Texas Basic Waste Water Operations Ch#03 Waste Water Characteristics

By weight, wastewater is 99.9% water. Various solids make up only 0.1% of wastewater. Since wastewater is mostly water, it is considered to weigh the same as clean water, 8.34 lbs/gal.

Laboratories report some wastewater characteristics as milligrams per liter (mg/L) or parts per million (ppm). Milligrams per liter equals parts per million. Wastewater characteristics are divided into four primary groups bacteriological, physical, chemical, and radiological.

Wastewater characteristics are divided into four primary groups bacteriological, physical, chemical, and radiological.

Bacteria are living organisms seen only with a microscope, but their effect is seen by the eye and detected by chemical tests. Bacteria are present in soil, air, and water. There are millions of bacteria in a milliliter of domestic wastewater. Many bacteria live in decaying organic matter and in the intestines of humans and animals. Some bacteria cause disease—these and other disease-causing microorganisms are called pathogens.

One way to classify bacteria is by the way they use oxygen. (aerobic, anaerobic, and facultative.)

Anaerobic bacteria cannot live when Dissolved Oxygen (DO) is present. They use chemically combined oxygen such as nitrates (NO3) and sulfates (SO4). They are active in anaerobic digestion and are associated with processes involving decomposition, odor, and septicity.

Facultative bacteria use dissolved oxygen or chemically combined oxygen. They can adapt to aerobic or anaerobic conditions. Because they adapt to aerobic or anaerobic conditions, facultative bacteria are the most common bacteria in wastewater treatment.

Raw domestic wastewater is fresh or septic, depending on the presence or absence of dissolved oxygen. Dissolved Oxygen (DO) in raw wastewater comes from the water supply, not from bacteria or chemicals. DO in wastewater indicates fresh wastewater. Public drinking water supplies are high in DO, which becomes available to bacteria in the collection system.

Septic wastewater is dark with a disagreeable odor. Septic wastewater contains no dissolved oxygen. Septic wastewater contains odorous gases produced by bacteria. Bacteria change wastewater from fresh to septic by depleting the dissolved oxygen as they consume organic material.

Chemical characteristics of wastewater include solids, grease, Dissolved Oxygen (DO), Oxygen (O2) demand, pH, and gases.

Suspended solids are those that are not dissolved in water. Suspended solids make up about 30% of the total solids. Filtering removes suspended solids. Total suspended solids are abbreviated as TSS. Dissolved solids in water are able to pass through a filter. Dissolved solids make up about 70% of the total solids.

Settleable solids are suspended solids, heavy enough to settle after standing for a time. Settleable solids should be reported as milliliters per liter (ml/L). The settleable solid test determines settling tank efficiency.

The types of solids are total solids, suspended solids, dissolved solids, settleable solids, inorganic solids, and organic solids

Organic material comes from plants, animals, or humans, living or once living. Examples of organics are sugar, butter, leather, and paper. Organic or volatile (combustible) solids are determined by burning the residue from the total solids test or the filter from the TSS test. The ash that remains after burning is an inorganic (or fixed) solid.

living or once living. Examples of organics are sugar, butter, leather, and paper. Organic or volatile (combustible) solids are determined by burning the residue from the total solids test or the filter from the TSS test. The ash that remains after burning is an inorganic (or fixed) solid.

Organic material is suspended or dissolved and makes up about 65% of the total suspended solids. Organic material produces odor as it decays and is stabilized by bacteria. Organics consist of carbohydrates, proteins, and greases. Carbohydrates decompose first due to simplicity. Decay by aerobic bacteria produces carbon dioxide and water. Anaerobic decay produces hydrogen sulfide, ammonia (NH3), methane, carbon dioxide, or organic acids. Protein is slow to decompose due to complexity. Protein aerobically decays into nitrates (NO3), carbon dioxide, and water, and anaerobically decomposes into ammonia and methane. Fecal matter is about 85% protein, and urine is about 35% protein.

Dissolved Oxygen (DO) in raw wastewater comes from the water supply, not from bacteria or chemicals. DO in wastewater indicates fresh wastewater. Public drinking water supplies are high in DO, which becomes available to bacteria in the collection system.

Dissolved Oxygen (DO) in raw wastewater comes from the water supply, not from bacteria or chemicals. DO in wastewater indicates fresh wastewater. Public drinking water supplies are high in DO, which becomes available to bacteria in the collection system.

Water DO depends on the water temperature. As water temperature rises, DO content decreases. As water temperature lowers, DO content increases.

