The aim of this work was to compare the performance of biochar from various food processing wastes of different origin for the removal of different nutrients from water. Eggshells (EGS), rice husk (RH), and coffee biochars were pyrolyzed at 400 and 800 °C and were examined for the removal of phosphates, nitrates, and ammonia nitrogen. The raw materials were also modified with magnesium chloride in order to investigate their sorption behavior. The highest sorption capacity (qmax) for phosphates and ammonium was observed with EGS pyrolyzed at 800 °C and was 11.45 mg PO43−-P/g and 11.59 mg NH3-N/g, while the highest nitrates sorption capacity was observed with the magnesium-modified RH pyrolyzed at 800 °C (5.24 mg NO3−-N). The modified EGS biochars pyrolyzed at 800 °C had almost the half the sorption capacity for phosphates and nitrates compared to the unmodified materials. The modification of RH pyrolyzed at 800 °C resulted in higher sorption capacity by 34 and 158% for phosphates and ammonium, respectively. The coffee raw and modified biochars were less efficient in nutrient removal compared to the other materials. The specific surface area values of the biochars examined is not a decisive factor for nutrient sorption. The reaction between magnesium and calcium (for the eggshell samples) ions with phosphates is responsible for the higher sorption efficiency. On the other hand, the presence of magnesium and calcium ions has a detrimental effect on the sorption of NH3-N.

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BACKGROUND Photogranules seem to be an alternative solution for wastewater treatment and biomass harvesting. The aim of our work was to investigate the formation of algal flocs as an efficient method for the treatment of wastewater and separation of algal cells. RESULTS The progressive change of activated sludge to algal flocs was evaluated under static and stirring conditions using a synthetic substrate (modified Blue Green‐11 medium) and the secondary effluent from an activated sludge wastewater treatment plant. Algal flocs were observed in all cultures by day 10 and a high chlorophyll concentration was detected in all cases reaching values up to 610–630 μg L−1 at the end of the experiment after 30 days. The size of flocs in all cultures at either static or mixing conditions ranged from 330 to 994 μm, resulting in biomass concentration from 330 to 660 mg L−1. The cultures in secondary effluent at static conditions presented the greatest size, and the mean diameter on days 10 and 30 was 250 and 994 μm, respectively. The cultures were efficient in nutrient removal and, by the end of the experiment, nitrates and phosphates were completely consumed. CONCLUSIONS Algal flocs were developed from activated sludge without adding any other flocculant and a highly efficient biomass was developed, which can easily settle and remove nutrients from the medium. © 2022 Society of Chemical Industry (SCI).

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