Sticks And Stones Drive Diversion Home

William M. Merry and John C. Glaub

It was five down and 45 to go. The Monterey Regional Waste Management District was way behind the state's 50 percent diversion goals, and with the year 2000 breathing down its neck, it knew it needed to do something effective - and fast.

It wasn't like the community wasn't trying. Two private haulers already operated material recovery facilities (MRFs) for processing curbside recyclables and some commercial waste. Other recycling efforts helped, but, at the end of the day, this group of communities only diverted between 5 percent and 15 percent of their waste.

Its solution? Capture and reuse parts of two large streams: construction and demolition waste, and wood and yard debris. As a result, the District constructed a MRF at its integrated waste management complex in Marina, Calif., which it owns and operates.

The facility, which processes self-haul and roll-off truck wastes, was designed with a throughput of 400 tons per day, based on a single shift with a second shift potentially doubling capacity.

The MRF processes mixed waste (with the exception of wet garbage) and source-separated wood and yard waste. A total of 60 percent of the mixed wastes and 90 percent of the wood and yard wastes are targeted for recovery.

Design Features The MRF, which was completed in April 1996, is located between the scales and the landfill on approximately 10 acres. The building contains a tipping floor and processing room which includes the mixed waste sorting line, wood and yard waste processing area (with a dedicated tipping area), metals processing area, loading dock, bulk materials loadout area and employee/public education wing.

A full, floor-to-ceiling wall separates the tipping floor from the processing room to isolate dust and noise.

Public and commercial vehicles use separate entrances and exits as well as tipping areas. All waste unloading takes place on a level floor to increase safety, control dust and help salvage materials. Dust also is controlled by overhead water misting, ridge ventilators and natural ventilation.

In the main processing room, dust is controlled by enclosing and ventilating the sorting rooms.

Processing System The mixed waste line is located in the main tipping room, fed by conveyors extending into the main tipping floor, while the wood and yard waste line is under a canopy along an external wall. The wood and yard waste line is fed both from a dedicated external tipping area as well as from inside the building.

The mixed waste processing line includes a recessed, live floor conveyor, incline conveyor, pre-sorting room, finger screen, secondary sorting room, unders transfer conveyor, cross-belt magnetic separator and divertors at the ends of the sorting line and unders transfer conveyor for loading roll off boxes.

The wood and yard waste processing line includes a recessed live floor conveyor, incline conveyor, finger screen for pre-screening of fines, inspection, sorting and operator station, metal detector, hammermill grinder, head-pulley magnetic separator, two-stage trommel screen for segregating the material into three products, transfer conveyors for screened materials and radial stacking conveyors for storing the materials in stockpiles.

Floor Design Since floors in MRFs are subject to high wear, several hardened floor treatments were selected. An absorption topping manufactured by Kalman Floor Company, Houston, was used in the areas with the greatest wear - the waste unloading area of the main tipping floor, including the area in front of the feed conveyor to the mixed waste line and an area in front of the feed conveyor to the wood and yard waste line.

A hardened aggregate mix was used in the vehicle maneuvering areas of the main tipping floor, the processing room, the bunkers of the mixed waste line and the area under the wood and yard waste equipment. Asphalt paving was used in outdoor areas, such as the wood and yard waste tipping and storage area, the chips and fines stockpile areas, the metals processing area, and the metals storage area.

The district's 2.3 MW landfill gas-to-energy plant generates electricity for the MRF and other on-site facilities. The excess is sold to Pacific Gas and Electric Company.

Managing The Tipping Floor The tipping floor spans more than 50,000 square feet. The salvage operation recovers material on the floor which is loaded into a trailer for processing and resale. Materials such as wood, yardwaste or metal is pushed directly to stockpiles. Items such as mattresses and tires are placed in boxes either along the walls or outside.

Loaders made by Caterpillar, Peoria, Ill., push wood and metal to their areas, feed the live floor conveyor and load unacceptable material into boxes for landfilling.

