Cicek, N. 2003. A review of membrane bioreactors and their potential application in the treatment of agricultural wastewater. Canadian Biosystems Engineering/Le génie des biosystèmes au Canada 45: 6.37-6.49. Membrane Bioreactors (MBRs) can be broadly defined as systems integrating biological degradation of waste products with membrane filtration. They have proven quite effective in removing organic and inorganic contaminants as well as biological entities from wastewater. Advantages of the MBR include good control of biological activity, high quality effluent free of bacteria and pathogens, smaller plant size, and higher organic loading rates. Current applications include water recycling in buildings, wastewater treatment for small communities, industrial wastewater treatment, and landfill leachate treatment. This paper summarizes the potential applications of the MBR technology for the treatment of wastewater from agricultural sources. Anaerobic digestion coupled with an aerobic/anoxic membrane bioreactor could be utilized for treating manure and wastewater from livestock operations to levels suitable for direct reuse or safe discharge to surface water bodies. Wastewater generated from industries such as slaughterhouses, meat, dairy, egg, and potato processing and liquor production could potentially be treated with MBRs resulting in compact systems producing high quality reusable water. Also effective removal of nitrates, herbicides, pesticides, and endocrine disrupting compounds may be achieved by MBRs.

A review of membrane bioreactors and their potential application in the treatment of agricultural wastewater

Accumulating evidence suggests that mitochondrial membrane permeabilization (MMP) is a rate-limiting step of programmed (developmental) cell death as well as stressinduced cell death, including in the context of anti-cancer chemotherapy or viral infection. This notion is re-enforced by the observation that the knock-out of proteins involved in the pathways leading to MMP or closely linked to MMP (Bax, Bak, Bim, AIF, cytochrome c, Apaf-1, caspase-9 etc.) results in a major phenotype. Recently, we have launched the working hypothesis that MMP may be a rate-limiting event of apoptosis induction even when cell death is initiated through a primary stimulus affecting other organelles than mitochondria such as nuclei (via p53 activation), lysosomes (via activation of cathepsins) or the endoplasmic reticulum (ER). The proapoptotic agents that specifically act on the ER include tunicamycin (TM, which inhibits N-linked glycosylation), brefeldin A (BFA, which inhibits ER-Golgi transport) and thapsigargin (TG, which inhibits the sarcoplasmic/endoplasmic Ca-ATPase SERCA). Whereas BFA and TG elicit a local unfolded protein response, TG depletes ER Ca and thus impinges on Ca signaling. Mouse embryonic fibroblasts lacking both Bax and Bak become resistant to apoptosis induction by TM and BFA, an observation that may be attributed to the obligatory participation of Bax and Bak in MMP induction, or alternatively, suggests an as yet poorly characterized function of Bax and Bak at the ER level. Indeed, Bax redistributes both to mitochondria and to ER upon apoptosis induction, and overexpression of Bax reportedly causes a loss of ER Ca content. To probe the importance of MMP for ER stress-induced cell death, we assessed the effects of two local MMP inhibitors, Bcl-XL and vMIA on cellular alterations provoked by TM, BFA, and TG (Figure 1). Bcl-XL is found inserted in intracellular membranes (in particular the outer mitochondrial membrane) and is known to stabilize the mitochondrial membrane barrier function by local interactions with pore forming proteins contained in the permeability transition pore complex, namely the voltage-dependent anion channel (VDAC), the adenine nucleotide translocase (ANT), and pro-apoptotic Bcl-2 family members. In contrast to Bcl-2, ± 14 no local ER effects have been described for Bcl-XL. 15 Viral mitochondrial inhibitor of apoptosis (vMIA) is encoded by the Cytomegalovirus UL37 gene, has no obvious structural similarity with Bcl-2-like molecules, and is exclusively found in mitochondrial membranes, where it specifically interacts with ANT but not with VDAC, as shown by mass spectroscopic identification of vMIAinteracting proteins and confirmed by co-immunoprecipitation assays. ± 18 TM, BFA, and TG induced signs of MMP in several different cell lines including B cell lymphoma BJAB (Figure 1a) and cervical carcinoma HeLa cells (Figure 1b). Such signs consist in the loss of the mitochondrial transmembrane potential (DCm), as determined by means of the DCm-sensitive fluorochrome, DiOC6 3 (Figure 1a), and the release of cytochrome c from mitochondria, as determined by immunofluorescence analysis (Figure 1b,c). Thus, both the permeability of the inner membrane (on which the DCm builds up) and that of the outer membrane (which retains cytochrome c) were compromised by the three different ER-targeted toxins. ER stress-induced MMP was an early event since it was detectable in a fraction of cells that still lack signs of chromatin condensation (not shown). Stable transfection with vMIA and Bcl-XL prevented ER stressinduced MMP (Figure 1a,b,c), both in BJAB and in HeLa cells. It has been reported that, in determined circumstances, for instance in type I cells stimulated by CD95 ligation, Bcl-2-mediated MMP inhibition is not sufficient for the prevention of apoptosis. Therefore, we assessed whether MMP inhibition would suffice to suppress apoptosis induction by TM, BFA, or TG. Clearly, vMIA and Bcl-XL overexpression did reduce the frequency of cells which manifest caspase activation (not shown), nuclear chromatin condensation (Figure 1b), phosphatidylserine exposure on the outer leaflet of the plasma membrane (as determined with an Annexin V-FITC conjugate, Figure 1d), and loss of viability (as determined by staining with propidium iodide, PI, Figure 1e). In conclusion, it appears that MMP inhibition by Bxl-XL or vMIA can protect cells against apoptosis induction by ERspecific toxins. Using a monoclonal antibody specific for the apoptogenic conformation of Bax (6A7), we determined the putative link between vMIA-induced (presumably ANTmediated ± 18 apoptosis inhibition and the Bax/Bak mediated MMP induced by ER stress. ER stress did induce an apoptosis-associated change in Bax conformation, linked to its aggregation in cytoplasmic spots (Figure 2f), some of which coincide with mitochondria (as determined by confocal microscopy, not shown). vMIA did prevent the apoptosis associated conformational change of Bax, as well as its aggregation, a finding that may link our previous observation that Bax and ANT can interact to induce MMP. In conclusion, it appears that ER stress can induce apoptosis through a reaction that depends on pro-apoptotic members of the Bcl-2 family (Bax, Bak) and which involves MMP as a critical step towards cellular demise. Rather than Cell Death and Differentiation (2002) 9, 465 ± 467 ã 2002 Nature Publishing Group All rights reserved 1350-9047/02 $25.00

