A low pressure gravity-driven membrane filtration (GDM) system for rainwater recycling: Flux stabilization and removal performance

Abstract

Rainwater is a nature resource, which can be widely used for non-potable and potable applications in water scared countries after appropriate treatment. Gravity-driven membrane filtration (GDM) process is a promising technology for decentralized rainwater treatment due to no backwashing, flushing and chemical cleaning. In this study, we established a single lab-scale GDM system for the stored rainwater (simulative cellar rainwater) treatment with two months operation, and a stored tap water was used as a compared system to evaluate the permeability and organics removal performance. Results showed that GDM exhibited a good performance for bacteria and turbidity removals, but the removal performance of DOC was undesirable due to the low rejection of low molecular-weight fulvic. Additionally, the permeate flux reached stable with the value of 6-6.5 L/mh during 60 days operation in the rainwater system, however, the tap water system stabilized only at 4 L/mh. Hydraulically reversible resistance accounted for large proportions (90%) of the total resistance, which indicated that the flux could be recovered by simple physical flushing. The bio-fouling layer adhered on the membrane surface was characterized at the end of the filtration experiment. Higher bio-activity with lower EPS (polysaccharides and proteins) contents of the fouling layer were found in the rainwater system compared with the control system, which was the main reason for the higher flux. These results show that rainwater can be treated in a single GDM process with low maintenance, which makes the process suitable for decentralized water supply.

Performance of an innovative gravity-driven micro-filtration technology for roof rainwater treatment

“…3, a great part of CODcr in the raw rainwater was removed after GDM treatment that achieved an effluent CODcr between 8~16.8 mg/L, well below the Recycling Water limits but slightly exceeded the standards for drinking water quality, contributed an average reduction of 65.5%. Nevertheless, previous studies have reported that the organic matters cannot be effectively removed by micro-filtration process, as stated by Ding et al [15], the removal rate of organic matter by micro-filtration process was lower than 20%, this discrepancy with current study may be attributable to the differences in properties of membrane adopted. Our observations demonstrated that in case of rainwater treatment, the GDM process using ceramic membranes enables a considerable reduction in these pollutants that cause CODcr.…”

“…Similarly, Wu et al have recorded that a pilot GDM systems were able to remove almost all of the particles (i.e., turbidity), 94% of viable cells, and most of TEP (41-85%) [43]. However, Ding et al reveal that DOC (especially the organics containing unsaturated bonds or aromatic chromophores) of rainwater were not removed well (lower than 30%) in GDM process [15]. Whereas in another study, Wu et al also found that GDM did not retain humics and low molecular weight neutrals during sea water treatment [32].…”

“…Emerged as a low energy consumption and chemical free technology, the gravity driven membrane (GDM) filtration process is receiving more attentions and has been introduced to treat rainwater prior to use [12][13][14]. Although the GDM process has demonstrated an excellent performance in removing the bacteria and suspended particles in surface water and wastewater treatment, however, this energy-saving technology still has some disadvantages, such as, the removal of low molecular-weight substances is not ideal [15]. Thus, new technologies targeting to improve the dissolved organic matter removal in GDM systems need to be explored.…”

“…However, it is noted that, compared to the hollow fibre membrane modules, the flat sheet membrane modules, can offer superior environment for the growth, movement and predation behaviour of eukaryotic in the bio-fouling layer, which is responsible for the reduction of bio-fouling layers on the membrane, (i.e., form an open, heterogeneous, and porous fouling layer), and consequently contribute to a relatively higher level of permeate flux. Moreover, since previous studies have stated that membrane fouling was primarily due to the deposition of soluble microbial products such as polysaccharides, proteins, and fulvic substances onto the membrane surface [21,22], the ceramic membrane, which possesses properties of higher hydrophilic, thus has the potential to prevent the formation of cake layer (because hydrophilic membrane can effectively prevent those substances from migrating to the membrane surface). Such characteristic offers a possibility to improve the overall permeate flux of GDM system.…”

Technical and economical viability of a graywater recycling system employing an integrated preliminary settlement and filtration process

“…To calculate benefitcost ratio and PBPs, future water price needs to be predicted. In this regard, due to water contamination and climate changes, the future drinking water price is expected to rise (Ding et al 2017). In practice, during 2004-2018, Beijing and Guangzhou had experienced 72.4 and 122% increases in household water prices, respectively, which suggests an annual increase of 5-9% in the next decade.…”