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This work investigated the effect of floc microstructure (size and fractal structure) and shear forces on dewatering processes, which are crucial for environmental and economical aspects in many industries. Due to limitations inherent In experimental investigations, a numerical code using the discrete element method and including some novel force models (polymer bridging force, elastic bending moment and a modified concept of rolling friction torque) was developed to simulate the consolidation behavior of flocculated systems. The code showed good agreement with experimental results. The elastic behavior of aggregates is known to depend on the backbone structure (stress bearing structure of the aggregate). However, there is little known about backbone structure. It was found that backbone represents a fractal structure with a fractal dimension value close to 1 and increasing with increase of aggregate mass fractal dimension. The dewatering process was characterized by compressive and hindered settling behavior. The numerical study of compressive rheology with different aggregate microstructure showed that the compaction results from a reduction of the correlation length rather than increase in fractal dimension. The compressive behavior is consistent with theoretical models at higher compressive stresses but is not well described at low compressive stresses. A semi- empirical model is presented describing the compressive rheology in both regions via a correction factor derived using dimensional analysis. The hindered settling behavior was in good agreement with the theoretical model based on the assumption of self similar structure. The investigation revealed that shear effect is not due entirely to hydrodynamics and can arise from the particle bonding mechanism alone. The study showed that low shear increases compressibility but high shear is detrimental. At low shear, bond bending at local voids results in solid densification. High shear increases kinetic energy and kinetic repulsion of the particles. The effect of shear is analogous to the anomalous behavior of the water density- temperature function. At low temperature bond breakage increases the density and at high temperature thermal expansion decreases the density. The investigation showed that shear increases the permeability due to bending of the structure in the shear direction, resulting in large pores.

Wastewater sludge is considered a valuable source of nutrients and energy. Freeze/thaw treatment is an efficient dewatering method for wastewater sludge management in First Nation communities located in cold climate conditions. Natural freeze/thaw is a simple, practical and low cost method, which can effectively dewater sludge. The objective of this research is to evaluate dewatering, nutrient recovery and organics separation of wastewater sludge originating from different wastewater treatment processes using freeze/thaw processing. The results of experiments showed the effectiveness of this method in sludge dewaterability and solubilisation of organics and nutrients. The sludge solid content increased by approximately 10-fold after treatment. It was effective in solubilisation of about 15.2%, 33.5% and 21.5% of total nitrogen, total phosphorus and total chemical oxygen demand to soluble one, respectively for the non-BNR sludge. However, anaerobic digestion of the solid cake post freeze/thaw treatment did not show enhanced methane yield compared with fresh sludge. / February 2017

The Government of Ontario plans to ban the land application of untreated septage; however, most town wastewater treatment plants do not have the capacity to accept septage. A combined reed bed – freezing bed technology has been successfully developed to dewater and treat septage. Lab column studies established that freeze-thaw conditioning can restore drainage in clogged sand drying beds dosed with common biological sludges and that septage can be dosed at 10 cm/week for 2.5-5.0 months before clogging is observed. Pilot studies showed that freezing beds can operate without the need for a cover with the applied sludge effectively melting any snow cover in regions with moderate snowfall. Septage freezing was successfully modelled following an accepted model for ice formation on water bodies while septage thawing was modelled using a regression analysis with initial frozen depth and precipitation found to be insignificant and degree days of warming controlling the rate of thawing. Model results were utilized to produce a freezing bed design loading map for North America based on temperature normals. Field scale planted and unplanted reed bed – freezing bed systems were constructed and tested with varying hydraulic loading rates (1.9-5.9 m/y) and solid loading rates (43-144 kg/m2/y) over a 5 year period resulting in a recommended design hydraulic loading rate of 2.9 m/y or 75 kg/m2/y. Drainage rates doubled after freeze-thaw conditioning compared to during the growing season, suggesting that freeze-thaw conditioning restores filter hydraulic conductivity. No effect of solid loading rate, planted versus unplanted filters and 7 versus 21 d dosing cycles on filter drainage was observed; however, drainage varied significantly with hydraulic loading rate. The filters separated almost all contaminants with filtrate equivalent to a low-strength domestic wastewater which can be easily treated in any municipal or decentralized wastewater system. The dewatered sludge cake had similar nutrient and solid content to a solid dairy manure and met biosolid land application standards in terms of metals and pathogens. The combined reed bed-freezing bed technology can provide a low-cost solution for the treatment and reuse of septage in cold-climate regions.

