Environmental Engineering Department, Faculty of Civil Engineering, Ege University,
Industrial development has not only brought prosperity to humanity but has created many dangerous problems as well. Industrial wastes are among these problems. These vary according to the production methods used and the goods produced. Some industrial wastes can undergo biodegradation; some are subject to partial decomposition; some are toxic to bacteria and cannot degrade biologically.
In this work, specific industrial effluents are studied for their degree of biodegradability. The method used in this study consists of examining the oxygen consumption and respiration activities during the biological degradation process carried out on
each effluent, e.g., brewery, textile industry, metal-processing and raw toxic tannery effluents. Results are evaluated and discussed.
The pollution of surface waters has reached tremendous dimensions at the present time. This is caused partly by domestic and partly by industrial wastewater from various sectors. Industrial production is the cause of many important pollution problems. The determination and classification of wastewater characteristics is mandatory for pollution abatement and for the design, construction and operation of waste treatment facilities.
The different technologies and processes used in industry create a broad spectrum of wastewater types. Therefore, technicians must consider the parameters defining the various wastewater characteristics and, if necessary, must try to find new and better
methods and techniques for determining the degree of pollution.
The effects of industrial wastewaters on bacterial life, which is very important in biological treatment, can be conveniently determined by measuring the respiration rates and changes in these rates at different dilutions in the laboratory. The adaptability of the microorganisms to the wastewater slugs and efficiency of treatment at various adaptation rates depending on the degree of concentration of pollutants is another important aspect of respiration kinetics.
In this paper, the degree of treatability of selected industrial wastewaters, taken from the İzmir Area, for which respiration activity measurements have been taken, is discussed.
OXYGEN CONSUMPTION and RESPIRATION RATES
Oxygen consumption is an indicator of respiration activity. In order to find out the oxygen consumption and aeration rates, Hixson and Gaden (1950) proposed the following basic relationship:
for zero oxygen consumption, where
C = 02 concentration in water (mg/L)
Cs= equilibrium 02 concentration in water (mg/L)
k = reaeration coefficient (h-1). (1)
Assuming that no oxygen enters the reactor with the influent and recycled waters,
C = oxygen concentration in reactor (mg/L)
CS‘ = saturation concentration of oxygen in water under operating conditions
k.= reaeration coefficient under operating conditions (h-1)
OV= respiration rates of microorganisms under operating conditions (mg/L -h)
The 02 concentration in the reactor reaches a fixed level after a certain period of reaeration. This is called the relative or virtual saturation value, C. Under these conditions C and C: are approximately equal and Eg. (2) becomes
The saturation value under the operating conditions is as follows:
Cf: may be determined from Eq. (4) by calculating k’ and measuring C: and OV values in laboratory set-ups.
For the reduction of pollutants in wastewaters, microorganisms, must consume them as substrate while also consuming oxygen. The oxygen present in the medium, therefore, is the sum of the oxygen consumed under operating conditions (OV) and residual oxygen (OC Reserve). Respiration under operating conditions is the sum of respiration for growth (substrate respiration) and endogenous respiration of the microorganisms. Industrial wastewaters are composed of many different constituents. Microorganisms that multiply in waste waters show different (substrate) respiration activities for each different constituent. As a result, oxygen consumption rates (mg02/k-h) are different for each different pollutant.
Oxygen consumption rates and the total solids content (amount of activated sludge), which indicate the microbial growth rates, are interrelated. The total oxygen consumption rate per unit of total solids content (mg O2/g-TS-h) is defined as the specific respiration rate, OVS. This parameter is related to the total respiration under operating conditions as follows:
By measuring and observing the changes in respiration activity (OV) and specific(OVS) we can determine the biological treatability of industrial wastewaters.
LABORATORY TEST SET-UP
The set-up used for the measurement of respiration activities exists in the Municipal Infra-Structure Institute of Stuttgart Technical University. Tests were carried out in the Institute’s laboratories.
The operation of the measurement system is shown in Fig. 1. The observed parameter in the system is dissolved oxygen change per unit time. DO values are transmitted to a recorder via membrane electrodes placed in each reaction vessel which has been filled with different dilutions of industrial waste waters. The reaction vessels are mixed at a constant speed, thermostatted and kept at 20°C. The contents of the vessels are inoculated with cultured microorganisms taken from a laboratory biological treatment model unit, a flow diagram of which is given in Fig. 2.
