The objective of this project was to develop a suitable procedure for the design, control and optimisation of the Tubular Filter Press. To this end, the following objectives were defined for this study: • To extend or improve upon the constant pressure compressible cake filtration model, predictive solution procedure, and standard laboratory characterisation techniques requlred to obtain the empirical model parameters, presented in Rencken (1992). A new generalised area contact constant pressure compressible cake filtration model was developed for both the internal cylindrical and planar filtration geometries. The model utilises a heuristically developed area contact function which relates the interparticle contact area to the solids compressive pressure within the cake. If the area contact is zero, the model reduces to the conventional point contact model as presented in Rencken ( 1992). The sludge used in this investigation was found to exhibit a negligible degree of area contact. A new pseudo variable pressure solution procedure was developed, that is an extension of the constant pressure solution procedure, to account for the initial variable pressure stage of the Tubular Filter Press operation. The pseudo variable pressure solution procedure was found to account accurately for the initial filtration behaviour observed during the pressurisation period of the Tubular Filter Press. However for the normal operation of the Tubular Filter Press. the difference between the output of the pseudo variable pressure and constant pressure solution procedures, was found to be insignificant. Wall friction in compression-permeability (C-P) cell tests was identified as a main source of error. The significance of wall friction was investigated using a specially constructed C-P cell. that enabled the transmitted pressure through the cake sample to be measured. The accuracy of the characterisation which had been corrected for the effects of wall friction, was found to improve the prediction of the filtration behaviour of the sludge significantly. The direct shear test was identified and documented as a feasible experimental procedure to determine the coefficient of earth pressure at rest. The coefficient of earth pressure is unique to the non-planar filtration geometries. The coefficient of earth pressure at rest was determined for the sludge used in this investigation. • To incorporate the constant pressure compressible cake filtration model and the associated predictive solution procedures into a user-friendly computer programme that will facilitate the design and optimisation of full-scale plants. The predictive solution procedures were incorporated into the Windows 95 computer programme, COMPRESS, that can be used for any constant pressure compressible cake dead-end filtration application where the filtration geometry is planar or internal cylindrical. A control and optimisation strategy for the continuous operation of the Tubular Filter Press has been proposed. To develop a regressive solution procedure, and incorporate this procedure into a user-friendly computer progranune, that will enable the empirical model parameters. normally obtained from standard laboratory-scale tests, to be obtained from actual filtration data. A regressive solution procedure was developed that utilises a direct search optimisation technique that is an extension of the COMPLEX method. The regressive solution procedure was incorporated into the Windows 95 program, REGRESS. The program utilises filtration data from any dead-end constant pressure filtration application of either planar or internal cylindrical geometry. REGRESS provides an effective means for determining the true physical or plant specific filtration characteristics of the sludge. The regressive solution procedure also enables the parameters specific to the new area contact model to be determined. The sludge characterisation obtained from regressing on filtration data was found to be a significant improvement in predicting the filtration behaviour, than the characterisation obtained from the standard non-filtration laboratory-scale methods, even after the C-P cell data had been corrected for the effects of wall friction. The programs COMPRESS and REGRESS should greatly assist in the design. control and optimisation of the Tubular Filter Press process. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

A collaborative pilot study of the microflora on biological activated charcoal (BAC) filters employed in the tertiary treatment of drinking water revealed the principle bacterial genera to be Pseudomonas, Alcaligenes, Achromobacter, Bacillus, Micrococcus, Corynebacterium, Chromobacterium, Microcyclus and Paracoccus. The microbial population of the filters paralleled seasonal carbon dioxide production. Of particular interest were the effects of the BAC miroorganisms upon precursors of trihalomethanes (THMs). Mixed populations of BAC microorganisms were cultivated for 50 days in a mineral salts-humic acid medium. It was concluded that (1) the BAC microflora enhances the absorptive capacity of the filters; (2) chemico-physical and biological processes operate in concert to lower the concentration of precursors of THMs; and (3) few bacterial pathogens establish themselves on the filters.

