The aim of the doctoral dissertation is to improve knowledge and understanding of small sanitation systems in terms of treatment processes and efficiency, their sustainability and implementation. The dissertation also explores the historical and current contexts that have shaped, and are shaping, the existing wastewater sector, dominated by large-scale centralised wastewater collection and treatment, and barriers to implementation of alternative, innovative sanitation solutions with higher resource recovery capacities, like source-separating systems.
Sixteen full scale on-site facilities for wastewater treatment in Sweden were investigated in the research the dissertation is based upon, including sand filters and package plants. Sand filters followed by alkaline phosphorus filters showed high P-removal capacity (>92%), whereas six (of 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, among others because of low temperature. High densities of indicator bacteria (intestinal enterococci and Escherichia coli) 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. The presence of organic contaminants was also investigated in the effluent of two package plants (12-30 PE). Levels of pharmaceuticals detected were within the range or higher than previously reported in effluents from conventional wastewater treatment plants, and included anti-inflammatories, β-blockers, ACE inhibitors, anticonvulsants and antidepressants. Effluent concentrations of phthalates were below those previously reported in the literature.
A scenario analysis comparing nine on-site sanitation options suggested that source separation of greywater and blackwater and urine diversion were the most sustainable options when nutrient removal and recycling were highly prioritised. A conventional sand filter or drain field were the most sustainable options when nutrient removal and recycling were less prioritised and, (in combination with chemical P-removal) when CO2 emissions and energy use and recovery were important aspects.
The planning of wastewater services was investigated in an interview-based study with water professionals. The general trend to opt for a centralizing approach was confirmed, whenever technically feasible, by connecting sewer pipes to a main treatment plant. Reasons mentioned by the interviewees 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 factors categorized as 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, alternative sanitation systems with higher resource recovery capacities have received less attention and institutional support, and their shortcomings were constantly highlighted during the period covered by a historical review (1974-2015).