Safe access to sanitation is at the core of the United Nations Sustainable Development Goal (SDG) #6. Currently, it is estimated that this goal cannot be met by 2030. Despite all kinds of administrational hurdles, meeting SDG#6 depends on considerable investment. In order to get a chance at fulfilling SGD#6, the most cost-effective wastewater management has to be identified. Wastewater can be managed in different ways ranging from central treatment plants connected to individual households through sewer networks down to tanker fleets servicing each household. Depending on the geographical setting, investment costs, operation and maintenance as well as social acceptance there is no single best solution. Instead, identifying the optimal wastewater management is highly localized and country-specific or even settlement-specific. Within this study we present a data-reduced scenario generation and assessment for wastewater management based on the ALLOWS method that can be applied to individual settlements. Results provide cost-ranked wastewater management scenarios that enable decision makers to select the most cost-effective and feasible scenario. Our study starts with a detailed step-by-step methodology of a data-reduced ALLOWS approach. The approach is applied to two small settlements in Jordan and Oman with comparable population size for which a set of five scenarios along a decentralization gradient is defined and generated: centralized, semi-centralized, decentralized, and on-site/tanker. Considering spatial specificities and country-specific cost data, the five scenarios are cost-ranked and discussed in view of the two settlement settings. For Jordan specific treatment costs range from 3.8 to 6.9 USD/m³of treated water and for Oman from 2.3 to 10.1 USD/m³. Although the scenario ranking differs, for both settlements the decentralized scenario is identified as the most cost effective, where wastewater is treated on-site for less-populated parts and by small cluster treatment plants for higher density parts. Further, potential extensions providing users with more functionality depending upon data availability for the data-reduced ALLOWS method are discussed. Using globally available data, the data-reduced can be applied worldwide. In view of SDG#6, we present a methodology that closes the gap between country-scale investment estimates and the most cost-effective wastewater management scenarios at settlement level.

Cities worldwide are facing problems to mitigate the impact of urban stormwater runoff caused by the increasing occurrence of heavy rainfall events and urban re-densification. This study presents a new approach for estimating the potential of the Management of Urban STormwater at Block-level (MUST-B) by decentralized blue-green infrastructures here called low-impact developments (LIDs) for already existing urban environments. The MUST-B method was applied to a study area in the northern part of the City of Leipzig, Germany. The Study areas was divided into blocks smallest functional units and considering two different soil permeability and three different rainfall events, seven scenarios have been developed: current situation, surface infiltration, swale infiltration, trench infiltration, trough-trench infiltration, and three different combinations of extensive roof greening, trough-trench infiltration, and shaft infiltration. The LIDs have been simulated and their maximum retention/infiltration potential and the required area have been estimated together with a cost calculation. The results showed that even stormwater of a 100 year rainfall event can be fully retained and infiltrated within the blocks on a soil with low permeability (k_f = 10⁻⁶ m/s). The cost and the required area for the LIDs differed depending on the scenario and responded to the soil permeability and rainfall events. It is shown that the MUST-B method allows a simple down- and up-scaling process for different urban settings and facilitates decision making for implementing decentralized blue-green-infrastructure that retain, store, and infiltrate stormwater at block level.

The protection of vulnerable groundwater resources and their optimal management is essential for the Hashemite Kingdom of Jordan to meet current and future water demands. Our overall objective was to analyse the water situation in the district of Bani Kinana, which has received a large number of Syrian refugees in the past, resulting in an increased water demand, which in turn leads to local water shortages and puts tremendous pressure on local groundwater resources. An integrated wastewater resources management (IWRM) approach to protect groundwater resources and to reduce the risk to local communities and ecosystems was developed, and the most cost-effective wastewater treatment system solution was identified, based on the ALLOWS tool (Assessment-of-Local-Lowest-Cost-Wastewater-Solutions). The results show that a large volume of drinking water is directed to the Jordan Valley and it is recommended that this water should be retained to meet current needs and the projected future demand of 8.3 MC in 2050. The ALLOWS tool revealed that the current practice of wastewater disposal by tanker is the costliest scenario in the long-term and will cause the pollution of groundwater resources. A tailored solution, such as the implementation of a cost-efficient semi-centralized wastewater treatment plant, would contribute significantly to protecting vulnerable water recourses.

• Urban block mapping and design storms to facilitate spatial planning of Nature Based Solutions (NBS) in urban catchments with limited information. • Spatial-economic scenarios to benchmark urban stormwater management strategies for stormwater volume exceeding the capacity of the sewer system. • Reduced project costs with most suitable allocation of distributed NBS compared to smaller and wide-distributed interventions. • NBS are more economically viable than grey alternatives, especially when designed for high flows.

This article studied how wastewater treatment performance of a short rotation forestry system was influenced by the seasonal operational changes under the extreme Mongolian winter conditions. For this reason, two beds planted with Willow (Salix spec.) and Poplar (Populus spec.) trees were operated over a period of two years under two different seasonal conditions: (A) “external winter storage” and (B) “internal winter storage” of pretreated wastewater. For operational condition A, the tree-bed was loaded with wastewater for only 4 summer months. For this operational condition it was considered that the treatment bed was fed with primary treated wastewater, which was stored in a sealed pond during the remaining 8 months. The other Bed B was irrigated throughout the year (12 months) with the same daily loading rate. In winter, the wastewater accumulated as ice in the tree-bed. Bed A, with external winter storage, showed mass removal percentage up to 95%, while the bed with internal winter storage showed mass removal rates up to 86% for pollutants such as COD, BOD₅, TN, and TP. A high yield of biomass was recorded for both beds with slight differences. Based on the results, a design recommendation was developed for full-scale systems of short rotation coppice irrigated with wastewater under various operational conditions, which show these systems to be a viable method for treating wastewater and producing biomass for energy production in Mongolia.