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

Anae r obic 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. 1

I ntro duc tio n: “Pa nc a ke s” 2

I ntro duc tio n: E g g s & Silo s 3

Ba c kg ro und –Bug ’ s-E ye Vie w SUBST RAT E Hydro lysis & Ac idific a tio n ORGANI C ACI DS (ACE T AT E ) Me tha no g e ne sis ME T HANE 4

Ba c kg ro und – A Clo se r Vie w I NE RT S SUBST RAT E PROT E I NS L I PI DS CARBOHYDRAT E S Hydro lysis AMI NO ACI DS, SUGARS, L ONG-CHAI N F AT T Y ACI DS, AL COHOL S F e rme nta tio n Ana e ro b ic PROPI ONAT E , BUT YRAT E , VAL E RAT E … Oxida tio n VOL AT I L E ACI DS Ho mo a c e to g e ne sis ACE T AT E HYDROGE N CO 2 ↔ HCO 3 - ME T HANE Ac e to c la stic Hydro g e no tro phic Me tha no g e ne sis 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 6

Ma ny Pro c e ss Va ria tio ns! F R W Sing le -Sta g e T he rmo philic Ba tc h-F e d T he rmo philic : F e e d • Re a c t • Withdra w • T e mpe ra ture Pha se d Ana e ro b ic Dig e stio n (T PAD) 7

Mo re Pro c e ss Va ria tio ns 2-Sta g e Ac id / Ga s Dig e stio n T he rma l Hydro lysis (Ca mb i / E xe lys™) So nic a tio n/ Ca vita tio n (So no lyze r ™ & Cro wn) Pre tre a tme nt & Sing le - Othe rs: (Bio Cra c k, O 3 , E nzyme s) Sta g e Me so philic AD 8

Sc o pe o f T his Wo rksho p BI OGAS HE AT 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! 9

Why Dig e st? 10

So lids De struc tio n Solids Before & After Digestion: 50 MGD Plant 70 60 WAS 50 Tons Solids per Day VSS 40 WAS FSS Δ = 33% 30 VSS Primary VSS 20 FSS 10 Primary FSS 0 Raw Sludge Digested Sludge 11

Pa tho g e n De struc tio n a nd VAR Required Time vs. Temp for Alternative 1 30 Required Contact Time (hours) V e c to r 25 A ttra c tio n R e duc tio n 20 15 No te : 10 me so philic 5 dig e stio n alo ne will no t g ive 0 Class A 130 132 134 136 138 140 b io so lids Contact Temperature (°F) 12

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 13

Co g e ne ra tio n a .k.a . C o mb ine d H e a t a nd P o 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 • 14

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 ! 15

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 ) 16

Wha t Are Yo ur Drive rs? Stabilization Solids for Beneficial Sustainability Reduction Reuse Energy Revenue Better Production (Tipping Fees) Dewatering 17

AD Che mistry – F o o d o r Po iso n? Substrate (Sludge, Codigestion) Ammonia Sulfides Volatile Acids 18

Alka linity a nd Buffe ring 10 Wa te r c he mist: Ammonia pK a = 9.3 – T itra te to pH 4.3, c a lc ula te 9 - ] [CO 3 = ] a nd [HCO 3 8 Ana e ro b ic mic ro b io lo g ist: Phosphoric Acid pK a = 7.2 7 Sulfide pK a = 6.9 – Multiple b uffe r syste ms Bicarbonate pK a = 6.4 – T itra tio n to 4.3 inc lude s 6 b ic a rb o na te (g o o d) a nd vo la tile a c ids (b a d) 5 – Pre fe ra b le to me a sure Volatile Acid pK a ’s = 4.8-4.9 VF A’ s & HCO 3 se pa ra te ly Titration endpoint 4 19

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 20

De sig n Crite ria • O rg a nic L o a ding R a te … e ithe r VSS o r COD • H ydra ulic R e te ntio n T ime … 15-25 da ys • OL R = So lids Co nc e ntra tio n / HRT OLR vs. HRT & Feed Concentration 10 Feed Concentration (%) OLR in lb/1000 ft 3 -day: 8 250 Note: 1.0 kg/m 3 -d = 6 200 62.4 lb/1000 ft 3 -d 4 150 HRT 100 2 0 10 15 20 25 HRT (days) 21

De sig n Crite ria • O rg a nic L o a ding R a te … e ithe r VSS o r COD • H ydra ulic R e te ntio n T ime … 15-25 da ys • OL R = So lids Co nc e ntra tio n / HRT OLR vs. HRT & Feed Concentration 10 Feed Concentration (%) 8 OLR in g/L-day: 4.0 Note: 1.0 kg/m 3 -d = 6 3.2 62.4 lb/1000 ft 3 -d 4 2.4 1.6 2 0 10 15 20 25 HRT (days) 22

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 Solids Residence Time in Completely Mixed Tank 100% 80% Fraction Retained Less than 40% of feed is retained for one full HRT. 60% Short-circuiting and dead volumes worsen the problem. 40% 20% 0% 0 1 2 3 4 (t / τ) - Number of Theoretical HRT's 23

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 . Me so philic dig e stio n a lo ne will no t yie ld Cla ss A. 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 . 24

L o 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 25

Que stions? Leonard E. Ripley, Ph.D., P.E., BCEE LER@Freese.com 26