BioCycle October 2009, Vol. 50, No. 10, p. 31
A waste audit at the San Diego Zoo identified key areas for increasing materials recovery and waste diversion.
Ellyn Hae and Deirdre Ballou

KNOWN primarily for facilitating endangered species reproduction, the San Diego Zoo in California is also a world famous leader in environmental conservation. The Zoo also extends its influence to the community in school assemblies and outreach programs by combining animal presentations with an environmental conservation message. With education central to its mission, the Zoo recognizes it is imperative to also lead by example.
To that end, the Zoo commissioned a waste audit by Recycling by Nature to independently evaluate the status of its materials recovery programs. The study showed that the Zoo’s existing recycling effort recovers nearly 74 percent of the total wastes generated, well above the California mandate of 50 percent. However, this includes construction and demolition (C&D) debris recovery. Without that concrete-heavy category, the recovery rate at the Zoo is 43 percent. The Zoo therefore wanted to identify the types and quantities of materials remaining in the waste stream, as well as assess options for recovery.
More than 3.5 million visitors come through the gates each year to see almost 5,000 animals living in buildings and grounds of every shape and function. The Zoo has 1,600 employees in numerous departments, including Food Services, Animal Care, Horticulture, Building and Grounds, and Operations. The first step of the audit was to define the current system with site inspections and interviews with key personnel.
Materials recovered for recycling consist of mixed paper, beverage containers, wood pallets, metals, food, green materials and a significant amount of manure (Table 1). These programs save the Zoo more than $79,000/year in avoided disposal costs. The primary workforces used for material recovery are the Building and Grounds (B&G) and Horticultural staff.
“Walking the talk” in 2008, the Food Services Department switched out polystyrene foodservice ware at all concessions and restaurants for compostable plates, bowls, cups and utensils made from corn and potato starch. The change occurred primarily in response to staff and patron requests to include environmentally sound service ware at the Zoo. At the outset of the purchasing change, a small portion of the compostable products were added to the composting program, but staff found that it was too hard to handle because the system is designed for green material. Drink tops and straws were eliminated long ago as they are hazardous to animals, although single-serve ketchup and mustard packages are still used.

WASTE AND RECYCLING COLLECTION
Eighty-two percent of the Zoo’s wastes are collected in 3-cy front-loading compactors, standard 3- and 4-cy bins, and a 40-cy roll-off for hard-to-handle materials. Two additional 40-cy bins were used to capture landscape trimmings and hard-to-handle organics such as bamboo, ivy and succulents. The first Recycling by Nature recommendation was to combine the separate organics bins into one and direct it to the Sycamore Landfill, which maintains equipment to process the harder to handle organics for alternative daily cover. This would reduce the cost by $25/ton and save the Zoo more than $4,000/year.
The walk-through portion of the audit revealed that configuration of containers was not as efficient as possible. Front-loading compactors were not being left in the compacted position, thereby not achieving maximum compaction. A training program was recommended, as well as the development of a compaction policy to reduce pulls and trips to the landfill. The estimated savings of these changes could be more than $11,000/year.
A document review showed that the average pull weight for the hard-to-handle materials roll-offs was 2.4 tons, whereas the standard pull weight for that sized container is 10 tons. Sampling of the bin found minimal oversized material. In fact, the materials in the bin mirrored those in the compactors, so a recommendation was made to purchase or lease a 30-cy compactor, and reserve use of the roll-off only for oversize material. Fewer pulls create a potential savings of $31,500/year.
Because the Zoo uses 3- and 4-cy bins, a significant portion of the waste disposed is commingled with waste from other businesses when collected by the waste hauler (Allied Waste Services). Therefore, the Zoo has no record of the total tonnage it disposes in its front-loading bins. To confirm the physical inspections of the frontloading bins, the audit also included crosscheck sampling at the landfill, coordinated with Allied Waste Services. For one week in May 2008, Allied emptied all frontloading bins and delivered the “Zoo only” material directly to the landfill for sampling. Therefore, the total amount of waste from the frontloading compactors was sampled and the total weight was identified. This procedure added a higher level of confidence to the observations made on site, as tonnage conversion factors were crosschecked by actual weights.
After the on-site and landfill inspection data were collected, the volumetric percentage composition information was converted separately into cubic yard equivalents. Then disposal pulls for each bin type were adjusted to reflect the actual tonnages hauled for the week sampled in May. Next the tonnages were extrapolated into a monthly total by bin type. Finally, annual volumes were extrapolated using park guest attendance as the varying factor, and cy/year generation estimates were converted into tonnages.

