Valorization of Agro-Industrial By-products: Use of Rice Husk as a Source of Microorganisms to Denitrification of Water

Abstract

Rice husk, which is an agricultural waste, provides a feasible alternative for the growth and propagation of denitrifying microorganisms. Nitrate and nitrite were removed using Immobilized Microorganisms (MO_IM) or Microorganisms in Solution (MO_SO). Microorganisms present in the rice husk biomass responsible for denitrification were identified as Pseudomonas, and other microorganisms have also been identified, as Oerskovia spp. Enterococcus sp. Bacillus mycoides and Escherichia coli. The influence of pH, temperature, C/N ratio and carbon source on biological denitrification were investigated. MO_IM and MO_SO consortium had optimal denitrifying performance at 25-30 °C and in pH 7-8. MO_SO has average denitrification efficiency larger than MO_IM. The MO_IM denitrification efficiency was more sensitive to pH changes than the MO_SO. Ethanol and sodium acetate were carbon sources for the denitrifying process. The efficiency of nitrate and nitrite removal using MO_SO and ethanol or acetate with 1:1, 1:2, 1:3 and 1:4 C/N ratios were equivalents and above 97.00%. The denitrifying process presented was robust and it presented nitrate removal close to 100% during 10 cycles.