Elsevier

Ecological Engineering

Volume 36, Issue 10, October 2010, Pages 1459-1468
Ecological Engineering

Anaerobic digestion of harvested aquatic weeds: water hyacinth (Eichhornia crassipes), cabomba (Cabomba Caroliniana) and salvinia (Salvinia molesta)

https://doi.org/10.1016/j.ecoleng.2010.06.027Get rights and content

Abstract

The aim of this study was to explore the potential of three aquatic weeds, water hyacinth, cabomba, and salvinia, as substrates for anaerobic digestion. A set of four pilot-scale, batch digestions were undertaken to assess the yield and quality (% methane) of biogas from each plant species, and the rate of degradation. A set of 56 small-scale (100 mL) biological methane potential (BMP) tests were designed to test the repeatability of the digestions, and the impact of drying and nutrient addition.

The results of the pilot-scale digestions show that both water hyacinth and cabomba are readily degradable, yielding 267 L biogas kg−1 VS and 221 L biogas kg−1 VS, respectively, with methane content of approximately 50%. There is evidence that the cabomba fed reactor leaked midway through the digestion therefore the biogas yield is potentially higher than measured in this case. Salvinia proved to be less readily degradable with a yield of 155 L biogas kg−1 VS at a quality of 50% methane.

The BMPs showed that the variability was low for water hyacinth and cabomba but high for salvinia. They also showed that the addition of nutrient solution and manure did not significantly increase the biogas yields and that drying was detrimental to the anaerobic degradability of all three substrates.

Based on these results treatment of both water hyacinth and cabomba by anaerobic digestion can be recommended. Anaerobic digestion of Salvinia cannot be recommended due to the low biogas yields and high variability for this substrate.

Introduction

Water hyacinth (Eichhornia crassipes), cabomba (Cabomba Caroliniana) and salvinia (Salvinia molesta) are introduced pest plants which are found in problematic quantities in several South East Queensland (SEQ, Australia) waterways and storages. They are all level 2 declared pest plants according to Queensland legislation and they are a significant threat to biodiversity, habitat and water quality at infested sites. They are also responsible for a number of other impacts including increased evaporation rates, interference with recreational activities such as swimming and boating and increased mosquito breeding sites (Qld Dept Primary Industries, 2009).

At present there are several different management approaches including physical removal by harvesters (e.g. for Cabomba), biological control (e.g. for Salvinia using the Salvinia Weevil), and application of herbicides (used for all three species) (Qld Dept Primary Industries, 2009).

Aquatic weeds are a reservoir of both energy and nutrients. Harvesting and anaerobic digestion could allow for both the energy and nutrients to be captured in a controlled manner which would ensure their removal from the reservoir system and value-added reuse. In cases where weeds are being physically removed from water bodies anaerobic digestion presents a well developed and feasible alternative treatment process (Malik, 2007).

Anaerobic digestion is the term used to describe the microbially mediated degradation of biodegradable materials in the absence of oxygen. The carbon, which is converted to carbon dioxide during aerobic degradation, is released as a mixture of methane and carbon dioxide. This biogas is a desirable product of the digestion as it contains significant energy potential (approximately 50 MJ kg−1 for methane (Wan, 2004) or approximately 25 MJ kg−1 for biogas at 75% methane content (Dasappa, 2005)). Other products are a solid residue which has potential as a soil conditioner and is considerably decreased in volume in comparison to the feed stream resulting in lower landfilling costs (if digestate is disposed rather than reused as soil amendment), and a liquid residue which retains much of the nitrogen (N) and phosphorous (P) and so has potential as a nutrient source.

