Anaerobic digestion of dairy wastewater by side-stream membrane reactors: Comparison of feeding regime and its impact on sludge filterability

Abstract

Feeding regime is one of the important parameters to consider when operating an anaerobic digestion (AD) since it can dictate which reactor configuration to use and impacts the stability performance and sludge behavior over time. This study compared the impact of the feeding strategy (continuous vs 15-min feeding every 4 h) on the performance of a side-stream anaerobic membrane bioreactor (AnMBR) and changes in sludge characteristics. Two 17.0 L side-stream AnMBRs were operated at 37 °C, treating dairy wastewater at 1.0–5.0 gCOD/L⋅d organic loading rate, 40 d sludge retention time, and equipped with an ultra-filtration membrane for sludge retention. The continuously-fed AnMBR showed 30–50% higher accumulation of proteins and carbohydrates over time, leading to more viscous and thicker sludge with 1.5 times lower specific methanogenic and protease activity compared to the batch-fed AnMBR. However, the specific resistance to filtration was 5-folds higher in the batch-fed AnMBR. This was likely due to the higher fraction of smaller sized particles, with over 38% of the particles having a size of < 10μm. This study confirmed that the feeding strategy impacts the sludge characteristics and has a major influence on the design and configuration of reactors treating dairy wastewater.