Effect of the Carbon Source on Nitrifying in an Activated Sludge System Treating Aquaculture Wastewater

Abstract

The nitrogen in the aquaculture wastewater can have significant effects on receiving water bodies like eutrophication and ammonia toxicity to fish communities. Removing nitrogen by nitrification-denitrification can reduce the potential impact of aquaculture wastewater discharge. Nitrification is affected by different factors including dissolved oxygen, temperature, pH, alkalinity, toxicity, unionized ammonia and substrate concentration. All these parameters affect ammonia-oxidizing and nitrite-oxidizing bacterial activity.The aim of this work is to study the effect of the carbon source on nitrifying bacterial activity in an activated sludge treating aquaculture wastewater.An activated sludge (AS) system was set up and operated continuously for 180 days. The operation was divided into two phases. During Phase I a source of organic carbon (CH 3 COONa) with a C/N level of 2.4 (operation days 1 to 101) was fed into the system, while in Phase II a source of inorganic carbon (NaHCO 3 ) with a C/N level of 16.2 was fed into the system (operation days: 102 to 180).The maximum NH 4 + -N removal efficiency was 49.7% during the Phase I, during which the NO 3 --N and NH 3 + -N concentrations were 37.1 ± 14.0 and 2.9 ± 1.1 mg/L, respectively. In Phase II, the maximum NH 4 + -N removal efficiency was 45% and NO 3 --N and NH 3 + -N effluent concentrations were 2.8 ± 0.3 mg/L and 210 ± 49 mg/L, respectively. Ammonia-and nitrite-oxidation decreased in Phase I from 0.231 ± 0.005 mg NH 4 + /gVSS min to 0.018 ± 0.004 mg NH 4 + -N/gVSS min and in Phase II from 0.049 ± 0.011 mgNO 2 --N/gVSS min to 0.010 ± 0.002 mgNO 2 --N/gVSS min.

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

“…This indicates that microbial cells can be disrupted by DC corona, which is in agreement with our previous research [26]. Although direct evidence of microbial cell disruption could be obtained from the visual inspection, it is difficult to tell which polarity of the DC corona has better pretreatment performance since the very fact concerned is not the degree of cell disruption but the release of organic matters into the sludge that act as a carbon resource in the following digestion process [1,27]. Accordingly, the measurementment of organic matter content released from the disrupted microbial cell to the sludge solution becomes a reasonable method to quantitatively estimate the pretreatment performance, which has been widely used by previous researchers [28,29].…”

“…This process leads to the consumption of nitrogen elements, thus resulting in the reduction of NH 3 -N in the WAS. In addition, the possible nitrification in sludge will oxidize ammonia into NO 3 - [27], which also leads to a decrease in NH 3 -N. Based on the viewpoints stated above, it is easy to understand why ΔN% decreases with treatment time.…”