HARD COD reduction – OZONE AND BAF
Combination of bio filtration with ozone have been found to be very effective , especially for the removal of organic content, natural Organic matters ,metals, and nutrients , such as , ammonia and phosphates. Use of bio filtration in combination with ozone (also known as Biologically Active Filtration) has been a proven technology for reduction of hard COD. The ozonation is supposed to breakdown the hard COD to simpler readily bio degradable compounds
Biologically Active Filtration: These are filters that contain Bio media. Media can be simple PVC/PP balls , combination of sand and anthracite and/or carbon media . The choice of the bio media will depend on the surface area required for the process. These are trickling filters ( slow speed) Biological treatment has been used in Europe to filter surface water for drinking purposes since the early 1900s and is now receiving more interest in India .Biological water treatment involves the use of naturally occurring micro-organisms in the surface water to improve water quality. Under optimum conditions, the organisms break down material in the water and thus improve water quality.
Hard COD from Effluents;
The bio degradability of each substance is dependent on the BOD/COD ratio. The lower the ratio, the less bio degradable the substance is . They are known as Hard COD. These Hard COD cannot be easily removed and requires combination of technologies for its removal. The essence is ozone breaks the Carbon to carbon double bonds that are most non bio degradable . This makes the following bio filtration step to easily eliminate the hard COD
Single stage ozone – bio filtration system can reduce COD up to 60 % and incorporating a second stage can reduce COD up to 80% COD .
Hard COD are often found in effluents of the paper and pulp industry , pharmaceutical industry and petrochemical industry
When do you consider Ozone-Bio filtration technique?
Using ozone for COD reduction is common. Ozone when used alone can be expected to reduce COD upto 30-35 % only . A combination of ozone with other technologies can improve this removal percentage as below
- Ozone alone – 30-35%
- Ozone and H2O2 – 60-70%
- Ozone and UV – 50-60%
- Ozone and single stage Bio filtration: – 60-65%
- Ozone with two stage Bio filtration: up to 85%
A good bio filtration system can also be designed to reduce BOD
So you can observe that you would chose the technology /combination depending on the extent to which you want the COD to be reduced . If your present system is efficiently removing COD then you can use ozone to polish and give you consistent results. If your present system is not capable of giving you the COD values you need, you need to consider combination technologies depending on the nature of the COD and the extent of COD reduction you need. Of course you need to work out the CAPEX and OPEX and see which is better for you.
It is also recommended that in all cases where the size of the project is large, it is always better to conduct laboratory trial first , then design a small pilot trial which would help you to upscale the requirement . Not doing so, means , you lose an opportunity to save large amounts of capital costs which otherwise may not be needed or you end up in process failures . There are no short cuts.
The use of ozone and BAF in drinking water treatment has various advantages and is used wherever water treatment authorities want to comply with the DBP rules
1) reduction in chlorine use and chlorine contact time – reduces operating costs
2) no formation of Hazardous by products
3) Increased TOC reduction ,
4) Process removes multiple contaminants together
5). With ozone media life is increased – hence operating costs reduced
6) disinfection by products such as Halo acetic acid and THMs are reduced