Equilibrium powdered activated carbon (PAC) concentrations of 20, 160, and 280 mg/L in activated sludge reactors treating cellulose acetate manufacturing wastewater were found to enhance substrate removal. The improved substrate removal as measured by COD averaged 20 percent. The apparent mechanism of improved removal was the stimulation of greater biomass growth. PAC addition increased the oxygen uptake rate (OUR), the observed cell yield coefficient (Ybbs) and the first order substrate removal coefficient (Kb) of the activated sludge system, which were operated at a temperature of 18°C and a biological solids retention times of fourteen days. The addition of PAC also improved the sludge settleability but this resulted in higher effluent suspended solids concentration because zone settling Velocity was the primary factor affecting effluent suspended solids. A type of activated sludge bulking, known as jelly formation, plagued the biological reactors but nitrogen addition appeared to solve the problem / Master of Science / incomplete_metadata

The purpose of this study was to investigate selective operational parameters and their effect on activated sludge settling and dewatering rates. Several laboratory scale reactors were used in this study and fed with various synthetic substrates. The sludges produced from these reactors were used to examine sludge settling and dewatering characteristics as the selected operational parameters were varied. This study intended to determine if: (1) qualitative shock loadings affect sludge dewatering and settling and will biological systems recover quickly under various conditions; (2) aeration basin dissolved oxygen concentration affects sludge settling and dewatering characteristics; (3) biopolymer content can be correlated with sludge dewatering rates such that biopolymer content can be used as a parameter to monitor sludge dewatering characteristics. Results from this study indicated that the shock loadings considered here significantly alter the sludge settling and dewatering characteristics of an activated sludge population. Shock loadings may cause shifts in the bacterial population, allowing undesirable microorganisms to predominate but activated sludge systems can recover from shock loadings caused by the introduction of a different substrate. Also, it was seen that activated sludge dewatering is directly affected by the dissolved oxygen level in the aeration basin and the minimum level required is 2.0 mg/L in a completely-mixed system. A definite relationship was noted between biopolymer production and sludge dewatering with high biopolymer content correlating with poor sludge dewatering and low biopolymer content correlating with good sludge dewatering. / Master of Science / incomplete_metadata

The activated sludge (AS) process used for treating high-strength cellulose acetate wastewater of Celanese Corporation, Pearisburg, Virginia, produces a sludge with poor flocculation and settling characteristics, particularly during the periods of shock organic loadings. Pilot-scale treatment units were set up to study the effects of a fixed film pretreatment on the stability of the AS process, using a new type of trickling filter (TF) media consisting of long plastic strips. The pretreated activated sludge (PAS) unit was compared with a control activated sludge unit (CAS). Different hydraulic and organic loadings were applied to the TF. The study confirmed the ability of a TF to provide greater stability to subsequent AS processes during periods of shock organic loading. The TF did not significantly improve the PAS system effluent quality and organic removal performance, even though the PAS sludge had better settle ability in terms of Sludge Volume Index and had less filamentous growth than the CAS system. The TF pretreatment confirmed its ability to act as a roughing filter. During the study, it reduced the organic loading on the AS system by 26 to 43 %, oxygen requirement of AS system by 38 to 62 %, the aeration volume requirement by 17 to 47 %, and the sludge production by 0 to 37 %. The PAS system required fewer nutrients than the CAS system. / Master of Science

Combined activated sludge-fixed film media treatment systems are an interesting innovation in treatment technology. By adding media into the aeration basin, increased biomass concentrations may be maintained with little or no increase in solids loading to the clarifier. The ideal combined system can treat higher organic and ammonia loadings than a conventional system, and is more resistant to temperature changes and shock loadings. Overloaded plants can be outfitted with media as an alternative to plant expansion, and initial designs of combined systems can result in smaller aeration basins and clarifiers in places of land scarcity. / Master of Science

A debate currently exists concerning whether or not oxygen uptake rate is a valid control parameter for monitoring the activated sludge process. A laboratory study was conducted to attempt to shed light on the controversy. Two bench-scale reactors were operated at steady state and under shock load. Oxygen uptake rate (OUR) was measured with the BOD bottle technique and with an on-line respirometer. The reliability of the results obtained from the BOD bottle technique was also of interest. No relationship could be deduced between effluent quality and oxygen uptake rate thereby suggesting that the latter would not be useful as a control parameter. As was concluded from the shock load data, the oxygen uptake rate varies very inconsistently at high organic loadings. It was found that the BOD bottle technique completely failed at very high organic loadings and gave meaningless results. The on-line respirometer, in spite of its high sensitivity, gave more realistic and consistent results. / M.S.

