fltil ii LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN (oZ- or O LU O - XI < - 2 CD LU |_ < or q: lu < CVJ 5 5 ^ < t UJ i CM LU or 3 Ll o LU < cr o -j < UJ LU h- LU CO X CO < LU or i- SUnOH l o>i o « ^ 5 u5 < Q) -^ "»* \ i *: * -^ 5 ^. ^ ^ O O 00 o CD O O C\J O sanoH 1 d>i express the total removal rate: C It =e- (ka * kb ' )l ■f-o «> where kb, is the first order biological removal rate. On the other hand, if the stripping is first-order and the biological removal is zero-order, Equation 6 expresses the total removal rate: V c o-«" ta(t) Ti&- (e " ka4/r stripping -17.00 cc/min/l. 60 50 40 30 Air stripping + biologicol treat. - (1st order kinetics) Air stripp/ng-48.0Q_ cc/min/l. (Zero order kinetics ) \ 2 4 6 8 AERATION TIME HOURS 10 FIGURE 5- REMOVAL OF ACETONE 12 100 90 - Ld O QA oc OU LU CL *• o O 70 \ 4— o f CD z 60 z < 2 UJ ir 50 q o o 40 30 2 4 6 8 AERATION TIME, HOURS 10 FIGURE 6 -REMOVAL OF BUTAN0NE 13 of BOD removed. If sufficient air is applied to obtain good "rolling action' 1 turbulence, then as much as three to four times this amount of air would not significantly improve the removal of volatile compounds. Also, few consti- tuents in a composite petrochemical waste are likely to be as volatile as the substrates acetone and butanone which were used in this study of combined physical stripping and biological treatment phenomena. Finally, it is recommended that, if the activated sludge process is to be used for biological treatment of petrochemical wastes, the plant should be designed for biological removal only and no allowance should be made for physical stripping unless laboratory studies indicate significant stripping can be effected. Any small amount of stripping which occurs would simply provide a small factor of safety against overloading. }k PART 2 TREATMENT OF NITROGEN DEFICIENT WASTES BY A MODIFICATION OF THE ACTIVATED SLUDGE PROCESS 15 ABSTRACT A method of treating nitrogen deficient wastes with a modification of activated sludge is proposed. Active bacterial cells are grown in one unit with nitrogen supplementation, and the excess sludge from this unit is utilized in the activated aerator to remove C.O.D. without any nitrogen supplementation. An F/M ratio of k was found to be optimum for the nitrogen supplemented unit whereas a ratio of 2 is needed for the activated aerator. This would save 50 percent of the nitrogen cost. High synthesis is en- couraged which results in savings of oxygen consumption compared to a con- ventional activated sludge. The time taken for 90 percent C.O.D. removal was 8 hours or less in many cases. Equations were presented for predicting the excess sludge with glucose, phenol and acetate substrates under nitrogen supplemented and nitrogen deficient conditions. 16 I. INTRODUCTION A. Nature and Importance of the Problem During the last two decades, industrial wastes have contributed increasingly to waste disposal problems. In many places industrial wastes are treated in conjunction with the domestic sewage. On the other hand, many sanitary districts have restricted or refused to accept the industrial wastes because of the treatment problems encountered. A single industry frequently discharges liquid waste with an organic load exceeding that con- tributed by a whole city of 25,000 to 50,000 inhabitants. Many of the chemical industries have considerable volumes of liquid wastes. Since the chemical reactions are not usually 100 percent efficient, a part of the various raw materials, reactants and products finds its way into the waste waters. Drinking water resources are becoming heavily polluted and it is becoming more imperative that these wastes be treated to reduce the pollutional load on the streams. Otherwise, these effluents pose a threat to the accustomed high quality of water available for consumption and necessary for continued industrial expansion. The petrochemical industries along with many others discharge a variety of organic materials. A common peculiarity of these wastes is that they are high in B.O.D. value and deficient in certain essential elements needed for normal biological stabilization. Nitrogen is the principal element often found to be deficient for the biological stabilization of industrial wastes. The sanitary engineer is confronted with such problems and is entrusted with the task of economically treating such wastes. 17 B. Purpose and Scope of the Study The object of this work was to determine the feasibility of treating petrochemical wastes, deficient in nitrogen, by a modification of the activated sludge process shown schematically below. PRIMARY SETTLING TANK NITROGEN ACTIVATED AERATION TANK RETURN SLUDGE -^ AERATOR CONVENTIONAL ACTIVATED SLUDGE It is known that bacterial cells can be placed in a nitrogen deficient substrate and aerated with subsequent reduction in filtrate chemical oxygen demand (C.O.D.) and increase in mixed liquor suspended solids (M.L.S.S.). It is reported that the substrate is converted into polysaccharides and such a conversion requires less oxygen. The resulting sludge is reported to be resistant to further bacterial degradation. Because of this, the inert polysaccharide sludge could be disposed of easily. Considerable savings 18 in the amounts of nitrogen to be supplemented are expected in this process. The process as shown above consists of dividing the primary effluent into two parts. One part is supplemented with a nitrogen source and is treated in a conventional activated sludge process. The excess sludge from this plant becomes the return sludge for the activated aerator. This unit has no nitrogen supplementation. The sludge from this unit after secondary sedimentation is wasted for final disposal. Petrochemical industries discharge a variety of organic chemicals. A study with a mixture of compounds would not be convenient from the stand- point of process parameters like filtrate C.O.D., M.L.S.S., oxygen uptake, etc. Hence, it was decided to study the process using pure compounds representative of those likely to occur in such wastes. Accordingly, two pure compounds were selected, phenol and acetate. Phenol was chosen to represent the aromatic ring structures and acetic acid was chosen to repre- sent the aliphatic straight chain compounds. A third substrate, glucose, was used as a check to compare with the results of past workers investi- gating the conventional activated sludge process. An acclimated culture developed on each of the above three substrates was maintained at equili- brium conditions to provide the seed for Warburg studies, which were in- tended to verify the feasibility of the process. The scope of the work consisted of determining the oxygen uptake, reduction in filtrate C.O.D. and increase in M.L.S.S. in a nitrogen de- ficient system, and comparing it with that of a nitrogen supplemented system. An attempt was made to find out the optimum C.O.D. /M.L.S.S. (F/M) ratio for maximum process economy with each of the three substrates. Another phase of the investigation was to find out the duration that a given initial M.L.S.S. concentration would continue to degrade the substrate in the absence of any external nitrogen source and with 100 percent return of the sludge. 