Valuing composting as an infrastructure investment
With the rising tide of cities embracing zero waste polices, organics diversion as a component of waste management infrastructure is taking the spotlight in regions around the globe. Valuing composting and other options can be challenging for decision-makers.
These infrastructure investments are usually long-term and capital-intensive. Sometimes, they require significant changes in systems and practices. Decision-making can be long, contentious, and emotionally charged.
The process isn’t easy — with good reason. Decision-makers may be asked to compare apples to oranges. Evaluation criteria may be old, flawed, or incomplete.
Living with an unwise decision costing millions of dollars can syphon revenues away from other projects for decades, cripple a community’s economic health, and stifle future development. When evaluating infrastructure options for long-term waste management, it pays to take the time to get it right.
Valuating composting for true sustainability
The organic fraction of the municipal solid waste (MSW) stream is derived from materials that came from plants and animals. Plants and animals are fed from and sustained by the soil. Therefore, organic wastes need to go back to the soil to replenish nutrients, microbial populations, and other elements necessary to soil health. This closes the recycling loop and makes soil replenishment a sustainable practice.
Since waste is considered a renewable resource, some management technologies may claim to be “sustainable” when they really are not – at least when talking organics. Any management strategy that does not return organics to the soil cannot be defined as a truly “sustainable” solution for biodegradable wastes.
There are four primary technologies used for organic waste management:
- Landfilling, with or without methane capture/utilization
- Thermal/incineration, with or without energy generation (WTE)
- Anaerobic digestion (AD)
AD produces a compostable waste stream. Landfilling and incineration do not. Therefore, landfilling and incineration, even when combined with energy generation, are not sustainable diversion choices for compostables. (An exception might be one WTE residual — biochar — but the jury is still out on toxicity of biochar derived from MSW.)
That’s not to suggest these technologies have no value for managing other types of waste. But they are the most wasteful options for organics, because failing to recycle biodegradable waste to replenish soil organic matter sets off a chain of impacts with cataclysmic potential:
- Without a regular infusion of organic matter, soil microbes can’t do their work. Soil becomes depleted and eventually dies.
- Soil texture is compromised and soil becomes compacted. Rain can’t percolate and root development is impeded.
- Dead dirt won’t hold water or nutrients, so irrigation systems are required to grow crops.
- Dead and dying soil requires heavy doses of synthetic chemicals to produce crops and turfgrass. Many of these inputs are made overseas from fossil fuels, depleting non-renewable resources in both manufacture and trans-oceanic shipping.
- Runoff from rain events and irrigation carry sediment, causing erosion upstream and siltation downstream.
- Expansive stormwater collection and treatment systems are needed to manage polluted runoff.
- Because more water is lost to runoff, less water is retained to maintain soil moisture and recharge aquifers, causing water shortages during dry periods.
Soil replenishment trumps energy generation
The U.S. EPA’s Waste Management Hierarchy offers guidance by ranking various options from most to least environmentally preferred. But there are multiple versions of waste pyramids floating around on the web. One may place composting above WTE, another will sit WTE on top of composting, while a third puts composting and WTE on the same level.
With this type of conflicting information, how are a community’s leaders to decide which option is best?
Energy derived from a renewable source like waste can be a good thing. But not when elements essential to human survival — food and water — are being offered up as sacrificial lambs to the energy gods.
Modern society relies so heavily on electricity and natural gas, it’s hard to remember that these utilities are a convenience, not a necessity. Humans managed to survive on this planet for eons without power companies.
But soil provides food and clean water, and both are needed to sustain life. While farmers can grow food without soil, the production of protein — whether sporting leaves, scales, shells, fins, wings or hooves — requires water. Even soil-less protein production requires water, as do grains, fruits, nuts, greens and other vegetables grown with or without soil.
It’s soil and its microorganisms that grab, trap, filter and clean water. To do that work, soil must offer those organisms nutrients, organic matter, and other elements of a welcoming environment.
Diminishing global water supply (in combination with population growth) is seen as the greatest threat to human existence. That should make recycling organic matter back to the soil an international priority.
People can (and do) live without electricity, natural gas and coal, but not without water. That’s why composting trumps energy generation when it comes to evaluating reuse and disposal strategies.
Composting, especially aerated systems, easily recycles the wet waste that causes problems for landfills and combustion technologies. While landfills have to deal with leachate and methane generated from decaying organics, incinerator-based disposal unnecessarily expends energy in an effort to set fire to high-moisture materials.
Although it makes up a significant portion of the MSW stream, at 5.2 million Btu/ton, food waste has the lowest Btu value of any constituent. When considering the typical WTE incinerator uses twice that amount of energy to burn the stuff when co-mingled with the entire MSW stream (about 5000-5500 Btu/pound or 10-11 million Btu/ton), combustion of high-moisture organics makes no sense.
Removing wet material like food waste from the stream would improve efficiencies of the entire WTE system. Unlike composting, which needs moisture to make the science work, wet materials and incineration are an oxymoronic pairing.
Remove organics from the municipal solid waste stream, and the energy required to burn the remainder drops. Landfills without organics wouldn’t need pricey gas capture systems, either. Fortunately, high-rate composting is a cost-competitive technology that can handle all organics ... sustainably.
And if the community is dazzled by the idea of making energy from garbage, composting is a bright star there, too. Though anaerobic digestion might be the more common non-combustion energy producer, composting with heat recovery also offers some attractive numbers.
Finding recent (bona fide) organic waste management research that compares all state-of-the-art, mainstream technologies within the same study is a challenge.
Private companies are not generally known to disclose financial information to outsiders, municipal operations aren’t always representative of the most economical or efficient examples, and some reports fail to draw a complete picture. (Begin reading at Section 3.1 of this study for a better understanding of the problems with many assessments and reports.)
Above all, when viewing consultant and engineering reports, insist on net revenue and net energy figures for all options. A responsible decision-maker can’t afford to be dazzled by an attractive output number that ignores the cost of required input, whether valuing composting or any other waste management technology.