I am handling an ETP of food processing plant. The COD: BOD ratio is between 3 and 4, keeps varing. I use Caustic soda for neutralization and further process is anerobic digestion folowed by anerobic digestion. I want to expand the plant by addition of one aerobic or anaerobic plant. Main aim is to reduce COD values drastically not to get biogas. Untreated water COD is about 5000 mg/Ltr
Any recommendation ?
I think it's not a big deal that your COD/BOD ratio varies. One essential information that it provides is that biological treatments are suitable for the effluent you are treating. In general, given the strength of your wastewater, I would recommend sticking to anaerobic digestion, as it is cheaper than an aerobic system, requires a smaller plant footprint, and usually performs better on the treatment of medium to high strength wastewater. What type of anaerobic digestion reactor are you using? The choice of a good anaerobic bioreactor is essential for the outcome you are looking for. Also, pretreatment operations to improve the hydrolysis process could yield better results.
In your case, laggon and ponds may be suggested, less expensive and could longer reduce COD/BOD demand
Dear Mr.
Mourad Amara Thank you, but the ponds and laggon will need a lot of space/ footprints and hence not feasible
Dear Shrikant,
In general, I agree with Mahomet Njoya but the best treatment process will depend on the specific type of food wastewater and on its composition.
Apparently your existing process "anerobic digestion followed by anerobic digestion" (= 2 anaerobic digestion stages?) seems not effective as you plan to add a 3rd anaerobic or aerobic stage. Hence if the present 2 digestion stages are sufficiently sized, then a tailored upgrade might be most cost-effective instead of adding a 3rd stage.
I agree with @Bruno Peeters, that very important is the specific type of food wastewater. But other information is missing:
what is the treatment goal ?, what should be the final concentration of BOD and COD in treated wastewater ?, what is the efficiency of the existing process ?, are there really two anaerobic stages, there? and many more.
The general recommendation to you is to install the aerobic polishing step. Aerobic treatment is capable to eliminate rest concentrations of COD and BOD from anaerobic treatment at least partially.
Best regards
Vit
Shrikant Ligade , I think you have answered your own question if you don't want to produce biogas. Most of this has been covered already, aerobic can reduce a footprint but the operational costs can be higher and require temperature control. Also, a clarifier and WAS/RAS equipment are typically required. One thing that is not mentioned is that an aerobic operation will maintain a culture specific to your effluent. If you are looking for examples maybe look for literature that utilizes a similar type of feed composition/character outside of COD/BOD, these are just general references.
You might add this type of anaerobic plant if you want a higher COD reduction efficiency.
As it is well explained by other researchers that any treatment plant is designed on the input parameters of influent and the desired output parameters / results.
Operating cost of an aerobic plant is always higher than an anaerobic one.
Why you want to add a 03rd anaerobic / aerobic digester when you already have 02 anaerobic digesters? Instead you should focus on the treatment efficiency of these digesters and do any rectification (if required).
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