by Michael Simpson Michael Simpson is a senior environ- mental scientist with the Tellus Institute of Boston.

Leaf and yard waste composting can produce economic benqfits for public and private users of waste- to-energy plants.

74 Resource Recycling September 1990

Integrating leaf and yard wastt composting with waste-to- energy facilities Since 65 to 70 percent of the waste stream is organic, it would seem obvious that composting should be an integral part of any recycling strategy. However, it is only relatively recently that composting has taken its place alongside multi-material, post-consumer waste recycling as a via- ble solid waste diversion tool. Composting is gaining prominente throughout the country because it is a cost-effective method for extending current disposal ca- pacity and reducing present and future environmental impacts. The result is sub- stantial savings to communities in their solid waste management costs.

For purposes here, composting is de- fined as a solid waste management technique in which the organic fraction of the waste stream is broken down, under controlled conditions, to a stable soil-like product that can be safely handled, stored and applied to the land. The controlled conditions of optima1 oxygen, moisture and temperature result in an efficient degradation while minimizing the potential for nuisance conditions and/or negative environmental impact.

Because the various organic fractions of the waste stream can be used in a com- posting process, a wide range of compost- ing techniques are possible, although the types of organic wastes targeted for com- posting will determine the technologies used.

Leaf and yard waste composting Solid waste composting and sludge com- posting systems are being used increas- ingly to manage solid wastes. Leaf and yard waste composting, however, has ex- panded at a much greater rate. This is particularly the case in states such as Massachusetts, Michigan, New Jersey and Pennsylvania. Of particular interest is the Commonwealth of Massachusetts, which has developed and implemented one of the few comprehensive state strategies in the country. In 1986, there were a few poorly run leaf piles, with even

fewer composting operations. In just f years, leaf and yard waste composi has become a viable solid waste mana ment option.

It is estimated that at least 2,000 n yard waste composting facilities will established in the U.S. within the next f years. Because of recent legislation in states and the District of Columbia b; ning disposal of leaves or all yard wast this estimate may fall short (see box).

In addition to states with existing lab Rhode Island is considering declari leaves as a “recyclable material,” whi under state law would effectively ban tl material from disposal within the sta Massachusetts is also in the process seriously considering a disposal ban the material.

There’s movement in the federal sectl too, as the U.S. Environmental Protectb Agency has stated that promoting tl management option of leaf and ya waste composting is a prior@ for its m nicipal solid waste program, more so th; municipal solid waste co-composting o tions.

Impact on waste-to-energy A journalist recently reported that tt “Cold War” between burning and rec cling is easing. He attributed this to tt ìnstitutionalization of an integrated al proach to solid waste management. Tt same may be said about leaf and yal waste composting.

One waste-to-energy facility operatc has put it simply: “1 put cold wet leave in the front end of my facility and get h( wet leaves out the back end.” This ma somewhat overstate the case, but it poinl to the very real possibility of increase emissions, increased ash generation, de creased burn efficiency and related in creased costs or loss of revenue from lea incineration.

In the final analysis, cost comparison! between composting leaves and bumi”! leaves will drive decisions about their uf

; .

timate disoosal. Those decisions will be made by public officials, as well as the private sector, based primarily on the avoided costs of disposal.

Of the numerous leaf and yard waste composting projects being operated in the same region as a refuse-to-energy facility, two have been investigated for a cost analysis - Temple Terrace, Florida and Pittsfield, Massachusetts.

Temple Terrace transports its waste to a field-erected, 1,200-ton-per-day refuse- to-energy facility. Pittsfield is the site of a modular co-generation, 240-ton-per-day burn facility. In both cases, the operators believe that there is an economic advan- tage by not burning leaves and yard wastes at the facility; however, the reasoning behind these positions is quite different.

Temple Terrace saves with composting Temple Terrace, Florida is a small bed- room community adjacent to Tampa. Waste is collected two times a week in packers and transponed ll miles to the Hillsborough County Resource Recovery Facility (HCRRF). A recent study during the wet season found that 45 to 50 percent

of the municipal waste stream was leaf and yard waste. During the dry season, this fraction drops to approximately 33 percent. In either case, the percentages are much higher than the 16 to 20 percent reported as national averages.

