The relationships between an activated sludge's particle size distribution and its specific resistance were investigated. Particle size distributions were rearranged by sludge storage, replacing sludge supernatant with alum sludge supernatant, and by polymer conditioning. Specific resistance was found to increase with decreasing mean particle size. The blinding coefficient (B) was used to show the influence of mean particle size on filter cloth blinding. Blinding was shown to occur only for mean diameters less than 40u. The use of the blinding coefficient also allowed the prediction of maximum and minimum values of specific resistance and showed blinded sludges to have underestimated specific resistance values. The coefficient of compressibility was shown to decrease with increasing mean particle size. The use of the coefficient of compressibility to predict vacuum filter yield was shown to be a valid relationship. / M.S.

Floc density measurements may play a significant role in analyzing sludge dewatering characteristics. A laboratory technique was developed to measure this property by means of isopycnic centrifugation. Four laboratory sludges were subjected to a series of dewatering tests: gravity thickening, centrifugation, vacuum filtration, and high-pressure dewatering. Each sludge was analyzed for changing macro- and micro-properties during increasing stages of dewatering. It was concluded that sludge thickening rates are influenced by aggregate volume fractions, sludge density, suspension porosity, and the total surface area occupied by sludge aggregates. The extent of mechanical dewatering is impacted by similar parameters; namely, floc volume fractions, sludge density, cake porosity, and the total surface area occupied by sludge floc. By interpreting the laboratory data, a model was formulated to describe changes in water distribution during the dewatering of sludges. This model includes a speculative view of the qualification and quantification of water-types. / Master of Science

The performance of Integrated Fixed Film Activated Sludge (IFAS) was evaluated for its effect on nitrification and denitrification in a bench scale biological nutrient removal (BNR) process configured as a Virginia Initiative Project (VIP) process. The IFAS systems consisted of a sponge - like biomass support system (Captor) operated in the aerobic zone of two independent treatment trains, and a fibrous biomass support system (Ringlace) operated in the aerobic zone of one independent treatment train. A fourth treatment train containing no biomass support system was operated as a control. A range of four aerobic MCRTs was studied, from 3.4 days to 1.7 days. All experiments performed for this research effort were conducted using domestic wastewater obtained directly from Blacksburg, VA and the Virginia Tech campus. Results indicated that the presence of the sponge - like biomass support media (Captor) freely floating in the aerobic zone mixed liquor greatly increased the ability of that system to achieve nitrification at temperatures of 12 degrees Celsius and aerobic suspended growth MCRTs as low as 1.7 days. A statistical t-test analysis demonstrated this with 99% confidence. Results early in the research, as well as previous research by Mitta (1994) indicated that fibrous biomass support systems (Ringlace) did not perform as well with respect to nitrification as did Captor, and experiments on Ringlace were discontinued midway through the research. Increased denitrification throughout the IF AS/Captor train was noted as a result of the increased nitrification. However, the use of Ringlace appeared to enhance denitrification which occurred in the aerobic zone. Further study is recommended to verify this data. A decrease in sludge production in the IFAS train containing Captor could not be statistically established. However, observed sludge yield coefficients for the IF AS/Captor train were consistently lower than those for the Control train. A statistical analysis was not performed, but the values varied considerably so that direct comparison was difficult. / Master of Science

