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Biopolymers are very favorable materials produced by living organisms, with interesting properties such as biodegradability, renewability, and biocompatibility. Biopolymers have been recently considered to compete with fossil-based polymeric materials, which rase several environmental concerns. Biobased plastics are receiving growing interest for many applications including electronics, medical devices, food packaging, and energy. Biopolymers can be produced from biological sources such as plants, animals, agricultural wastes, and microbes. Studies suggest that microalgae and cyanobacteria are two of the promising sources of polyhydroxyalkanoates (PHAs), cellulose, carbohydrates (particularly starch), and proteins, as the major components of microalgae (and of certain cyanobacteria) for producing bioplastics. This review aims to summarize the potential of microalgal PHAs, polysaccharides, and proteins for bioplastic production. The findings of this review give insight into current knowledge and future direction in microalgal-based bioplastic production considering a circular economy approach. The current review is divided into three main topics, namely (i) the analysis of the main types and properties of bioplastic monomers, blends, and composites; (ii) the cultivation process to optimize the microalgae growth and accumulation of important biobased compounds to produce bioplastics; and (iii) a critical analysis of the future perspectives on the field.

A novel strategy of using microalgaeChlorella vulgarisfor simultaneous bio-treatment of petrochemical wastewater and lipid production was developed in the present study. Phycoremediation was carried out in 30 days. The profile of fatty acids was identified, and the specifications of biodiesel including saponification value, iodine value, cetane number, long-chain saturated factor, cold filter plugging point, cloud point, allylic position equivalent and bis-allylic position equivalent were predicted by BiodieselAnalyzer® software. Besides, polycyclic aromatic hydrocarbons were determined in both wastewater samples and produced lipid. The observed data showed that biodiesel fromC. vulgariswas superior to petrodiesel in terms of suitability in diesel engines. Moreover, contamination of petrochemical wastewater can influence the expression of a variety of genes in algae. To investigate the effectiveness of contamination on the expression of lipid synthesis as well as three photosynthesis genes, a real-time polymerase chain reaction assay was used to quantify transcript levels ofPsaB(photosystem I reaction center protein subunit B),psbC(an integral membrane protein component of photosystem II), andrbcL(a large subunit of ribulose-1,5-bisphosphate carboxylase oxygenase). Furthermore, the gene expression level ofaccD(acetyl-coenzyme A carboxylase carboxyl transferase subunit beta, chloroplastic) was studied to discover the effect of wastewater on lipid production. The results showed that when diluted petrochemical wastewater (50%) was used as a media forC. vulgariscultivation, these genes expression significantly increased. For 50% diluted wastewater, the maximum removal of BOD, COD, total nitrogen, and total phosphor has been 30.36%, 10.89%, 69.89%, and 92.59%, respectively.

Globally, petroleum has been the largest source of energy consumption compared to other energy sources such as natural gas and coal. As a result of high demand for petroleum as an energy source, contamination takes place due to maintenance, production, exploration, storage, transportation and accidental release, yielding in substantial ecological impacts. The contaminations of petroleum in the presence of soil have a negative impact on human health and the development of plant growth. According to this, there is an imperative need to investigate on environmental-friendly remediation strategies to eliminate petroleum contaminants in soil. Among different remediation technologies, bioremediation is recognized as a clean soil treatment technology due to its advantages of safety, no secondary pollution, and economy. For bioremediation of contaminated soil, biochar (BC) applications may provide new solution for polluted soil problems. BC has displayed a good potential to remedy soil contaminants owed to its wide availability of the necessary feedstock, sustainable nature, cost-effective feasibility, high efficiency, large internal surface area and desirable physicochemical surface properties. The usage of BC may include sequestration of carbon, improvement fertility of soil, remediation, as well as recycling of agricultural waste. This paper provides a review on current properties and preparation of BC and its usage as an ameliorant, amendment or sorbent for remediation of contaminated soil. Different research and published papers in this field reveal that the potential of biochar for contaminated soil remediation relies on its physical and chemical properties, which are considerably influenced by the feedstocks, pyrolysis conditions and pyrolysis technologies. The results show that the pyrolysis conditions can affect the BC structure and composition and thus its adsorption capacity. Pyrolysis temperature influences the adsorption characteristics of BC by changing the surface functionality, surface area, pore distribution and mineral concentration of BC. It is important to produce BC at optimum pyrolysis temperatures to maximize inorganic and organic contaminant adsorption. The results also indicate that BC obtained through microwave pyrolysis has better yield and quality than those produced from conventional pyrolysis.

