TABLE 141 Types of Biochemical Oxygen Demand

Type

Acronym

Total

Particulate

Soluble

Colloidal

Carbonaceous

Nitrogenous tBOD

pBOD

sBOD

coBOD

cBOD

nBOD

Figure 14.1 Types of BOD. There are several types of BOD that enter an activated sludge process. Total BOD is the sum of all types of BOD found in the influent to the activated sludge process. Forms of particulate BOD are the solids such as cellulose that can be degraded. Much particulate BOD is removed in the primary clarifier, and unless adequate HRT is provided in the aeration tank, par-ticulate BOD is adsorbed to the surface of floc particles in the aeration tank and is not degraded. Forms of nonparticulate BOD are soluble BOD such as ammonia ions and sugars and colloids such as proteins and lipids. Soluble BOD passes through the primary clarifier into the aeration tank. Colloidal BOD that is adsorbed to solids that settle in the primary clarifier is removed in the primary clarifier. Colloidal BOD that enters the aeration tank, like particulate BOD, is not degraded unless adequate HRT is provided. Colloidal BOD is adsorbed to the surface of floc particles in the aeration tank. There are two forms of soluble BOD: nitrogenous and carbonaceous. Nitrogenous BOD consists of ammonium ions and nitrite ions. These two ions can be oxidized under appropriate conditions in the aeration

Figure 14.1 Types of BOD. There are several types of BOD that enter an activated sludge process. Total BOD is the sum of all types of BOD found in the influent to the activated sludge process. Forms of particulate BOD are the solids such as cellulose that can be degraded. Much particulate BOD is removed in the primary clarifier, and unless adequate HRT is provided in the aeration tank, par-ticulate BOD is adsorbed to the surface of floc particles in the aeration tank and is not degraded. Forms of nonparticulate BOD are soluble BOD such as ammonia ions and sugars and colloids such as proteins and lipids. Soluble BOD passes through the primary clarifier into the aeration tank. Colloidal BOD that is adsorbed to solids that settle in the primary clarifier is removed in the primary clarifier. Colloidal BOD that enters the aeration tank, like particulate BOD, is not degraded unless adequate HRT is provided. Colloidal BOD is adsorbed to the surface of floc particles in the aeration tank. There are two forms of soluble BOD: nitrogenous and carbonaceous. Nitrogenous BOD consists of ammonium ions and nitrite ions. These two ions can be oxidized under appropriate conditions in the aeration rotifers and free-living nematodes consume bacteria and protozoa. Collectively the bacteria and the higher life forms make up the food web in the activated sludge process (Figure 14.3).

Protozoa that are commonly found in activated sludge processes that nitrify are Epistylis and Vorticella. Besides rotifers and free-living nematodes, other multicellular, microscopic organisms found in activated sludge process that nitrify include bristleworms, flatworms, and waterbears (Figure 14.4). In order for these higher life forms to be present and active in an activated sludge process, the process must be stable. Activated sludge processes that nitrify are stable; that is, they contain a relatively high concentration of MLVSS and dissolved oxygen, low e¿uent cBOD, and no inhibition or toxicity.

The higher life forms are strict aerobes and are free-living soil and water organisms that enter the activated sludge process through I/I. The organisms are sensitive to changes in dissolved oxygen concentration and the presence of inhibitory or toxic wastes. Because nitrifying bacteria also are strict aerobes and are sensitive to changes in dissolved oxygen concentration and the presence of inhibitory or toxic wastes, the presence of higher life forms is expected during nitrification, and their absence or inactivity is expected when nitrification is lost.

Substrates immediately available to the bacteria and the food web consist of soluble cBOD. This type of BOD passes quickly through the cell wall and cell membrane of bacteria and is easily degraded. Forms of soluble cBOD that enter bacterial cells include simple acids, alcohols, and sugars.

Particulate BOD is made available to bacteria and the food web only after it has been solublized into simple molecules that can enter the bacterial cell. Solublization of pBOD occurs if adequate hydraulic retention time (HRT) is provided in the aeration tank and the g-

tank. Carbonaceous BOD consists of two forms: recognizable and nonrecog-nizable. Recognizable forms of carbonaceous BOD are simplistic one-, two-, three-, or four-carbon unit acids and alcohols. These forms of BOD can enter the cells of nitrifying bacteria and inhibit the enzymatic systems of the bacteria that oxidize ammonium ions and nitrite ions. Nonrecognizable forms of BOD are numerous and include sugars, amino acids, and long-chain acids and alcohols. These forms of BOD cannot enter the cells of nitrifying bacteria and cause inhibition. Recognizable and nonrecognizable forms of BOD can be oxidized under appropriate conditions in the aeration tank.

