The effects of a continuous dose of 0.5 mg/l nickel on activated sludge performance at varying COD:TKN ratios were investigated. Continuous flow, complete mix, bench-scale reactors were operated over a range of mean cell residence times, and COD removal efficiency, biokinetic coefficients, extent of nitrification, and nickel removal evaluated at each. Data from two earlier studies, in which 0.5 and 1 mg/l nickel doses were applied to similar units, were included for comparison. Organic removal efficiency was not impaired for the nickel doses considered. Biokinetic coefficients and nitrate production were also unaffected by 0.5 mg/l nickel. In contrast, one mg/l nickel sharply inhibited nitrification, caused an apparent decrease in reactor solids concentration, and related biokinetic changes in coefficients. Nickel removal was erratic. / Master of Science

This study investigated the influence of nitrogen and sludge age change in reactor performance and biopolymer production in activated sludge systems. The qualitative and quantitative analyses of the naturally occurring biopolymers were performed and the results were correlated to sludge a settling characteristic and effluent quality. In order to obtain the sludge samples for the analyses, two completely mixed, continuous flow activated sludge systems were maintained during this research. Raw wastewater from the Celanese Fiber Plant located at Narrows, Virginia was utilized as the influent. Nitrogen was added in the feed solution as ammonium sulfate. The sludge age was changed from ten to five days for both systems. Biopolymers were extracted from the sludge floc matrix using pH-adjustment technique followed by centrifugation. The total biopolymer contents were analyzed for protein and carbohydrate concentrations. High molecular weight biopolymers were also analyzed following gel filtration. The sludge settling characteristics were measured in terms of Sludge Volume Index and effluent quality in terms of effluent turbidity. The results indicated that the relationship between total biopolymer concentrations and sludge settling characteristics is culture specific. No consistent relationship was observed between total biopolymer concentrations and effluent turbidity and/or SVI. Additional nitrogen in a reactor system promoted production of high protein content biopolymers. However, no significant improvement in effluent quality of the reactor was noticed by the additional nitrogen. Deficiency of nitrogen in a reactor system promoted the production of high carbohydrate content biopolymers. The high concentration of carbohydrate biopolymers seemed to correspond directly to the high effluent turbidity. / M.S.

The purpose of this research was to conduct a laboratory study to determine the effects of nickel on the completely-mixed activated sludge process. Continuous-flow bench-scale reactors were operated at COD:TKN ratios of approximately 1.0:1 and 0.5:1 by varying the nitrogen concentrations in the feed solutions. Each unit received a COD concentration of 400 mg/l and was dosed continuously with a nickel concentration of 0.77 mg/l. The mean cell residence time was utilized as the operational control parameter to assess the influence of nickel on organic removal efficiency, on the degree of nitrification, and on the maximum yield and the microbial maintenance energy coefficients, Y_max and k_d. The results obtained in this study indicated that the soluble COD removal efficiency of the heterotrophic microorganisms was not affected by the 0.77 mg/l nickel concentration. The low continuous nickel dose to the reactor, however, appeared to stimulate the heterotrophic growth or to cause a replacement of the bacteria with a species of nickel-tolerant microorganisms. At the same time, the nickel appeared to stress the heterotrophs and to cause an increase in their maintenance energy requirement. Nitrification was found to be inhibited by the low nickel concentration, and this inhibition was not reduced by operating the reactors at lower COD:TKN ratios. / Master of Science

The effect that mean cell residence time (MCRT) had on the dewaterability of biological sludges was examined in this study. Aeration basin sludge and waste activated sludge from a full scale domestic wastewater treatment facility, in addition to sludges produced from two laboratory scale reactors fed with a synthetic substrate and a primary effluent-dog food mixture, respectively, were used to perform dewatering tests. The sludges were evaluated at various MCRT values for optimal dewatering resistances, optimal conditioning requirements, and optimal compressibility conditions. Specific resistance determinations were made using a 3uchner funnel apparatus to evaluate all of the above mentioned parameters. Also particle size analyses were performed on all sludges to investigate how particle size affected dewatering resistance and conditioner requirements, and also to investigate how MCRT affected particle size. All particle size determinations were made using a HIAC PC-320, twelve channel particle size analyzer. Results from the study revealed that plants can operate under extended aeration and still maintain good sludge dewatering characteristics. Likewise, by varying MCRT shifts in particle size distribution and corresponding changes in dewatering resistance were noted in the laboratory reactors. However, no optimum MCRT with respect to dewatering could be founded. Particle size proved to be the most important parameter affecting dewatering, and it was affected by conditioning, periods of anaerobiosis, and MCRT in the laboratory reactors. / Master of Science

