Small Sanitation Systems – Treatment Efficiency, Sustainability and Implementation

Sammanfattning: The current socio-technical wastewater system is being challenged by emerging global issues such as climate change, eutrophication and resources scarcity. The future of the urban/rural water management requires exploring new innovative solutions that enables closing the loops of resources. On-site and decentralized wastewater systems are seen as emerging solutions, partly because of their flexibility, as they increase the potential for recovery and reuse of resources like nutrients. At the smallest scale, on-site wastewater treatment systems are widely present in rural and peri-urban areas globally. Acceptable levels of nutrient and bacterial discharges are often not met which contributes to environmental degradation and health risks. Various treatment options have different environmental, economic or social impacts but can also contribute with increased benefits such as nutrients or energy recovery. The overall aim of this doctoral thesis is to improve knowledge and understanding of small sanitation systems in terms of treatment processes and their efficiency, sustainability and implementation. At a greater scale, the thesis explores the historical and current contexts that have shaped, and are shaping, the existing wastewater sector. Sixteen full scale on-site facilities in Sweden were investigated in this thesis, including sand filters and package plants. Sand filters followed by alkaline phosphorus filters showed good removals of organic matter and high P-removal capacity (>92%). Six of the 11 investigated package plants showed >78% phosphorus removal (including chemical precipitation and alkaline phosphorus filters as treatment steps). Nitrogen removal was generally low in the package plants, likely because of the low average temperatures, and appeared to be manly caused by sedimentation of particulate organic nitrogen. Denitrification was observed to a limited extent in facilities with water/sludge recirculation. High densities of indicator bacteria were found in the effluent of most facilities, as the removal rates were low, often exceeding the EU Bathing Water Directive’s limits for excellent water quality in terms of intestinal enterococci and Escherichia coli. Pharmaceuticals detected in the effluent of package plants were within the ranges or higher than those previously reported in effluents of conventional wastewater treatment plants and included anti-inflammatories, β-blockers, ACE inhibitors, anticonvulsants and antidepressants. In contrast, concentrations of phthalates were lower than the effluent concentrations previously reported in the literature. In terms of sustainability performance, a multi-criteria analysis using indicators showed the importance of setting clear priorities when planning wastewater systems. A comparison of nine on-site sanitation options under three scenarios showed that the most sustainable options when nutrient removal and recycling were highly prioritized were source separation of greywater and blackwater, followed by urine diversion (Scenario 2). A conventional sand filter and a drain field were the most sustainable options when nutrient removal and recycling were of less importance (Scenario 1), and (in combination with chemical P-removal) when CO2 emissions and energy use and recovery were important aspects (Scenario 3).When planning wastewater services for a given area, results of interviews with water professionals confirmed the general trend to opt for a centralizing approach, whenever technically feasible, by installing pumping stations and connecting sewer pipes to a main treatment plant, in contrast to building decentralized systems. Mentioned reasons included the robustness of the system, simplicity of operation and maintenance and protection of the receiving waters. Identified barriers hindering implementation of alternative sanitation solutions with focus on resources recovery included legislative factors (lack of requirements and law interpretation), technical factors (immature technologies, uncertainties), organizational factors (lack of initiative, competence and experience) and economic factors (financial limitation, lack of incentives). From a historical perspective, strong governmental control and continuous enforcement of environmental requirements drove the expansion and strengthened the large-scale centralised sanitation system in Sweden. Alternative sanitation systems with focus on resource recovery received less attention and institutional support in comparison, and their shortcomings were constantly highlighted during the studied period (1974-2015).Overall, this thesis contributes to understanding of small sanitation systems in terms of treatment efficiency, factors affecting their performance and sustainability, as well as increasing knowledge of current and previous management regimes and planning in the wastewater sector at different scales and in the context of a paradigm shift from “waste treatment” to “resources recovery”.