Utilization of the activated sludge process is widespread although many of the mechanisms that make it work are still relatively misunderstood. Recent studies have indicated that dual substrate limitations may occur in the process. Several misconceptions in the basic fundamentals regarding the rates and mechanisms involved in oxygen transfer to wastewater systems also exist. This research investigation examined the effects of the mean cell residence time and wastewater stoichiometry on the operation of the completely mixed activated sludge process under a dual substrate limitation. At low mean cell residence times (θ_c) the system was growth C limited with respect to carbon and at high mean cell residence times the system was oxygen limited. Oxygen transfer studies were conducted to ascertain the relationship between the steady state oxygen transfer coefficient (K_La) and the oxygen uptake rate of the mixed liquor (R). The objectives of this research were accomplished by operating two continuous flow bench scale activated sludge units at COD:TKN ratios of 6.07:1 and 0.65:1. Reactor-1 was operated at a COD:TKN = 6.07:1 and was always growth limited with respect to organic carbon while Reactor-2 was operated at a COD:TKN = 0.65:1 and was carbon limited at low mean cell residence times and oxygen limited at high θ_c values. Mean cell residence time served as the primary control parameter during the laboratory studies and was varied form approximately 2.5 to 21.0 days. Theoretical studies were also conducted in which biokinetic and stoichiometric equations were used to develop a model to simulate the process operating under carbon and oxygen limitations. The model was found to yield results that were similar to the actual experimental data collected. Further refinement of the model by including inhibition functions would result in a model with better predictability. Examination of the experimental data collected during the laboratory study revealed several interesting conclusions. Operation of the activated sludge process at a low COD:TKN ratio (0.65:1) and under an oxygen limitation at high mean cell residence times can result in high levels of free ammonia and nitrite that will lead to a deterioration in effluent quality. Increased removal efficiencies for COD, TKN and NH₃-N can be achieved by operating the process at a high COD:TKN ratio (6.07:1). Steady state oxygen transfer coefficients determined in the mixed liquor of the reactors indicated there was a direct relationship to the oxygen uptake rate of the activated sludge (R). This observation is quite significant since standard aeration theory states that K_La is constant for a given aeration device. Nonsteady state K_La values determined on the effluent from each reactor indicated that K_La was a constant. Alpha and beta coefficients determined from nonsteady state tests on wastewater effluent from each reactor showed no trend with the mean cell residence time. / Ph. D.

This study was undertaken to evaluate the dewatering characteristics of a bench-scale belt filter press and a full-scale screw press, and to develop a suitable bench-scale test to simulate dewatering in a full-scale screw press. Tests were conducted to determine the effect of pressure and shear on dewatering of anaerobically digested, alum, waste activated, and pulp and paper sludges. The first part of the study involved tests conducted on a bench-scale belt filter press. Pressure was varied to develop performance characteristics with respect to cake and filtrate solids, and polymer demand. The second part of the study consisted of mixing intensity tests conducted to evaluate the effect of shear on dewatering in sludges. The third part of the study involved field evaluation of dewatering performance using a full-scale screw press. Tests were conducted to determine the shear produced in the dewatering process and to assess its effect on polymer conditioning requirements. The tests indicated that the polymer demand produced by the belt filter press simulator and the screw device was minimal. Rather, a substantial polymer demand was observed as a result of shear in the pipes and pumps during full-scale screw press dewatering operations. A combination of a high speed mixing device and a free drainage tester was capable of predicting polymer conditioning requirements for a full-scale screw press. Individual sludge performance characteristics varied with pressure producing changes in cake solids and filtrate quality. / M.S.