This study was undertaken to examine the polymer mixing requirements for sludge dewatering with a belt filter press. This involved correlating full-scale field studies to small scale laboratory testing. Bench testing involved the use of a high-speed mixer and two sludge dewatering response tests: the capillary suction time test and the time-to filter test. Full-scale testing measured the belt press response to belt speed, sludge throughput, and polymer dose. Data indicated that the conditioning and dewatering scheme of the three belt filter presses was a low shear, low total mixing energy operation. The Gt, or total mixing energy, of these operations was in the range of 8,000-12,000. Optimal dose predicted by the bench-scale testing correlated well to the optimal dose for maximum cake solids coming off the belt filter press. Also, the amount of water removed from the sludge with the belt press was largely a function of the type of solids present in the sludge and less of a function of the number of rollers or residence time in the press. / Master of Science

The dewatering of arsenic-containing residuals is a process that has received little study in the past. Arsenic that has been removed from water by sorption to ferric or aluminum hydroxides can accumulate in residuals to concentrations many times higher than in the source water. The first part of this study evaluates the effectiveness of lime conditioning as a method for immobilizing this arsenic. As the pH is increased with addition of caustic soda or soda ash, soluble arsenic concentration increases dramatically. However, as the pH is increased with lime, very little arsenic is released back into the water. On the basis of previous research this phenomenon might be attributed to the formation of a calcium arsenate solid. However, this study indicates it is more likely that the soluble calcium neutralizes the negative surface charge on the hydroxide solids at high pH and enhances arsenic sorption compared to when calcium was absent. In many cases arsenic-containing residuals are stored in lagoons and allowed to reside there for months or even years. Many parameters may affect the soluble arsenic concentration and speciation in these lagoons. The second portion of this study gives some baseline conditions for these lagoons, both with and without microbial activity and biological organic matter. In these practical situations it appears that lime can assist in keeping arsenic sorbed to the solids and prevent its release to the environment. / Master of Science

Ett avgörande steg i avloppsvattenrening med aktivslammetoden är att slammet kan avskiljas från det renade vattnet. Detta sker oftast i sedimenteringsbassänger. Sedimenteringsproblem är dock vanliga på många avloppsreningsverk, vilket kan leda till att föroreningar följer med utgående vatten. Studier om slamegenskaper är därför viktiga för att öka förståelsen för vilka faktorer som påverkar sedimenteringen och vad som kan göras för att minska problemen. I detta examensarbete har ett mindre avloppsreningsverk i Lövsta utanför Uppsala studerats. Ungefär en tredjedel av flödet till verket kommer från ett närliggande slakteri. Verket har återkommande problem med flytslam i slutsedimenteringsbassängen. Syftet med arbetet var att – genom litteraturstudier, provtagning, fullskaleförsök och analys – identifiera orsaker till flytslamproblemen. Även förslag till åtgärder skulle läggas fram. En utvärdering av reningsprocessen genomfördes dels utifrån befintliga mätdata, dels genom utförligare provtagningar och mätningar som gjordes under en treveckorsperiod i oktober. Höga nitrathalter observerades i vattnet, särskilt i den utjämningstank där flödesutjämning och förbehandling av slakterivattnet sker. De höga nitrathalterna, i kombination med en lång slamuppehållstid i slutsedimenteringsbassängen, bedömdes vara orsaken till flytslambildningen eftersom båda dessa faktorer gynnar uppkomsten av kvävgas genom denitrifikation. Det är denna gas som lyfter slammet från botten av bassängen till ytan. Två möjliga åtgärder för att lösa flytslamproblemen bedömdes vara genomförbara. Den ena var att öka bortpumpningen av slam från botten av slutsedimenteringsbassängen, för att förkorta slamuppehållstiden. Den andra var att denitrifiera vattnet innan det når slutsedimenteringen. Av dessa förslag ansågs det senare vara mer tilltalande ur både ekonomisk och miljömässig synvinkel. En strategi för att denitrifiera vattnet bedömdes vara intermittent luftning av utjämningstanken. Denna luftningsstrategi tillämpades under en försöksperiod på tio veckor. Nitrathalterna mättes en eller två gånger i veckan under försöksperioden. En sänkning av nitrathalterna observerades: från 182 mg/l till som lägst 60 mg/l i utjämningstanken och från 65 mg/l till som lägst 18 mg/l i luftningsbassängen. Sänkningen var dock inte tillräcklig för att förhindra flytslambildning i sedimenteringsbassängerna. Den ofullständiga denitrifikationen berodde troligtvis på för låga BOD-halter i utjämningstanken. Vidare undersökningar behövs för att utvärdera och optimera kvävereningen