Description
Study Guide for Exam 2
Sewage Treatment: Chapter 6
∙ Prior to the late 19th century, open cesspools were primarily used for sewage disposal
∙ Flush toilet
∙ Spread of waterborne diseases, such as cholera and typhoid fever ∙ First municipal sewer system not constructed until 185 in Chicago ∙ First sewage treatment facility not completed until 1886 in New York City
The Goal of Sewage Treatment
Reduce the level of water contamination
Removes SS, BOD, and pathogens from raw sewage
Not effective for removal of nitrogen and phosphorus
∙ Characteristics of domestic waste are welldefine, little variability ∙ Industrial sewage is highly variable
May contain toxic organic substances, pesticides, and heavy metals)
∙ Basic design of most STPs are very similar (Packaged STPs)
Primary Treatment (Physical Treatment)
∙ Steps involved with primary treatment are as followed:
Bar Screen (vertical bars; 5 to 10cm apart; trap any trash that would interfere in the treatment of the facility. We also discuss several other topics like Why analyzing the external environment is important?
*** Removal of BOD and suspended solids***
Grit Chamber (the velocity of water is decreased; to a point where it allows substances such as (e.g sand) to settle out in the grit chamber Primary Clarifier (Primary settling tank)
The velocity is zero; it has STOP
Any settable or floatable solids are all remove by a mechanical device; the solid materials that are removed in the primary
clarifier is referred to as the primary sludge.
Primary sludge comes from the primary clarifier
∙ Treatment of sewage that only involves the treatment of primary sludge is termed primary sewage treatment
∙ Primary treatment typically removes 3040% of the BOD; its accomplished by removing all solids and organic materials We also discuss several other topics like What are the key properties of the rule?
Secondary Treatment for BOD Removal (Biological Treatment) If you want to learn more check out What is a group of organisms of the same species living in a particular geographical region?
Don't forget about the age old question of What are the visceral effector organs?
∙ Biological Treatment Relies on bacteria and other organisms to eliminate much of the organic matter
∙ Most commonly used methods are activated sludge and tricking filter processes
Trickling Filter
Consists of cylindrical tank 23m in depth and filled with rocks (210cm in diameter)
Sewage effluent from the primary clarifier sprayed over the surface of rocks by rotating arms
High diversity of organisms (Different species e.g protozoans, fungi, rotifer, amoeba, salmonella)
Activated Sludge
Consists of rectangular tank, 35 m deep
Effluent from the primary clarifier is pumped into one end and exits the other end We also discuss several other topics like Which department of the u.s. government is responsible for designating groups as “foreign terrorist organizations”?
Residence time 48 hours
Sewage aerated vigorously from below
Highly specialized organisms; No high diversity of organisms as the trickling filter
***If it goes into anaerobic process, then we have a problem***
If you want to learn more check out Which type of association positive, negative, close to 0 would you expect to be true about the association between the length of the forearm and the length of the foot?
Percent Removal of BOD and SS
∙ Activated sludge is more efficient from the trickling filter but with the activated sludge, there are more sludge created than the actual filter
Key Points:
We can say that, following primary treatment, BOD removal is <50%. Primary Treatment in process solid removal ~50%
Primary + trickling filter in process is greater than 80%
Septic Tank
∙ The purpose of the septic tank is to separate solids from the wastewater, store and partially decompose as much solid material as possible, while allowing the liquid ((or effluent) to go to the drainfield.
∙ Its job is to hold the wastewater long enough to allow solids to settle down to the bottom forming sludge, while the oil and grease floats to the top as scum.
∙ Mostly found in homes; like having your own personal private sewage plant in your garden; if taken care of, it can last a long time and serves as a good removal of BOD and SS
∙ BOD removal is 2565% and suspended solids is 4075%
Relying on microorganisms in this tank (e.g bacteria, fungi) to break down the organic matter that goes down the tank. Depending on the usage and the number of individuals inhabiting the home, the volume that its uptake needs to be considered.
