Epsilon Archive for Student Projects

Abstract

There are an abundance of environmental problems in the world today, some of which can be traced back to a lack of proper sewage treatment. Human toilet waste, also called blackwater, is discharged untreated into the environment where it can contaminate water bodies, including drinking water sources. However, blackwater is an excellent source of plant available nutrients, and can be used as a fertilizer after proper treatment. The risks involved in the reuse of blackwater include pathogenic microorganisms, heavy metals, and pharmaceutical substances. This study however focuses only on the inactivation of pathogenic microorganisms during blackwater treatment. The aim of this study was to optimize a current blackwater treatment method at a plant in Hölö, Sweden, and confirm that the treated blackwater reached the required microbial reductions based on SPCR 178 (SP, 2012). The current method treats 30 m³ of blackwater within 2 weeks through an increase of the materials temperature to 40°C and then the addition of 0.5% urea, based on the wet weight. The method in this study treats 160 m³ with a similar treatment procedure, but rather than heating all of the treated blackwater only one third (60 m³) was heated to 40°C and then mixed with the other two thirds (100 m³) which remain at ambient temperature. After the blackwater was mixed, 1% urea (based on the wet weight) was stirred in to ensure an even distribution, after which the treatment lasted 21 days. The study was performed twice (set 1 and set 2), with samples being taken six times per set. Samples were analyzed for physiochemical properties (temperature, pH, total nitrogen and ammonia concentrations) and microorganisms (Ascaris suum eggs, Enterococcus spp., Salmonella spp., thermo tolerant coliform bacteria/E.coli, f-RNA bacteriophages, and somatic coliphages). The temperature, after the heated blackwater was mixed in with the blackwater at ambient temperature, started at approximately 17°C and then decreased to around 11°C by day 21. After the addition of 1% urea, the total-Nitrogen concentration rapidly increased and then remained constant. The pH increased during the first week and then reached a steady state. The total ammonia Nitrogen (TAN) also increased over the 21 days, appearing to reach a somewhat steady state in the last week. Salmonella spp. reached the required inactivation (absent in 25 g of sample based on the wet weight) by days 4 and 2 in sets 1 and 2 respectively. TtC/E.coli reached below the detection limit (1 CFU ml⁻¹) by day 7 in both sets, which is below the <1000 CFU g⁻¹ (TS) required for the certification. The only microorganism which didn’t reach its required end-product concentration (<1000 CFU g⁻¹ [TS]) by day 21 was Enterococcus spp. Further studies using a combination of different amounts of heated and unheated blackwater in addition to different urea doses are needed to find the ideal treatment of the blackwater, where the required sanitization goals are met using the most cost efficient parameters.