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.

This study presents the dewatering assessment of a marl quarry with the future pit lake level predictions. The objectives of the study were / (1) to determine the dewatering requirements that would allow for the continuation of the quarrying operations in the deeper parts of the quarry, (2) to design an optimum dewatering system compatible with the site hydrogeological conditions and quarrying plans, (3) to assess the environmental impacts of dewatering on the local water (surface and ground water) resources and users, and (4) to predict the future pit lake level and flooding period for different meteorological conditions. To these ends, previous investigation reports and maps have been compiled and reviewed and field investigations have been conducted. During the field investigations pumping and observation wells were drilled and installed. After installation, in situ tests were conducted to determine aquifer parameters. It was found that properties of the material is conducive to the dewatering activities that will be necessary for the deepening of the open pit of the marl quarry. A groundwater model was developed based on the field data gathered. According to this model dewatering trenches will be needed to dewater the pit. The model predicted that operating these dewatering trenches would create an elongated cone of depression that will sufficiently lower the groundwater table so that quarrying operations can proceed. Lowering of the water table may produce a negative impact on groundwater resources within the aerial extent of the cone of depression. This potentially negative impact was investigated with model simulations and has been found that the impact to the resources would be negligible. Three scenarios were evaluated as possible dewatering discharge disposal solutions. The preferred scenario included the discharge of this water to the stream, which is flowing on the western side of the quarry. The pit will start to fill with water immediately after the dewatering operations stopped. In order to predict the pit lake flooding period and final lake elevation, pit lake hydrologic model was developed. The simulations predict that the final pit lake elevation would be at 991 m. The pit lake will rise to this level at approximately 72 years after closure.

Solid-liquid contact angle is an important parameter in many particulate processes of the mineral, ceramic and chemical industries. In particular, modification of the contact angle through surface active agents plays a crucial role in froth flotation of minerals. In the case of flat solid surfaces, direct measurement of the contact angle is possible. However, such flat surfaces can not be obtained with finely divided solids typically encountered in flotation applications. Then, indirect methods based on powder beds as thin layers of powders deposited on glass plates or packed columns are used for the determination of apparent contact angles. This thesis presents an alternative novel method based on the capillaric dewatering of filter cakes for the measurement of the receding contact angle and correlates the contact angles measured as such with column wicking and micro-flotation test results of zircon and rutile mineral particles. The experimental procedure is simple and fast. The results have proven that the proposed method is reliable and give a good measure of the contact angle in the absence and presence of surface active non-wetting agents.

Achieving microbial compliance levels in biosolids storage is complicated by the unpredictable increase of Escherichia coli (E. coli), which serves as an important indicator for pathogen presence risk. Meeting required microbial specifications validates sludge treatment processes and ensures that a safe product is applied to agricultural land. Controlled indicator monitoring provides confidence for farmers, retailers and the food industry, safeguarding the sludge-to-land application route. Following mechanical dewatering biosolids products are stored before microbial compliance testing permits agricultural application. During storage, concentrations of E. coli bacteria can become elevated and prevent the product from meeting the conventional or enhanced levels of treatment outlined in The Safe Sludge Matrix guidelines. Literature research identified innate characteristics of sludge and ambient environmental parameters of storage which are factors likely to influence E. coli behaviour in stored biosolids. The research hypothesis tested whether E. coli growth and death in dewatered sewage sludge can be controlled by the modification of physical-chemical factors in the cake storage environment. Parameters including nutrient availability, temperature, moisture content and atmospheric influences were investigated through a series of laboratory-scale experiments. Controlled dewatering and the assessment of modified storage environments using traditional microbial plating and novel flow cytometry analysis have been performed. At an operational scale, pilot trials and up-scaled monitoring of the sludge storage environment have been conducted enabling verification of laboratory results. Understanding the dynamics of cell health within the sludge matrix in relation to nutrient availability has provided a valuable understanding of the mechanisms that may be affecting bacterial growth post-dewatering. The importance of elevated storage temperatures on E. coli death rates and results showing the benefits of a controlled atmosphere storage environment provide important considerations for utilities.

