Atık boyutunun ve karakterizasyonunun havalandırmalı bioreaktörlerde atık stabilizasyonuna etkisi

Effect of particle size and characteristic of waste on waste stabilization: application of pilot scale simule aerated bioreactor

Özet

Ülkemizde ve dünyada katı atıkların bertarafı için en yaygın olarak kullanılan yöntem, atıkların depolanmasıdır. Katı atıklar, bu depolama alanlarında anaerobik prosesler sonucu bozunmaktadır. Gerekli önlemlerin alınmaması durumunda, anaerobik bozunma sonucunda depolama alanlarından oluşan sızıntı suyu ve depo gazı çevresel sorunlara neden olmaktadır. Son yıllarda katı atıkların aerobik bioreaktör depolama alanlarında depolanması konusunda araştırmalar ve uygulamalar yaygınlaşmaya başlamıştır. Söz konusu alanlarda, atıklar daha hızlı bir şekilde bozunmakta ve daha kısa sürede stabil hale gelmektedir. Aerobik bioreaktör depolama alanlarında oluşan sızıntı suyu miktarlarında azalma sağlanırken kalitesinde artış gözlenmektedir. Metan gazı oluşumu ise önemli ölçüde azalmakta veya tamamen bitmektedir. Böylelikle, bir yandan depolama alanının faydalı kullanım ömrü artarken, diğer yandan da depolama alanının rehabilitasyonu ve sızıntı suyu arıtım maliyetlerinde düşüş olmaktadır. Bu çalışma kapsamında, bioreaktör depolama yöntemi simüle bioreaktörlerde pilot ölçekli olarak denenmiştir. Sızıntı suyu geri devirli ve havalandırmalı iki simule bioreaktörlerde, atık boyutunun ve karakterizasyonunun atık stabilizasyonunu, sızıntı suyu ve depo gazı kalitesini ne yönde etkilediği incelenmiştir. Bu amaçla, reaktörden biri ham atıkla doldurulurken diğeri aynı atığın 80 mm 'lik elekten elenmesiyle elde edilen elek altı atıkla doldurulmuştur. Karışık ham atığın ve elek altı atığın organik madde içeriği yaklaşık olarak % 58 ve % 66 olarak belirlenmiştir. Çalışma sonucunda elde edilen veriler, organik madde içeriğinin artmasının ve atık boyutunun küçülmesinin,;, sızıntı suyu oluşumunu hızlandırdığı, sızıntı suyu kalitesini iyileştirdiği ve atık stabilizasyonunu hızlandırdığı belirlenmiştir.

Abstract

Sanitary landfills are widely used fort he disposal of Municipal Solid Waste (MSW) primarily due to their economical and convenient advantages. However leachate and gas generation from landfills may pollute the environment if not properly managed. Landfill designs include soil and/or plastic barriers above and below the waste in an attempt to reduce the infiltration of moisture into the waste mass and thus into the environment. This design method induces anaerobic decomposition of waste. Many of the world's landfills are becoming significant risks to the environment. Over time, anaerobic decomposition of wastes can have negative effects on landfill operations, which actually increase the potential for risks to human health and the environment. In addition, an extended post-closure care period is required to maintain the final cap because the settlement that occurs as organic material in the landfill continues to decompose. In recent years, due to the advance knowledge of landfill behavior and decomposition processes of waste, there has been a strong thrust to upgrade existing landfill technology, as a bioreactor landfill. The bioreactor landfill has been defined as "A sanitary landfill operated for the purpose of transforming and stabilizing the readily and moderately decomposable organic waste constituents control to enhance microbiological processes. The bioreactor landfill significantly increases the extent of waste decomposition, conversion rates and process effectiveness over what would otherwise occur within the landfill. Managing landfills as bioreactors has been suggested as an environmentally alternative and bioreactor landfills offer many environmental and financial benefits including accelerated stabilization of the waste which reduces the long-term potential for groundwater contamination and should allow for shorter post-closure care periods, accelerated methane production which makes recovery most cost-effective and more rapid settlement which creates additional volume for waste disposal during useful operating life. Techniques used to enhance biological degradation of waste, in bioreactor landfills, are shredding, leachate recirculation, aeration, pH adjustment, temperature control and addition of nutrient and sludge. In this study, the effects of waste size and characterization on the waste stabilization and. leachate characterization were investigated in two simulated aerated bioreactors landfill. The reactors constructed using metal cylinder with a length of 5.65 m and diameter of 2.5 m. auxiliary equipments consisted of water/leachate recirculation system and air injection system. Both of them were operated with leachate recirculation. One of them (Rl) was loaded with raw waste and the other one was loaded with sieved waste having a diameter smaller than 80 mm. The average specific weights of the wastes were 670 kg/m3 in Rl and 1040 kg/m3 in R2. The percentage of organic content is 58% in Rl and 66% in R2. The leachate recirculation rates were 0.42 and 0.21 I/ton waste-day in Rl and R2, respectively. Leachate recirculation volume was determined according to moisture content of waste. Air injection rates were adjusted according to gas measurements. The air injection rates in Rl and R2 were, respectively, 1.819 and 1.565 m3/ton waste-day. Waste stabilization and leachate quality was improved in these recirculation volumes and air injection rates. pH, electrical conductivity, alkalinity, chloride, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD),. ammonium nitrogen (NH4-N), Total Kjedhal Nitrogen (TKN), nitrate (NO3), alkaline and heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Ca, K, Mg, Na) concentrations in leachate and pH, moisture, carbon / nitrogen (C/N) ration, alkaline and heavy metal (Cd, Cr, Cu, Ni, Pb, Zn, Ca, K, Mg, Na) concentrations in solid waste samples were regularly monitored. Additionally, waste temperatures in reactors were measured daily and settlement was calculated according to height of waste. A decreased trend of the organic load, measured as chemical oxygen demand and biochemical oxygen demand, was observed. Leachate analyses showed that the Rl and R2 could remove above 44% and 87% of chemical oxygen demand and 81% and 94% biochemical oxygen demand from leachate. At the end of study, waste settlement reached 25% and 15% mainly due to decomposition of the organic matter. The average pH value was in the range of in leachate and at about 8 in solid waste samples. The results of this study show that size reduction of MSWs contributed to stabilization of solid waste, increase the treatment characteristics of leachate. Bioreactors operated with leachate recirculation and aeration and loaded with sheared waste was found suitable for waste stabilization and improved leachate characterization.