Theses supervised by Prof. Dr. Ayşe Filibeli
12 theses · Dokuz Eylül University
Minimization of excess sludge production
Large amounts of waste sludge are produced with the removal of biodegradable compounds and organic or inorganic matter in municipal and industrial wastewater treatment plants for disposal. It is expected that, in near future, sludge production and the regulation limits for disposal alternatives cause an increase in costs for sludge disposal. The current approach to sludge minimization is the reduction of volume of wet sludge and the reduction of dry mass of sludge. The volume of wet sludge for disposal is reduced significantly with the increase of the sludge solid content by dewatering. The reduction of dry mass of sludge leads to the reduction of solid content and volume and this strategy should be fovoured, beause it allows the immediate reduction of sludge dry mass during its production in the biological treatment stage.The fundamental aim of this thesis is the reduction of sludge production during the biological treatment. All of the techniques for sludge reduction described in this thesis suitable for implementation during the wastewater treatment plants, not after the sludge production, often by retrofitting the specific additional equipment. Two of these techniques were carried out experimentally and evaluated within the scope of this thesis. The effectiveness of ozonation integrated in activated sludge process and oxic-settling anaerobic (OSA) process were investigated on sludge reduction, especially.In the first stage of the study, Box-Behnken Statistical Design Program was used in order to determine the optimum operational conditions. Optimum hydraulic retention time (HRT), solid retention time (SRT) and initial COD (CODi) values for maximum COD removal were determined as 25 h, 25 d and 400 mg/L, respectively. After the determination of optimum operational conditions of activated sludge process, two systems were operated in parallel under these optimum conditions during 45 days until the steady state conditions and the effluent quality and sludge properties of the systems were monitored. When the steady-state conditions were reached, specific batch tests were carried out in order to investigate the biodegradability of disintegrated sludge and determine optimum ozone dose prior to the modification with the addition of ozonation unit to one of the activated sludge process. Optimum ozone dose for return activated sludge disintegration was determined as 0.05 gO3/gTS in terms of disintegration degree with 56.2 %. The higher doses improved disintegration degree, slightly.After the ozone dose optimization study, the effectiveness of partial ozonation of return activated sludge was investigated for the minimization of excess sludge production using ozonation coupled with activated sludge process in two stages. In the first stage of the ozonation, in ozonated system, 10 % of return activated sludge (0.1 QR) was ozonated every day during a month with optimum ozone dose and recirculated to the aeration tank. No excess sludge was withdrawn from the ozonation coupled with activated sludge process. The other activated sludge system was remained unmodified and operated as a control run with optimum operational conditions. Excess sludge was withdrawn every day due to SRT. 43 % observed sludge yield (Yobs) reduction could be achieved in ozone run during the operation period. At he the end of the operation, the 56 % of Yobs reduction was observed in ozone system compared to control system. In ozone run, the effluent quality was weakened slightly in term of COD and NH4-N removal. Sludge settling properties represented by SVI was improved in ozone run. Ozone run had lower dewaterability characteristics with higher CST values. The filterability of sludge was lower in ozone run than control run in terms of SRF.In the second stage of the ozonation 800 mL of the return sludge corresponded to 20 % of of the return activated sludge (0.2 QR) was ozonated with optimum ozone dose. 73 % Yobs reduction could be achieved in ozone run during the operation period. At the end of the operation, the 62 % of Yobs reduction was observed in ozone run compared to control run. The effluent quality was weakned slightly in term of COD and NH4-N removal in ozone run. Sludge settling properties was improved in ozone run in terms of SVI. Lower dewaterability characteristics in ozone run were proved with CST values. The filterability of ozonated sludge was lower than control run in terms of SRF.After the application of ozonation to activated sludge system, one of the system was modified by inserting anoxic tank to comprise OSA system. The other system was remained unmodified as a control system. A specific volume of return activated sludge of OSA system was subjected anaerobic conditions (-250 mV of low ORP level every day. OSA and control system were operated during 45 days. The sludge reduction efficiency and effluent quality were