Development of membrane bioreactor (MBR) process applying novel low fouling membranes

Abstract

Water is a part and parcel of human life. Water contaminated from industry and agriculture with heavy metal ions, pesticides, organic compounds, endocrine disruptive compounds, nutrients (phosphates, nitrates, nitrites) has to be effi-ciently treated to protect humans from being intoxicated with these compounds or with bacteria. Clean water as basis for health and good living conditions is too far out of reach for the majority of the population in the world (Bionexgen, 2013). Water recycling is now widely accepted as a sustainable option to re-spond to the general increase of the fresh water demand, water shortages and for environmental protection. Water recycling is commonly seen as one of the main options to provide remedy for water shortage caused by the increase of the water demand and draughts as well as a response to some economical and environmental drivers. The main options for wastewater recycling are industri-al, irrigation, aquifer recharge and urban reuse (Pidou, M., 2006). Among the industrial wastewaters, the textile industry is long regarded as a water intensive sector, due to its high demand of water for all parts of its pro-cedures. Accordingly, textile wastewater includes quite a large variety of con-tents, chemicals, additives and different kinds of dyestuffs. The main environ-mental concern with this waste water is about the quantity and quality of the water discharged and the chemical load it carries. To illustrate, for each ton of fabric products, 20 – 350 m3 of water are consumed, which differs from the color and procedure used. The quality of the textile wastewater depends much on the employed coloring matters, dyestuffs, accompanying chemicals, as well as the process itself (Brik et al., 2006). MBR technology is recognised as a promising technology to provide water with reliable quality for reuse. It provides safely reuse water for non-potable use. But the treated textile wastewater by MBR technology alone can’t comply with the reuse or discharge standard in many countries due to its colouring matters and dyestuffs remained in the effluent, if otherwise, MBR is associated with other technology like NF, RO, other processes or the applied membrane is modified or a novel MBR is applied. Fouling is another limiting factor for worldwide application of MBR technology especially in high-strength industri-al wastewater like textile wastewater. Moreover, membrane fouling is regarded as the most important bottleneck for further development of MBR technology. It is the main limitation for faster development of this process, particularly when it leads to flux losses that cleaning cannot restore (Howell et al. 2004). In this thesis work, a novel membrane bioreactor (MBR) process was devel-oped by modifying a applied commercial PES UF membrane in MBR module by nano-structured novel coating through polymerisable bicontinuous micro-emulsion (PBM) process with the purpose of having higher hydrophilicity and low fouling propensity. Before starting the MBR experiments, some characteri-sation tests such as SEM, AFM images analysis, roughness measurements, pore geometry, contact angel, standard salt rejections, model textile dye rejec-tions were performed. In addition, fouling tests using two laboratory cross flow testing units were conducted as well. To reach the ultimate goal of research, 6 sheets of novel coated membranes with size of 30 cm × 30 cm were prepared and these were used to prepare a three-envelope MBR module of 25 cm × 25 cm in size (total membrane area 0.33 m2) similar to that of a commercially available three-envelope PES UF MBR module. This novel MBR module was tested in a submerged lab-scale MBR pilot plant (tank volume ca. 60 L) for about 6 months using model textile dye wastewater (MTDW) as test media for all experiments with the aim of having uniform compositions with respect to time. The tests were done based on carefully selected operation conditions. Prior to testing of the novel membrane module MBR, experiments were carried out with a commercial PES UF MBR module using the same pilot plant set up and the same selected operating conditions for about 10 months. After comple-tion of trials with the novel coated MBR module, similar experiments were carried out again with a commercial PES UF MBR module to check the simi-larity of the biological sludge conditions and other operation conditions as well. In short, the sequences of the experiments were as follows: Commercial PES UF MBR (10 months) →novel membrane coated MBR (6 months)→PES UF MBR (1.5 months) The ultimate goal of the experiments was to compare the results between the commercial MBR and novel coated MBR module in order to demonstrate im-provement regarding fouling propensity and permeate water quality. The performance analysis shows that the novel coated MBR module compared to the commercial MBR module has 7% points higher COD removal efficien-cy, 20% points higher blue dye removal efficiency, high antifoul-ing/antimicrobial properties, resulting in a very low-fluctuating and highly ro-bust MBR process which looks promising with regard to economic viability. Since the newly developed MBR module worked excellent on laboratory scale it consequently should be deployed at an industrial site to be tested with real ii wastewater. Therefore, this novel three-envelope MBR module is on the way to be tested with real wastewater in a textile factory in Tunisia. The findings of these on-site pilot trials will serve as a basis for further improvement and even-tually pilot trails with larger membrane area will be addressed