Figure 14.2 Ciliated protozoa, rotifers, and free-living nematodes. Examples of ciliated protozoa that commonly are found in an activated sludge process include the free-swimming ciliates Coleps (a) and Litonotus (b), the crawling ciliates Aspidisca (c) and Euplotes (d), and the stalked ciliates Carchesium (e) and Opercularia (f). Free-swimming ciliates have cilia on all surfaces of the body, while crawling ciliates only have cilia on the ventral or "belly" surface, and stalked ciliates have cilia only around the mouth opening. Rotifers and free-living nematodes (worms) are found less frequently and in small numbers in an activated sludge process than ciliated protozoa. Examples of rotifers that commonly are found in an activated sludge process include Daphnia (g) and Philodina (h). Free-living nematodes are found in the activated sludge process in an elongated form (i) and coiled form (j).

Figure 14.2 Ciliated protozoa, rotifers, and free-living nematodes. Examples of ciliated protozoa that commonly are found in an activated sludge process include the free-swimming ciliates Coleps (a) and Litonotus (b), the crawling ciliates Aspidisca (c) and Euplotes (d), and the stalked ciliates Carchesium (e) and Opercularia (f). Free-swimming ciliates have cilia on all surfaces of the body, while crawling ciliates only have cilia on the ventral or "belly" surface, and stalked ciliates have cilia only around the mouth opening. Rotifers and free-living nematodes (worms) are found less frequently and in small numbers in an activated sludge process than ciliated protozoa. Examples of rotifers that commonly are found in an activated sludge process include Daphnia (g) and Philodina (h). Free-living nematodes are found in the activated sludge process in an elongated form (i) and coiled form (j).

Figure 14.3 The food web. Within the activated sludge process or aeration tank there is a food web in which energy and carbon are transferred "upward" from one organism to another organism. The basis for the food web is the BOD that enters the aeration tank. The BOD contains carbon and energy. The energy is found in the form of chemical bonds. As bacteria break the chemical bonds, the bacteria obtain carbon and energy for life, and they reproduce. Protozoa consume the bacteria. The carbon and chemical energy within the bacteria are transferred to the protozoa. There are five groups of protozoa that eat bacteria. These groups are the amoebae, flagellates, free-swimming ciliates, crawling ciliates, and stalked ciliates. Higher life forms (rotifers and free-living nematodes) consume the protozoa. The carbon and chemical energy within the protozoa is transferred to the rotifers and free-living nematodes. The carbon and chemical energy within the rotifers and free-living nematodes is again transferred to a higher life form— the bristleworms. The transfer of carbon and energy throughout a community of organisms is known as the food web.

Figure 14.3 The food web. Within the activated sludge process or aeration tank there is a food web in which energy and carbon are transferred "upward" from one organism to another organism. The basis for the food web is the BOD that enters the aeration tank. The BOD contains carbon and energy. The energy is found in the form of chemical bonds. As bacteria break the chemical bonds, the bacteria obtain carbon and energy for life, and they reproduce. Protozoa consume the bacteria. The carbon and chemical energy within the bacteria are transferred to the protozoa. There are five groups of protozoa that eat bacteria. These groups are the amoebae, flagellates, free-swimming ciliates, crawling ciliates, and stalked ciliates. Higher life forms (rotifers and free-living nematodes) consume the protozoa. The carbon and chemical energy within the protozoa is transferred to the rotifers and free-living nematodes. The carbon and chemical energy within the rotifers and free-living nematodes is again transferred to a higher life form— the bristleworms. The transfer of carbon and energy throughout a community of organisms is known as the food web.

