14. Biosolids, Eutrophication, and Marine Dead Zones Flashcards
What is sewage sludge?
Residual, semi-solid material left from the sewage treatment process
What are biosolids?
Sewage sludge that has been treated
What treatments can be done to sewage sludge to transform them into biofuels?
- Treatment includes digestion (aerobic or anaerobic) and usually additions of liming agents.
- Both treatments reduce pathogens and stabilize the material.
- Other treatments include de-watering and pelletization.
Benefits of biosolids (6)
- High organic matter content
- Improves soil structure
- Improves water & nutrient holding capacities
- Rich in N, P, S
- Rich in micronutrients (usually overlooked with chemical fertilization)
- Inexpensive amendment (especially for farms that do not have access to animal manures)
Concerns with the safety of biosolids
- Trace metals
- Pathogens
- Organic contaminants
- PPCPs
- Antibiotic resistant material
- Odorous vapours
- N & P (contributes to nutrient loading of water bodies)
- Chlorinated organics
Biosolids concentration of microbes
Biosolids contain large concentrations of microbes relative to average topsoil, but similar or lower amounts compared to manure. Notable are the high levels of fecal coliforms.
Benefits of having large concentrations of microbes in biosolids (2)
- Increase in organic matter decomposition rates
- Increase in mineralization of N & P (and other nutrients)
Problem with having large concentrations of microsolids in biosolids
Some are pathogenic, i.e. very high fecal coliform count
Biosolid treatments to reduce the amount of microbes (4)
- Digestion (aerobic & anaerobic)
- Alkalinization
- Composting
- Heat-drying
Organic contaminants in biosolids
(concentration ; characterstics) (3 points)
- Concentrations in biosolids are generally low, below levels where we would expect acute toxicity.
- Most are volatile, removed during treatment process.
- They are biodegradable (at differing rates), most are degraded/partially degraded during treatment process, or will be broken down in soil soon after application (exceptions are dioxins/furans which can persist)
Use of biosolids regulations in Canada (3)
- Requires complete analysis (performed by the STP)
- Requires a government-approved NASM plan that includes overall nutrient goals, method of application, timing, crops, soil type, slope, etc…
- Application is limited to specific distances from residences, wells, aquifers, surface water
Where else besides agricultural lands can biosolids be applied? (5)
- Forests & reforestation sites
- Rangeland
- Mine reclamation sites
- Landfill reclamation sites
- Grave pit / quarry reclamation sites
Sources of environmental contamination with PPCPs
Human medicine & Veterinary medicine
What is an emerging conern for biosolids?
PPCPSs (pharmaceuticals and personal care products)
Growth promoting hormones (GPH) (5 points)
- Growth hormones are used in the livestock production in order to increase lean muscle tissue
- Usually administered as an ear implant, or in feed
- Use first started in the beef industry: castration (removal of testes) of steers removed the source of androgens (male hormones that can make meat tougher?)
- Much concern has focussed on human health effects from ingesting meat
- Environmental effects largely unknown
Why are concerns emerging for PPCPs in biosolids? (6 points)
- We’re basically at the stage where we are able to detect very trace amounts of these (ppm→ppb→ppt) in biosolids (and in soil and water systems … and in some cases in breast milk, dairy milk, meat tissue)
- The current idea is that since their concentrations are orders of magnitude below the concentrations in medication/household products, they do not pose a risk to human health
- As far as environmental health…? There are more opinions than actual data.
- The data that does exist varies greatly, especially which chemical(s) are actually selected for investigation
- Much of the ecotox data is based on acute toxicity.
- Our knowledge of chronic toxicity, endocrine disruption, behaviour effects data, are limited but growing ……
Antibiotics (6 points)
- Antibiotics (and anti-parasitics) are routinely supplied in the feed in poultry, hog, dairy, cattle production
- They are incorporated into animal feed to improve growth rate and feed efficiency
- Sick animals are further treated with therapeutic doses of antibiotics
- As most antibiotics are poorly adsorbed in the gut of animals, the majority are excreted unchanged in feces and urine
- Three important groups of antibiotics used in livestock: tylosin, tetracycline, sulfonamides
- Generally antibiotics used in human medicine are not used as veterinary medicine
What is the main concern about antibiotics?
Antibiotic resistence
Antibiotic resistence (3 points)
- Bacterial communities often respond to antibiotic selection pressure by acquiring resistance genes, i.e. mobile genetic elements that can be shared horizontally between species. (Example: genetic transfer through plasmids)
- Environmental microbial communities maintain diverse collections of resistance genes, which can be mobilized into pathogenic bacteria.
- Humans and animals are endangered by the inability to treat infections with effective antibiotic treatments
Eutrophication (def)
A sudden increase of a formely limiting nutrient in an aquatic environment (usually P), leading to overgrowth of algae and grazing bacteria and subsequent oxygen depletion
Cyanobacteria (3 characteristics)
- photosynthesizing bacteria
- N fixing
- growth generally limited by P
Anthropogenic sources of N & P loading (7)
- Agriculture
- Municipal wastewater treatment plants
- Sewage
- Septic systems
- Industrial wastewater
- Storm water
- Atmospheric deposition
Main are agriculture and municipal wastewater treatment plants
What do we call the resulting proliferation of phytoplankton (cyanoacteria) following eutrophication?
