Remediation of trace organic contaminants from biosolids: Influence of various pre-treatment strategies prior to Bacillus subtilis aerobic digestion

Abstract

Biosolids from wastewater treatment plants is a crucial channel for the transfer of trace organic contaminants (TrOCs) from wastewaters to the soil, which necessitates the treatment of the biosolids prior to any application. The present study evaluated the effect of four different pre-treatment strategies on biosolids valorization and the subsequent removal of TrOCs during bioaugmentation with Bacillus subtilis. On analyzing the biosolids, out of the 72 TrOCs investigated, eight pharmaceuticals (total concentration of 157.2 ± 43.4 µg/kg), and two pesticides (total concentration of 18.8 ± 5.8 µg/kg) were detected. It was observed that when the biosolids was augmented with B. subtilis for 28 days, 52% TrOCs removal with a total suspended solids (TSS) reduction of 12% was achieved. In order to enhance the effect of aerobic digestion, four different pre-treatment strategies – alkali, ultrasonication, freeze-drying and enzymatic, were employed for biosolids management. Among these strategies, alkali pre-treatment showed the maximum TrOCs removal of 63% with 8% reduction in TSS, followed by ultrasonication, where the TrOCs removal was 32% with 5% TSS reduction. On comparing the combinational effect, the aerobic digestion of enzyme pre-treated biosolids showed an enhanced TrOCs removal of 90%, which also incurred TSS reduction of 18%, followed by the alkaline treated, freeze-dried and ultrasonicated biosolids. Thus, this study establishes B. subtilis aided aerobic digestion as an effective process for biosolids treatment and explains the impact of pre-treatment processes on TrOCs and TSS removal.