Performance of Compostable Food Servicware in a High Solids Digester Followed by Composting

Transcription

1 Perfrmance f Cmpstable Fd Servicware in a High Slids Digester Fllwed by Cmpsting Tim Gdman Octber 16, rd Annual RAM/SWANA Cnference & Shw 1

2 Cmparisn f Cmpsting and Anaerbic Digestin Anaerbic Digestin Occurs in the absence f xygen. Odrs easier t cntrl due t prcess being enclsed. Prduces methane which can be harvested as an energy surce. Higher capital cst. Wrks well fr high nitrgen materials. Cellulsic and carbn based materials can be difficult t prcess. Requires 3 4 weeks f digestin fllwed by up t 8 weeks f cmpsting f digestate t prduce a mature prduct. Cmpsting Occurs in the presence f xygen. Odrs mre difficult t cntrl due t prcess being utside. N emissins which can be harvested as an energy surce. Lwer capital cst. Requires a balance between nitrgen and carbn surces. Takes weeks f cmpsting and curing time t get a mature prduct. And the bugs are different! 2

3 Organisms Invlved in Cmpsting Actinmycetes Fungi Bacteria Macr & Micr Fauna 3

4 Organisms Invlved in Anaerbic Digestin Hydrlytic Bacteria Fermentative Bacteria Acidgenic Bacteria Methangenic Bacteria 4

5 Assumptins abut Cmpstable Fd Serviceware in Anaerbic Digesters The general assumptins based largely n a variety f lab-scale testing. Assumptins: Under mesphilic perating temperatures, n change will be bserved in the prducts. Under thermphilic perating temperatures, sme change in the prducts will be nticed (defrmatin, clr-change, brittleness). If the slid digestate is further prcessed using aerated cmpsting methds, prducts will cmplete the bidegradatin and disintegratin prcess. Wet digesters nt as effective in prcessing cmpstable prducts. Mst pre-screen feedstck befre grinding, pumping & mixing. Typically send whatever gets screened ut t landfill as ppsed t a cmpsting step. 5

6 Cmmercial-Scale Field Test Prject Participants NatureWrks BIOFerm Energy Systems University f Wiscnsin Oshksh Prject Objectives Determine the behavir f Inge PLA cmpstable fd serviceware in a cmmercial scale, dry anaerbic digester perated under mesphilic temperatures ( C r F). Determine the behavir f the digested items in a simulated cmmercial cmpsting envirnment. 6

7 Facility Descriptin Year f Cnstructin: 2011 (first cmmercial-scale, dry fermentatin AD facility in Nrth America) Owner: UW Oshksh Fundatin Develper: BIOFerm Energy Systems Feedstcks: 10,000 TPY f fd waste, yard waste, animal bedding and curbside rganics Energy Prductin: 370 kw f cntinuus electrical pwer 7

8 Gas cllectin, strage & treatment. University f Wiscnsin Oshksh Dry Digester Prcess Flw Gas Strage & Treatment Gas Gas runs CHP unit t generate heat & electricity Overhead nzzles spray a micrrganism-rich slutin t ptimize the prcess. Gas Generatr Electricity Heat Perclate Tank Heat Fermentatin Chamber Organics Perclate Recirculatin Organics are laded int fermentatin chambers and prcessed fr 28 days. In-flr heating system running at a mesphilic temp f104 0 F. (40 0 C). Slid Digestate t Aerbic Cmpsting Slid digestate t cmpsting site fr further prcessing. 8

9 AD Trial Methdlgy Based n the typical makeup f the incming feedstck a recipe was develped fr the test samples. Fresh material 45% (yard waste, fd waste, structural material) Recycled digestate 45% Cmpstable Fd Serviceware (CFS) 10% (cmpstable cups, utensils/dinnerware, cffee/tea bags, cmpstable liner bags) This mix f materials was put in nine (9) nyln mesh bags durable enugh fr the digestin prcess while still allwing liquids (perclate) t flw thrugh freely. Apprximately 50 lbs. f this mix was put in each bag. 9

10 AD Trial Methdlgy The bags were placed int ne f the fermentatin chambers alng with that day s lad f rganic materials and was then cvered with a layer f bimass t encurage heat and mass transfer. The chamber was then clsed and left t ck fr 28 days. Perclate is added n a regular schedule and temperatures in bth the chamber and the nyln mesh bags were mnitred. 10

