Göksu nehri dip tarama çamurlarının geotekstil tüp ve santrifüj yöntemleri ile susuzlaştırma performansının araştırılması ve karşılaştırılması
Investigation and comparison of the dewatering performance of Goksu river dredged sediments using geotextile tube and centrifuge methods
Yazar: NİHAN KESKİN
Danışman: DR. ÖĞR. ÜYESİ ÜMİT KARADOĞAN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Yüksek su içerikli tarama çamurlarının etkili bir şekilde susuzlaştırılması süreci üç temel aşamadan oluşmaktadır. İlk aşama, bu çamurların taranarak çıkarılmasıdır. Bu aşama genellikle sistematik bir şekilde gerçekleştirilir ve genellikle diğer aşamalardan daha basittir. İkinci aşama, taranmış çamurların çökelme ve yoğunlaşma işlemidir. Bu aşamada, genellikle mekanik yöntemlere ek olarak kimyasal bir katkıya ihtiyaç duyulur. Bu katkılar çamurun yoğunlaşmasına ve daha hızlı çökelmesine yardımcı olur. Üçüncü ve son aşama ise yoğunlaşan çamurun susuzlaştırılması işlemidir ve sürecin en karmaşık aşamasıdır. Bu aşamada, geotekstil tüple susuzlaştırma metodu ve geleneksel santrifüj gibi metotlar kullanılmaktadır. Bu susuzlaştırma metotları üzerine birçok çalışma yapılmış olsa da, bu metotların susuzlaştırma performanslarının ve maliyetlerinin karşılaştırıldığı bir değerlendirme bulunmamaktadır.
Bu çalışmada, geotekstil tüp susuzlaştırma metodu ve santrifüj metodunun susuzlaştırma performanslarının karışılaştırmalı değerlendirilmesini sunmak amacıyla Göksu Nehri'nin iki farklı bölgesinden alınan dip tarama çamurunun susuzlaştırılması üzerine çalışılmıştır. Öncelikle Göksu Nehri'nden alınan yüksek su içerikli dip tarama çamurlarının indeks özellikleri belirlenmiştir. Ardından çamur numuneleri ile uyumlu poliakrilamid çeşidini belirlemek amacıyla 5 farklı anyonik poliakrilamidin kullanımıyla Jar Test gerçekleştirilmiştir, çamur ile uyumlu poliakrilamidi belirledikten sonra da optimum dozajı belirlemek için bu poliakrilamid ile 5 farklı dozajda Jar Test çalışılmıştır. Daha sonra seçilen poliakrilamid ile geotekstil tüp susuzlaştırma ve santrifüj metodlarının Göksu Nehri çamurları üzerindeki susuzlaştırma etkinlikleri araştırılmıştır. Geotekstil tüp susuzlaştırma metodunun laboratuvar ölçekli çalışması için iki boyutlu hızlı susuzlaştırma testi (RDT), santrifüj metodu için ise 50 ml falkon ile çalışan basket santrifüj kullanılmıştır.
Bu çalışma sırasında, poliakrilamid kullanımı floklaşmayı artırdığı için her iki metot için de susuzlaştırma verimini artırdığı gözlenmiştir. Ayrıca, poliakrilamid kullanımı susuzlaşma verimini artırırken filtre kekinin katı madde oranını da artırmaktadır. Poliakrilamid dozajının artışı santrifüj metodunda flokların dağılmasına, bu da kekin katı madde oranının düşmesine, filtratın bulanıklaşmasına yol açmıştır. Her iki numune için de elde edilen kekin, santrifüj susuzlaştırma yöntemiyle daha yüksek katı madde oranına ulaştığı gözlemlenmiştir. Bunun durumun santrifüj metodunda çamura etkiyen merkezkaç kuvvetinden kaynaklı olduğu düşünülmektedir.
Susuzlaştırma performanslarının karşılaştırılmasından sonra sahada gerçekleştirilen çalışmalarda genellikle süzüntü suları çamurun tarandığı ortama geri deşarj edildiği için süzüntü suyu kalite analizleri yapılmıştır. Bu analizler sonucu elde edilen sonuçlar süzüntü suyunun rekreasyonel amaçla kullanıma ve içme suyu elde edilebilecek kalitede olduğunu göstermiştir. Göksu Nehri dip tarama çamurunun susuzlaştırılması sırasında ortaya çıkan süzüntü suyunun nehre geri deşarj edilmesinin ve susuzlaştırma sırasında süzüntü suyunun yer altı suyuna sızmasının bir sorun teşkil etmeyeceği sonucuna varılmıştır.
