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Abstract

H₂O₂-advanced oxidation process facilitated by microwave (MW-AOP) or radiofrequency (RF-OP) was investigated for release of valuable products from three organic slurries: fats, oils, and grease (FOG), thickened waste activated sludge (TWAS), and dairy manure. Mixtures of FOG either with dairy manure or with TWAS were treated using MW-AOP (batch 2450MHz, 1kW). The degradation followed peroxidation mechanism to produce lower molecular weight substrates such as short-chain fatty acids which would be less inhibitory to microbes. Nutrients and metals released in the treated solution would sustain microbial growth in a biological system. FOG content for the mixtures in the MW-AOP treatment should be less than 75% by total solids (TS) weight to prevent oxidation to CO₂. RF-OP (batch 27.12MHz, 6kW) was utilized to treat solid fraction dairy manure for disintegration of solids and nutrient release. High H₂O₂ dosages above 1 gH₂O₂/gTS required a longer hold time for full reaction, resulting in improved release of nutrients and soluble chemical oxygen demand but increase in the process cost and treatment time. The results indicated that the energy consumption during this process was greater than the energy potential of the substrate indicating that it is probably not cost effective for the treatment of separated dairy manure solids. A pilot-scale 915MHz, 25kW continuous-flow MW-AOP system was operated treating TWAS, which was then fed continuously into a single up-flow anaerobic sludge reactor (UASB) reactor, or a two-phase UASB system consisting of a completely stirred tank reactor (CSTR) in acid phase and UASB in methane phase. The organic loading rate (OLR) reached maximum of 15.7 – 18.2 g volatile solids(VS)/L/day in all reactors without evidence of souring; There was no difference in specific methane potential (SMP) between CSTR and UASB reactors. VFA accumulated in the acid phase when SRT was less than 1 day. In both systems the SMP was maintained between 10.1 and 18.2 gVS/L/day at 133±45 and 138±73 LCH4/VS-added for single and two-phase system respectively. Theoretical methane yield was achieved between 7 – 8 day HRT. No difference between the two systems in terms of methane performance as a function of hydraulic retention time was determined.