Pilot-scale AnSBR treatment of winery wastewater
Sigge, G O
University of Stellenbosch. Department of Food Science
Burger, A J
Objectives and Rationale
The aim of this study was to design a pilot-scale anaerobic sequencing batch reactor (AnSBR) to investigate the optimisation of operational parameters with regards to pH, mixing intervals and feed time.
Prediction models had to be developed to predict the optimal parameters for the treatment of winery wastewater. To accomplish this a central composite design was used to establish the operational parameters for the above mentioned parameters. The effect of these parameters was investigated to determine their influence on the AnSBR performance. Alkalinity, VFA, VFA:alkalinity ratio, pH polyphenol reduction, sodium absorption ratio, methane %, COD reduction, COD ultimate and TSS were monitored during this experiment. Another objective of the study was to be able to characterise winery effluent with regards to the COD using near infrared (NIR) spectroscopy. The AnSBR had to be able to treat winery effluent in the range of 0 – 10 000 mg.L-1COD and remain stable. Anaerobic granules were acclimatised during the early part of the wine season so as to withstand high COD load. The reactor had a working volume of around 200 L and roughly 100L was decanted every day. Once acclimatisation occurred the CCD was followed to determine the operational parameters. The following efficiency parameters were COD reduction, methane percentage, VFA:alkalinity ratio, polyphenol reduction percentage, TSS of reactor effluent and sodium absorption ratio.
Winery wastewater could be characterised with regards to COD at wavelength range of 2254 – 2278 nm. An RMSEP of 738 mg.L-1 was achieved which indicates that COD can be predicted to within 10% of error using NIR which is a rapid, non- destructive and a green method. A result like this shows its potential to screen winery wastewater or use it in-line in a reactor to monitor an important operational parameter. The results of the CCD indicate that the AnSBR was able to successfully treat winery effluent with COD values ranging from 0 – 10 000 mg.L-1 COD. Average COD reductions of 68.32 % were achieved along with a stable VFA:alkalinity of 0.23, average methane percentage of 61%, polyphenol reduction of 53.35% and average ultimate COD of 1 766 mg.L-1. The optimal conditions for the selected parameters was a pH within 6.7 – 7.3 with a pH of 7.3 being optimal. It was shown that a feeding time of approximately 180 minutes was optimal along with a mixing interval of 84 minutes (10s every 84 minutes).
Key Conclusion of Discussion
These results verify previous work done by Laing & Sigge on the earlier Winetech study on AnSBR technology at lab-scale, and it indicates similar optimal conditions for the treatment of winery effluent. The experiment could be done over another season or it could be upscaled to treat higher volumes in order to investigate its potential further. Recommendations for further design would be to have a properly sealed reactor, with no floating lid to maximise the gas capture. Mechanical mixing can be employed instead of a liquid recirculation in such a small system as the pump shears the bacteria reducing the reactor’s effectiveness.
Recommendation to Industry / Key take-home message
AnSBR technology shows potential to treat winery wastewater and lower COD levels to more manageable levels. NIR technology also shows potential to be used to monitor wastewater quality rapidly, which can be crucial in any wastewater treatment system. Industry should consider investigating a full-scale AnSBR at a small winery for further research and economic feasibility.