Enhancement of Waste Activated Sludge Protein Conversion and Volatile Fatty Acids Accumulation during Waste Activated Sludge Anaerobic Fermentation by Carbohydrate Substrate Addition: The Effect of pH

Abstract

Volatile fatty acids (VFAs), the carbon source of biological nutrients removal, can be produced by waste activated sludge (WAS) anaerobic fermentation. However, because of high protein content and low carbon to nitrogen mass ratio (C/N) of WAS, the production of VFAs, especially propionic acid, a more preferred VFA than acetic acid for enhanced biological phosphorus removal (EBPR), is limited. After the addition of carbohydrate (rice was used as the model matter) to the WAS anaerobic fermentation system to balance the C/N ratio, the effect of pH on WAS protein conversion and VFAs production was investigated in this paper. Experimental results showed that the addition of carbohydrate matter caused a remarkable enhancement of WAS protein conversion and protease activity, and an apparent synergistic effect between WAS and carbohydrate matter was observed. The study of pH effect revealed that pH influenced not only the total VFAs production but the percentage of individual VFA. The maximal VFAs production (520.1 mg COD per gram of volatile suspended solids (VSS)) occurred at pH 8.0 and a fermentation time of 8 d, which was more than three times that at uncontrolled pH (150.2 mg COD/g VSS). The analysis of the composition of VFAs showed that propionic acid ranked first at pH 6.0-9.0 (around 50%) whereas acetic acid was the dominant product at other pHs investigated. Thus, the suitable conditions for propionic acid-enriched VFAs production were pH 8.0 and a time of 8 d. Further investigation showed that as there was more fermentation substrate consumption with lower biogas generation at pH 8.0, improved VFAs production was observed. Also, the key enzymes relevant to propionic acid formation exhibited the highest activities at pH 8.0, which resulted in the greatest propionic acid content in the fermentative VFAs. The 16S rRNA gene clone library demonstrated that Clostridia, beta-Proteobacteria, and Bacteroidetes were the dominant microbial community when the current anaerobic fermentation system was operated at pH 8.0. With the fermentative VFAs as the additional carbon source of municipal wastewater, the EBPR performance was significantly increased.

Assess the Denitrification Potential of Fermented Biosolids Based on Their Specific Denitrification Rate (Sdnr)

“…However the difference is not as significant, because for both sets, the results were still much lower than the minimum required C/N ratio of 20:1 (or ideally of 30:1) to be considered as an effective external carbon sources. [3] Note that the C/N ratio or rbCOD/NH 4 + is the most important independent variables in this experiment. Because the fermented biosolids would be added back to the anoxic zone as external carbon source, hence a lower C/N ratio would means: with the same amount of added carbon, more nitrogen would be introduced back into the system.…”

Utilization of Volatile Fatty Acids from Microalgae for the Production of High Added Value Compounds

“…The purpose behind mixing different waste streams is the development of a substrate with a balanced carbohydrate: protein ratio, which in turn answers for a balanced C/N ratio. According to various experiments [27,28] it has been found that a higher C/N ratio (around 20/1-30/1) can be beneficial to the microorganisms responsible for acidogenesis. Furthermore, it is believed that the carbohydrate amount can have a synergistic effect with WAS.…”

“…The composition of the acid fraction of the liquid product depends on various variables, like the type of waste stream used and the fermentation conditions (pH, fermentation time, etc.) [1,28]. The pH value for example plays an important role in the synthesis of different VFA.…”

“…Propionic acid is supposed to enhance the efficiency of biological phosphorus removal from wastewater, when VFA are used as a carbon source for nutrient removal [28]. For that reason, Feng et al mixed WAS with boiled rice in order to produce a rich in carbohydrates substrate suitable for VFA production.…”

Distillation Cleanup Preceded GC Determination of Short-Chain Monocarboxylic Acids in Aqueous and Solid Samples of Wastewater Origin

“…Polyethylene glycol (PEG) [7][8][9][10][11], generally treated with nitroterephthalic acid [1,[12][13][14][15] to deactivate alkaline sites, is most often used as a stationary phase for separation of short-chain fatty acids. Other polar stationary phases were also applied to analyse water samples; for example polybiscyanopropyl (90%) -cyanopropylphenylsiloxane (10%) stationary phase to determine acids extracted from plants [16].…”