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Endoplasmic reticulum stress-induced cell death requires mitochondrial membrane permeabilization

The effects of the lengths of aeration and nonaeration periods on nitrogen removal and the nitrifying bacterial community structure were assessed in intermittently aerated (IA) reactors treating digested swine wastewater. Five IA reactors were operated in parallel with different aeration-to-nonaeration time ratios (ANA). Populations of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were monitored using 16S rRNA slot blot hybridizations. AOB species diversity was assessed using amoA gene denaturant gradient gel electrophoresis. Nitrosomonas and Nitrosococcus mobilis were the dominant AOB and Nitrospira spp. were the dominant NOB in all reactors, although Nitrosospira and Nitrobacter were also detected at lower levels. Reactors operated with the shortest aeration time (30 min) showed the highest Nitrosospira rRNA levels, and reactors operated with the longest anoxic periods (3 and 4 h) showed the lowest levels of Nitrobacter, compared to the other reactors. Nitrosomonas sp. strain Nm107 was detected in all reactors, regardless of the reactor's performance. Close relatives of Nitrosomonas europaea, Nitrosomonas sp. strain ENI-11, and Nitrosospira multiformis were occasionally detected in all reactors. Biomass fractions of AOB and effluent ammonia concentrations were not significantly different among the reactors. NOB were more sensitive than AOB to long nonaeration periods, as nitrite accumulation and lower total NOB rRNA levels were observed for an ANA of 1 h:4 h. The reactor with the longest nonaeration time of 4 h performed partial nitrification, followed by denitrification via nitrite, whereas the other reactors removed nitrogen through traditional nitrification and denitrification via nitrate. Superior ammonia removal efficiencies were not associated with levels of specific AOB species or with higher AOB species diversity.

Effects of aeration cycles on nitrifying bacterial populations and nitrogen removal in intermittently aerated reactors.

Improvement in post-treatment of digested swine wastewater

Wastewater nitrogen removal in Sbrs, applying a step-feed strategy: from lab-scale to pilot-plant operation.

A continuous-flow intermittent aeration (IA) process has been studied for nitrogen removal from anaerobically digested swine wastewater with high ammonium content. High nitrogen removal efficiency of average 91% total Kjeldahl nitrogen and 92% NH4-N was achieved in an IA system with an alteration of 1-h aeration and 1-h nonaeration. Nitrification and denitrification were found to be responsible for the nitrogen removal in the system. Nitrite and nitrate in the effluent were less than 1.0 mg/L and 8.0 mg/L, respectively. The specific nitrification and denitrification rates of the single-sludge IA culture were determined through batch experiments as 2.79–3.70 mgNO3-N/g volatile suspended solids-h and 0.59–1.03 mgNO3-N/g volatile suspended solids-h, respectively. In the IA process, the aeration period created favorable conditions for nitrifying bacteria (dissolved oxygen = 4–6 mg/L and oxidation-reduction potential = 80–100 mV), while the nonaeration period provided good environment for denitrifying bacteria...

Bin Liu

Papers

Nitrification/Denitrification in Intermittent Aeration Process for Swine Wastewater Treatment