ENHANCING VOLATILE FATTY ACIDS YIELDS FROM WASTE ACTIVATED SLUDGE TREATED BY HYBRID OXIDATION WITH OZONE AND SODIUM PERCARBONATE

The volatile fatty acids (VFAs) are a valuable source of hydrogen on fuel industry or precursors of polyhydroxyalkanoates, a highly in trend and non-toxic bioplastics. However, the VFAs generation costs are expensive. Therefore, this study proposed a recycling solution of the waste activated sludge (WAS) into VFAs by non-conventional treatment with tandem steps of energic and slow oxidation in alkaline media by hybrid treatment with ozone and sodium percarbonate (SPC), followed by semi-aerobic fermentation at 22oC. The aim of this study consists on the synergic effect of O3 and SPC on generating radicals to solubilise and oxidise the organic content, while the fermentation enhances the biological and chemical activity in acquiring VFAs, besides no harm residuals effectiveness. By appling this method, the VFAs production increased 33 times than the conventional method (which includes fermentation at 37oC), while O3 or SPC treatment showed little effect. However, the highest impact is given by WAS low biodegradability and high total solids content which may significantly diminishe the VFAs. Given the laboratory testing level and the refractory of WAS, the method proves that its efficiency is comparable with other methods, but is considerably a suitable green solution in terms of costs, energy demand and input materials, where no auxiliary substances are needed. Moreover, the method enhances the WAS dehydration and inhibits the CO2 emission which achieves the waste reduction and net-zero emissions requirements of the Circular Economy Plan.