How Do Bacteria Clean Waste Water?

Bacteria play an integral part of the process of breaking down and processing wastewater. Bacteria have performed this function in nature for millennia, yet for all of our technology, modern septic tanks and municipal wastewater treatment plants rely on bacteria to do a lot of the work. Not every type of bacteria present in wastewater helps to break it down; certain types use the same method to achieve their goal.

History

• Bacteria are single-celled life forms that perform very specific functions. Both "good" and "bad" bacteria exist: Bacteria in your intestines help you to digest food, while bad bacteria sitting on your skin can into a cut and cause an infection. Beneficial and harmful bacteria exist in wastewater as well. Bacteria fall into two major categories: aerobic and anaerobic, as well as some that straddle both categories. Aerobic bacteria need oxygen to function, while anaerobic bacteria do not. Different wastewater treatment systems use both types. Varieties of Bacillus bacteria operate especially well in both types of systems and are not pathenogenic (toxic).

Aerobic Bacteria

• Aerobic bacteria operate in open systems that supply a readily available amount of oxygen. Examples of this include composting toilets, wetlands and wastewater holding ponds. These bacteria consume organic waste and oxygen, and they expel water and carbon dioxide as waste products. These bacteria play a vital part in ecosystems such as wetlands because they create the carbon dioxide needed for water plants to thrive and help maintain water levels depleted by evaporation. In wastewater plants, the water undergoes an involved filtering process before entering the holding ponds and receives chemical disinfecting before leaving the plant.

Anaerobic Bacteria

• Anaerobic bacteria operate in closed systems such as septic tanks. They consume organic waste and excrete methane and hydrogen sulfide gas, which are toxic, or septic. The wastewater enters the septic tank, where it sits as it separates into a scum layer, middle layer of "clean" water and a sludge layer. The bacteria work in the sludge layer, eating as much of the edible portions of the waste as possible. The inedible remnants are pumped periodically. The water in the middle layer remains full of harmful bacteria and viruses, so it still requires filtering. This water enters leach lines, a snaking trail of perforated pipes under the ground, where the soil filters the water as it percolates into the groundwater supply or evaporates into the air.

Potential

• Scientists constantly seek new ways to use bacteria to process wastewater more efficiently, allowing municipal systems to use less energy and produce no waste. The plants need to filter out any harmful chemicals, such as nitrates and perchlorate, as well as other toxins, using systems that use a lot of energy to operate and consume large amounts of water. In addition, the filtered waste requires disposal or incineration, since it remains toxic. These bacteria need hydrogen to process these chemicals and convert them into harmless forms---a difficult and, at times, impossible process. Researchers at Arizona State University have found a practical way to provide hydrogen through the use of a membrane.

Function

• The experimental membrane, called a membrane biofilm reactor (MBfR), contains fibers that pump out hydrogen for the use of the bacteria sitting on its surface. The end result is clean water and harmless end products such as nitrogen gas and chloride ions. This process occurs at room temperature with no heavy-duty pumping or filtering mechanisms; thus, it costs less than other systems.