Sources of Taste and Odor Problems:
The sources are mostly organic in nature

a) naturally occurring compounds,
b) wastewater,
c) industrial wastes,
d) human activities in watersheds, and
e) plant growths that cause problems, like algae
f) decaying vegetation

Naturally occurring compounds, sulfur, large organic deposits, etc can impart taste and odors to the water source

Municipal wastewater treatment effluent, contains a wide mixture of organic materials. In wastewater treatment, some of these compounds may be partially oxidized and produce odor, especially when chlorine is utilized for disinfection.

Chlorinated wastewater effluent may have a chlorinous odor, due to the formation of chlor-organic compounds.

Chlorinated water in the water distribution system:
When you "taste" or "smell" chlorine in the water, it is most always because there is "too little" being dosed. When we are feeding chlorine, and ammonia or other carbon-based compounds are in the water, the chlorination process produces a "combined chlorine residual" potentially creating dichloramines, trichloramines, and chlor-organic compounds with accompanying taste and odor characteristics. When the chlorination feed rate passes "the breakpoint" a "free chlorine" residual is achieved, as the compounds such as these are fully oxidized creating a free chlorine residual that is basically free from taste and odor-related problems. (SEE THE CHAPTER ON DISINFECTION for a full discussion on breakpoint chlorination.) So if you smell or taste chlorine, one can ADD slightly more to eliminate this problem…by moving into breakpoint chlorination status.

Wastewater has a relatively high concentration of nitrogenous compounds. These may release ammonia which reacts with free chlorine to produce nitrogen trichloride. This compound has a very irritating odor, especially around the buffered type chlorine residual analyzers!

Industrial wastes:
Phenols
Hydrocarbons from refinery wastes
ethyl acrylate
N-butyl mercaptan

Copper, zinc, and other metals produce characteristic tastes.

Human activities in watersheds: destruction of plants and their subsequent decaying leaves, etc., has been shown to create tannic acids, etc., which may impart taste and odors. The use of chemical pesticides, herbicides, fertilizers, solvents, petroleum products, etc. all have the capability of causing taste and odors.

Plant growths that cause problems, like algae:
Algae are most significant of all causes of taste and odor problems.
a) wide distribution
b) extensive number of species
"Musty odors" are usually the result of two compounds: a) geosmin and
b) methylisoborreol (MIB)
* both are produced by many of the blue green and Actinomycetes species
* both chemical compounds are resistant to oxidation

As algae grow and eventually die and decompose they affect the water quality in the following manners:
Dissolved oxygen, pH, hardness, alkalinity, all add additional organic materials which increase the ozone or chlorine demand, and may even require upstream carbon adsorption for removal

Some freshwater algae are toxic:
Anabaena (a blue-green) with skin problems; fish kills as the result of oxygen depletion &/or toxins by blue-green algal blooms; algal blooms have been related to gastrointestinal illnesses as a result of toxins released.

Decaying vegetation usually causes taste, odor, and color problems. The decaying process also releases methane (CH4), increasing the potential for THM formation. As operators we must optimize the upstream coagulation, flocculation, sedimentation processes in order to minimize the impacts of these elements on downstream processes. The goal is to improve taste and odor qualities by removing these organics prior to the disinfection process, especially if it is by chlorination.

Major problem algal groups:
GENERAL: There are 30,000 species of algae. Many create sour, sweet, or bitter tastes. Some others may create dry or metallic, or oily or slick, or harsh tastes.

Chlorophyeae - green algae; they produce a fishy or grassy odor and taste.

Cyanophyceae - blue-green algae; anabaena and aphanizomenon are examples of taste and odor producers in this group...this blue-green group is the worst of the offenders! This group is primarily the "slime producers."

Diatomaceae - green and brown colored cell walls; decomposing organisms create a fishy odor in the spring and fall. Asterionella is an excellent example of this group. This group is known to coat or bind the surface of any downstream filters, resulting in a) less water being produced and b) more frequent backwashing of the filters

Factors affecting algal activity:
a) water depth
b) nitrogen and phosphorous are the important nutrient contributors in the proliferation of algae in raw water sources.
c) body of water size
d) amount of shoreline in relation to depth
e) water temperature
f) watershed nutrient pool, extent of erosion
g) watershed soil type

TREATMENT
The treatment is best described as "preventative measures!" The prevention of taste and odors in the raw water source is the best course of action (treatment).

Watershed protection measures:
a) development
b) control of chemical applications and chemical use
c) nutrient control
d) isolation of naturally occurring taste and odor sources from the water course
e) elimination/isolation of swampy, wetland-type areas, if permitted!

Watershed, lake, reservoir treatment measures:
a) algal control with copper sulfate

The effectiveness depends upon:
1) Not all species of algae are affected by the same dosage rate of the copper sulfate, as some species are more resilient than others.
2) More effective if the pH is between 8 and 9
3) Trout and salmon sensitivity occurs with dosages >0.14 mg/L
4) most other fish, the sensitivity is >0.5 mg/L
5) apply in the reservoir with prescribed grid and proper dosage

Proper dosage rates and application:
1) if the alkalinity of the water being treated is > 50 mg/L in the top two feet of the raw water source, dose 5.4 lb/acre-ft which is equivalent to 1 mg/liter in the top two feet of water depth.
2) if the alkalinity of the water being treated is < 50 mg/L, a dosage rate of 0.9 lb/surface acre is applied, which use equivalent to 0.3 mg/L
3) Drag apply or spray apply the chemical. It causes a watercolor change from green to a grayish-white within minutes; there'll be no algae for two to three days

The quantity of nutrients, the temperature of the water in the upper reaches of the reservoir or impoundment, and the intensity of the sunlight obviously affects the re-growth rate.

b) chlorination... chloramination of smaller bodies of water
c) may place powdered carbon on the surface of small reservoirs to block photosynthesis; (be ready-this creates a mess); also helps to adsorb algal by-products
d) Pond or water impoundment covers: install to block the sunlight; install covers that do not contribute to taste or odor problems themselves and are approved by the health department for installation.

Raw Water Sources: other activities
a) sample and analyze for algal activity once per week and trend of the results
b) refer to previous years and data for comparison and anticipation of problems

Treatment plant control measures:
a) adsorption:
activated carbon dosing: GAC and PAC (fine particles) for both taste and odor control

b) chemical oxidations:
potassium permanganate dosage
ozonation dosage
chlorine dioxide (ClO2) dosing

Water Treatment Impacts
a) copper sulfate & other preventative measures
b) disinfection
c) recycle streams and wash water recovery

Aeration
The following is a summary of aeration influences on Taste and Odor Problems. For a complete discussion, please see the chapter on aeration.
Regarding "aeration"
a) precipitates iron and manganese
b) drives off certain dissolved gases such as carbon dioxide, hydrogen sulfide, and methane
c) if using compressors or blower's smaller bubbles are more effective than larger ones;
d) removes some taste or odor problems of some minerals, highly volatile materials, and some organic industrial wastes
e) only partially effective in oxidizing or removing algal by-products like oils, and tastes
f) high dissolved oxygen levels are corrosive, may cause air binding of filters; 2 to 4 mg/L is generally acceptable - recommend that dissolved oxygen be kept below the saturation level
g) can cause floating floc in sedimentation basins if over-aerated

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