Flatworms Process

Figure 14.4 Bristleworm, flatworms, and waterbears. The bristleworm (a) in the activated sludge process is segmented and possesses hairy structures or bristles that enable the worm to move through the soil. Flatworms appear in several interesting forms (b and c). The worm is ''flat'' only on the ventral or "belly" surface, while the curved dorsal or "back" surface may possess "spines" (b) or scalelike

Figure 14.4 Bristleworm, flatworms, and waterbears. The bristleworm (a) in the activated sludge process is segmented and possesses hairy structures or bristles that enable the worm to move through the soil. Flatworms appear in several interesting forms (b and c). The worm is ''flat'' only on the ventral or "belly" surface, while the curved dorsal or "back" surface may possess "spines" (b) or scalelike

TABLE 14.2

Examples of Recognizable Soluble cBOD

cBOD

Chemical Formula

Number of Carbon Units

Methanol

CH3OH

1

Methylamine

CH2NH2

1

Ethanol

CH3CH2OH

2

n-Propanol

ch3ch2ch2oh

3

/-Propanol

(CH3)2CHOH

3

n-Butanol

CH3(CH2)2CH2OH

4

t-Butanol

(CH3)3COH

4

Ethyl acetate

CH3CO2C2H5

4

Aminoethanol

CH3NH2CH2OH

2

necessary enzymes for solublizing pBOD are produced. For example, cellulose cannot enter bacterial cells unless the cellulase enzyme is produced and solublizes it.

Colloidal BOD is made available to bacteria and the food web only after it too has been solublized into simple molecules that can enter the bacterial cell. Colloidal BOD is solublized in similar fashion as pBOD. Examples of coBOD are proteins and lipids. When proteins are solublized, amino acids are produced. When lipids are solu-blized, fatty acids are produced. Simple amino acids and simple fatty acids can enter bacterial cells.

Particulate BOD and colloidal BOD that are not solublized in the aeration tank are wasted from the tank. Wasting of pBOD and coBOD occurs when each form of BOD is adsorbed to floc particles, and the floc particles are wasted from the activated sludge process to a digester. It is in the digester where large quantities of pBOD and coBOD are degraded.

Soluble cBOD consists of two types, recognizable and nonrecog-

nizable. The difference between these two types of cBOD is based on g-

plates (c). Many flatworms have a forked tail. Waterbears are an odd-looking organism. From the dorsal (d) or lateral (e) appearance of the waterbear, four appendages or ''legs'' can be observed. Clawlike structures may be found at the end of each appendage. Bristleworms, flatworms, and waterbears are soil and water organisms that enter activated sludge processes through inflow and infiltration. They are strict aerobes and are ''sensitive'' to the lowest concentrations of inhibitory or toxic wastes. Therefore these higher life forms are found in large, active numbers under stable operating conditions.

their ability to inhibit nitrification. Recognizable, soluble forms of cBOD are simplistic molecules that are able to enter the cells of nitrifying bacteria and inactivate their enzyme systems (Table 14.2). This form of cBOD must be degraded significantly or completely by organotrophs in the aeration tank in order for nitrify bacteria to oxidize ammonium ions and nitrite ions. Nonrecognizable, soluble forms of cBOD are large, complex molecules such as proteins and starches that are not able to enter the cells of nitrifying bacteria.

Although all bacteria require water, only a few actually require dissolved oxygen. The lack of dependence of bacteria on dissolved oxygen is due in part to the fact that oxygen is not highly soluble in water. Therefore most bacteria are capable of using a molecule other than dissolved oxygen for the degradation of substrate, that is, respiration.

Dissolved oxygen is the free or chemically uncombined oxygen in wastewater. Since wastewater or the bacterial degradation of wastes has avidity for oxygen, oxygen dissipated quickly in wastewater. Nitrification contributes to the rapid loss of oxygen within wastewater.

Several important oxygen requirement or tolerant groups of bacteria are recognized (Table 15.1). Significant bacterial groups with respect to their oxygen requirement or tolerance include strict or obligate aerobes, such as nitrifying bacteria and some floc-forming bacteria; facultative anaerobes, such as many organotrophs; and strict or obligate anaerobes, such as methane-forming bacteria.

Strict aerobes use only free molecular oxygen for respiration, while facultative anaerobes use free molecular oxygen for aerobic respiration or substitute another molecule, for example, nitrite ion or nitrate ion, for anaerobic respiration. Many facultative anaerobes also are able to ferment. Fermentation, for example, alcohol production, occurs when bacteria use one organic molecule to degrade another organic molecule.

Oxygen is used in the aeration tank by bacteria for three major

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  • Angelico
    What is particulate bod total bod soluble bod?
    1 year ago

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