In addition to the production of biofuel there are several other advantages to harvesting of aquatic weeds. Removal of plant biomass from the waterways will lead to decreases in the organic carbon load to the anaerobic bottom waters and sediments of the reservoirs and therefore decrease the uncontrolled release of methane from the surface of the water storage (Dalal et al., 2008). Methane has 21 times the greenhouse impact of CO2 and so its release to the atmosphere is of concern. Organic carbon input is widely regarded to be one of the controlling factors on the in situ formation of methane in water storages (St Louis et al., 2000). Creation and capture of methane under controlled conditions during anaerobic digestion of harvested aquatic weed will lead to a decreased greenhouse gas release as the biogas is burned to harvest renewable energy and all off-gases are converted to carbon dioxide which has a net zero GHG potential since it is derived from plant matter (i.e. short-cycle carbon).

A considerable number of studies have been conducted to investigate anaerobic digestion of water hyacinth. Many studies have reported similar yields, in the range of 200–300 L biogas kg−1 VS and around 140–200 L methane kg−1 VS (Ferrer et al.; Anand et al., 1991, Moorhead and Nordstedt, 1993, Kumar, 2005) for reviews see Gunnarsson and Petersen (2007) and Malik (2007). However, some authors have reported very high yields from water hyacinth. For example, Vaidyanathan et al. (1985) reported a yield of 430 L methane kg−1 VS during batch digestions of water hyacinth while Chin and Goh reported a yield of 671 L biogas kg−1 VS (cited in Malik, 2007). In the case of Vaidyanathan et al. (1985), the authors were not able to achieve similar yields under semi-continous digestion conditions with the yield falling back into the range reported by other authors.

Shiralipour and Smith (1984) point out one possible reason for the difference in results by noting that the shoots of water hyacinth produce considerable more gas than the roots. Due to the heterogenous nature of plant biomass it is possible that digestions giving very high yields have been fed with a greater proportion of shoots than roots.

While the existing literature points out the promise of water hyacinth as a feedstock for anaerobic digestion, similar research into the potential of other aquatic weeds species, such as cabomba and salvinia, as feedstocks for digestions processes is relatively scarce.

The aim of this project is to investigate the potential to recover bioenergy from three of the main aquatic weeds affecting SEQ waterways and storages, by using these weeds as a feedstock for an anaerobic digestion process. Specifically, the experiments are designed to reveal the rate of degradation, the yield of biogas (per kg of weed) and the quality of the biogas (% methane) for each of the plant species studied. The impacts of drying the biomass and nutrient addition during the digestion process are also assessed.

Section snippets

Sample collection

During a single field trip on 26th March 2009, 30–40 kg (wet mass) of each of the three weeds to be tested were collected. Each weed was collected from a different lake in the Sunshine Coast region of Queensland, Australia. Water hyacinth was collected from Wappa Dam, Cabomba was collected from Lake McDonald and Salvinia was collected from Ewan Maddock Dam. Cattle manure, used as an external nutrient source and as a control substrate, was collected from a dairy farm adjacent to Wappa Dam. All

Biological methane potential tests (BMPs)

Along with the large scale digestions of the three substrates a series of 56 small scale (100 mL) biological methane potential tests were carried out to test the variability of the digestion method, the weed substrates and the impact of adding excess nutrients or conducting the digestion without manure.

Conclusions

In agreement with results from the literature, water hyacinth proved to be a promising substrate for anaerobic digestion with its digestion resulting in high biogas and methane yields (267 L kg−1 VS and 140 L kg−1 VS, respectively). The potential of cabomba as a substrate for anaerobic digestion is as high as that of water hyacinth with the BMP tests revealing a potential yield of 322 ± 21 L biogas kg−1 VS. This yield was not confirmed by the pilot-scale digestion because a leak from the reactor led to

Acknowledgement

This work was funded by the South East Queensland Water Corporation (Seqwater) under a collaborative research agreement with the University of Queensland, School of Engineering (grant RM number 2009000067).

Cathryn O'Sullivan's research interests centre on the interaction between engineering and microbiology in natural and engineered systems, particularly in the areas of nutrient cycling, sustainable waste management and biofuels. At the time that this work was completed she was a post-doctoral fellow with the BioMass BioEnergy group at the University of Queensland. Cathryn has since left UQ and is now based in the Plant Industry unit of the CSIRO in Perth, Australia. Her new projects investigate

References (37)

  • K.K. Moorhead et al.

