Evolution on qualities of leachate and landfill gas in the semi-aerobic landfill

Availableonlineatwww.sciencedirectcomScienceDirectENVIROSCIENCE0742Evolution on qualities of leachate and landfill gas in thesemi-aerobic landfillHUANG Qifei", YANG Yufei, PANG Xiangrui 3, WANG Qi'1. Research Institute of Solid Waste Management, Chinese Research Academy of Emvironmental Sciences, Bejing 100012, China.g be3. School of Municipal and Environmental Engineering, Harbin instinte of Technology, Harbin 150001, ChinaReceived 26 June 2007; revised 30 July 2007: accepted 23 August 2007AbstractTo study the characteristics of stabilization in semi-aerobic landfill, large-scale simulated landfill was constructed based on the semi-aerobic landfill theory. Consequently, the concentrations of chemical oxygen demand(COD), ammonia nitrogen, and nitrite nitrogen,and the pH value in leachate, as well as the component contents of landfill gas composition(methane, carbon dioxide, and oxygen)inlandfill were regularly monitored for 52 weeks. The results showed that COD and ammonia concentrations declined rapidly and did nothow the accumulating rule like anaerobic landfill, and remained at about 300 and 100 mg/L, respectively, after 48 weeks. Meanwhile,the descending rate reached 98.9% and 96.9%, respectively. Nitrate concentration increased rapidly after 24 weeks and fluctuatedbetween 220-280 mg/L after 43 weeks. The pH values were below 7 during the first 8 weeks and after that leachates appeared to bealkaline. Carbon dioxide was the main composition in landfill gas and its concentration remained at a high level through the wholestabilization process. The average contents of carbon dioxide, oxygen, and methane varied between 19 vol. %-28 vol %, 2 vol%-8vol % and 5 vol. %-13 voL %, respectively. a relative equilibrium was reached after 48 weeks. The highest temperature in the landfillchamber could amount to 75.8 degrees centigrade.Key words: semi-aerobic landfill; stabilization; leachate: landfill gasIntroductionculation. After that, the bioreactor landfill technique wasstudied and then applied by several countries in Northanitary landfilling is still one of the principal methods America and Europe. Carson(1995) pointed out that theof municipal solid waste disposal at present. However, bioreactor landfilling technique has been widely used incurrent landfill disposal techniques consider landfill site the United States. Robison er al. (1983)reported thatas a passive waste storage system, and waste in land- leachate recirculation can not only accelerate biodegrafill is isolated from water and gas. The biodegradation dation of organic compounds, but also shorten the timeof organic compounds is restricted for low moisture in required for stabilization from several decades to 2-3landfill, which cannot provide microorganism with feasible years. In a leachate recirculation test conducted in Americaconditions(Bookter and Ham, 1982). The dumped refuse Sonoma County landfill site, the general range of decreasewill biodegrade slowly, which lengthens the process of in the area recirculated by leachate can reach 20% of thelandfill stabilization. Accompanied by different settlement, landfill site depth, while in contrast just 8%(Leckie erlandfill gas and leachate were discharged, which can last aL., 1979). The study of Yazdani et al.(1977)showed thatfor decades or even centuries and result in a significant the capability of accommodation and lifespan of bioreactornegative impact on the environment. Therefore, several landfill were 12.6% higher than the conventional landfillsscholars started to seek new landfill techniques to acceler- Raynal et al. ( 1998)reported that in two-phase bio-reactorate the landfill stabilization process and to weaken leachate as the activity of producing methane was weakened, morefermented products that were deoxidized more easily werIn the 1970s, Pohland(1980)demonstrated that with produced. Thereby, advantageous conditions to accelerateleachate recirculation, landfill can be used as a relatively lanecontrolled anaerobic filter to treat leachate, provide ac- repor中国煤化工paa9mcelerated waste stabilization, and reduce the volume of the tirCNMH Galue to reach wleachate by maximizing evaporative losses during recir- shortened, and Tandtill stabilization was accelerated.Bioreactor landfill technology has several advantages,Comespondingauthor.E-mail:huangqf@vip.sina.com.such as: increased moisture content: enhanced activities ofHUANG Qifei et almicroorganism;accelerated stabilization process; reduced 1 Materials and methodscontent of organic pollutants in landfill consideratelyHowever, leachate recirculation can lead to the inhibition 1.1 In situ scale simulated semi-aerobic landfill conof methanogenesis as it may cause high concentrationsof organic acids (low pH), which are toxic for themethanogens(Liliana et al., 1997). Ensiling problem To study the characteristics of the semi-aerobic landfillmay occur in a landfill cell, particularly at a high lev. stabilization process, in situ simulated semi-aerobic land-el of recirculation