In the proposed study, biochar will be produced from selected vegetable waste (spent coffee grounds and tea leaf residue) through pyrolysis. The sorption mechanisms (adsorption and desorption) of the persistent toxic substances (PTS) mixture, including arsenic (As), zinc (Zn), lead (Pb), mercury (Hg) (total and methylmercury (MeHg)), dichlorodiphenytrichloroethane (DDT), phthalates esters (PAEs), perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by different size of vegetable-based biochar will be investigated.

3600 tonnes of food is wasted each day in Hong Kong and all of them still end up in our overloaded landfill sites which is undoubtedly not sustainable. The major aim of the present study is to investigate the feasibility of recovering the vegetable waste and turning them into biochar for production of vegetable-based biochar fish feed for growing freshwater fish (grass carp (Ctenopharyngodon idella). It is expected that the vegetable-based biochar fish feed can prevent the accumulation of pollutants in fish meat by retaining pollutants through sorption. Furthermore, it was known that pollutants uptake in the human body is controlled by different gut microbiota. Similarly, this may also be true in freshwater fish. However, there is limited information on the role of fish gut microbiota in the uptake of pollutants. Therefore, there is an urgent need to investigate if the vegetable waste-based biochar fish feed can enhance the fish gut microbiota and subsequently lower the bioaccessibilities of pollutants in fish gastrointestinal tract as well as improve fish growth and fish immunity. In the proposed study, biochar will be produced from selected vegetable waste (spent coffee grounds and tea leaf residue) through pyrolysis. The sorption mechanisms (adsorption and desorption) of the persistent toxic substances (PTS) mixture, including arsenic (As), zinc (Zn), lead (Pb), mercury (Hg) (total and methylmercury (MeHg)), dichlorodiphenytrichloroethane (DDT), phthalates esters (PAEs), perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) by different size of vegetable-based biochar will be investigated. The growth performance of fish fed by the fish feed mixed with biochar will be compared with commercial formula feed in laboratory scale growth experiments and the optimal results will be applied in the field trials. More importantly, the fish immunity parameters, the microbial community in fish gut, and the bioaccessibility of the above contaminants, as well as the body burden of these chemicals in the fish will also be identified for assessing the fish health and risks to human health after consumption of these fish. The present study can help fill the research gap in the relationship between pollutants uptake, fish immunity, the microbial community in fish gut and biochar and also contribute to ecotoxicology.