Kees Roest

A review on dynamic membrane filtration: Materials, applications and future perspectives

This paper presents a comprehensive evaluation of the current status of dynamic membrane (DM) technology as an alternative to membrane bioreactor (MBR) systems. DM filtration makes use of a physical barrier (e.g. cloth or mesh) on which a cake layer is formed. It is already used in traditional filtration systems, but applications in biological wastewater treatment are still at its infancy. Dynamic filtration of sludge has lower risk of fouling and requires less energy and lower capital costs compared to MBR. A review of the state-of-art in both DM materials and configurations is presented. Factors affecting DM performance are discussed in order to determine the optimum and critical approaches for membrane operation. Future perspectives to enhance the applicability and functionality of the technology regarding the treatment and membrane performance are presented.

Recovery of a Nitrosomonas-like 16S rDNA sequence group from freshwater habitats

In order to study the diversity of ammonia-oxidising bacteria in freshwater habitats, including sediments, a molecular approach focused on the sequencing of 16S rDNA was adopted. 16S rDNA sequences showing affinity with the beta-subgroup of ammonia-oxidising bacteria were recovered by specific PCR of directly isolated DNA from freshwater samples, and samples from brackish water and Glyceria maxima rhizosphere were included in the analysis for comparison. The ammonia oxidiser-like sequences recovered from several locations, which exhibit differences in the composition of their total microbial communities as indicated by denaturing gradient gel electrophoresis, formed a strong monophyletic cluster including Nitrosomonas ureae. This is the first report presenting sequences from an apparently dominant group of Nitrosomonas-like organisms among the beta-subdivision of ammonia-oxidising bacteria in freshwater environments. This group of sequences extends the known diversity within the beta-subgroup of ammonia-oxidisers. The new sequences related to Nitrosomonas ureae do not match with some published primers and probes designed for the detection of Nitrosomonas species, which may explain why these sequences have not previously been detected in freshwater habitats. The sequence diversity detected within this group of sequences was minimal across the environments examined, and no patterns of distribution were indicated with respect to environmental factors such as sediment depth or location.

Molecular monitoring of microbial diversity in expanded granular sludge bed (EGSB) reactors treating oleic acid

Abstract A molecular approach was used to evaluate the microbial diversity of bacteria and archaea in two expanded granular sludge bed (EGSB) reactors fed with increasing oleic acid loading rates up to 8 kg of chemical oxygen demand (COD) m(-3) day(-1) as the sole carbon source. One of the reactors was inoculated with granular sludge (RI) and the other with suspended sludge (RII). During operation, the sludge in both reactors was segregated in two layers: a bottom settled one and a top floating one. The composition of the bacterial community, based on 16S rDNA sequence diversity, was affected most during the oleate loading process in the two reactors. The archaeal consortium remained rather stable over operation in RI, whereas in RII the relative abundance of Methanosaeta-like organisms became gradually weaker, starting in the bottom layer. In the range of oleate loads evaluated, 6 kg of COD m(-3) day(-1) was found as the maximum value that could be applied to the system. A further increase to 8 kg of oleate-COD m(-3) day(-1) induced a maximal shift on the microbial structure of the sludges. At this time point, methanogenic acetoclastic activity was not detected and only very low methanogenic activity on H(2)/CO(2) was exhibited by the sludges.

Water recovery from sewage using forward osmosis.

This research is part of the Sewer Mining project aimed at developing a new technological concept by extracting water from sewage by means of forward osmosis (FO). FO, in combination with a reconcentration system, e.g. reverse osmosis (RO) is used to recover high-quality water. Furthermore, the subsequent concentrated sewage (containing an inherent energy content) can be converted into a renewable energy (RE) source (i.e. biogas). The effectiveness of FO membranes in the recovery of water from sewage has been evaluated. Stable FO water flux values (>4.3 LMH) were obtained with primary effluent (screened, not treated) used as the feed solution. Fouling of the membrane was also induced and further investigated. Accumulated fouling was found to be apparent, but not irreversible. Sewer Mining could lead to a more economical and sustainable treatment of wastewater, facilitating the extraction of water and energy from sewage and changing the way it is perceived: not as waste, but as a resource.

Enrichment and detection of microorganisms involved in direct and indirect methanogenesis from methanol in an anaerobic thermophilic bioreactor.

To gain insight into the microorganisms involved in direct and indirect methane formation from methanol in a laboratory-scale thermophilic (55°C) methanogenic bioreactor, reactor sludge was disrupted and serial dilutions were incubated in specific growth media containing methanol and possible intermediates of methanol degradation as substrates. With methanol, growth was observed up to a dilution of 108. However, when Methanothermobacter thermoautotrophicus strain Z245 was added for H2 removal, growth was observed up to a 1010-fold dilution. With H2/CO2 and acetate, growth was observed up to dilutions of 109 and 104, respectively. Dominant microorganisms in the different dilutions were identified by 16S rRNA-gene diversity and sequence analysis. Furthermore, dilution polymerase chain reaction (PCR) revealed a similar relative abundance of Archaea and Bacteria in all investigated samples, except in enrichment with acetate, which contained 100 times less archaeal DNA than bacterial DNA. The most abundant bacteria in the culture with methanol and strain Z245 were most closely related to Moorella glycerini. Thermodesulfovibrio relatives were found with high sequence similarity in the H2/CO2 enrichment, but also in the original laboratory-scale bioreactor sludge. Methanothermobacter thermoautotrophicus strains were the most abundant hydrogenotrophic archaea in the H2/CO2 enrichment. The dominant methanol-utilizing methanogen, which was present in the 108-dilution, was most closely related to Methanomethylovorans hollandica. Compared to direct methanogenesis, results of this study indicate that syntrophic, interspecies hydrogen transfer-dependent methanol conversion is equally important in the thermophilic bioreactor, confirming previous findings with labeled substrates and specific inhibitors.

Selective enrichment of Geobacter sulfurreducens from anaerobic granular sludge with quinones as terminal electron acceptors

A quinone-respiring, enrichment culture derived from methanogenic granular sludge was phylogenetically characterized by using a combined cloning-denaturing gradient gel electrophoresis (DGGE) method, which revealed that the consortium developed was dominated by a single microorganism: 97% related, in a sequence of 1520 base pairs, to Geobacter sulfurreducens. The enrichment culture could grow with acetate, formate or H2 when humic acids, the humic model compound, anthraquinone-2,6-disulfonate (AQDS), or chelated Fe(III) was provided as a terminal electron acceptor. The occurrence of a humic acid- or quinone-respiring microorganism in the microbial community of a wastewater treatment system suggests that this type of microorganisms may play a potential role in anaerobic bioreactors treating humus-containing wastewaters.