İki metodun performans karlıştırmasından sonra her iki metodun da yaklaşık yatırım ve işletme maliyetleri belirlenmiş ve maliyet açısından da değerlendirme yapılmıştır. Maliyet açısından bakıldığında santrifüj metodu için yatırım ihtiyacı olmasına karşılık geotekstil tüp susuzlaştırmada yatırım ihtiyacı bulunmamaktadır. İşletme maliyetleri açısından karşılaştırıldığında ise iki metotun işletme maliyetlerinin birbirlerine yakın olduğu görülmüştür.
Göksu Nehri tarama çamurunda yapılan testlerden elde edilen sonuçlar, her iki metod ile de etkin bir susuzlaştırmanın sağlanabildiğini göstermiştir. Ancak her metodun kendine göre avantaj ve dezavantajları bulunmaktadır. İki metodun en berlirgin farkları, geotekstil tüp ile susuzlaştırma santrifüj susuzlaştırmaya göre daha yavaş ve alan ihtiyacı yüksek bir metot iken, santrifüj susuzlaştırmanın yüksek yatırım maliyeti, yüksek elektrik sarfiyatı ve tecrübeli operatöre ihtiyaç duymasıdır. Her iki metot ile de verimli susuzlaştırma sağlanabilmesinden kaynaklı projenin koşullarına göre metod tercihi yapılabilir.

Abstract:
The effective dewatering process of high-water-content dredged sludges consists of three key stages. The first stage involves the dredging of these sludges from underwater. This stage is typically carried out systematically and is considered simpler compared to the subsequent stages. The dredged sludge is typically extracted from underwater using pumps and transported to the shore (working area) through pipes. This process is executed with a specific order and meticulousness. The second stage is the settling and thickening process of the dredged sludges. During this stage, a significant portion of water within the sludge is separated, resulting in a denser consistency. Besides mechanical methods, chemical additives are often employed to facilitate this thickening process. Chemical additives such as various coagulants and flocculants help in aggregating sludge particles and accelerating the settling process. The use of these chemicals promotes faster settling and thickening of the sludge, thereby facilitating a more efficient dewatering process in subsequent stages. The third and final stage involves the dewatering of the thickened sludge. This stage is the most complex and requires technical expertise. Various dewatering techniques are employed to minimize the water content within the thickened sludge. Among these methods are geotextile tube dewatering, which involves filtering the sludge through large geotextile bags, and centrifugal dewatering, a traditional method used for many years to dewater various sludges by rapidly spinning them to separate water. Despite numerous studies on these dewatering methods, there lacks a comprehensive evaluation comparing their dewatering performances and costs. This gap complicates the determination of which method is more effective and cost-efficient. Therefore, further research and comparative studies in this field are crucial for selecting the appropriate dewatering method and optimizing the dewatering process.
In this study, a comprehensive research was conducted aiming to compare the dewatering performances of geotextile tube dewatering method and centrifugal method. For this purpose, a study was carried out on the dewatering of bottom dredged sludges taken from two different locations of the Göksu River. Initially, the index properties of high-water-content bottom dredged sludges from the Göksu River were meticulously determined. Subsequently, Jar Test was performed using five different anionic polyacrylamides. This test aimed to determine which polyacrylamide would provide better flocculation and faster settling of the sludge, thus identifying the most compatible polyacrylamide with the sludge. Following the determination of the most compatible polyacrylamide with the sludge, Jar Test was conducted with this polyacrylamide at five different dosages to determine the optimum dosage. This process provided the necessary information to find the most effective chemical dosage for the dewatering process and maximize the effectiveness of this chemical additive. The dewatering efficiencies of geotextile tube dewatering and centrifugal methods on Göksu River sludges were comprehensively investigated using selected polyacrylamide. For the laboratory-scale study of geotextile tube dewatering method, Rapid Dewatering Test (RDT) was employed, which yielded results comparable to dewatering with full-scale geotextile tubes, hence it was preferred. For the centrifugal method, a basket centrifuge operating with 50 ml capacity falcon tubes was used.
