Anae r obic Dige stion F undame ntals What are the y de sig ne - - PowerPoint PPT Presentation

Anae r

• bic Dige stion

F undame ntals

What are the y de sig ne d fo r?

Leonard E. Ripley, Ph.D., P.E., BCEE

Senior Process Engineer / Freese and Nichols, Inc.

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I ntro duc tio n: “Pa nc a ke s”

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I ntro duc tio n: E g g s & Silo s

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Ba c kg ro und –Bug ’ s-E ye Vie w

SUBST RAT E ORGANI C ACI DS (ACE T AT E ) ME T HANE

Hydro lysis & Ac idific a tio n Me tha no g e ne sis 4

VOL AT I L E ACI DS

Ba c kg ro und – A Clo se r Vie w

SUBST RAT E

PROT E I NS CARBOHYDRAT E S L I PI DS I NE RT S AMI NO ACI DS, SUGARS, L ONG-CHAI N F AT T Y ACI DS, AL COHOL S PROPI ONAT E , BUT YRAT E , VAL E RAT E … ACE T AT E HYDROGE N

ME T HANE CO 2 ↔ HCO3

• Hydro lysis

F e rme nta tio n Ana e ro b ic Oxida tio n Ho mo a c e to g e ne sis Ac e to c la stic Me tha no g e ne sis Hydro g e no tro phic Me tha no g e ne sis 5

A L ittle Mo re Ba c kg ro und

Mesophiles

Preferred temperature: 95°F (35°C) Moderate activity rate More efficient at metabolizing carbohydrates

Thermophiles

Preferred temperature: 130°F (55°C) Higher activity rate More efficient at metabolizing proteins Higher potential for odor generation

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Ma ny Pro c e ss Va ria tio ns!

Sing le -Sta g e T he rmo philic T e mpe ra ture Pha se d Ana e ro b ic Dig e stio n (T PAD)

F

Ba tc h-F e d T he rmo philic :

R W

• F

e e d

• Re a c t
• Withdra w

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Mo re Pro c e ss Va ria tio ns

Pre tre a tme nt & Sing le - Sta g e Me so philic AD

So nic a tio n/ Ca vita tio n

(So no lyze r ™ & Cro wn)

T he rma l Hydro lysis

(Ca mb i / E xe lys™)

Othe rs:

(Bio Cra c k, O 3, E nzyme s)

2-Sta g e Ac id / Ga s Dig e stio n

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Sc o pe o f T his Wo rksho p

Sing le -Sta g e Me so philic A “simple ” pro c e ss, with ma ny de sig n a nd o pe ra ting c o mple xitie s!

BI OGAS HE AT

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Why Dig e st?

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So lids De struc tio n

10 20 30 40 50 60 70 Raw Sludge Digested Sludge Tons Solids per Day

Solids Before & After Digestion: 50 MGD Plant Primary FSS Primary VSS WAS FSS WAS VSS VSS FSS

Δ = 33%

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Pa tho g e n De struc tio n a nd VAR

No te :

me so philic dig e stio n alo ne will no t g ive Class A b io so lids

5 10 15 20 25 30 130 132 134 136 138 140 Required Contact Time (hours)

Contact Temperature (°F)

Required Time vs. Temp for Alternative 1

Ve c to r Attra c tio n Re duc tio n

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Bio g a s Pro duc tio n / Purific a tio n

• Pipe line sa le
• Ve hic le fue ling

(Se e Aug WE F Hig hlig hts)

Photos: City of Grand Junction, CO

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Co g e ne ra tio n

a .k.a . Co mb ine d He a t a nd Po we r

• Re duc e e ne rg y purc ha se
• Re c o ve r “wa ste ” he a t
• Se ll po we r b a c k to g rid

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Co dig e stio n o f truc ke d wa ste s

• Re duc e o rg a nic lo a ding to liq uids tre a tme nt
• T

ipping fe e s fro m dive rsio n o f MSW o rg a nic s

• Ge ne ra te mo re me tha ne → mo re e le c tric ity/ ste a m

No t limite d to F a ts, Oil, a nd Gre a se !

