Pretreatment of Biogas Slurry by Modified Biochars to Promote High-Value Treatment of Wastewater by Microalgae

Abstract

High concentrations of contaminants such as ammonia nitrogen and organic matter in full-strength wastewater severely inhibit the growth of microalgae, contributing to lower biomass accumulation and contaminant removal efficiency. To overcome this limitation, modified biochars prepared from pine sawdust and sugarcane bagasse were used in this study as an adsorbent–desorbent for the pretreatment of wastewater to promote the growth of microalgae. The results showed that the two modification methods (acid/alkaline modification and magnesium salt modification) used in the experiment could increase the abundance of oxygen-containing functional groups. Moreover, magnesium salt modification could effectively improve the pore structure of biochar surfaces and increase the specific surface areas. Compared with the pristine biochars, the adsorption performance of the modified biochar was found to be significantly higher for nutrients in wastewater. The adsorption capacity of the acid/alkaline-modified pine sawdust biochar reached 8.5 and 16.49 mg∙g−1 for ammonia nitrogen and total organic carbon in wastewater, respectively. The magnesium salt modified pine sawdust biochar achieved a more comprehensive nutrients adsorption capacity of 15.68, 14.39, and 3.68 mg∙L−1 for ammonia nitrogen, total organic carbon, and total phosphorus, respectively. The mechanism of ammonia nitrogen adsorption was mainly the complexation of surface -OH functional groups, while the adsorption mechanism for phosphate was mainly the complexation of -OH and Mg-O functional groups and the chemical precipitation of MgO or Mg(OH)2 attached to the surface.

Bibliometric analysis of wastewater treatment with microalgae in the period 1985–2023

“…, Paulo deSousa et al (2023),Wang et al (2023), and Krasaesueb et al (2023) used Chlorella vulgaris, Scenedesmus sp., Chlorococcus AY122332.1, and Synechocystis SphU (mutant cyanobacteria), respectively, as simple strains. On the other hand,Gu et al (2023) did not specify the strain of microalgae used. The NH 4 removal was 100%, 94%, 91%, 45%, and 98%, respectively; while that of PO 4 varied from 71 to 97%.Nutrient removal, by microbial consortium and the combination of strains from Chlorella vulgaris, Scenedesmus sp., Chlorococcum sp., and Oscilatoria sp., was performed byNagabalaji et al (2023) and removed 86.6% of NH 4  .…”