(314c) Recovery of High-Value Chemicals from Organic Waste: Economic Potential and Logistical Issues

Hexanoic (C6) and caprylic Acid (C8) are chemicals of high value due to their versatility, high demand, and relatively high energy density [1]. Studies have shown that such chemicals can be recovered from different types of organic waste streams such as biomass waste, food waste, and municipal solid waste; but such studies have not evaluated economic effectiveness [1-4]. In this work, we present supply chain models to study the economic potential and logistical issues associated to the recovery of C6 and C8 from different kinds of organic waste. We conduct a case study using real data from the State of Wisconsin.

In our supply chain framework, we consider four different sources of organic waste (urban centers, wastewater treatment plants, large dairy farms, and landfills), three different types of waste products (cow manure, sludge residues from wastewater treatment, and food waste) and five different types of waste processing technologies. We assume that 2-4% of the chemical oxygen demand (COD) in the waste streams can be converted as C6 or C8 [5,6]. The constraints in the model involve product balances and conversion constraints, capacity constraints, and logical constraints associated to technology sizing and placement. The objective function is to maximize total profit which includes capital and transportation costs and revenue from the recovered product. We conduct the following studies: a) trade-off analysis of profit against total amount of treated waste in the state, b) effect of uncertainty on yield factors and on prices of waste, C6, and C8, c) effect of waste mixing, and d) comparison of profitability from C6/C8 against the popular biogas (C4) recovery alternative.

Preliminary results indicate that, under current market conditions, it is profitable to recover C6 and C8 from organic waste and that much higher mobility can be achieved compared to C4. The results can be refined by conducting experimental studies that resolve uncertainties in key yield factors and technology costs.

References:

[1] Angenent L T, Richter H, Buckel W, et al. Chain elongation with reactor microbiomes: open-culture biotechnology to produce biochemicals. Environmental science & technology, 2016, 50(6): 2796-2810.

[2] Grootscholten T I M, Strik D, Steinbusch K J J, et al. Two-stage medium chain fatty acid (MCFA) production from municipal solid waste and ethanol. Applied energy, 2014, 116: 223-229.

[3] Kucek L A, Xu J, Nguyen M, et al. Waste conversion into n-caprylate and n-caproate: resource recovery from wine lees using anaerobic reactor microbiomes and in-line extraction. Frontiers in Microbiology, 2016, 7.

[4] Grootscholten T I M, dal Borgo F K, Hamelers H V M, et al. Promoting chain elongation in mixed culture acidification reactors by addition of ethanol[J]. Biomass and Bioenergy, 2013, 48: 10-16.

[5] Neves L, Oliveira R, Alves M M. Co-digestion of cow manure, food waste and intermittent input of fat[J]. Bioresource Technology, 2009, 100(6): 1957-1962.

[6] Ge S, Usack J G, Spirito C M, et al. Long-term n-caproic acid production from yeast-fermentation beer in an anaerobic bioreactor with continuous product extraction[J]. Environmental science & technology, 2015, 49(13): 8012-8021.