Phoenix Composting Facility Rises From Desert Floor

RESOURCE INNOVATION

Phoenix Composting Facility Rises From Desert Floor

An aerated mass bed system is used for composting yard trimmings, and eventually food waste. An elevating face turner moves material 22 feet laterally on the pad in each turning event.

THE City of Phoenix, Arizona opened its new $13.3 million Turned Aerated Pile (TAP) composting facility in April 2017. Conceived in 2014 under the initiative known as "Reimagine Phoenix," it was a result of the City's adopted solid waste diversion goal of 40 percent by 2020. The 27-acre facility is located adjacent to the 27th Avenue Transfer Station complex at the City's new Resource Innovation Campus. The composting facility is nearing the end of its commissioning, and is the first project to begin operating at the Resource Innovation Campus. Initially sized to process up to 55,000 tons/year, plans are to quickly expand to 110,000 tons/year. The site has the potential to scale to 220,000 tons/year as diversion programs grow.

New 55,000 tons/year facility currently processes yard trimmings, but is gradually incorporating commercial food waste.

Craig Coker

"We decided to include the composting facility in our new Resource Innovation Campus as we envision a robust hub for innovators building Phoenix's circular economy and generating economic development at the Campus," explains Stacy Hettmansperger, Operations Manager for the Phoenix Department of Public Works. "In addition to composting, a new palm fronds recycling-to-animal feed operation is opening with the City's partner, Palm Silage. The City is actively seeking to develop partnerships with businesses

to take additional items from the waste stream and create economic activity on the campus."

TECHNOLOGY AND FEEDSTOCKS

The TAP system, provided by Green Mountain Technologies (GMT), uses a mass bed design situated on an aerated concrete pad with computer controlled reversing positive/negative aeration. The facility utilizes a Vermeer CT1010 turner for turning the mass bed piles. Curing uses the same turned mass bed configuration but the concrete surface

October 2017BioCycle 17

Aeration piping is housed in a gravel bed below the concrete slab with nozzles flush with the slab surface. The aeration system can be run in all positive, all negative, or in a reversing positive-negative loop.

tion of yard trimmings was initiated; residents receive tan 90-gallon wheeled carts. No plastic bags or food waste are allowed in the carts. "Once the curbside green organics collection program is expanded beyond its current pilot area of the city, we will determine how to implement a residential food waste program that accounts for contamination concerns," notes Hettmansperger.

OPERATIONS AND MANAGEMENT

The City of Phoenix contracted with

WeCare Denali Organics (formerly

WeCare Organics) to operate the com-

posting facility. Incoming feedstocks

are handled in one of two ways. Self-

haul customers drop off brush and

Photos courtesy of the City of Phoenix yard trimmings in a designated drop-

off area, which can, and does, include

does not have aeration trenches. The than 4-feet long, and less than 24 inches material in plastic bags. These are

2.3 acres of active and curing pad con- in diameter. Trash must be separated hand sorted before going through

crete surface is capable of processing out and unloaded into designated areas. a Vermeer 6000 horizontal grinder.

the Phase I throughput of 55,000 tons/ The City collects MSW from resi- Larger loads of green waste, like those

year including biofilters, blowers and dential accounts, with the exception arriving under the Certified Organics

unloading and equipment turning areas. of Homeowner's Associations and mul- Program, are dropped in a designat-

"While we have land, we wanted to con- tifamily units. A pilot curbside collec- ed unloading zone near the Vermeer

serve space, so we opted for a com-

grinder, which has the capacity

posting approach that had minimal

to store seven 30-cubic yard (cy)

footprint, which led us to the GMT

loads. Food waste will be handled

system," notes Hettmansperger. While the initial commission-

What Is CMAR?

in the same way to prepare the materials prior to placement on

ing is based only on yard trim-

the aeration pad.

mings and landscaping residuals, the City has programs in place and is gradually receiving food

THE Construction Manager at Risk (CMAR) is a project delivery method that entails a commitment by the Construction Manager

Ground feedstocks are moved into the primary composting area where eight to ten-foot deep piles

waste. "We have been operating a (CM) to deliver the project within a Guaranteed are built with a front-end loader.

small pilot project at our 27th Ave Maximum Price (GMP) which is based on the "We designed the system with

Transfer Station since 2015, ini- construction documents and specifications eight aeration zones oriented on

tiated by the city sponsored zero at the time of the GMP plus any reasonably four pads," explains Michael Bry-

waste events in downtown Phoe- inferred items or tasks. The CMAR provides an-Brown, CEO of GMT. "High

nix for Super Bowl XLIX," says professional services and acts as a consultant aeration rate is provided at the be-