evaluated. After the completion of continuous operation, some batch experiments were conducted in order to investigate sludge reduction mechanisms in OSA process.In OSA system, 62 % reduction efficiency was obtained in yield production in OSA system during the operation. OSA system was also achieved 58 % reduction efficiency of Yobs compared to control run at the end of the operation. It was found that COD concentrations in the effluent in the OSA system were lower than that in the effluent of the control run due to the additional substrates from the anaerobic tank. The NH4-N removal efficiency in OSA system was lower compared to control run during the operation period due to denitrification. The setteability characteristics of sludge was also found better than that of the control system in terms of SVI. Higher CST values were obtained in control system compared to OSA system during the long term operation. It was revealed that the OSA system enhanced the filterability of sludge.In order to investigate the sludge decay theory in OSA sistem, two batch experiments with sludge taken from aeration tank of control and OSA systems were carried out. The aim of the first batch experiment was to investigate the relationship among sludge anaerobic reaction time, sludge lysis and sludge yield. The sludge reduction in terms of Yobs caused by sludge decay in OSA batch reactor was 40 % compared to control batch reactor for the first batch experiment. In the second batch test, the investigation of the energy uncoupling theory was aimed. The sludge reduction in terms of Yobs caused by energy uncoupling in OSA batch reactor was 5 % compared to control batch reactor.When the sludge reduction techniques used in this thesis were compared as modified activated sludge processes; the activated sludge process ozonated of 0.2 QR showed better Yobs reduction efficiency than that the fist stage of ozonation process (ozonation with 0.1QR) and OSA system during the operation period. The effluent quality of control systems were better than that modificated systems in terms of COD and nitrogen removal capacity however, the effluent quality of the modificated systems were at satisfactory level. The sludge characteristics of activated sludge were changed even slightly for some paramaters after the application of sludge minimization techniques.Consequently, the ozonation based on cell lysis-cryptic growth mechanism is an applicable and effective technique integrated to the activated sludge process for the minimization of excess sludge production. Besides, it was revealed that the OSA process especially based on sludge decay and energy uncoupling metabolism can be used as another simple effective method for sludge reduction.Keywords: excess sludge minimization, modification of activated sludge process, ozonation, OSA process.
Mesophilic anaerobic digestibility of pre-trated sludges
Anaerobic digestion has an important role in sludge management as stabilization method. Disintegration methods have taken important role before stabilization to disrupt the sludge flocs and microbial cell walls and improve the stabilization quality. So, these methods improve sludge biodegradability in terms of more biogas production and sludge minimization.In this thesis, among the pretreatment methods microwave pre-treatment, alkaline pre-treatment and the combination of these methods were investigated with experimental studies to see the effectiveness of biodegradation and biogas production on anaerobic digestion. Sludge sample was taken from the return line of secondary sedimentation tank of the municipal wastewater treatment plant in Izmir.At the beginning of the studies, disintegration applications have taken part for deciding the most appropriate method. According to the results, application of microwave pre-treatment improved anaerobic digestion performance as more stabilization and biogas production.At the continuation of the experiments, lab-scale anaerobic reactors were used. Reactors were operated as batch and semi batch system under mesophilic conditions for thirty days. Results showed that volatile solids reductions and biogas productions were higher for the digesters fed with disintegrated sludge than non-disintegrated digesters. All applied method showed a positive effect on anaerobic sludge biodegradability. When comparing the applied methods in terms of sludge digestion performance, batch reactor that include 75 percent microwave pretreated sludge gave higher volatile solids reductions and higher biogas in comparison with 50 percent microwave feeded reactor. But, anaerobic semi-continuous reactors were operated with the 75 percent feeding ratio gave the best results with respect to methane production and volatile solids reduction. 50 percent microwave feeded batch reactor gave lower efficiencies then the other two reactors in terms of methane production. At the same time, disintegration processes did not affect sludge dewatering properties positively.
