Solid Waste Management

Discards or solid wastes (non-wastewater) from human activities in Sonoma County can be classified into many categories. For purposes of this analysis, discards are discussed as

 Recycling has been shown to reduce the use of energy when compared to the production of materials using virgin feedstocks (with substantial savings for materials such as aluminum). As well, there are significant environmental benefits that accrue from returning organic material into the soil. Re-use also reduces energy use. These aspects of solid waste management are covered elsewhere in this document This section focuses on the GHG reductions achieved by making productive use of the landfill gas (LFG) generated by Sonoma County’s Central Disposal Site.

LFG and energy production

The organic fraction of the waste discarded into landfills decomposes and generates LFG as a by-product of the process. Typical Central Disposal Site LFG contains about 55% methane (CH4) and 44% carbon dioxide (CO2) with the remainder composed of moisture and trace organic compouds. The methane component of LFG is referred to as biogas. There is no chemical difference between this biogas and the natural gas used in residences and business for heating and cooking, except its age. This biogas is (mostly) a product of recent biological activity, while natural gas was formed millions of years ago. For this reason biogas can be considered a renewable energy substitute for natural gas.

 Federal law requires that the LFG produced by landfills be controlled due to its explosion and pollution risks. The least expensive method to satisfy this requirement is to collect the gas in a system of pipes and collection wells inside the landfill and then burn the gas in a flare.

 There are several ways to capture the energy value of the biogas for beneficial use. The two most common are to (1) burn the LFG directly for heat in industrial applications, i.e., boilers or (2) use it as fuel in internal combustion engines to generate electricity. In these approaches, the LFG is minimally processed to remove moisture and any particulates, referred to as condensate.

 Another, less frequently used method is to further process the LFG to remove the moisture, most of the CO2 and other minor components of the LFG to produce “pipeline-quality” methane. This biogas can be used for any function that natural gas is used, including vehicle fuel.

Sonoma County LFG

 About 3,000 standard cubic feet per minute (scfm) of LFG is currently (2005) being generated from the Sonoma County disposal site.  LFG from the central landfill contains about 560 Btu/scfm, equivalent to nearly 17 therms/minute or 24,000 therms/day. As additional waste is deposited, the volume of gas generated also increases. Forecasts of future gas production indicate that at least an additional 1,000 scfm will be produced within 5 years, or 32,000 therms/day.

Currently, the LFG generated at the Central Landfill is collected and used as fuel for a 7.5-megawatt LFG-to-electricity power plant.  A pilot project is underway to install equipment to process some of this LFG to produce biogas that will be compressed and used as fuel for the County’s transit bus fleet.  By mid-2005, all of Sonoma County Transit’s heavy-duty bus fleet (46 vehicles) will be powered by compressed natural gas (CNG) using about 75 therms per bus per day or 3,450 therms/day for the entire fleet.

 Based on these calculations, within five years, the Central Landfill could produce enough energy to generate 7.5 MW of electricity, and 8,000 therms/day of biogas. Assuming ½ of the biogas production is used for the County bus fleet, an additional 4,000 therms/day is available for other uses, such as the garbage collection vehicle fleet.

 If the bus fleet were run on LFG instead of CNG, 20 tons/day (7300 tons/year) of GHGs would be avoided.

 If the power plant runs 24 hours/day, 365 days/year (8760 hours) at full power output (7.5 MW), 23,980 tons of GHGs would be displaced annually. The County operations currently use 22,369,365 kWh annually (2004) which accounts for 8164 tons of GHGs.

Recommendations

In 2003, the County approved the Countywide Integrated Waste Management Plan (CoIWMP). This plan should be fully implemented to continue to increase diversion rate of waste from landfill. Some of the features of the plan include:

• Construction and demolition debris recycling
• Expanded yard waste and organics collection
• Expanded floor sorting/drop-off recycling facility at the Central Landfill
• Build an anaerobic digester to convert the organic fraction of the waste that is concurrently landfilled to produce biogas

 In order to expand the existing organic waste collection system, each Sonoma County city work with its its refuse collection company to establish a collection services for segregated food wastes from commercial sources.

 The new food waste stream could be used along with other organics as feedstock for the anaerobic digester. This would increase the biogas production from Sonoma County waste products.

These recommendations are based on the assumption that the reduction of waste being landfilled will result in reduced greenhouse gas emissions, due to reduced landfilling and the subsequent emission of landfill gas and/or through reduced emissions associated with the manufacturing and transportation of products.

Modern solid waste management uses an hierarchy of approaches;

First - REDUCE the amount of waste created through efficient use of resources, more durable products, less packaging, buying less stuff, etc.

Second - REUSE products and packaging as much as possible, i.e., thrift stores, coffee mugs instead of single-use cups, reuseable produce crates/pallets, etc.

Third - RECYCLE discards, including products, packaging, and organics (through composting).

Finally, after doing all the above, landfill what's left, and then collect and use the landfill gas productively through energy production.

Specific local actions include:

Organics

• Reduce the volume of organics handled by the solid waste collection system through on-site/home composting
  • • this reduces the emissions associated with moving this material from the generator to the compost facility or disposal site as well as the emissions generated by production of synthetic fertilizers offset by use of organic soil amendments
    • encourage and support small scale on-site composting, i.e., business, schools, etc., to complement the regional composting program
• Use highly putrecible organic wastes, e.g. food discards, as an energy source (through anearobic digestion).

Products

• Support EPR (extended producer responsibility) legislation at local, state and federal levels
• Purchase locally manufactured products
  • Government agencies can use purchase preferences for items with recycled content and produced locally.
  • Educate residents and businesses on purchasing decisions - identify products with lower and higher carbon emissions
• Enact a local carbon tax on products with significant associated emissions

Packaging

• Eliminate through local ordinance the use of polystyrene takeout food containers
• Ban plastic bags
• Encourage or require reusable packaging
• Mandatory recycling systems for large waste generators

• Require multi-tenant commercial/residential building owners/managers to provide on-site access to recycling containers/service