genom intermittent luftning. / One of the most crucial steps in wastewater treatment with activated sludge is the separation of sludge from the treated effluent. This is most often done by sedimentation in clarifiers. Sedimentation problems are, however, common in many wastewater treatment plants, causing higher concentrations of pollutants in the effluent. Research on sludge characteristics is therefore important to increase the knowledge about which factors affect the sludge settling properties and what can be done to minimize problems. In this master thesis a small wastewater treatment plant in Lövsta outside Uppsala, Sweden, was investigated. About a third of the influent water to the plant comes from a slaughterhouse situated nearby. The plant suffers from recurrent problems with rising sludge in the secondary clarifier. The purpose of this thesis was to – through literature studies, sampling, full scale experiments and analysis – identify causes for the rising sludge problem. Also, suggestions to remedy the problem were to be presented. An evaluation of the treatment process was conducted from existing measurement data and from sampling and measuring done for three weeks in October. High concentrations of nitrate were found in the water, especially in the equalization tank, where flow equalization and primary treatment of the slaughterhouse wastewater takes place. The high concentrations of nitrate, in combination with a long sludge retention time in the secondary clarifier, were judged to be the reason for the formation of rising sludge. Both of these factors stimulate the development of nitrogen gas through denitrification. This gas lifts the sludge from the bottom of the clarifier to the water surface. Two possible solutions to the rising sludge problem were considered feasible. One was to increase the pumping of sludge from the bottom of the secondary clarifier, to decrease the sludge retention time. The second was to denitrify the water before it reaches the clarifiers. Of these two suggestions, the second was regarded as more appealing from both an economical and an environmental point of view. One method to denitrify the water was deemed to be intermittent aeration in the equalization tank. This aeration strategy was implemented for ten weeks. Nitrate concentrations were measured one or two times a week for this period of time. A decrease in nitrate concentrations was observed: from 182 mg/L to at its lowest 62 mg/L in the equalization tank, and from 65 mg/L to at its lowest 18 mg/L in the aeration tank. The decrease was, however, not enough to prevent formation of rising sludge in the clarifiers. The incomplete denitrification process was thought to be due to low concentrations of BOD in the equalization tank. Further studies need to be carried out to evaluate and optimize the nitrogen removal through intermittent aeration.

Thesis (PhD (Food Science))--University of Stellenbosch, 2009. / In the absence of anaerobic granules, anaerobically digested sewage sludge is frequently used to seed industrial upflow anaerobic sludge blanket (UASB) reactors. Because of its flocculent nature, start-up with digested sludge instead of granular sludge proceeds much slower and presents various operational problems. Any manner in which the granulation of digested sludge can be enhanced would benefit UASB reactor start-up and application in developing countries such as South Africa. The main objective of this dissertation was to improve granulation and reduce UASB reactor start-up by using pre-treated digested sludge as seed. The sludge was pre-treated based on the batch granulation-enhancement model of Britz et al. (2002). The main aim of the model was to improve extracellular polymer (ECP) production of lactate-utilising populations by applying short-term controlled organic overloading in a mechanically agitated environment. The batch granulation-enhancement (pre-treatment) process was applied to an ECP-producing digester strain, Propionibacterium jensenii S1. Non-methanogenic aggregates were formed when batch units were incubated on a roller-table instead of a linear-shake platform. Larger, more stable aggregates were obtained in the presence of apricot effluent medium. Preliminary batch granulation-enhancement studies confirmed that using the roller-table as mixing system had a positive influence on batch granulation-enhancement. The roller-table showed the most potential for handling larger volumes in comparison to a linear-shake waterbath and linear-shake platform. The addition of 450 mg.L-1 Fe2+ at the start of the study also influenced aggregate