Hettmansperger. "For the pilot, we to the owner in the design development and ginning of the process, delivering

have been focusing on city spon- construction phases. Often times, the CMAR air at 5 cubic feet per minute/cy

sored special events and on back- also provides some of the actual construction (cfm/cy). Aeration then steps down

of-house food waste collection at of the project depending on the availability of to match the biological activity as

Phoenix Sky Harbor Internation- bidders and the expertise the company has. In it moves across the aeration pad,

al Airport, along with the Phoenix addition to acting in the owner's interest, the delivering air at 4 cfm/cy in Zones

Convention Center and material CMAR must manage and control construction 3 and 4, and at 3 cfm/cy in Zones 5

from private haulers. In August, costs to not exceed the GMP because con- and 6 while the compost meets the

these food waste sources slowly tractually, any costs exceeding the GMP that Process To Further Reduce Patho-

began to be incorporated into the are not change orders are the financial liability gens (PFRP) requirement and fi-

composting facility commission- of the CMAR.

nally to 2 cfm/cy in Zones 7 and

ing process."

Generally, the CMAR will give the Owner a 8 by the end of the aeration pad.

To increase organics diversion GMP prior to bidding the project. Included in

Air is delivered through 1,400

to achieve the 40 percent goal, the this GMP is a contingency line item to take self-cleaning air sparger nozzles

City offers a discounted tip fee to care of bid overages, reasonably inferred items in each pad. "During a turning

customers that deliver clean green and other project related items that may arise event, the operator opens all the

organics through the City's Cer- during construction. By giving the Owner the dampers of the positive aera-

tified Organics Program. Partici- GMP prior to bids, the CMAR assumes the risk tion system, which allows air to

pants receive the reduced tip fee of bids coming in higher as it is contractually blow at high pressure to allow the

if loads contain only presorted ap- bound to deliver the project per the plans and sparger nozzles to blow clear," he

proved green waste, unbagged, less specifications and any additional allowances adds. Piles are turned every three

as defined in his GMP.

18BioCycle

October 2017

to four days using a Vermeer CT1010 elevated face turner, moving everything 22 feet laterally on the pad in each turning event. Phase 1 aerated and turned composting lasts about 27 days, followed by 18 days in Phase 2 of just turning without air and 10 days in static pile curing for a 45-day total production cycle.

The aeration piping is housed in a gravel bed below the concrete slab with nozzles flush with the slab surface and clean-out ports spaced along the perimeter of the aeration pad. The aeration system can be run in all positive, all negative, or in an automatic reversing positive-negative loop, using the differential between upper and lower temperature sensors in each zone. If the temperature at the bottom of a pile is high, air pressure (positive aeration) is used. If the upper part of the pile is hotter, suction pressure (negative aeration) is used. Odor management in the initial two zones is provided by 6-inch thick "biocovers" made from compost, and by a 11,750 square foot (sf) standalone biofilter for processing air collected by the suction blowers.

"An interesting element about designing this facility was deciding what type of aeration is best during the heat

of a Phoenix summer day," notes BryanBrown. "We were concerned that delivering very hot ambient air to the biofilter while in suction would overheat the biofilter and we wanted to take advantage of the cool night air to cool down pile temperatures."

Water management is an important part of the design, given the high temperatures and arid conditions of the Phoenix area. Incoming yard trimmings only have a moisture content of about 30 percent. The site has a 50,000-gallon underground tank for the capture and storage of process water (a combination of condensate and captured rainfall runoff). The pressure blower is equipped with a misting ring using nonpotable well water to saturate the feed air with cool water, which drops process air temperatures from 122?F to 82?F. The negative aeration manifold drains to a concrete tank for condensate reuse below a Y-fitting between the blowers and the distribution piping. All the aeration supply piping is 18-inch or 24-inch diameter pipe. The Vermeer CT1010 turner is equipped with a 350 gallon/minute irrigation reel to remoisten material during turning events.

One unique aspect of operating a composting facility in a desert envi-

ronment is the need for a Dust Control Plan, which is stipulated in WeCare Denali's contract with the City of Phoenix. "Dust control is a very big issue here," explains Chris Seney, the contractor's operations manager. "We have had extensive training by City and [Maricopa] County staff on minimizing wheel track-out of dirt onto City streets." The contract requires WeCare Denali to comply with the City's air quality permit with Maricopa County Air Quality Department and to adhere to a maximum opacity of 20 percent at any time. All vehicles leaving the site must be tarped or covered. WeCare Denali is also required to have an Odor Control Plan that involves daily human and field olfactometer monitoring and immediate corrective action if a City-verified complaint is registered.

