Korean Journal of Environmental Agriculture Korean J Environ Agric. 2016;35(2):121-127. Korean Online ISSN: 2233-4173 Published online 2016 May 23. http://dx.doi.org/10.5338/kjea.2016.35.2.12 Print ISSN: 1225-3537 Research Article Open Access 기질과접종액의비율이도계가공장슬러지열가수분해액의메탄생산퍼텐셜에미치는영향 오승용, 윤영만 * 한경대학교바이오가스연구센터 Effects of Substrate to Inoculum Ratio on Biochemical Methane Potential in Thermal Hydrolysate of Poultry Slaughterhouse Sludge Seung-Yong Oh and Young-Man Yoon * (Biogas Research Center, Hankyong National University, Anseong 17579, Korea) Received: 2 May 2016 / Revised: 14 May 2016 / Accepted: 16 May 2016 Copyright c 2016 The Korean Society of Environmental Agriculture This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ORCID Seung-Yong Oh http://orcid.org/0000-0001-9116-8279 Young-Man Yoon http://orcid.org/0000-0001-9294-8277 Abstract BACKGROUND: Anaerobic digestion is the most feasible technology because not only the energy embedded in organic matters can be recovered, but also they are stabilized while being degraded. This study carried out to improve methane yield of slaughterhouse wastewater treatment sludge cake by the thermal pre-treatment prior to anaerobic digestion. METHODS AND RESULTS: Slaughterhouse wastewater treatment sludge cake was pre-treated by the closed hydrothermal reactor at reaction temperature of 190. BMPs (Biochemical methane potential) of the thermal hydrolysate was tested in the different S(Substrate)/ I(Inoculum) ratio conditions. COD(Chemical oxygen demand) and SCOD(Soluble chemical oxygen demand) contents of thermal hydrolysate were 10.99% and 10.55%, respectively, then, the 96.00% of COD was remained as a soluble form. The theoretical methane potential of thermal hydrolysate was 0.51 Nm 3 kg -1 -VS added. And BMPs were decreased from 0.56 to 0.22 Nm 3 kg -1 -VS added when S/I ratio *Corresponding author: Young-Man Yoon Phone: +82-31-670-5665; Fax: +82-31-670-5666; E-mail: yyman@hknu.ac.kr were increased from 0.1 to 2.0 in the VS content basis. Those were decreased from 0.32 to 0.13 Nm 3 kg -1 -COD added when S/I ratio were increased from 0.1 to 2.0 based on COD content. The anaerobic degradability of VS basis have showed 196.9%, 102.2%, 80.7%, 67.4%, and 39.4% in S/I ratios of 0.1, 0.3, 0.5, 1.0, and 2.0, respectively. Also the COD of 119.6%, 76.3%, 70.1%, 69.0%, and 43.1% were degraded