## 3 Decentralized Treatment Systems
### Wastewater Treatment  
Domestic sewage needs the removal of chemical contaminants and disinfection before being discharged or employed for different uses. Both physico-chemical or NBS can be effective in domestic WW treatment, especially when in combination [135]. The different steps of a wastewater treatment train can produce both water for non-potable uses and drinking water, as demonstrated at the full scale by [PERSON] et al. [136]. In this work, the mixture of gray- and blackwater from a restaurant not connected to the sewage system was treated in a vertical flow constructed wetland (VFCW) with an area of 60 m\({}^{2}\). The effluent from the VFCW passed through an MF membrane, an AC filter, a softener, a UF membrane, an RO membrane and a vessel containing ion exchange resins. Finally, the remineralized effluent was disinfected by an LED-UV system, obtaining potable water for different uses at the restaurant. The VFCW was tested for six months and the filtration system for three months by analyzing water samples two and three times per week, respectively. All the CW effluent's parameters were within the discharge limits, and it was further used for toilet flushing. The direct potable reuse of reclaimed water poses the issue connected with the presence of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), which cannot be overlooked in selecting the suitable water treatment. [PERSON] et al. investigated the fate of ARB and intracellular and extracellular ARGs after each treatment step of an advanced water treatment facility producing drinking water from domestic secondary effluent. The water treatment facility was a multibarrier system including pre-ozonation, coagulation, flotation, dual-media filtration, main ozonation, Biological Activated Carbon (BAC), GAC, UF and disinfection. In the final product, the amount of ARG and ARBs were reduced to levels below the DL (one copy per 100 mL). The main ozonation and the UF had the highest removal efficiencies on resistance determinants [137]. An NBS treatment of domestic sewage to the quality of drinking water was carried out for almost 2.5 years in a pilot plant using a septic tank, compost beds and denitrification, phosphorus and AC beds. With an active area of 3 m\({}^{2}\) per person and an HRT of 6 days (excluding the 8-day HRT of the septic tank), the plant allowed for a mean reduction of 99%, 95% and 98% in BOD, COD and TSSs, respectively. Drinking water requirements in terms of oxidation and turbidity were met by the reclaimed water that was also suitable for supplying groundwater. This natural treatment train enables the reuse of many macro- and microelements that accumulate in the compost bed (80% woodchips) which, during a few years of cleaning process, turn into compost to be used for fertilization in home gardens [138]. The nutrient removal from domestic WW can be performed by another NBS, a hybrid need bed CW (HRBCW) used as secondary and tertiary treatment. The HRBCW operated in three stages in series: a surface flow (SF) system, a vertical flow (VF) system and, lastly, a horizontal flow (HF) system, planted with Malaysian native aquatic plant _Scirpus grossus on a_ three-layer medium of gravel at the top, river sand and larger gravel in the bottom. The system with a 3-day HRT achieved an average removal of 84.7 and 71.0% for NH\({}_{4}\)-N and PO\({}_{4}\)-P, respectively. The HRBCW-planted system showed significantly higher performance than an unplanted one, and this combination of the VF and HF systems can improve the efficiency of contaminant removal because of the presence of both aerobic and anaerobic processes [139]. Decentralized remediation processes can often exploit solar irradiation, saving energy costs. The NEWgeneratorTM system is a solar-powered automated WW treatment unit performing an anaerobic MBR treatment, a nutrient capture by ion exchange and carbon sorption and disinfection by EC.