Characterization and treatment of wastewater from blue crab (Callinectes sapidus) processing facilities

The process wastewater from three blue crab processing plants in Virginia was characterized. Most of these effluent streams were highly concentrated. For example, the retort water from the cookers exhibited the following concentrations: BOD₅ = 14,000-29,000 mg/L, TSS = 650-6,200 mg/L, TKN-N = 2,500-4,000 mg/L, NH3-N = 70-160 mg/L and Total Phosphorus= 100-185 mg/L. One process effluent contained chloride concentrations exceeding 100,000 mg/L.

Analysis of production and effluent characterization data from two mechanized plants revealed that wastewater volumes and concentrations varied significantly between the two plants. Both plants exhibited highly variable daily and seasonal production.

Treatability studies were completed on the process wastewater because discharge limits exist for TSS, Oil and Grease and in some cases BODs and ammonia. Settling and filtration studies were performed on these effluents. The organics and nutrients in the wastes were highly soluble and limited reduction of COD (18-65% reduction), BOD₅ (9-49% reduction), TKN-N (9-62% reduction), and TP (10-66%) was achieved by filtration.

Acidification of the concentrated effluents caused some coagulation of the contents. Coagulation by pH adjustment was most effective between pH 3.0-4.0. TSS removals of 76- 93%, and BOD5 removals of 6-30% were achieved by pH adjustment, thereby showing promise as a pretreatment method.

Anaerobic biological treatment systems appear promising for the treatment of wastewater from blue crab processing plants (effluent BOD₅s ranged from 150-420 mg/L), especially for cooker effluent. However, there is concern that salt from the Harris Claw operation will decrease anaerobic treatment performance and that effluent NH3 and TSS levels will need to be further reduced to meet permit limits. Pretreatment of process wastewater by means of pH adjustment did not improve anaerobic treatability.