Anaerobic and photocatalytic treatments of post-hydrothermal liquefaction wastewater using H₂O₂

Hydrothermal liquefaction (HTL) of cyanobacteria is a promising process for energy generation. However, post-HTL wastewater (PHWW) contains high amounts of organic matter and toxic compounds. This study investigated photocatalysis and anaerobic digestion (AD) for the treatment of PHWW from Spirulina conversion. H₂O₂ was used as an external oxidant in the photocatalysis or as a pretreatment in the AD process. The effect of different concentrations of H₂O₂ was evaluated. Greater CH₄ production and higher COD reduction were observed when pre-treated PHWW was used. In the photocatalytic treatment, color and COD reduction reached 93.1% and 23.4%, respectively, with the addition of H₂O₂. When a combination of the oxidative pretreatment and AD was applied, a maximum energy recovery of 66.7% was reached, while the photocatalysis reached a maximum of 61.5%. Use of the best conditions with proper dilutions resulted in higher growths of the Spirulina cultivation compared to that with conventional algal media.