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I mpro ve (Usua lly) De wa te ra b ility

• L

e ss po lyme r c o nsumptio n

• Be tte r thro ug hput
• Hig he r c a ke c o nc e ntra tio n

(lo we r truc king / dispo sa l $$) BUT … hig he r po te ntia l fo r struvite fo rma tio n w/ BNR!

(Ma g ne sium Ammo nium Pho spha te )

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Wha t Are Yo ur Drive rs?

Stabilization for Beneficial Reuse Solids Reduction Energy Production Revenue (Tipping Fees) Sustainability Better Dewatering

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AD Che mistry – F

• o d o r Po iso n?

Substrate (Sludge, Codigestion) Ammonia Volatile Acids Sulfides

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Alka linity a nd Buffe ring

Wa te r c he mist:

– T

itra te to pH 4.3, c a lc ula te [CO 3

=] a nd [HCO 3

• ]

10 9 8 7 6 5 4 Ammonia pKa = 9.3 Phosphoric Acid pKa = 7.2 Sulfide pKa = 6.9 Bicarbonate pKa = 6.4 Volatile Acid pKa’s = 4.8-4.9

Ana e ro b ic mic ro b io lo g ist:

– Multiple b uffe r syste ms – T

itra tio n to 4.3 inc lude s b ic a rb o na te (g o o d) a nd vo la tile a c ids (b a d)

– Pre fe ra b le to me a sure

VF A’ s & HCO 3 se pa ra te ly

Titration endpoint

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F ro m Bug ’ s-E ye to Big Pic ture …

Dig e ste r mixing

– Bring b a c te ria a nd fo o d to g e the r – Avo id g rit de po sitio n & lo ss o f vo lume – Pre ve nt (re duc e ) fo a ming

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De sig n Crite ria

• Org a nic L
• a ding Ra te … e ithe r VSS o r COD
• Hydra ulic Re te ntio n T

ime … 15-25 da ys

• OL

R = So lids Co nc e ntra tio n / HRT

2 4 6 8 10 10 15 20 25 Feed Concentration (%) HRT (days)

OLR vs. HRT & Feed Concentration

OLR in lb/1000 ft3-day: 100 150 200 250

Note: 1.0 kg/m3-d = 62.4 lb/1000 ft3-d

HRT

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De sig n Crite ria

• Org a nic L
• a ding Ra te … e ithe r VSS o r COD
• Hydra ulic Re te ntio n T

ime … 15-25 da ys

• OL

R = So lids Co nc e ntra tio n / HRT

2 4 6 8 10 10 15 20 25 Feed Concentration (%) HRT (days)

OLR vs. HRT & Feed Concentration

OLR in g/L-day: 1.6 2.4 3.2 4.0

Note: 1.0 kg/m3-d = 62.4 lb/1000 ft3-d

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De sig n Crite ria

• HRT

a nd dig e ste r pa ss-thro ug h

– Se rio us implic a tio ns fo r pa tho g e ns, re -g ro wth, o do rs

0% 20% 40% 60% 80% 100% 1 2 3 4 Fraction Retained (t / τ) - Number of Theoretical HRT's

Solids Residence Time in Completely Mixed Tank

Less than 40% of feed is retained for one full HRT. Short-circuiting and dead volumes worsen the problem.

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Clo sing T ho ug hts …

De pe nding o n de sig n a nd o pe ra tio n, me so philic dig e stio n is a sta b le , ro b ust pro c e ss with ma ny b e ne fits & o ppo rtunitie s fo r c o dig e stio n & b io g a s utiliza tio n Dig e stio n do e s ha ve dra wb a c ks: susc e ptib le to to xins, fo a ming (No c ardia), a nd o ve rlo a ding . Histo ric a l c o nc e rns a b o ut o do rs c a n b e e limina te d with fixe d c o ve rs a nd ma na g e me nt o f o ff-g a ssing . Me so philic dig e stio n a lo ne will no t yie ld Cla ss A.

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L

• ts o f Optio ns …

“Optimum” de sig n de pe nds o n:

• Utility’ s o b je c tive s
• Ca pita l a va ila b ility
• Ope ra ting c o sts
• E

ne rg y c o sts

• Re g ula tio ns
• Custo me r de ma nds

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Que stions?

Leonard E. Ripley, Ph.D., P.E., BCEE

LER@Freese.com

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