Performance of Green Microalgae-Activated Sludge and Diatom-Activated Sludge Co-Cultures in Kitchen Wastewater Treatment: Nutrient Removal Efficiency and Cellular Fatty Acid Profiling

Kitchen wastewater, characterized by elevated levels of organic matter and nutrients, requires efficient treatment solutions to mitigate its environmental impact. Conventional treatment methods are often energy-intensive and inefficient for decentralized or small-scale applications. This study investigates the sustainable treatment of kitchen wastewater by assessing nutrient removal efficiency and fatty acid profile in two different co-culture systems: System A (green microalga and activated sludge) and System B (diatom and activated sludge). The reactors were operated in semi-continuous mode at five distinct solid retention times (SRTs) (2, 4, 6, 8, and 10 days), with monitoring of key parameters including dissolved organic carbon, total nitrogen, and phosphates. The biomass obtained from both systems was analyzed for fatty acid composition after treatment. The removal of carbon and nitrogen was found to be comparable in the two setups. Chlorophyll concentration increased with increasing SRT in these co-cultures. At 10 days of SRT, the average chlorophyll concentration in System A was 6.5 mg/L, while in System B it was 4.9 mg/L. System A generated significantly greater proportions of polyunsaturated fatty acids across several SRTs in comparison to System B. The differences in fatty acid composition make System A more suitable for colder climates, where biodiesel must maintain adequate fluidity, while System B produces biodiesel with superior oxidative stability. This work establishes the feasibility of employing tailored algae-activated sludge co-cultures for integrated wastewater treatment and biodiesel production, demonstrating a sustainable methodology for simultaneous resource recovery and development of application-specific biofuels according to their fatty acid profiles.