19 I I. LITERATURE SURVEY A. Activated Sludge The activated sludge process has been one of the best methods of treating wastes for the last 50 years. Fundamentally it is a biological process, in which the heterogeneous spectra of organisms are brought into intimate contact with the waste in the presence of sufficient dissolved oxygen. It has been shown that the organisms utilize the waste for two basic purposes. A portion of the substrate removed by activated sludge is used for cell synthesis and storage products and consumes little oxygen (22). The remainder undergoes oxidation, which is called respiration, to supply the required energy for the metabolism. Total B.O.D. removal = oxidation + synthesis (1) (respiration) (growth) It is known that the respective amounts channelled into the above processes depend on a number of conditions: (1) The type of organism and its state of activity (phase of growth) (2) The total number of organisms (initial M.L.S.S.) and its acclimation to the waste (3) The nutritional aspects of the waste and the availability of dissolved oxygen. The mechanism of removal of dissolved and suspended solids from the waste has been described in the literature. The major steps in the biochemistry of the oxidative system are summarized by Weston and Eckenfelder (20) as fol lows: 20 (1) Initial high rate removal of B.O.D. on contact with biologically active sludge due to reactions between the enzymes and the organic constituents. (2) Removal of B.O.D. in direct proportion to cell growth . (3) Oxidation of biological cell material (endogenous respiration) with concurrent low rate of B.O.D. remova 1 . Activated Aeration: Chasick (1) has described a modification of the activated sludge process called activated aeration. The process was an outgrowth of the idea of re-utilizing the excess activated solids wasted from the secondary settling tank of a conventional activated sludge process. The object of this modification was to partially treat more sewage and ob- tain greater B.O.D. removal with less total oxygen uptake. The activated aeration system, shown diagrammat ica 1 ly earlier, was used in New York to treat domestic sewage having low B.O.D. The effluent was of intermediate quality and suitable for the local conditions. A portion of the primary effluent was treated in a conventional activated sludge unit. The excess sludge wasted from the conventional activated sludge process was active and still capable of utilizing organic matter. Activated aeration took advantage of this capacity of the waste sludge to remove organic material on a one-pass, no-recycle basis. The waste sludge was transferred to another aeration tank called an activated aerator into which the remaining portion of the primary effluent was ad- mitted. The M.L.S.S. concentration was very low in the tank (75 mg/£) . The contents were aerated for two hours and allowed to settle. There was good synthesis and the final M.L.S.S. were 225 mg/0 . The sludge from this process was wasted. The B.O.D. removal was 70 to 75 percent and the overall 21 efficiency of such a split treatment was about 82 percent. Considerable savings in air compression power costs and reduction in excess sludge volume were claimed to be the advantages of this process. According to Torpey and Chasick (18) the efficiency of the plant was slightly improved when the detention time was increased to four hours. Process stability was said to have been achieved and flexibility of operation realized. This system has worked well with dilute sewage in New York for the last eight years . B. Nutritional Requirements of Activated Sludge It is generally conceded that the removal of organic pollutants from waste water is accomplished primarily by bacteria and that rapid re- moval depends upon unrestricted bacterial reproduction. The removal rate would be greatest when the waste is properly balanced nutritionally. For the bacteria in activated sludge, in addition to a carbon source, nitrogen, phosphorus and sulfur are considered to be the elements needed in measurable quantities. The carriage water generally contains the necessary sulfur in the form of sulfates and also other trace elements. Domestic sewage is nutritionally balanced since it contains excess nitrogen and phosphorus. With industrial wastes, much attention has been given to the nutritional aspects so that they can be successfully treated by the activated sludge process . Helmers et a 1 . (8), while working with sulfite liquor, reported a B.O.D./ni trogen ratio of 20 and B.O.D. /phosphorus ratio of 100, was necessary for successful removal of waste by the activated sludge process. They also reported that the sludge filtering characteristics may influence the amount of nutrients to be added. Poorer floe formation and less B.O.D. removal 22 was reported by Greenberg and Kaufman (6) in phosphorus deficient wastes. Critical phosphorus requirement for development of activated sludge was given as 1/238 of the B.O.D. Helmers et a 1 . (9) reported that the nitrogen requirement directly affected the B.O.D. removal and sludge growth. Rate of B.O.D. reduction was not affected until the ratio of nitrogen/volatile matter fell below 7 percent. The critical nitrogen requirement for cotton- i kiering waste was reported as J>-k lbs/100 lbs B.O.D. removal. The nitrogen requirement has been observed by Weinberger (19) to decrease with increasing aeration solids for a given B.O.D. loading due to less synthesis. The nitrogen requirement diminished rapidly as B.O.D. loading decreased and increased to maximum of about 5 lbs per 100 lbs of B.O.D., regardless of the aeration solids concentration. All of the above information was for conditions allowing cell reproduct ion, and normal proto- plasm formation was the result. Available Nitrogen: According to Sawyer (19) only nitrogen present in the form of ammonia is considered as 100 percent available for the bacteria. Urea must be hydrolysed before it is available as a nitrogen source. Helmers et a 1 . (8) found that nitrogen present in the form of organic nitrogen was not completely available. They indicated 30 to 70 percent of the organically bound nitrogen was available to the bacteria, depending on the character of the waste. Symons and McKinney (17) worked with activated sludge using acetate as the substrate and found that nitrogen in any of the three forms, ammonia, nitrate, and nitrite, could be used as a source of nitrogen. Symons and McKinney (17) also concluded that even in the absence of nitrogen the purification process continued and the sludge removed the substrate. However, the final product of the bacterial metabol i sm was no longer true protoplasm but a different product, high in polysaccharides. 23 Symons (17) has shown that partial satisfaction of the nitrogen requirement could still result in a stable system. Holme (10) has shown that in an E. coli culture, the glycogen content increased from 2 to 20 percent when the cells were subjected to nitrogen starvation. Gaudy and Engelbrecht (k) reviewed the major differences in system behaviour for nitrogen deficient systems (respiring conditions) and nitrogen balanced systems (growth con- ditions). They concluded that, regardless of the presence of extra-cellular nitrogen, the organisms responded to shock loads, resulting in a rapid increase of sludge mass. It was evident from their studies that for a temporary successful removal of B.O.D. by active cells, no nitrogen source need be supplied. They proposed the possibility of an amino acid pool existence within the bacterial cell. The necessary enzymes were produced to metabolize the waste using this amino acid pool, in the absence of an external nitrogen source. However, the end product of metabolism was high in carbohydrate content and low in protein. C. Polysaccharide Production and C.O.D. Removal in the Absence of Nitrogen Wilkinson (21) studied, in pure culture, the influence of growth limiting nutrients other than carbon and energy source on the production of polysaccharides by bacterial cells. He selected type 5^+, of Klesibel la aeroqenes because of its simple growth requirements. When he lowered the level of nitrogen source in the medium until it became limiting, the amount of polysaccharides produced per cell rose to a maximum level. This increase was reflected in both the intracellular and extra-cellular polysaccharides. When the experiment was repeated with phosphorus and sulfur source similar results were obtained. In all cases polysaccharide production, as measured by the polysaccharide to nitrogen ratio of the cells, reached a maximum. 