Materials and Methods

하수슬러지 최종 처분을 위한 대안을 검토하기 위하여 국내 B시의 G‒

하수처리시설 제1처리장을 대상으로 하여 가상플랜트를 구축한 후 시뮬 레이션을 수행하였다. G‒하수처리시설 제1처리장은 일일 시설용량 500,000㎥ 규모 <표 1>의 공공하수처리시설로써, 2012년 기준으로 일평 균 약 432,376㎥/일의 하수를 처리하고 있다¹⁾. G‒하수처리시설은 일차침 전과 생물학적 질소인 제거공정(BNR, Biological Nutrient Removal)으 로 구성되어 있고, 유입하수 수질은 TBOD 144mg/L, TSS 143mg/L, TN 40mg/L 및 TP 4.5mg/L로 전형적인 국내 도시하수처리시설 유입하

1) 2012년 G‒공공하수처리시설 운영자료 참조

160 _ 생태환경논집 [Vol.2, no.2 : 수환경 모니터링과 진단]

가상플랜트를 이용한 하수슬러지 감량화 방안 검토 _ 161

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Items Unit Raw Wastewater Thickened Sludge

Flow rate¹⁾ ㎥/d 432,376 1,339

TBOD mg/L 144 19,621

TCODcr mg/L 276 47,723

TSS mg/L 143 40,269

Total Nitrogen mg/L 40 1,492

Total Phosphorus mg/L 4.5 1,153

Alkalinity mg/L as CaCO₃ 194 ‒

<표 1> Characteristics of raw wastewater and thickened sludge of G‒WWTP

Note‒1) Design capacity of G‒WWTP is 500,000㎥/d as daily max flow rate Source) Operation data(Average) of G‒WWTP during 2012

Case Sludge Treatment Process Final

Treatment Case‒1 Centrifuge

Incineration Case‒2 Thermal Hydrolysis + Centrifuge

Case‒3 Anaerobic Digestion + Centrifuge

Case‒4 Thermal Hydrolysis + Anaerobic Digestion+Centrifuge

<표 2> Scenario of sludge treatment process for final disposal

Operation parameters Unit Value Conversion ratio¹⁾ of Ss to BOD₅ unitless 0.25 Fraction of cell debris, fd unitless 0.08 Conversion ratio of Xs²⁾, Xbh³⁾, Xba⁴⁾ to Ss⁵⁾ unitless 0.40

<표 3> Simulation conditions for thermal hydrolysis

Source) WEF, WERF, EPA, 2012 Note‒2) Xs; Slowly biodegradable substrate Note‒3) Xbh; Biomass(Heterotrophs) Note‒4) Xha; Biomass(Autotrophs) Note‒5) Ss; Readily biodegradable substrate

4) 2012년 G‒하수처리시설 탈수기 운영자료 참조

가상플랜트를 이용한 하수슬러지 감량화 방안 검토 _ 163

Operation parameters Unit Value Solids retention time for each reactors days 28~30

Reactor temperature ℃ 35

Yield coefficient, Y unitless 0.08

Decay coefficient /d 0.023

Ratio of Methane gas in biogas unitless 0.65

<표 4> Simulation conditions for anaerobic digestion

<그림 1> Influent flow rate of G‒WWTP in 2012

<그림 2> Influent BOD and COD of G‒WWTP in 2012

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<그림 3> Influent TSS of G‒WWTP in 2012

<그림 4> Influent TN and TP of G‒WWTP in 2012

Operation parameters Unit Value

Water Contents in Cake¹⁾ % 74 ~ 85

Polymer dosage²⁾ % as dry

solids 0.5 ~ 1.45 Ratio of Solids Separation unitless 0.95 Specific Gravity of Solids unitless 1.2

<표 5> Simulation conditions for centrifuge for dewatering

source) Operation data from G‒WWTP, 2012

가상플랜트를 이용한 하수슬러지 감량화 방안 검토 _ 165

Note‒1)

<그림 5> Comparison of Water contents in dewatered cake vs VS in influent sludge(operation data of G‒WWTP), 2012

Note‒2)

<그림 6> Comparison of water contents in dewatered cake vs polymer dosage for centrifuge(operation data of G‒WWTP), 2012

166 _ 생태환경논집 [Vol.2, no.2 : 수환경 모니터링과 진단]

