Summary: A process is under investigation for the manufacture of dicalcium phosphate by the hydrolosis of concentrated superphosphate containing recycled monocalcium phosphate. The hydrolysis also results in the formation of an aqueous solution of monocalcium phosphate and free phosphoric acid. The phases are separated, followed by washing and drying of the solid dicalcium phosphate. The wash water is used in the hydrolyzer. The solution is returned to the superphosphate production step, where phosphate rock and additional phosphoric acid are added, and where water is evaporated to form the solid superphosphate.Pilot plant results have indicated that filtration rates vary widely under almost identical mixing conditions, presumably due to variations in particle size ranges. It was thought worthwhile, therefore, to study the effects of different mixing variables on the relative particle sizes as indicated by the settling rates of the mixture.

This dissertation presents an experimental investigation of fluid flow, proppant settling and horizontal proppant transport in hydraulic fractures. The work is divided into two major sections: investigation of proppant settling in polymer-free surfactant-based viscoelastic (VES) fluids and development of a new method of proppant injection, referred to as Alternate-Slug fracturing. VES fluid systems have been used to eliminate polymer-based damage and to efficiently transport proppant into the fracture. Current models and correlations neglect the important influence of fracture walls and fluid elasticity on proppant settling. Experimental data is presented to show that elastic effects can increase or decrease the settling velocity of particles, even in the creeping flow regime. Experimental data shows that significant drag reduction occurs at low Weissenberg number, followed by a transition to drag enhancement at higher Weissenberg numbers. A new correlation is presented for the sphere settling velocity in unbounded viscoelastic fluids as a function of the fluid rheology and the proppant properties. The wall factors for sphere settling velocities in viscoelastic fluids confined between solid parallel plates (fracture walls) are calculated from experimental measurements made on these fluids over a range of Weissenberg numbers. Results indicate that elasticity reduces the retardation effect of the confining walls and this reduction is more pronounced at higher ratios of the particle diameter to spacing between the walls. Shear thinning behavior of fluids is also observed to reduce the retardation effect of the confining walls. A new empirical correlation for wall factors for spheres settling in a viscoelastic fluid confined between two parallel walls is presented. An experimental study on proppant placement using a new method of fracturing referred to as Alternate-Slug fracturing is presented. This method involves alternate injection of low viscosity and high viscosity fluids into the fracture, with proppant pumped in the low viscosity fluid. Experiments are conducted in Hele-Shaw cells to study the growth of viscous fingers over a wide range of viscosity ratios. Data is presented to show that the viscous finger velocities and mixing zone velocities increase with viscosity ratio up to viscosity ratios of about 350 and the trend is consistent with Koval’s theory. However, at higher viscosity ratios the mixing zone velocity values plateau signifying no further effect of viscosity contrast on the growth of fingers and mixing zone. The plateau in the velocities at high viscosity ratios is caused by an increase in the thickness of the displacing fluid and a reduction in the thin film of the displaced fluid on the walls of the Hele-Shaw cell. Fluid elasticity is observed to retard the growth of fingers and leads to growth of multiple thin fingers as compared to a single thick dominant finger in less elastic fluids. Observations show the shielding effect is reduced by fluid elasticity. Elastic effects are observed to reduce the thickness of thin film of displaced fluid on the walls of Hele-Shaw cell. The dominant wave number for the growth of instabilities is observed to be higher in more elastic fluids. At the onset of instability, the interface breaks down into a greater number of fingers in more elastic fluids. Experiments are performed in simulated fractures (slot cells) to show the proppant distribution using alternate-slug fracturing. Observations show alternate-slug fracturing ensures deeper placement of proppant through two primary mechanisms: (a) proppant transport in viscous fingers formed by the low viscosity fluid and (b) an increase in drag force in the polymer slug leading to better entrainment and displacement of any proppant banks that may have formed. The method offers advantages of lower polymer costs, lower pumping horsepower, smaller fracture widths, better control of fluid leak-off and less gel damage compared to conventional gel fracs. / text