2k The value of this maximum varied according to the growth limiting nutrients. He gave the following values for the maximum. Polysaccharide : N i trogen 32:1 Polysaccharide ; Phosphorus 40: 1 Polysaccharide : Sulfur 17:1 Symons and McKinney (17) have shown that acetate can be metabolized even in the absence of a nitrogen source. The C.O.D. removal was good and the solids accumulation was more than in conventional activated sludge units. Such a system worked for 3 to k weeks, before it failed, with 100 percent return of the sludge. Earlier Helmers et al , (9) mentioned that wastes were stabilized even with a limiting nitrogen source but the resulting sludge was not good for vacuum filtration. Gaudy and Engelbrecht (3) found with glucose sludge, that the increase in sludge concentration under respiring conditions (in the absence of nitrogen source) was nearly parallel to that found under growth conditions. More of the substrate removed was accounted for by synthesis under respiring conditions. Under growth conditions, the increase in sludge mass was primarily attributed to creation of new cells; whereas in the case of the nitrogen deficient systems, polysaccharides accumulated in the sludge. Moreover, in both systems the organic load was removed at essentially the same rate and with the same solids production. There was a net accumulation of polysaccharides in the system deficient in nitrogen and operated without wasting, as shown by Symons and McKinney (17). However, the accumulation of solids depended on the time of aeration, initial M.L.S.S. and type of substrate. Gellman and Heukelekian (5), after studying the relationship between B.O.D. loading and volatile suspended solids accumulation for several industrial wastes, formulated the relationship S » a L r - b S a (2) 25 S = Resultant net accumulation of VSS (lbs) L = B.O.D. removed in lbs/day S = M.L.V.S.S. in lbs a The, constant, a, represents the fraction of B.O.D. removed which is synthe- sized into new biological sludge. The constant, b, is the coefficient representing the mean rate of endogenous respiration expressed as a percent of the total M.L.S.S. per day. The results of Symons and McKinney (17) would indicate that the value of, a, will increase in case of nitrogen deficiency. Wuhrman (22) concluded that excess sludge produced by sludge growth is necessarily a function of the same factors which govern optimum purification performance. At a constant plant loading it is expected that excess sludge will increase with decreasing mixed liquor concentrations until the sludge load exceeds the metabolic capacity of organisms. With the same B.O.D. loading net sludge production at M.L.S.S. of 800 mg/7, was 67 percent higher than at 3200 mg/^ of solids at a temperature of 20° C. D. Air Requirement of Activated Sludge The activated sludge process is an aerobic process requiring an oxygen residual of at least 0.5 mg/# according to Porges et a 1 . (13) if the system is to operate properly. The demand for oxygen is a direct func tion of biological metabolism and is characteristic of the sludge mass and waste. The total oxygen requirement of a bio-oxidation system was given by Eckenfelder and O'Connor (2). Oxygen requirement/day =a' (B.O.D. removed/day) + b' (M.L.V.S.S.) (3) a' = fraction of the B.O.D. removed, which is used to provide the energy for growth and is equal to (I - a) 26 b' = coefficient representing the endogenous respiration rate. For a variety of industrial wastes the value of a' had been found to be 0.35 - 0.55. Factors Affecting Oxygen Uptake: Wuhrman (22) while working with glucose acclimated sludge, brought the bacterial cells, which were previously washed in phosphate buffer, so as to be free from any external nitrogen, in contact with the same substrate in the absence of a nitrogen source. He found 15 to 18 percent of the substrate has been respired. The rest was syn- thesized into new sludge. This was oxidative assimilation in the absence of an external nitrogen source. However, the percentage respired increased to 50 percent in the presence of ammonia nitrogen. He concluded, this was due to the assimilation of ammonia which is a process of high energy expenditure. He also concluded that the amount of oxygen consumed by sludge during removal of a certain fraction of oxidizable nutrient (sugar) from solution, may vary within wide limits depending on the other metabolites present such as nitrogen. Such wastes, when supplemented with an assimilable nitrogen source, might exert very high oxygen demand. Thus the availability of nutrients will influence the coefficient, a 1 , in equation 3- This was confirmed in the work of Symons and McKinney (17) in which oxidation in the presence of low nitrogen resulted in a large accumulation of sludge of high polysaccharide content and, hence, in a 1 owe r f ra c t i on ox i d i z ed . The concentration of trace elements often exhibits a far more _(-.(. +_!- j-J- pronounced effect on oxygen uptake. Mg , Mn , Fe , etc., form co-factors for respiratory processes. Their absence will result in lower oxygen con- sumption according to Oginsky and Umbreit (12). For the same B.O.D. load, oxygen uptake varied with the initial M.L.S.S. The growth phase of bacteria also influences the oxygen uptake. 27 Oxygen Uptake Rate: The oxygen uptake rate will vary with time of aeration as the sludge passes through the various phases, depending on the concentration of sludge employed and the C.O.D. of the waste. If the (FrM) C.O.D. to M.L.S.S. ratio is low, the initial rate will be high. Due to rapid initial removal of C.O.D. under these circumstances, the uptake rate will decrease rapidly and approach endogenous level. If the C.O.D. to sludge ratio is high, a low rate will be maintained for a long period of time as the C.O.D. removal and oxidation process continues. If the sludge is not acclimated to the waste, an initial lag period of low oxygen uptake is exhibited. . Later, the waste is metabolized and the oxygen uptake rate increases, once acclimation has taken place. When the organisms, acclimated to the waste, were thoroughly mixed with the waste, especially with a high M.L.S.S., it was observed that there was considerable reduction in the C.O.D. of the substrate within a short time of contact. This high initial drop in C.O.D. is attributed to adsorp- tion and absorption by Smith and Ullrich (15). Gaudy and Engelbrecht (k) had also concluded that this phenomenon is absorption in the case of soluble substrates. Such a process needs much less oxygen than when the substrate is oxidized. Storage and Oxidation: Gellman and Heukelekian (5) found the rates of purification (C.O.D. removal) of various industrial wastes to be much higher and even several fold that of their respective oxygen uptake rates. Porges et a 1 . (13) obtained a B.O.D. reduction rate of six times the oxidation rate while working with 1000 mg/,0 of M.L.S.S. and skimmed milk waste of 1000 mg/£ concentration. They found 80 percent of the C.O.D. was removed in one hour while the oxygen uptake corresponded to only 50 per- cent of the C.O.D. removal, thereby inferring cell storage or absorption. This stored material was utilized subsequently. A portion of the C.O.D. 28 removed was oxidized to carbon dioxide and water. Another portion was synthesized into cell complex with a low immediate oxygen demand while the remainder is converted and stored as an insoluble glycogen-1 ike substance. However, the oxygen demand of the mixed sludge continues at a high rate while the storage product is utilized and then decreases to the endogenous rate, if aerated long enough. E. Sludge Characteristics of Nitrogen Deficient Wastes One of the most important aspects of nutritionally deficient wastes is their effect on biological predomination. A partly nitrogen deficient waste will permit the predominance of fungi over bacteria according to McKinney (11), since fungi form protoplasm with a lower nitro- gen content than bacteria. The fungi are filamentous and hinder the set- tling of sludge. According to Symons and McKinney (17). the polysaccharide sludge was resistant to further biological degradation and was described as inert volatile matter. Helmers et a 1 . (9) have shown that low nitrogen sludges tend to have poor settling characteristics and might impair vacuum f i 1 1 rat ion . F. Energy Considerations : Nutrition Limitation During bacterial respiration, the substrate is oxidized with the release of energy. In an actively metabolizing system this energy is usefully employed by the cell for the synthesis of new protoplasm. When a nitrogen source is absent, the cell is faced with the problem of dissipating this energy, since it is no longer producing new protoplasm. Gunsalus and Stanier (7) described the following three possible mechanisms of energy 29 dissipation by the cell other than the formation of new protoplasm. (I) Poly- meric products like polysaccharides are accumulated either in storage form or as unusable waste. The excess energy is impregnated in the form of high energy bonds into these products. (2) While degrading a substrate, the energy which is given off during the breaking of the molecules, is harnessed by the bacteria in the form of high energy bonds known as Adenosine Tri Phosphate (A.T.P.). This A.T.P. bond is broken by a specific enzyme called A.T.P.