With this large fraction of yard wastes in the waste stream, Temple Terrace de- cided to investigate composting as a waste diversion strategy. This method had the potential of avoiding disposal fees and substantial transportation costs. Adding curbside collection of yard waste required a minimum of recapitalization on the city’s part. Each resident already re- ceived twice-a-week trash collection, so it was easy to designate one of the weekly pickups for the large volume of yard waste available. The major new cost for a sepa- rate yard waste collection program would be the public education campaign.

Based on initial studies of the per- centages of yard wastes in Temple Ter- race’s waste stream, it was estimated that 2,173 tons of yard waste would be gener- ated annually. The annual transportation costs saved by the City from not trucking the yard wastes to the burn facility would be $3,532 per year (see Table 1). Over the 20-year contract period with the

. . transportation costs transportation costs i i ‘atTempleTerrace(1) ‘atTempleTerrace(1)

1 > 1 >

HCRRF energy recovery plant Gas ,. $1,373 Labor 1.901 Operation 8 maintenance(2) 31089 Subtotal ,. $6,363 Composting -site GaS 337 ‘, Labor 950 Operation & maintenance 1.544 \,. Subtotal 2.831 Avoided transpotiation costs saved by compost site option $3,532

(1) Costs are based on shipment of 2.173 tcns of yard wastes “nual.ly.

(2) Truck casts only.

HCRRF, avoided transportation costs would save the city $70,640 in current dol- lars.

Temple Terrace’s yard waste stream is composed of a high percentage of green wastes, specifically grass. Also, vegeta- tion in this part of Florida appears to be

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76 Resource Recycling September 1990

composed of materials high in lignin and other complex cellulose compounds that resist rapid degradation. The limited site size at the proposed composting location was also a consideration in designing the composting system. These factors pointed to a pre-processing step to mix and size reduce the material thoroughly. A tub mill grinder is ideally suited for pre- processing the wastes.

Temple Terrace uses the “windrow- turn” composting method. A front-end loader aerates and mixes the material, with the schedule for turning the windrows ,- determined by monitoring interna1 pile temperatures. An estimated 327 staff hours per year were dedicated to turning

W Table 2 - Annual composting processing costs for Temple Terrace (1)

Pre-processing Front-end loader:

Gas $253 Labor

,Operations å maintenank 592 440

WHO tub grinder, operation 70 Subtotal $1,989.

Wndrow formation Front-end loader: \

Gas 138 ‘,. Labor ‘_ $81 ’ <; Operations & maintenance -- gfg Subtotat

.Assumes wllection costs for garbage and yard I

k$$f la based on 2,173 tons of yard wastes. C&

mmes a lO-year afnorti2ation. *mates ,,for administration, publii educatiin d public relations, and iah-atoty tests. L-

these piles. The annual cost for pre- processing and actively composting the 2,173 tons of yard wastes is $9,881, or $4.55 per ton (see Table 2). This figure does not reflect the temperature monitor- ing or recordkeeping activities required.

When the amortized costs for pur- chasing a piece of equipment for pre- processing are included, the annual cost for composting the 2,173 tons of yard wastes is projected to be $40,172 (see Table 3). The cost per ton wíll be between $18 and $19. It is assumed that the yard

waste COlleCtiOn Costs will not substan- tially add to the city's overall municipal solid waste costs.

COmpOSting the leaves and yard wastes provides a significant savings over delivering it to the energy recovery facility (see Table 4). A total of $86,357 is saved per year, or $39.74 per ton. When the city substitutes the compost produced for soil it purchases, additional savings can be realized. With the avoided cost of soil pur- chase ($43,476), the composting option shows an annual savings of $129,833.

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In a composting environment, the Sure Sak Lawn & Leaf Bag will degrade to tissue paper consistency in about three months and break down almost com- pletely within one year. Like all Ruffies trash bags, the Sure Sak compost bag degrades into an inert, non-toxic powder that contains no heavy metals.

