IIT Bombay Finds Partially Treated Wastewater Cleaning Itself With Pollutant Eating Bacteria
A recent study at the Indian Institute of Technology Bombay (IIT Bombay) finds an interesting observation of partially treated wastewater from refineries that carry bacteria that can remove the organic contaminants from it. The research was led by Prof. Suparna Mukherji, Department of Environmental Science and Engineering, IIT Bombay.
The researchers worked on biofilters, water filters that use microorganisms, like bacteria to remove pollutants. The researchers provided a substratum- in this case, a column of pure quartz sand – onto which the bacteria cling to get to work.
The researchers designed a biofilter made of an acrylic cylinder measuring 45 cm in length and 2 cm in diameter. They filled it with pure quartz sand to a depth of 15 cm. The filtration process begins by allowing secondary treated refinery wastewater, which has undergone the removal of toxic chemicals, to flow through the biofilter at a controlled rate of 1 to 10 mL per minute.
The wastewater flowing through the sand leads to the formation of a biofilm, made of several different types of bacteria enmeshed in extracellular polymeric substances secreted by the bacteria, on the grains of sand.
How it works?
As the water flows through the sand bed, bacteria present in the water/wastewater get adsorbed onto the sand. The attached bacteria replicate and secrete extracellular polymeric substances to form a biofilm on the surface of the sand grains. Bacteria grow using dissolved oxygen, organic carbon, and other nutrients from the water flowing through the sand bed
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This biofilm in turn eats away at the organic contaminants in the water. Degradation of organic compounds containing nitrogen releases inorganic nitrogen in the form of ammonium, which is further converted to nitrate. Although some removal of nitrate may have occurred, build-up of nitrate was observed after biofiltration.
What are the key findings?
The team analysed the Chemical Oxygen Demand (COD), Total Organic Carbon (TOC), and Assimilable Organic Carbon (AOC), which are measures of the various organic compounds in the water. Analysis of COD and TOC allows researchers to estimate the concentration of organic contaminants in the water. Remarkably, they observed a significant reduction in COD, TOC, and AOC after just two recirculations of the wastewater through the biofilter.
The team also used a technique called GCxGC TOF MS, which stands for Gas
chromatography Time of Flight Mass spectrometry, to detect and quantify specific organic compounds in the water.
“Recirculating the wastewater up to 12 times resulted in maximum reduction in COD and TOC of 62% and 55%, (by more than half) respectively. GCxGC TOFMS revealed that several of the identified target (harmful) compounds could not be detected in the wastewater after 12 recirculations, suggesting 100% removal”, the team lead said.
The nitrates produced by the bacteria during filtration, through conversion of other forms of nitrogen, caused a build-up of nitrates in the treated water which is undesirable. However, refineries commonly employ reverse osmosis (RO) as the final treatment step. This process can reduce the level of nitrates in the final effluent,” says Prof. Mukherji.
Biofiltration can also reduce the deposition and accumulation of unwanted material on the RO membranes by reducing AOC.
The study also delved into the biofilter’s microbial community. It turned out that the predominant bacteria belonged to a group called Proteobacteria. The group is known for their ability to break down complex organic compounds like polynuclear aromatic hydrocarbons (PAHs), which are harmful to living organisms. The Proteobacteria group includes helpful bacteria like Sphingomonadales, Burkholderiales, Rhodobacterales, and Rhodospirillales, all recognized for their role in cleaning up hazardous pollutants.
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Sand biofiltration method stands out for its simplicity, meaning it could be an accessible solution for many industrial plants worldwide. It could significantly reduce the environmental footprint of oil refineries. With pure quartz sand being easily available, the overall cost of building and maintaining such a biofilter at large scales remains very low, making the filtration economical.
Prof. Mukherji, said “We would like to explore this process further using other types of media and with different types of water/ wastewater”.
