Characterization of the extracellular polymeric substances and microbial community of aerobic granulation sludge exposed to cefalexin

This study characterizes the extracellular polymeric substances and bacterial community composition of aerobic granules exposed to cefalexin (CLX). The presence of CLX potentially decreases granular stabilities, resulting in a lowered granule diameter. Chemical oxygen demand and NH4+-N removal efficiencies were slightly decreased and the denitrification process was inhibited with CLX addition. Extracellular polymeric substance contents were significantly increased in aerobic granules exposed to CLX. The shifts of fluorescence intensities and peak locations in 3D-EEM fluorescence spectra indicated changes of EPS components. High-throughput sequencing analysis showed aerobic granules with CLX addition in synthetic wastewater had superior diversity of microbial species, and this was the reason that the level and components of EPS changed. The species richness for bacteria was increased from 341 to 352, which was revealed by Chao1. The Shannon index of diversity rose slightly from 3.59 to 3.73 with CLX addition. The abundance of Proteobacteria significantly decreased, while the abundance of Bacteroidetes and Chloroflexi underwent a highly significant increase in aerobic granules exposed to CLX.

How world's best public relations practice was not, but might have been achieved, in respect of a "biosolids" (stabilised sewage sludge) project

This is a case study which criticises the way a water authority has been trying to introduce “biosolids” (stabilised sewage sludge) projects. Two proposed projects have been abandoned after outcry by communities neighbouring earmarked sites. At the time of writing a third project was going ahead. This local scale clash reflects contests which are cropping up globally as water authorities are restricted in their use of land or sea dumping and ordered to introduce environmentally sustainable practices. The case study ends with a discussion of a strand of cultural theory which might have given the water authority a better understanding of the public issues involved. The article concludes that understanding cultural theory might assist organisations achieve world best practice in public relations when they face some of the pressing environmental and safety concerns of the 21st century.

Influence of mechanical mixing rates on sludge characteristics and membrane fouling in MBRs

The influence of shear intensity (G) induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in membrane bioreactors (MBRs) was investigated. Four MBRs were operated at different mechanical mixing conditions. The control reactor (MBR0) was operated with aeration only supplemented by mechanical stirring at 150, 300, and 450 rpm in MBR150, MBR300, and MBR450, respectively. It was found that the MBR300 demonstrated minimum rate of membrane fouling. The fouling potential of the MBR300 mixed liquor was lowest characterized by the specific cake resistance and the normalized capillary suction time (CSTN). Moreover, it was found that the mean particle size reduced with an increase in the shear intensity. These results reveal that membrane fouling can be significantly mitigated by appropriate shear stress on membrane fibers induced by mechanical mixing condition.

Granular Activated Carbon (GAC) adsorption in tertiary wastewater treatment : experiments and models

Wastewater treatment has always been a major concern in the developed countries. Over the last few decades, activated carbon adsorption has gained importance as an alternative tertiary wastewater treatment and purification process. In this study, granular activated carbon (GAC) adsorption was evaluated in terms of total organic carbon (TOC) removal from low strength synthetic wastewater. This paper provides details on adsorption experiments conducted on synthetic wastewater to develop suitable adsorption isotherms. Although the inorganics used in the synthetic wastewater solution had an overall unfavourable effect on adsorption of organics, the GAC adsorption system was found to be effective in removing TOC from the wastewater. This study showed that equation of state (EOS) theory was able to fit the adsorption isotherm results more precisely than the most commonly used Freundlich isotherm. Biodegradation of the organics with time was the most crucial and important aspect of the system and it was taken into account in determining the isotherm parameters. Initial organic concentration of the wastewater was the determining factor of the model parameters, and hence the isotherm parameters were determined covering a wide range of initial organic concentrations of the wastewater. As such, the isotherm parameters derived using the EOS theory could predict the batch adsorption and fixed bed adsorption results of the multi-component system successfully. The isotherm parameters showed a significant effect on the determination of the mass transfer coefficients in batch and fixed bed systems.

The in situ physiology of "Nostocoida limicola" II, a filamentous bacterial morphotype in bulking activated sludge, using fluorescence in situ hybridization and microautoradiography

The in situ physiology of the actinobacterial bulking and foaming filamentous bacterium "Nostocoida limicola" II was studied by fluorescence in situ hybridization/microautoradiography. Substrate assimilation patterns of pure cultures of this bacterium were different to those seen in activated sludge biomass samples. There was no evidence to suggest that "N. limicola" II preferred hydrophobic substrates, but evidence was produced to support the view that it is metabolically active under anaerobic conditions in activated sludge.