anaerobically in S/I ratios of 0.1, 0.3, 0.5, 1.0, and 2.0, respectively. CONCLUSION: BMPs obtained in the S/I ratios of 0.1 and 0.3 was overestimated by the residual organic matters remaining at the inoculum. And inhibitory effect was observed in the highest S/I ratio of 2.0. The optimum S/I ratios giving reasonable BMPs might be in the range of 0.5 and 1.0 in S/I ratio. Therefore VS biodegradability of thermal hydrolysate was in 67.4-80.7% and COD biodegradability showed 69.0-70.1%. Key words: Anaerobic Digestion, Biochemical Methane Potential, Substrate to Inoculum Ratio, Thermal Hydrolysis 서론 유기성폐자원의혐기소화기술은기후변화의주요원인인이산화탄소를줄이고화석연료를대체하기위한신재생에 121
122 Oh et al. 너지개발측면에서많은연구가진행되고있다. 혐기소화기술은산소 (O 2) 가없는환원상태에서혐기미생물 (Anaerobic microorganism) 화학반응을통해유기물중의유기탄소 (C) 를메탄 (CH 4) 으로전환시키는기술이다. 혐기소화에서미생물의화학반응은크게가수분해 (Hydrolysis), 산생성 (Acidogenesis), 초산생성 (Acetogenesis), 메탄생성 (Methanogenesis) 의 4 단계로진행된다. 혐기소화초기의가수분해반응은입자상또는교질상의고분자유기물을용해성의저분자유기물로전화시키는단계로오랜시간을요하는반응속도결정단계 (Rate determining step) 이다 (Van Lier et al., 2008). 최근에는혐기소화효율의증진을위해혐기소화이전에유입원료의가수분해를촉진시키는방법으로열화학적전처리연구가진행되고있으며, Neyens 과 Baeyens(2003), Carlsson 등 (2012) 은하수슬러지등의열화학적전처리를통해혐기소화효율이증진된다고보고한바있다. 우리나라에서는가축분뇨, 음식물쓰레기, 하수슬러지를이용한혐기소화시설이상용화되어보급되고있으며, 혐기소화를위한원료확대를위해농업부산물, 도축부산물, 수산부산물등을이용한혐기소화연구가활발히진행되고있다. 다양한유기성바이오매스의혐기소화효율은메탄생산퍼텐셜 (Biochemical Methane Potential, BMP) 시험을통해얻어지는단위유기물당메탄생산량으로평가한다. BMP 시험은각종바이오매스의혐기적분해율을평가하는기본적인방법으로혐기소화조효율과경제성에영향을미치는주요인자이며, 혐기소화조의설계와유지관리에있어필수적인설계인자이다. BMP 는표준상태 (0, 1atm) 에서휘발성고형물 (Volatile solid, VS) 또는화학적산소요구량 (Chemical Oxygen Demand, COD) 의함량을기준으로하는단위유기물당메탄생산량 (Nm 3 kg -1 -VS added 또는 Nm 3 kg -1 -COD added) 을말하며, 유기물표현방식의선택은시료의특성, 연구자의주관적판단에의해채택된다. BMP 는 Hungate(1969) 가혐기성미생물의배양방법을개발한이후많은연구자들에의해사용되어왔으며, Owen 과 Chynoweth(1993), Angelidaki 과 Sanders (2004), Hansen 등 (2004) 등에의해시험분석법이제안된바있다. 현재독일과미국에서는각각 VDI4630(2006) 과 ASTM E2170-01(2008) 과같은 BMP 표준분석방법을마련하여운용하고있으나아직까지국내에서는 BMP 표준분석방법이마련되어있지않다. BMP 의측정은장비의종류, 혐기미생물접종액과기질의물리화학적특성, 접종액의미생물활성도, 배지의양분균형, 반응기의 ph, 반응기내여유공간 (Head space) 의정도, 반응기의교반방법등다양한분석환경의영향을받는다 (Shelton and Tiedje, 1984; Angelidaki et al., 2009; Shin et al., 2011a). 특히혐기미생물접종액과기질의물리화학적특성의영향은 BMP 측정에있어서매우중요한영향인자이다. 국외에서는 Liu 등 (2009), Neves 등 (2004), Raposo 등 (2009) 이가축분뇨, 작물부산물, 음식물쓰레기, 해바라기유박등의다양한바이오매스의혐기소화특성을파악하기위하여기질과접종액의특성및기질과접종액의비율이 BMP 에미치는영향에대한연구를진행한바있다. 국내에서는 Shin 등 (2011a), Shin 등 (2011b) 과 Kim 등 (2012b) 이기존 BMP 측정방법들을고찰하고국내외각종바이오매스의 BMP 를보고하였다. 