Often we lump all algae in lagoons, retention ponds and lakes as a "bad." it is important to know the difference between proper algae growth with benefits of providing needed oxygen and undesirable algae blooms along with "toxic" algae.
The oxygen producing photosynthetic organisms found in water consist of eukaryote algae and prokaryote blue-green algae (also known as cyanobacteria). The green algae are complex organisms that range from single cells to larger plant-like kelp. In general, the green algae is beneficial in that it removes ammonia nitrogen from the water and produces vital oxygen used by other life forms.
There are other forms of eukarytoic algae: brown, yellow, and red. While not as common in freshwater as green algae, some of the other eukaryotic algae cause problems such as red algae (rhodophyta) that during blooms causes toxic red-tide in marine environments.
Most of our "algae" problems come from the prokarytoic blue-green algae. These organisms also known as cyanobacteria are able to fix nitrogen from the atmosphere or use nitrogen found in fertilizer runoff. What promotes blooms in most water bodies is high phosphate entering the system as this is usually the limiting nutrient. The cyanobacteria form blue green mats that rise to the surface during daylight hours. During bloom events the cyanobacteria cause pH swings where photosynthesis creates high pH during daylight hours and due to respiration of carbon dioxide during dark hours a drop in pH at night. While the green algae can do the same pH swing, they are usually not as likely to bloom unless sufficient nitrogen is present in addition to phosphate to create excessive growth.
During summer months, cyanobacteria are often a nuisance due to their production of odors and bad tastes from MIB and Geosmin. When conditions promote a bloom, cyanobacteria can produce compounds that are toxic to neurons, cell membranes, and liver cells. As a group these toxins are termed - cyanotoxins. Recent research has revealed in addition to acute toxicity, cyanotoxins can lead to chronic problems including a link to ALS (Lou Gehrig's Disease).
Wastewater often exists under anaerobic conditions in collection systems and in large facultative/anaerobic ponds. When you have organics, bacteria, and an anaerobic/anoxic environment, you can produce both hydrogen sulfide and odorous organic compounds.
For hydrogen sulfide (H2S) production, you must have sulfate in the wastewater. When you combine sulfate and domestic sewage in an anaerobic reducing environment (normally an ORP < -200 mV) - you will give sulfur reducing bacteria an environment in which they thrive. These organisms convert oxidized sulfur species to S= and hydrogen sulfide. A very toxic and odorous compound, H2S is the focus of most odor control programs.
We often ignore the odors caused by volatile organic acids formed by other bacteria when they start decomposition of domestic sewage under anaerobic conditions. In this case various sugars, proteins, and fatty acids are converted into short chain organic acids. In an anaerobic digester with methanogenic bacteria, the short chain volatile fatty acids are converted into methane gas and carbon dioxide. However, normal collection systems and ponds do not support much methanogen activity as they are not "anaerobic enough" ~ reducing environment that is not sufficiently negative on a consistent basis. When the short chain volatile acids enter in zones of turbulence, aeration, or greater surface area, the volatile acids enter the atmosphere which the human nose detects at very low concentrations. Common wastewater organic acid and their associated odors are given below:
Last week was Labor Day and I thought about the organisms that are the "workers" in biological waste treatment. During operations we look at aeration, flows, chemical feeds, effluent residuals, and other parameters; but we rarely consider the "biology" in a biological treatment system.
The biological waste treatment unit is designed to optimize the environment where microbes convert wastes into new cells, carbon dioxide and water. Engineers often refer to Mixed Liquor Suspended Solids (MLSS) as "bugs". Rather than being a homogenous "bug", the MLSS contains a blend of live and dead bacteria, protozoa, particulates, biological polymers, and in "older" sludge we have metazoa ~ more complex organisms such as rotifers, tardigrades and bristle worms. The actual percentage of living bacteria in the floc is between 10 - 15% in most systems. The protoza work by consuming living and dead bacteria which actually helps remove particulates from the water and improves floc formation.
So next time you see biological waste treatment systems in operation, think about the billions of tiny microbes in each liter of water that do the work, 24 hours a day, 7 days a week.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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