Case Analysis of Wastewater Treatment Project for Citrus (<i>Citrus aurantium</i> L.) Extract Production

The extract of citrus (<i>Citrus aurantium</i> L.) plays a significant role in medical and pharmaceutical applications due to its rich content of hesperidin, methyl hesperidin, and other compounds. However, wastewater generated from citrus extraction contains substances such as pectin, which readily encapsulate biochemical strains and inhibit their activity. This severely impairs the function of biochemical degradation processes, posing significant challenges in wastewater treatment. This project employs a “dissolved air flotation + iron-carbon fluidized bed” pretreatment process to remove pectin and enhance wastewater biodegradability, followed by a combined “upflow anaerobic sludge blanket (UASB) + anoxic-oxic (A/O)” biochemical unit to eliminate organic pollutants. Operational results indicated that the influent water quality for the project ranged from pH 4.5 to 6.5, with chemical oxygen demand (CODcr) ≤ 9800 mg/L, ammonia nitrogen ≤ 40 mg/L, suspended solids (SS) ≤ 2000 mg/L. The pretreatment process achieved a pectin removal rate exceeding 87%, significantly enhanced biodegradability, and stabilized the biochemical oxygen demand (BOD)/CODcr ratio at approximately 0.4. The final effluent quality achieved a pH range of 6 to 9, CODcr ≤ 500 mg/L, ammonia nitrogen ≤ 25 mg/L, SS ≤ 400 mg/L, consistently meeting the discharge standards specified in the “Integrated Wastewater Discharge Standard” (GB 8978-1996) for pipe discharge. This combined process offers stable and reliable effluent quality with simple and efficient management. It holds significant reference value and promising application prospects for wastewater treatment in industries such as plant extraction and fruit processing.