Investigating the performance of a novel Anaerobic Sequencing Batch Reactor (AnSBR) and optimisation of operational parameters to treat synthetic winery wastewater

Currently the South African agricultural sector withdraws approximately 70% of the freshwater resources, which is of great concern considering the forecast increase in water withdrawals due to the expected increase in required food production. The wine industry, in particular, produces large amounts of wastewater to produce 1 L of wine. This winery wastewater legally requires treatment before it can be disposed of into the environment or be sent to municipal treatment plants. Treatment is required for winery wastewater due to the high volumes of wastewater (seasonal production) and due to the winery wastewater’s chemical characteristics (high COD concentrations, high salinity and sodicity, high nutrient content, acidic pH and polyphenol concentrations) which are detrimental to the environment if discharged. Treated wastewater should rather be used for irrigation to partially relieve the strain on freshwater withdrawals by the agricultural industry. Re-using treated wastewater is an advantageous alternative to ensure freshwater sustainability. Research and development are still ongoing to develop more cost effective winery wastewater (WW) treatment options. Anaerobic digestion (AD) is a compatible and successful treatment option to treat this highly biodegradable winery wastewater. Only some AD processes have, however, been successfully applied in the wine industry. One specific process, the Anaerobic Sequencing Batch Reactor (AnSBR) is still under development, but has potential due to it’s kinetic advantage (alternating F:M ratios (food to microorganisms)), flexible mode of operation which is advantageous for varying wastewater production volumes (batch system (shorter feeding time) or fed-batch system (semi-continuous, longer feeding time) and due to it having good control systems, the effluent can be withdrawn from the process when it complies with legislation parameters. This process therefore requires optimisation at a laboratory scale as the limited number of operational parameters in literature vary greatly. Therefore, the main objective of this study was to investigate the feasibility of the AnSBR to specifically treat synthetic winery wastewater and to optimise the operational parameters that affect the efficiency of the process. The study was sub-divided into different Experimental Phases (A – D). The aim of Phase A and C was to investigate the feasibility of the novel AnSBR (14.7 L) to treat a synthetic winery wastewater substrate at COD’s ranging from 1 000 – 7 000 mg.L. At a COD of 4 000 mg.L (Phase A) a 88% COD reduction occurred, the alkalinity was approximately at 3 000 mgCaCO3.L, the total Volatile Fatty Acid (VFA) concentration at 125 mg.L and the pH was effectively controlled at ca. 7.2 by the 2 M KOH chemical dosing system. At a COD of 7 000 mg.L (Phase C) an 80% COD reduction occurred, the alkalinity was approximately at 3 000 mgCaCO.L3, the total VFA’s = 500 mg.L and the pH was effectively controlled at ca. 7.2. A central composite experimental design (CCD) was used to optimise three independent parameters at a fivelevel design at COD = 4 000 mg.L (Phase B) and COD = 7 000 mg.L (Phase D). The parameters investigated were: � = pH; � = feeding time (shorter feeding time (batch process) vs. longer feeding time (fed-batch process)) and � = mixing frequency (mixing set for 10 s every � min). The data was used to fit a regression coefficient model from which response surface methodology (RSM) plots Stellenbosch University https://scholar.sun.ac.za