Sustainable and eco-friendly approach for phosphorus recovery from wastewater by hydrothermally carbonized microalgae: Study on spent bio-char as fertilizer

Abstract This study focuses on phosphorus recovery from simulated aqueous environment by hydrothermally carbonized microalgae biomass. A detailed study on parameters influencing adsorption such as time (10–60 min), temperature (10–60 °C), agitation speed (50–250 rpm) and bio-char concentration (0.3–1.5 g/L) was carried out. Batch studies showed a maximum 90 % phosphorus removal for a concentration of bio-char of 1.5 g/L, agitation speed of 150 rpm, temperature of 60 °C and at 60 min. The adsorption experimental data fitted well with Pseudo-first order kinetics and Langmuir isotherm models with correlation coefficient (R2) value of 0.99 and 0.97 respectively. According to Langmuir model, phosphorus and ammoniacal nitrogen adsorption capacity of bio-char was 2505 and 6.7 × e4 mg/g with least error. To avoid leaching of ammonia and phosphorus to atmosphere, the spent bio-char was activated with ammonia and phosphorus solubilizing bacteria and tested as fertilizer. Pot experiments performed with tomato plant showed that spent bio-char is an excellent fertilizer and comparable to commercial di-ammonium phosphate (DAP). The plants cultivated with spent bio-char fertilizer have reached an average height of 22 ± 0.5 cm and their chlorophyll contents were 24.5 ± 0.42 mg/g. This study provides a proof of concept and it can be extended to real time wastewater in future. This study is an example of sustainable approach towards recovery of valuable phosphorus from aqueous environment and using it as fertile soil amendment.