Desalination and Water Treatment 201 (2020) 13–19 www.deswater.com October doi: 10.5004/dwt.2020.26020 Pilot system of microfiltration and reverse osmosis membranes for greywater reuse Taísa Machado de Oliveiraa,*, Cláudia Telles Benattib, Célia Regina Granhen Tavaresc aDepartment of Chemical Engineering, State University of Maringa, UEM, Gastao Vidigal Avenue 2431, CEP 87050-714, Maringa, Parana, Brazil, email: [email protected] (T.M. de Oliveira) bDepartment of Civil Engineering, State University of Maringa, UEM, Colombo Avenue 5790, CEP 87020-900 Maringa, Parana, Brazil, email: [email protected] (C.T. Benatti) cDepartment of Chemical Engineering, State University of Maringa, UEM, Colombo Avenue 5790, CEP 87020-900 Maringa, Parana, Brazil, email: [email protected] (C.R.G. Tavares) Received 6 April 2019; Accepted 24 April 2020 abstract Nowadays, one of the most interesting issues for wastewater recycling is the on-site treatment and reuse of greywater. It is reclaimed for non-potable on-site purposes (i.e., irrigation and toilet flushing). A dual membrane process for greywater treatment, low-pressure microfiltration (MF) membrane followed by a reverse osmosis (RO) process. The MF pretreatment was able to tolerate unfavorable variations in feed greywater and presented high removal efficiencies of apparent color, turbidity, and suspended particles. Consequently, the RO membrane system could be operated at a higher permeate flux and lower frequency of chemical cleaning. It has been verified that the method has recorded removals of turbidity, apparent color, total suspended solids, linear alkylbenzene sulfonate, and organic matter parameters up to 90%. Results achieved in the present study revealed that the membrane process was a technically viable alternative for greywater treatment. The effluent quality emphasized the possibility of reusing domestic sewage for purposes other than consumption, such as car washing and toilet flushing. Keywords: Domestic reuse; Greywater; Microfiltration; Reverse osmosis; Pilot scale; Treatment 1. Introduction higher pathogen content. In addition, as the greywater is the major source of wastewater generated in households The main challenge for the maintenance and preser- or office buildings [2,5], the source separation will greatly vation of water resources is to minimize the discharge of reduce the wastewater volume that must be diverted to domestic effluents. This is usually done by aerobic diges- biological treatment, as well as improve the operational tion, which is energy-intensive with a large footprint [1,2]. conditions of the biological treatment by maintaining the One of the options is domestic reuse. For this, it is necessary biological oxygen demand (BOD ) of the wastewater in to separate the domestic effluent into greywater, produced 5 relatively stable levels [6,7]. from bathtubs, showers, hand basins, laundry machines Some points relating to greywater still must be high- and kitchen sinks, and blackwater, produced from the toi- lighted. Greywater is an important source of urban water lets [3,4]. Greywater usually allows easier treatment than that may be suitable for relatively easy on-site treatment blackwater, which contains higher organic matter load and and reuse [5,7]. Greywater reuse will decrease freshwater * Corresponding author. 1944-3994/1944-3986 © 2020 Desalination Publications. All rights reserved. 14 T.M. de Oliveira et al. / Desalination and Water Treatment 201 (2020) 13–19 use, and minimize the demand and global costs on drink- storage tank, a volume calculated based on the total of grey- ing water supplies [5]. Due to its characteristics, 30% of water generated during a whole day, thus guaranteeing the the organic fraction, and 9%–20% of nutrients, it may be a homogenization of the water derived from a variety of gen- beneficial source of irrigation water in yards [5,8]. However, erating sources. The greywater included wastewater from greywater has several factors that affect quantity and quality, baths, showers, hand washbasins, washing machines, and before proposing a treatment system, it is necessary to char- dishwashers. acterize the greywater generated in the residence to avoid both under and over-design of the treatment system [9,10]. 