Biological treatment is a promising alternative to conventional air-pollution control methods, but thus far biotreatment processes for odor control have always required much larger reactor volumes than chemical scrubbers. We converted an existing full-scale chemical scrubber to a biological trickling filter and showed that effective treatment of hydrogen sulfide (H₂S) in the converted scrubber was possible even at gas contact times as low as 1.6 s. That is 8–20 times shorter than previous biotrickling filtration reports and comparable to usual contact times in chemical scrubbers. Significant removal of reduced sulfur compounds, ammonia, and volatile organic compounds present in traces in the air was also observed. Continuous operation for >8 months showed stable performance and robust behavior for H₂S treatment, with pollutant-removal performance comparable to that achieved by using a chemical scrubber. Our study demonstrates that biotrickling filters can replace chemical scrubbers and be a safer, more economical technique for odor control.

There is actually a common consensus in using biological technologies for the treatment of organic wastes. For instance, composting is used for aerobic biological stabilisation of organic wastes. The amount of materials and the variety of wastes composted are increasing. However, composting is inherently a process generating gaseous emissions. Greenhouse gases (GHG) such as carbon dioxide, methane and nitrous oxide from compost are of special relevance for global warming. Although a part of these gases is inherent to the process, another important part can be abated by low-cost biological technologies such as biofiltration and its variations. This article reviews the emission of GHG from composting gases, from detection and measurement to minimisation and abatement. Special emphasis is given to the measurement of GHG to obtain reliable emission factors for the different composting technologies. These factors will help to compare different waste treatment options based on overall analysis tools such as life cycle assessment. A specific chapter is related to carbon and nitrogen dynamics in the composting matrix, and their consequences on the production of carbon and nitrogen gases. Finally, we present a review of the best available practices to minimise the GHG emissions from composting and the final treatment of composting off-gases.