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Abstract: The use of high-ash containing biomass for energy application leads to serious problems during the conversion process and affects the quality of the resulting fuel products. In this study, the effect of demineralization treatments on the hydrothermal liquefaction (HTL) of wastewater algae biomass (WAB) was investigated. Three different acid-treatments were selected for the study: acetic acid (AA), formic acid (FA), and sulfuric acid (SA). The HTL products distribution, the quality and chemical composition of biocrude oil from treated and untreated biomass (UBM) were compared. The HTL experiments were conducted using a 40ml tubular reactor at a reaction temperature of 300oC, retention time of 60 minutes, and 100 psi initial headspace pressure with pure N2 as the process gas. Results revealed that demineralization treatments significantly improved the biocrude oil yield from 17 %daf (dry, ash-free weight) up to 25 %daf, and the aqueous phase products from 50 %daf up to 61 %daf, while there was no significant effect on the yield of gaseous products (6 – 7 %daf). The solid residue yield was all lower in treated biomass (7 – 15 %daf) compared to that from UBM (26% daf). The highest biocrude oil yield (25% daf) was obtained from AA and FA. However, the highest biocrude oil energy recovery (ER) of 41.83 ± 1.87% was obtained from the FA, which is about 52% higher than that from UBM. The ultimate, GC-MS and thermogravimetric (TG) analyses showed the biocrude oil obtained from demineralized biomass are comparable in quality and did not vary much from the biocrude oil obtained from UBM. 

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