Debris boxes are placed strategically on the tipping floor for wood, metal or other items. A Cat forklift with a rotating head is used primarily to move and empty boxes.

A Catepillar excavator is used to feed the mixed waste line, to reduce the material to pieces less than four feet long and to remove items such as wire, rope, sheet plastic, carpet, long metal and large concrete. The excavator also increases safety by replacing people working on the tipping floor.

Mixed Waste Processing Line The mixed waste sorting line includes 18 sorting stations. Two to six people work eight presort stations picking wood, metal, cardboard and inerts, and one to four people work the sorting stations after the screen, picking paper, wood, metal and containers. More sorters are added when conditions warrant or increased diversion is necessary.

The design allows for negative sorting of some material - particularly wood and cardboard - including loads of waste wood roofing shakes and some cardboard-rich loads.

A finger screen manufactured by Mill Power, Tualatin, Ore., removes two-inch minus material, primarily dirt, for use as landfill alternative daily cover.

The screen removes between 10 percent and 20 percent of the material. Not all waste streams will contain this high of a percentage of inert material, highlighting the importance of conducting a wastestream analysis prior to equipment selection.

The mixed waste line ends with a divertor to fill alternate debris boxes.

Wood And Yardwaste Line The wood and yardwaste processing line uses an electric powered hammermill manufactured by Peterson Pacific Corporation, Eugene, Ore. The unit uses a horizontal plunger to feed the material into the rotating hammers.

A hopper was constructed over the top to prevent flying debris.

The live floor conveyor feeds the wood line. A vibrating finger screen manufactured by Mill Power is used ahead of the wood hog to screen out the one- inch minus material.

About 20 tons per day (tpd) of fines are removed by the screen, representing 15 percent to 20 percent by weight of the material passing over the screen. This results in significantly improved hammer-tip life.

On the other hand, customers using the ground wood fines for mulch complain that there was too little "dirt" fraction.

Problems also resulted from material "spearing" into the screens, and of material floating on top of the screen, such as vines or pine branches. The screen's decline was modified to correct the problem.

A trommel is located downstream from the wood hog. Final uses for ground material include composting, mulch, colored wood chips and some hog fuel.

Workers rotate positions on the sorting line every two hours and may be reassigned to work on the tipping floor in salvaging or may be reassigned along the picking line.

The wood line is operated with a loader operator, a plant operator and, as required, a sorter. The sorters pick approximately 30 to 50 tons (60 percent diversion) of material each day.

A significant amount of hazardous and prohibited materials are detected in the wastestream, particularly on the tipping floor. Hazardous materials commonly are found by the sorters as well.

During the first year of operation, approximately 200 gallons per month (10 gallons per day) of hazardous and prohibited materials were recovered from both the tipping floor and the sorting line.

Flammable material that is not reusable is sent for recycling at a hazardous waste facility at a cost of $10 per gallon, which does not include the staff's time.

Workers are trained and then have periodic instruction on topics such as hazardous materials management and lockout and tag-out procedures.

Diverted Materials Some of the materials, such as direct-haul wood and yardwaste are source-separated, although the mixed waste sorting line is the heart of MRF diversion. Bulky, heavy and hard-to-handle materials are recovered on the tipping floor, such as large wood pieces and large appliances.

Other diverted material includes:

* metal (20 percent);

* C&A (14 percent); and

* wood waste (23 percent)

The district designed and constructed its MRF with room to increase its capacity to achieve the state's mandated 50 percent diversion rate. This includes modifications or additions to the sorting line.

Initial success with the MRF, however, has resulted in a nearly 25 percent diversion rate. Adding this to the materials processed at the privately owned facilities in the district and other community recycling efforts, and the total diversion rate is between 30 and 40 percent.

Controlling Costs Partnering was a key component in project cost control (see chart on page 32). A one-day partnering session was held following the contract award attended by all of the major contractors and the design team owner and members. A mission statement was signed by the members, which resulted in facility construction costs, with change orders, less than 3 percent above the original project budget.