The Anaerobic Digester
∙ Principal purpose
To stabilize the sludge and reduce its volume
∙ Receives sludge from the primary and secondary clarifiers ∙ Alternatives to using the digester:
Incineration
Deposition in a sanitary landfill (odor problem)
Some form of land application (odor problem) e.g land farming *** NIMBY (NOT IN MY BACKYARD) ***
∙ Products of the anaerobic digester
Digested sludge
Supernatant fluid
Gases (primarily methane), other gases (e.g ammonia, sulfide) ∙ Operation
It must be heated (methane) to be digested
27 35℃
∙ Barriers for land application of wastes:
Lack of land to receive it
Contamination from toxic substances
Public attitude (NIMBY)
Smell
Organic fertilizers or soil conditioner Treated sludge
Tertiary Treatment
∙ In the U.S, tertiary treatment means nutrient removal (this is a chemical process)
Nitrogen and phosphorus removal
∙ Based on formation of insoluble compounds
Chemical precipitation
∙ Phosphorus removal is easier and cheaper than nitrogen removal ∙ Precipitate may be chemically processed to recover the phosphate commercial value as a fertilizer
Nitrogen Removal: Most of the inorganic nitrogen in the effluent from the secondary clarifier is in the form of ammonium (NH ) not the oxidized forms ₄ such as nitrate (NO )₃
By adding lime or CaO at a high Ph, you can remove both at the same time (Phosphorous and nitrogen)
Methods:
∙ Ammonia stripping is the most common technique used for the removal of nitrogen from sewage
pH must be elevated; NH is converted to NH ₄ ₃
Bring pH back to neutral position
The efficiency of this technique is reduced; temperature drop (decreases or sets cold), the solubility of the NH increases; it hard to ₃ drive off vigorous eration
Temperature and climate affect nitrogen removal
∙ Anaerobic denitrification is a biological procedure start off with NH comes primary treatment, oxidize to nitrate through vigorous ₄ eration, nitrate is converted to N . Denitrification is aerobic process ₂
∙ Breakpoint Chlorination removal of nitrogen chlorination of our drinking water sewage treatment disinfection chlorine,
Hypochlorite ion, hypochlorous acid
Must reach a breakpoint (Nitrogen tied up)
When chlorine is adding with water. COMBINED RESIDUAL MUST COME FIRST before using free residual
Ammonia and organic nitrogen are key reactants demanding chlorine in raw water to form chloramines
∙ Monochloramine
∙ Dichloroamine
∙ Trichloroamine
Land Application of Sewage
∙ Valuable resource
∙ Potential problems
Pathogens
Nitrates (Midwest)
Heavy metals (contaminated soil and groundwater)
Chapter 7: Pathogens in Natural Waters
∙ Disposal of Human Excreta Without Sewers (Alternative Methods) Pit privy or one of its variants (like an outhouse)
Retention containers (construction sites and portal potty) Short water transport (septic tank; cesspools; stabilization ponds) Indiscriminate ground and/or water disposal (2/3 of world’s population uses one of these 4 methods; clear majority of
population utilize method #4; dumping your wastes on to the ground)
Classification of most human pathogens
Key Points: 3rd world populations have suffered from sewage carry pathogens; countries such as Peru and Mexico must live, work and reproduce in situation of high population density thus resulting in sewagecarry pathogens and epidemics
∙ Viruses
∙ Protozoans
∙ Helminths (intestinal worms)
∙ Bacteria
Sources of Pathogens
Found in human excrement of infected persons
Carriers
Permanent; person harbor pathogens in the body following the infection; have the infection, organism is never cleared from the body; carry it for the rest of their lives but no longer have the signs or symptoms; small percentage of individuals have this certain type of carrier
Temporary; individuals that harbor the organism, pass it down to others while they are sick or nearing a recovery period. Once they are totally recovered, they are no longer a carrier
Zoonoses animal transmission
OUTBREAK = EPIDEMIC
Bacterial Pathogens Associated with Waterborne Diseases
Salmonella (Salmonellosis) and Shigella (Shigellosis)
Salmonella typhi is the best known of the salmonellosis
Pathology
Passes into the stomach; multiply in the intestines; if it doesn’t clear from system or go untreated; potentially enter in the blood; after that, it’ll probably be bad; Once salmonella is in the blood, it establishes itself in the bone particularly the periosteum (membrane covering of the bones). Periosteum covers the bone and if this occurs multiplies there, individuals that experience this condition will end up with chronic arthritis. Once it’s in the blood, it can travel to various organs in the body and travel up to the spinal fluid, which will result in meningitis or result in pneumonia, which result in death.