Incorporation of biochar in cementitious materials is a promising solution in the mitigation of environmental pollutants by partially cutting off the consumed ordinary Portland cement and reducing the amount of waste disposal in landfills. This work studied the partial replacement of cement by biochars having a different chemical composition and its effect on the performance of cement mortars. The feedstocks for biochar production were selected from biomass wastes produced in agro-industrial and forestry sectors in Portugal. They included olive stone, rice husk and wood chips from residual forest biomass. Biochars were produced at 500 ℃ using a slow pyrolysis process. The biochars were added at different cement replacement rates; 0.5, 1, 2 and 4 wt% of cement weight. XRD and TGA were used to elaborate the effect of biochar on the hydration products. Effect of biochar addition on the capillary water absorption, compressive and flexural strength of cement mortar was analyzed. The results suggested that the biochars contributed to the promotion of hydration products. Cement replacement with 4 wt% olive stone and rice husk biochars was associated with a slight increase of 28-days compressive strength. Rice husk biochar showed the best long-term mechanical performance due to its pozzolanic reaction in the matrix. No significant changes were observed in the water absorption of cement mortar after the addition of 4 wt% biochar as cement replacement. The research outcomes suggested the beneficial effect of cement replacement with biochars from olive stone and rice husk up to 4 wt% with comparable properties.

Increasing cement production in construction sector and waste generation in industrial sectors are of the major sources of CO2 emission. For decades, it has been the concern of environmentalists to convince constructors and researchers to find sustainable solutions targeting aforementioned problems. The attempts focused on identification of wastes to be successfully complied with construction materials. Biochar has recently received attention due to several environmental and technological advantages, shortly include carbon sequestration, low thermal conductivity, chemical stability and low flammability. For this reason, biochar is recognized as an efficient candidate for cement or lightweight aggregates replacement in building materials. Biochar addition could result in a reduction of capillary absorption in mortar paste. Besides, its addition accelerates cement hydration and restricts shrinkage cracking in cement mortar. The present review categorizes all the biochar critical features affecting the performance of cementitious materials. The effect of biochar addition as filler and cement replacement on the workability, hydration, mechanical and transfer properties of cement paste/composites is reviewed in this paper. From the data collection, an optimum biochar content around 2% is shown to contribute to the improvement of mechanical properties. The gaps in the literature are identified and the future research plans are proposed.

Widespread application of non-renewable energy resources such as fossil fuels is limited mainly due to their adverse environmental impacts by increasing the amount of greenhouse gas (GHG) emissions. A solution to limit fossil-fuel pollution is the use of renewable energy resources. In the recent years, microalgae have received considerable attention as a suitable feedstock for biofuel production. Microalgae can grow in various aquatic wastewater media and are able to produce biomass, lipids, and hydrocarbons. Using different types of wastewaters as media for algae cultivation could not only reduce their freshwater footprint but also the costs associated with algae cultivation and biofuel production. This chapter presents an overview on various algal cultivation systems as well as on optimization of algal cultivations, while downstream processes including harvesting and drying of microalgae and lipid extraction systems are also reviewed and discussed. Subsequently, different microalgae biofuel production pathways are presented. Finally, the applications of microalgae in integrated systems, i.e., in wastewater treatment and biodiesel production systems and biofixation of carbon, are scrutinized.