A high strength industrial wastewater was treated in a bench-scale activated sludge reactor modified by the addition of biomass support media to the aeration tank. Two experimental biomass support systems (BSS) and one conventional activated sludge system were operated at different mean cell retention times (mixed liquor MCRTs). Three separate media were tested, NOR-PAC and Linpor used as free-floating supports, and BIONET used as a fixed-bed support. The effect of the media on substrate and oxygen utilization, and solid-liquid separation was investigated. Substantial attached growth did not occur on the NORPAC and BIONET media. The attached biomass concentration in the Linpor systems increased with increased media concentration. The ratio of attached volatile solids to total volatile solids (attached volatile solids + MLVSS) decreased with increased mixed liquor MCRT. The advantages of the BSS would occur at low mixed liquor MCRTs. Both the BSS and control systems achieved greater than 94% COD removal and substrate utilization rates (mg/h) did not significantly change during the experiments. Therefore, both systems were substrate limited. The substrate limitations caused decreased oxygen uptake rates of the attached biomass with increased mixed liquor MCRT. The sludge settling of the Linpor systems was a function of mixed liquor MCRT, filamentous upsets, and the presence of the media. Enhanced settling was observed in the Linpor system only at the 3 day mixed liquor MCRT experiment. / Master of Science

The object of this investigation was to determine, by the concept of specific resistance, the effect of certain variables on the filterability of calcium sulfate sludge resulting from lime neutralization of synthetic, return sludge seeded, sulfuric acid samples, The variables investigated were rate of mixing, rate of lime addition, degree of neutralization, return sludge loadings and acid concentration. Mixing rate and lime addition rate are factors effecting the characteristics and filterability of calcium sulfate sludge. Slow lime addition provided a more effective return sludge than did rapid lime addition. Slow sample mixing produced a more filterable sludge than did rapid mixing for a given lime addition rate. The degree of sample neutralization appeared to have only a minor effect on the filterability of the sludge, with the filter ability improving as the final pH of the sample decreased. The sample return sludge dosage appeared to have only a minor effect on the filterability of the resulting sludge with filterability decreasing as return sludge loadings increased. A complete evaluation of the effect of return sludge loading cannot be made, however, until these studies are expanded to include the optimum return sludge loading for the given acid-lime system. The values of specific resistance obtained were influenced by the resistance of the filter paper. For samples with similar dry solids concentration the effect is approximately the same; however, the amount of filter paper interference decrease with increased sample dry solids concentration. For varying acid concentrations there was a minor decrease in specific resistance as the acid concentration, and dry solids concentration, of the samples increased. This decrease was thought to be due to decreasing amounts of filter paper interference rather than improved sludge filterability. / Master of Science

The effect of solids retention time (SRT) or sludge age on activated sludge properties and effluent quality was investigated using laboratory scale reactors. It was found that an increase in SRT resulted in an increase in effluent solution polysaccharide, with the < 3,000 daltons (3K) size fraction contributing up to 68 percent of solution polysaccharides. The feed consisted of low molecular weight, readily degradable protein, suggesting that the observed increases in protein and polysaccharide were due to increased release of exocellular microbial product (EMP). The increase in solution protein and polysaccharide resulted in an increase in effluent chemical oxygen demand (COD). The increase in effluent COD was not accompanied by a similar increase in effluent biological oxygen demand (BOD), indicating that the EMPs released were resistant to biodegradation. At the highest SRT, the resistance to shear decreased and the capillary suction time (CST) increased. Following an initial increase, the sludge volume index (SVI) decreased at higher SRT. / Master of Science

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