## 3 Decentralized Treatment Systems
### Graywater Treatment
This issue was investigated by comparing the effectiveness in CEC removal of a CW and an MBR. The study highlights the different pathways acting in the two remediation systems and the different removal rates of these pollutants. Complete removal was not obtained, but more than the 80% of personal care products were removed both in the CW and MBR systems [127]. As mentioned before, the remediation carried out in CWs can be completed by physico-chemical treatments. In the work reported by [PERSON] et al., a coagulation-sedimentation process was applied before to treat the GW by a horizontal subsurface flow CW coupled with a vertical flow CW. A residence time of two or three days produced an effluent for which parameters were in accordance with the rules in force in Egypt both regulating the discharge and allowing the effluent reuse [128]. Conversely, a post-treatment was applied to water treated in a vertical flow CW hybrid system planted with _Phragmites australis_ (PA). CW effluent was passed on a column filled with combined, locally available, absorbent materials: incinerator bottom ash (IBA), rice husk, pumice, dried stems of _Phragmites australis_ and activated carbon (as control). The research pilot plant included two feed tanks, three columns and a vertical flow planted filter unit. This hybrid system was evaluated during 20 weeks, and it efficiently removed COD, NO\({}_{3}-\)N and PO\({}_{4}-\)3 up to 90.35%, 100% and 90.2%, respectively. Concerning the absorbents, it was concluded that IBA and dried stems of PA were the most effective material to reach the irrigation water quality [129]. In particularly disadvantaged areas, GW can be treated by even simpler systems, representing great improvements for the communities. GW from wash basins at a rural public school located in a semi-arid, extensively cultivated region in Chile has been treated to obtain water to reuse in plant irrigation by a low-cost pilot system. Different adsorbent materials, AC, sand and zeolite, were tested. Concerning fecal coliforms, the simple filtration systems were effective, achieving concentrations that comply with the regulations for irrigation of recreational and ornamental areas and, in many cases, also for urban uses [130]. The largest study on GW remediation by physical separation processes was designed and tested at a United States Army installation using UF and RO. The UF, RO and disinfection equipment of the pilot system were housed in a shipping container. A large volume of graywater from showering, over 380,000 L, was treated over a 6-month period. The UF step achieved BOD removal of \(>\)95% and reduced the concentrations of six (cholesterol, diethyl phthalate, 3-beta-coprostanol, cotinine, pentachlorophenol and 6-acetyl-1,1,2,4,4,7-hexamethylletraline) of the seventeen detected micropollutants to a non-detectable level, and a 44% reduction in triethyl citrate was obtained. However, the remaining micropollutants were not removed, and the water quality of the UF effluent did not meet the set guidelines for potable water. The RO system was able to operate at a water recovery rate of 75% most of the time [131]. Another modular water reuse (WR) system treating graywater has been developed to improve energy-water security in a remote Alaskan community. First, GW was pretreated by a series of cartridge filters (sizes 1 \(\upmu\)m, 0.45 \(\upmu\)m and 0.2 \(\upmu\)m). Next, water was treated sequentially by NF and RO operating in batch concentration mode. After these filtration steps, two UV contact lamps provided at least 5.5-log removal for viruses. The final treated water was sent to a tank, which stores clean water for domestic use. Post-treatment disinfection was performed by an ozone-generating UV light to maintain water quality without the addition of chemical disinfectants [132]. MBRs have been proven and recommended as the most efficient method for graywater treatment and reuse.