Feasibility study on water reclamation from the sorting/grading operation in mandarin orange canning production

Abstract

The mandarin orange canning industry consumes a large quantity of fresh water, and discharges a similarly high volume of wastewater. If insufficiently treated, this effluent can seriously impact the environment. Water conservation and wastewater minimization can facilitate wastewater treatment. In this study, four filtration treatments were investigated to improve effluent quality from the sorting/grading operation at two mandarin canning factories for the purpose of water reclamation. The combined treatment consisting of a bag filter, activated carbon filter and precision filter yielded the best water quality improvement. The resulting elimination ratios for Chroma, turbidity, total sugars, pectin, and chemical oxygen demand were individually 27.64%, 55.56%, 22.55%, 21.35% and 42.22%. The treated water was clear and free of odor, and the pH was 6.7 ± 0.2. When the residual chlorine concentration was greater than 0.5 mg/L, the total bacterial count in the treated effluent was less than 10 CFU/mL and the coliform group was not detected. Further, the physicochemical and microbial parameters of the treated water conformed to the Chinese Standard of Drinking Water Quality except for chemical oxygen demand (38.60 ± 7.00 mg/L), which was mainly due to the saccharides in oranges. The results for the combined treatment of chlorination, bag filter and activated carbon filter at pilot scale indicated the feasibility of water reclamation during the sorting/grading step of full scale mandarin orange processing. At an average usage of 3500 t/d fresh water for a mandarin canning production line having a daily output of 100 metric tons, the water saving efficiency achieved with this combined treatment could reach 34.28%. A factory of this capacity can pay back the required investment for the treatment technology in the third production season, and will simultaneously save 373,840 Yuan. The cost-effective approach to water reclamation identified in this study minimized wastewater generation and facilitated clean production in a mandarin orange canning factory. The results indicate that a recycling process to enable water re-use can be implemented in food processing industries if it will not affect food safety. Such an approach to water management is beneficial to the coordinated and sustained development of economy, society, resources and environment.