또한 Kim 등 (2012a) 과 Kim 등 (2012b) 은양돈분뇨의열전처리에서기질과접종액의비율이 BMP 에미치는영향을보고하고있으나 BMP 연구는일부농업부산물에한정되고있는상황이다. 따라서본연구에서는도계가공장에서발생하는폐수처리슬러지의열가수분해액의혐기적유기물분해율을평가하기위하여기질과접종액의비율을달리하여 BMP 를측정하였으며, 휘발성고형물과화학적산소요구량기준으로수열탄화액의혐기적유기물분해율을분석하였다. 재료및방법 시험재료본연구에서는충청남도진천에위치한도계가공장의폐수처리시설에서발생하는유기성슬러지케이크의열가수분액 (Thermal hydrolysate) 을대상으로하였으며, 실험에사용한슬러지케이크의이화학적특성은 Table 1 과같다. 채취한슬러지의열화학반응은외부전기히터 (Heater) 에의해열원을공급하는 2 L 용량의밀폐형회분식압력반응기에 1 kg 의시료원물을정량투입후 190 에서실시하였다. 반응기의온도는반응기내부에설치한온도계측기로제어하였으며, 운전시간은승온시간 40 분, 반응시간 1 시간으로하였다. 또한열가수분해반응기는반응기내부온도의균질화를위하여내부에교반기를설치하였으며, 반응기의내부압력은반응온도별로발생하는내부포화수증기압조건으로유지하였다. 열가수분해반응을마친잉여슬러지수열탄화액은정성여과지 (Qualitative filter paper No. 1, Advantec MFS, Inc., Dublin, Califonia, USA) 로여과하여 BMP 시험에공시하였다. 이론적메탄퍼텐셜 (Theoretical methane potential; B th) 분석이론적 BMP는 Boyle(1976) 의혐기적유기물분해반응 Table 1. Chemical characteristics of sludge cake Parameters ph TS a) VS b) COD Cr c) TN d) NH 4 + -N - ------------------------------------------- (%, w/w) ------------------------------------------- Sludge cake 7.30 20.99 18.80 e) 26.59 (0.08) 1.32 0.17 a) Total solid, b) Volatile solid, c) Chemical oxygen demand, d) Total nitrogen, e) Values in parentheses are standard deviations.
Effects of S/I Ratio on BMP of Sludge Hydrolysate 123 Table 2. Chemical characteristics of inoculum Parameters ph TS a) VS b) c) COD Cr TN d) NH + 4 -N Alkalinity - -------------------------------- (%, w/v) -------------------------------- (% as CaCO 3) Inoculum 8.81 3.78 (0.05) e) 2.25 3.31 (0.06) 0.43 0.32 (0.01) 2.09 (0.03) a) Total solid, b) Volatile solid, c) Chemical oxygen demand, d) Total nitrogen, e) Values in parenthesis mean standard deviations. 식과유기물산화반응식 (Eq. 1, Eq. 3) 을이용하여시료의원소분석결과로부터화학양론적으로계산하였다. 표준상태 (0, 1기압 ) 에서 VS 함량을기준으로산출하는이론적 BMP (B th-vs) 는 Eq. 2와같으며, COD 를기준으로산출하는이론적메탄생산퍼텐셜은 Eq. 4와같다. 여기서 COD 기준의이론적메탄생산퍼텐셜 (B th-cod) 은 0.35 Nm 3 kg -1 -COD added 이다. (Eq. 1) (Eq. 2) 공간은 N 2 가스로충진후고무마개와알루미늄캡을이용하여 2중으로밀폐시켰으며, 38 항온배양기에서일일 1회손으로반응기를흔들어교반하면서 90일간배양하였다. 또한접종액에서발생하는메탄가스를보정하기위하여접종액만을투입한 3반복의혐기반응기를시료와동일한조건에서운영하였다. 접종액의이화학적성상은 Table 2와같다. 