Evaluation of Biogas Production through Anaerobic Digestion of Aquatic Macrophytes in a Brazilian Reservoir

Abstract

Aquatic macrophytes are important components of aquatic habitats. However, the overgrowth of aquatic plants can cause severe problems for the management of bodies of water. As a result, these plants must be removed and disposed of as waste. However, the usage of this biomass as a substrate in biogas plants would appear to be more beneficial. The present work deals with the anaerobic digestion (AD) of macrophytes species that cause inconvenience to power generation at hydroelectric plant in Minas Gerais - Brazil. The study examines the following macrophytes species; Salvinia molest Oxycarium cubense, Eichhornia crassipes, Pistia stratiotes and Brachiaria. The experiments were carried out as stainless steel reactor with temperature, agitation and pressure control. As pre-treatment of macrophytes was used heat treatment at 120°C and pressure of 1.6 atm. The maximum methane content was 60% during 40 days digestion time, for Brachiaria of higher lignin content. The result obtained, mainly with Brachiaria demonstrates the efficiency of pre-treatment for the lignocellulosic samples.

Biogas from aquatic plants: A bioenergetics incentive for constructed wetlands usage

“…The content of structural carbohydrates also indicates residues from macrophytes as an interesting raw material to produce biofuels [ 25 ]: cellulose 42–43%, lignin 7–17%, and hemicellulose 9–13% ( Table 1 ). Low levels of lignin are beneficial to AD because it resists breakdown by enzymatic hydrolysis, inhibits microbial access to other carbohydrates, and delays the production of biogas [ 16 , 28 ]. Water hyacinth and Egeria densa [ 47 ] contain the lowest level of lignin, possibly due to its small aerial part, which does not require support.…”

“…Biogas from cattail and water hyacinth contained CH 4 in levels of 56%, 46%, 43%, and 30% reported for the water lettuce, O. cubense, water hyacinth, and Salvinia, respectively [ 28 ].…”

“… Eichhornia crassipes Water hyacinth 751 ± 6 ∗ 7.5 ± 0.9 43.01 ± 0.1 12.3 ± 0.5 1.79 Our study. ∗ 12.12 21.63 25.94 1.16 [ 28 ] 700–850 23.3 38.1 30.2 3.15 (N org ) [ 26 ] 795 7.72 35.0 24.8 2.13 [ 25 ] 64.1 18.9 ∗ ∗ ∗ [ 16 ] Azolla microphylla Water fern 720 10.13 27.4 15.67 2.8 [ 25 ] Egeria densa – 800 6.33 39.54 7.81 ∗ [ 47 ] Lemna minor Water lentils 770 4.1 28.8 22.3 2.53 [ 25 ] …”

“…The literature mainly shows water hyacinth (Eicchornia crassipes) as a substrate, reporting up to 400 L biogas . kg −1 made of plant [ 16 , 18 , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] ]. [ 31 ] estimated that one ton of macrophyte and seaweed mixes could generate up to 3900 kWh.…”

“…Therefore, it is possible to use residual plant biomass from CW to produce biogas and biofertilizer, including CW in the context of the circular economy [ 25 , 26 , 28 , 32 ]. Residues of macrophytes can serve as a substrate for local methane production and this used in heating systems, for example, on a rural property or generate electricity.…”