Wastewater characterization and treatment at a blueberry and carrot processing plant

Carrot and blueberry processing wastewaters were tested to determine total suspended solids (TSS) and organics (COD and BOD5) levels before and after wastewater treatment. Wastewater treatment by filtration through 1/8″ and 1/16″ reels provided no significant reduction in either TSS, COD or BOD5. Blueberry wastewater was found to have TSS concentrations of 297 ± 85 mgL−1, BOD5 concentrations of 1013 ± 292 mgL−1, a maximum respiration rate of 10.3 mg(L h)−1 and COD concentrations of 1947 ± 388 mgL−1 before discharge. The final effluent of carrot processing wastewater had TSS concentrations of 3030 ± 2975 mgL−1, BOD5 concentrations of 2780 ± 1848 mgL−1, a maximum respiration rate of 65 mg(L h)−1 and COD concentrations of 6363 ± 2760 mgL−1. After acclimatization, extended respiration tests indicated a dramatic reduction in oxygen demand was possible in post-reel wastewater, with a 75% reduction in respiration rate over 150 h for blueberry wastewater and an 85% reduction in respiration rate over only 20 h for the more organically-rich carrot wastewater. Bench-scale treatments of preliminary settling, alum coagulation and sedimentation, and aeration were performed on the carrot processing wastewater. Preliminary settling and coagulation-sedimentation were highly effective for TSS removal, achieving 99% reduction in TSS as compared to raw wastewater, but were not effective for organics removal, however, aeration for eight hours with activated sludge achieved 73% removal of COD and 42% removal of BOD5, indicating that biological treatment was the most promising avenue for organics removal from carrot processing wastewater.