Dissolved Oxygen (DO) in raw wastewater comes from the water supply, not from bacteria or chemicals. DO in wastewater indicates fresh wastewater. Public drinking water supplies are high in DO, which becomes available to bacteria in the collection system. Water DO depends on the water temperature. As water temperature rises, DO content decreases. As water temperature lowers, DO content increases. This is an inverse relationship (Figure 3.3). Saturation means the water contains as much DO as it can hold at a given temperature and pressure. Perform the DO test as soon as the sample is taken as oxygen content changes quickly.

Biochemical Oxygen Demand (BOD). The BOD test measures the oxygen depleting effect of wastewater on the receiving stream. The BOD indicates wastewater strength. The test (Figure 3.4) measures oxygen consumed as organics are oxidized biologically and chemically during five days of incubation at 20°C (68°F). The BOD is typically referred to as BOD5 because of the five-day incubation period. BOD in raw domestic wastewater varies from 100 to 300 mg/L. NOTE: BOD5 specifically refers to the 5 day test while BOD refers to a specific value given as a result of the BOD5 test or Biochemical Oxygen Demand in general so the answer should be BOD5. BOD and BOD5 should not be used interchangeably but frequently are by TEEX.

The BOD5 test measures oxygen consumed as organics are oxidized biologically and chemically during five days of incubation at 20°C (68°F). NOTE: mthis is what i mean when i say BOD and BOD5 should not be used interchangeably. if they had said it as i had in this explanation it would have given away half the answer and eliminated incorrect options.

The population equivalent is defined as 0.17 pounds of BOD a human produces per day. The population equivalent factor is used to mathematically determine the number of humans (population) contributing waste. Additionally, if the population factor is known, the BOD can be mathematically determined. The TCEQ and EPA use the BOD test to determine treatment efficiency. Generally, the test is not useful for daily process control because it takes five days to complete. However, it can be useful if BOD analysis is done on a routine basis and results are generated on a daily basis.

pH measures acidity or basicity of a solution. The scale ranges from 0 to 14 with 7.0 being neutral. pH stands for potential hydrogen ion concentration.

Acidic water has a pH below 7.0, and alkaline or basic water has a pH above 7.0.

Dangerous gases are produced during bacterial decomposition of organics in wastewater. These gases include the following: • Methane (CH4) • Hydrogen sulfide (H2S) • Carbon dioxide (CO2)

Methane (CH4). Anaerobic decomposition of organic matter produces methane. It is colorless, odorless, explosive, and does not support life. Anaerobic digester gas is about 65% methane and 35% carbon dioxide. The methane can be used to heat the anaerobic digester or to fuel equipment. Methane is natural gas, the same gas used in homes and industry.

Hydrogen sulfide (H2S). Anaerobic decomposition of organic sulfur compounds produces hydrogen sulfide. This gas is toxic, has a rotten egg odor, is combustible, and slightly heavier than air. Hydrogen sulfide corrodes metal and concrete. Use respiratory protection such as a Self-Contained Breathing Apparatus (SCBA) or ventilating equipment in the presence of hydrogen sulfide.

Carbon dioxide (CO2). Decomposition of organic carbonaceous material produces carbon dioxide and water. Carbon dioxide is odorless, colorless, heavier than air, and corrosive when mixed with water. This gas does not support combustion and, in sufficient concentration (>10%), is suffocating. Use a SCBA in the presence of carbon dioxide or ventilate the atmosphere.

Sampling is the basis of good treatment, but careless sampling can cause a treatment error. When sampling for permit reporting, follow procedures specified in the permit. Good results depend on a representative sample, proper technique, and preserving the sample. A good sample depends on the sampling point.

Select a point where mixing is thorough and the wastewater quality is uniform. Mixing is important because heavy solids settle and light solids float. If a gallon sample is to represent a million-gallon flow, it must be uniform.

Collect a grab sample at any point or time. Grab samples test wastewater conditions at a given time or treatment point.

If testing the efficiency of a plant unit, collect an influent sample at any time, and an effluent sample at a time corresponding to the unit’s detention time. This is a timed grab sample.

A composite sample consists of several portions collected at intervals and mixed together. The amount of sample used in testing must be proportional to the flow at the time of sampling. This type of sample is representative of the flow and is used for state monitoring requirements such as BOD and solids tests. Storing composite samples in temperatures between 38° and 40°F (near 4°C) will prevent bacterial decomposition prior to testing. The following formula may be used to determine a composite sample: ((Flow (MG) at time of sample X Total volume (mL)) / (Average flow (MG) X # of samples)) NOTE: MG = Millions of Gallons