Abstract
The hydrocarbon-based economy is moving at a large pace to a decarbonized sustainable bioeconomy based on biorefining all types of secondary carbohydrate-based raw materials. In this work, 50 g L−1 in COD of a mixture of food waste, brine and wastewater derived from a biodiesel production facility were used to produce organic acids, important building-blocks for a biobased industry. High salinity (12–18 g L−1), different reactors configuration operated in batch mode, and different initial pH were tested. In experiment I, a batch stirred reactor (BSR) at atmospheric pressure and a granular sludge bed column (GSBC) were tested with an initial pH of 5. In the end of the experiment, the acidification yield (ηa) was similar in both reactors (22–24%, w/w); nevertheless, lactic acid was in lower concentrations in BSR (6.3 g L−1 in COD), when compared to GSBC (8.0 g L−1 in COD), and valeric was the dominant acid, reaching 17.3% (w/w) in the BSR. In experiment II, the BSR and a pressurized batch stirred reactor (PBSR, operated at 6 bar) were tested with initial pH 7. The ηa and the VFA concentration were higher in the BSR (46%, 22.8 g L−1 in COD) than in the PBSR (41%, 20.3 g/L in COD), and longer chain acids were more predominant in BSR (24.4% butyric, 6.7% valeric, and 6.2% caproic acids) than in PBSR (23.2%, 6.2%, and 4.2%, respectively). The results show that initial pH of 7 allows achieving higher ηa, and the BSR presents the most suitable reactor among tested configurations to produce VFA from wastes/wastewaters with high salinity.
Highlights
Biogas is the primary product obtained in anaerobic digestion (AD) processes that present the double advantage of stabilizing biodegradable waste materials and producing renewable energy
In experiment I batch stirred reactor (BSR) and granular sludge bed column (GSBC) were tested with an initial pH of 5 and salinity of 12 g L−1
VFA concentration attained the maximum in BSR-5, while in the GSBC-5 VFA were much lower and almost constant over the experiment (Figure 2a,b)
Summary
Biogas is the primary product obtained in anaerobic digestion (AD) processes that present the double advantage of stabilizing biodegradable waste materials and producing renewable energy. AD processes are being explored to obtain other products, such as organic acids, that may be used as building-blocks for chemicals and biofuels, replacing the need for fossil fuel-based products. These present a higher market value when compared with the energy production from biogas [1]. Salinity and pH are two important operating variables that can drive the process, resulting in the interruption or continuation of steps, such as the accumulation of VFA or production of biogas [2]. Low pH inhibits the methanogenic activity [3], thereby favoring the accumulation of by-products of the initial stages of AD, including
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