Browsing by Author "Khararjian, Hraj Armen"

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    Aerobic biological treatment of a colloidal wastewater
    Khararjian, Hraj Armen (Virginia Polytechnic Institute and State University, 1976)
    The purpose of this study was to examine a modification of the activated sludge process known as contact stabilization. Both batch and continuous flow experiments were conducted under highly controlled laboratory conditions using a wastewater containing colloidal organic material to delineate process fundamentals. The colloidal wastewater used was prepared from yogurt, beef extract and various mineral salts. Batch type experiments were conducted at 0, 23, 43, and 54 percent colloidal percentages based on a chemical oxygen demand, COD basis. Four different food to micro-organism ratios were used at each colloidal percentage. Measurements of filtered and settled CID, oxygen uptake and mixed liquor suspended solids, MSS, were used to monitor waste stabilization. Continuous flow type experiments were conducted on two model treatment units. One unit was similar to a completely mixed activated sludge process, and the other a model of the contact stabilization process. Both of these units were operated at steady state conditions on a sludge age basis to compare treatment between each unit. Appropriate measurements were made to determine percent waste stabilization and waste sludge production at each steady state condition studied. From the results of the batch study, it could be concluded that not all colloidal wastes are subject to a period of adsorption onto biological floc and then released back into solution as was believed previously. Furthermore, using batch experiments for toxicity determinations as suggested previously was found to lead to erroneous results. Results from the continuous flow portion of the study indicated that the completely mixed and contact stabilization processes both have similar COD removal efficiencies when compared on a total sludge age basis. It was also found that sludge production was lower in the contact stabilization system when compared to the completely mixed system. A mathematical model was developed based on results of the continuous flow experiments that can be used by design engineers when designing a process and can also be used by a treatment plant operator to optimize process operation.
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    A study of nitrification kinetics
    Khararjian, Hraj Armen (Virginia Polytechnic Institute and State University, 1973)
    One autotrophic and two heterotrophic chemostats were operated during the study period. The autotrophic unit was operated using an inorganic synthetic ammonium medium to provide a culture of nitrifying organism and to study cell yield. The two heterotrophic units were operated with a feed containing 50 and 100 mg/l COD respectively along with the inorganic ammonium medium to determine the effects of heterotrophic activity on the nitrification process. The parameters monitored included mixed liquor suspended solids, suspended solids concentration in the effluent and influent; effluent ammonia and nitrate nitrogen concentration. The culture from the autotrophic unit was used as inoculum of nitrifying organisms for the other phases of the study. These phases of the study included determination of the effect of ammonium concentration, temperature and pH on nitrification. Temperature was found to be the main controlling factor for nitrification. An equation for the sludge age required at operating temperature was developed and a graph was prepared to determine the MLSS required, for a given influent BOD and the determined sludge age, that will assure nitrification on yearly basis. Changes in the pH within the range of 7 to 9 were found to have no significant influence on the nitrification rate. The nitrification rate decreased at pH outside this range. It was found that the presence of heterotrophic activity had no effect on the nitrification. In fact the presence of heterotrophic biomass was found desirable because of the improvement in the effluent quality.