One of the biggest problems the world is currently experiencing is wastewater treatment. Numerous pollutants are released into water bodies by enormous amounts of effluents from varied sources. This paper provides a concise summary of the state of the art in AOPs, biological treatment, and their efficient application for the degradation of the numerous recalcitrant organic contaminants found in wastewater. The employment of a photoreactor is necessary for the efficient execution of the majority of photocatalytic processes. This review examines the effectiveness of several reactor configurations with varying geometries. Integrating different AOPs and AOPs with biological approaches for degrading pollutants in wastewater was also discussed. It is important to emphasize that an integrated AOP/biological system produces by-products that are not hazardous, uses little energy, and completely degrades pollutants. The review also outlines the challenges and issues of wastewater treatment for an environmentally and economically feasible process.

Lignocellulosic biomasses (LCB) are sustainable and abundantly available feedstocks for the production of biofuel and biochemicals via suitable bioconversion processing. The main aim of this review is to focus on strategies needed for the progression of viable lignocellulosic biomass-based biorefineries (integrated approaches) to generate biofuels and biochemicals. Processing biomass in a sustainable manner is a major challenge that demands the accomplishment of basic requirements relating to cost effectiveness and environmental sustainability. The challenges associated with biomass availability and the bioconversion process have been explained in detail in this review. Limitations associated with biomass structural composition can obstruct the feasibility of biofuel production, especially in mono-process approaches. In such cases, biorefinery approaches and integrated systems certainly lead to improved biofuel conversion. This review paper provides a summary of mono and integrated approaches, their limitations and advantages in LCB bioconversion to biofuel and biochemicals.

Human civilization will need to reduce its impacts on air and water quality and reduce its use of fossil fuels in order to advance towards a more sustainable future. Using microalgae to treat wastewater as well as simultaneously produce biofuels is one of the approaches for a sustainable future. The manufacture of biofuels from microalgae is one of the next-generation biofuel solutions that has recently received a lot of interest, as it can remove nutrients from the wastewater whilst capturing carbon dioxide from the atmosphere. The resulting biomass are employed to generate biofuels, which can run fuel cell vehicles of zero emission, power combustion engines and power plants. By cultivating microalgae in wastewater, eutrophication can be prevented, thereby enhancing the quality of the effluent. Thus, by combining wastewater treatment and biofuel production, the cost of the biofuels, as well as the environmental hazards, can be minimized, as there is a supply of free and already available nutrients and water. In this article, the steps involved to generate the various biofuels through microalgae are detailed.

The pharmaceutical wastewater was treated by coupling solar photo-Fenton process with an aerobic sequential batch reactor (SBR). Pharmaceutical wastewater has high COD and very low BOD and hence it is difficult to treat them biologically. The main purpose is to determine optimal photo-Fenton conditions (i.e., pH, ferrous ion concentration, H₂O₂ dosage and treatment time) for making wastewater biocompatible and suitable for subsequent biological treatment. Solar photo-Fenton process enhances biodegradability and a significant enhancement of biodegradability was found at the optimum conditions of pH = 3, H₂O₂ = 5 g L^–1, Fe²⁺ = 1 g L^–1 and irradiation time = 60 min. At this condition BOD₃/COD ratio increased from 0.015 to 0.54. The coupled solar photo-Fenton with SBR process obtained COD removal of 98% and the effluent COD concentration was found to be 100 mg/L, which meets the requirements of the discharge standard.