Anaerobic co-digestion of Baltic seaweeds with wheat straw and straw pellets: Synergetic effects on biomethane yield and kinetic biodegradability constant

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Abstract

Cladophora sp. and Ulva intestinalis are green macroalgae abundantly available in the Baltic Sea. Their low degradability could hamper the fully exploitation as resource for energy recovery through anaerobic digestion. For this reason, a co-digestion with lignocellulosic biomass represents a viable solution. This study aims to assess the potential effectiveness of the use of seaweed from Latvian nearshore co-digested with lignocellulosic biomass both in terms of increased BMP and kinetic constant of biodegradability. Specifically, biomethane potentials (BMP) in batch tests of 100 ml were assessed co-digesting Cladophora sp. and Ulva intestinalis from the Gulf of Riga with wheat straw and straw pellet from Brescia Region (Italy). The BMP tests were performed to evaluate the synergetic effect of co-digestion through a synergy index. A mechanical pre-treatment was also executed and its final effect assessed on the mono- and co-digestion experimental trials. The co-digestion ratio (seaweed/lignocellulosic biomass) used based on the volatile solids content was 1:1. The used ratio substrate-to-inoculum was 1:3 on total solid base. The inoculum use was sewage sludge was collected waste water treatment plant in the Riga district. Two different rounds of experiments with duration of 30 days were performed in order to have a more consistent analysis of results. Results for mono-digestion show the lowest BMP for Ulva intestinalis (277.7 ± 8.6 mL CH4/gVS) and the highest for the Cladophora sp. 523.3 ± 23.24 mL CH4/gVS. The straw pellet and wheat straw present values in a range of 395.6 ± 25.07 mL CH4/gVS and 470.4 ± 7.40 respectively. The effect of the co-digestion results in a slight increase of the synergy index (i.e. from 1.9% to 4.7%) but not for all the co-digestion trials. The higher effect was detected for co-digesting of finely treated straw pellet and Ulva intestinalis. The kinetic degradation constant improvements are evident for all the tested trials with the most evident effect for finely treated Ulva intestinalis in the mono-digestion conditions (i.e. 53.8%). The experiments show that the co-digestion with seaweeds and lignocellulosic can be beneficial.

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Romagnoli, F., Dorella, M., Gruduls, A., Collotta, M., & Tomasoni, G. (2019). Anaerobic co-digestion of Baltic seaweeds with wheat straw and straw pellets: Synergetic effects on biomethane yield and kinetic biodegradability constant. In Energy Procedia (Vol. 158, pp. 854–860). Elsevier Ltd. https://doi.org/10.1016/j.egypro.2019.01.221

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