The MRF expense budget is approximately $1 million per year, the majority being personnel costs and the remainder maintenance and operation costs. The debt service is approximately $500,000 per year.

With operating expenses at approximately $1.5 million per year, the cost to process an average ton of material on the mixed waste sorting line is about $25 to $30 per ton. The cost to divert an average ton of material, assuming roughly a 50 percent diversion rate from the sorting line, would amount to $50 to $60 per ton.

The largest percentage of materials, inerts, diverted under district programs have the smallest revenue potential. The MRF tipping floor accepts 150 to 200 tpd, or 45,000 to 60,000 tons per year (tpy) of mixed waste at $30 per ton, representing $1.35 million to $1.8 million in gross revenue from tipping fees.

Clean wood and yard waste comes into the site at a tipping fee of $15 per ton. Approximately 20,000 tpy of wood and yard waste are delivered to the site for processing, representing around $300,000 in revenues.

The ground wood product is sold in a developing market for between $3 and $5 per ton. The cost to operate the wood line including debt service, personnel and operations and maintenance costs, is about $370,000 per year, resulting in a processing cost of approximately $18 to $19 per ton.

Using district generated electrical power saves approximately $90,000 per year in MRF-related operational expenses.

The district also operates a "Last Chance Mercantile," where materials are salvaged from the wastestream. Items range from appliances and furniture to books, tools and construction materials. Annual revenues approach $150,000.

Financing To finance the facility, the Monterey Regional Waste Management Authority (a joint-powers authority comprising member district communities) issued $12.8 million in Integrated Waste Management Revenue Bonds. These funds also included construction of a resale building and a household hazardous waste facility in addition to the MRF.

The project was rated "A+/A-1" by Standard and Poors. The authority entered into a letter of credit agreement with the Dai-Ichi Kangyo Bank Ltd. for a twenty-year term with a variable interest rate.

Variable-rate financing may save the authority between $200,000 to $400,000 annually in interest, since the variable rate is two points below a fixed rate. During 1996, the variable interest rate was as low as 2.5 percent.

Where To Go From Here The district's MRF operations are the backbone - approximately two-thirds - of the community's diversion efforts which achieved slightly more than 30 percent. The district operations are capable of achieving the state's mandated diversion goal by adding more personnel - perhaps two shifts - and more equipment.

The staff is satisfied with the facility performance after one year, but express concern about the inevitable costs to this community and across the state to implement programs to achieve California's goal.

A more sensible approach for the state may be to implement reasonable and cost-effective programs tailored to each community to achieve a 30 percent to 50 percent diversion rate, keeping sight of 50 percent as a goal, but not striving to achieve that diversion rate at any cost.

William M. Merry is the district engineer for the Monterey Regional Waste Management District, Marina, Calif., and John C. Glaub is director of waste processing at Norcal Waste Systems Inc., San Francisco.

* Integrated Waste Management Complex: 479-acre landfill; drop-off recycling center, household hazardous waste, landfill gas-to-energy, reuse, administrative and maintenance facilities; concrete and asphalt recycling; composting

* Area Served: 853 square miles in western Monterey County, population of 170,000

* Total Under-Roof Area: 103,116 square feet (98,750-square-foot MRF + 4,366 square-foot employee/public education wing)

* Employees: 25 (18 laborer positions open, but normally only 6 to 12 positions are occupied currently. More can be added if the need for increased diversion arises. Laborer average wage: $6 per hour)

* MRF Equipment: Peterson Pacific Corp. wood hog hammermill; Bay-Con boxes/bins; Kalman Floor Company Inc. absorption topping; Mill Power Inc. vibrating conveyors and finger screens; Central Mfg. trommel; Krause Mfg. Inc. super structure and conveyors; Wel D Way Inc. troughing idler conveyors; Weigh-Tronix Inc. truck scales and monitors; Keith Mfg. Co. conveyors; Metal Detectors Inc. metal detector; Dings Co. Magnetic Group magnets; Caterpillar 924F loaders; Caterpillar DP-40 forklift.