Seafood processor in Manta Ecuador has a high strength wastewater with TSS as high as 20,000 mg/l, FOG 700 mg/l, COD of 13,000 mg/l and BOD of 6,000 mg/l. Wastewater is discharged into Pacific Ocean across the street from the factory. Current treatment plant produces effluent with TSS of 150 mg/l, FOG of 80 mg/l, COD of 800 mg/l and BOD of 400 mg/l on average. New laws require that seafood processing streams that are discharged to the Ocean have TSS below 100 mg/l, FOG below 50 mg/l or better, COD below 500 mg/l and BOD below 250 mg/l. Plant has a very limited space to further treat their effluents. An MBBR System was designed, installed and is currently operated to help meet regulatory requirements. This manuscript describes design and operation of the MBBR System.
Keywords: seafood processing wastewater, MBBR polishing, ocean discharge
Seafood manufacturing produces high strength wastewater with high amounts of TSS, FOG, COD, BOD, TKN and often high TDS. Wastewater is usually treated by DAF to remove TSS, FOG and some COD/BOD. However, in some areas where water is discharged into the lagoon or Ocean, particularly in towns that depend on tourism, stricter regulation require further treatment, often with bioreactors to remove dissolved COD, BOD and TKN.
Current wastewater process at this plant is quite impressive but had few weak areas. The existing wastewater treatment process starts with blood removal treatment and then proceeds to grit removal and screening. DAF with aluminum sulfate and anionic flocculant is used to flocculate and float TSS and FOG. After that water is aerated and clarified for foam removal of some proteins. The effluent is then treated with zeolite/sand/anthracite filters. After that water is treated with ozone and discharged to the Ocean.
Water has very high conductivity of 30,000 microS. Therefore anionic flocculant used is less efficient and after the DAF TSS are over 250 mg/l and FOG around 150 mg/l. We showed that if using a specialty anionic high conductivity flocculant A-190 K from KEMIRA (100% charge, sulfonate active groups) one can further reduce TSS below 100 mg/l, and FOG below 50 mg/l. Sludge can also be improved from 8% dry solids to 19% dry solids resulting in significant savings to the plant.
We also showed that if needed ozonization process can be enhanced by using ozone/hydrogen peroxide treatment. Up to 30% more BOD's can be removed that way. Finally, sometimes some blood appears in water after DAF. We showed that replacing aluminum with ferric sulfate as coagulant can improve on blood BOD removal, if it becomes necessary. Up to 15% more of BOD's can be removed that way.
Goals and Objectives
Design, test and implement polishing step that would bring the plant into compliance with the current regulations. Since final BOD can be 250 mg/l and available space is very limited we theorized that aerobic MBBR would be the best technology to bring the plant into compliance. At 50 GPM average flow, 75 GPM maximum flow, we had around 14 m - 12 m -7 m of available space to build MBBR, clarifier and sludge storage tanks. Many other companies suggested that it is impossible to build a polishing bioreactor within the available space.
The Pilot Study
MBBR laboratory pilot study showed that at available HRT we can indeed start with 400- 500 mg/l of BOD and up to 50 mg/l of FOG and produce effluent with less than 250 mg/l of BOD and less than 10 mg/l of FOG (future requirement) and less than 500 mg/l of COD. Tanks will have to be filled 60% by volume with the high density polyethylene MBBR media with surface area of 650 m2 /m3 . Pilot study showed that if needed we can combine microbes growing on media with some suspended microbes up to 1,500 mg/l of MLSS ('home made IFAS').