numbers positively. These studies revealed that pre-treatment results varied depending on the seed sludge source. A denaturing gradient gel electrophoresis (DGGE) method was applied for the detection of Archaea in digested sludges and UASB granules. In addition, a methanogenic marker containing methanogens important to the granulation process was constructed to aid identification. The positive influence of DMSO and “touchdown” PCR on the elimination of artifactual double bands in DGGE fingerprints were also demonstrated. Results revealed that only one of the four digested sludges tested contained Methanosaeta concilii (critical to granular nuclei formation) while it was present in all the UASB granules regardless of substrate type. Four digested sludges were obtained from stable secondary digesters. DGGE indicated the presence of M. concilii in all sludges. The Athlone 4Sb-sludge was the only sludge which exhibited measurable methanogenic activity during substrate dependent activity testing. The ST-sludge showed the highest increase in volatile suspended solids (VSS) particles ≥0.25 mm2. Laboratory-scale UASB reactor start-up was done with both sludges and start-up proceeded better in the Athlone 4Sb-reactor. Athlone 4Sb-sludge batches were pre-treated in a rolling-batch reactor in the presence of either lactate or sucrose and used to seed lab-scale UASB reactors B (sucrose seed) and C (lactate seed). Start-up efficiencies were compared to a control (Reactor A). Overall Reactor B was more efficient that the control. At the end of the study the Reactor B sludge had a higher methanogenic activity than the control reactor. It also had the highest increase in VSS ≥1.0 mm2. Pre-treatment of digested sludge in the presence of sucrose, therefore, aided granulation and reduced UASB reactor start-up time.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

<p>Slamsvällning orsakar stora problem i avloppsreningsverk med biologisk rening i aktivt slamprocesser. Slamsvällning orsakas av filamentösa (trådformiga) bakterier, som inverkar negativt på slammets sedimenteringsegenskaper.</p><p>Himmerfjärdens vattenreningsverk har drabbats av detta problem som leder till ett stabilt lager av slam på ytan av sedimenteringsbassängen som inte sedimenterar.</p><p>För att lösa detta problem behandlades returslammet från sedimenteringsbassängen med ozon för att minska mängden filamentösa bakterier i returslamflödet. Ozon är en starkt oxiderande gas, som är väl användbar för icke-specifik bekämpning av slamsvällning. När ozon kommer i kontakt med den filamentösa bakteriens cellvägg penetreras det in i cellen, varvid cellen lyserar.</p><p>Ozonbehandlingen resulterade i en förminskning av antalet filamentösa bakterier. Ozonbehandling av returslam förbättrade sedimenteringsegenskaperna hos svällande slam utan att påverka andra viktiga mikrobiologiska processer t.ex. nitrifikation.</p> / <p>Bulking sludge causes major problems in wastewater treatment plants that deal with biological nutrient removal in activated sludge processes. Bulking sludge is caused by filamentous bacteria, which have a negative impact on the sludge settling properties.</p><p>Himmerfjärden wastewater treatment plant suffers from this type of problem with bulking sludge which creates a stable layer at the surface that does not settle in the clarifier.</p><p>In order to solve this problem, on site generated ozone was used to decrease the amount of filamentous bacteria in the return activated sludge flow. Ozone is a strong oxidant is suitable for non-specific bulking control. It stresses the filamentous bacteria causing inactivation through cell wall disintegration.</p><p>The ozone treatment resulted in decreased abundance of filamentous bacteria. Ozone treatment of the recycled activated sludge improves the settling properties of bulking sludge, without interfering with other important microbiological processes e.g. nitrification.</p>