Seney, who formerly ran an 1,100 tons/day biosolids composting facility in Southern California, arrived in Phoenix in February 2017 after WeCare Denali won the contract. "I immediately had to hire 12 staff from scratch," he says. "We were able to find qualified people by focusing on the landscape supplies, aggregates, and mining industries." Seney has been doing extensive

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October 2017BioCycle 19

training of the new staff, augmented by ing a multiyear turfgrass study with develop a circular economy."

training from the various equipment the Departments of Public Works and The facility operations contract with

suppliers and from the staff at GMT. Parks and Recreation. It partnered with WeCare Denali Organics went into ef-

"Fortunately, my last composting facil- Arizona State University to design the fect in February 2017. It is a three-year

ity was in a hot, desert environment," structure of the study and conduct the contract with two optional two-year

he observes, "so I knew how to teach sampling and soil analysis. The Public renewal periods for a total potential

our staff my Heat Stress Plan and

contract value of $16.5 million.

safety training programs." The staff at the Phoenix facility be-

The City of Phoenix offers a

The contract requires WeCare Denali to handle a minimum of

gins work in the summer at 5:30 a.m. and stops operating equip-

discounted tip fee to customers that

2,500 tons/month of organics and has a 25 percent revenue-sharing

ment at 1:30 p.m. Material is accepted at the facility until 5:00

deliver clean green organics through

provision with the City on sales of compost and landscape products.

p.m. Monday through Friday and until 3:00 p.m. on Saturdays.

its Certified Organics Program.

In addition, the City gets 1,000 cy/year of compost for free, and a

COMPOST MARKETS

discounted rate on orders above Works Department has been providing 1,000 cy. For any loads above 5 percent

At the end of the 45-day production free compost from its pilot composting contamination by weight, WeCare De-

cycle, the compost is screened with a area to utilize at study plots within six nali can charge the City a higher per

Doppstadt SM 726 trommel that can do City parks and demonstration areas at ton processing fee to account for the

a 2-way split into compost, and overs. three downtown plazas. The purpose of additional resources required to sort

Residual film plastic and stones in the the study is to confirm the benefits of the material. Any loads delivered to

overs are removed with a Komptech compost on the turf compared to tradi- the composting facility above 10 per-

Hurrifex.

tional turf management practices. "Af- cent contamination by weight can be

Chris Seney is still working on the ter the first year of the study, we were rejected. Green organics contamina-

compost marketing plan, but expects really able to break down some of the tion is defined as "small animal waste,

to sell the products under the same institutional silos that existed between logs, painted or treated wood, large tree

brand names as other WeCare Denali our City departments," notes Hettmans- stumps and solid waste."

contract operations -- WeCare Com- perger. "The study has increased inter- The City of Phoenix originally solic-

post?, WeCare Engineered SoilsTM and est and awareness about compost across ited consultant proposals in June 2014

WeCare RoofmixTM. The City has been the City and how increasing green or- to design the facility. It elected to build

supporting the marketing by conduct- ganics diversion and use of compost can the project as a combination of design-

build and Construction Manager At

Risk (CMAR, see sidebar). "We teamed

with a local architect firm, which was

valuable, as the City wants work to go

to local firms," explains Bryan-Brown.

"The CMAR firm, Arrington Watkins

and construction firm Brycon Construc-

tion pulled this job off in five months.

They did the Value Engineering design

review in mid-October 2016 and had a

ribbon -cutting in mid-April 2017."

Cooperation between designers, tech-

nology providers, contractors, and City

departments is one common theme in

the successful three-year journey from

drawing board to start-up operations.

The 27th Avenue Compost Facility is

the first solid waste infrastructure proj-

ect in the United States, and the first

project in Arizona, to earn Envision

recognition from the Institute for Sus-

tainable Infrastructure. The Envision

system rates sustainable infrastruc-

ture across the full range of environ-

mental, social and economic impacts.

The facility has also been nominated

for an Arizona Forward Environmen-

tal Excellence Award in the category of

Public Sector Site Development. This

is an important award that has been

considered the "Academy Awards" for

Arizona sustainability.

m

Craig Coker is a Senior Editor at BioCycle and CEO of Coker Composting and Consulting () near Roanoke VA. He can be reached at ccoker@.

20BioCycle

October 2017

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