A bacterial or algal bloom
Problems resulting from eutrophication (4)
- Some groups of cyanobacteria produce toxins that can make humans and animals sick
- i.e. Microcystis aeruginosa release the toxic compound “microcystins” which are chemically very stable, can persist under a variety of aqueous conditions, withstands boiling
- As phytoplankton die, their decomposition uses up O2; water body becomes increasingly anoxic leading to hypoxia ….
- Kills fish, and all other aquatic organisms that require O2
- Increases turbidity (i.e. reduces light penetration) in the water column, changes ecosystem structure (i.e. blocks sunlight to macrophytes that release oxygen in lakes)
Remediation techniques to eutrophication (3)
- Chemical treatments
- Dredging Lake sediments
- Ecological restoration
Chemical treatment example & how it works
The addition of aluminum sulphate Al(SO4)3
* Binds dissolved P → reduces bioavailable P
* Binds colloidal organic matter which then settles out → increased water transparency
Pros of chemical treatmens (2)
- Fast
- Cost effective
Cons of chemical treatments (5)
- Does not necessarily reduce microcystis species (nor their concentration of toxins),
- Can lower pH,
- Al3+ is toxic at large concentrations,
- Fe is less effective under anoxic conditions because it is reduced.
- Short term fix to long term problem (algal bloom can just be recreated)
Dredging lake sendiments
Addresses the problem of “internal P loading” (i.e. release of P stored in sediment)
Pro of dredging lake sediments
Has been successful in lake restoration however, effectiveness depends on specific hydrologic characteristics of water body (shallow seems to recover better than deep) and sediment characteristics
Cons of lake dredging (2)
- Time consuming & costly (requires repeated dredging over several years)
- Short term fix to long term problem
Ecological restoration
Promoting a mosaic of macrophyte (aquatic plants) populations
Pros of ecological restoration (5)
- Release O2 via photosynthesis
- Reduce turbidity (improve transparency)
- Compete with algae & cyanobacteria for nutrients (N & P) and space
- Some species release allelopathic compounds that inhibit algae growth
- Provide habitat for zooplankton, help restore food web
Cons with ecological restoration (5)
- Can be difficult to establish (start with floating macrophytes and eventually introduce partially submerged, then fully submerged organisms)
- Time consuming restoration
- For some recreational lakes, an abundant macrophytic community may be undesirable
- Can’t do large scale
- Not ideal for recreational lakes (now there’s a bunch of plants in the way for swimming)
What is something to note if we want these restoration techniques to work?
They only work if external N & P loading has been reduced to sustainable levels
How can we reduce N & P loading to water bodies? (2)
- Reduce the release of N & P into the environment
- Reduce the translocation of N & P to waterbodies
Will the use of fertilizer grow in time?
Yes, bc as population grows so does the production of food and hence the use of fertilzier
What are sources of nitrate?
Nitrate is usually introduced into groundwater through widespread or diffuse sources, commonly called non-point sources, which can be hard to detect.
These sources can include:
* Leaching of chemical fertilizers
* Leaching of animal manure
* Groundwater pollution from septic and sewage discharges.
Environmental health concerns of nitrate
- Nitrate is considered relatively non-toxic, a high nitrate concentration in drinking water can harm infants by reducing the ability of blood to transport oxygen.
- In babies, especially those under six months old: Methaemoglobinaemia, or commonly called “blue-baby syndrome,” results from oxygen deprivation caused by drinking water high in nitrate. Death can occur in extreme cases
What are marine dead zones?
Dead zones are zones of hypoxic (low-oxygen) areas in the world’s oceans and large lakes
What are marine dead zones caused by?
“Excessive nutrient pollution (N, P) from human activities coupled with other factors deplete the oxygen required to support most marine life in bottom and near-bottom wate; creating marine dead zones.
(Near bottom water → devoid of most fish and invertebrates)
Excess N, P → marine eutrophication → algal blooms → dead zone
Steps of marine dead zones (4)
- Fertilizers, sewage and nutrients from farming flow down rivers
- Nutrients stimulate massive algae blooms
- Algae die and sink to the bottom, where bacterial decompostion uses up dissolved oxygen
- Water becomes anoxic and kills marine life that cannot flee
Denitrification
NO3- → NO2- → NO → N2O → N2
When does N2O (nitrous oxide) build up
N2O (nitrous oxide) builds up if much NO3- is present
* Prevalent in hypoxic ocean waters i.e. dead zones
* Greenhouse gas
What does sequential buildup of NO2- and N2O indicate?
It indicates metabolism of denitrigying bacteria
Concentrations of NO2-, NO3- and N2O overtime in a marine dead zone
- NO2- : more at the very beginning then goes down quickly
- NO3-: peaks near the beginning then goes down
- N2O: increases later and to a smaller extent