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Recycling 77

September 1990

. . m Table4 - Net benefit from composting yard && overenergy recovery

in Temple Terrace (1)

Cost per ton Energy recovery transportation

cost and tip fee $126,529 ‘$58.23 Less annual cost of composting Annual savings for community

gg Jgl ./. .

(1) Cqst figures are based on 2,173 annual tons of yard wastes. -. ” .-

Projected over the 20-year life of the energy recovery facilíty, the savings would total $2.6 million.

Pittsfield sees benefits, too In the previous example, a composting option for leaf and yard wastes provided a significant benefit to the public sector. However, the private sector can also benefit from diverting leaves to a com- posting option.

In Pittsfield, Massachusetts, the mo- tivating forte to compost leaves carne from the operator of the waste-to-energy facility. Over the years, this operator had

seen a substantial increase in the amount of leaves comíng ínto the facílity. Thís ín- crease could be attributed both to popula- tion growth and urban expansíon in the region. Because of this influx, the autumn increase in total municipal solid waste ar- rivíng at the door began to strain the capa- bility of the facility.

Finally, it reached the poínt that material had to be díverted to a contíngency landfíll some distance away. The added cost for diverting waste to thís back-up landfill was borne by the waste-to-energy facility. In addition, the operator felt that the leaves tipped at the facility resulted ín a reduced

burn effíciency, whích had ramifications both for emission control and for ash gen- eration.

The Pittsfield facility is a modular burn facilíty with two 120-ton-per-day uníts. The plant is operated at approximately 110 tons per day per furnace, six days a week, producing steam that is piped to an adjacent paper mill. In 1988, the operator decided to diveri the leaves to a compost site adjacent to the facility’s primary ashfill. The leaves are collected ín plastic bags and delivered to the composting site. Debaggíng was performed by índíviduals who were paíd 10 cents per bag. In 1988, 700 tons of leaves ín 88,570 bags were delivered and debagged at the compost site. The resulting debagging costs were $8,857. In the first year, the annual com- posting cost was $13,039, or approxi- mately $18 to $19 per ton (see Table 5). The compost is used for final cover at the ash landfill.

However, the operator realízed a number of cost benefits to offset the ex- penses of composting. Any leaves cross- ing the típping scale were charged a dís- posal fee of $31 .15 per ton. This in itself would translate to an annual net íncome

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n i&le5 i Comfiostin~‘cost fi0; L-I .._ c leaves in Pittsfìeld,

1999 (1) clebagging 88,570 bags @ $O.lOktag .’ $8,857 Whdrow formation Front-end loader:

Gas $43 Labor ,. :., 105 Operation & maintenance 75

Subtotal Windrow-tuming Front-end loader:

Gas ,’ ‘Labor -’

’ Operations & maintenance !s!J Subtotal ” 1,788 m (2) 2.173 Total estimated operating costs $13,039 Cost per ton $18.63

(1) Cost figuras are for 700 tons of leaves generated annually.

(2) Moniforing, administrath, pubk r&afions, etc.

Another positive impact from compost- íng was the íncreased ability of the operator to maintain a steady feed rate to the furnace. When large quantíties of wet leaves enter the facility, the operator must reduce the feed rate of the waste into the burner to maintain the conditions needed for a complete burn. It was estimated that 3,000 to 6,000 pounds of steam produc- tion per hour were lost when large amounts of fall leaves went through the system.

In addition, the efficiency of burn has a direct effect on the control of stack emis- sions within acceptable levels. According to the operator, the dense wet leaves tend to sink in the burner, resulting ìn the fìre burning only on the top of the material. Periodìcally, the burners have to be “pumped out” to remove moist non- burnable material that could clog the grates and/or ash feed. This pump-out process normally occurs once a week dur- ing which time the burner is shut down. With the inclusion of leaves, this process had to be done once a day and took up

to the facílity of about $8,766 from divert- to two hours. ing the 700 tons of leaves to the compost- It is estimated that a two-hour downtime ing site. \ results in a loss of 20,000 pounds of steam

per hour, Or 40,000 pounds per day during leaf season. In addition, it was ascer- tained that the required pump-out process generates approximately one extra box (12 tons per box) of ash residue every two days, or three boxes per six-day week. Again, thís is an added cost to the facility.