Commonly found in animals
Shigella
Responsible for severe case of Diarrhea (Bacilly dysenteriae)
*** As far as Salmonella survival in natural water, they survive by a low temperature and water that has a high amount of magnesium present; raw sewage***
Escherichia coli (indicators of disease potential)
Intestines of all warmblooded animals (including humans) Enteropathogenic serotypes (0157:H7)
Survival in water
Fecal coliforms are indicators of disease potential
Severe Diarrhea
Early 90s; fruits and vegetables contamination
Large amount of fecal coliforms in the water result in Salmonella contamination; E. coli are mostly found in sewage or untreated sewage; hazards associated with water borne disease
Campylobacer
Individuals who travels to countries/overseas experience this disease in a form of severe diarrhea
Causes Campylobacteriosis
Among most common bacterial infection of humans throughout the world
More commonly isolated from fecal specimens than either Salmonella or Shigella
Symptoms: diarrhea, fever, abdominal pain (cramping)
Cholera caused by Vibrio cholera
Diarrhea (ricewater stools) **
Vomiting
Suppression of urine
Rapid dehydration
Fall of blood pressure
Subnormal temperature
Complete collapsedeath can be rapid
Treated with infusion of electrolytes (liquid into the body); IV and antibiotics is also given
Considered to be there all the time in some countries, has been considered a potential biological warfare
Roughly 210% or more of the human population are healthy carries Outbreaks usually associated with contaminated water supplies Epidemics common in certain parts of the world
Leptospirosiscaused by Leptospira
Excreted in urinenot normally found in feces
Transmission to humans usually involves contact with water in which infected animals have urinated
In the U.Sconfined mostly to summer recreational period and are associated with swimming in polluted waters
Hogs farms, hogs urinate into the streams, kids go out and play in these streams, that allows the organisms to pass in the skin and into the bloodstream
Associated in the summer with swimming in polluted waters Involve kidneys, liver, and central nervous system
Often severe and may be fatal
Giardia lamblia – causes giardiasis
Symptoms: Diarrhea (severe), weakness, weight loss, abdominal pain (a lot of gas), cramping, nausea. Most common symptoms is greasy stools.
Occurs in two forms
∙ Freeliving or trophozoite
∙ Encapsulated cyst form (ingested with contaminated water, lost its cyst, and goes to the trophozoite form. Seen a lot of
outbreaks in surface waters; mountain streams.
∙ In both forms, the individuals can become infected
Outbreaks
∙ “Backpackers Disease”; Individuals go out to the mountains and drink the water from the mountain streams
Seen in daycare centers; pass it to one another; sharing tangible objects Seen more frequently in children; also, seen in adults but difficult to diagnose; must take stools sample to diagnose it; Symptoms is water treated
Prevention
∙ Water purification tablet (Not effective). Filtration of water is the best method for prevention
Number of communities have experienced GRD due to the lack of proper filtration procedure for drinking water.
Cryptosporidium
∙ More resistant to chlorination (1000 resistant to chlorination as compare to GRD)
∙ Much worse
∙ Has occurred in communities where treatment plants did not provide filtration
∙ Worse outbreak in GA 2 years ago; 400,000 individuals infected; filtrating process of H2O was broken/malfunctioning
∙ Prevention: Must put a filtration process into effect
Entamoeba histolytica causes disease of the large intestine called amoebiasis
Disease syndrome
∙ Mild syndrome diarrhea alternating with constipation
∙ Severe amoebic dysentery; protozoans’ burrows into the
intestines and sometimes the intestines are ruptured.