2.2. Description of the membrane pilot plant The treatment at some places is preferred to be done at household levels, where residents build their small treat- MF and RO trials were carried out on a pilot-scale ment plants and reuse water for themselves [11,12]. The membrane system. Fig. 1 presents a general scheme of onsite household greywater treatment requires a process the treatment process employed. The raw greywater was that can be easily operated and monitored by inhabitants, be poured into the storage tank 1, which contained a sub- compact, low cost, and produce good-quality effluent that merged pump (B1) controlled by a level switch. This pump is safe for reuse [12,13]. Greywater is generally reclaimed was inside an aluminum net with 1 mm mesh size open- for various applications, such as non-potable reuse (flush- ings to retain clothing fibers, hairs, and other residues. ing toilets, irrigation, washing cars, recharging aestheti- The greywater was then suctioned by a pressurized pump cally pleasing natures, or under groundwater systems) [14]. (B2) into the MF module (tank 2) and the permeate was In terms of various applications, the reclaimed greywater conducted to the storage tank 3. The transmembrane pres- should meet appropriate water quality standards or guide- sure (TMP) and velocity were controlled by an electronic lines to ensure its safe and sustainable reuse [15,16]. panel. The permeate from the storage tank 3 was pumped Greywater treatment and reuse schemes have already (B3) into the RO system which contained a spiral-wound been piloted in many countries around the world, employ- cartridge. The permeate from the RO unit was then con- ing different methods of treatment resulting in varying ducted into the storage vessel (tank 4), while the retentate/ levels of system complexity and cost [17–20]. Thus, to meet concentrated effluent was discarded. greywater reuse standards, various membrane-based tech- MF system consisted of one module with two parallel niques have been widely adopted to treat greywater for hollow fibers submerged membranes. The MF was provided producing water with superior quality [21]. Because this by the Brazilian Company PAM Membranes (Rio de Janeiro, technology can be very efficient for allowing high rates of Brazil). The fibers were made of polyamide material, dis- contaminants removal, the low necessity of chemical prod- tributed vertically, and fixed in the extremities of the car- ucts to conduct the treatment, smaller area to implement tridges. The upper extremity received the aperture of filter- the treatment unit, and lower production of residues, the ing fibers for the permeate exit. MF was operated in a cross- membrane separation processes (MSP) can be more com- flow configuration. Details on the membrane cartridges are petitive in terms of costs in relation to a conventional treat- listed in Table 1. ment system [22]. A pilot system treating real greywater in RO system used for the tests contained a 6.3 cm diam- a grey house with an ultrafiltration hollow-fiber submerged eter × 53.3 cm length stainless pressure vessel. Housed membrane bioreactor (MBR) achieved removals of approxi- within the pressure vessel was a 6.1 cm diameter RO mem- mately 87% of chemical oxygen demand (COD) and 80% of brane provided by FilmTecTM membranes (Minnesota, USA) anionic surfactants, and total suspended solids (TSS) were (Model Number TW30-2521), as described in Table 2. reduced from 95 mg L−1 in the influent to 8 mg L−1 in the Previous data collected about the used household effluent [5]. However, there is still a lack of information on cleaning products showed that chlorine was an element the behavior of membrane systems under real conditions present in the commonly used chemicals. Thus, a carbon fil- in the case of single houses. ter was installed in the piping of the RO supply to prevent Thus, this paper aims to monitor a pilot system for the presence of chorine in the RO module, as the RO mem- on-site greywater treatment in a single household in Brazil, brane was intolerant to this element. The activated carbon with a focus on treated greywater quality and membrane may be used to remove chlorine with little degradation or performance during 60 d of operation. The treatment system damage to the carbon [23], so the carbon filter prevented included an MSP with pressured microfiltration (MF) and possible membrane damage due to the presence of chlorine. reverse osmosis (RO) membranes. The evaluation of grey- water treatment was conducted based on the monitoring of 2.3. MF performance physicochemical parameters to assess greywater quality. To determine the performance of the MF, the pilot sys- tem was operated for a period of 60 d for 8 h a day at the 2. Materials and methods residence understudy, totaling 480 h of operation. Four cycles of 120 h of operation were performed and evalu- 2.1. Collection location ated. The system was operated at a TMP of 0.50 ± 0.05 bar. The treatment system was implemented in a 4 per- The TMP remained constant, resulting in the reduction of sons-household (useful area of 390 m2), located in Brazil. permeate flux over time. The times for filtrate and back- The residential sewer line was adapted to separate grey- washing pulses were 30 and 2 min respectively. There was water from blackwater. Then, blackwater was directed into no additional stirring in the vessel. Also, the permeate flux the sewer system, while greywater was directed into a 600 L was monitored to determine the backwashing efficiency in T.M. de Oliveira et al. / Desalination and Water Treatment 201 (2020) 13–19 15 Fig. 1. Schematic representation of the pilot system B1 – Hydrobloc pump D300 X 32501 KSB submerged suction pump of the affluent.