In this study, water hyacinth was converted into highly flammable bio-oil through a two-step catalytic pyrolysis approach. A three-pronged approach, based on biochemical pretreatment of the biomass, use of clinkered catalyst, and an additional pyrolysis step, was adopted to produce highly upgraded bio-oils. Fresh, putrefied, and microbe treated water hyacinth was pyrolyzed into oil, gas, and solid residue. The oil product of the first step of pyrolysis contained 9.42%, 36.72%, and 30.38% of combustible liquids by mass, respectively. The fractional distillation of the oil product of fresh, putrefied, and microbe treated samples resulted in 11.56%, 7.1%, and 31.67% of residue by mass, respectively. These residues were repyrolyzed, and the oil and gas products of the first and second step of the pyrolysis were further analyzed for their chemical composition. After two-stage pyrolysis, the amount of the highly upgraded oil was increased to 34.34%, 58.31%, and 43.21% by mass, respectively. The bio-oils, obtained from fresh, putrefied, and microbe treated-samples, were significantly different in terms of their chemical nature and the number of compounds.

Change of the mass of bio-oil with temperature

Water hyacinth was used as biomass and brick powder, obtained by crushing a burnt/clinkered brick, was used as a catalyst. Water hyacinth was collected during the month of April 2016 from a stream in the Mardan area of Khyber PakhtunKhwa, Pakistan. During April, the water hyacinth was abundantly available in the fresh water streams due to warmness of the season. Since the dense growth of the water hyacinth suppresses the concentration of nutrients in the water and consequently the growth of algae, (38, 39) the collected biomass samples were almost free from algae. The samples were properly cleaned, dried, and processed for the production of bio-oils through multistep pyrolysis. The fully dried samples were named as fresh, putrefied, and microbe treated water hyacinth. The methods of preparing the biomass samples are explained in the following.

Distillation profiles of bio-oils obtained from fresh, putrefied, and microbe treated biomass

Resource Utilization: Water hyacinth is an invasive plant species that can proliferate rapidly, causing ecological problems in water bodies. Converting it into bio-oil through pyrolysis provides a method for utilizing this abundant biomass resource effectively.

Renewable Energy: Bio-oil produced from water hyacinth can serve as a renewable energy source. It can be used directly as a fuel for heating or electricity generation, or further refined into transportation fuels such as biodiesel or bio-jet fuel.

Reduced Greenhouse Gas Emissions: Burning fossil fuels releases carbon dioxide into the atmosphere, contributing to climate change. Using bio-oil from water hyacinth as a substitute for fossil fuels can help reduce greenhouse gas emissions since the carbon in bio-oil is derived from atmospheric carbon dioxide during the plant's growth.

Waste Management: By converting water hyacinth into bio-oil, it helps mitigate the environmental impacts of this invasive species. Harvesting and processing water hyacinth for bio-oil production can also help prevent its uncontrolled growth, which can disrupt ecosystems and harm biodiversity.

Distillation profiles of bio-oils obtained from fresh, putrefied, and microbe treated biomass

Growing Demand for Renewable Energy: With increasing concerns about climate change and the need to reduce greenhouse gas emissions, there is a growing demand for renewable energy sources. Bio-oils produced from water hyacinth offer a sustainable alternative to fossil fuels, thereby attracting interest from industries seeking to meet renewable energy targets.

Government Policies and Incentives: Many governments worldwide are implementing policies and incentives to promote the use of renewable energy sources and reduce dependence on fossil fuels. Subsidies, tax credits, renewable energy mandates, and carbon pricing mechanisms can create a favorable market environment for bio-oil production from water hyacinth.

Environmental Regulations: Stringent environmental regulations aimed at reducing air pollution and carbon emissions drive industries to seek cleaner alternatives to conventional fuels. Bio-oils produced from water hyacinth offer a low-carbon alternative with potentially lower emissions, making them attractive for compliance with environmental regulations.

Waste Management Solutions: The invasive nature of water hyacinth poses significant challenges for water bodies worldwide. Converting water hyacinth into bio-oil not only provides a renewable energy source but also offers a sustainable solution for managing this invasive species, thereby addressing environmental concerns.

Comparison of boiling points and amounts of the bio-oils.