Donma-çözülme'nin arıtma çamurları susuzlaştırılabilirliği üzerine etkileri

Abstract

Bu çalışmada, donma-çözülme ile şartlandırma yönteminin aktif çamurun susuzlaştırılabilirliği üzerine etkisi incelenmiş ve ülkemiz için bu yöntemin bir uygulaması alan donma-yatağı tasarımı ve boyutlandırılması yapılmıştır. Birinci bölümde çamur kaynakları ile bu kaynaklardan meydana gelen çamur miktarının nasıl bulunacağı ele alınmıştır. İkinci bölümde çamurun fiziksel, kimyasal ve biyolojik özelliklerinden kısaca sözedilmiştir. Üçüncü bolümde çamur suyunun alınması için kullanılan vakum filtre, basınçlı filtre, santrifüj, çamur kurutma ve donma yataklarından sözedilmiştir. Dördüncü bölümde çamurun kimyasal madde ile şartlandırılması, optimum daz tayini ve donma-çozülme yöntemi ile ilgili daha önceki çalışmaları içeren bir literatür araştırması verilmiştir. Beşinci bölümde Uzun Havalandırmalı Aktif Çamur Sistemi ile çalışan evsel atıksu arıtma tesisi son çökeltme tankı çıkışından alınan dört adet aktif çamur numunesi üzerinde yapılan; kimyasal şartlandırma, optimum doz tayini ve donma-çözülme ile şartlandırmaya ait deney sonuçları ve bunların kritikleri verilmiştir. Yedi gün süre ile dondurulup çözülen numunelerin özgül direnç değerlerinde önemli bir azalma görülmüş fakat bu numunelerde kimyasal şartlandırma daha iyi sonuçlar vermiştir. Sekiz gün süre ile dondurulup çözülmeye bırakılan numunenin özgül direnç değeri ise kimyasal şartlandırma sonucu elde edilen özgül direnç değerinden daha düşük olmuştur. Laboratuvar ölçekte hazırlanmış olan kum yataklardan süzme işlemine ait veriler de bu sonuçları desteklemiştir. Altıncı bölümde Donma-Çözülme'nin bir uygulaması olan Donma Yatağına ait tasarım esasları ve bir örnek verilmiştir. Yedinci bölümde deneysel çalışmalardan elde edilen sonuçlar özetlenmiş ve öneriler sunulmuştur.

Sludge Deuıatering is a severe problem far mast uıater and uıasteuıa ter treatment facilities. This problem is compounded in cold regions because of the harshness af the climate and the remoteness of most communites. Equipment and spare parts are difficult to obtain, and skilled operators are scarce. Far these reasons, complex mechanical deujatering methods are often undesirable. Some natural methods of deuıatering, such asdrying beds, have been used, but ta be effective they must be aversized ta campensate far the shart drying seasan. A simple and mora appropriate method af deujatering sludges in cald climates is ta use natural freeze-thau. Several investigators have shouın that freezing follauıed by thauıing effectively conditians sludges and makes them easier ta deuıater. Freeze-thauj canditianing appears ta be effective an ali aqueaus sludges as long as they are not flash-frozen. Idhen uıater in sludge freezes, it excludes colloidal and suspended solids pushing the solids ahead of the frezen front. The colder the final temperature and the langer the frazen sludge starage time, the greater the effect af freeze thauı an the sludge deuıaterability after thauıing. The most dramatic effect an deuıaterability results from the rate of freezing, uıith slow freezing rates producing better devatering sludges. These results suggest that if the freeze thauı system is ta be placed into commercial operatian, thin layers of sludge must be frazen slauıly far long periads, thereby pramoting the grouıth of crystals that uıill exclude the solid particles and promote partide aggregation. A specially designed unit operation utilizing natural freeze- thauı far sludge deujatering has been suggested by several investigatars. Cambining the cancepts presented in the literatüre and observations of sludge freezing operatians on drying beds and -xiv- laga§ns, a neuı operatian mas called a sludge freezing bed ujaa developed. Ta maximize sludge detıiatering by natural freeze-thau this bed includes the follauıing features: 1- it is designed ta apply in sevsral thin layers rather than a singls thick layer. Each layer is applied as soon as the previous layer has frozen. This uill increase the freazing rate and maximizes the total depth af the sludge uıhich can be applied. 2- The bed is covered ta prevent snaıu and rain from entering it. This feature is critical if the bed is ta utilize ali af the available freezing time in the uinter. An öpen freezing bed uıould have less capacity because snauı accumulatians an the surface uould slom douın the freezing rate. Alsa, snau removal uıould be practically impossible if a large snouıfall accured saan after sludge u/as applied. in this case the operatör uould have ta delay snau remaval until the frazen sludge ums thick enaugh ta suppart snouj remaval equipment. A covering ujould alsa prevent rainfall fram reuıetting the thauıed sludge. 