Comparative study of biological nutrient removal (BNR) processes with sedimentation and membrane‐based separation

Abstract

A membrane-enhanced biological phosphorus removal (MEBPR) process was operated in parallel with a conventional EBPR (CEBPR) process under challenging operating conditions to uncover fundamental differences in their ability to remove chemical oxygen demand (COD), nitrogen (N), and phosphorus (P) from municipal wastewater. Both systems exhibited the same potential to achieve excellent soluble-P removal when a favorable COD to P ratio was maintained in the influent. The MEBPR train generated a superior effluent quality when measured as total P. The CEBPR effluent contained significantly lower levels of nitrates due to the extra denitrification occurring in the sludge blanket of the secondary clarifier. The observed sludge yield in the MEBPR system was estimated to be between 0.23 and 0.28 g VSS/g COD, and this was 15% lower than the CEBPR sludge yield. When the influent volatile fatty acids (VFAs) became limiting, the CEBPR train exhibited better performance in the removal of soluble-P, due to the higher observed sludge yield and an overall greater denitrification activity that led to a more efficient use of VFAs in the anaerobic zone. After experiencing a severe deterioration of the biological P activity in both processes, the MEBPR train exhibited faster recovery than the CEBPR side. In this experimental work, it was demonstrated that an MEBPR process can sustain long-term satisfactory bio-P performance at HRTs as low as 7 h. However, the lower sludge yield and the reduced denitrification capacity are two important factors that impact the design of high rate membrane-assisted biological nutrient removal (BNR) processes.

Biological nitrogen and phosphorus removal in UCT-type MBR process

“…The comparison of sludge production in UCT-type MBR system is shown on Figure 7. Average sludge production for Mode 1, 2 and 3 was 0.28, 0.38 and 0.39 g VSS/g COD, respectively which was similar to other researchers (Lesjean et al 2003;Ramphao et al 2004;Monti et al 2006;Toit et al 2007). Although operating MLSS of lab unit was higher than BNR activated sludge, the characteristics of sludge production in UCT-type lab MBR is similar to other BNR activated sludge.…”

“…Recent investigations (Lesjean et al 2003(Lesjean et al , 2005Ramphao et al 2004;Monti et al 2006;Toit et al 2007) on the modification of MBR have shown that the biological removal of both N and P was successfully achieved with anaerobic-anoxic-oxic process trains with high solids concentrations. In UCT-like modification of MBR, the membrane unit was principally used as a replacement of settling tank.…”

Contribution of microfiltration on phosphorus removal in the sequencing anoxic/anaerobic membrane bioreactor

“…Some studies reported the good phosphorus removal performance (around 70% removal efficiency) even with poor condition of low F/M and long SRT [13,14,20,21]. Others showed the high P-removal efficiency of above 90% with a sufficient organic loading of above 300 mgCOD/L [17,18,31]. The value in parentheses is a standard deviation It seems that the organic loading rate, characteristics of feed (VFA/TP ratio), and carbon source type are still important factors on biological P-removal even in a MBR [32].…”

“…The high P-removal of more than 70% was achieved even with the long solids retention time (SRT) of 72 days without any external carbon sources. Adam et al [15] and Patel et al [16] reported the successful EBPR with the modified MBR systems with the SRT of 20 days and with a high ratio of short chain volatile fatty acids (VFAs) to total phosphorus in the feed [17]. Lesjean et al [18] installed a sidestream membrane unit combined with a University of Cape Town (UCT) process in a pilot plant scale, which provided anaerobic, anoxic, post-anoxic and aerobic stages, consecutively, in a separated reactor with a two-way internal recycle; one was from the anoxic to the anaerobic reactor, and the other from the aerobic to the post-anoxic reactor.…”

Enhanced reduction of excess sludge and nutrient removal in a pilot-scale A2O-MBR-TAD system

“…Table 4 shows survey results regarding the use of MBR in combination with known conventional BNR systems. Some of these were the works of Zhang et al (2009), Kim & Nakhla (2009), Khor et al (2006), and Monti et al (2006). It is well known that the prolongation of SRT in MBR lowers the sludge yield (Khor et al 2006).…”