-ase, present in the cell. Such a process permits the trapped energy to be dissipated as heat. (3) The cell tries to activate shunt mechanisms bypassing energy-yielding reactions or by requiring a greater expenditure of energy for priming. Priming is defined as the initiation of a biochemical reaction. Experiments of Senez et a 1 . (14) with nitrogen limited growth i showed a depressed growth rate without decreased substrate turnover - e.g. a metabolic rate independent of growth. This would be possible only if some mechanisms either bypassing A.T.P. generation or permitting its dissipation at a uniform rate were present in the cell. This is an example of the third postulate in the previous paragraph. 30 III. PROCEDURES AND EXPERIMENTAL TECHNIQUES A. Acclimated Cultures Activated sludges, acclimated to glucose, phenol, and acetate were maintained in separate tanks. The cultures were maintained in an active state by daily wasting of 2/3 of the total mixed liquor contents of the tank. They were all batch fed daily with 1 gm/; as C.O.D. of the respective substrate. The daily feed is given below: Substrate as C.O.D. 1000 mg/; Phosphate Buffer as P0, , PH. 7.0 10 mg/; NH^ CI 500 mg/0 Mg S0 4 .7H 2 250 mg/; i Fe S0 /+ -7H 2 10 mg/; Ca C1 2 '2H 2 10 mg/;, Mn S0^-H 2 10 mg/; Regular determinations were made for the M.L.S.S. and 23 hour filtrate C.O.D. The settling characteristics of the sludge were observed by shutting off the air flow. Ammonia and organic nitrogen were determined occasionally to check the nitrogen content of the sludge. After equilibrium was established as judged by constant M.L.S.S. and a high fraction of C.O.D. removal, Warburg studies were initiated to verify the efficacy of the process . M.L.S.S. were determined by the membrane filter technique. However, the C.O.D. was determined by the modified C.O.D. procedure, which uses 1/5 of the recommended quantities, and a titrant of 1/5 of the recommended normality. All other tests were carried out as per Standard Methods (16) 31 B. Warburg Studies The procedure for each experiment consisted of withdrawing a volume of the mixed liquor from the seed tank, which had been fed 23 hours earlier and allowing the solids to settle. After the solids had concen- trated, the supernatant was syphoned off above the sludge blanket and the solids were washed in a physiological salt solution to remove extra -cellular nitrogen. This solution had the same salt concentrations to which the seed was acclimated except that the nitrogen source was absent. After three successive elutr iat ions, the dilution factor was 250. Hence the ammonia i nitrogen content was 1/250 of the original ammonia nitrogen. The approxi- mate concentration of the solids was determined optically using a spectro- photometer. Then the solids were divided into two equal portions. Nitrogen source, in the form of ammonium chloride, was added to one portion at the concentration of 500 mg/i! and the concentrated sludge was diluted with the physiological salt solution to the desired concentration of M.L.S.S. The second portion was not supplemented with any nitrogen source and was diluted to the required concentration of M.L.S.S. The M.L.S.S. concentration and filtrate C.O.D. of these seed sludges were determined. The initial filtrate C.O.D. was necessary to determine chloride interference in the seed sludges. The ammonia and organic nitrogen content were determined on each of the seed sludges. To determine the increase in M.L.S.S., rate of oxygen uptake and reduction of C.O.D. with time under nitrogen deficient conditions, eight Warburg flasks were set up with the same substrate concentration and M.L.S.S. concentration as prepared above. The seed was ten milliliters consisting of all nutrients and a double concentration active cells. Ten milliliters of substrate was added, thus making the flask contents 20 ml in total. The nutrients salts concentration was the same in the flask as that to which the 32 seed was acclimated. The central well in the Warburg flask was filled with 1 ml of a 10 percent potassium hydroxide solution so as to absorb the carbon dioxide produced during bacterial metabolism. Eight more flasks were set up under the same conditions and supplemented with nitrogen. The manometers of the Warburg apparatus were filled with mercury instead of Brodie solution to permit taking of oxygen uptake readings over a prolonged period of time. The maximum vacuum permitted was 50 mm. The temperature of the water bath was maintained at 25° C throughout the entire study. One flask from each of the above groups was removed at 1 hour or 1.5 hour intervals and analysed i for M.L.S.S. and filtrate C.O.D. One flask was reserved for endogenous respiration from each group. Another flask in each group was kept for determining the ammonia and organic nitrogen at the end of the experiment. The Warburg study was discontinued when the oxygen uptake decreased to the endogenous rate or at the end of eight hours, whichever was earlier. Three different concentrations for each of the three substrates were selected. They were 500, 1000 and 2000 mg/,0 as C.O.D. Warburg studies with food : microorganisms (F : M) ratios of k, 2, 1 and 1/2 were conducted for each of the above concentrations. This was repeated with all the three chosen substrates namely, glucose, phenol and acetate. The procedures fol- lowed were identical in all respects. C. Duration of Substrate Removal with 100 Percent Return Sludge Under Nitrogen Deficient Conditions Glucose Substrate: In this study four small activated sludge tanks of 1.5 liter capacity were started with thoroughly washed active cells These cells were taken from the acclimated activated sludge tanks described 33 earlier. The ammonia-ni trogen content of the M.L.S.S., after three succes- sive elutriations, was approximately mg/i>. These four tanks received 100, 200, 600 and 1000 mg/i respectively of washed glucose acclimated sludge. These systems were operated without sludge wasting. The evaporation loss was corrected with distilled water. The pH of the tank contents was adjusted i daily to J. These tanks received at the initiation of the experiment the same amount and concentration of nutrients (described in the previous sec- tion) to which they were acclimated earlier with the exception of the nitro- gen source. They were all fed daily 1000. mg/^ as C.O.D. of the substrate. No more nutrients were added. A sample of 25 ml was taken out daily for the determination of M.L.S.S. and filtrate C.O.D. and this volume was replenished with the physiological salt solution. An extra 25 ml of sample was with- drawn on alternate days for the determination of ammonia and organic nitrogen This volume was replaced with distilled water. The above study was repeated with phenol and acetate acclimated cultures and their respective substrates under the same conditions as described above. This study was terminated when there was no further degradation of the substrate as indicated by the accumulation of substrate for at least three days. The criteria for the accumulation was the 23 hour filtrate C.O.D. value. 