11 AD Trial Methdlgy After 28 days, the chamber was pened and all material was unladed. The nyln mesh bags were intact and the digested material was remved frm each bag. Samples f the cmpstable plastics were cllected fr labratry analysis t determine the amunt f bidegradatin. 11

12 Cmpst Trial Methdlgy Tw trial cmpst bunkers designed t simulate standard cmmercial windrw systems and perate under thermphilic cmpst cnditins Windrw A Digestate, yard waste (50/50) and digested CFS Windrw B Digestate, yard waste (50/50) and fresh CFS (weighed, separated and crushed) Of the apprximately 45 lbs. f CFS placed in each windrw, 40 lbs. were placed in lse and 5 lbs. placed in a nyln mesh bag and buried in the piles. Piles turned semi-weekly; temperatures checked and recrded befre each turning. Samples f CFS were taken frm each pile fr labratry analysis ver the 8 week duratin f the cmpst trial. 12

13 Cmpst Trial Methdlgy Suth Pile AD Pre-Treated Nrth Pile Nn-AD Treated 13

14 Using Mlecular Weight as a Degradatin Indicatr The first stage f PLA degradatin is usually the reductin f mlecular weight (Mw) by hydrlysis. Fragments f lactic acid are prducts f the hydrlysis prcess with micrrganisms t prduce carbn dixide, water and slid bimass. Thugh mderately stable under mesphilic temperatures, PLA hydrlysis can be accelerated under thermphilic temperatures (abve 50 0 C). 14

15 Bidegradatin Testing Methdlgy & Results The Mw fr a variety f prducts (clear cups, ht cups, ht cup lids, cutlery, etc.) were used as a baseline with samples drawn after 28 days in the digester and again ver an 8 week perid frm the simulated cmpsting piles. Mw testing was used t cmpare: Pre-prcessing samples Pst-AD samples Pst-AD + cmpsting samples Pst cmpsting samples 15

16 Mlecular Weight Clear Cld Cup in AD and Cmpst Anaerbic Digestin Phase Aerbic Cmpsting Phase Weeks Clear Cup in Cmpst Only Clear Cup in AD then Cmpst 16

17 Ht Cup Lid in AD and Cmpst 100,000 90,000 80,000 70,000 60,000 50,000 40,000 30,000 Anaerbic Digestin Phase Aerbic Cmpsting Phase 20,000 10, Lid in AD then Cmpst Lid in Cmpst Only 17

18 Mlecular Weight Cutlery in AD and Cmpst 50,000 45,000 40,000 35,000 Anaerbic Digestin Phase Aerated Cmpsting Phase 30,000 25, Weeks Cutlery in AD Fllwed by Cmpsting Cutlery in Cmpsting Only 18

19 Prject Results Visual Observatins General characteristics f the AD digestate cming ut f the fermentatin chamber included: Whle, recgnizable fd waste was nt fund Tea bags and cffee bags were nt fund Cmpstable plastics were fund t be brittle and defrmed Inge PLA-cated paper was brken dwn Cmpstable plastic bags were mstly intact but shwed signs f disintegratin 19

20 Prject Results Visual Observatins Observatins f the cmpstable prducts in the cmpsting piles shwed: In as little as 3 weeks, mst f the CFS in the AD pre-treated pile had disintegrated beynd detectin. After 6 weeks, very little (< 5%) CFS remained visible in either pile. Start f Trial The mst cmmnly fund cmpstable items fund in the piles at the end f the trial were ht cup lids and parts f clear cld cups. End f Trial 20

21 Prject Cnclusins Dry Anaerbic Digestin (Mesphilic Temperatures) Nticeable change in the visual characteristics f the cmpstable prducts. Ttal breakdwn f PLA-cated paper and tea/cffee bags. Cmpstable plastic cld cups and cutlery were recgnizable and generally intact but defrmed int a melted appearance. Mw testing f the cmpstable prducts after 28 days in the digester cnfirms a partial breakdwn f mlecular structure (bidegradatin). Aerbic Cmpsting (Thermphilic Temperatures) Mst significant disintegratin f cmpstable plastic material bserved. After 4 weeks Less than 5% f all the AD pre-treated cmpstable prducts were detected in Windrw A. After 6 weeks Less than 5% f all the fresh cmpstable prducts were detected in Windrw B. Dry fermentatin shrtens the subsequent aerbic cmpsting by n less than tw weeks. 21