The capacity and efficiency of melter slag (provided by New Zealand Steel) to remove heavy metals and suspended solids from stormwater samples are studied in this thesis. A series of batch tests were carried out to investigate the adsorption-desorption mechanism of the slag to remove heavy metals (Cd2+, Zn2+ and Cu2+) from working solutions. The results showed that all the tested metallic ions could be removed by mixing the melter slag with the working solutions. Adsorption and ion exchange are the dominant mechanisms in this process. The adsorption capacity follows the descending order of Cu2+ > Zn2+ = Cd2+. Varied binding energy of different metallic ions to the slag resulted in competitive adsorption between ions.A variety of substances: inorganic salts (KCl, NaCl, KNO3 and sea water), organic acids (citric and tartaric) and inorganic acids (nitric and carbonic), were tested as desorbing agents to recover the used slag. Citric acid in sea water was found to be the best in terms of desorption efficiency and cost-effectiveness.The column tests were carried out to simulate the filtration bed in laboratory conditions. Stormwater samples were collected from residential and commercial areas in Auckland. The synthetic stormwater samples were prepared from clay and metallic ion solution. Both samples were used as feeding solutions in the tests. The removal efficiencies of suspended solids and metallic ions (Zn2+, Cd2+ and Cu2+) vary depending on different operation conditions. They are in inverse proportion to the grain size of the melter slag and the influent flow rate. The higher removal efficiency of Zn2+ than that of suspended solids infers that metallic ions are removed by both precipitation and adsorption.

The tubular filter press is a novel tubular configured filter press for the filtration or dewatering of sludges. The unique features of the filter press are: (i) during the cake deposition cycle, cake is deposited on the internal walls of a self-supporting array of horizontal collapsible porous fabric tubes; (ii) during the cake removal cycle, cake is dislodged from the tube walls by means of a roller cleaning device and the dislodged flakes of cake are hydraulically transported out of the tubes by the feed sludge which is simultaneously re-circulated at a high flow rate through the tubes. The two main problems experienced on a prototype tubular filter press, which was erected at a water treatment plant to dewater the sludge from the clarifier underflow, were: (i) tube blockage problems during the filtration cycle; (ii) low cake recoveries (high cake losses) during the cake removal cycle. The following objectives which were defined for this study, were regarded as fundamental prerequisites for any solution of the two main problems: (i) to develop a predictive dead-end internal cylindrical model for compressible cake filtration inside a porous tube; (ii) to investigate the cake losses during the cake removal cycle of the tubular filter press; (iii) to develop a predictive unsteady-state internal cylindrical cross-flow microfiltration model for a non-Newtonian sludge which, when filtered, produces a very compressible cake. (An alternative to dead-end filtration during the filtration cycle of a tubular filter press is low axial velocity cross-flow filtration). On the basis of the objectives the study was divided into three separate investigations. To date no one has developed a model which incorporates the cylindrical configuration of the filter medium for dead-end compressible cake filtration inside a porous tube. The most comprehensive model for dead-end external cylindrical compressible cake filtration is that of Tiller and Yeh (1985). This model was adapted for internal cylindrical compressible cake filtration. In essence the model by Tiller and Yeh (1985) requires the solution of a system of two ordinary differential equations in order to calculate the radial variation of solids compressive and liquid pressures in a compressible filter cake deposited externally on a cylindrical surface. The relevant equations were derived for internal cylindrical compressible cake filtration and it was found that one of the differential equations changes from: dPl/dr = H1/2nrK (external cylindrical) to dPl/dr = H12nrK (internal cylindrical). The other differential equation remains unaltered for internal cylindrical compressible cake filtration. A batch of waterworks clarifier sludge from the prototype tubular filter press was used for experiments to evaluate the performance of the internal cylindrical filtration model. The cake produced by the filtration of this sludge had to be characterized for the model. Compression-permeability data were obtained over a wide solids compressive pressure range. A Compression-Permeability (C-P) cell was used for high solids compressive pressures (10 kPa<_ ps<_400 kPa) and settling tests were used for low solids compressive pressures (0,0065 Pa <_ ps < 525,6 Pa). The cake was found to be very compressible (compressibility coefficient = 0,989). Empirical equations of the form, K' = Fps - b and (1 - E) = B pbs , were derived from the C-P cell and settling tests to relate permeability and porosity to solids compressive pressure. The equations were slightly different to those proposed by Tiller and Cooper (1962). The predictions by the internal cylindrical compressible cake filtration model were compared to the results of constant pressure internal cylindrical filtration experiments, at filtration pressures of 100 kPa, 200 kPa and 300 kPa, using the waterworks clarifier sludge. The internal diameter of the filter tube which was used for the experiments was 26,25 mm. The model accurately described the results of the filtration experiments in terms of volume of filtrate, average cake dry solids concentration, filtrate flux and internal cake diameter. The differences between external cylindrical, internal cylindrical and planar compressible cake filtration were highlighted. Since the tubular filter press is a novel process, the cake losses during the cake removal cycle have not been investigated before. An investigation was therefore conducted into the cake losses which occur during the cake removal cycle. The same batch of clarifier sludge was also used for the investigation of cake losses during the cake removal cycle at filtration pressures of 100 kPa and 300 kPa. It was found that significant cake losses occurred due to: (i) the shear of the cleaning fluid prior to the action of the rollers (losses varied between 10 % to 20 % of the deposited cake dry solids); (ii) the combined action of the rollers when dislodging the cake and the hydraulic conveyance of the dislodged flakes of cake (losses varied between 30 % to 40 % of deposited cake dry solids). A new shear model, which was developed, accurately predicted the cake losses and increase in internal cake diameter and average cake dry solids concentration, which occurred due to the shear of the cleaning fluid. For the shear model the sludge (cake) rheology was determined using a capillary-tube viscometer. It was found that the sludges exhibited Bingham plastic behaviour in the solids concentration range: 3,58 % m/m <_Cs <_16,71 % m/m. The cake losses due to the action of the rollers and hydraulic conveyance of the dislodged flakesof cake decreased markedly as filtration pressure and filtration time were increased, while a decrease in path length for hydraulic conveyance of dislodged cake flakes resulted in a mild decrease in these cake losses. A literature review revealed that to date only one mathematical model (Pearson and Sherwood, 1988) is available for the unsteady-state cross-flow microfiltration of a non-Newtonian sludge which, when filtered, produces a compressible cake. A new unsteady-state internal cylindrical axial convection shear model (for laminar flow of the feed sludge) was developed for cross-flow microfiltration of a Bingham plastic sludge which, when filtered, produces a very compressible cake. Similar to the approach by Pearson and Sherwood (1988) this model is a combination of the dead-end internal cylindrical compressible cake filtration model and the "cleaning fluid" shear model. The major difference between the new model and the model by Pearson and Sherwood (1988) is that unlike the convection-diffusion model of Pearson and Sherwood (1988), diffusive and shear induced diffusive back-mixing of particles were assumed to be negligible. The existence of a shear plane within the cake forms the basis of the model. Those cake layers with a yield stress less than the shear stress exerted by the flowing feed sludge at the inner cake wall are convected along the shear plane. It was assumed that the axial convection of the solids in the moving cake layer along the shear plane is the sole mechanism for removal of solids deposited at the cake surface. The model was compared to the results of cross-flow microfiltration experiments at one filtration pressure (300 kPa) and cross-flow flow rates of 0,84 l / min; 1,58 l / min; 2,43 l / min and 4,44 l /min. The model accurately described the variation of filtrate flux, internal cake diameter and average cake dry solids concentration during the unsteady-state time period. The model, however, had to be "extended" by incorporating empirical equations for changes in permeability and porosity (due to further cake compaction) to obtain a good fit between the model and experimental results during the pseudo steady-state time period. The results of all three investigations provide a greater understanding of the cake deposition process (during both dead-end and cross-flow filtration modes) and the cake removal process for the tubular filter press. This should assist in finding solutions to the two main problems which were experienced on the prototype tubular filter press. / Thesis (Ph.D.)-University of Natal, Durban, 1992.