Hydrothermal carbonisation (HTC) could form the basis for rendering human faecal wastes safe whilst at the same time generating a carbon-rich material (hydrochar) and providing prospects for the recovery of energy. The work presented here has an objective of the search for optimal conditions for the HTC conversion of human faecal waste. Primary sewage sludge (PSS) and synthetic faeces (SF), of various moisture contents, were used as feedstocks to investigate the kinetics of decomposition of solids during HTC over a range of reaction times and temperatures. Decomposition was found to follow first-order kinetics, and the corresponding activation energies were obtained. Temperature was of primary importance to influence solid decomposition. Higher temperatures resulted in higher solids conversion to hydrochar. The energy contents of the hydrochars from PSS carbonised at 140 200oC for 4 h ranged from 21.5 to 23.1 MJ kg 1. Moisture content was found to affect the HTC process and feedstocks, with higher initial moisture contents resulted in lower hydrochar yields. The effect of reaction conditions on the characteristics of the hydrochar, liquid and gas products from HTC of faecal material, and the conditions leading to optimal hydrochar characteristics were investigated using a Response Surface Methodology (RSM). Models were developed here which could aid in the identification of reaction conditions to tailor such products for specific end uses. The results showed that the amount of carbon retained in hydrochars decreased as temperature and time increased, with carbon retentions of 64 77% at 140 and 160oC, and 50 62% at 180 and 200oC. Increasing temperature and reaction time increased the energy content of the hydrochar from 17 19 MJ kg 1 but reduced its energy yield from 88 to 68%. HTC at 200oC for 240 min resulted in hydrochars suitable for fuel, while carbonation at 160oC for 60 min produced hydrochars appropriate for carbon storage when applied to the soil. Theoretical estimates of methane yields resulting from subsequent anaerobic digestion (AD) of the liquid by-products are presented, with the highest yields obtained following carbonisation at 180oC for 30 min. In general, HTC at 180oC for 60 min and 200oC for 30 min resulted in hydrochars having optimal characteristics, and also for obtaining optimal methane yields. Maillard reaction products were identified in the liquid fractions following carbonisations at the higher temperatures. It was also found that the TOC, COD and BOD of the liquid products following HTC increased as the reaction temperature and time were increased and that these would require further treatment before being discharged. The results indicated that the gaseous phase following HTC contained carbon dioxide, nitrogen dioxide, nitric oxide, ammonia, and hydrogen sulphide indicating that additional treatment would be required before discharge to the atmosphere. In order to identify the optimum conditions leading to greater filterability of slurry resulted from HTC, the effects of reaction temperature and time on the filterability of PSS and SF slurries were investigated and optimised using RSM. It was shown that filterability improved as the reaction temperature and time at which the solids were carbonised was increased, with the best filtration results being achieved at the highest temperature (200°C) and longest treatment time (240 min) employed here. The specific cake resistance to filtration of the carbonised slurries was found to vary between 5.43 x 1012 and 2.05 x 1010 m kg 1 for cold filtration of PSS, 1.11 x 1012 and 3.49 x 1010 m kg 1 for cold filtration of SF, and 3.01 x 1012 and 3.86 x 1010 m kg 1 for hot filtration of SF, and decreased with increasing reaction temperature and time for carbonisation. There was no significant difference in specific resistance between cold and hot filtration of SF. The RSM models employed here were found to yield predictions that were close to the experimental results obtained, and should prove useful in designing and optimising HTC filtration systems for generating solids for a wide variety of end uses. Mass and energy balances of a semi-continuous HTC of faecal waste at 200oC and a reaction time of 30 min were conducted and based on recovering steam from the process as well energy from the solid fuel (hydrochar) and methane from digestion of the liquid by-product. The effect of the feedstock solids content and the quantity of feed on the mass and energy balances were investigated. Preheating the feed to 100oC using heat recovered from the process was found to significantly reduce the energy input to the reactor by about 59%, and decreased the heat loss from the reactor by between 50 60%. For feedstocks containing 15 25% solids (for all feed rates), energy recycled from the flashing off of steam and combustion of the hydrochar would be sufficient for preheating the feed, operating the reactor and drying the wet hydrochar without the need for any external sources of energy. Alternatively, for a feedstock containing 25% solids for all feed rates, energy recycled for the flashing off of steam and combustion of the methane provides sufficient energy to operate the entire process with an excess energy of about 19 21%, which could be used for other purposes.