3- The sides af the bed are left öpen ta allauı free air circulatian. Houıever, a half-mall ar lauvered uıall is recammended ta prevent drifting snauı fram entering the bed. Alsa, the roof is made to be transparent sa that solar radiation can help thau and dry the sludge in the spring. Incoming salar radiatian in the uıinter is expected ta be negligible because af the sun's lauı azimuth and the likelihoad af the snouj an the raaf. Önce thauıing is complete in the freezing beds,the remaining solids are removed mith a frant-end laader ar ather equipment. The sludge freezing bed cauld be used as the sole method of deujatering ör in combinatian tuith ather methods, such as drying beds. If used as the only method of deuıatering, a starage facility is needed ta cantain the sludge during the summer months. The storage facility cauld be a lagaon, tank, ör a digester ifexcess capacity uere available. If used in combination uıith ather deuatering methods, the bed is sized to handle the uıinter sludge production only. A cambinatian of freezing and^drying beds is particularly attractive in temperate regions because both methods can be aperated under opti¬ mum climatic conditians for natural deujatering. -XV- In this study, the effect of freeze thaw conditioning on dewaterability of waste-activated sludge is investigated, and, a, freezing bed which is an application of this method is designated for our country. The sludge sources and quantities are given in the first chapter. After the sludge from water and waste water treatment facilities are defined, the quantities and physical characteristics of it are presented in a table. In the second chapter; physical, chemical and biological characteristics of the sludge from water and waste water treatment facilities are described. The specific gravity which is one of the physical characteristics is defined, and, after its approximately value is given, it is described how to calculate. Then, the chemical components of ' digested and undigested sludge are shown in the table. The clasif ication of total solids in the sludge is defined andtheir analysis methods are given. The table including the sludge solids concentration for various treatment processes is presented. Sludge volume index defining the sludge settling characteristics is described. The particle size of the sludges and its importance for various treatment units are discussed. The water forms in the sludge are defined. The reological characteristics of the sludge is explained..At the end of the definition of the physical characteristics of the sludge, the specific resistance to filtration is defined. - ' In the definition of the chemical characteristics of sludge, calorific and composting values are discussed. In the definition of the biological characteristics of sludge the patogen microorganisms and the enzymes in the sludge are shortly described. -xvi- In the third chapter, several sludge dewatering processes such as vacuum filtration, filter-press, centrifugatian, sludge drying beds and freezing beds are discussed, and, sludge treatment and disposal methods are shown in the table. In the forth chapter, the literature review including the sludge conditioning and the freeze-thaui conditioning of the sludge are presented. The chemicals used for conditioner are claslfied, and, the previous studies including the affect of the polymer and sludge characteristics on the selection of polymer type and dose requirement are presented in this chapter. The experimental studies far the specific resistance to filtration of the various sludge types were discussed using the different polymer types as conditioners. In a result of these studies, it was provided that the specific resistance to filtration was decreased by addition of the suitable polymer type. Obtainable minimum specific resistance to filtration was depended an the initial specific resistance tofiltration and the solids concentration on the filter cake was increased by the addition of the polymer, in the mast-of the sludge types. Also, the studies for the freezing process of the sludges are given in this chapter. Inthis studies it is shownthat the freeze-thaw process was more effect on the sludge including the smaller particles and on the longer freezing times and on the lower freezing temperatures. The freezing beds as an application of