3^ IV. RESULTS 1. Warburg Experiments A.l. Glucose: substrate concentration 500 mg/£ as C.O.D. With this substrate concentration, four experiments were conducted with approximate initial M.L.S.S. of 100, 280, kkO and 1070 mg/7 . under both nitrogen supplemented and nitrogen deficient conditions. The last two experiments are shown on Figures 1 and 2 depicting the C.O.D. removal, oxygen uptake and increase in M.L.S.S. with respect to time. The other relevant data are shown in Table I. in the Appendix. The results with 100 and 280 mg/i! initial M.L.S.S. under nitrogen supplemented conditions are shown subsequently in the section on synthesis of protoplasm. The results with the nitrogen deficient systems under identical conditions, were re- jected and not included, since 90 percent C.O.D. removal was not obtained within the prescribed detention time of 8 hours. A. 2. Glucose: substrate concentration 1000 mg/$ as C.O.D. Four more Warburg experiments were conducted with approximate initial M.L.S.S. concentration of 250, 500, 1000 and 2000 mg/£ under both nitrogen supplemented and nitrogen deficient conditions. All the data are shown in Table I in the Appendix. The results are plotted in Figures 3 - 5- The experiment with 250 rnq/g, initial M.L.S.S. was not included in the data since it did not satisfy the 8 hour time limit criterion. A. 3. Glucose: substrate concentration 2000 mg/# as C.O.D. The F/M ratios were k, 2 and 1. The last experiment is included in Table I in the Appendix and shown in Figure 6. The experiments with 500 mg/7, , and 800 mg/,0 of initial M.L.S.S. were not satisfactory so far as 90 percent of C.O.D. removal in 8 hours was concerned and were excluded. B.l. Phenol: substrate concentration 500 mg/7, as C.O.D. Three experiments were conducted with approximate initial M.L.S.S. of 200, 35 500 and 1000 mg/0. They are shown in Figures 7 to 9. The results are included in Table II in the Appendix. B.2. Phenol: substrate concentration 1000 mg/# as C.O.D. Four experiments were conducted with F/M ratios of approximately k t 2, 1 and 1/2 respectively. The study with a F:M ratio of k was omitted from the data. However, there were two experiments with a ratio of 2. The results are shown on Figures 10 to 13 and included in Table II in the Appendix. B.3. Phenol: substrate concentration 2000 mg/£ as C.O.D. Only one experiment was satisfactory for inclusion in the data and is represented in Table II in the Appendix and in Figure 14. C.I. Acetate: substrate concentration 500 mg/# as C.O.D. Four experiments were conducted with approximate F/M ratios of k, 2, 1 and 1/2. In case of the nitrogen deficient system, the higher ratio did not prove satisfactory and, hence, was not included in Table III in the Appendix. These data are plotted in Figures 15 to 17- C.2. Acetate: substrate concentration 1000 mg/0 as C.O.D. Four experiments were carried out with approximate initial M.L.S.S. of 250, 500, 1000 and 2000 mg/# respectively. The results are given in Table III in the Appendix. Only the last three experiments satisfied the criteria set in this study and are shown in Figures 18 to 20. C.3. Acetate: substrate concentration 200 mg/# as C.O.D. Only two experiments were conducted with an initial M.L.S.S. of 500 and 1000 mg/# . The system with a F:M ratio of k, under nitrogen deficient conditions did not satisfy the requirements of 90 percent C.O.D. reduction in 8 hours and, hence, it was rejected. The experiments with F/M ratio of approximately 2 are shown in Figure 21. The relevant data are included in Table Ml in the Appendix. 36 2. Operational Characteristics with No Solids Wasting The object of this study was to evaluate the length of time that an active cell mass would continue to degrade the replenished substrate without any nitrogen source. In this study, no wasting of sludge was per- mitted. The feed was given daily and the 23 hours filtrate C.O.D. and M.L.S.»S. were determined daily. The results of this study are given for all the three substrates in Table IV in the Appendix. Ammonia and organic nitrogen determinations were determined on the contents of the tanks on alternate days. The ammonia nitrogen was zero every time for all the units The C.O.D. removed per day by each of the systems is plotted against t in days and is shown separately for each substrate in Figures 22 to 2k, :i me 3- Protoplasm Productions Since the continuous production of active cells is the core of this process, Warburg studies were conducted with low initial M.L.S.S. under nitrogen supplemented conditions to find the favorable F/M ratio for maximum cell production. The substrates were the same as described earlier. The concentrations of the substrates were 500, 1000 and 2000 mg/i>, . Only the results of those experiments which could satisfy the criterion of 90 percent C.O.D. reduction in 8 hours are shown in Table V in the Appendix. 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ID « «■ 2 CO ul z UJ o o tr z • ■ V * * \ - ro CM o CI/ 'Bui) 9NINIVW3U 00 UJ en O o o ° 2 o O o x IO csj 2 c en ) cc O o o (l/fiui) SS1W o o o o o o IO o o o o o z Z3 _J *• tO o D (|'/6uj) SSirM c > o ■300 200 100 c u > o (|/6uj) 3»Vldn N39AX0 c > o O O o c > / o ° ° O tf > ^ v. \ *- X z 2 "■ ■" LL. z UJ © o or / wo to UJ 2 Id h »- z \ ^^ "" CM < 1- * ^v ^^ UJ o \ \ " "™ < o o O O CO Ci / 6uj) QNiNivway a*oo o o o o o ?, o o CM w ^ CO ^ C 1 1 1 ) o o (|/'6ui) ssiw o o S S o o *• o O o rO CM • CO CM ^ C ) CI / bm) 3>IVJ.dn ' N39AX0 O o ° ° o o o x IO CM 2 C O in o <1- > ' 66 V. DISCUSSION Sludge Production It was observed that, within the limitations set for these experiments, the solids production was characteristically higher for the nitrogen deficient systems than for the nitrogen supplemented systems with phenol and glucose, irrespective of substrate concentration. The acetate systems yielded slightly lower solids in the nitrogen deficient units. However, the difference was negligible in all cases, from an engineering v iewpoint. The tables given in the Appendix are all calculated on the basis of 90 percent C.O.D. removal. These values will be used in this discussion. The graphs shown in Figures 1 to 2 1 are plotted beyond 90 percent C.O.D. removal to show the trend. Figures 1 to 6 show graphically the solids production with the glucose substrate under the different conditions studied. Figure k reveals that with the glucose substrate and an F/M ratio of 1, the increase of solids with a nitrogen deficient system was 66 percent whereas the nitrogen supplemented system had an increase of 63 percent. All other experiments with glucose depicted this trend. With phenol as the substrate, the same trend was found as noted in Figures 7 through 14. With acetate as the substrate, the solids produc- tion was characteristically greater in the nitrogen supplemented systems than in the nitrogen deficient systems as noticed in Figures 15 through 21. The variations were slight but consistent. f As expected, the results show that with higher F/M ratios higher synthesis results, irrespective of the substrate. An example of this is seen in Figure 15, with an acetate substrate of 500 mg/H and an initial 67 M.L.S.S. of 220 mg/0 . Under nitrogen deficient conditions, the net accumu- lated solids were 170 mg/,0 . On the other hand Figure 17, with an acetate substrate of 500 mg/,0 and with an initial M.L.S.S. of 870 mg/i for the same conditions as in Figure 15, shows an accumulated solids of only 35 mg/£ . This relationship between the solids production and the F/M ratio was con- sistent in all Warburg experiments, under both nitrogen supplemented and nitrogen deficient conditions with all three substrates. For the biological oxidations, the sludge production can be com- puted from the following considerations. As described earlier a portion of the C.O.D. removed results in the increase of the M.L.S.S. The solids accumulation is governed by the synthesis and the endogenous respiration and can be represented as follows: A = a F - b M or, A F k M " a M " b (4) where, A = increase in M.L.S.S. in lbs/day F = C.O.D. removed in lbs/day M = initial M.L.S.S. in lbs a = portion of the C.O.D. removed that is synthesized b = mean rate of endogenous respiration expressed as a percent per day This equation