During this study, observations regarding the use of polyacrylamide have shown that this chemical significantly enhances the flocculation process, thereby increasing dewatering efficiency for both dewatering methods. Polyacrylamide promotes the aggregation of sludge particles into larger flocs, which facilitates more effective separation of water. This process not only enhances the overall efficiency of the dewatering process but also increases the solid content of the filter cake. The filter cake is the solid waste obtained after dewatering, and the use of polyacrylamide increases the solid content of this cake, resulting in a drier and denser cake. However, increasing the dosage of polyacrylamide has led to some adverse effects in the centrifugal method. Higher dosages have caused flocs to disperse, resulting in a decrease in the solid content of the obtained cake and cloudiness in the filtrate. The filtrate is the liquid obtained after dewatering, and cloudiness indicates that solid particles in the water have not fully separated. This underscores the importance of carefully adjusting the dosage of polyacrylamide in the centrifugal method. Analyses for both samples have indicated that cakes obtained from the centrifugal dewatering method have a higher solid content. This is believed to be due to the centrifugal force exerted on the sludge in the centrifuge, which spins rapidly to separate water from the sludge. This centrifugal force facilitates tighter aggregation of sludge particles, thus forming a denser cake.
After a comprehensive comparison of dewatering performances, field studies were conducted considering that filtrate waters are generally discharged back into the environment where the sludge was dredged. Quality analyses of the filtrate water were performed to assess the extent to which the water meets quality standards during the dewatering process. The data obtained from these analyses have shown that the filtrate water is suitable for recreational purposes and meets the quality standards for potential drinking water use. This finding indicates that the dewatering process is environmentally safe and sustainable. It has been determined that the discharge of filtrate water, which emerges during the dewatering process of Göksu River bottom dredged sludge, does not pose any adverse environmental impact when reintroduced into the river. It has also been concluded that infiltration of the filtrate water into groundwater does not present a problem. This demonstrates that the dewatering process does not harm both surface and groundwater, and these waters can be safely reintegrated into the natural cycle. Filtrate water quality analyses confirm that the methods and chemicals used during the dewatering process are environmentally safe. These findings serve as an important reference for ensuring environmental safety in dewatering projects conducted in the field. The high quality of the filtrate water proves that the dewatering of dredged sludges has been conducted correctly and effectively without causing harm to the environment. The conclusion that the discharge of filtrate water obtained during the dewatering of Göksu River bottom dredged sludge is safe reinforces the importance of preserving water resources and ensuring sustainable use in such projects. These results support the applicability and reliability of similar approaches in future dewatering projects.
Approximate investment and operational costs for each method were determined, and a comprehensive cost evaluation was conducted. From a cost perspective, it was observed that the centrifugal method requires significant initial investment. This investment is attributed to the high costs associated with acquiring and installing the centrifuge device. In contrast, the geotextile tube dewatering method does not require such an initial investment. Geotextile tubes can be installed and operated with lower- cost equipment and materials, significantly reducing initial investment costs. In terms of operational costs, a comparison revealed that the operational costs of both methods are quite similar. The centrifugal method tends to maintain certain levels of operational costs due to high energy consumption and the need for continuous device maintenance. Regular expenses for energy consumption and maintenance are necessary to ensure the effective operation of the device. On the other hand, while the geotextile tube dewatering method is more cost-effective in terms of energy consumption, operational costs are maintained at a certain level due to the need for regular tube replacement and maintenance. Therefore, it has been concluded that the operational costs of both methods are comparable. This cost evaluation plays a crucial role in selecting the most suitable dewatering method for a project. In addition to investment and operational costs, evaluating both methods in terms of performance and efficiency helps determine the method that best meets the project's needs. The centrifugal method, despite its high initial cost, provides rapid and effective dewatering, whereas the geotextile tube dewatering method offers a sustainable option in the long term with lower initial costs and energy consumption. Comparing these two methods in terms of cost and performance is critical for making informed decisions in projects.
According to the results of the dredged sludge tests conducted in the Göksu River, effective dewatering can be achieved with both methods. However, each method has its own specific advantages and disadvantages. The geotextile tube dewatering method operates more slowly compared to centrifugal dewatering and requires more space. On the other hand, the centrifugal dewatering method has disadvantages such as high initial investment costs, high electricity consumption, and the requirement for experienced operators. Both methods can provide effective dewatering, therefore the choice between them can be determined based on the specific characteristics of the project. For example, if the project area is large and there are no time constraints, the geotextile tube dewatering method may be suitable. However, in situations where time is critical or space is limited, the centrifugal dewatering method might be more appropriate, taking into consideration cost and operational details.
In conclusion, the most suitable dewatering method for the project should be chosen based on a consideration of the advantages and disadvantages of each method, tailored to the project's requirements.