Master of Science

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.

<p>Hedesunda reningsverk är beläget i södra delen av Gävle kommun och hanterar avloppsvatten från Hedesunda samhälle och ett fåtal närbelägna byar. Antalet anslutna personer är strax över 1500. Reningsverket byggdes på 1960-talet och byggdes om i slutet av 1990-talet. Vid ombyggnaden anlades torkbäddar för avvattning av det slam som produceras vid reningsverket. Inledningsvis fungerade dessa torkbäddar bra men sedan 2005 har slammet i bäddarna inte avvattnats i önskad omfattning.</p><p> </p><p>Syftet med detta examensarbete var att utreda hur slamavvattningen i Hedesunda ska se ut i framtiden. Utgångspunkten var att den nuvarande lösningen är otillräcklig och att en förändring är nödvändig. Inledningsvis delades frågeställningen upp i två separata delar: avvattning av slammet och avsättning för avvattnat slam. Fokus låg på ekonomiska och miljömässiga aspekter av slamhantering och en sammanvägning av dessa gjordes där så var möjligt.</p><p> </p><p>Frågan om hur avvattningen bör se ut undersöktes genom att en enkät skickades ut till nio olika företag som levererar avvattningsutrustning. Dessa fick svara på 17 frågor om vilken lösning de ansåg vara bäst lämpad för reningsverket i Hedesunda. Sammanlagt samlades sex olika svar in. Utöver dessa undersöktes även alternativet att restaurera de befintliga torkbäddarna närmare. Detta skedde bland annat genom provtagning och analys av slammet i bäddarna. De olika alternativen för slamavvattning sammanställdes och jämfördes genom att varje undersökt parameter delades in i intervall som gav olika betyg. De tre alternativ som enligt denna undersökning ansågs bäst lämpade var att restaurera de befintliga bäddarna, att anlägga vassbäddar eller att installera en mindre silbandpress.</p><p> </p><p>Då slammet avvattnats återstår frågan kring hur det avvattnade slammet ska hanteras. Detta undersöktes genom att två alternativ studerades närmare. Dessa var att fortsätta med den nuvarande hanteringen som är kompostering och tillverkning av anläggningsjord eller att certifiera slammet genom REVAQ och sprida det på åkermark. Ett försök till att skatta kostnaden för de båda alternativen gjordes, bland annat genom att frågor ställdes till de kommuner/driftbolag som idag är certifierade enligt REVAQ. Kostnaden för certifiering och spridning på jordbruksmark är betydligt mycket högre än kostnaden för kompostering. Certifieringsalternativet innebär dock en större måluppfyllelse i och med att fosfor återförs till produktiv mark.   </p><p> </p><p>Resultatet av studien är ett konkret förslag på hur slamavvattning och avsättning för slam vid Hedesunda reningsverk kan skötas i framtiden. Detta förslag innebär att de nuvarande torkbäddarna restaureras och att möjligheterna att certifiera flera delar av Gästrike Vatten AB:s verksamhet utreds närmare. Att enbart certifiera slam från Hedesunda reningsverk anses ekonomiskt orimligt.</p> / <p>Hedesunda wastewater treatment plant (wwtp) is located in the southern part of Gävle municipality in Sweden. The wwtp treats wastewater from Hedesunda community and a few nearby villages. All in all there are approximately 1500 persons connected to the plant. Hedesunda wwtp was originally built in the 1960’s and was restored in the late 1990’s. At the restoration sludge drying beds were built on the site for sludge dewatering. Initially, these beds worked fine but since 2005 the dewatering result has not been satisfactory.</p><p> </p><p>The objective of this master thesis has been to investigate different alternatives for a more effective sludge handling at Hedesunda wwtp in the future. Initially the sludge handling process was divided into two different parts: sludge dewatering and management of dewatered sludge. The focus has been on economical and environmental aspects of sludge handling and where it’s been possible these factors have been weight together.</p><p> </p><p>The question of how a more effective dewatering of sludge could be achieved was answered by a questionnaire that was sent to different companies that supply dewatering equipment to the Swedish market. Altogether six answers were collected. Besides these answers the option of restoring the existing sludge drying beds was also considered. The latter was done by sampling and analyzing sludge in the existing beds, among other things. The different options for dewatering were compiled and compared in a matrix where every parameter was split up in intervals and assigned grades. Three options that received the highest total grade were considered the best options. These were: restoring the sludge drying beds, reed beds and a small belt filter press.</p><p> </p><p>The matter of how to handle the dewatered sludge was simplified to a study of only two alternatives. These were to continue the present handling or to certify the sludge according to REVAQ and use it as fertilizer. Attempts to estimate the cost for the two alternatives were made. The cost for certification is higher than the cost for composting, but to certify the sludge will lead to a higher target achievement.</p><p> </p><p>The study resulted in concrete suggestions for how the sludge at Hedesunda wwtp can be handled in the future. This suggestion states that the existing sludge drying beds should be restored and that the possibility to certify several wwtp:s within Gästrike Vatten AB should be investigated. It is not considered economically plausible to certify sludge from Hedesunda wwtp alone.</p>