presumes a straight line relationship between the solids accumulation per lb of solids and F/M ratio. This equation implies that when F is zero, A/M is equal to - b, the mean rate of endogenous respira- tion. This means that when the external food source is absent, there is a decrease in solids mass proportional to the endogenous respiration. As long 68 as an external substrate is available, it is questionable whether endogenous respiration occurs (3). In an actively metabolizing system such as in those described in this work, b, could be neglected without inducing much error. The usual value for the coefficient, b, is 3 to 5 percent per day. For a study like the one presented here, the value of, b, for an 8 hour period would be less than 2 percent. Considering that the growth equation is only an estimate, this value is negligible. Neglecting the endogenous respiration, the equation for the accumulation of the solids is A F M " 3 M (5) Such an equation is convenient to predict the increase in sludge mass. Fig- ures 29, 30 and 31 show the fractional increase in M.L.S.S. vs C.O.D. loading rate for the substrates glucose, phenol, and acetate, respectively, for nitrogen supplemented and nitrogen deficient systems. The coefficient, a, has a higher value for nitrogen deficient systems for glucose and phenol in comparison with the nitrogen supplemented systems. Since the coefficient, a, has a lower value for acetate under nitrogen deficient conditions than under nitrogen supplemented conditions, there is a possibility that the end products of metabolism might not be only polysaccharides. Gaudy and Engelbrecht (3) proposed the possibility of lipid synthesis storage from hydrocarbon and fatty acid wastes. This may account for the lower synthesis with acetate under nitrogen deficient conditions. No attempt was made in this study to identify the end products of metabolism. However, the result of this experiment should not be compared directly with that of Symons and McKinney (17). Their experiment with acetate was con- ducted under different operational conditions in that the unit was fed daily and operated without wasting for 35 days. Over this prolonged period they had more solids accumulation in the nitrogen deficient system as compared to 69 the nitrogen supplemented system. In systems supplemented with nitrogen, the protoplasm formed was oxidized more completely during the extensive endogenous period, whereas the polysaccharides formed in the nitrogen de- t ficient system were not oxidized as completely. Hence, there was a build up of the solids in the nitrogen deficient units. In the present study, each system was discontinued as soon as 90 percent C.O.D. was removed so that the effect of endogenous respiration was minimized. From Figures 29, 30 and 31, the following values were obtained for the coefficient, a, and the units are lbs solids/lbs C.O.D. Glucose Acetate Phenol Nitrogen supplemented 0.45 0.42 0.23 Nitrogen deficient 0.50 0.31 0.30 The value of, a, can be used as an index of the biological energy level of the substrate. The magnitude of, a, indicates the comparative energy based on C.O.D. available to the microorganisms. From this study it was observed that glucose yielded the most energy, acetate was second and phenol yielded the least amount of energy. The same conclusions can be reached by com- paring the oxygen uptake under identical conditions. The phenol concentra- tion was actually 420 mg/f as phenol in a solution of 1000 mg/i as C.O.D., whereas the weight of glucose was 940 mg for the same C.O.D. On a substrate weight basis, there was slightly more solids production with phenol than with glucose and acetate. Oxygen Consumption With a few minor exceptions, it is seen from Figures 1 to 21 that with each of the three substrates the nitrogen deficient systems consumed • 70 + 0> -z. U.|S CM If) - o V ® X o Q O CO CO Z i O s i in LlI Q z CD UJ Q K 1- 3 Z z _J UJ UJ co UJ _l o u. *\ o Q. Q. UJ Q o NX 3 C/) z UJ °*k z CD UJ O o or «^, & •0. or z o h \ ° z i 1 1 J i r\ IO C\J q cvi ir> Q SS"IW (W/V) SS1W7 IO o , o 71 O ro u.|: o fO o 2 UJ X O O Q O ® o -T r Q LU UJ LU 2 O LU — CO HI O LU W 2 o »- a: ^ o ro in CO o Li. Q O CO CO _l o 2 m d iq cvi Q CM If) If) d (w /v) 72 b.| z 4. CM * ~z. __ 6 o rO II I \ ^> # <|z \ (D U. \ \® u| 2 I £ ir> 2 o rO ii \ Q ® CO O r ° O CO _J Q_ 5 p • \ w O z UJ z Q w \° \ — lO Q 3 UJ 1- 1- ' _J z z CO EME ICIE _i "- — q 8: S ™" 3 co z UJ T ® Z CD UJ O DC O H \ \®Qp d E z H J Z i i 1 1 o lO o io o m CO CM* — (W/V) - 6 SS11AI ssii/v y O 73 slightly less oxygen as compared to the nitrogen supplemented systems. However, the difference in total oxygen uptake was so small that it has little engineering significance. In this study oxygen utilization per gram of C.O.D. removed was calculated for the interval in which 90 percent C.0.0. reduction occurred. This varied with the substrate concentration and F/M ratio. As the F/M ratio decreased from 5 to 1 the oxygen uptake per gram of C.O.D. removed increased. This trend was seen with all the three substrates. However, with a very low F/M ratio, the oxygen demand per gram of C.O.D. removed was found to be very low. Based on the F/M ratios, these following different trends were noticed. (a) When the F/M ratio is high, more of the substrate removed resulted in synthesis. A moderate oxygen demand was noted and this demand was exerted for an extended period. An example of this is seen in Figure 27, with phenol substrate of 500 mg/JJ concentration and F/M ratio of 3- The oxygen uptake per gram of C.O.D. was 485 rng per gram and the average rate of oxygen uptake was 69 mg/hour and this demand lasted for 7 hours, (b) When the F/M ratio is 1 or 2, the oxygen uptake per gram of C.O.D. re- moved is higher as compared to the previous case. Since a higher number of organisms are present, a higher portion of the substrate removed is oxidized and this exerts a high oxygen demand. A typical example of this situation is shown in Figure 8, with phenol substrate of 500 mg/# concentration and F/M ratio of 1. The oxygen consumed per gram of C.O.D. removed was 650 mg and average rate of oxygen uptake was 93 mg/hour and this demand lasted for 7 hours. (c) At low F/M ratios of 1/2 or 1/3, the organisms absorb more of the substrate on contact only. The phenomenon of absorption became quite significant. Rapid removal of C.O.D. occurred by this process and it is assumed that this was converted to stored food. A case in point is shown in 74 Figure 9 with phenol substrate of 500 mq/l concentration and an F/M ratio of about 0.5- The oxygen uptake per gram of C.O.D. removed was 415 mg/,0 . In this case a small amount of total C.O.D. removed is oxidized and more is stored in the cell. Because of a smaller amount being oxidized, a system like this would have a lower oxygen demand than the previous case noted in (b). If such a waste is aerated long enough, the stored food is metabolized, ultimately exerting a high oxygen demand. In fact, it was noticed that the same rate of oxygen uptake continued for 2 to 3 hours after the C.O.D. was depleted. With a nitrogen deficient waste passing through the activated aerator, tHere is no need to oxidize the stored food since that sludge is not recycled. The nitrogen deficient systems required longer aeration time as compared to the nitrogen supplemented systems. However, such a difference in time is noticed with high F/M ratios only. Examples of this are seen in Figures 3, 7 and 10. With a phenol substrate concentration of 500 mq/P, and initial M.L.S.S. of 350 mg/f, as shown in Figure 7, the time taken for 90 percent C.O.D. reduction under nitrogen supplemented condition was 7 hours whereas under nitrogen deficient condition it was 8 hours. Hence the total oxygen uptake noticed would be slightly higher in the latter case. However, the total oxygen uptake would be nearly the same if it is evaluated on the basis of gram of C.O.D. removed. Rate of Oxygen Uptake Characteristically with higher M.L.S.S., the oxygen uptake rate was greater but the time taken for metabolizing the substrate was shorter. This