회분식혐기반응기의바이오가스발생량측정은 2% 황산에 resazurin 0.1% 를함유하는수주차식가스량측정기를사용하였으며 (Williams et al., 1996; Beuvink et al., 1992), 발생바이오가스는 Eq. 5와같이온도와수분을보정하여표준상태 (0, 1기압 ) 에서의건조가스부피로환산하여누적메탄생산곡선을구하였다. BMP 산출을위한누적메탄생산곡선은 Modified Gompertz model(eq. 6) 을이용하여 SigmaPlot(SigmaPlot Version 10.0, Systat Software Inc., San Jose, Califonia, USA) 으로해석하였다 (Lay et al., 1998). (Eq. 3) (Eq. 4) (Eq. 5) 이때, V dry gas 는표준상태 (0, 1기압 ) 에서의건조가스의부피, T는반응기의운전온도, V wet gas at T 는반응기운전온도 (38 ) 에서의습윤가스의부피, P는가스부피측정당시의대기압, P T 는 T 에서의포화수증기압 (mmhg) 이다. exp exp (Eq. 6) 메탄생산퍼텐셜 (Ultimate methane potential; B u) 시험 BMP 시험에사용한접종액 (Inoculum, I) 은경기도안성에위치한한경대학교바이오가스상용화연구시설에서채취하였다. 채취한혐기소화액은 2 mm 체를통과시킨후, 38 항온배양기에서배양하여소화액중의이분해성의유기물과잔여가스를충분히제거한후사용하였다. 각처리구별기질 (Substrate, S) 은기질의 VS 함량과접종액의 VS 함량의비율 (S/I ratio) 을 0.1, 0.3, 0.5, 1.0, 2.0가되도록조정하여투입하였다. 회분식반응기는처리구당 3반복으로 serum bottle을이용하였다. 반응기의용적 (Total volume) 은 160 ml, 유효용적 (Working volume) 은 80 ml, 상층부여유공간 (Head space) 은 80 ml로하였다. 반응기의상층부여유 이때, M은누적메탄생산량 (ml), t는혐기배양기간 (days), P는최종메탄생산량 (ml), e는 exp(1), R m 은최대메탄생산속도 (ml day -1 ), λ는지체성장시간 (lag growth phase time, days) 이다. 혐기적유기물분해율 (Anaerobic biodegradability) 은 VDI4630(2006) 에따라평가하였으며, VS 함량기준의혐기적유기물분해율 ( ) 은 Eq. 7과같으며, COD 함량기준의혐기적유기물분해율 ( ) 은 Eq. 8과같다. (Eq. 7)
124 Oh et al. Table 3. Chemical characteristics of sludge cake and thermal hydrolysate Parameters ph TS a) VS b) COD Cr c) SCOD Cr d) TN e) NH 4 + -N SS f) - ------------------------------------ (%, w/v) -------------------------------- (g L -1 ) Alkalinity (% as CaCO 3) Thermal hydrolysate 6.03 6.64 g) 6.28 10.99 (0.08) 10.55 (0.05) 0.96 0.33 0.05 (0.006) 0.93 a) Total solid, b) Volatile solid, c) Chemical oxygen demand, d) Soluble chemical oxygen demand, e) Total nitrogen, f) Suspended solid, g) Values in parentheses are standard deviations. Table 4. Elemental composition and theoretical methane potential of thermal hydrolysate Parameters Elemental composition C H O N S --------------------------------- (%, w/w) --------------------------------- B th a) (Nm 3 kg -1 -VS added) Thermal hydrolysate 45.5 7.9 26.2 13.0 0.0 0.51 a) Theoretical methane potential. 이때, 는 VS 기준유기물분해율 (%), 는바이오가스의부피 (Nm 3 ), 는바이오가스중메탄과이산화탄소의질량분율 (kg Nm -1 ), 는기질의질량 (kg), 는투입기질의 VS 농도 (g g -1 ), 는투입기질의 VFA 농도 (g g -1 ), 0.93은투입 VS 중이론적인바이오가스전환율이다. (Eq. 8) 이때, 은 COD 기준유기물분해율 (%), 는바이오가스중메탄의농도 (%, v/v), 는투입기질의질량 (kg), 는투입기질의 COD 함량 (g g -1 ), 0.32 는투입 COD 중이론적메탄전환율이다. 시험분석바이오가스의가스성분분석은 TCD(Thermal conductivity detector) 가장착된 Gas chromatography(clarus 680, PerkinElmer, Waktham, Massachusetts, USA) 를이용하였다. 컬럼은 HayesepQ packed column(3 mm 3 m, 80~100 mesh size) 을이용하였으며, 고순도아르곤 (Ar) 가스를이동상으로사용하여 30 ml min -1 의운전상태에서주입부 (Injector) 온도 150, 컬럼부 (Column oven) 90, 검출부 (Detector) 150 에서분석하였다 (Sorensen et al., 1991). 