Effects of Different Carbon Sources on Denitrification Efficiency Associated with Culture Adaptation and C/N Ratio

Abstract

Stringent effluent limitations for nitrogen necessitate an accurate interpretation of the design and operation conditions of biological nitrogen removal systems. In this study, the effects of the nature of the organic substrate on biomass adaptation and response to different C/N ratios in terms of denitrification efficiency were investigated. A relatively high chemical oxygen demand (COD) utilized /NO x -N reduced ratio of 8.1 was obtained when an excess amount of readily biodegradable carbon was supplied, which is suggested as the conversion of substrate surplus into storage polymers. An anoxic yield of 0.64 g cell COD/g COD for a four-compound substrate mixture (acetate, propionate, ethanol and glucose), 0.63 g cell COD/g COD for a two-compound substrate mixture (acetate and propionate), and 0.5 g cell COD/g COD for methanol were calculated. Fluorescence in situ hybridization analysis showed that the b-subclass of proteobacteria was dominant in the seed and in cultures adapted to both the fourcompound and the two-compound substrate mixture, whereas in the methanoladapted culture significant amounts of b-proteobacteria were detected. The biocommunity composition, the type of organic compound and the COD/NO 3 -N ratio strongly influence the nitrate reduction and carbon utilization profiles. Methanol has been shown to select for a denitrifying population consisting of Paracoccus and Hyphomicrobium vulgare genera, when used as only external carbon source.

Anoxic–aerobic SBR system for nitrate, phosphate and COD removal from high-strength wastewater and diversity study of microbial communities

“…This observation supported complete denitrification of influent nitrate as ∼0.4 g/L of nitrate is converted to N 2 O in the current system. SDNR was observed to be within a range of 22.1-31.2 mgNO 3 -N/gVSS.h which is comparable to other reports where acetate was used as the sole carbon source during anoxic conditions [24,34]. Determination of y HD as well as denitrification through controlled experiments was beyond the scope of the study.…”

“…COD consumed /NO 3 removed were calculated to be in a range of 2.9-4.07 mg COD/mg NO 3 in the long anoxic phase. The required COD consumed /NO 3 removed ratio for complete denitrification, without PHA storage or biomass growth, is the theoretical minimum of 2.86 g COD/g nitrate [24,34,47]. The observed high COD consumed /NO 3removed were attributed to microbial energy storage in form of PHB, which was confirmed both by Sudan black staining and chloroform extraction method.…”

“…Additionally, high COD is essential to enrich DNPAOs over general denitrifying heterotrophs [8] and surplus carbon source sustains complete denitrification without nitrite accumulation [24,45]. This was further substantiated by absence of any nitrate or ammonia build up in LASA-SBR, ruling out the possibility of dissimilatory nitrate reduction to ammonia.…”

“…Determination of y HD as well as denitrification through controlled experiments was beyond the scope of the study. However, y HD has been determined through numerical interpretation of the COD consumed to bring about maximum reduction of nitrate in the medium [24]. The average y HD was observed to be 0.12 mg COD produced /mg COD removed which was very low compared to other reports due to a low ATP yield with nitrate (that is 40% lower than with oxygen) [35].…”

“…t = duration of anoxic condition, VSS = Volatile Suspended Solid in g/L Similarly under anoxic growth conditions y HD for the long anoxic period was determined as per Eq. (2) [24,25].…”