***In these cases with GRD, Cryptosporidium and Entamoeba histolytica, they all eliminated through the feces***
Viral Pathogens Associated with Waterborne Diseases
∙ Infectious Hepatitis (also known as hepatitis A)
Excreted in feces of infected persons
Passed by individuals through infected water
High resistance to chlorination
Difficulties in diagnosis; “where was the exposure??”; Being consumed and see symptoms within 30 days of exposure
∙ Poliomyelitis
Not significant health problem in U.S today
Chlorination resistance
Protozoans (most resistant) > viruses > bacterial pathogens (least resistant) Helminths Associated with Waterborne Diseases
∙ Taenia saginata (beef tapeworm)
Swallowing water with containing eggs; found in sewage
∙ Ascaris lumbricoides (ascariasis)
Long whiteworm appearing through the nose
“roundworm”
∙ Schistosoma (schistosomiasis)
Blood fluke
Life cycle: enter the body through skin between the toes where the skin is tender; produce a very annoying dermatis condition, sometimes referred to as “swimmers itch”; Once it goes through the circulatory system, it can go to the lung; (liver and intestines are most affected) Intermediate host snails
As far as good hygiene, there is no cases in the U.S but every year, thousands are diagnosed and the reason for this, is because individuals are coming to the U.S with Schistosoma
Tests for Pathogens
∙ General approach is to look for an indicator organism
∙ IMPORTANT POINT: Presence of an indicator organism would be taken as evidence of sewage pollution
Ideal Indicator Organism
The organism is proportional in abundance to the number of pathogens in the water and survives at least as long as the pathogens outside the intestinal tract
The organism is easily detectable and present in greater quantity than any potential pathogen
The organism is absent from the aquatic environment unless the water has not been polluted with sewage or animal excrement
The organism must be present consistently in high concentrations in raw sewage
Problems
Was believed that all coliform bacteria were of fecal origin
∙ Only E. coli of the family Enterobacteriaceae is found exclusively in feces
∙ Guidelines were rewritten regarding identification of fecal coliforms
∙ If you were going to separate fecal coliform from other coliforms; you use an increased temperature for the growth of or culture of fecal coliforms; E. Coli will grow at 44.5 degree centigrade which means its thermally tolerant as compare to the other coliforms. Typically, when you are growing bacteria, you grow at 35 degree centigrade but if you increased the temperature say for a water bath, E. coli will grow at 44.5. You’re able to separate fecal from the others.
You have a suction flask with a funnel that is clamp to the top; between that funnel and the top of the suction flask, there is a gridded glass top where you can put your filter paper, and this filter paper has grids in it. The pore size of this gridded glass is .45µm. So, your water sample is passed through the filter, taken off and put in a small petri dish containing a selective type of medium, its incubated at 35 degree centigrade, after 24 hours, you can count coliform products if present.
Within this fermentation you have contains Lactose broth (purple color), there’s is an inverted tube that fit inside the fermentation tube, take a water sample and put it in the broth and incubated at 35 degree, if there’s fermentation of the lactose broth occurs by the organisms utilizing this lactose broth, if present it will convert from lactose broth to lactic acid indicating that the pH has dropped thus having an acid production, thus resulting purple turning to yellow indicating that we have acid production. Coliforms is a gas
producer. If the result is negative (no growth or growth without gas) If the result is positive + (growth with gas in the inverted vial)
Treatment of Public Water Supplies (Water Purification)
∙ Basic Steps:
Sedimentation
Coagulation (removal of solids for our drinking water)
o Filtration (WE DO NOT FILTER SEWAGE but we are required to put a filtration in place for drinking water); remove any remaining solids in the water before going to the distribution system
o Charcoal removes taste and odors from the water; removes bacteria cells and protozoans (e.g GRD; cryptosporidium)
Disinfection THM formation
o Major concerns formation of Trihalomethanes example of THM would be chloroforms and bromoform
o Shown to be carcinogenic
o Areas where drinking water is from surface waters (e.g lakes) particularly areas that are high in organic matter during the summer time; when you have a lot of organic matter, the likely of THM formation is greater
o THM formation is an issue but there’s alternatives. Ozonated water is an alternative. Problem very expensive. But when added ozone doesn’t from THM; very expensive
o UV radiation is another alternating for chlorination; inexpensive, don’t have THM; GRD can survive UV light; However, when process through filtration, you may not see GRD. More likely to see modern treatment plants using UV radiation
o Chlorine Dioxide (another alternative for chlorination) very expensive very potent for disinfection Main advantage is that you can check chlorine concentration through the distribution system. Not able to check with UV radiation or ozone
Chapter 8: Toxicology (Fate and Transport)
∙ Physical/Chemical Properties
Water solubility
Octanol water partition coefficient (Kow)
Vapor Pressure
Soil adsorption coefficient (Koc)
Water solubility
Mobility
Stability or breakdown
Accumulation
Bioaccumulation
Sorption (refers to ad and or ab)
*** The higher the water solubility (dissolve in water) of a chemical, the more likely it is to be mobile, and the less likely it is to be accumulative, bioaccumulative, volatile, and persistent; and a highly soluble chemical is prone to biodegradation and metabolism that, may detoxify the parent chemical*** If the water solubility was lower, then all these factors would be in reverse.
KEY POINT: Water Solubility
∙ Kow = [organic chemical in octanol phase] divides [ organic chemical in water phase]. Measure and report if a chemical prefer to be in a liquid state, water state, or prefer to dissolve
∙ High Kow means its more than likely liquid soluble
∙ The higher the Kow, the greater the affinity of the chemical to bioaccumulate and/or bioconcentrate in the food chain, the greater its potential for sorption in soil, and the lower its mobility.