The objective of this study was to use applied and naturally-occurring geochemical tracers to study the hydrology of clay settling areas (CSAs) and the hydrological connectivity between CSAs and surrounding hydrological landscapes. The study site is located on the Fort Meade Mine in Polk County, Florida. The surface of the CSA is covered in desiccation cracks which swell and shrink in response to wetting and drying. Bromide was used as an applied tracer to study hydrological processes in the upper part of the CSA. Bromide infiltrated rapidly and perched on an uncracked massive sublayer. Bromide concentrations attenuated in the upper part of the profile without being translated vertically down through the lower part of the profile suggesting that bromide was lost to lateral rather than to vertical downward transport. Infiltration and lateral flow were rapid suggesting that preferential flow through desiccation cracks and other macropores likely dominates flow in the upper part of the profile. Naturally-occurring dissolved constituents and stable isotopes of hydrogen and oxygen were used as naturally-occurring tracers to study the hydrological connectivity between the CSA and the surrounding hydrological landscape. The relative contributions of source waters were determined using a two-end, mass-balance mixing model with sodium as a conservative natural tracer. On average, water samples downgradient from the CSA were ~80% rainfall/ambient water and ~20% CSA water. Discharge from the CSA to the surrounding surface water bodies and surficial aquifer occurs laterally over, through, and/or under the berms and/or vertically through the thick uncracked massive sublayer. However, the precise flowpaths from the CSA to the surrounding hydrological landscape are unclear and the fluxes remain unquantified, so the effects of CSAs on the hydrology of the surrounding and underlying hydrological landscape also remain unquantified.

This work reports an investigation of colloidal suspensions during sedimentation in what is known as the intermediate concentration range; one notoriously difficult to study. Two materials were examined: titanium dioxide P25 nanoparticles and magnesium hydroxide. The characterisation of these materials highlighted their high tendency to form aggregates under certain conditions. By the use of laser diffraction, measurements of the cluster size were conducted at under various conditions of shear. The use of sonication energy suggested the identification and classification of two classes of clusters related to their strength: high strength , and low strength clusters. A mathematical model which considered cluster formation and the occurrence of breakage predicted the aggregation and disaggregation kinetics. The approach was based on cluster-cluster interactions rather than particle-particle interactions. The results obtained by particle size analysis were compared with the size obtained using permeability analysis and settling velocity. In both cases the calculated sizes were comparable with the data obtained from size analysis; however, for magnesium hydroxide the predicted cluster size was a little higher and this may be due to the formation of channels giving faster settling. For the titanium dioxide it was noticeable that different mixing strategies exhibited different cluster size, network formation and settling behaviour. Finally, a novel modelling approach based on the presence of clusters rather than particles is presented. It is a combined model which considers the settling curve divided into two zones: a zone below the gel point modelled by a Kynch type approach and a zone above the gel point modelled by consolidation theory. This combined approach was only applicable to the settling data of titanium dioxide, where the settling data encompassed the gel point and the gel point could be identified by consideration of the Richardson and Zaki plots. For magnesium hydroxide, only the consolidation model was needed as all the initial settling concentrations were above the gel point.

No description available.

No description available.

The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy than in the aerobic one, generating approximately twice as much soluble chemical oxygen demand (COD) by cell lysis. Increased COD favoured production of extracellular polymers in ozonated reactors, enhancing flocculation and improving settling. Floc stability was also strengthened in prolonged operation in alternating treatment, resulting in declined solids destruction. Dewaterability was better in alternating reactors than in aerobic ones indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation. Ozone successively destroyed indicator estrogenic compounds, contributing to total estrogen removal from wastewater. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits and had less negative impacts on processes in the alternating treatment, although after prolonged operation, benefits could become less significant. The alternating anoxic/aerobic reactor achieved twice the nitrification rates of its aerobic counterpart. Higher removal rates of estrogens were associated with higher nitrification rates, supporting the contention that the nitrifying biomass was responsible for their removal. The alternating treatment offered the better estrogen biodegradation. Microbial populations in both reactors were examined with fluorescent in situ hybridization. Dominance of rapid nitrifiers like Nitrosomonas and Nitrobacter (79.5%) in the alternating reactor, compared to a dominance of slower nitrifiers like Nitrosospira and Nitrospira (78.2%) in the aerobic reactor were found. The findings are important to design engineers, as reactors are typically designed based on nitrifiers’ growth rate determined in strictly aerobic conditions.

