The urge for alternative forms of energy to meet the demands of the ever-growing population is a primary concern throughout the world. With the improvement in technologies, biomass seems to be a potential feedstock for conversion to bio-oil by either pyrolysis or hydrothermal liquefaction (HTL). The latter is advantageous as wet biomass can be used directly without any pretreatment, and HTL also produces useful byproducts along with bio-oil. The use of oleaginous microorganisms such as algae, bacteria, and yeasts as biomass feedstocks for the HTL process is more beneficial compared to other conventionally used feedstocks such as lignocellulosic biomass, owing to their high oil content and fast growth rate even on cheaply available substrates. This paper provides an insight into the advantages and detailed information on different oleaginous microorganisms, their composition, and the use of wastewater as their substrate for cultivation. It also emphasizes HTL as an appropriate thermochemical conversion process for biomass processing and production of bio-oil as well as the different process parameters affecting the HTL technology. An integrated HTL based sustainable biorefinery approach for resource recovery in the form of energy is also discussed in detail, along with the future research perspectives in this field. Graphical abstract

Rising concerns over water scarcity, driven by industrialization and urbanization, necessitate the need for innovative solutions for wastewater treatment. This study focuses on developing an eco‐friendly and cost‐effective biochar‐zeolite composite (BZC) adsorbent using waste materials—spent coffee ground biochar (CGB) and steel slag zeolite (SSZ). Initially, the biochar was prepared from spent coffee ground, and zeolite was prepared from steel slag; their co‐pyrolysis resulted in novel adsorbent material. Later, the physicochemical characteristics of the BZC were examined, which showed irregular structure and well‐defined pores. Dye removal studies were conducted, which indicate that BZC adsorption reach equilibrium in 2 h, exhibiting 95% removal efficiency compared to biochar (43.33%) and zeolite (74.58%). Moreover, the removal efficiencies of the novel BZC composite toward dyes methyl orange (MO) and crystal violet (CV) were found to be 97% and 99.53%, respectively. The kinetic studies performed with the dyes and phosphate with an adsorbent dosage of 0.5 g L⁻¹ suggest a pseudo‐second‐order model. Additionally, the reusability study of BZC proves to be effective through multiple adsorption and regeneration cycles. Initially, the phosphate removal remains high but eventually decreases from 92% to 70% in the third regeneration cycle, highlighting the robustness of the BZC. In conclusion, this study introduces a promising, cost‐effective novel BZC adsorbent derived from waste materials as a sustainable solution for wastewater treatment. Emphasizing efficiency, reusability, and potential contributions to environmentally conscious water treatment, the findings highlight the composite's significance in addressing key challenges for the removal of toxic pollutants from the aqueous solutions.Practitioner Points: A novel biochar‐zeolite composite (BZC) material has been synthesized. Excellent removal of dyes by BZC (~95%) was achieved as compared to their counterparts The kinetic studies performed suggest a pseudo‐second‐order model. BZC proves to be highly effective for multiple adsorption studies. Excellent reusability showed potential as a robust adsorbent