Treatment of fruit juice processing wastewater by chemical precipitation and recovery of phenolic substance from formed treatment sludge

In this study, recovery of total phenolic substances with Soxhlet extraction, (SE) ultrasound assisted extraction (UAS) and super critical CO2 (SC-CO2) extraction methods from chemical sludge obtained with chemical precipitation (FeCl3/PACS, Ca(OH)2/PACS, perlite/PACS, FeCl3/cationic polyelectrolyte) of lemon processing wastewater (LPW) was investigated. Effect of used coagulants/flocculants in chemical precipitation process on COD and total phenolic content (TPC) removal were also researched. Additionally, surface response method was used to determine optimum treatment conditions. According to ANOVA analysis, it was concluded that pH is a more important variable than coagulant/flocculant doses for all chemical precipitation experimental sets. The highest removal efficiencies for COD and TPC was obtained in FeCl3/PACS set (COD: 72.0%, TPC: 93.7%). Optimum dose values were determined as pH: 4, FeCl3: 3000 mg/L, PACS: 400 mg/L for FeCl3/PACS, pH: 6.5, Ca(OH)2: 1500 mg/L, 300 mg/L for Ca(OH)2/PACS, pH: 5.5, PACS: 7000 mg/L, perlite: 50 gr for perlite/PACS, pH: 4.5, FeCl3: 500 mg/L, polyelectrolyte: 4 mg/L for FeCl3/ polyelectrolyte. Additionally, obtained TPC removal efficiencies were determined as 55%, 35%, 57% and 58%, respectively. For the recovery of TPC from the precipitated chemical sludge, three different extraction methods (SE, UAS and SC-CO2) were used. Operating conditions were 4 hours with 95% ethanol for SE, 90 min with 95% ethanol and 35 kHz for UAE and 200 bar, 50 oC, 2 h, 95% ethanol for SC-CO2, and obtained maximum TPC concentrations under these working conditions were determined as 39.03 mg GAE/g, 8.81 mg GAE/g extract, 4.34 mg GAE/g extract, respectively. On the other hand, TPC recovery efficiencies (RTPC) for all chemical sludge were SE>UAS>SC-CO2. According to the results of this study, it was concluded that coagulation-flocculation process can be a useful pre-treatment process for the treatment of fruit juice processing industry wastewater.