The capacity and efficiency of melter slag (provided by New Zealand Steel) to remove heavy metals and suspended solids from stormwater samples are studied in this thesis. A series of batch tests were carried out to investigate the adsorption-desorption mechanism of the slag to remove heavy metals (Cd2+, Zn2+ and Cu2+) from working solutions. The results showed that all the tested metallic ions could be removed by mixing the melter slag with the working solutions. Adsorption and ion exchange are the dominant mechanisms in this process. The adsorption capacity follows the descending order of Cu2+ > Zn2+ = Cd2+. Varied binding energy of different metallic ions to the slag resulted in competitive adsorption between ions.A variety of substances: inorganic salts (KCl, NaCl, KNO3 and sea water), organic acids (citric and tartaric) and inorganic acids (nitric and carbonic), were tested as desorbing agents to recover the used slag. Citric acid in sea water was found to be the best in terms of desorption efficiency and cost-effectiveness.The column tests were carried out to simulate the filtration bed in laboratory conditions. Stormwater samples were collected from residential and commercial areas in Auckland. The synthetic stormwater samples were prepared from clay and metallic ion solution. Both samples were used as feeding solutions in the tests. The removal efficiencies of suspended solids and metallic ions (Zn2+, Cd2+ and Cu2+) vary depending on different operation conditions. They are in inverse proportion to the grain size of the melter slag and the influent flow rate. The higher removal efficiency of Zn2+ than that of suspended solids infers that metallic ions are removed by both precipitation and adsorption.