Application of aerobic sludge stabilization supported with different pretreatment techniques
In this lab-scale study, alkali and microwave pretreatment methods were used as pretreatment techniques to modify sludge stabilization. The study consists of three main parts. In the first optimization part, optimum operational conditions of microwave pretreatment alone and combined alkaline and microwave pretreatment applications were determined to obtain the most effective sludge stabilization. Central composite design (CCD) was used as a statistical method and disintegration degree (DD) was used as a criteria of solubilization.In the second part of the study, effect of previously determined optimum pretreatment method on performance of organic matter degradation and dewaterability characteristics of mesophilic aerobic digestion as a stabilization process was investigated by operating a lab-scale semi ? batch aerobic digester during 30 d. Results were compared with the results of a parallel unpretreated sludge fed aerobic digester. Inoculum sludge which was provided from aerobic digester of municipal wastewater treatment plant (WWTP) in Manisa, and feed sludge which was provided from return line of secondary sedimentation of domestic WWTP in Izmir were mixed to prepare content of aerobic digester.In the third part of the study, thermophilic aerobic digestion was operated for 30 d, and the effect of thermophilic temperature range on performance of organic matter degradation were evaluated. Analysis were carried out periodically and feeding were carried out daily. Organic matter degradation efficiency of reactors were evaluated according to vector attraction requirements of US Environmental Protection Agency (EPA). As different from other parameters, oxygen uptake rate (OUR) and observed yields (Yobs.) were carried out to demonstrate the accuracy of findings of this study.
An appraisal of setting environmental strategy for airports and a case study of their contribution to global warming from Turkey
Aviation is a rapidly growing sector as the world economy has grown. Transportation of passenger and freight is increasing continuously, making air travel the fastest growing sector amongst all transportation types. The global air transportation system has economic and social benefits, while simultaneously environmental impacts are created. Mitigation of environmental affect to the environment is becoming a major challenge in this century. In addition, progress on noise reduction is also an important environmental issue. Carbon footprint of airports has been managed by Airport Council International (ACI) with the Airport Carbon Accreditation (ACA) program. The program assesses and recognizes the efforts of airports to manage and reduce their carbon emissions with four levels of certification: 'Mapping', 'Reduction', 'Optimization' & 'Neutrality'. Carbon footprint has to be calculated, reported and independently verified in accordance with ISO14064 Green House Gas Accounting Standard. The definitions of emissions footprints used by Airport Carbon Accreditation follow the principles of the World Business Council for Sustainable Development (WBCSD) and the World Resources Institute (WRI) ?Greenhouse Gas Protocol? Corporate Accounting and Reporting Standard. The carbon footprint calculations were made by the Greenhouse Gas Protocol (GHG Protocol) worksheets. In this thesis international aviation organizations and international aviation standards were evaluated as a review. International aviation standards were evaluated related to environmental issues of airports. The basic principles of the carbon footprint calculation of Izmir Adnan Menderes Airport International Terminal were studied. Direct and indirect emission sources related data were collected and were entered to the GHG Protocol worksheets. The verification was made according to the ISO 14064 standard for level 1- mapping level. The carbon footprint calculations were made for aircrafts B738, A319 and A320 with several assumptions. These types of aircrafts were the first 3 types that are obtained from the statistical air traffic data for 2007 to 2010. Keywords: Aviation standards, sustainability, airport, carbon footprint
The investigation of carbon accounting and management tools for different sludge treatment and disposal methods
The term carbon footprint, as a result of the increasing awareness of global warming, a term that has become very popular recently. Most of the greenhouse gases that cause global warming, although there are naturally in nature, a result of industrial processes increased with industrialization, human activities cause significant of these gases into the atmosphere. Wastewater treatment plants are recognized as one of the great contributors of GHG emissions. The scope of this thesis is examining the effect of wastewater treatment plants and especially sludge treatment and disposal methods on the carbon footprint. The aim of this thesis is to investigate the carbon footprint of different sludge treatment and disposal methods.
