Anaerobic Membrane Bioreactor (AnMBR) for the Treatment of Cheese Whey for the Potential Recovery of Water and Energy
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A single-stage Anaerobic Membrane Bioreactor (AnMBR) for the treatment of cheese whey and its co-digestion with cattle slurry was investigated with the aim of potentially recovering water and energy from the wastewater. A 9 L reactor coupled to an ultrafiltration flat sheet membrane module in an external configuration was employed. This configuration enabled the proper separation of solids from permeate. Cheese whey was stored at room temperature and its chemical oxygen demand (COD) varied between 51 and 80 g/L. The reactor was operated at an average hydraulic retention time (HRT) of 15 days and at an organic loading rate (OLR) of 1.2–8.4 kg COD/(m3·day). During operation a COD removal average of 91% ± 7% was achieved. The biogas production ranged from 0.2 to 0.9 m3 biogas/kg COD removed and its methane content was 51–73%. From these results, a potential energy recovery of 2.4 kWh/kg COD removed was calculated. Microbial community analysis showed that bacteria belonging to the orders Bacteroidales and Clostridiales became the most prevalent. The bioreactor was dominated by acetotrophic methanogenesis. The co-digestion of cheese whey with cow manure (3:1) did not decrease NaOH consumption for pH control. Water reuse for cleaning purposes is possible if permeate pH is maintained at 6. Prior to the scaling-up of the system, a pilot scale test would be necessary to optimise membrane performance. The use of AnMBR technology at a real scale would be appropriate since it is a compact technology which permits both energy and potential water recovery after permeate post-treatment, thus constituting a further step towards the establishment of a broader a circular economy approach.