Bioreactor landfills represent a new approach to landfill operations. Historically, efforts were focused on preventing any incursion of water into the compacted waste, while simultaneously collecting and removing any naturally occurring leachate. This dry storage concept meant that conditions for natural waste decomposition were absent and materials as compostable as newsprint could remain pristine and readable for 50 years or more. Conversely, in the bioreactor approach, moisture content of the waste is maintained by recirculation of leachate at a level that enhances biodegradation. With this reuse, the expense of leachate treatment is all but eliminated, while the faster pace of decomposition means there is a significant reduction in post-closure management and operational costs.
In an optimized bioreactor landfill, leachate is recirculated, typically alongside stormwater, wastewater, and even treatment plant sludges, to maintain a steady level of moisture throughout the landfill itself. While many landfills simply pump leachate through repeatedly, bioreactor landfills are carefully controlled to maintain a specific level of moisture when adding leachate and water into the landfill. This moisture accelerates decomposition and encourages biological forces to take hold. The moisture content, combined with aerobic microbial action, decomposes the waste. Landfill mass also decreases as biodegradable components are digested, creating space for up to 30% more garbage.
Bioreactor landfills come in three primary types, aerobic, anaerobic, or hybrid. In aerobic bioreactors, leachate is removed from a bottom sump, piped into storage, and then re-circulated into the landfill along with supplemental air that’s evenly distributed through a network of pipes. The resulting increased aerobic microbial action not only speeds up decomposition but can reduce the amount of dangerous byproducts like VOCs, toxic leachate and methane.
In an anaerobic bioreactor, leachate and water are mixed and recirculated, but without supplemental air. Biodegradation occurs without oxygen and anaerobic microbes produce methane gas much earlier and at a higher rate than traditional landfills. This model is generally preferred when the landfill is set up to capture methane and use it for onsite power needs or sold as a sustainable natural gas. When methane production is initiated early and sustained at a high rate through anaerobic action, the landfill may exhaust the decomposable waste and therefore cease producing methane and other landfill gasses early. In some cases, post-closure monitoring can be completed in as little as 10 years.
A hybrid bioreactor landfill accelerates decomposition by alternating between aerobic and anaerobic treatment of the waste. This rapid cycling quickly degrades organics while collecting and removing landfill gas.
There are interesting benefits to bioreactor landfills, and some of those benefits are likely to become more and more attractive to future landfill operators:
- Complete decomposition and biological stabilization can occur over a few years vs a few decades in traditional “dry tomb” landfills.
- Lower toxicity and lower mobility of waste processed through aerobic and anaerobic digestion.
- Reduced cost for leachate disposal
- Regained landfill space up to 30% due to increased density of digested biomass.
Reduced post-closure care, potentially from 40 years to fewer than 10.