Fig. 1: Laboratory set-up for measurement of respiration activities
A fixed volume of 65 ml inoculum material taken from the aeration unit in Fig. 2 is poured into the reaction vessel in Fig. 1, For each run the total solids content is determined.
Fig 2: Laboratory biological treatment model unit-flow diagram
Different dilutions of industrial wastewaters taken from breweries, tanneries, textile and metal-plating plants in the İzmir area are prepared, by adding 1, 2, 5, 10, 15, 20, 30, 40, 50 ml of each wastewater to the reaction vessels containing the inoculums, and then by filling the vessels with clarified municipal wastewaters taken from the discharge lines of pretreatment units. The dilution plan is shown in Table 1.
The dissolved oxygen reduction in each reaction vessel is continuously recorded. The DO values show different reduction rates for each industrial wastewater at each different dilution. The reduction lines found by connecting the reduced DO values have a specific slope, which is defined as the respiration activity under operating conditions, OV (mg O2/l-h).
Table 1: Dilution Ratios of Industrial Wastewaters
|Volume of Industrial Wastewater||Volume of Activated|
|Volume of Pretreated|
Fig. 3 summarizes the respiration activity changes at different dilutions in graphical form. In Fig. 4 the respiration activity values (OV) and plots obtained from these values for brewery, textile, tannery, and metal-processing wastewaters tested at various dilutions are shown.
Table 2 shows the total solids contents and their changes for each industry (TS). The relationship between the total solids contents in activated sludge and the respiration activity has been made use of in calculating the specific respiration activity (OVS) (mg O2/g-TS-h). In plotting the curves in Fig. 5, logarithmic (OVS) values are used.
Table 2: Total Solids Contents of Industrial Wastewaters Tested
|Efes Pilsen Brewery||2.285|
|Kula Textile Mill||2.576|
|İzmir Metal Plating||2.740|
|İzmir Leather Manufacturing Plant||2.671|
Fig. 3: Recorded respiration activities for brewery wastes at various dilutions
Fig. 4: Respiration rates for several dilutions of industrial wastewater
Fig. 5: Specific respiration values for several dilutions of industrial wastewater
DISCUSSION of RESULTS
Untreated wastewaters taken from four industries in the İzmir Area: brewery, tannery, textile production and metal-plating industries, are tested for their biological treatability. The raw effluent water from each industry is mixed with screened and settled (pretreated) municipal wastewater at different ratios, inoculated and tested, using the respirometric dilution method. Graphical representations are made of the volumetric dilution ratio, raw industrial sample activated sludge, versus 1. Specific respiration activity, OVS, and 2. respiration activity, OV. From these graphical results it is to be noted that for metal-plating wastewater, with an increasing volume of industrial effluents OVS values decrease, and especially at ratios exceeding 30% the decrease in OVS becomes substantial. An increase in industrial wastewater volume resulting in increased dilution ratios causes decreasing OVS ratios as a rule. Typical of each industry is the rate of decrease in OVS values. This may be observed in wastewaters from other industrial sectors, like breweries and textile plants. Test runs and graphical evaluations with these wastewaters, however, do not show as sharp decreases as the metal-plating wastes. On the other hand, graphical representations of the respiration activity, OV, with respect to several percentage dilutions show that with an increased percentage of industrial wastewater a decrease in respiration activity results. For tannery wastes a rapid decrease in OV is noted for an increased percentage of mixtures, while with metal-plating wastewater a decrease in OV starts only after a volumetric ratio of 23.1% is reached.
From Fig. 4, it may be noted that the different industrial sectors might be classified according to their OV decrease rates. The most rapid OV decrease is seen in metal-plating wastewater, while textile, tannery and brewery wastewaters are listed in the order of decreasing OV reduction rates with respect to increased percentage of mixing.
From the test results, it may be concluded that brewery wastes may easily be treated biologically after mixing with municipal wastewater, even at high mixing ratios. Tannery and textile mill wastewaters, on the other hand, may be digested by bacterial activity rather easily without a major decrease in the respiration rates already obtained in the municipal wastewater treatment. Metal-plating waste, however, cannot be biologically treated alone, and is only treatable when extremely diluted with municipal wastewaters. At lower dilution ratios, treatability is reduced as bacterial life is endangered due to toxicity resulting in decreased respiration activity.
