Designing full-scale biodigestion plants for the treatment of vinasse in sugarcane biorefineries: How phase separation and alkalinization impact biogas and electricity production costs?

Abstract

Anaerobic digestion (AD) is the most suitable approach for the management of vinasse in sugarcane distilleries because both environmental adequacy and bioenergy recovery could be achieved through biogas production. Because the literature lacks data on the implementation and operation of full-scale AD plants for enhanced energy recovery from vinasse, this study presents different designs for AD plants applied to vinasse in large-scale distilleries, considering both single-and two-phase schemes and different alkalizing strategies. Investment and operating costs and biogas and electricity production costs were obtained for each case. The results indicate that phase separation is economically feasible when scaling up AD plants in biorefineries. Despite the higher capital and operating costs in such schemes, the estimated biogas and electricity production costs reached equivalent or lower values compared with those of single-phase AD layouts, depending on the alkalizing strategy used. With respect to the alkalizing strategy, the best results were associated with sodium hydroxide dosing and/or effluent recirculation, with electricity costs reaching values 1.8-to 2.3-fold lower than grid electricity. In contrast, the competitive use of sodium bicarbonate in AD plants for treating vinasse requires further dosing optimization.

Hydraulic retention time on vinasse stabilisation with limestone in the acidogenic phase of anaerobic digestion

“…Despite the high cost of building one more reactor, this process yields more biogas, as reported by FERRAZ JÚNIOR et al (2016) who obtained 25.7% more biogas when comparing to biogas produced by a single-stage system. Lately, FUESS et al, (2017) confirmed previous results simulated for full-scale, and e results confirmed that phase separation is economically feasible when scaling up. In spite of the higher capital and operating costs in such schemes, the estimated biogas and electricity production costs reached equivalent or lower values compared to those of a single-phase.…”

“…Hence, with these characteristics, it is possible to confirm that the cost of the limestone used with a final price of U.S. $ 69m -3 is much lower than the costs reported by TORRES et al (2008) for hydrated lime (Ca (OH) 2 ), which was about U.S.$ 320m -3 . The calcium content reported in the present experiment reassure us about the observations of FUESS et al (2017), who reported that in addition to the economic aspects of dosing NaHCO 3 and NaOH as alkalizing agents for sugarcane vinasse, some environmental implications of the alkalinization process should be considered, in particular regarding to the role of sodium ions (Na + ) in soils ferti-irrigated with biodigested vinasse, because the Na + ions act as highly dispersive agents, when hydrated, by disrupting the stable aggregates of the soil, which may drastically reduce water infiltration due to clogging.…”

“…The equation y=0,0003x 2 +0.0386x+0.41 represents the VA/ TA variation with the high correlation coefficient (r 2 =0.97). Results showed that the acids formed were readily neutralized and did not influence pH and could be an answer to the difficulties reported by FUESS et al (2017) as limiting factor for the scale-up of the anaerobic digestion in the sugarcane mills. With the use of limestone, the pH and the VA/TA was maintained at appropriate values without the need for a disperser, since the neutralization is made during the formation of the acids.…”

“…Vinasse application as a fertilizer on sugarcane crops around the sugarcane mill or distillery is already sufficient to prove that it is not only a residue, but one product that presents some great applications, such as hydrogen and methane production in two-stage reactors (FU et al, 2017), the production of hydrogen or also the microbial biomass for animal feed supplementation (PIRES et al, 2016). FUESS et al (2017) considered that anaerobic digestion is the most suitable approach for the management of vinasse in sugarcane distilleries because both environmental adequacy and bioenergy recovery are achieved through biogas production. It must not be forgotten the environmental concerns associated with irrigation vinasse (FUESS & GARCIA, 2014).…”

Integração do biogás de vinhaça na matriz energética de Ribeirão Preto, Estado de São Paulo

“…Esse custo apresentado na Tabela 8-1 pode ser considerado conservador, pois é consideravelmente superior ao obtido por Fuess et al (2017) que chegou ao valor de R$ 0,13/Nm³ de biogás a partir dos custos de construção de um sistema de biodigestão. Apesar dessa vantagem, calculada com custos anualizados, devem ser estudados os indicadores de viabilidade econômica de cada cenário, cujos resultados são mostrados a seguir.…”