The effects of varied concentrations of a natural sewage grease on the oxidative activities of activated sludge were investigated in an effort to determine the feasibility of using activated sludge as a treatment method for wastes high in grease content. The method employed to measure the oxidative activities of the activated sludge was the standard Warburg respirometer technique. Cumulative net BOD curves were plotted to determine the magnitude of the oxidation. Total grease analyses were performed throughout the test period to establish a definitive pattern of depletion by oxidation. The experimental results indicated that the grease was completely assimulated within 24 hours and that there were no adverse pH changes during the course of oxidation. On the basis of the experimental evidence activated sludge shows great promise as a treatment method for wastes high in grease content. / Master of Science

Due to the unpredictable nature of sludges, it is imperative to test a sludge from every new process in order to design the sludge handling equipment properly. In this study, sludge from the Virginia Initiative Plant, a pilot scale unit employing the UCT biological nitrogen and phosphorus removal process, operating at Lambert's Point Primary Treatment Plant in Norfolk, Virginia, was tested against sludge from a conventional activated sludge process. A bench scale waste activated sludge unit was employed for the purpose. Tests were conducted to compare batch thickening, vacuum dewatering and centrifugal dewatering characteristics of both sludges. The results obtained indicated both sludges to be highly comparable in all the areas of testing. The results obtained have also been explained in terms of AVI, a measure of sludge floc water content, a fundamental sludge property. Due to the similar nature of the sludges, previously established design criteria can be used for designing the sludge handling equipment for BPR sludges. / M.S.

In the recent past more and more attention has been given by sanitary engineers to the problem of nitrogen removal in sewage treatment. This attention is brought about by several problems associated with nitrogen. First, in some locations, such as our southwest United States, there is both an essentially constant supply of water and an increasing demand for water. This calls for water recycling. or reuse, as a means of meeting the demand for potable water. An accumulation of impurities, such as compounds of nitrogen, can limit the recycling of water. One such substance is nitrate nitrogen, which when in excess of ten parts per million can cause the disease methemo-globinemia in bottle-fed infants. / Master of Science

The microbial populations in the Hoechst-Celanese activated sludge were examined. Heterotrophs, denitrifiers, sulfate-reducers, protozoa and filamentous bacteria were enumerated. Variations in microbial populations were compared with influent and effluent constituent concentrations, and with aeration basin characteristics, such as dissolved oxygen and F/M ratio, to determine whether any microbial type could be used by plant operators to monitor process performance. Results indicated that filamentous bacteria may be useful to plant operators for monitoring process performance because an inverse relationship between filamentous bacteria, food-to-microorganism ratio and sludge volume index was suggested by this study. Protozoa may also be useful for operators, although more data is needed. Microthrix parvicella and Type 0041 were the most common filament types. Filament Type 1701 was most prevalent during a period of low dissolved oxygen. A strong relationship between stalked ciliates and effluent quality was mention in the literature, but was not found in this study. Enumeration methods were evaluated. / Master of Science

The performance of fibrous biomass support media (Ringlace) and porous spongelike biomass support media (Captor) was evaluated for enhanced nitrification and denitrification in a pilot-scale Virginia Initiative Project (VIP) biological nutrient removal (BNR) process. Four separate pilot-scale treatment trains were constructed and operated during this research. Three of the four treatment trains were operated with fixed film media (Ringlace/Captor) incorporated in the aerobic zone of the system and are referred to as the Integrated Fixed Film Activated Sludge (IFAS) systems. A fourth treatment train (Control train) was operated without any fixed film media. All experiments in this research were performed using domestic wastewater from Blacksburg, Virginia, and the Virginia Tech campus. Enhanced nitrification was observed in the IFAS system containing porous biomass support media (Captor) that was freely suspended in the mixed liquor of the aerobic zone. Near-complete nitrification was observed in the IFAS system containing Captor media even at total suspended growth MCRTs as low as 5.6 days and a 12°C liquid temperature. Significantly higher nitrification rates were observed in the IFAS system containing Captor media compared to both the IFAS system containing Ringlace media and the control train. However, there was less denitrification in the aerobic zone of the IFAS systems containing Captor media compared to the Ringlace media systems. Enhanced nitrification could not be statistically shown in the IFAS system containing Ringlace media. The overall nitrification rates in the Ringlace media system were about the same as the control train for the MCRTs and temperatures used during this research. However, a significantly greater amount of denitrification was observed in the aerobic zone of the IFAS system containing Ringlace media compared to both the IFAS system containing Captor media and the control system. Microscopic examination of the growth on the fixed film media (Ringlace and Captor) showed that red worms always grew on the Ringlace media, and were detrimental to performance on at least one occasion. Methods for controlling the worms were developed and applied successfully. During certain operating phases, lower sludge productions and observed sludge yields were measured in the IFAS system containing Ringlace media. However, a Statistical difference could not be calculated between the sludge production in the Ringlace media system and the control system. Lower sludge production and observed sludge yield were also observed in the IFAS system containing Captor media, but only two data points were available and a Statistical t-test analysis was not possible. / Master of Science