Removals of Some High- and Low-Density Polyethylene (HDPE and LDPE), Polypropylene (PP) and Polyvinyl Chloride (PVC) Microplastics Using Some Microalgae Types, Energy Production and Energy Recovery

Waste plastic conversion involves the treatment of plastic waste to transform in different forms of energy (heat, electricity, liquid fuels). Plastic can be converted into different forms of biofuel via thermochemical conversion methods (gasification, pyrolysis and liquefaction). Algal biomass can be converted into different forms of biofuel (crude bio-oil, bioethanol, biogas, biodiesel and bio-hydrogen) well as value added chemicals. Microalgal cells can accumulate more lipids over a shorter life cycle, they are discussed as a promising feedstock for third-generation biodiesel. The utilization of microalgae as biofuel feedstocks offers an economic, ecofriendly alternative to the use of fossil fuels the aim of microplastics (MPs) removals. Interactions between MPs and microalgal cells could enhance several important features for possible microalgal harvest and MPs accumulation. One hypothesis is microalgal biomass hypothesis can accumulate lipids and carbohydrates under microplastic stress, supporting biomass conversion into biodiesel and bioethanol. In such systems, algal cells act as bio-scavengers for MPs, binding the particles to algal surfaces or incorporating them into their cells; they are filtered from the water body and finally destroyed by further downstream processing of the polluted biomass. In this study, in order to determine biofuel (1-butanol) and methane gas [CH4(g)] production; High- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), and polyvinyl chloride (PVC) MPs were removed using biomass composed of microalgae Chlamydomonas reinhardtii and Chlorella vulgaris. The algal inhibition test results proved that small groups of MPs with a size of ≈ 100 nm did not show algal inhibition. According to the algae inhibition test results, the production of 1-butanol from 100 mg/l microalgae biomass under aerobic conditions were determined as 93 ml/g for HDPE, 236 ml/g for LDPE, 387 ml/g for PP and 459 ml/g for PVC. According to the algae inhibition test results, the production of CH4(g) from 400 mg/l microalgae biomass under anaerobic conditions were measured as 452 ml/g for HDPE, 510 ml/g for LDPE, 529 ml/g for PP and 541 ml/g for PVC. 91.26%, 94.52%, 98.34% and 96.17% energy recoveries were measured for HDPE, LDPE, PP and PVC MPs, respectively, after microalgae biomass experiments, at pH=7.0 and at 35oC. Maximum 98.34% energy recovery was obtained for PP MPs after microalgae biomass experiments, at pH=7.0 and at 35oC.