the freeze-thaw method are defined, and, a table for the dewaterability at the various sludge types frozen in the freezing beds is given. These results are determined by the pilot-scale studies. The freezing and thawing models for design depths are presented. In the fifth chapter the experimental results and their criticals on the conditioning with polymer and on the optimum dose determination and on the freeze-thaw conditioning of the four sludge samples taken from secondary settling tank of the domestic water treatment plant are discussed. The polymer make up and addition are described and the calculation methods used for determining the specific resistance to filtration are discussed. Also, the specific resistance to filtration values for the various sludge types are presented in the table. -xvii- The specific resistance to filtration is determined by means of Buchner Funnel test. Then, dewaterability of the sludge conditioned by chemicals and the frozen-thawed sludge is compared with each other based on the totaland suspension solids content and initial specific resistance to filtration values. The raw sludge, the conditioned sludge and the frozen- thawed sludge are filtrated on the sand beds prepared laboratory-scale and the volumes versus the timeare recorded. The specific resistance to filtration value of the sludge is decreased by the freeze-thaw conditioning, but, this value is more larger for the sludge samples conditioned by chemicals. The specific resistance to filtration value of the frozen-thawed sludge sample during the eight days is more smaller than the sludge conditioned by chemical. The data obtained from the filtration with sand beds supported these results. In the sixth chapter, after the design criteria of the freezingbed is given, the design example of freezing bed is accomplished for our country. The advantages of the freezing beds are given, and operation of the freezing beds is described. The freezing and thawing models of the design depths are discussed. The values for Sankamxs village are used in the example of the freezing bed design. In this example, the limited factor is freezing depth and this value is used for calculations. The requirement of the area for only freezing bed is 1028 mz and for combination of the freezing and drying beds is 1290 m2 (drying bed 856 m2 + freezing bed 434 m2), and only for drying bed is 1460 m2. The plan and section of the freezing bed is given at the end of thischapter. In the seventh chapter, the results from experimental studies are summarized and evaluated for our country. Based an these results, the recommendation is given for our country. Also, A scheme showing the parts of the climatic reagions for our country is presented in this chapter. In according this scheme the mast suitable region for the freezing beds is the fourth region. The combination of the freezing and drying beds is recommended in this region. xviii- BÖLÜM 1. GİRİŞ Çevre Mühendisliğinde, su ve kullanılmış su tasfiyesi sırasında önemli hacimde çamur meydana gelir. Çoğu zaman bu çamurların, çevreye zarar vermeden uzaklaştırılması büyük problemler çıkarmasının yanında malî açıdan da ilâve bir yük getirir. İçme suyu tasfiye tesisinden çıkan çamurlar uzaklaştırılırken, organik almadıklarından zararları az olur veya hiç almaz. Ancak depolama. ve yer işgali yönünden problem doğururlar. Kullanılmış su tasfiye tesisinden çıkan çamurlar organik asıllı olduklarından zamanla çürürler, etrafa kötü koku yayarlar ve hastalık yapan mikroorganizmaları üreterek tehlikeli almaya başlarlar. Bu çamurları zararsız hale getiren ünitelerin yapımında büyük hacimli çamurlar, büyük hacimde üniteler gerektireceğinden tesis maliyetini artırırlar. Kullanılmış su tasfiyesinde meydana gelen çamur, tasfiye edilen suyun % 1-6'sını teşkil etmekle beraber, çamur tasfiye ünitelerinin maliyeti tüm tesis için ilk yatırım maliyetinin % SO-^D'ına işletme masrafı ise tüm işletme masrafının % 5D'sine ulaşabilir. Bu bakımdan çamur hacminin düşürülmesi ; çamur tasfiyesi ve uzaklaştırılmasının maliyetini azaltacaktır. Bu ise çamurun yoğunlaştırılması veya katı madde yüzdesinin artırılması ile mümkündür. Bu maksatla çamur yoğunlaştırma veya çamur suyunun alınması işlemleri uygulanır. Çamur yoğunlaştırmada katı madde muhtevası % 15 'e kadar çıkarılabilir; bu durumda çamur, sıvı özelliğinde olup pompa ile basılabilir. Çamur suyunun alınması işlemleri ile katı madde muhtevası % 20'in üzerine çıkarılır ki; bu durumda çamur, katı özelliğinde olup kürek veya başka bir aletle kolayca