시료의원소분석은원소분석기 (EA1108, Thermo Finnigan LLC, San Jose, Califonia, USA) 를사용하였으며, 총고형물 (Total solid, TS), 휘발성고형물 (Volatile solid, VS), 화학적산소요구량 (Chemical oxygen demand, COD Cr), 용해성화학적산소요구량 (Soluble chemical oxygen demand, SCOD Cr), 총질소 (Total nitrogen, TN), 암모니아태질소 (NH + 4 -N), 알칼리도 (Alkalinity), 휘발성지방산 (VFA, Volatile fatty acid) 등은표준분석법 (APHA, 1998) 에따라 3반복으로수행하였다. 결과및고찰 열가수분해액의특성도계가공장폐수슬러지케이크의열가수분해액의성상은 Table 3과같다. 열가수분해액의 ph는 6.03이었으며, TS 6.64%, VS 6.28% 로 TS 함량의 94.58% 를차지하였다. 열가수분해액의 COD는 10.99%, SCOD이 10.55% 로약 96.00% 의유기물의대부분이용해성물질로존재하였다. Kim 등 (2012) 은양돈분뇨를 200 270 온도범위에서에서열가수분해한결과 COD가 6.2 9.6%, SCOD가 6.1 8.8% 로나타났으며, SCOD의비율이 91.7 98.4% 의범위를보였다고보고한바있어본연구결과와유사하였다. 열가수분해액의 TN은 0.96% 이었으며, NH + 4 -N은 0.33% 를보여높은질소수준을나타내었다. 이러한높은질소농도는열가수분해액을혐기소화하는경우고농도의암모니아성질소생성에따라암모니아저해영향의문제가있을것으로판단된다. 이론적메탄생산퍼텐셜도계가공장폐수슬러지케이크의열가수분해액의구성원소와원소분석결과로부터 Boyle(1976) 의혐기적유기물분해반응식을이용하여산출한이론적 BMP는 Table 4와같다. 열가수분해액의구성원소는탄소 (C) 45.5%, 수소 (H) 7.9%, 산소 (O), 26.2%, 질소 (N) 13.0% 로나타났으며, 이론적 BMP 는 0.51 Nm 3 kg -1 -VS added 이었다. S/I 비율에따른메탄생산퍼텐셜도계가공장폐수슬러지열가수분해액의혐기소화특성
Effects of S/I Ratio on BMP of Sludge Hydrolysate 125 Table 5. Model parameters by the modified Gompertz model and ultimated methane potentials estimated from the cumulative methane production data S/I ratio P a) (ml) Rm b) (ml day -1 ) λ c) (day) B u-vs d) (Nm 3 kg -1 -VS added) Ultimate methane yield B u-cod e) (Nm 3 kg -1 -COD added) 0.1 73.79 8.02 0 0.56 0.32 0.3 150.11 11.35 0 0.37 0.21 0.5 231.37 15.57 0.31 0.35 0.20 1.0 448.54 20.60 0.65 0.34 0.19 2.0 597.96 16.32 6.65 0.22 0.13 a) Methane production, b) Specific methane production rate, c) Lag phase time, d) Ultimated methane potential in the basis of VS content, e) Ultimated methane potential in the basis of COD content, f) Values in parentheses are standard deviations. Cumulative methane production(nml) 700 600 500 400 300 200 100 S/I ratio 0.1 S/I ratio 0.3 S/I ratio 0.5 S/I ratio 1.0 S/I ratio 2.0 0 0 20 40 60 80 100 Fermentaion time(days) Fig. 1. Cumulative methane production curve optimized by Modified Gompertz model in different S/I ratios. 을파악하기위하여기질과접종액의비율 (S/I ratio) 을달리하여 90일간중온혐기소화를실시하였다. 이로부터얻은누적메탄생산곡선과 Modified Gompertz model을이용하여최적화한곡선은 Fig. 1과같다. 