trend was the same under both nitrogen supplemented and nitrogen de- ficient conditions. Table I in the Appendix, shows that with a glucose 75 substrate of 1000 mg/7 concentration, the average oxygen uptake rate per gram of C.O.D. removed varied from 38 mg/iVhour with an initial M.L.S.S. of 265 mg/£ to 109 mg/^/hour for an initial M.L.S.S. of 840 mg/£ . The manometers of the Warburg apparatus were read at one or one and half hour intervals. The average rate of oxygen uptake was computed from these readings. In initiating the experiment, Warburg flasks were left open to the atmosphere for 5 minutes in the water bath so as to equili- brate the flask contents to the bath temperature. With high solids, the rate was usually very high during the first few minutes. With a M.L.S.S. concentration of 213*+ mg/£ for the same 1000 mg/# substrate concentration the oxygen uptake rate was 7^ mg/|/hour based on a 1 hour reading. This value was lower than that for the system with 840 mg/,0 M.L.S.S. It is probable that a high percentage of the Ik mg/f,/hour oxygen uptake might have been exerted in the first few minutes and hence the rate would have been much higher. Unfortunately the Warburg manometers were read only once an hour. Hence, the true rate was not accurately determined for those cases in which a very high initial oxygen uptake rate existed for a small fraction of the f i rst hour. Detention Time vs F/M Ratio As stated previously, the substrates were metabolized in both the nitrogen deficient and nitrogen supplemented systems. It was observed that the time taken for 90 percent C.O.D. reduction was primarily dependent on the F/M ratio. A higher F/M value required a longer detention time. A low F/M value resulted in rapid removal of substrate but the oxygen rate was very high. 76 Solids Production with Nitrogen Supplementation In the conventional activated sludge portion of the scheme under study, biological solids were continuously produced. Since a high F/M ratio encourages synthesis, a low initial concentration of M.L.S.S. was used with a proper nitrogen source supplemented. A comparison of the amount of syn- thesis can be seen in Figure 25, with glucose substrate of 500 mg/,0 concen- tration. An initial M.L.S.S. of 100 mg/£ or F/M ratio of 5 resulted in a 270 percent increase in sludge mass with 290 mg of oxygen uptake per gram of C.O.D. removed. On the other hand, an initial M.L.S.S. of 280 mg/7. or F/M ratio of 2, produced only 68 percent increase in sludge mass with an in- creased oxygen uptake equal to 3^5 mg/gm of C.O.D. removed. The phenol and acetate systems showed similar trends. In Figure 27, with a phenol substrate of 500 mg/ l concentration and F/M ratio of 3-5, it was noticed that the increase in solids was 1 50 percent. Acetate with a concentration of 2000 mg/i 1 . and F/M ratio of k, as shown in Figure 28, gave rise to 151 percent increase in sludge mass. For the same concentration and F/M ratio, the solids production depended on the energy yield from the substrate. Glucose is a higher energy substrate and hence conducive to greater solids production. A lower energy substrate like phenol yielded lower amounts of solids since a higher fraction of the re- moved substrate was oxidized to supply the energy needed for the metabolic process . Considering the whole data presented in these experiments and within the limitations set for the experiments, it is observed that an F/M ratio of k is optimum with nitrogen supplementation for protoplasm production. If the initial M.L.S.S. is lower than the above value, the substrate load may exceed the metabolic capacity of the organisms. In such cases, the substrate removal is not accomplished within 6 to 8 hours. 77 Nitrogen Savings The process has proven to be effective with all three substrates. Since no nitrogen supplementation is necessary in the portion of the flow treated in the activated aerator, the nitrogen savings are approximately proportional to the flow through the activated aerator. Table VI tabulates the expected savings in the nitrogen cost with each of the three substrates at various concentrations. All the quantities in this table were computed from Tables I to V in the Appendix. The first four columns in Table I deal with the solids production and optimum F/M ratios of the activated i sludge portion of the process. The next three columns describe the opera- tional parameters of the activated aerator. The minimum feasible F/M ratio was taken from the existing data. An F/M ratio of 2 seems to be suitable under optimum conditions. In order to arrive at the proportion of the total flow through the activated aerator the following calculations were made. 1 1 »i s assumed that the waste is homogeneous and of constant C.O.D. The solids accumulated in the conventional activated sludge unit are known. If x fraction of the flow was routed through the conventional unit, the excess solids would be equal to x times A M.L.S.S. The remaining fraction of the flow (1-x) passes through the activated aerator and the initial M.L.S.S. or optimum F/M ratio is known. The excess solids from the conventional activated sludge unit should be equal to the required initial M.L.S.S. for the activated aerator. By equating the M.L.S.S. produced, the proportion of the flow through each unit is computed. x times ^M.L.S.S. = (1-x) initial M.L.S.S (6) conv. act. sludge activated aerator The savings in nitrogen cost is dependent on the type of substrate and on CO o < CO z LU o 0C CO LU +■» nj — CO O 3 < — O "v. U. 1- < x: JC •_ . — cn C Lc 3 r> vO J" O O VO LA r^ ^ u CO O < S-S trt g c l, 3 ^r CO \D u •— •— O 1- X 4-1 rtj L. 1 — -0 0) m CO 0) <^~ LA rA O < CO TJ \ P>» -a- LA 4-> _) 0) cn J" LA O T3 — 2: 0) E CM 0) c z 4-1 — T3 > — E 4-< 3 u E 2: ••- < •— V. 4-J c Lu <0 ■ CM *— ._ QC E 1/1 ID a o 4J o Cl. Ift co <=* t/> CO ^* _j cn — 2: E C 0) (A E u JC ro a> !_ *J {A jQ 3 3 •— CO cm — — CA O O — — CO o CM CM — V. >s. "V, — — -3- 78 -3- ro J" O O -3" CO fA vO CM O LA O LA o •J- o CM o LA O LA O VO CO vD vO CO CO vO CA -a- LA CA CA f<\ LA CM O J" vO CM CM -d- CM vO — O LA CM LA -3- LA fA CO O LA -4" LA CO CO CM O O LA vO CM O LA O CM CM J- — CA CM CM LA CM CO -3" O LA LA r» — CM co CA \0 vO -3" vO J" CA \0 — LA — LA CM PA CM LA CM CM CO vO r-^ CM la r^ LA O VO — — CM CM CM J" »— CA co CM LA -cf- CO CO LA CO LA vD CO CO 2: LA LL. LA -3" — - CO CM CM CM CM J- O «^ c ^. O cn 03 4-> ) continued to degrade the substrate at the rate of 1000 mgA per day for 9 days. The system with an initial M.L.S.S. of 160 mg/$ lasted for only 3 days. The same trend was seen in Figures 23 and 2k with phenol and acetate substrates. This study indicated that in case of emergency when cell production is hindered, the process can still maintain its efficiency. The settled sludge from the activated aerator could be recycled during temporary diffi- culties. Also, nitrogen could be supplemented at the head end of the activated aeration unit to convert it into a conventional process. Under normal operating conditions, the process is quite stable since no deleterious sludge is recycled. 