The amount and type of cohesive sediment found in gravel river beds can have important implications for the health of aquatic biota, surface/groundwater interactions and water quality. Due to landscape disturbances in the Elbow River watershed, increased sediment fluxes have negatively impacted fish habitat, water quality and water supply to the City of Calgary. However, little is known about the source of cohesive sediment and its interaction with gravel deposits in the Elbow River. This research was designed to: 1) quantify the transport properties (critical shear stress for erosion, deposition, porosity, settling velocity, density) of cohesive sediment and 2) evaluate the potential for coarse gravel to entrap cohesive sediment in the Elbow River. A 5m annular flume was used to conduct erosion and deposition experiments using plane and coarse bed conditions. The critical shear stress for deposition and erosion of the Elbow River cohesive sediments was 0.115Pa and 0.212Pa, respectively. The settling velocity of the cohesive sediment had an inverse relationship between floc size and settling velocity for larger flocs, due to a decrease in floc density with increased size. Cohesive sediment moved from the water column into the gravel bed via the coupling of surface and pore water flow. Once in the gravel bed, cohesive sediments were not mobilized from the bed because the shear produced by the flume was less than the critical shear to mobilize the gravel bed. Using a model developed by Krishnappan and Engel (2006), an entrapment coefficient of 0.2 was determined for the gravel bed. Entrapment coefficients were plotted against substrate size, porosity and hydraulic conductivity, demonstrating a relationship between entrapment coefficient and these variables. It was estimated that 864kg of cohesive sediment is stored in the upper 0.08m of a partially submerged point bar in the Elbow River. Accordingly, when flow conditions are sufficient to mobilize the gravel bed and disturb the amour layer, cohesive materials may be entrained and transported into the Glenmore Reservoir, where it will reduce reservoir capacity and may pose treatment challenges to the drinking water supply.

The effectiveness of partial ozonation of return activated sludge for enhancing denitrification and waste sludge minimization were examined. A pair of nitrifying sequencing batch reactors was operated in either aerobic or alternating anoxic/aerobic conditions, with one control and one ozonated reactor in each set. The amount of solids decreased with the ozone dose. Biomass in the anoxic/aerobic reactor was easier to destroy than in the aerobic one, generating approximately twice as much soluble chemical oxygen demand (COD) by cell lysis. Increased COD favoured production of extracellular polymers in ozonated reactors, enhancing flocculation and improving settling. Floc stability was also strengthened in prolonged operation in alternating treatment, resulting in declined solids destruction. Dewaterability was better in alternating reactors than in aerobic ones indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation. Ozone successively destroyed indicator estrogenic compounds, contributing to total estrogen removal from wastewater. Denitrification rate improved up to 60% due to additional carbon released by ozonation. Nitrification rates deteriorated much more in the aerobic than in the alternating reactor, possibly as a result of competition created by growth of heterotrophs receiving the additional COD. Overall, ozonation provided the expected benefits and had less negative impacts on processes in the alternating treatment, although after prolonged operation, benefits could become less significant. The alternating anoxic/aerobic reactor achieved twice the nitrification rates of its aerobic counterpart. Higher removal rates of estrogens were associated with higher nitrification rates, supporting the contention that the nitrifying biomass was responsible for their removal. The alternating treatment offered the better estrogen biodegradation. Microbial populations in both reactors were examined with fluorescent in situ hybridization. Dominance of rapid nitrifiers like Nitrosomonas and Nitrobacter (79.5%) in the alternating reactor, compared to a dominance of slower nitrifiers like Nitrosospira and Nitrospira (78.2%) in the aerobic reactor were found. The findings are important to design engineers, as reactors are typically designed based on nitrifiers’ growth rate determined in strictly aerobic conditions.