Hedesunda reningsverk är beläget i södra delen av Gävle kommun och hanterar avloppsvatten från Hedesunda samhälle och ett fåtal närbelägna byar. Antalet anslutna personer är strax över 1500. Reningsverket byggdes på 1960-talet och byggdes om i slutet av 1990-talet. Vid ombyggnaden anlades torkbäddar för avvattning av det slam som produceras vid reningsverket. Inledningsvis fungerade dessa torkbäddar bra men sedan 2005 har slammet i bäddarna inte avvattnats i önskad omfattning.   Syftet med detta examensarbete var att utreda hur slamavvattningen i Hedesunda ska se ut i framtiden. Utgångspunkten var att den nuvarande lösningen är otillräcklig och att en förändring är nödvändig. Inledningsvis delades frågeställningen upp i två separata delar: avvattning av slammet och avsättning för avvattnat slam. Fokus låg på ekonomiska och miljömässiga aspekter av slamhantering och en sammanvägning av dessa gjordes där så var möjligt.   Frågan om hur avvattningen bör se ut undersöktes genom att en enkät skickades ut till nio olika företag som levererar avvattningsutrustning. Dessa fick svara på 17 frågor om vilken lösning de ansåg vara bäst lämpad för reningsverket i Hedesunda. Sammanlagt samlades sex olika svar in. Utöver dessa undersöktes även alternativet att restaurera de befintliga torkbäddarna närmare. Detta skedde bland annat genom provtagning och analys av slammet i bäddarna. De olika alternativen för slamavvattning sammanställdes och jämfördes genom att varje undersökt parameter delades in i intervall som gav olika betyg. De tre alternativ som enligt denna undersökning ansågs bäst lämpade var att restaurera de befintliga bäddarna, att anlägga vassbäddar eller att installera en mindre silbandpress.   Då slammet avvattnats återstår frågan kring hur det avvattnade slammet ska hanteras. Detta undersöktes genom att två alternativ studerades närmare. Dessa var att fortsätta med den nuvarande hanteringen som är kompostering och tillverkning av anläggningsjord eller att certifiera slammet genom REVAQ och sprida det på åkermark. Ett försök till att skatta kostnaden för de båda alternativen gjordes, bland annat genom att frågor ställdes till de kommuner/driftbolag som idag är certifierade enligt REVAQ. Kostnaden för certifiering och spridning på jordbruksmark är betydligt mycket högre än kostnaden för kompostering. Certifieringsalternativet innebär dock en större måluppfyllelse i och med att fosfor återförs till produktiv mark.      Resultatet av studien är ett konkret förslag på hur slamavvattning och avsättning för slam vid Hedesunda reningsverk kan skötas i framtiden. Detta förslag innebär att de nuvarande torkbäddarna restaureras och att möjligheterna att certifiera flera delar av Gästrike Vatten AB:s verksamhet utreds närmare. Att enbart certifiera slam från Hedesunda reningsverk anses ekonomiskt orimligt. / Hedesunda wastewater treatment plant (wwtp) is located in the southern part of Gävle municipality in Sweden. The wwtp treats wastewater from Hedesunda community and a few nearby villages. All in all there are approximately 1500 persons connected to the plant. Hedesunda wwtp was originally built in the 1960’s and was restored in the late 1990’s. At the restoration sludge drying beds were built on the site for sludge dewatering. Initially, these beds worked fine but since 2005 the dewatering result has not been satisfactory.   The objective of this master thesis has been to investigate different alternatives for a more effective sludge handling at Hedesunda wwtp in the future. Initially the sludge handling process was divided into two different parts: sludge dewatering and management of dewatered sludge. The focus has been on economical and environmental aspects of sludge handling and where it’s been possible these factors have been weight together.   The question of how a more effective dewatering of sludge could be achieved was answered by a questionnaire that was sent to different companies that supply dewatering equipment to the Swedish market. Altogether six answers were collected. Besides these answers the option of restoring the existing sludge drying beds was also considered. The latter was done by sampling and analyzing sludge in the existing beds, among other things. The different options for dewatering were compiled and compared in a matrix where every parameter was split up in intervals and assigned grades. Three options that received the highest total grade were considered the best options. These were: restoring the sludge drying beds, reed beds and a small belt filter press.   The matter of how to handle the dewatered sludge was simplified to a study of only two alternatives. These were to continue the present handling or to certify the sludge according to REVAQ and use it as fertilizer. Attempts to estimate the cost for the two alternatives were made. The cost for certification is higher than the cost for composting, but to certify the sludge will lead to a higher target achievement.   The study resulted in concrete suggestions for how the sludge at Hedesunda wwtp can be handled in the future. This suggestion states that the existing sludge drying beds should be restored and that the possibility to certify several wwtp:s within Gästrike Vatten AB should be investigated. It is not considered economically plausible to certify sludge from Hedesunda wwtp alone.