Table 6 summarizes the added income gaíned from increased steam production as a result of the leaves being diverted to the composting site. The avoided costs associated with less ash generation and avoided soil purchases for final cover at the ashfill are also included. A net benefit of $61,966 is estimated for one year’s op- eration during leaf season. For a newly constructed modular energy recovery facìlity, with a life expectancy of 20 years, the operator could see a savings of more than $1.2 million.

Conclusion The estimates provided for these two examples are admittedly rough. In order for communities or private facilities to make the decision to divett leaves and yard wastes to a compostíng option, a more precise cost accounting may be

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79 Resource Recycling September 7990

W .Table6 .’ - Benefit of diverting leaves from energy recovpry to composting in Pittsfield (1) -

Income . ’ Tipping fee income

(700 tons @ $31 .l Siton) $21,805 Increased steam production, due to faster

throughput feed 21,000 Increased steam production, due to

decreased “pump out” frequentiy 7,000 Subtotal ’ _ $49,805 Avoided costs Reduced ash generation (2) 16,800 Avoided soil purchase 8.400 Subtotal 25,200 Total annual benefit - $75,005 Less total composting costs ($13.039 Total annual net benefit $61,966

(1) Cost is based on 700 tons of leaves per year. (2) Ash disposal estimates were based on the cost of disposal of the ash at the back-up ash

, disposal site for the facility.

necessary. Nevertheless, the economic of the waste stream to recycling and/or 8nd environmental benefits seem appar- composting options. ent; so much so that EPA has released EPA estimates that 10 percent of the draft regulations requiring all burn 25 percent will be leaves and yard wastes. facilities to meet a 25 percent div,ersion EPA’s reason for requiring 25 percent di-

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the waste disposal problem may diffuse P’ Ir tl- SI SI Yi

otential not-ih-my-back-yard ofposition. I many parts of the country, especially lose experiencing a disposal capacity iortfall, waste-to-energy will be a viable Yid waste management option. Leaf and 3rd waste composting can only make this qtion more palatable. RR

Stateqwith legislãte .w vard wate ba& -:<$f &3&j Connecticut Dístrict of

Columbia Florida

,

Effectiie MateriaIs date banned

1991 Leaves only .

1989 Yard wastes 1992 Yard wastes

Illinois 1990 Yard wastes Iowa 1991 Yard wastes Minnesota 1992(2) Yardwastes k? Missouri 1992 Yard wastes New Jersey 1988 . Leaves only North Carolina 1993 Yard wastes

1 1 1 Ohio 1993 Yard wastes :

III Pennsylvania 1990 Leaves pnfy! Wisconsin 1993 Yard waste$

(1) Yard wastes include leaves, grass, prun~ trae trimmings. y- ;::,,:\ 8

(2) Yard wastes are banned by 1990 from g fopolitan region of Minneapolis and St. F

Recycting September 1990

version is that removing this recoverable waste from a burn facility is the best avail- able control technology for ensuring re- duced emissions and ash generation. These new air emission regulatons are in line with EPA’s previously released Agenda forAction, which stated a national goal of recycling 25 percent of the waste stream.

The two examples indicate that the re- moval of this material not only makes en- vironmental sense, but economic sense as well. With EPA’s new regulations, a community or region will need to take an integrated approach to the waste stream before a burn facility is sited and built. In implementing recycling and composting with a waste-to-energy option, a facility either can be sized down or can take waste from a larger geographic region. This second option is important in those areas that are experiencing disposal ca- pacity shortfalls from landfill closures.

In either case, the overall risks and en- vironmental costs for society are reduced. In addition, if a waste-to-energy facility has a recycling and composting com- ponent, it may be a more acceptable op- tion for a host community to a burn facility. In other words, an integrated solution to