Membrane technology can be utilised for the high purification and desalination of water. However membrane filtration processes are commonly impeded by membrane fouling, which can lead to flux decline and an overall reduction in separation efficiency within the process. Therefore the aim of this research study was a comprehensive investigation of the issue of biofouling on industrial RO membranes through molecular biology techniques, characterisation of surface charge of foulant bacteria and RO membrane surface and AFM imaging and force measurements on clean and fouled membranes for the determination of adhesion force and micromechanical properties. The laboratories within Gwangju Institute of Science and Technology, South Korea and Swansea University, Wales were equipped for the scope of this research work. Research focused on the extraction of microbial DNA obtained from fouling layers on the surface of Reverse Osmosis Membranes obtained from the Fujairah Water and Power Plant, UAE. The use of the culture independent method of the molecular technique based on the 16S rDNA sequence and constructed gene libraries, was then used to determine the bacterial species that caused significant fouling on the RO membrane. Four bacterial species isolated from the fouling layer from the RO membrane were characterised in terms of electrophoretic mobility and zeta potential to determine the cell surface charge within various industrial relevant environments for the elucidation of cell adhesion mechanisms to the membrane surface. AFM images of virgin and fouled membranes were obtained and analysed to reveal the roughness of the surface which could influence fouling and the surface charge of the membranes were measured through the method of streaming potential at various industrial relevant environments to further elucidate the mechanisms of cell adhesion to the membrane surface. Force measurements were performed to reveal the adhesion force and elasticity values of virgin, process fouled and purposely fouled with the four bacterial isolates, to determine process behaviour in various environmental conditions. Through this research and future work, it is hoped that a rational strategy for economic and effective cleaning processes will be developed which will maintain efficient membrane operation and prolong membrane life, thus enabling the reduction of operating costs of such processes.

A method for removing chemical contaminants, such as phenol, from a stream of waste water has been proposed. The method uses a device for contacting water with activated carbon, called a "panel bed". In this device, water flows across a bed of activated carbon retained within a set of parallel louvers. Construction permits contaminants in the entering stream of water to be adsorbed on carbon particles, starting from the entrances of the spaces between the louvers. A pulseback technique is used to remove the region containing "contaminated" activated carbon. Pulseback is applied periodically after appropriate intervals of operation. This research aims to determine operating characteristics of a panel bed and focuses on the study of pulseback. From a previous design of a panel bed filter for removing fly ash from stack gases, and from a basic study of characteristics of activated carbon adsorption isotherms, a panel bed was constructed which was believed to be suitable for contacting activated carbon with waste water. Pulseback consists of a reverse transient flow of water across the panel bed of activated carbon. Detailed descriptions of pulseback equipment, data on the spill of carbon that accompanies pulseback, and correlation of the carbon spill data are included. The carbon spill during pulseback appears to correlate with "active time", where this term refers to the time during which a reverse pressure difference, created by the reverse transient flow of water, exceeds a critical minimum value necessary for any spill at all to occur. For the specific design of equipment used in this study, the spill is relatively small if the active time is less than 60 milliseconds. Beyond 60 milliseconds, for the specific equipment used, the spill is linear with active time, and occurs at a rate that appears related to Zenz's modification of the Francis weir formula to describe efflux of solids from a static bed through an opening. / Master of Science