AUDIT FINDINGS FOR ORGANICS
The waste stream assessment sampling results presented in Table 2 indicate that the Zoo disposes of approximately 2,724 tons, or 41,759 cy annually (excluding C&D). When calculated in tons, organic materials were the largest percentage of the Zoo’s overall disposed waste stream at approximately 40 percent (1,070 tons), dominated by manure (28 percent), and food (11 percent). The manure was found in both the bagged and unbagged portions of the wastes disposed. Because dung and food is dense, the tonnage contribution is relatively large, while the corresponding cubic yard information shows manure and food at only 15 percent of the waste stream by volume. Both numbers are important, as one indicates the volume of space occupied in the waste bin and the other indicates the potential tonnage for recovery.
Further investigation determined that the manure was being disposed of for two reasons. Most importantly, the majority of the uncaptured manure is carnivorous, which is bagged and disposed to ensure there is no pathogen transfer. Also, approximately 100 tons of the uncaptured manure came from the Children’s Zoo petting paddock, which did not have a suitable manure pick up location.
It should be noted that the Zoo recycles more than 1,643 tons/year of manure using a low-tech, but highly effective collection system: it is shoveled by hand by Roger, an athletic 65-year-old who’s heard every joke about shoveling poop. He drives a 10-cubic yard truck around the Zoo, and shovels the herbivore manure over his shoulder into the truck. When full, the material is delivered to a composting facility near the Wild Animal Park. A pick up location for the Children’s Zoo is being planned.
Excess produce from Zoo concessions is collected from four of the seven mid-sized locations and composted in a vermicomposting program. This simple program consists of a 2-cy worm bin, with shredded paper from the administrative offices to absorb excess moisture. The program captures about 100 lbs/week, and the resulting compost is applied on site. The Zoo also maintains a home composting education area in the Children’s Zoo, with various home composting/vermicomposting bins for guests to view active composting. Coffee grounds from the Zoo espresso cart make up a significant portion of the feedstock used for the demonstration area. However, a lot of food remains in the waste stream (Table 2). Food is generated from the four restaurants, catering, seven mid-sized concessions and many more mobile kiosks.
All parties were surprised that more than 35 percent of wastes disposed were green materials (978 tons), since the Zoo collects, chips and composts its green materials on site. After discussion with staff, it was determined that three factors contributed to the high levels of disposed green materials. First, the hard to handle roll-off bin area doesn’t have a dedicated section to separate green. Second, any foliage that is removed from any primate or carnivorous animal enclosure is bagged and disposed. And last, staff were unsure of what could be composted and what couldn’t. Therefore, a staff training session with development of a written policy was recommended.
Walk-throughs and landfill sampling led to two further recommendations. Beverage containers consisting of plastic and aluminum comprised about 2.5 percent of the total wastes disposed by weight. This number is higher than most facilities. In fact, commercial wastes usually contain about 1 percent beverage containers by weight. The Zoo presently maintains bins for collection of glass, plastic and aluminum beverage containers. However, the waste audit showed that more than two million containers are discarded each year.
Therefore, it was recommended that the Zoo implement a policy of ensuring there is a recycling container next to every trash container. This gives visitors a choice of whether to dispose or recycle the container. Staff estimated that 130 containers would be needed to maintain a 1:1 ratio of recycling to trash containers. Additionally, recycling bin signage should be changed to read “bottles and cans,” as they are meant to receive only beverage container bottles and aluminum cans.

INCREASING DIVERSION
Finally, organics recycling opportunities need to be investigated to increase recycling and avoid additional disposal costs. Three options are presently being explored:
Option 1: Composting of all of the organics (including green materials, food waste, compostable serviceware, paper, manure and carnivore manure) would occur on site in a unique exhibit format. This would maximize recovery and cost reduction. It would consist of an in-vessel system combined with CO2 capture and a greenhouse. Grant funds would be solicited to develop interactive displays to educate visitors about the benefits of composting, capturing CO2, and its use to increase plant growth.
Option 2: An on-site, “behind the scenes,” in-vessel system for the above organics to maximize volume reduction, with curing off-site.
Option 3: Continue existing practices with additional capture of food waste, compostable paper, bagged carnivore manure and compostable products for delivery to the City of San Diego’s Miramar Composting Facility.
The audit revealed that almost 78 percent of the total wastes currently disposed (by weight) are compostable materials consisting of manure, landscape materials, paper, food and compostable products (excluding C&D). New programs can increase the Zoo’s recycling rate to more than 87 percent, and see return on investment (ROI) quickly. Whichever option is implemented, the San Diego Zoo is committed to leading the way in connecting people with wildlife and conservation.

Ellyn Hae is the owner of Recycling by Nature, an environmental consulting group. Deirdre Ballou is Conservation Education Specialist for the San Diego Zoo.