∙ High solubility means low Kow
∙ Low solubility means high Kow
∙ Determines if the chemical is likely to be liquid soluble; if so then we have a problem; suggest that we may have food chain contamination
Volatilization
A chemical with a low vapor pressure, high adsorptive capacity, or high water solubility is less likely to volatilize into the air
A chemical that has high water solubility, it’s not going to be volatile A chemical that has a high Kow, it’s likely to be more volatile
Soil Sorption (Koc)
A value that has been assigned to a chemical and describes the ability to bind to soil
Soils must contain organic carbon/organic matter to produce a Koc The Koc value assigned to a chemical describes its capacity to bind to soil The higher the Koc value of a chemical, the more likely it will adsorb to soil,
be less mobile, less soluble in water, persist in the environment, and bioaccumulate
High Koc = Kow means it’s more likely to be liquid soluble
Adsorption
The physicalchemical process by which a soil ties up chemicals in the environment so that they are not released or are very slowly released in the environment (bound residues—based on charge)
Binding of soil particles based on charge when we are talking about adsorption
Absorption
A chemical that is absorbed in soil can be released in any environment like water being released from a sponge
Higher concentration in the soil than outside of the soil
“squeezing water out of a sponge”
∙ Mechanisms altering chemical characteristics:
o Photolysis; if a chemical absorb sunlight, then it’s likely to be transformed through the process of photolysis. If produces, result would be degradation product. Not metabolized
o Biodegradation; typically, can take place in all environmental compartments
o Metabolism; cannot take place in all environmental compartments, plants and animals produce metabolize, which is a result of
metabolism
o Hydrolysis reaction with water but high hydrolytic product
Toxicology
The quantitative study of the effects of harmful substances or stressful conditions on organisms
Environmental Toxicology (EcoTox)
o Concerned with the incidental exposure of plants and animals, including humans to pollutant chemicals and unnatural environmental stresses
Toxicity Concepts
∙ Surface waters are the primary recipients of waste materials o As long as the consequences of waste discharges are not injurious to the uses of the body of water or otherwise do not impair its, integrity, then the body of water is not polluted.
∙ Uses that can adversely affected by toxic pollution include:
o Water supply
o Fishing
o Irrigation
o Navigation
o Recreation
∙ Injury of the integrity of the body of water implies harm done to the aquatic ecosystem (biota within the system)
o Fish
o Insects
o Planktonic microorganisms
o Aquatic plants
∙ To protect the uses or the aquatic ecosystem from injury contaminant levels must be kept below a certain “safe” threshold
o Note that the toxicity threshold varies among species
Toxicity is an alternation or impairment of the normal functions of organisms caused by an exposure to or ingestion of a compound or mixture of compounds
Acute (exposure to organisms that will result in some type of crisis; to be shortterm exposure; high dose; signs or symptoms that will develop quickly
Chronic (more of a Sublethal; exposed to over a long period of time often through its entire life period; at a low amount of exposure thus resulting signs and symptoms with a lower dose compared to being seen in acute exposure
Lethal (exposure result in death; organism’s dies
Sublethal (like chronic; modification in behavior such as reproduction and developmental effect)
Cumulative (Occurs with organic phosphate; an effect that occurs in the organism because of excessive exposures.
Toxicity and Its Measurement
∙ Toxicity levels of compounds for aquatic organisms have been established by scientists in toxicity bioassay tests
The most important parameter of interest in the toxicity bioassay test is the dose or concentration that results in a LD50
Dose vs. Concentration
Concentration is a measure of the amount of dissolved substance contained per unit of volume. The dose is how much of that substance you take.
***KEY POINTS: Toxicity of a chemical substance is strongly influenced by the dose***
∙ Lethal dose or concentration (LD or LC)
Implies that an exposure to organism has resulted in death
∙ Effective dose or concentration (ED or EC)
Term used when other than lethal effects are considered such as impact on reproduction or respiratory stress
Toxicity and Its Measurements (Types of Toxicity Tests)
∙ Static Test (1Gallon pickle jar (use for static test); Within each pickle jar, you water, fish; same number of fish in each jar. Testing concentrations of unknown at different level concentration. Easiest and cheapest to do. Problems associated These fishes are in the same water through entire testing period; accumulation of waste product in the fishes thus resulting in depletion of the amount of oxygen present; chemicals added to the jar may cause a depletion in the oxygen might be depleting oxygen.
