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September 14, 2014
A Discussion from the Shrimp List
Laurent Queffelec (email@example.com): We are facing discussions with environment agencies concerning our shrimp packing plant. Houses have been built closer and closer to the plant each year, and there are complaints from residents about odors coming from the plant. The odor probably comes from the sodium metabisulfite in the wastewater and the associated microbial populations in the water treatment process.
I would be very interested in learning how other companies have managed this issue.
Dallas Weaver (firstname.lastname@example.org): Increasing the dissolved oxygen (DO) in the wastewater ponds will convert the bisulfite to sulphate, but you’ll have to watch the pH, which may get too low. Treat the wastewater pond like you would a shrimp pond: no heavy anaerobic sediments, high DOs, good mixing, pH in the 7s—and it won’t stink as much.
Larry Drazba (email@example.com): Laurant, I have had a lot of practical experience with this problem, and there is an easy solution. You are right, it’s not suspended solids that are causing the odor, it’s the sodium metabisulfite. I eliminated my oxidation lagoon and then filtered the residual waste with a drum filter, removed the oils and greases and injected ozone into the remaining water, which I sprayed on a tropical flower nursery, a process that got rid of a lot of the COD. Instead of odor problems we received environmental awards.
Dallas Weaver (firstname.lastname@example.org): Larry, good suggestion for very fast oxidation from a small treatment system. My approach, using natural oxidation with aeration, takes time and volume with a long residence time.
As residential development approaches processing plants, the land value increases making physically smaller treatment system more economically attractive. With cheap land, big aerobic lagoons look good.
Larry Drazba (email@example.com): Dallas, the oxidation lagoon works, but the amount of aeration has to be carefully calculated, and the weather has to be taken into account. We always had trouble when the skies were overcast and the oxidation lagoon went anoxic. Then the smell was very noticeable. My system eliminated the variability and/or need to over build the aeration system for cloudy days.
Dallas Weaver (firstname.lastname@example.org): I also like the much smaller footprint of your approach and the ability to automate the system with tight controls. Oxidation lagoons without odor have to be operated like aerobic shrimp ponds that can handle overcast days and algae crashes, while maintaining DO.
John Birkett (email@example.com): Laurent, by using a biological reactor in your water treatment plant with the required oxygen input and the right bacterial population to get rid of nitrogen, fats and carbon residuals, you should not have a mayor problem with organic residual odors, so something is wrong with your wastewater treatment plant. The metabisulfite residuals won’t prevent the plant from doing the treatment required, so check your O2 calculation and the activated bacteria in your reactors. If you are using only oxidation ponds, it will be very difficult to avoid foul smells.
Source: The Shrimp List (a mailing list for shrimp farmers). Subject: Wastewater Treatment. September 8–9, 2014.
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