8/7/2019 Compostable Plastics Trail at Municipal Operations
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T E S T I N G F O O D S E R V I C E P R O D U C T S
C O M P O S T A B l E S T R I A LA T M U N I C I P A L Y A R D T
R I M M I N G SO P E R A T I O NSTABLISHED in the mid-1980s,the
Miramar Greenery compostingfacility currently operates on 75acres
in the City of San Diego, Cal-ifornia. The facility annually
pro-cesses over 100,000 tons of organicmaterial. In the past
decade, the
city's Environmental Services Department(ESD) launched a food
scrap composting pro-gram to service large, local commercial
in-stitutions (e.g., public venues, stadiums) atthe Greenery.Source
separated food scraps are deliveredto the Greenery and unloaded
into a horse-shoe-shaped barrier of ground yard trim-mings. The
load is mixed with those trim-mings and placed into an open window.
After10weeks ofturning and watering, the mate-rial is screened into
half-inch compost, 2-inch mulch and 4-inch overs using aKomptech XL
star screen. The 11 regularparticipants in the food scrap program
con-tribute approximately 2,500 tons/year offood scraps.Each
generator receives extensive train-ing at their site and a 6-month
trial beforebeing accepted as a regular participant. Twoof the
existing participants are the SanDiego Earth Fair and the San Diego
CountyFair. Various other zero waste events in thecity are
accommodated as well.Unlike many composting facilities, theGreenery
does not preprocess, shred or grindfood scraps before incorporating
them into
windrows. The Greenery also does not acceptany incoming organic
material in bags,whether traditional plastic or compostable.Bags
inhibit the staffs ability to easily iden-tify contamination. These
two operationalvariables contribute to the structure of theentire
food scrap composting program.I N IT I A T I N G T H E T R IA LIn
anticipation of receiving more partici-
pants in the food composting program, theESD decided to initiate
a compostable prod-
28 BroCYCLE
Materials in the selectedproducts included plastic
(e.g.,PLA,starch-based polymersand blended resins), paper,paper
with linings, bagasse,wood and pressed leaves. Anitem number was
assigned toeach product.
C ity co nd uctss tudy todeterminewh eth er p ro du ctslabeled
ascom postableand/orb io degradab lewou ldsu ccessfu lly b rea
kdown in its openw indrowcom postingprocess .
Pa ig e Ha i le y
ucts trial. Many prospective participants epressed interest in
single-use compostablproducts; however, past feedback fromGreenery
operations staff indicated thathese products did not typically
breakdownthe city's composting process. The goal of thstudy was to
verify if compostable producdegrade in the Greenery's composting
prcess and also to identify tableware producthat would be accepted
in food scrap loads.The project began with market researc
and selection of 105 different compostablproducts to test.
Selection was based on sugestions from current and prospective
foscrap program participants as well as locavailability,
diversification ofuses, cost anan assortment of material
composition. M
AUGUST 20
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---------------------------- --- - - -,---terials in the
selected products includedplastic (such as polylactic acid (PLA),
starch-based polymers and blended resins), paper,paper with
linings, bagasse, wood andpressed leaves. The majority ofthe
productsselected meet American Society for Testingand Materials
(ASTM) standards (eitherASTM D6868 or ASTM D6400 standards
forbiodegradability and compostability), andmany have Biodegradable
Products Insti-tute (BPI) certification. However, some prod-ucts
that have not undergone ASTM evalua-tion were intentionally tested
as well. All ofthe products were bought off the shelf orthrough
websites in January 2010.An item number was assigned to eachproduct
and individual portfolios were cre-ated. Information in the
portfolio included
manufacturer identification number (UPCor SKU), brand and
manufacturer, material
or resin type, supplier, certifications andstandards met. The
portfolio also includedphotographs of each product, initial
mea-surements, and a detailed description.E X PE R IM E N T D E S I
G N A N D R E S U L T SMesh onion bags were used to contain
thesamples and compost feedstock - approxi-
mately 30 percent compostable/biodegradable products and 70
percent ac-tive compost (food scraps and yard trim-mings) by
volume. Each bag held three tofour samples of a given product with
an av-erage ofthree to five product types equalinga total of 15 to
20 items per bag.To expose materials to the most ideal com-posting
conditions, the bags were placed in
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the center of an active composting windrow.After the first week,
with temperatures hov-ering around 145F,!the bags were removedand
the windrow was aerated using a Scarabturner. The contents of the
bags were emp-tied, sifted through, and the samples
wereindividually evaluated for decomposition.The evaluation
included photographs, mea-surements and a detailed description
ofeachproduct. Particular attention was given to \any changes in
color, texture, size and frag- Imentation. After evaluation, the
bags werereconstituted using the same feedstock andplaced back in
the center of the windrow.The bags were removed from the windrowand
samples evaluated once every two weeks.over the 10 week study.,The
final time the bags were removed, allsample fragments were
collected and eachitem's final measurement was taken. Eachproduct
portfolio was analyzed and thenclassified into five categories of
degradationdepending on the percentage of decomposi-tion: 0 to 24
percent, 25 to 49 percent, 50 tot74 percent, 75 to 99 percent, and
100 per-cent. For example, if a product's remainingmeasurement was
greater than 80 percent ofthe original, then the product degraded
lessthan 75 percent and it was categorized as ao to 24 percent
biodegradation rate.
Tab le 1. B i o de g ra d a ti on r es u lt sP e rc en t o f T o
ta lDegradat ion (% ) N um ber o fProducts0-2425 -4950-7475
-99100
56138
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The results of the study are summarizedin Table 1. More than
half of the 105 prodtucts did not biodegrade greater than 25
per-Icent! Four products degraded between 25 to74 percent, three
products degraded be-tween 75 to 99 percent, and 37 of the
105products completely degraded.Further analysis of the data
determinedthe majority of the 37 products that corn-s
pletely biodegraded were made of PLA.lInfact, 26 ofthose were
comprised of pure PLA(i.e. PLA without the inclusion of any
addi-tives for desired plastic characteristics suchas strength,
malleability or heat resistance).On the other hand, all the other
materialtypes tested had very inconsistent results.For example,
seven bagasse products, from avariety of manufacturers, completely
de-graded; however, 20 other bagasse productsdid not. None of the
compostable cutlery1showed any real sign of degradation All
Mesh bags contained the samples andcompost feedstock. They were
lined up
numerically in the windrow.