열가수분해액의최종 BMP와 Modified Gompertz model의인자들은 Table 5 에나타내었다. S/I 비율이 0.1에서 2.0으로증가할수룩 VS 를기준으로하는최종 BMP는 0.56에서 0.22 Nm 3 kg -1 -VS added 로감소하였으며, COD를기준으로하는최종 BMP는 0.32에서 0.13 Nm 3 kg -1 -COD added 으로감소하는것으로나타났다. 이때 S/I 비율 0.1에서는 VS 기준최종 BMP(0.56 Nm 3 kg -1 -VS added) 는앞에서구한이론적 BMP(0.51 Nm 3 kg -1 -VS added) 과비교하여높은수치를나타내었다. Yoon 등 (2014) 은돼지도축장에서발생하는혈분, 내장류, 장내잔재물의 S/I 비율에따른혐기소화연구에서 S/I 비율이 0.1일때최종 BMP가기질의이론적 BMP를초과하는결과를보고한바있다. 따라서 S/I 비율이낮을경우에는접종액에잔존하는유기물로인하여기질의최종 BMP가과대하게평가될수있다. Modified Gompertz mode을이 용하여구한최종메탄생산량 (P) 은 S/I 비율 0.1에서 73.79 ml를보였으며, S/I 비율의증가와함께증가하여 2.0에서는 597.96 ml를나타내었다. 최대메탄생산속도 (R m) 는 S/I 비율 0.1에서 8.02 ml day -1 을보였으며, S/I 비율 1.0에서 20.60 ml day -1 으로가장높았다. 지체성장시간 (λ) 은 S/I 비율 0.1과 0.3에서 0 day로나타나낮은 S/I 비율에서는지체성장기없이빠른메탄생산이이루어졌으며, S/I 비율이 0.5에서 2.0으로증가할수록지체성장시간또한 0.31에서 6.65 day로증가하여 S/I 비율의증가는지체성장시간을증가시키는것으로나타났다. 특히 S/I 비율 2.0에서 6.65 day 의긴지체성장시간을보인것은반응기운전초기에혐기미생물의메탄생산에저해영향이있었던것으로판단된다. Ferrer 등 (2008) 은유기성슬러지를 70 에서열가수분해시킨결과고온혐기소화의효율이증가하였다고보고하였고, Yoneyama 등 (2006) 은 180 에서우분의열가수분해에따른혐기소화효율의증가를보고한바있다. 이와같이일반적으로열가수분해반응은입자상유기물을가용화시켜용해성유기물의함량을증가시키고가수분해단계의반응을촉진시킴으로써메탄가스의생산효율을증가시킨다. 이러한연구결과와는반대로열가수분해전처리가혐기소화효율을저해할수있다는연구결과도있다. Martins와 Van Boekel (2005) 과 Ajandouz 등 (2008) 은유기성슬러지의열화학적처리에서난분해성물질이생성되고, 이러한물질은혐기미생물에저해작용을일으킬수있다고보고한바있다. 이는고온의열처리과정에서탄수화물이아미노산과반응하면서갈변반응 (Maillard reaction) 에의해멜라노이딘 (melanoidin) 과같은난분해성물질을생성하기때문이다. 따라서 S/I 비율의증가가누적메탄생산곡선의지체성장시간을연장시키는결과를볼때, 도계가공장폐수슬러지를열가수분해시키는과정 (190 ) 에서일부난분해성의열가수분해산물이생성되는것으로생각된다. 이러한갈변반응은온도와 ph, 수분의활동도에따라발생량을달리하는것으로보고 (Martins et al., 2000) 되고있으며, 100 이하의낮은온도영역에서도갈변반응이관찰되었다는연구결과 (Martins and Van
126 Oh et al. Table 6. Organic composition characteristics and anaerobic biodegradability in sludge, liquid and solid fraction of sludge S/I ratio D VS a) D COD b) ---------------------- (%, w/w) ---------------------- 0.1 196.9 119.6 0.3 102.2 76.3 0.5 80.7 70.1 1.0 67.4 69.0 2.0 39.4 43.1 a) Anaerobic biodegradability estimated in the basis of VS content, b) Anaerobic biodegradability estimated in the basis of COD content. Boekel, 2005) 도있다. 또한 Kim 과 Jeon(2015) 은동일한온도에서열가수분해를진행하더라도반응기의승온시간, 반응기내교반효율에따라갈변반응의정도가차이를보인다고하였다. S/I 비율별유기물분해율평가 Table 6은 Eq. 7과 Eq. 8(VDI4630, 2006) 에따라계산된열가수분해액중유기물의혐기적분해율을나타낸다. VS 기준유기물분해율은 S/I 비율 0.1과 0.3에서 196.9%, 102.2% 로나타나이론적인분해율 100% 를초과했고, S/I 비율이 0.5에서 2.0으로증가함에따라유기물분해율은 80.7% 에서 39.4% 로감소하였다. COD 기준유기물분해율에서도 S/I 비율 0.1에서 119.6% 로이론적인분해율 100% 를초과하였으며, S/I 비율이 0.3에서 2.0으로증가함에따라 76.3% 에서 43.1% 로감소하였다. VDI4630(2006) 에서는혐기소화조투입기질에대하여분해된유기물의약 7% 정도가혐기미생물의바이오매스축적에이용되는것으로보고하고있다. 