∙ Recirculation Test a large aquarium that has fishes water pumped out into a fishing apparatus and pumps back in; removing waste product that are produce by the fish and keep the water purified without removing the test chemicals. Doesn’t deplete the chemicals that’s being test but it remains some water quality. Very expensive.
∙ Renewal Test (much like static test except duplicate jar setup that have identical solution. Concentration doesn’t change and are put into cleaner water. Putting them in a cleaner jar periodically
∙ Flowthrough Test (Gulf Breeze Florida; Testing chamber from a surrounding creeks or rivers floats into the testing chambers located in the labs organisms are exposed to oxygen rich water ONLY ISSUE: Deal with the water coming out. Welloxygenated; stable concentration; continuous removal of metabolic waste. A reallife exposure; most expensive and but the most accurate
Toxicity and Its Measurement (Bioaccumulation and Biomagnification)
∙ In the 1960sImpact of DDT use was realized (Silent Spring, Rachael Carson)
Biologists noted a large discrepancy between the DDT levels in organisms of different trophic levels
MAJOR PROLEMS ASSOCIATED WITH DDT Lost of certain birds, affected the endocrine system, low amount of calcium going into the eggs
Higher the trophic level of the organism, the higher the bodily concentration of DDT and some other compounds
The book claimed that DDT and other pesticides had been shown to cause cancer and that their agricultural use was a threat to wildlife, particularly birds.
Toxicity and Its Measurement Terms
∙ Bioaccumulation/bioconcentration accumulating the chemical in question of water, foods, or air. It gets bioconcentrated into certain tissues. Liquid soluble in soil than water; biodegradable
∙ Biomagnification if the chemical is going to be pass from one trophic level to another
∙ Bioconcentration factor ratio of the concentration of the toxic in the tissue versus that in the water
∙ Bioaccumulation factor the intake from food to the organisms and water to the organisms
∙ Biomagnification factor Known the concentration of a certain trophic level and comparing that concentration at a lower trophic level. Higher trophic level compare to a lower trophic level
Bioaccumulation takes place under field conditions. It is a combination of chemical bioconcentration and biomagnification. The extent of chemical bioaccumulation is usually expressed in the form of a bioaccumulation factor (BAF) which is the ratio of the chemical concentrations in the organism (CB) and the water (Cw)
Interactions between toxic substances (mixtures) – What are the effects of two or more toxic substances present in the water at the same time?
∙ The present water quality guidelines make no allowance for interactions between toxicants
∙ “If a general guideline in establishing water quality criteria is to be mistaken on the side of overprotection and if detailed information on
the interactions between combinations of toxicants is not available, then the assumption of strictly additive interactions would seem preferable to the assumption of no interactions at all”
When one substance antagonizes the other, then we are looking at infraadditive interaction
Maybe one hour cause the other to be more toxic, now we are looking at supraadditive interaction
So, if we use these 3 three lines and our assumptions, then the chemical is strictly additive, and it turns out that it is infraadditive, then we underestimate the toxicity. Likewise, with the same question with supraadditive.
If one assumes that there are no interactions or that the interactions are strictly additive, then the toxicity of a mixture of toxicants can easily be calculated
If the interactions are supraadditive, infraadditive, or antagonistic, then one must have detailed information about the nature of the interactions to calculate the toxicity of the mixture.
The assumption of strictly additive interactions would appear to be conservative in all cases except the case in which the true interactions are supraadditive.
Chapter 9: Industrial Pollution
∙ Industrial waste water
Majority of problems are brought about by one or more of the following:
High BOD
High concentration of suspended solids
Presence of toxic substances
∙ Oxygen Sag
Some wastewaters may be exceedingly high in BOD Pulp mills
Sugar refineries
Food processing plants
Production of Pulp by Chemical Methods
∙ Sulfite process
Use of sulfurous acid (H2SO3), calcium, magnesium, or some other base to cook wood. The cooking solution is acidic
BOD is about 1000mg/l
∙ Kraft process
Wood chips are cooked in a basic medium containing sodium hydroxide (NaOH) and sodium sulfide (Na2S)
About 95% of the cooking chemicals are recycled
Effluent is about 100 times less toxic than sulfite mill effluent ∙ Wood sugars and other readily metabolized organic substrates contribute a substantial amount of BOD