Treatment of landfill leachate in upflow sludge blanket reactor / completely stirred tank reactor system

Sızıntı sularının yukarı akışlı çamur yatak / tam karışımlı tank reaktör sistemlerinde arıtılması

Abstract

Solid waste landfills may cause severe environmental impacts if leachate and gas emissions are not controlled. Leachate generated in municipal solid waste landfill contains large amounts of organic and inorganic contaminants. Leachate may also have a high concentration of metals and contain some hazardous organic chemicals. Due to the hazards arising from the presence of nitrogen compounds in water and groundwater sources, the discharge of these compounds must be minimized. After methanation phase, the leachates contain relatively low concentrations of degradable organic matter but high concentrations of ammonia nitrogen. The slow leaching of nitrogen from solid waste in municipal solid waste landfills results in high concentrations of ammonia in the landfill leachate. The removal of organic material based on chemical oxygen demand (COD), biochemical oxygen demand (BOD) and ammonium nitrogen from leachate is the usual prerequisite before discharging the leachates into natural waters. Anaerobic treatment methods are more suitable for the treatment of concentrated leachate streams, offer lower operating costs, the production of usable biogas product, and production of a pathogen free solids residue which can be used as a cover material. High-rate anaerobic processes such as upflow anaerobic sludge blanket reactor (UASB) and anaerobic filter (AF) have been shown to be efficient in the treatment of leachate having a COD higher than 800 mg/l and the BOD/COD ratio higher than 0.3. In this study, the treatability of leachate produced from the food wastes in a lab-scale simulated anaerobic reactor was investigated, in two-stage sequential upflow anaerobic sludge blanket reactor (UASB)/ aerobic completely stirred tank reactor (CSTR). The experiments were performed in two UASB reactors and a CSTR reactor, having effective volumes of 2.5 l and 9 l, respectively. Hydraulic retention times in anaerobic and aerobic stages were 1.25 and 4.5 days, respectively, through 42 days at a constant flowrate of 2 l. They were operated at 37 C using an electronic heater located in the medium part of the reactor. The system was operated under steady-state conditions at COD removal efficiencies of 43-60 % in the first UASB reactor while 85 % COD removal efficiency was obtained in the aerobic reactor through 30 day, before continuous study. After the start-up period the COD concentration of leachate was steadily in creased from 5400 $mgl^{-1}$ to 20000 $mgl^{-1}$. Organic loading rates (OLRs) were increased from 4.3 to h kg $CODm^{-3}.d$ by increasing the COD concentration from 5400 $mgl^{-1}$ to 20000 $mgl^{-1}$. The effluent of th first anaerobic UASB reactor (Run 1) was used a, the influent of the second UASB reactor (Run 2 while the effluent of the second UASB reactor wa, used as the influent of the aerobic CSTR reacto (Run 3). COD removal efficiencies were 58 (mini mum value) and 79 (maximum value) at a OLR o 12.8 kg $m^{-3}.d$ in the first UASB reactor. COD removal efficiencies in the whole system (two step UASB+CSTR) were 96-98 % at the aforementioned OLR. Inert COD values were measured in all organic loading rates for Run 1. Inert COD was measured as approximately 10 % of total COD value Ammonium removals were insignificant in the an aerobic runs. But, $NH_4-N$removal efficiency wa approximately 99.6 % in the effluent of the aerobi stage. The volatile fatty acid (VFA) concentration c leachate increased from 1400 $mgl^{-1}$ to 2300 $mgl^{-1}$ by increasing the OLR from 4.3 kg $CODm^{-3}.d$ to 16 kg, $CODm^{-3}.d$ in Run 1 reactor. The VFA concentration of Run 1 reactor was higher than Run 2 reactor during the operation period. pH values of the Run 1 an Run 2 reactor were approximately neutral value During the operation period, quantity of total and methane gas increased. Total and methane gas quantity of Run 1 reactor was higher than Run 2 reactor. Quantity of methane gas was measured 5.9 and 0.71 $ld^{-1}$ at OLR of 16 kg $CODm^{-3}.d$ in Run 1 and Run 2 reactors, respectively. The maximum methane percentages of the first and second UASB reactors were 64 % and 43 % at OLR of 12.8 kg $m^{-3}.d$ 4.2 kg $m^{-3}.d$ and influent COD concentrations of 16000 $mgl^{-1}$ , 4160 $mgl^{-1}$ respectively. The methan yields in Run 1 ve Run 2 reactors were 0.35 m3 methane gas $kg^{-1}COD$ nremoved and 0.39 m3 methane gas $kg^{-1}COD$ nremoved at a OLR of 12.8 $kg/m^3.d$ and a COD concentration of 16000 $mgl^{-1}$ respectively. $H_2S$ gas was not detected in the anaerobic reactors.

Özet

Bu çalışmada yiyecek atıkları içeren anaerobik katı atık reaktöründen oluşan sızıntı sularının yukarı akışlı çamur yatak (YAÇY)/ sürekli karıştırmak tank (SKT) reaktör sistemlerinde anaerobik/aerobik arıtılabilirliği incelenmiştir. Deneyler iki YAÇY reaktör ve bir aerobik SKT reaktörde 42 gün sürdürülmüştür. Bu çalışmadan önce sistem 30 gün kararlı koşullarda YAÇY'de % 43 ile % 60 KOİ ve aerobik reaktörde % 85 KOİ giderim verimleri ile çalıştırılmıştır. Besleme debisi 2 $lgun^{-1}$ ve anaerobik reaktörlerde yukarı akış hızı 0.25 m $lgun^{-1}$ olmuştur. Kimyasal oksijen ihtiyacı (KOİ) konsantrasyonlarının 5400 den 20000 mgl^{-1}$ ye artırılmasıyla 4.3- 16 kgKOİ.$m^{-3}.gun^{-1}$ lük organik yüklemelerde çalışılmıştır. Birinci YAÇY çıkışı (Sistem 1) ikinci YAÇY reaktöre (Sistem 2) bağlanmış, onun çıkışı aerobik SKT reaktöre (Sistem 3) verilmiştir. 12.8 kg $m^{-3}. gun^{-1}$ organik yükleme hızında (OYH) KOİ giderme verimleri birinci YAÇY reaktörde minimum % 58 maksimum % 79 iken toplam sistemde minimum % 96 maksimum % 98 dir. Aerobik kademede $NH_4-N$ giderme verimi % 99.6 dır. Birinci ve ikinci YAÇY'ler için maksimum metan yüzdeleri 12.8 kg $m^{-3}. gun^{-1}$ lük organik yükleme ve 16000 $mgl^{-1}$ giriş KOİ konsantrasyonunda % 64; 4.3 kg $m^{-3}. gun^{-1}$ lük organik yükleme ve 5400 mgt1 giriş KOİ konsantrasyonunda % 43 olarak gerçekleşmiştir. Sİ ve S2 reaktörleri için sırası ile 12.8 kg m'3.gün'1, 4.2 kg m"3.gün'1 OYH ile 16000 $mgl^{-1}$ ve 4160 $mgl^{-1}$ KOİ konsantrasyonlarında metan verimleri 0.35 m3 metan gazı $kg^{-1}$ KOİ giderilen ve 0.39 m3 metan gazı $kg^{-1}$ KOİ giderilen bulunmuştur.