The purpose of the study was to evaluate which method for emptying of septic tanks that contributed with the lowest particle content in outgoing water during the period of a year. The methods for emptying in the comparison was mobile dewatering using polymer, complete pump-out and mobile dewatering using mechanic separation. Within the study, wastewater was sampled from septic tanks third compartment, however, only from septic tanks that were dewatered using polymer. Samples were taken one time before emptying followed by five occasions after emptying. The results from those samples were compared to previously existing results from complete pump-out and mobile dewatering using mechanic separation. Due to differences in method for sampling, the comparison in the discussion was limited to; samples taken before emptying and two weeks after emptying from septic tanks that had been completely pumped-out and dewatered using mechanic separation. The samples taken before emptying showed the particle content after using the septic tanks for a year since the previous emptying. Based on those samples there were no significant difference between mobile dewatering using polymer and complete pump-out or between mobile dewatering using polymer and mobile dewatering using mechanic separation. Two weeks after emptying the lowest particle contents were found in septic tanks that had been completely pumped-out followed by the two dewatering methods.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / Polymers used as flocculants in the secondary sludge dewatering process are one of the most expensive inputs in these plants. The disadvantage is that these polymers cannot be recycled. Currently, controlling of polymer dosing rate is done by trial and error method. It has been shown that huge savings can be made by optimising the polymer dosing using rheological properties. It is not an easy task to optimise this process because of changing sludge characteristics on a daily, seasonal and annual basis. To try and optimise polymer dosing and polymer concentration, the variation in rheological properties needs to be understood first. The correlation between the process parameters and the rheological properties needs to be determined. There is currently no database of rheological properties of secondary wastewater sludge feeding belt filter presses available. To address these issues, a 12 week assessment of the rheological properties of the sludge feed to the belt filter press before and after conditioning in four wastewater treatment plants in Cape Town was conducted. The rheological properties were determined using an MCR-51 rheometer with parallel plate geometry under controlled temperature. After concluding the assessment, a 3-level Box-Behnken factorial trial was conducted at Plant K wastewater treatment plant to statistically analyse the correlation and/or interactions between the process parameters (sludge feed flow rate, polymer dosing concentration, polymer dosing rate and belt press speed) and the rheological properties of the sludge to optimise the plant performance.

Modification of softwood kraft pulp by the addition of either polysulfide (PS) or sodium borohydride (NaBH4) has been shown to increase the pulp yield due to a higher retention of glucomannan.  The pulps with higher yield gave a paper with higher tensile index than reference pulp, especially at lower degrees of refining. The higher yield pulps also showed a greater porosity of the fibre wall, indicating an increase in the swelling potential of the fibres. This can lead to increased fibre flexibility and increased joint strength between the fibres and to the higher handsheet tensile index. However, the swelling increase associated with the higher hemicellulose content could also make dewatering more challenging because of the higher water retention of the pulp. The results of this study show however that the positive influence of the increase in yield (fewer fibres and a more open sheet structure) dominates over the negative influence of the higher hemicellulose content on the dewatering properties, especially at lower refining energy levels. Studies simulating full-scale tissue machine dewatering conditions showed that pulps with a higher yield and a higher hemicellulose content had a higher tensile index at the same dryness. Moreover, the same dryness level was achieved in a shorter dwell-time. A given tensile index was also achieved with less refining energy. Increasing the yield and hemicellulose content by the addition of either an oxidizing or a reducing agent in the softwood kraft pulping process thus has a potential for giving high quality fibres for tissue paper production with less refining energy and lower drying energy costs. / <p>Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 inskickat.</p><p>At the time of the defence the following papers were unpublished: paper 2 submitted.</p>

