Abstract:
The objective of this research was to investigate the effect of using supplements which were acid fermentation products of primary sludge (AFP) or molasses distillery wastewater (MDW) as an alternative external carbon source for improvement of the removal efficiency and sludge settleability of a biological nutrient removal (BNR) system to treat domestic wastewater (DWW). The experimental research was designed as lab-scales of both a Modified University of Cape Town (MUCT) process and an acid fermenter with a three phase experiment and seven operating conditions. The experimental results, in the first phase, to find out the optimum SRT (10, 20 and 30
days) for MUCT system operation with DWW, showed that the SRT of 20 days was the best operating condition to obtain the COD, TKN and TP removal efficiencies (p<0.05), with averages of 92 %, 95 % and 44 %, respectively. The supplemental glucose as a pre-external carbon source in the second phase with a COD/TKN ratio in the influent of 10:1, resulted in significantly higher COD, TKN and TP removal efficiencies compared to those of the first phase (p<0.05), with averages of 94 %, 96 % and 82 %, respectively. For the third phase, the supplemental MDW with a COD/TKN in the influent of 9.7:1 yielded significantly higher removal efficiencies of TN (average of 75 %) and
TP (average of 96 %) and a higher sludge settleability or a lower DSVI (diluted sludge volume index) value of about 126 ml/g) than those operated with DWW with a COD/TKN ratio in the influent of 5:1 or supplemental AFP (p<0.05). But a high red-brown molasses color and a significantly higher COD concentration remained in the effluent (p<0.05). Using the supplemental AFP with a COD/TKN in the influent of 5:1, it appeared that the TN (average of 65 %) and TP (average of 33 %) removal efficiencies and sludge settleability (average DSVI of 169 ml/g) were significantly lower than those of the first phase (p<0.05) with severe biological foaming occurring in the aeration tank.
It could be concluded that acid fermentation products of primary sludge was not suitable for the improvement of BNR performance, especially when domestic wastewater contained a relatively high nitrogen concentration and molasses distillery wastewater was also not suitable to be used as an external carbon source for the BNR system due to the high concentration of COD and color remaining in the effluent.