Ranking of pre-treatment technologies for reverse osmosis for water recovery

Agro-industries are a life-line for sustainable future of human kind. However, the wastewater generated by agro-industries poses direct threat to the same sustainable future by polluting the freshwater sources when discharged into those freshwater sources. Thus, we need both advanced treatment technologies to treat those wastewater streams generated and better reuse practices for the treated effluents. Reverse osmosis (RO) is one of the advanced treatments to treat dissolved solids that are present in agricultural wastewater streams. But, RO is very sensitive to suspended solids (SS) present in the wastewater streams. Those SS can foul the RO membrane and make it ineffective in producing treated effluent at desired rates. Therefore, suitable pre-treatment scheme is necessary to treat the agro-wastewater streams before passing through RO. This study focuses on the qualitative and quantitative ranking of the available conventional and modern pre-treatment technologies as pre-treatment for RO. This study considers wastewater that has been treated through a secondary treatment system for example activated sludge process as the target water that needs pre-treatment. Based on qualitative ranking of conventional pre-treatment options, the Lime clarification/Granular Media filtration (GMF) option is ranked as the best; whereas finescreens/ micro-screens option ranked as the least preferred option based on the scores they attained in treating the water quality parameters that are considered essential. Based on the quantitative ranking, the low pressure membrane technology such as ultra-filtration (UF) stood first and microfiltration (MF) stood last.

A preliminary study on the volume reduction of pre-treatment sludge in seawater desalination by forward osmosis

Forward Osmosis (FO) can be applied to recover water from the pre-treatment sludge of seawater reverse osmosis process. This study investigated the effect of the concentration of two draw solutions (MgCl₂ and NaCl) in the reduction of Fe(OH)₃ sludge volume and the effect of cross flow velocity on flux through FO membrane. Higher the concentration of NaCl and MgCl₂ higher the water flux observed. However, the percentage increase was not significant due to the occurrence of internal concentration polarisation. MgCl₂ draws marginally increased water flux than NaCl, when the conditions of feed and draw solutions were similar. Increase in cross flow velocity (from 0.25 to 1.0 m/s) marginally changed the flux with both draw solutions as higher cross flow velocities were unproductive to beat the external CP effect along the membrane surface. However, at 1 m/s, highest fluxes were obtained for both draw solutions.

Effect of feed temperature and membrane orientation on pre-treatment sludge volume reduction through forward osmosis

This study focuses on volume reduction of pre-treatment sludge as well as on dilution of reverse osmosis (RO) concentrate through emerging forward osmosis (FO) technology where RO concentrate draws water from the pre-treatment sludge (feed solution) in order to reduce pre-treatment sludge volume and increase the RO water recovery. Experiments were carried out using two different types of sludge i.e. (1) synthetic pre-treatment sludge (Lab sludge) which has lower salinity and (2) actual sludge from Perth Seawater Desalination Plant, Australia (Perth Seawater Desalination Plant (PSDP) sludge) which has higher salinity. Effect of membrane orientation (FO and pressure-retarded osmosis (PRO) modes) and temperature of pre-treatment sludge on permeate water flux was investigated. There was a significant increase in water flux from 3.2 to 10.2 LMH (i.e. ~3 times higher) when temperature increased from 20 to 40°C for Lab sludge in PRO mode. However, there is no significant effect of temperature on water flux in FO mode for Lab sludge. On the contrary for PSPD sludge, there was no effect on water flux with increase in temperature at PRO mode. Dissolved ions in the porous side increased the severity of concentrative internal concentration polarization; hence, it could reduce the flux. There was no significant change in water flux when temperature increased from 20 to 40°C for PSDP sludge in FO mode. However, higher amount of water has permeated from Lab sludge compared to PSDP sludge in FO mode. © 2014 © 2014 Balaban Desalination Publications. All rights reserved.

Electrospun granular hollow SnO2 nanofibers hydrogen gas sensors operating at low temperatures

In this paper, we present H2 gas sensors based on hollow and filled, well-aligned electrospun SnO2 nanofibers, operating at a low temperature of 150 C. SnO2 nanofibers with diameters ranging from 80 to 400 nm have been successfully synthesized in which the diameter of the nanofibers can be controlled by adjusting the concentration of polyacrylonitrile in the solution for electrospinning. The presence of this polymer results in the formation of granular walls for the nanofibers. We discussed the correlation between nanofibers morphology, structure, oxygen vacancy contents and the gas sensing performances. X-ray photoelectron spectroscopy analysis revealed that the granular hollow SnO2 nanofibers, which show the highest responses, contain a significant number of oxygen vacancies, which are favorable for gas sensor operating at low temperatures. © 2014 American Chemical Society.

Application of enhanced membrane bioreactor (eMBR) to treat dye wastewater

An enhanced membrane bioreactor (eMBR) consisting of two anoxic bioreactors (ARs) followed by an aerated membrane bioreactor (AMBR), UV-unit and a granular activated carbon (GAC) filter was employed to treat 50-100 mg/L of remazol blue BR dye. The COD of the feed was 2334 mg/L and COD:TN:TP in the feed was 119:1.87:1. A feed flow rate of 5 L/d was maintained when the dye concentration was 50 mg/L; 10 L/d of return activated sludge was recirculated to each AR from the AMBR. Once the biological system is acclimatised, 95% of dye, 99% of COD, 97% of nitrogen and 73% of phosphorus were removed at a retention time of 74.4 h. When the effluent from the AMBR was drawn at a flux rate of 6.5 L/m(2)h, the trans-membrane pressure reached 40 kPa in every 10 days. AMBR effluent was passed through the UV-unit and GAC filter to remove the dye completely.