An Assessment of Different Integration Strategies of Hydrothermal Carbonisation and Anaerobic Digestion of Water Hyacinth

Abstract

Water hyacinth (WH) is an invasive aquatic macrophyte that dominates freshwater bodies across the world. However, due to its rapid growth rate and wide-spread global presence, WH could offer great potential as a biomass feedstock, including for bioenergy generation. This study compares different integration strategies of hydrothermal carbonisation (HTC) and anaerobic digestion (AD) using WH, across a range of temperatures. These include (i) hydrochar combustion and process water digestion, (ii) hydrochar digestion, (iii) slurry digestion. HTC reactions were conducted at 150 °C, 200 °C, and 250 °C. Separation of hydrochars for combustion and process waters for digestion offers the most energetically-feasible valorisation route. However, hydrochars produced from WH display slagging and fouling tendencies; limiting their use in large-scale combustion. AD of WH slurry produced at 150 °C appears to be energetically-feasible and has the potential to also be a viable integration strategy between HTC and AD, using WH.

Characterisation of Congolese Aquatic Biomass and Their Potential as a Source of Bioenergy

“…The slagging and fouling behaviour of the biomass was determined according to predictive indices: the alkali index (AI), bed agglomeration index (BAI), acid-base ratio (Rb/a), slagging index (SI), fouling index (FI) and slag viscosity index (SVI); as described previously. Indices were calculated based on the inorganic oxide content of the biomass, determined via XRF analysis; further details on the calculations can be found here [10,25]. The interpretation of each index is described in Table 2.…”

“…E BMP values were expressed as (mL CH 4 gVS −1 ). More details on the methodology can be found here [10]. The headspaces of E BMP reactors were flushed with nitrogen before starting the test, to ensure anaerobic conditions.…”

“…For large-scale production purposes, algae can be cultivated in both freshwater and marine environments, in either open culture systems such as lakes, ponds or basin raceways; or in highly controlled closed culture systems called photobioreactors [5]. Focus has mainly been directed towards the use of microalgae species; however, macroalgae and other freshwater aquatic macrophytes have also received attention in recent years [9,10]. One such macroalgae is Ulva spp., including Ulva lactuca, which can be found throughout the marine environments of the Republic of Congo.…”

A Comprehensive Evaluation of the Existing Approaches for Controlling and Managing the Proliferation of Water Hyacinth (Eichhornia crassipes): Review

“…Another study indicated that the biochar obtained from WH pyrolysis could serve for heavy metal adsorption, and could be used for bioremediation application (Hasan et al, 2021). In addition, an integration strategy of hydrothermal carbonization (HTC) and anaerobic digestion (AD) using WH, showed that hydrochars and process waters from HTC process, could be valorized for a solid combustion fuel and biomethane production (Brown et al, 2020). Besides bioenergy, WH valorization showed its importance in the agricultural sector as well.…”

“…The first appearance of the species dates back to 1816 in Brazil. Subsequently, it was introduced as an ornamental plant to America at the end of the 1800s (Brown et al, 2020). Its appearance in Africa was in the early 1900s, and in Europe in the 1930s (Yan et al, 2016).…”