82 VI. ENGINEERING SIGNIFICANCE Treatment of nitrogen deficient wastes by the activated aeration process proposed in this study, has been shown to be practical. Within 8 hours of aeration, 90 percent C.O.D. reduction was obtained with all the three substrates depending on the concentration and F/M ratio. A high F/M ratio encouraged high synthesis in the nitrogen supple- mented and nitrogen deficient units. A ratio of k seemed to be the optimum value for the nitrogen supplemented unit. In the activated aerator an F/M ratio of 2 appeared to be optimum for all three substrates. With the above ratios it is expected that the supplemented nitrogen savings would be about 50 percent. Depending upon the nature of the waste, the above optimum ratios are likely to be modified and consequently the proportion of the flow through each of the two units will be modified. Economy in Oxygen and Nitrogen For nitrogen deficient waste, if the nitrogen supplied is to be conserved, synthesis must be restricted and oxidation should be increased. This is practiced in the conventional activated sludge plants by maintaining high M.L.S.S. In such cases the loading rates are less than 30 pounds of B.O.D. per 100 pounds of solids per day and the air requirements in these low synthesis plants approach 1200 to 1 800 cu . ft. per pound of B.O.D. removed . On the other hand if the oxygen is to be conserved, synthesis must be encouraged and accordingly more nitrogen has to be supplemented. This is achieved in practice by maintaining low M.L.S.S. in the aeration tank. In these cases, the loading rates are in excess of 30 pounds of B.O.D. per 83 100 pounds of solids per day and the air requirements in such high synthesis plants vary from 500 to 700 cu . ft. per pound of B.O.D. removed. The modification presented in this study maintains high synthesis with its accompanying low air requirements as well as low nitrogen supple- mentation cost. The detention time in this treatment process is 8 hours or less and this compares favorably with the conventional activated sludge process. This process does not require extra detention volume and hence there would be no increase in the capital outlay. This process can be adopted in the existing activated sludge plants with minor cost since most have two or more aerators and settling tanks. This method of treatment is likely to produce about 10 percent excess sludge. The sludge settling properties should be comparable with that of a nitrogen supplemented system. Because of a lack of a nitrogen source, an effluent of low fertilizing value would be expected from this process. This is a desirable aspect of an effluent to minimize the plankton blooms in the receiving bodies of water. This process is flexible in operation and exhibits excellent stability. In case of emergency, the settled sludge from the activated aerator unit could be recycled. The process efficiency is. still maintained. It appears that a higher fraction of the flow can be treated in the activated aerator by recirculating part of the settled sludge even under normal con- di t ions . 84 VII. CONCLUSIONS From this study, the following conclusions have been drawn. 1. The activated aeration process is feasible and 90 percent C.O.D. removal can be obtained within 8 hours with all three substrates at various F/M ratios. 2. The time taken for C.O.D. removal under nitrogen deficient conditions is comparable to that of a nitrogen supplemented system with F/M ratios less than 2. 3. There is a negligible difference in the total oxygen uptake between the two systems. k. The oxygen uptake rates differ in both cases with the rate of oxygen uptake being lower with nitrogen deficient systems than with nitrogen supplemented systems. 5. It appears that the activated aeration process is not effi- cient when the F/M ratio is higher than two. 6. The synthesis of active bacterial cells is optimum with an F/M ratio of k under nitrogen supplemented conditions. 7. This process works well and is independent of the strength of the waste within reasonable limits. 8. This system is stable since no deleterious cultures are recycled. 9. The solids production was greater in the case of glucose and phenol under nitrogen deficient conditions whereas with acetate solids pro- duction was less under similar conditions. 10. An activated sludge can continue to purify the substrates studied even in the absence of an exogenous nitrogen source for 3 to 8 days depending upon the concentration of the initial M.L.S.S. . 85 VIII. BIBLIOGRAPHY 1. Chasick, A. H., "Activated Aeration at the Wards Island Sewage Treatment Plant," Sewage and Industrial Wastes, 2£, 1059 095*0 2. Eckenfelder, W. W. , and O'Connor, D. J., Biological Waste Treatment , Pergaman Press, New York (1961) 3. Gaudy, A. F., Jr., and Engelbrecht, R. S., "Basic Biochemical Considera- tions During Metabolism in Growing vs Respiring Systems," 3rd Biological Waste Treatment Conference, Manhattan College, New York (I960) 4. Gaudy, A. F., Jr., and Engelbrecht, R. S., "Quantitative and Qualitative Shock Loading of Activated Sludge Systems," Journal of the Water Pollu- tion Control Federation, 3_3_, 805 (1961) 5. Gellman, I., and Heukelekian, H., "Studies of Biochemical Oxidation by Di rect Methods, III. Oxidat ion and Puri f icat ion of Industrial Wastes by Activated Sludge," Sewage and Industrial Wastes, 2J5, 1 1 96 (1953) 6. Greenberg, A. E., Gerhard, Klein, and Kaufman, W. J., "Effect of Phos- phorus on the Activated Sludge Process," Sewage and Industrial Wastes, 27, 3, 277 (1955) 7. Gunsalus, I. C, and Stanier, R. Y., " The Bacteria Metabolism ," Vol. II. Energy Excess: Nutrient Limitation, p. 47-50, Academic Press, New York (I960) 8. Helmers, E. N., Frame, J. D., Greenberg, A. E., and Sawyer, C. N., "Nutritional Requirements in the Biological Stabilization of Industrial Wastes, II. Treatment with Domestic Sewage," Sewage and Industrial Wastes, 2J_, 884 (1950 9- Helmers, E. N., Frame, J. D., Greenberg, A. E., and Sawyer, C. N., "Nutritional Requirements in the Biological Stabilization of Industrial Wastes, III. Treatment with Supplementary Nutrients," Sewage and Industrial Wastes, 24, 496 (1952) 10. Holme, T., "Symposium on Polysaccharides," Prague (1958) 11. McKinney, Ross E., Microbiology for Sanitary Engineers , 118, McGraw Hill Publishing Company, New York (1962) 12. Oginsky, E. L., and Umbreit, W. W., " An Introduction to Bacterial Physiology ," W. H. Freemen Company, San Francisco (1954) 13. Porges, N., Jasewicz, L., and Hoover, S. R., "Principles of Biological Oxidations," 1-3, Biological Treatment of Sewage and Industrial Wastes , Vol. 1, Aerobic Oxidations, Edited by J. McCabe, and W. W. Eckenfelder, Jr., Reinhold Publishing Corporation, New York (1956) 14. Senez, J. C, and LeGa 1 1 , J., "Compt. Rend. Acad. Sci.," 25J0, 404 (I960), Abstract Quoted by Gunsalus and Stanier. 86 15. Smith, M. W., and Ullrich, A. H., "The Biosorption Process of Sewage and Waste Treatment," Sewage and Industrial Wastes, 23_, 12^8 (1950 16. Standard Methods for Examination of Water and Waste Water , 11th Edition, American Water Works Association, (1961) 17- Symons, J. M., and McKinney, R. E., "The Biochemistry of Nitrogen in the Synthesis of Activated Sludge," Sewage and Industrial Wastes, 30, 7, 875 (1958) 18. Torpey, W. N., and Chasick, A. M., "Principles of Activated Sludge Operation," 3-^> Biological Treatment of Sewage and Industrial Wastes , Vol. 1, Aerobic Oxidations, Edited by J. McCabe and W. W. Eckenfelder, Jr., Reinhold Publishing Corporation, New York (1956) 19. Weinberger, L. W., Doctoral Thesis, M.I.T. (1950), Abstract Reported by Sawyer, C. N., 1-1, Biological Treatment of Sewage and Industrial Wastes , Vol. 1, Aerobic Oxidat ion, Edi ted by J. McCabe and W. W. Eckenfelder, Jr., Reinhold Publishing Corporation, New York (1956) 20. Weston, R. F., and Eckenfelder, Jr., "Application of Biological Treat- ment to Industrial Waste, I. Kinetics and Equilibria of Oxidative Treatment," Sewage and Industrial Wastes, 27, 7, 802 (1955) 21. Wilkinson, J. F., Abstract Bacterial Reviews, 22_, 58 (1958) 22. Wuhrman, K., "Factors Affecting Efficiency and Solids Production in the Activated Sludge," 1-4, Biological Treatment of Sewage and Industrial Wastes , Vol. 1, Aerobic Oxidation, Edited by J. McCabe and W. W. Ecken- felder, Jr., Reinhold Publishing Corporation, New York (1956) 87 X o < 00 tO O X I- to Z LU 0_ X UJ o cc GO L- O J= o (TJ c o O Q) <4- o) >. a o • en x UO « E W v. ^ en e <4- CTJ > *J u < a. (u 3 a- 0) C irt E <» l. — -* .c I- to C 0) a> -* CD (TJ x a. -* «=^ en m s >» *■> CD X Q- £ O =) 0) LO i/i to 03 —J 5 ^ to to <1 _) < CT> — l/l ^ c -J O -Z E (TJ tO — t/> +-> _l — S C cn E Q O Ll o "v. cn E "— "=3 (TJ d C O — o Cn E O 10 L. (TJ O to a. E _J CL — Z < 8 LA CA cn LA 00 — O — — O O LA vO la O LA CA vO CM -3- O O O O CA LA -d" LA -tf — vO CA O LA -o a) — c a) E CD a. CL 3 LA to vO c 0) cn O la 1- 00 4-> CM LA CM 00 CM LA LA ca LA LA CM CM o LA O r** ca -d - LA LA CO O ca LA — O 00 CA 8 -a- vO CM — o ca CM 00 CM -d- O CA LA VO o CO CM o ("A LA f-x. 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