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Oxygen is supplied to the mixed liquor in an aeration tank by dispersing bubbles into the tank. Oxygen transfer is a two stage process. First, oxygen is dissolved in the wastewater by aeration. Then, the dissolved oxygen is taken up by the microorganisms to metabolize the organic matter.
ANAEROBIC SLUDGE DIGESTION
See Sludge/Anaerobic Sludge Digestion
Bicarbonate is the major form of alkalinity. In excessive amounts, bicarbonates, in conjunction with calcium, may cause scale formation in heated waters. See Total Alkalinity.
The presence of calcium in water supplies results from passage through or over limestone, dolomite and other calcium containing deposits. Small concentrations of calcium carbonate combat corrosion of metal pipes by laying down a protective coating. Higher levels of calcium salts can precipitate when heated to form scale in boilers, pipes and cooking utensils. Calcium contributes to the total hardness of water. There is no aesthetic objective or maximum acceptable concentration set for calcium. See Total Hardness.
Carbonates can only exist if the pH of the water exceeds 8.3. This seldom occurs in natural waters. No aesthetic objective or maximum acceptable concentration has been set for carbonates alone. See Total Alkalinity.
Concentrations of chloride in excess of 250 mg/L may impart a salty taste to the water. Therefore, the aesthetic objective is set at a maximum of 250 mg/L. However, the salty taste is variable and dependent on the chemical composition of the water. No evidence has been found to indicate that ingestion of chloride is harmful to humans. A high chloride content may harm metallic pipes and structures as well as growing plants.
Effluent is the finished wastewater leaving the secondary clarifiers and entering the discharge pipe.
Hydroxide contributes to the total alkalinity of a water. It is almost never present in natural waters. See Total Alkalinity.
At levels above 0.3 mg/L, iron stains laundry and plumbing fixtures and causes undesirable taste. The precipitation of excessive iron causes a reddish brown color in the water. It may also promote the growth of iron bacteria, leaving a slimy coating in piping. The presence of iron bacteria can also cause a “rotten egg” odor in the water and a sheen on the surface of the water. The aesthetic objective is set at a maximum of 0.3 mg/L.
Magnesium is present in all natural waters and high levels in groundwater are probably the result of contact with magnesium-containing rock formations. Magnesium is a major contributor to water hardness and may also contribute undesirable tastes to drinking water. The aesthetic objective is set at a maximum of 200 mg/L.
Manganese can cause staining to plumbing and laundry, and undesirable tastes in beverages. Also, it may lead to the accumulation of bacterial growth in the piping. The aesthetic objective is set at a maximum of 0.05 mg/L.
Mixed liquor is a mixture of return activated sludge with the aerated primary effluent.
The maximum acceptable concentration of nitrate in drinking water is 45 mg/L. In excessive amounts it contributes to the illness known as methemoglobinemia in infants. Sources of nitrate in water include decaying plant or animal material, agricultural fertilizers, manure, domestic sewage or geological formations containing soluble nitrogen compounds.
Natural waters usually have pH values in the range of 4 to 9 and most are slightly basic (i.e. greater than 7) because of the presence of bicarbonates and carbonates. Corrosion effects may become significant at a pH below 6.5 and scaling may become a problem at a pH above 8.5. For this reason an acceptable range for drinking water pH is from 6.5 to 9.0.
Potassium ranks seventh among the elements in order of abundance, yet its concentration in most drinking waters seldom reaches 20 mg/L. There is no maximum acceptable concentration or aesthetic objective set for this element.
Is performed in tanks where the wastewater is slowed down enough to allow particulate solids to settle out of suspension. These solids are used in the aeration tanks as activated sludge (mixed liquor). In these tanks floating materials (fat/grease) are prevented from entering the discharge liquid and are collected by a mechanical skimmer. Secondary clarifiers are usually used as the finishing process in wastewater treatment. We have three clarifiers.
SECONDARY WASTEWATER TREATMENT
Secondary wastewater treatment is a wastewater treatment process used to convert dissolved or suspended materials into a form more readily separated from the wastewater being treated. Usually the process follows primary treatment by sedimentation. The process commonly is a type of biological treatment process followed by secondary clarifiers that allow the solids to settle out from the wastewater being treated -- that is exactly what we do -- the process consists of our aeration tanks and our secondary clarifiers.
SLUDGE/ANAEROBIC SLUDGE DIGESTION
Sludge is the solids in the wastewater. The purpose of sludge digestion is to convert bulky, odorous, raw sludge to a relatively inert material that can be rapidly dewatered with the absence of obnoxious odors. The bacterial process consists of two successive processes that occur simultaneously in digesting sludge. The first stage consists of breaking down large organic compounds and converting them to organic acids along with gaseous by-products like carbon dioxide, methane, and trace amounts of hydrogen sulfide. This step is performed by a variety of facultative bacteria operating in an environment devoid of oxygen. In order for digestion to occur, second-stage gasification is needed to convert the organic acids to methane and carbon dioxide. Stability of the digestion process relies on proper balance of the two biological stages. We use a primary and a secondary digester to complete this process.
Weathering of salt deposits and contact of water with igneous rock provide natural sources of sodium. Another potential source of sodium in water supplies is the water-softening process which replaces calcium and magnesium (hardness) with sodium. Persons on sodium restricted diets should consult with physicians. The aesthetic objective is set at a maximum of 300 mg/L.
Specific conductivity is a measure of the ability of water to carry an electric current. This ability depends on the presence of ions and is therefore an indication of the concentration of ions (i.e. dissolved solids) in the water. Waters with high dissolved solids generally are of inferior palatability and also may leave a white film on dishes, etc. The aesthetic objective for total dissolved solids is 1500 mg/L and is approximately equivalent to a conductivity of 1500 uS/cm.
Sulfate occurs naturally in water and may be present in natural waters in concentrations ranging from a few to several thousand mg/L. Concentrations in excess of 500 mg/L, especially if the magnesium content is also high, may have a laxative effect or cause gastrointestinal irritation. It may also result in a noticeable taste. The aesthetic objective is set at a maximum of 500 mg/L.
SUM OF IONS / TOTAL DISSOLVED SOLIDS
Sum of ions indicates the concentration of ions in the water (i.e. dissolved solids). The aesthetic objective for total dissolved solids is a maximum of 1500 mg/L. See Specific Conductivity.
Alkalinity is a water's acid-neutralizing capacity and is primarily a function of carbonate, bicarbonate and hydroxide content. Excessive alkalinity levels may cause scale formation. The aesthetic objective is set at a maximum of 500 mg/L.
TOTAL COLIFORM BACTERIA
The presence of coliform organisms is an indication of pollution. The maximum acceptable concentration for total conforms is no organisms detectable per 100 mL of sample. If any coliform organisms are detected, the site should be resampled, and if the presence of coliforms is confirmed, the appropriate corrective action should be taken.
Water hardness is mainly caused by the presence of calcium and magnesium and is expressed as the equivalent quantity of calcium carbonate. Scale formation and excessive soap consumption are the main concerns with hardness. When heated, hard waters have a tendency to form scale deposits. Depending on the interaction of other factors such as pH and alkalinity, hardness levels between 80 and 100 mg/L are considered to provide an acceptable balance between corrosion and incrustation. Water supplies with a hardness greater than 200 mg/L are considered poor but tolerable; those in excess of 500 mg/L are unacceptable for most domestic purposes. Because water softening may introduce undesirably high quantities of sodium into drinking water, it is recommended that a separate unsoftened supply be used for drinking and cooking. The aesthetic objective is set at a maximum of 800 mg/L.
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