Effects of carbon to nitrogen ratio on the performance and stability of aerobic granular sludge

Abstract

The purpose of this study was to assess the nutrient salts removal efficiency and stability of the aerobic granular sludge (AGS) by change in C/N (carbon to nitrogen) ratio. The laboratory-scale experiments were performed to analyze the removal efficiencies for organic matter and contents of nitrogen, MLSS, sludge volume index, and extracellular polymeric substances (EPS) under C/N ratio conditions of 5.0, 10.0, 15.0, and 20.0. The microorganisms were observed using optical microscope and the microbial communities were analyzed using pyrosequencing. The increase in C/N ratio from 5.0 to 20.0 increased the organic matter and nitrogen removal efficiency to 95.9 and 79.1%, respectively. For the EPS contents, an influencing factor of granule stability, the polysaccharides to protein (PS/PN) ratio increased from 0.55 to 0.79. For the microbial community, the <i>Thauera</i> was the most common genus in ending phase occupying 63.7%. This microorganism is regarded as one contributing to organic matter degradation and improved production of EPS including AGS of microorganism, thus, may be an explanation of the results of this study such as increase in organic material in AGS and improvement of denitrification efficiency and contents of EPS with increase in C/N ratio.

Nitrogen Removal with Aerobic Granules – Effect of Dissolved Oxygen and Carbon/Nitrogen Ratio

“…These results (Fig. 1a) are in agreement with Kim et al, 7 Kim and Ahn, 9 and Kocaturk and Erguder. 6 In a study conducted under anoxic-aerobic regime with acetic acid as the carbon source, Kocaturk and Erguder 6 reported COD removal efficiency of 63-79 % at ratios COD/N 1-7.5, efficiency of 76-90 % at COD/N 10, and at COD/N 20 and 30 the efficiency of COD removal of 94 % and 93 %, respectively.…”

“…COD removal efficiencies of 78.9, 86.7, 92.7, and 95.9 % were recorded in exper-iments under aerobic regime with acetate as the carbon source, at ratios of COD/N 5, 10, 15, and 20. 7 However, in experiments with high MLSS concentration, such as 8 g MLSS l −1 , the high COD removal efficiency of 89.4-95.6 % was recorded at C/N ratio lower than 2. 27 Kim et al 7 showed that the microorganisms' diversity decreased with the increase in the COD/N ratio from 5 to 20, and the increase in COD/N ratio had a direct effect on the stability of aerobic granules.…”

“…7 However, in experiments with high MLSS concentration, such as 8 g MLSS l −1 , the high COD removal efficiency of 89.4-95.6 % was recorded at C/N ratio lower than 2. 27 Kim et al 7 showed that the microorganisms' diversity decreased with the increase in the COD/N ratio from 5 to 20, and the increase in COD/N ratio had a direct effect on the stability of aerobic granules. Zhao et al 28 reported that the gradual dominance of heterotrophic bacteria occurred with the increase in COD/N ratio, thus, decreasing the number and diversity of microorganisms.…”

“…5−7 Granule disintegration during long-term bioreactor operation is associated with low COD/N, typical for municipal wastewater, such as COD/N 1, 8 COD/N 2.5, 9 COD/N 5. 6,7 Within the granules, dense and compact structures of activated sludge there exist dissolved oxygen (DO) and substrate gradient. Therefore, aerobic processes such as degradation of organics and nitrification take place on the surface of the granule, while anoxic processes such as denitrification occur inside the granule (simultaneous nitrification and denitrification).…”

Migration and transformation of heavy metals during the microwave-assisted thermal hydrolysis of sewage sludge

“…The color depth was correlated with the soluble protein content and could be measured by a spectrophotometer under the wavelength of 500 nm. The soluble polysaccharide was measured using the phenol-vitriol colorimetry method (Kim et al 2020). Furfural and hydroxymethyl furfural could be generated by the dehydration of polysaccharide using concentrated sulfuric acid.…”