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 (MOIM) or Microorganisms in Solution (MOSO). 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. MOIM and MOSO consortium had optimal denitrifying performance at 25-30 °C and in pH 7-8. MOSO has average denitrification efficiency larger than MOIM. The MOIM denitrification efficiency was more sensitive to pH changes than the MOSO. Ethanol and sodium acetate were carbon sources for the denitrifying process. The efficiency of nitrate and nitrite removal using MOSO 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.
Highlights
Safe water is crucial for humans, plants, and animals (Abu Hasan et al, 2020)
The microorganisms used in this study were immobilized in rice husk biomass (MOIM) or suspended microorganisms in solution (MOSO)
Pseudomonas (GRAM negative), Oerskovia spp. (GRAM positive Bacilli), Enterococcus sp. (GRAM positive Cocci), Bacillus mycoide (GRAM positive Bacilli), and Escherichia coli (GRAM negative) are isolated from rice husk biomass. These bacteria form a biofilm in the growth medium and these biofilms are responsible for the process of biological denitrification of the water samples tested
Summary
Safe water is crucial for humans, plants, and animals (Abu Hasan et al, 2020). Nowadays, water quality preservation is an important environmental issue where agricultural activities, industrial and domestic effluents are the main contamination sources of water (Júnior et al, 2007; Shamsollahi & Partovinia, 2019).In many parts of the world, groundwater and superficial waters are widely used as drinking water. Water quality preservation is an important environmental issue where agricultural activities, industrial and domestic effluents are the main contamination sources of water (Júnior et al, 2007; Shamsollahi & Partovinia, 2019). Human activity increased nitrate (NO3-) concentration in groundwater and superficial waters due to human activity (Hou et al, 2019; Wan et al, 2015). Nitrate cause eutrophication and toxic algal blooms in receiving waters. It is identified as one of the hazardous contaminants in drinking water, it can cause blue baby syndrome and nitrate reduction to nitrite induce the formation of carcinogenic nitrosamines (Fan & Steinberg, 1996)
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