Assessing possible applications of waste organic solid substances as carbon sources and biofilm substrates for elimination of nitrate toxicity from wastewater

This work aimed to find inexpensive alternatives that could serve both as carbon source and biofilm carrier for heterotrophic denitrification in treating nitrate contaminated waters. To ascertain cost efficiency, the effectiveness of four different waste organic solid substances (WOSS) like sugarcane bagasse (SB), coconut shell (CS), aegle shell (AS), groundnut shell (GS), and the equal-volume mixture of all (Mix) were assessed in batch experiments. Subsequently, the best performing (Mix) substrate was evaluated in column mode of experiments under different experimental conditions and the optimized values were verified as bed depth of 30-40 cm, hydraulic retention time (HRT) of 24-26 h, and flow rate of 1.5 mL/min. In optimum conditions, real domestic wastewater was successfully denitrified over a period of 2 months. The first-order reaction with R2 in the range of 0.96-0.99 better described the denitrification process both in batch and column studies. Mix substrate further contributed to a speedy establishment of active denitrifying consortia consisting of Stenotrophomonas, Bacillus, and Ochrobactrum as the dominant genuses. The study validated the possible application of the selected Mix substrate as a potential substrate for biological denitrification process.