The differences in pollutant export from identical land areas treated with fertilizer and/or composted domestic wastewater sludge (compost) were evaluated. Three plots were constructed with a Glenelg silty clay soil and seeded with Falcon fescue (Festuca 'Falcon'): Plot 1 received conventional fertilizer; Plot 2 received a combination of compost and reduced conventional fertilizer; and Plot 3 received only compost. Runoff was collected and analyzed for soluble orthophosphate as P, total soluble phosphorus as P, total phosphorus as P, soluble ammonia as N, soluble Kjeldahl nitrogen as N, total Kjeldahl nitrogen as N, nitrite plus nitrate as N, total suspended solids, chemical oxygen demand, cadmium, copper, lead, nickel, zinc, chromium, and iron. Compost was found to improve moisture retention in the soil and crop, sustain plant growth during excessive dry periods, improve the quality of the crop, reduce runoff, and reduce soil erosion. The export of all pollutants was reduced by the use of compost. The use of fertilizer in combination with the compost did not provide any observable benefit. Instead, the fertilizer provided excessive soluble orthophosphate, total soluble phosphorus, and oxidized nitrogen which were subsequently exported from the test plot. The increased export of soluble Kjeldahl nitrogen may have been caused by excess insoluble N from the fertilizer application, which may have reacted with the organic matter, forming soluble organic nitrogen. The use of compost as a soil amendment significantly reduced the pollutant export which, in turn, reduced the potential impact on receiving waters. / M.S.

The dewatering characteristics of polyaluminum chloride (Hyper⁺Ion 1050A) sludges were investigated using lab-scale tests including specific resistance to filtration (r*), capillary suction time (CST), and sludge pH. The effects of chemical conditioning (lime and cationic polymer) and mixing intensity (Gt) upon the sludge dewatering characteristics in a pilot-scale plate and frame press were also studied. The dewatering characteristics of the Hyper⁺Ion sludges were found to be dependent upon the influent water turbidity conditions; specifically, the ratio of aluminum coagulant to total dry solids in the sludge. Lime was an effective conditioner for doses that produced a sludge pH value in the range of 11.5 to 11.8 which, again, was a direct function of the aluminum coagulant fraction in the sludge. Cationic polymer and a combination of lime and polymer were also effective conditioning schemes when the appropriate dose and mixing intensity were applied. / Master of Science

During the thickening process of sludges with intermediate to high solid concentrations three settling regimes are typically encountered, namely, zone, transition, and compression regimes. Recent studies have indicated that the validity of Kynch's formulation, which is the most widely used for sizing settling basins, is limited to the zone settling regime. His formulation is based on the solids mass balance equation and does not consider the role of the rising sediment at the bottom of the settling basin. This limitation is rectified in this study by using a dynamic equation, a second order non - linear partial differential equation for the effective pressure of the solid particles. The equation is solved by using the finite element method. The so obtained effective pressure is used with an appropriate constitutive relation for the volume fraction of solids, to determine the variation of the solids content within the deposited material, and the height of the falling mudline. / Master of Science

The major constraints to food production in West Africa are related to the lack of suitable lands. Consequently, farmers incorporate organic amendments and wastewater to improve their yields. Within some limits, such wastes enhance soil fertility and can improve its physical properties. However, the advantages of using organic waste as fertilizer and soil amendment should be assessed with possible environmental and toxicological impacts due to the potential presence of heavy metals. The objective of this study was to assess the effect of organic amendments on heavy metal distribution in soils and vegetables in market gardens in Senegal. Organic amendments and soils samples were collected from four sites in eastern and southern Senegal. Samples were analyzed for physicochemical properties including particle size, total heavy metals, carbon content, nutrients, and pH. A sequential extraction procedure was conducted to determine heavy metal sinks. Results showed that sites were sandy in nature, low to medium in organic carbon content (8300 to 36600 mg kg-1), and had pH ranging from 5 to 7.9. The sequential extraction procedure showed that metals were distributed in the more stable soil fractions: Fe-Mn oxide, organic and residual. The highest soil metal concentrations in soils were found in Pikine and Rufisque sites. Plant samples were collected from these two sites and analyzed for total metal content. Results showed that all metal concentrations in soils, organic amendments, and vegetables were within the safe limits proposed by the World Health Organization, with the exception of Cd, Pb and Zn levels in vegetables. / Master of Science