Phosphorus recovery as a struvite from sewage sludge applying Box-Behnken experimental design method
Phosphorus (P) is one of the fundamental element for all living organisms. Phosphorus recovery technologies are developing day by day because of the realizing the importance of phosphorus. While recovering the phosphorus, pipeline's clogging problem which is one of the most important problem in wastewater treatment facilities is minimized and sludge storage problem decrease. In this study, phosphorus recovery potential of sludge filtrate which obtained by electro dewatering process was investigated. In this process, recycled sludge of secondary settling tank of Bolu Municipal Wastewater Treatment Plant was used. Phosphorus were recovered as a struvite which consists of magnesium, ammonium and phosphorus. Parameters, affecting the phosphorus recovery such as temperature, mixing time and concentration of the added magnesiumhydroxide are searched for determining the optimum conditions for the phosphorus recovery. Pumice stone was used for struvite crystals. Experimental results were evaluated by using the Box Behnken Design and Minitab 17 statistical software method. At the continuation of the experiments, determined three independent variables and three values for each independent were applied to the filtrate samples of sewage sludge . Determined ranges are 24-80 0C for temperature, 30-60 minutes for mixing time and 0.1-2.0 M for magnesiumhydroxide concentration. According to the comparison results between predicted and observed phosphorus recovery values R squared was found 0.91. The maximum phosphorus recovery condition was found at 800C sample temperature, 2.0 M magnesiumhydroxide concentration and 45 minutes mixing time and the maximum value for phosphorus recovery was found as 15.8125 mg PO4-P /L. According to our experimental and statistical studies' results phosphorus recovery percent is reached 37 percent as a maximum value. Temperature of the sample and magnesiumhydroxide concentration are the most important factors which affect the phosphorus recovery. Keywords: Phosphorus recovery from sewage sludge, struvite, wastewater treatment plant problems, MAP
The investigation of sludge disintegration using oxidation processes
In this thesis, the feasibility of oxidation techniques as biological sludge disintegration purpose was investigated to improve anaerobic digestion performance, to increase stabilization degree and to increase biogas production with experimental studies. Fenton process, ozone oxidation and ultrasonic treatment as advanced oxidation processes were applied to biological sludge samples preceding anaerobic sludge digestion. Biological sludge was sampled from the municipal wastewater treatment plant in Izmir, Turkey, which has extended aeration activated sludge plant with nutrient removal facilities.In the first stage of the study, experiments were carried out to optimize the process conditions for floc disintegration. All applied methods allowed to destruction of microbial sludge cells resulting in an increased biodegradability. Among the methods, ultrasonic treatment gave the maximum disintegration degree.In the second stage of the study, sludge digestion studies were carried out using lab-scale anaerobic reactors. Reactors were operated both as batch and as semi batch system. The reactors were operated in mesophilic conditions for thirty days. Experimental results showed higher volatile solids reductions and higher biogas productions for the digesters fed with disintegrated sludge. All applied method showed a positive effect on anaerobic sludge biodegradability. When comparing the applied methods in terms of sludge digestion performance, ozone oxidation and ultrasonic treatment gave much closed results and ultrasonic treatment gave the best results in terms of methane production. Fenton process had lower efficiencies then the other two methods in terms of methane production. When comparing the operation types in terms of sludge digestion performance, semi batch systems had better digestion performance than batch system. On the other hand, disintegration processes had no positive effect of sludge dewatering properties.
