Waste Accumlation Odors

Source and Meaning of Odors 

The primary odor-causing compounds in lakes and bay waters, particularly those containing organic waste sediment, are produced by microorganisms decomposing organic matter under anaerobic (oxygen-free) conditions. 

These compounds include: Sulfur Compounds: Hydrogen Sulfide: Characterized by a rotten egg odor, it is generally produced by fish kills, the accumulation of bottom mud, and the reduction of sulfate in anaerobic environments. Volatile Organic Sulfur Compounds (VOSCs): These include thioethers and thiols. Thioethers: Such as dimethyl disulfide (DMTS), diethyl disulfide (DMTS), and diethyl disulfide. These are often associated with sewage/swamp odors. Thiols: Such as methyl mercaptan, dimethyl sulfide, and carbon disulfide. 

Nitrogenous Compounds: Ammonia: Formed from the breakdown of proteins and has a pungent odor. Indole: A compound associated with septic/swamp odors. Other Organic Compounds: Geosmin and 2-Methylisoborneol (2-MIB): These are metabolic products of planktonic and benthic organisms such as cyanobacteria (blue-green algae), actinomycetes, and fungi, particularly in eutrophic waters. These cause an earthy or musty odor. Aldehydes and monoaromatics (e.g., toluene) can be significant odor components in wastewater and sludge management areas. 

Basic Mechanism of Odor Formation: Rich organic matter (dead algae, plant debris, waste, etc.) accumulated on the lake or bay bottom is decomposed by microorganisms in the absence of sufficient oxygen (anaerobic conditions). This decomposition process, particularly the breakdown of organic matter containing sulfur and nitrogen, leads to the formation of the foul-smelling gases and compounds mentioned above, which have low odor thresholds. Bacteria that produce odor-causing compounds (such as hydrogen sulfide, methyl mercaptan, dimethyl sulfide, geosmin, etc.) by decomposing organic waste are active at different temperature ranges depending on their environment and specific species. 

The main bacterial groups involved in this process can be divided into three main categories based on their optimum activity temperatures: Psychrophiles (Cold-loving): Optimum Growth Temperature: 15{C}-20{C}. They can be active in cold lake and bay sediments, especially during the winter months or in deep waters. 

Mesophiles (Warm-loving): Optimum Growth Temperature: 20{C}-30C. This is the most common group in nature and aquatic ecosystems. They play a key role in organic matter degradation and odor formation, especially in lake and bay sediments near the surface, which warm up in summer, and in wastewater treatment plants. The proliferation of cyanobacteria and actinomycetes, which produce compounds that cause musty odors such as geosmin, is generally observed when water temperatures exceed 20°C. 

Thermophiles (Heat-loving): Optimum Growth Temperature: 45°C to 65°C. They are rare in the sediments of natural aquatic environments, but are active in hot springs or the thermophilic digesters of waste treatment plants. In summary, the most critical role in odor formation in lake and bay sediments is played by mesophilic bacteria, which are most active during periods of increased water temperature (summer months). The optimum temperature range for these bacteria is generally between 20°C and 40°C.