The purpose of this study was to investigate the qualitative and quantitative characteristics of high molecular weight exocellular materials (biopolymer) produced in biological waste treatment systems and examine the relationship between biopolymer and sludge settling and dewatering properties. The biopolymer that interfered with sludge filtration was a high molecular weight (>10⁵) anionic biocolloid composed partially of proteins, carbohydrates and humic acids. The relationship between supernatant biopolymer and sludge settling and dewatering characteristics is system specific. Sludge dewatering rates and supernatant biopolymer concentration vary drastically as sludge pH was increased from pH 3.0 to pH 10.0. Supernatant biopolymer and sludge specific resistance increased as sludge pH increased. Particle size analysis of biological sludge showed an increase in particles with mean size less than 10 microns as sludge pH was increased. No significant relationship was observed between sludge settling and biopolymer concentration in the sludge supernatant. / Master of Science

A microcomputer simulation model was developed to compare sludge disposal alternatives for an urban region. The model calculates both capital and operation costs for sludge treatment and disposal operations. For a study of an urban region with an equilibrium wastewater generation rate of 44.74 million m³/yr, the optimum sludge disposal alternative was dedicated land disposal for a baseline analysis of wastewater sludge treated by gravity thickening and anaerobic digestion. The capital cost at system equilibrium is $6.09 million and the total cumulative operation and maintenance cost over 100 years is $103.2 million. The operation and maintenance cost is 94% of the total capital and cumulative operation and maintenance cost. A description of the investigation and the criteria used for selection of this sludge disposal alternative ls included / Master of Science

This study compared the sludge characteristics of a lab-scale Air Products (A/O) and a conventional activated sludge system. The sludges were analyzed for operational properties and the exocellular biopolymers of each sludge was characterized. Operational analysis mainly consisted of measurements of settling (SVI) and dewatering (specific resistance, CST) parameters at each sludge age. Biopolymers were measured using pH extraction followed by gel filtration and subsequent analysis for carbohydrate and protein concentrations. The results showed a high degree of similarity between the two systems both operationally and with respect to biopolymer characteristics. The A/0 system did produce a lower effluent soluble COD at sludge ages below 5 days. Also, the A/O system showed some consistent differences in the distribution of bound and unbound fractions of protein and carbohydrate ECP but these had no discernible· effect on sludge operational characteristics. In addition relationships between unbound ECP and effluent BOD, bound HMW ECP and SVI, and phosphorus and Mg uptake were observed, with varying degrees of consistency, in this study. / Master of Science

Colloidal gas aphrons (CGAs) are typically a 55 to 70% dispersion of 50 +/- 40 micron-sized air bubbles in water. Generation of CGAs has proceeded to allow continuous production of up to 80 liters per minute. Previous laboratory testing has demonstrated the effectiveness of CGA flotation for removing fine particulates, such as coal fines, food wastes, phosphate slimes, algae, as well as oils from contaminated solutions. This study involved comparing CGA flotation versus dissolved air flotation (DAF) in a wastewater treatment sludge media. Initially, laboratory tests were conducted to see if field testing was warranted, and to screen possible surfactant chemicals to be used in any such field testing. Three surfactants were tested individually; sodium dodecylbenzene sulfonate (NaDBS), alkyl dimethyl benzyl ammonium chloride (BTC-824), and cetyl pyridinium chloride (CPC). From the laboratory results and observations, it appeared that the CGA flotation tests using both NaDBS and CPC were more effective than DAF. Tests using BTC-824 were inconsistent due to bubble instability. Overall, the laboratory results and observations seemed encouraging, and field testing was initiated. Next, four field tests were conducted at Pepper's Ferry Regional Wastewater Treatment Authority (PFRWTA) in which CGA flotation was used to try and enhance the performance of a DAF system. Tests were conducted by adding CGAs directly into the sludge influent line of PFRWTA's DAF system. Although CPC gave the best laboratory results, NaDBS was used in the field testing due to its availability and cost. Results from all four field tests showed that a more concentrated effluent sludge was obtained when CGA flotation was used to enhance DAF. The field test results for the raffinates were inconclusive. Overall, the results from the field testing seem promising. From these tests, CGA flotation appears to be an improvement over DAF in producing more concentrated effluent sludges when tested in a wastewater treatment sludge media. CGA flotation could enhance and/or possibly replace DAF in certain industrial applications. / Master of Science