A novel way of water reuse in a decentralized wastewater treatment system, applicable in the city of the future

The increase in the water and energy demand in urban cities comes with the need to develop smart eco-friendly solutions to promote the best use of these resources. Greywater reuse can contribute as an important practice in sustainable cities to reduce the pressure on water and energy resources. This study aimed to design and evaluate the performance of a decentralized pilot-treatment system composed of a moving bed biofilm reactor (MBBR) followed by an up-flow filter and UV disinfection to treat greywater from showers and hand basins for toilet flushing. Additionally, a heat exchanger was placed before the MBBR to study its performance on promoting energy recovery for water heating. The pilot was located in Hulst, the Netherlands, at the Pureblue Water company’s installations. The monitoring of the overall system performance, as well as its units, in removing organic matter, nutrients, total suspended solids (TSS), and recovering energy from greywater were performed. Results showed that the system was able to reduce all the parameters analyzed (chemical oxygen demand - COD, total nitrogen -TN, total phosphorus (TP - PO4-P), pH, and turbidity) to most of the greywater reuse safety standards found in the literature. Moreover, the system presented COD, TN, and TP removal efficiencies of 69%, 42%, and 53%, respectively corresponding to a population equivalent of 120 inhabitants. The filter showed TSS removal from 44% to 52% associated with a suspended solids loading capacity of 4 TSS COD g/L (with a breakthrough time of 21 hours). While the MBBR was able to treat the organic load of 2.58g COD/m2.d. In addition, the heat exchanger presented from moderate to high efficiencies (from 39% to 92%) in recovering heat for water heating. The pilot plant showed to be an excellent way to promote sustainable water and energy use in the cities of the future