By continuing such tests with various industrial effluents, optimum dilution ratios can be determined for a mixed treatment plant. Also information on the ease of treatment and toxicity can be obtained by this method. The method is applicable to all industrial wastewaters and gives important knowledge on treatability without the necessity of making elaborate laboratory analyses, which increase the cost of design appreciably.
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Taygun, N. (Turkey) Great variations are observed in the nutrients existing in industrial wastewater, depending on their type. In the industrial wastewater you used, there was a nitrogen and phosphate deficiency. Did you compensate for this by adding nitrogen and phosphate from some external source?
Samsunlu, A. (Turkey) : The section of my model plant comprising of the aeration and final settling tanks (Fig. 2) was operated with domestic wastewater, although the actual plant was operated with only industrial wastewater. From this section I took the activated sludge containing the cultured microorganisms and added specific amounts of industrial wastewater without changing its structure in any way. I then examined the nutrients in the activated sludge taken from the domestic wastewater, which was held constant at 65 m2. I was particularly interested in the degradability of the wastewaters when mixed.
Sarıkaya, H. Z. (Turkey): Instead of taking a volumetric mixture of domestic and
industrial wastewaters, wouldn’t it have been better to take their BOD and COD ratios? Since the pollution load of the industrial wastewater used will vary, the volumetric ratios may give erroneous results.
Samsunlu, A. (Turkey): In another section of my work the BOD and COD of the
wastewaters were measured, but the ratios obtained have not been presented here.
Sarıkaya, H.Z. (Turkey): How do you explain the reduction in respiration rate
which occurs with an increase in the proportion of industrial wastewater, as shown in the graphs? Can it be due to a nutrient deficiency?
Samsunlu, A. (Turkey) : I do not think so. The proportion of activated sludge
to which the industrial wastewater was added was always 50% or more. In the first three experiments carried out, the nutrient level was quite high. To my mind, I attribute the decrease in respiration rate more to the fact that the industrial wastewater was not readily biodegradable since the bacteria could not adapt to the environment. This is supported by other studies I conducted on industrial wastewater, including that from the pharmaceutical industry, phenol and brewery wastewater.
Sarıkaya, H.Z. (Turkey): Why did you choose your method of measuring the respiration rates, rather than the Warburg respirometer?
Samsunlu, A. (Turkey): You know that there are at least 13 or 14 different methods, chemical and others, for measuring the amount of oxygen. The method I chose was readily available at Stuttgart University, where it has been successfully used for the last few years. It was developed there in order to overcome the difficulties envisaged with the Warburg method with regard to the recording of results and the length of time involved.
Tabasaran, O. (Germany): Could you give further information on the adaptation phenomenon?
Samsunlu, A. (Turkey): From the investigations which I conducted on phenol, pharmaceutical, tannery and brewery wastewaters, I have observed that when adaptation of the microorganisms takes place, there is a marked increase in respiration activity and a subsequent increase in treatment efficiency. Adaptation can be achieved when industrial wastewater is fed at a constant amount to the municipal wastewater treatment plant. If, however, there is a shock feeding, the bacteria are greatly affected, and the respiration activity, including the endogenous respiration, falls to the minimum level.
Velioğ1u, S. G. (Turkey): Were you able to prevent any oxygen change when transfer¬ring your samples from İzmir to Stuttgart?
Samsunlu, A. (Turkey): Yes. The samples were transferred to the laboratories there and refrigerated within 2 or 3 hours.
Velioğ1u, S. G. (Turkey): Did you make any pH measurements in the course of your investigations? I would have thought that acidity would be present in the waste discharged from the metal industry.
Samsunlu, A. (Turkey): The pH of one sample was taken, but we did not take any pH values related to dilution. In any case the dilution level was held constant.
Velio41u, S. G. (Turkey): In other words, after a composite sample was made, the
pH value was not measured. Can you give any figures for the BOD of the wastewater from the brewery – for example, 100 or 1000?
Samsunlu, A. (Turkey): As you know, samples from a brewery and measurements have
to be taken at different times. I do not have the re-sults here now. As far as I remember, the BOD value varies between 700 and 1200 for a period of five days.
Velioğlu, S. G. (Turkey): Couldn’t the reduction in respiration rate with the in-
crease in the amount of brewery wastewater be attributed to the excessive organic loading – a DOD level of between 700 and 1200?
Samounlu, A. (Turkey): Certainly. We are working on a method of increasing the
total solids content in the aeration tank when a shock feeding is given to the microorganisms.