The urban sprawl creates a gap between producers and consumers and the a sustainable circuitof nutrients and energy is difficult to maintain. Many times the waste that is created in urbanareas is not reused and the circuit is lost. In this project, wastewater treatment is looked atwith the view point that resource recovery is possible through energy production and reuse ofnutrients. In order to optimally run each process step at a wastewater treatment plant forimproved resource recovery, more knowledge is needed in order to not disregard the finaleffluent quality. The goal of this project was to develop a model in MATLAB/Simulink for achemically enhanced primary clarifier at a wastewater treatment plant. The potential ofproducing more biogas and reducing the aeration energy needed in the biological treatmentstep was looked at by focusing on describing the settling velocity of suspended solids.Experimental analysis on settling properties for solids was performed on sampled wastewaterentering the primary settler after changing the addition of chemicals prior in the process line.The wastewater samples were homogenized and then rapidly vacuum pumped up in a column.The solids in the column could thereafter settle and was retained in a cup at the bottom. Themass of total suspended solids (TSS) was classified in five different settling velocity classes,each class assigned a characteristic settling velocity. The experimental procedure followed theViCA's protocol (French acronym for Settling Velocity for Wastewater). A settler, much likethe secondary settler in the Benchmark Simulation Model No. 2 (BSM2), a 10 layer nonreactivetank was modeled. The mass balance in each layer of the settler was decided by thevertical solid flux in the tank and built on the characteristic settling velocity gained from theexperiments. Re-circulation of excess sludge from the subsequent steps at the plant showed toeffect the settling properties of the sludge in the primary settler. The components of TSSshowed to have the largest effect on the distribution of settling velocity. The variation in doseof both coagulant and cationic polymer prior the primary settling tank showed to effect theparticle settling distribution somewhat. A first simulation with an applicable dynamic influentscenario was run. Despite any proper calibration the model gave fairly good predictions ofmeasured TSS in the effluent and sludge outtake water. / När urbana områden växer uppstår svårigheter i att bibehålla ett hållbart kretslopp av energioch näringsämnen. Avståndet mellan producent och konsument ökar och många gångeråteranvänds inte det avfall som städerna producerar och det hållbara kretsloppet bryts. Dettaprojekt har fokuserat på resursåteranvändningen i avloppsvattenhanteringen genommöjligheterna som finns i energiproduktion i form av biogas samt återanvändning avnäringsämnen genom slamåterförsel. Mer kunskap behövs inom varje processteg för attoptimalt använda avloppsreningsverk för förbättrad resurs-återvinning så att inte utgåendevattenkvalitet blir lidande. Målet med projektet var att utveckla en modell iMATLAB/Simulink för primärsedimentering med kemisk fällning. Experimentelltanalyserades sedimentationsegenskaperna hos primärslam genom provtagning avavloppsvatten inkommande till försedimenteringen efter tillsatser av fällnings-kemikalier.Proverna homogeniserades och vakuumpumpades sedan snabbt upp i en kolonn. Detpartikulära materialet i kolonnen kunde därefter sedimentera och fångades upp i en kopp ibotten. Den sedimenterade massan av totalt suspenderat material (TSS) klassificerades i femolika sedimenteringshastighetsklasser och varje klass tilldelades en karakteristisksedimentationshastighet Det experimentella förfarandet följde ViCA’s protokoll (franskförkortning för sedimentationshastigheter för avloppsvatten). En modell av ensedimentationstank, ungefär som för sekundär-sedimenteringen i Benchmark SimulationModel No. 2 (BSM2), utvecklades som en 10 lager icke reaktiv tank. Massbalansen i varjelager bestämdes av det vertikala flödet av partiklar och beräknades med de experimentelltframtagna karakteristiska sedimentationshastigheterna. Återcirkulering av överskottsslam frånde efterföljande reningsstegen visade sig ha stor påverkan på slammetssedimentationsegenskaper i försedimenteringen. Typen av TSS-komponenter hade den störstainverkan på fördelningen av sedimentationshastigheter. Variationen i dos av bådefällningskemikalie och katjonspolymer före primär-sedimenteringstanken hade en visspåverkan på fördelningen. En första simulering med ett sannolikt dynamisk inflödesscenariokördes. Utan någon riktig kalibrering av modellen gav den ändå en relativt realistisk prognospå TSS i utgående vatten och i slamuttaget. / I samarbete med forskningsgruppen ModelEAU, Quebec, Kanada