How do Bacteria lower COD and BOD? | Basics in simple language

Have you ever wondered how bacteria reduce COD and BOD? Wonder no more. Here is a simplified sketch on the process. Bacteria, though smaller than few microns, are the main workforce inside the ETP. A healthy ETP system has a good dose of right bacteria in it to eat away pollutants. The key word here is “right bacteria. “ But what does one mean by “right bacteria”?  How do bacteria eat those pollutants? Do they have microscopic mouth and teeth to chew on chemicals? Let’s understand few basics of microbiology to answer this question.

First thing we ought to know is that bacteria are different than terrestrial animals. They do not have distinct body parts like mouth, eyes, ear, brain, heart nervous system etc. They are more like tiny bags full of biochemicals.  Chemicals move in and out of bacteria through small pores on the bacterial surface. Infact microbes are more than a mere porous bag of biochemicals. They are more like a chemical factory where more than 100’s of different chemical reactions are taking place simultaneously.

All these reactions are happening in the same vessel at ambient temperature and neutral pH. These reactions do not interfere with each other nor do they produce any byproducts! So what is this bacterial factory producing?  It’s producing parts to assemble a new complete factory out of itself. A biochemical factory that re-produces itself. Isn’t that exciting? And this is what all life forms do. This is what all biochemical reactions inside bacteria are geared to do. To enable an organism to make copies of itself and continue its species.

Biochemical reactions happening inside the bacteria can be divided in to two separate categories. Catabolic reactions and Anabolic reactions. Catabolic reactions lead to breakdown of complex chemical compounds in to smaller simpler components. Anabolic reactions lead to joining of these monomers to make complex compounds. These both happen inside the bacteria simultaneously. So why is a bacteria breaking down complex compounds and rebuilding them again? Confused?  Let’s consider an analogy to understand this. It’s like you have a huge godown in front of you and you want to break down that godown and build your office there instead. So you start with first breaking that godown to clear space. But while you do that you break it down neatly to take out intact bricks from the wall, separate glass-panes from the windows without breaking any, uproot tiles without breaking them and then store them neatly in stacks for reuse. You break down the godown and get all building blocks separated and then reuse those parts to build an entirely new building, the office. Those bricks in the office wall, those tiles on the floor are all the same but the building is different.  It’s because the design is different. The design is different because your engineer used the blueprint of an office design and not of a godown.

Bacteria grow in this way.  They take complex chemical compounds and break them in simpler smaller monomers that are then reused to build biological molecules (called macromolecules) for the bacterial growth. So do bacteria have a blueprint like we do to build a building? Yes, and that’s the DNA. It is the DNA that decides all the characters of the bacteria. Just like the blueprint decides the characteristics of the building.

Once the bacteria builds enough macromolecules to build a new microbe it then makes two copies of the DNA and then splits the cell into two parts each part receiving one copy of DNA and those newly made macromolecules. The cycle goes on forever doubling bacteria everytime.

As a result of this, chemicals in water are taken up by bacteria to be broken down and reassembled into bacterial components. These bacteria settle down as sludge leading to decrease in COD and BOD of the effluent. Pollutants are converted into bacterial biomass. The most critical step here is the breakage of the chemical compounds in to simpler ones.

Most of the bacteria are similar in their anabolic pathways but they differ in their catabolic pathways. Bacteria vary in their ability to break down different chemical compounds. Specific bacteria are better than others for breaking down specific type of compounds.  Hence, to get effective degradation one must consider applying a consortium of microbes capable of complete digestion rather than using a single bug system.