Enzymatic treatment effects on aerobic sludge stabilization
Water/wastewater treatment processes have produced sludge in different characteristics and quantities. The sludges should be processed and disposed of in accordance with the environmental health criteria for environmental reasons. For many authorities and engineers, the effective sludge management is still a big challenge since the investment and operational costs of sludge processing have an important part of overall plant?s costs. Sludge dewatering process has a central role in sludge management for many operations like storage, transport. But, the dewaterability characteristics of sludges can vary depending on their sources and the applied processes. The methods for effective processing cover the methods -thickening, stabilization, conditioning, dewatering-, and the final disposal alternatives- incineration, land application.The main purpose of this thesis was to investigate the effects of hydrolytic enzyme additions on dewaterability performance of activated sludge during aerobic digestion process. Activated sludge was fed to the reactors as a feeding material. The parameters ? pH, electrical conductivity (EC), salinity, oxidation reduction potential (ORP), capillary suction time (CST), zeta potential, suspended solids content, dry solid content, organic matter- were analyzed to determine the sludge characteristics. Reactor performances with and without enzyme additions were monitored. Experimental results showed that the enzyme additions provided enhanced sludge disintegration. Enzyme added reactors showed considerably superior better performance in terms of organic matter reduction and EPS degradation when comparing the control reactor.This thesis as part of a project examining the effects of hydrolytic enzymes in biological sludge stabilization gives important research results to determine the floc disintegration mechanisms by enzymes during aerobic sludge digestion.
Commissioning of wastewater treatment plants and evaluation of different stages of options
In this study commissioning period is examined with the examples. Actions before andduring commissioning are examined with examples to give the view points to theengineers. The solutions for the possible problems are that may happen duringcommissioning are given.Compact plant is analyzed with different treatment options. These are carbon removal,carbon removal with nitrification, carbon removal with nitrification plus denitrification andextended aeration. The oxygen consumptions, sludge productions, necessary adjustmentsover the process and treatment efficiencies of the wastewater treatment plant are examinedaccording to the German rules and standards for activated sludge plants. All the parametersfor each process are calculated and summarized. Different treatment options are comparedto each other and liability of each options for the typical wastewater treatment plant isexamined.
A case study ISO 14001 and OHSAS 18001 applications for an industrial plant produced composite samples
ISO 14001 and OHSAS 18001 standards are very important for both companies and employees. Both ISO 14001 and OHSAS 18001 are indispensible for organizations and employees as they bring many advantages with them. The companies become more prestigious as they implement these two world wide known standards. On the other hand, employees work in a healthy and safe environment and they are protected against any sudden and unfortunate occupational accident. Details of ISO 14001 and OHSAS 18001 are shown and analyzed. We examined these two important bodies of standards to show the importance of environment, safety and health in companies.There are many examples from different countries in the thesis. The purpose of this is to provide adequate information about the applicability of ISO 14001 and OHSAS 18001. In these examples, it is clearly seen that every company which implement these standards see the benefits in terms of lowering occupational accidents and occupational illnesses, and increasing company?s prestige, etc.Keywords: ISO 14001, OHSAS 18001, cleaner production, health and safety, management, environment, risk assessment, documentation, materials, methods, manufacturing, waste, measurement.