volumes resulting in an imbalancefill was constructed based on the theory of semi-aerobicbetween acidogenesis and methanogenesis (Lay et allandfilling. The schematic configuration of simulatedsemi-aerobic landfill is presented in Fig. 1. The dimensions1997). The study performed by Pohland (1980)showed of simulated landfill were 21 m x 3.8 m x 6 m. Highthat recirculation at landfills is practiced to accelerate thedecomposition of readily degradable organic compounddensity polyethylene(HDPE)membrane was laid on thelandfill foor, and the leachate collecting pipes of 20 cmHowever, Leachate ammonia nitrogen concentraton may in diameter were installed on the HDPE membrane. Thenaccumulate to higher level than during conventional singlepipes were covered with gravels. Three erect windpipes of20 cm in diameter were fixed on the part of the leachateo In the late 1960s, Japanese scholar presented the concept collecting pipe. The erect windpipes were perforated andsemi-aerobic landfilling(Masataka et al, 1986). Inprotected by gravel cages(40 cm in diameter) to vail airsemi-aerobic landfill site, air entered the leachate collect- Howing and penetrating into land layer. After that, munic-ing pipe, which was not full of leachate and air flow wastrengthened for the temperature difference between the pal solid waste was filled in, and landfill gas collectinginner and outside of the landfilling pile; therefore, some at different altitude. The simulated landfill was sealed withof researched results have shown that semi-aerobic land fll. plastic membrane finallying can not only accelerate the landfill stabilization processand reduce organic substance concentration in leachate andthe production of methane in semi-aerobic landfill, butalso reduce ammonia concentration in leachate. Masatakareported that about 90% organic substance in waste wereconverted into gas phase(mainly as Coz and N2)in semi-aerobic landfilling treatment, while 90% organic substanceLeachate collection pipewere converted into leachate phase in anaerobic landfillFlg. 1 Schematic of semi-aerobic landfill. MSW: municipal solid wastetreatment after three years(Yasushi and Masataka, 1997). MSW: municipal solid wasteCompared with an anaerobic landfilling treatment, theconcentrations of BOD and cOd in leachate were slightlylower in the semi-aerobic landfilling treatment(Basri et 1.2 Municipal solid waste used in experimentsaL, 2000). Onay and pohland (1998)simulated a series ofThe simulated semi-aerobic landfill was filled with 250landfill cells operated under methane producing, nitrifying, t of shredded(diameter in the range of 5-20 cm)and denitrifying environments. Leachate concentrations of compacted municipal solid waste. The com920-1400 mg/L nitrite were generated in a refuse reactor waste used in the experiments is given in Table 1.hat was supplied with air and the leachate was cycled toa denitrification reactor where ammonia removal rangedTable 1 Components of experimental municipal solid wastefrom 91% to 93%. They concluded that the use of leachaterecirculation in simulated landfill bioreactors was feasibleProportion(%)for the in situ removal of ammonia nitrogen. Wang Qis lab Food50814.5design for the Sanitary landfill site can greatly shorten the Plastictime for stabilization of the landfill site, favorable for quick Mey0.19utilization of the landfill site Dong et al., 2000).Dust2681At present, several researches have focused on theariations of leachate quality in semi-aerobic landfillingtechnology; however, the results on the characteristicsof stabilization in semi-aerobic landfill have not beer13 Analytical methodseported. Therefore, the purpose of this research was toal annual rainfallstudy the characteristics of stabilization in semi-aerobic records中国煤化工 llected frolandfill systematically by means of constructing a large- landfillCNMHGchemical oxygenscale simulated semi-aerobic landfill, and to study the demandd nitrate-nitrogencharacteristics of leachate quality, and variation of landfill concentration, which is in accordance with the nationalgas component contents and temperature in landfillstandard of water quality. Landfill gas collected fromEvolution on qualities of leachate and landfill gas in the semi-acrobic landfilllandfill was analyzed for methane, oxygen, and carbon compounds were degraded into small molecule organicdioxide concentration once per week. The temperature compounds, which could be dissolved in leachate, thusof landfill layer was monitored on line and data were resulting in the COD concentration increase (Morris etcollected once per hour.aL., 2003). As large-scale aerobic area existed, the cir-cumstance had small change in semi-aerobic landfill, and2 Results and discussiontherefore, had little effect on the activity of microorganism,and at the same time, the degree of aerobic degradation was2.1 Variations in leachate quantityhigh, not so much little molecule organic compounds weredissolved in leachate as in anaerobic landfill, and the coi2. 1.1 Dynamic variations of CODconcentration in semi-aerobic landfill presented a stable