(312a) Bioproducts from High-Strength Wastewater with the Carboxylate Platform Via Methane-Arrested Anaerobic Digestion

In circular economy, valorizing low- and negative-value waste streams into valuable products are essential to minimize waste and pollution, reduce dependency on fossil fuels, and combat climate change. With the growth of global economy, large quantities of high-strength wastewater (HSW) are discharged into the environment, resulting in severe problems. When treating HSW, traditional treatment processes are hindered by low treatment efficiency or high operation costs. Thus, a new cost-effective HSW treatment process needs to be developed to efficiently valorize HSW with low carbon footprint.

The carboxylate platform incorporating methane-arrested anaerobic digestion (MAAD) is a promising alternative to sustainably produce high-value bio-derived chemicals and fuels from waste streams. In this study, a novel process based on the carboxylate platform was developed to simultaneously treat HSW with bio-based carboxylic acid production.

This study firstly addresses technical issues with process development with a focus on MAAD. Specifically, a robust microbial consortium with high salt toxicity tolerance was selectively established and enriched to achieve high waste conversion and acid productivity. A blend stream of dairy and brewery wastewater with elevated chemical oxygen demand (COD) concentration (>70 g/L) was tested as the feed HSW. The effects of wastewater characteristics, microbial consortia structure, digester operation mode (batch and semi-continuous), and operating conditions (e.g., temperature, substrate concentration, and pH) on MAAD performance were investigated at bench scale (500-mL). The MAAD process was then scaled up and optimized at lab-scale digester (14-L), and the most stable condition of hydraulic residence time (HRT) 3 days, pH 6.0, and 40 °C was selected for further scale-up. Semi-continuous pilot-scale MAAD (100-gal) produced a total acid concentration of around 40 g/L with COD conversion greater than 70%. A new kinetic model was developed to predict the total acid productivity in semi-continuous MAADs. Different cost-effective separation methods (e.g., membrane, adsorption, electrodeionization) were evaluated to determine the most suitable approach to harvest carboxylic acids from MAAD broth. Further, this study compares different downstream technology approaches with the aid of techno-economic assessment (TEA). The results show that the newly developed process has the potential for large-scale application and is a successful example of the waste-to-energy technologies to transform low- or negative-value waste streams into high-value bioproducts.