Corrigendum to “Application of aqueous alkaline extraction to remove ash from algae harvested from an algal turf scrubber” [Algal Res. 35 (2018) 370–377](S2211926418304867)(10.1016/j.algal.2018.09.006)

The authors regret that a transcription error resulted in erroneous reporting of total ash, CHNOS, total solids recovered, total organics, and elemental ash composition in treated biomass, as described in the following summary. The authors would like to apologise for any inconvenience caused. Summary: An error in data transcription resulted in erroneous reporting of total ash, CHNOS, total solids recovered, total organics, and elemental ash composition in treated biomass. These errors impacted Figs. 3, 4, 5, and 6. Organic loss due to alkaline extraction is much greater than originally reported. A flawed approach to equate total recovered solids with total organic recovery led us to believe that alkaline extraction of silica was greatly reducing the ash content of algal turf scrubber biomass. Instead, total ash removal was offset by loss of organic material, resulting in little change to the relative amount of ash in the recovered material. Elemental analysis (CHNOS) of untreated and alkaline treated ATS biomass (80 °C, 1.0% NaOH) indicates a 48% reduction in elemental carbon due to alkaline extraction; 64% of total silica was removed under the same experimental conditions. Corrigendum Fig. 3 [Figure presented] Corrigendum Fig. 3. Effect of initial aqueous extractions on the elemental composition (carbon, hydrogen, nitrogen, oxygen, and sulfur-CHNOS), volatiles content, chlorides, total ash, and total organics (top) and on the elemental ash composition as a wt% of the total ash (bottom). Data shown are the mean ± standard deviation, n = 3. Fig. 3 indicates that less organics were present in the alkaline extracted sample than water-washed and untreated samples. The corrected values show that total ash, as a percentage of the total recovered solids, either does not change appreciably (water wash) or increases slightly (alkaline extraction). Corrigendum Fig. 4 [Figure presented] Corrigendum Fig. 4. Percent removal of specific ash components on a molar basis (Top); and removal of specific ash components compared to the overall removal of ash on a relative % basis (Bottom). These values were calculated by subtracting the relative removal of total ash by the relative removal of the ash species. Data shown is the mean ± standard deviation, n = 3. Fig. 4 shows the effect of treatment on the absolute removal of individual elements. The percent change in the amount of individual elements due to water washing or alkaline extraction indicates removal for positive values. Zero values indicate that insignificant amounts of the ash species were removed. Negative values suggest that an enriching effect of ash species due to organic loss. Corrigendum Fig. 5 [Figure presented] Corrigendum Fig. 5. Recovery of total solids and removal of silica on a wt% basis following a aqueous ash removal tests performed across an experimental matrix that spanned temperature (25, 50, and 80 °C) and NaOH loading (0.0, 0.5, 1.0, and 1.5 wt%). In addition a final set of conditions at 80 °C and 2.0 wt% NaOH are shown. Data shown is the mean ± standard deviation, n = 3. The original published figure utilized Si and K concentrations in the aqueous phase and their removal rate to estimate the removal of all other ash species. The figure was updated to only include the percentage of silica removed based on initial composition and the amount of silica measured in solution. Corrigendum Fig. 6 [Figure presented] Corrigendum Fig. 6. Removal of silica (wt%) and total solids recovery (wt%) from ash removal tests conducted in Parr reactors. Water extraction tests were conducted at 130 °C and alkaline extraction tests were conducted at 100 °C and 130 °C with sodium hydroxide concentrations of 1.0% (wt%). Data shown is the mean ± standard deviation, n = 3. The figure was updated to only include the percentage of silica removed based on initial composition and the amount of silica measured in solution.