aerated Ponds - Final Step
Requires a polishing pond (non-turbulent area) for microbial solids to settle before discharge.
Aerobic Aerated Ponds - Treatment Efficiency Factors
Organic loading (higher load = lower quality), Oxygen (more needed with higher load), Temperature (colder = lower microbial activity).
Aerobic-Anaerobic Aerated Ponds - Mixing
Not completely mixed. Large portion of solids settle, undergoing anaerobic decomposition at the bottom.
Aerobic-Anaerobic Aerated Ponds - Decomposition
Bacteria decompose organic matter (some oxidized to nitrates, sulfates, CO2; rest used for cell growth). Bacteria excrete polymers/slime, promoting floc formation for settling.