Parameters Unit Value Temp.

coeffi cient

<Kinetic coefficients for Heterotrophic bacteria>

Maximum specific growth rate at 20℃, ㎛ g VSS / g VSS / d 6 1.072

Half‒velocity constant at 20℃, Ks mg bCOD / L 20 1

Half‒velocity constant at 20℃, Knh mg NH4N / L 0.05 1

Synthesis yield coefficient at 20℃, Yh g VSS / g bCOD 0.67 1 Decay coefficient for heterotrophic bioamss at 20℃, bh g VSS / g VSS / d 0.62 1.12 Fraction of cell mass remaining as cell debris at 20℃, fp Unitless 0.08 1

Anoxic growth factor, ng Unitless 0.8 1

Anoxic hydrolysis factor, nh Unitless 0.4 1

Anaerobic hydrolysis reduction factor, nfe Unitless 0.4 1

Maximum specific hydrolysis rate, kh L / mgCOD / d 3 1.116

Slowly biodegradable half saturation coefficient, kx g COD / g COD 0.03 1.116

Oxygen inhibition coefficient at 20℃, Koh mgO2 / L 0.2 1

Saturation coefficient for alkalinity (HCO3‒), Kalkh mole HCO3 / ㎥ 0.1 1

<Kinetic coefficients for Nitrifiers and etc.>

Maximum specific growth rate at 20℃, ㎛n g VSS / g VSS / d 0.8 1.103

Half‒velocity constant at 20℃, Kn mg NH4N / L 1 1

Synthesis yield coefficient at 20℃, Ya g VSS / g NH4‒N 0.24 1 Endogenous decay coefficient at 20℃, ba g VSS / g VSS /d 0.15 1.072 Oxygen half saturation coeff. for autotrohphs growth, Koa mgO2 / L 0.4 1 Ammmonification rate of soluble organic nitrogen, ka L / mgCOD / d 0.08 1.072

Nitrate half saturation cefficient, Kno mgN / L 0.5 1

Saturation coefficient for alkalinity (HCO3‒), Kalka mole HCO3 / ㎥ 0.5 1

<Kinetic coefficients for PAOs (phosphorus‒accumulating organisms)>

Synthesis yield coefficient at 20℃, Ypao g VSS / g COD 0.45 1 Endogenous decay coefficient at 20℃, bpao g VSS / g COD / d 0.2 1.072 Raio of Phosphorus release / VFA uptake, fpo4_rel g P / g COD 0.5 1 Saturation coefficient for phosphate, Kp g VSS / g VSS / d 0.01 1 Saturation coefficient for alkalinity (HCO3‒), Kalkp mole HCO3 / ㎥ 0.1 1 Rate for lysis of Poly‒phosphate(Xpp), bpp ㎥ / g VSS / d 0.2 1.072 Fraction of Phosphorus in the active PAO mass g P / g VSS 0.38 1

Maximum ratio of g P / g Xpao g P / g Xpao 0.4 1

Saturation coefficient for acetate, Ksa mg COD / L 4 1

Saturation coefficient for phosphorus in storage of PP, Kps mg P / L 0.2 1 Inhibition coefficient for PP storage, Kipp g Xpp / g Xpao 0.02 1 Saturation coefficient for PHA, Kpha g Xpha / g Xpao 0.01 1

<Stoichiometric parameters for sludge, nitrogen and etc.>

SS to COD ratio for Xi g SS / g CODxi 0.75 1

SS to COD ratio for Xs g SS / g CODxs 0.75 1

SS to COD ratio for Xbh, Xba and Xpao g SS / g CODbm 0.9 1

<표 6> Simulation parameters for activated sludge Model

가상플랜트를 이용한 하수슬러지 감량화 방안 검토 _ 167

Parameters Unit Value Temp.

coeffi cient Nitrogen contents in active microbes, inbm g N / g COD 0.086 1 Nitrogen content of endogenous / inert mass, inxs_i g N / g COD 0.06 1 Phosphorus content of biomass (Xbh, Xba), ipbm g P / g COD 0.02 1 Phosphorus content of particulate substrate (Xs), ipxs g P / g COD 0.01 1 Phosphorus content of intert particulate COD (Xi), ipxi g P / g COD 0.01 1 Ss and X to BOD5 conversion factor in effluent g BOD / g COD 0.66 1