Ultrasonic disintegration of sewage sludge
The production of excess sludge is one of the most serious challenges in biological wastewater treatment plants. Treatment and disposal of excess sludge in a biological wastewater treatment system requires high cost which has been estimated to be 50?60% of the total expense of wastewater treatment plant (Metcalf & Eddy, 2004; Egemen et. al., 2001). A common method for the biodegradation of excess sludge is biological treatment by anaerobic digestion. Anaerobic digestion is commonly used for stabilization and solid reduction of treatment plant sludges. Anaerobic digestion is a slow process because of the hydrolysis stage which is the rate-limiting step of the sludge degradation. That disadvantage is prominanced for the treatment of excess sludge which is the final product of the treatment of meat processing sludge due to its high oil and high organic material contents. In order to improve hydrolysis and anaerobic digestion performance, disintegration was developed as the pretreatment process of sludge to accelerate the anaerobic digestion and to increase degree of stabilization (Bougrier et. al., 2005)The main purpose of this thesis was to investigate the effects of ultrasonic pre-treatment on excess sludge disintegration at different specific energy inputs with low ultrasound frequency (20 kHz). Meat processing sludge containing high organic materials and oil content was chosen as sludge sample for the experimental studies which disintegration degree (DD) that used as the main parameter for evaluation of disintegration performance of sludge. Solid reductions with the ultrasonic pre-treatment were monitored total solids (TS), total organic solids, suspended solids (SS), and volatile suspended solids (VSS) measurements. Effects of ultrasonic disintegration on supernatant characteristics on meat processing industry sludges were also investigated. Biochemical methane potential (BMP) assay was carried out in order to monitor methane production as the indicator of improvement anaerobic biological degradation preceding ultrasonic treatment. In addition, the effect of ultrasonic pre-treatment on sludge filterability was evaluated depending on CST measurements of raw and pre-treated sludge samples.The experimental results showed that 30000 kJ/kgTS of supplied energy is efficient for disintegration of meat processing sludge. Higher specific energy inputs then 30000 kJ/kgTS led to a mineralization phenomenon preceding a solubilization phenomenon and because of that disintegration degree (DD) decreased. The protein results showed that sludge solids were hydrolyzing during the ultrasonic pre-treatment. Biochemical methane potential (BMP) results obtained in this study suggest that ultrasonic pre-treatment significantly enhanced the biodegradability of biological sludge than sludges that not pre-treated. Maximum methane production was observed for 30000 kJ/kgT and 136% higher biogas production in pre-treated sludge was obtained comparing to the raw sludge at the end of the 40 days of incubation period. Sludge?s supernatant characteristics were also affected by the ultrasonic pre-treatment. For 30000 kJ/kgTS, the soluble chemical oxygen demand (SCOD), dissolved organic carbon (DOC), total nitrogen (TN), total phosphorus (TP) in sludge?s supernatant increased by 487%, 290%, 3230%, and 870%, respectively. Depending on CST data, there was a negative effect of ultrasonic pre-treatment on sludge filterability even for very low specific energy levels.Keywords: anaerobic digestion, sewage sludge, ultrasonic pre-treatment, disintegration
Atıksu arıtma tesislerinde farklı arıtma modifikasyonları ile fazla çamur oluşumunun azaltılması
Excess sludge production is the main problem in biological treatment processes. Sludge minimization is important for transportation cost and disposal operation during the wastewater treatment. New wastewater treatment standards are resulting a rise in decracing of sludge production. Sedimentation, dewatering, treatment and disposal of solid matter during aerobic wastewater treatment is reguired high operational cost. Waste activated sludge (WAS) is a by-product which produced by microorganisms utilizing dissolved and organic pollutants in wastewater. The costs for sludge treatment is expensive, which has been forecasted to form 30-60% of the total operational costs of wastewater treatment plants. A principle approach to solve about sludge problems are to decrease the amount of sludge produced in biological process. So, the development of modern processes and technology for decreasing sludge production in biological treatment stage to need. All these strategies are modifications of the common activated sludge process for better results. This thesis summarized the strategies that is has been preffered to categorize different methods for the plant place where the minimization takes place. This study discusses the current sludge minimization technologies applied in the water line (such as lysis-cryptic growth, uncoupling metabolism, anaerobic treatment) or in the sludge line (physical, chemical and biological pre-treatment methods) and their advantages, disadvantages. In this study, two different real-time biological wastewater treatment plant operating data obtained and the excess sludge amounts due to operational differences, spesific energy consumption rates, spesific sludge production rates and the amount and cost effects on sludge removal methods were explained in detail. If the thermal hydrolysis process, which is the physical method application of sludge minimization processes, applied for two plants with comparison, the results will be examined and it is shown that sludge minimization will be possible and operating costs will be reduced.