The removal mechanisms of soluble manganese [Mn (1l)] through mixed-media filters were investigated. Experimentation was directed toward the continuous supply of an oxidant during column filter studies. Free chlorine (HOCl, OC1â ) was chosen to increase soluble manganese removal efficiency because chlorine is readily available and inexpensive. Filter media from four different water treatment plants were used in this study. Continuous-flow filter columns were operated in the presence and absence of 2.0 milligrams per Liter (mg/ L) free chlorine. Maintaining constant influent manganese concentrations of 1.0 mg/L and flow rates of 2.5 gallons per minute per foot squared (gpm/ft2), the operational pH values of 6-6.2, 7.8 and 8.8 were investigated. Results indicate that a continuous feed of free chlorine (2 mg/L) applied to the filter columns could increase manganese (II) removal efficiency. However, the amount and oxidation state of the MnOx(S) surface coating initially on the media and the influent pH had major influences upon the uptake of soluble manganese. From numerous Mn (II) uptake studies with different media and varying pH conditions, oxide-coated filter media continuously regenerated with free chlorine could result in increased soluble manganese removal through adsorption upon the MnOx(s) surface coating and subsequent oxidation directly on the media surface. The relationships of manganese removal and chlorine consumed were also explored. To further investigate the mechanisms of free chlorine oxidation for the removal of reduced manganese, pH 5.0 backtitrations were conducted following exhaustion of the filter media. The exposure of such low pll conditions to columns operated in the presence and absence of HOCI would ascertain if oxidation of the adsorbed Mn²⁺ was always occurring, regardless of an oxidant feed. Results indicated that in the absence of HOCI, the mechanisms for manganese removal on oxide-coated filter media were adsorption only. With the additional of HOCI, the adsorbed Mn²⁺ is oxidized directly on the surface of the media, thereby, continuously regenerating the surface oxide coating. Additional work was begun to ascertain if free chlorine could be used as a viable alternative to potassium permanganate (KMnO₄) regeneration of oxide-coated filter media. Preliminary findings indicate from column cycling experiments that free chlorine could be used to regenerate oxide-coated filter media prior to backwashing. / Master of Science

This study evaluated alternatives to continuously regenerated greensand for iron and manganese removal. Specific objectives were (1) to investigate the applicability for removing soluble manganese by adsorption and oxidation onto the surface of manganese oxide-coated media, and (2) to develop mathematical models to predict the removal of soluble manganese both in the presence and absence of free chlorine. Results from a pilot-scale experiment in Columbus, Indiana, showed that when the filters were operated in a conventional oxidant addition mode (i.e., with the addition of HOCI and KMnO₄) the anthracite-sand and anthracite-sand-garnet configurations both provided efficient treatment because of the reduced rate of head loss. Further experiments, without the use of KMnO₄ or greensand, equally removed manganese by adsorption and oxidation onto oxide-coated media; however, the treatment process resulted in reduced head loss and oxidant costs. Results from this study and other previous research demonstrated that manganese removal by oxide coatings is an efficient and functional treatment mechanism. However, little quantitative information was available to predict these processes. Therefore, mathematical models were developed to help predict design and operational conditions needed to implement oxide-coated media as a treatment process. Two separate models were developed to predict (1) the continuous removal of soluble manganese in the presence of free chlorine (continuous regeneration model), and (2) the eventual breakthrough of soluble manganese without oxidant addition (intermittent regeneration model). Each model was derived from chemical reaction, mass balance, or isotherm equations and was further developed by a sensitivity analysis and parameter estimation. The two models were then verified by predicting manganese removal from independent research. The continuous regeneration model can help predict the removal of soluble manganese by adsorption and oxidation on the surface of oxide-coated media and is useful in the design of filters for continuous Mn(Il) removal. The intermittent regeneration model effectively predicts the performance of filters without the addition of an oxidant and is useful for treatment plants which cannot apply chlorine continuously to their filter applied water. / Master of Science

Integrating ultrafiltration (UF) membranes in lieu of traditional media filters within conventional surface water coagulation-flocculation-sedimentation processes is growing in popularity. UF systems are able to produce low turbidity filtered water that meets newer drinking water standards. For typical drinking water applications, UF membranes require periodic chemically enhanced backwashes (CEBs) to maintain production; and citric acid is a common chemical used for this purpose. Problems may arise when the backwash recycle stream from a citric acid CEB is blended with raw water entering the coagulation basin, a common practice for conventional surface water plants. Citric acid is a chelating agent capable of forming complexes that interfere with alum or ferric chloride coagulation. Interference with coagulation negatively affects settled water quality. Acetic acid was investigated as a potential substitute for citric acid in CEB applications. A jar testing study was conducted to compare the impacts of both citric acid and acetic acid on the effectiveness of aluminum sulfate (alum) and ferric chloride coagulants. Citric acid was found to adversely affect coagulation at lower acid to coagulant (A/C) molar ratios than acetic acid, and a coagulation interference threshold was identified for both acids based on settled water turbidity goals recommended by the U.S. Environmental Protection Agency (EPA). Pilot testing was conducted to assess the viability of acetic acid as a UF CEB chemical. Acetic acid CEBs maintained pilot performance in combination with sodium hypochlorite CEBs for filtering a raw California surface water. It is believed that this is the first ultrafiltration membrane process application of acetic acid CEBs for municipal potable water production in the United States.