During the water treatment process, each processing unit releases the sludge from the sedimentation process, and the wastewater from the rapid sand wash and filtration process, to the wastewater pond followed by the wastewater sedimentation pond. The sediment sludge is allowed to enter the sludge thickening pond while the supernatant is recycled for further treatment. The sludge is released to the sludge pond where it is treated with certain chemicals and squeezed to form the sludge cake. The sludge cake is removed and transported by a legitimate cleaning service company to an authorized location. The present study is focused on the investigation of the feasibility of recycling the wastewater and the dewatering of the sludge from the water treatment plant. The analysis of the samples collected from the wastewater treatment plant showed that the recycled supernatant had a pH of 7.16~8.21, a conductivity of 371.1~769.1 £gmho/cm, a total dissolved solid (TDS) of 193.3~399.9 mg/L, and a turbidity of 0.901~54.3 NTU. The suspended solids (SS) of the recycled supernatant was found to be 0.4~45.6 mg/L, lower than the standard value in the Effluent Standards (50 mg/L). The ammonia nitrogen (NH3-N) and the Total Organic Carbon (TOC) of the recycled supernatant were found to be 0.06~1.5 mg/L and 1.533~17.437 mg/L, respectively. The analysis of the Chemical Oxygen Demand (COD) of the wastewater treatment plant showed a concentration of 12.1~128.5 mg/L in the sample of the recycled supernatant. The COD in the Effluent Standards is required to be no more than 100 mg/L. For sludge conditioning and dewatering, a sludge conditioning experiment was conducted in the laboratory to plot the curve of the experimental result. The curve was used for the actual sludge conditioning and dewatering in the Fongshan Water Treatment Plant to verify the feasibility of the application for the actual process in the water treatment plant.

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.