    Batch anaerobic digestion of water hyacinth: effects of particle size, plant nitrogen content and inoculum volume

    Bioresource Technology

    (1993)
  • W.F. Owen et al.

    Bioassay for monitoring biochemical methane potential and anaerobic toxicity

    Water Research

    (1979)
  • A. Shiralipour et al.

    Conversion of biomass into methane gas

    Biomass

    (1984)
  • V. Singhal et al.

    Biogas production from water hyacinth and channel grass used for phytoremediation of industrial effluents

    Bioresource Technology

    (2003)
  • V.K. Verma et al.

    Biogas production from plant biomass used for phytoremediation of industrial wastes

    Bioresource Technology

    (2007)
  • S.A. Abbasi et al.

    Effect of temperature on biogas production from aquatic fern Salvinia

    Indian Journal of Technology

    (1991)
  • S.A. Abbasi et al.

    Use of aquatic weed Salvinia (Salvinia-Molesta, Mitchell) as full partial feed in commercial biogas digesters

    Indian Journal of Technology

    (1992)
  • APHA

    Standard Methods for the Examination of Water and Wastewater

    (1989)
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    Cathryn O'Sullivan's research interests centre on the interaction between engineering and microbiology in natural and engineered systems, particularly in the areas of nutrient cycling, sustainable waste management and biofuels. At the time that this work was completed she was a post-doctoral fellow with the BioMass BioEnergy group at the University of Queensland. Cathryn has since left UQ and is now based in the Plant Industry unit of the CSIRO in Perth, Australia. Her new projects investigate the interaction between soil microbes and plants with a focus on nutrient transformations at the soil–root interface.

    Beth Rounsefell is currently completing her PhD with the BioMass BioEnergy group. Her project investigates the co-treatment of blackwater and solid waste in a two-stage, anaerobic co-digestion system in terms of the operational efficiency and the achieved pathogen destruction of the reactor under a range of continuous and shock loadings. Alongside her research work she is employed by the Gold Coast City Council as a Special Projects Officer developing the 2020 Waste Management Strategy for the city. In this position she engages with government, industry and the community to investigate the feasibility of employing a range of state of the art waste management technologies within the Gold Coast region.

    Alistair Grinham is a research fellow with the Centre for Water Studies at The University of Queensland. The current research focus of this group is the development of robust hydrodynamic and eutrophication models of freshwater storages. The model development runs concurrently with and often determines data collection needs. The data requirements are wide ranging from metreological forcings to greenhouse gas flux.

    A/Prof. Bill Clarke is the Program Director of the Environmental Engineering undergraduate degree and Director of the BioMass BioEnergy Group (BmBe) at the University of Queensland. The BmBe conducts research on organic solid and liquid waste degradation processes, including anaerobic digestion, landfill test cells, vermicomposting, and trickle flow processes for refractory organic compounds. A/Prof. Clarke has an established research record in the control of degradation processes, most recently winning an ARC Discovery grant on the production of H2 from organic waste. A/Prof Clarke has also conducted a number of industrial research projects, including the design and building of full scale prototype digestion processes for waste bananas, MSW and integrated food waste and blackwater slurries.

    James Udy has been involved in the design and implementation of the estuarine/marine and freshwater components of the Ecosystem Health Monitoring Program (EHMP) in S.E. Queensland. He acted as the “Research and Development Coordinator” for the estuarine/marine component for the last 5 years. James is currently the principal scientist at seqwater, responsible for delivering research appropriate to management needs with an annual budget of approx $4M. In this role he is actively developing improvement to existing monitoring programs to use new technologies and provide a timelier reporting framework to meet management requirements.

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    Permanent address: Plant Industry Unit, Centre for Environment and Life Sciences, CSIRO, Underwood Ave, Floreat, WA 6014, Australia.

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