The main water transport properties of clay brick are critically examined in respect of suction and water content. An experimental investigation is carried out to compare the sorptivity and vacuum saturation porosity with suction and “porosity” tests in the standards. The water retaining ability (desorptivity) of freshly mixed hydraulic lime and cement mortars is examined and the effect of hydraulicity, pozzolanic and non-pozzolanic additive materials, binder particle size and the chemistry of mix water on the water retentivity of these mortars are investigated. The inter-relationship of substrate (brick) suction and desorptivity of freshly mixed wet lime and cement mortar are investigated. It is shown that the initial setting time of dewatered freshly-mixed mortars is reduced by a factor of up to 80% and the final setting time is reduced by a factor of 60%. The extent of this reduction depends on hydraulicity. For the cured mortars, following dewatering in the wet state, the compressive and flexural strengths are increased by about 40% for cement mortar and by more than 3 times for lime mortar. The sorptivity of hardened cement and lime mortars is reduced by 80%. These results have implications for the British and European standards where mortars are cast in impermeable steel moulds in which dewatering cannot occur prior to setting. The accuracy of the methodology of the American Petroleum Institute (API) pressure cell technique for testing the water retaining ability of fresh mortars was critically examined. An experimental investigation was carried out in two parts, first by changing the controlled variables of the experimental set up. Second the consequences for the results obtained were evaluated. Experimental verification is undertaken of the fundamental Sharp Front equation S=(2KΨf)^(1/2) which describes the inter-relationship of capillary pressure, sorptivity, porosity and hydraulic conductivity.

This study was conducted to address the controlling factors of biosolids stability as they relate to mesophilic anaerobic digestion, dewatering processes and digestion enhancement by wet sludge disintegration technologies. The working hypothesis of this study is that digestion performance; nuisance odor generation and the degree of digestion enhancement by wet sludge disintegration are directly related to anaerobic floc structure and its interaction with shearing forces. Mesophilic digestion was studied in two modes of operation, convention high rate and internal recycle mode to enhanced digestion using a wet sludge disintegration device. The internal recycle system operated on the premise that stabilized sludge would be removed from the digester disintegrated, either by mechanical shear or ultrasonic disintegration for this study, and returned it for to the digester further for further stabilization. Both benchscale and full-scale demonstrations found this mode of digestion enhancement to be effective for mechanical shear and ultrasonic disintegration. It was also determined that volatile solids destruction in both conventional and enhanced mesophilic anaerobic digesters can be reasonably predicted by the concentration of cations in the sludge being treated. It was found that depending on the disintegration device used to enhance digestion performance was influenced by different cation associated fractions of the sludge floc. Along with the improvement of digester performance, overall biosolids stability was investigated through of volatile organic sulfur emissions from dewatered biosolids. In doing so, a method to mimic high solids centrifugation in the laboratory was developed. The centrifugation method identified three major factors that contribute to the generation of odors from biosolids: shear, polymer dose, and cake dryness. The inclusion of shearings suggest that one means of reducing odors from biosolids generated by centrifugation is to use a shear enhanced digestion technology to degrade odor precursors, such as amino acids, within the digester prior to dewatering. Furthermore, the mechanical shearing within a digester is thought to be similar to that of mechanical shear enhanced digestion; therefore, the floc properties that control the digestion process would control observed odor generation. / Ph. D.

Sludge treatment and disposal are one of the most important parts of sewage treatment. These are economically challenging parts, and therefore emphasis is placed on effective dosing. The dose should be as small as possible but also the highest dry matter output. The main target of this diploma thesis is therefore to show that it is possible to achieve the same or better degree of drainage of the sludge if different flocculant/coagulant ratio is applied to the sludge. Diploma thesis deals with determination of the optimal combination of chemical doses during sludge dewatering. The thesis contains two parts, practical and theoretical. The theoretical part consists of research, overview of processed research and works in the area of sludge dewatering. The second part is a description of laboratory measurements and evaluation of results.