따라서앞에서구한이론적 BMP(0.51 Nm 3 kg -1 -VS added) 에서약 7% 는혐기미생물의증식에이용되고실질적으로메탄가스로전환가능한이론적 BMP는 0.47 Nm 3 kg -1 -VS added 으로평가된다. 또한 COD 기준의이론적메탄생산퍼텐셜은 0.35 Nm 3 kg -1 -COD added 으로알려져있으나 VDI4630(2006) 에서는혐기미생물증식에이용되는부분을제외하고이론적 BMP를 0.32 Nm 3 kg -1 -COD added 으로설정하여유기물의혐기적분해율을산출하고있다. 이와같이혐기미생물의증식에이용되는분해유기물의양을고려하는경우 VS 기준유기물분해율은 S/I 비율 0.1과 0.3에서 100% 를초과하였고, COD 기준유기물분해율은 S/I 비율 0.1에서 100% 를초과하는것으로나타났다. 따라서본연구에서도계가공장폐수슬러지열가수분해액의최종 BMP 측정을위한 S/I 비율은 0.5 1.0의범위가적정한것으로판단되며, S/I 비율 0.1과 0.3은접종액중의유기물에서유래하는메탄에의해최종 BMP가과대평가될수있고, S/I 비율 2.0은열가수분해액의혐기소화저해작용이일어날수있는것으로분석되었다. 결론 본연구는도계가공장에서발생하는폐수처리슬러지의혐기소화효율을증진시키기위하여 190 반응온도에서열가수분해하여전처리한후 S/I 비율을달리하여폐수슬러지열가수분해액의혐기소화특성을분석하였다. 열가수분해액의 COD와 SCOD는각각 10.99% 와 10.55% 로약 96.00% 의유기물이용해성물질로존재하였다. 열가수분해액의이론적 BMP는 0.51 Nm 3 kg -1 -VS added 로나타났으며, S/I 비율 0.1에서 2.0으로증가할수룩 VS 기준최종 BMP는 0.56에서 0.22 Nm 3 kg -1 -VS added 로감소하였으며, COD 기준최종 BMP는 0.32에서 0.13 Nm 3 kg -1 -COD added 으로감소하는것으로나타났다. S/I 비율 0.1과 0.3은접종액중의유기물에서유래하는메탄에의해최종 BMP가과대하게평가되는문제가나타났으며, S/I 비율 2.0은열가수분해액의혐기소화저해작용에의해낮은 BMP를보이는문제가나타났다. 따라서폐수슬러지열가수분해액의 BMP 측정을위한적정 S/I 비율은 0.5 1.0이었으며, S/I 비율 0.5, 1.0에서 VS 기준 BMP는 0.35과 0.34 Nm 3 kg -1 -VS added 이었고, COD 기준 BMP는 0.20와 0.19 Nm 3 kg -1 -COD added 으로 나타났다. Acknowledgment This work was supported by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries (IPET) through Agri-Bio industry Technology Development Program, funded by Ministry of Agriculture, Food and Rural Affairs(MAFRA)(Project No. 314010-04-2-HD040) References Ajandouz, E. H., Desseaux, V., Tazi, S., & Puigserver, A. (2008). Effects of temperature and ph on the kinetics of caramelisation, protein cross-linking and Maillard reactions in aqueous model systems. Food Chemistry, 107(3), 1244-1252. Angelidaki, I., & Sanders, W. (2004). Assessment of the anaerobic biodegradability of macropollutants. Re/ Views in Environmental Science & Bio/Technology, 3(2), 117-129. American Public Health Association. (1998). Standard methods for the examination of water and wastewater, 20th ed. Continental Edition, USA. Beuvink, J. M. W., Spoelstra, S. F., & Hogendorp, R. J. (1992). An automated method for measuring time-course of gas production of feedstuffs incubated with buffered rumen fluid. Netherlands Journal of Agricultural Science, 40(4), 401-407.
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