Peracetic acid (PAA) stands out as a safe and environmental-friendly oxidant and disinfectant which has been effectively used in wastewater treatment. Chemical oxygen demand (COD) is a very popular analysis in wastewater treatment; however, the interference of residual PAA on the COD measurement is still unknown. In this context, this study investigated the implications of applying the COD analysis in PAA-based treatment. Each 1 mg·L−1 of PAA increased the COD concentration around 13.5 mg O2·L−1. Residual PAA and hydrogen peroxide (H2O2) were efficiently neutralized by sodium metabisulfite (SMBS) at the optimal SMBS/PAA ratio of 10.2:1 in a wide pH range (5 to 9). The effect of PAA addition on the COD concentration was evaluated in different water matrices (potassium hydrogen phthalate and wastewater solutions). The COD results with the SMBS addition at optimal SMBS/PAA ratio were lower than the ones without it. It may happen due to the neutralization of residual H2O2/PAA and the complexity of the water matrices which can interfere in the COD results. This study discussed the impact of the residual H2O2/PAA neutralization before the COD analysis, and this investigation can be used as a practical guideline for the correct COD measurement in PAA-based treatment.

Nutrient availability plays a crucial role in microalgae growth in domestic wastewater. In this study, we investigated the impact of different nitrogen and phosphorus ratios (5:1, 10:1, and 20:1, m∙m⁻¹), and the addition of inorganic carbon on microalgae growth and nutrient uptake from domestic wastewater. Microalgae biomass achieved values ranging from 0.54 to 1.41 g·L⁻¹. The cultivation process had maximum removal efficiencies of 83.7% for soluble chemical oxygen demand (sCOD), 74.0% for total Kjeldahl nitrogen (TKN), and 100.0% for ammonia (NH₃) and orthophosphate (PO₄³⁻). All the NH₃ and PO₄³⁻ concentrations from domestic wastewater without supplementation were completely removed on the fourth day of cultivation. Moreover, no significant differences in microalgae growth, and NH₃ and PO₄³⁻ removals were observed between the conditions with and without nutrient supplementation on the fourth day of cultivation. This study has shown the feasibility of growing microalgae in domestic wastewater without any nutritional supplementation. Further investigations are required to check the long-term performance, energy requirements, and economic viability of this system for wastewater treatment and the production of nutrient-rich biomass for agricultural applications.