In the last decade, Sargassum spp. seaweed species have caused massive flooding on the Caribbean Sea coasts. These seaweed species have a high content of recalcitrant compounds, such as insoluble fibers and polyphenols, which generate low methane yields in anaerobic digestion (AD). This study investigated the effect of solid–liquid separation of Sargassum biomass on biodegradability and methane yield. A biochemical methane potential (BMP) test was conducted with both fractions and raw biomass (RB). A mass balance was developed to assess the distribution of the components. The obtained liquid fraction (LF) showed high biodegradability and a high methane production rate, and it generated a methane yield of 159.7 ± 7.1 N L kg VS⁻¹, a value that corresponds to approximately twice that achieved with RB and the solid fraction (SF). The component distribution analysis showed that about 90% of total solids (TS), volatile solids (VS), ash, carbon, and cellulose were retained in the SF. In conclusion, the LF had high biodegradability and methane yield. This suggests the potential for LFs of Sargassum biomass to be treated in large-scale high-load reactors; however, studies applied to SFs are needed because they retain a large amount of organic matter with low biodegradability.

The aim of this paper is to describe a study of the anaerobic digestion of industrial citrus solid waste (ISCW) in both batch and semi-continuous modes for the production of bioenergy without the elimination of D-limonene. The study was conducted at the pilot plant level in an anaerobic reactor with a working volume of 220 L under mesophilic conditions of 35 ± 2 °C. Cattle manure (CM) was used as the inoculum. Three batches were studied. The first batch had a CM/ISCW ratio of 90/10, and Batches 2 and 3 had CM/ISCW ratios of 80/20 and 70/30, respectively. In the semi-continuous mode an OLR of approximately 8 g total chemical oxygen demand (COD)/Ld (4.43 gVS/Ld) was used. The results showed that 49%, 44%, and 60% of volatile solids were removed in the batch mode, and 35% was removed in the semi-continuous mode. In the batch mode, 0.322, 0.382, and 0.316 LCH₄ were obtained at STP/gVS_removed. A total of 24.4 L/d (34% methane) was measured in the semi-continuous mode. Bioenergy potentials of 3.97, 5.66, and 8.79 kWh were obtained for the respective batches, and 0.09 kWh was calculated in the semi-continuous mode. The citrus industry could produce 37 GWh per season. A ton of processed oranges has a bioenergy potential of 162 kWh, which is equivalent to 49 kWh of available electricity ($3.90).

This article presents the application of a novel system for the treatment of fruit and vegetable waste (FVW) using the combination of treatment by the application of the liquid fraction to an anaerobic hydrolytic bioreactor and a constructed wetland. The batch-fed anaerobic bioreactor (AB) had an average organic loading rate of 44 g COD/L-d and a hydraulic residence time (HRT) of 24 h for the degradation of the liquid fraction of the FVW with an average COD removal of 55%. Subsequently, the constructed wetlands (CWs) were fed a subsurface vertical flow of the effluent from the AB by stepwise concentration increments from 1 to 12 g COD/L and a HRT = 72 h until the limit conditions of the operation were identified. For the tropical ornamental species of the CWs in red volcanic gravel (RVG) and RVG + polyethylene (PE) supports, the monoculture of Hippeastrum rutilum and Spathiphyllum wallisii presented removals of COD, Tot-P, and TKN of 90%, 80%, and 85%, respectively. The polycultures with both species exceeded 90% effectiveness. At the end of both processes, a concentration of ~0.5 g COD/L was achieved, confirming that the use of these technologies together constitutes an efficient system for the treatment of the liquid fraction of FVW.