Treatability of landfill leachate treatment in anaerobic fluidized bed reactors

Katı atık depolama alanı sızıntı suyunun kalitesi oldukça değişken olup birçok endüstriyel atıksuya göre daha geniş aralıkta bir kirlilik yüküne sahiptir. Bu çalışmada, İstanbul Avrupa yakası, Kemerburgaz (Odayeri) katı atık düzenli depolama alanı sızıntı sularının Anaerobik Akışkan Yataklı Reaktör’de (AAYR) arıtılabilirliği araştırılmıştır. Çalışmanın yapıldığı akışkan yataklı reaktörün çapı 10 cm, yüksekliği 165 cm, etkili hacmi 13 L’dir. Yatak malzemesi olarak 0.5 mm’lik filtre kumu kullanılmış ve sabit yatak yüksekliği 70 cm’dir. Organik Yükleme (OLR) sekiz kademede sırasıyla 2.5; 4.5; 8; 12; 18; 27; 37 ve 20 kgKOİ/m3-gün olarak yapılmıştır. Giderilen KOİ başına üretilen gaz miktarı parametresi izlenerek reaktör kontrol altında tutulmuştur. KOİ giderimi, birinci kademede %80’ler civarında iken, sonraki kademelerde %90’lar seviyesine ulaşmış ve sistem yaklaşık 6 haftada kararlı hale gelmiştir. Yükleme artırıldıkça biyogaz üretimi de artmıştır. Sekiz kademede gerçekleştirilen organik yüklemede biyogaz üretimleri, 14 - 203 L/gün arasında değişmiştir. Sistem her yükleme kademesinde kararlı hale ulaştığında, giderilen KOİ başına üretilen toplam gaz miktarı 0.51-0.53 L/gKOİgid.gün olarak elde edilmiştir. Yapılan ölçümlerde toplam gazdaki metan içeriği %75 olarak bulunmuştur. Reaktörün üç noktasından (30, 80 ve 110 cm) kum numuneleri alınarak biyofilm gelişimi izlenmiştir. Tutunmuş biyokütle konsantrasyonunun (Xatt) taban ve tepe noktaları arasındaki değer farkı %3 ile %38 arasında değişmiştir. Yaklaşık yedi ayda ortalama biyokütle konsantrasyonu 70.000 mgUAKMatt/L değerine erişmiştir. Anahtar Kelimeler: Sızıntı suyu, anaerobik arıtma, akışkan yataklı reaktör, biyogaz üretimi.The sanitary landfill method for ultimate disposal of municipal and industrial solid wastes is widely used in many countries around the world. The leachate generated from a landfill site containing organic, inorganic and heavy metal compounds, is a complex mixture with foul odour. The flow rate and composition of sanitary landfill leachate vary depending on the site, season and age of the landfill. Leachate from young landfill is usually high-strength wastewaters consisted of 10000 - 70000 mg/L COD, pH of 7-8 and several toxic/hazardous components. The main applicable methods for leachate treatment include biological, chemical and physical treatment processes. Many investigators have studied treatment of the sanitary landfill leachate using coagulation-flocculation, electro-Fenton method, Sequencing Batch Reactor (SBR), combined electro-Fenton oxidation and SBR, membrane processes Upflow Anaerobic Sludge Blanket (UASB) reactors and moving-bed biofilm process. The fixed film reactors such as biofilter and fluidized bed reveal a greater efficiency than the conventional systems. The advantage of fluidized bed processes is the accumulation of a large amount of biomass by natural attachment, including high volumetric flow rates, short retention times and good stability performance. The fluidized bed technology has been successfully applied for the treatment of industrial wastewaters, and also the removal of nitrate, phosphorus and refractory/toxic organic. The Anaerobic Fluidized Bed Reactors (AFBR) have many advantages over the aerobic treatment processes due to lower energy costs and low sludge production. These reactors have been operated with different wastewaters and a large range of organic loading rate values between 3-150 gCOD/L day. Anaerobic fluidized bed reactors have been applied to different wastewaters for various Volumetric Loading Rates (VLR) ranging from a few kg COD/m3.d to as much as 150-180 kg COD/m3.d. Although anaerobic biological processes often present the most economical solutions for high strength wastewater treatment, Advanced Oxidation Processes (AOPs) provide an effective means of treating biorefractory compounds with efficient process control. In this study, treatability of leachate from Odayeri sanitary landfill located on the European part of Istanbul was investigated in an anaerobic fluidized bed reactor. The experiments have been performed in a pilot-scale fluidized bed reactor having an inner diameter of 10 cm, a height of 165 cm and an effective volume of 13 L. The reactor media was typical filter sand having an arithmetic mean diameter of 0.5 mm and a fixed bed height of 70 cm. The AFBR experiments were carried out by increasing the Organic Loading Rate (OLR) from 2.5 to 37 kg COD/m3.day in eight operating steps. During 270 days of the operation, the feed rate (Qf) and the Hydraulic Retention Time (HRT) were 13 L/d and 1 day, respectively. Ammonia removal efficiency appeared to be very low, however, ammonia inhibition did not occur during the study. COD removal increased from 80% to 90% with increasing organic loading rates and the AFBR attained steady state conditions with a COD removal of 90% after 6 weeks. The AFBR systems have the characteristics of three-phase fluidized bed reactors due to the biogas formation. Therefore, the classic solid?liquid fluidized bed can be obtained introducing a correction factor for the biogas effects. Biogas production in the AFBR continuously increased during the leachate treatment process. The biogas production rate (Qgas) (L/d) obtained as 14 L/d after 20 days of the operation, also increased with increasing the OLR and the influent COD.Good biogas production yield (Ygas ) was obtained as 0.51-0.53 L biogas per g CODrem with a methane (CH4) content of 75%. The attached biomass concentration (Xatt) amounted to about 90% of the total biomass concentration and showed an increase throughout the bed between the ranges 3-38%. The mean attached biomass concentration also increased up to 70000 mgVSSatt/L in the last two months. Keywords: Landfill leachate, anaerobic treatability, fluidized bed reactor, biogas production