As an alternative to conventional wastewater treatment, the use of source-separating wastewater systems is growing in popularity. This study evaluated processes at RecoLab, a source-separating wastewater treatment and recovery plant, which treats blackwater, greywater and food waste streams from the nearby residential area of Oceanhamnen, in Helsingborg, Sweden. The focus of the study was on the blackwater stream which included the biogas production and the struvite precipitation and ammonia stripping processes which recovered nutrients in the form of phosphorus and nitrogen. The objectives were to analyse the variation in quantity and quality of incoming blackwater to RecoLab during 2023 and to quantify the mass flows of total solids, chemical oxygen demand, phosphorus, and nitrogen throughout the blackwater treatment process. Furthermore, the end products, including biogas, sludge, and recovered nutrients were analysed in terms of quantity and quality and then compared with products from conventional wastewater treatment plants. Data collected during 2023, including water samples and flow measurements at various points in the blackwater treatment process, were used to calculate mass balances of the investigated parameters. From the results, it was seen that the anaerobic digestion in RecoLab produced more biogas than most conventional wastewater treatment plants (150 m3 CH4/week or approximately 88 kWh/PE/year), with the biogas having a large impact on the total solids and chemical oxygen demand mass balances. The digestion yielded a sludge with low heavy metal concentrations (13 mg Cd/kg P), making it safe for agricultural use. Low metal concentrations were also found in the struvite (0.68 mg Cd/kg P), although decreasing metal concentrations over time point to a diffuse source of leaching in the equipment. The nutrient recovery as sludge and struvite, a recovery of 27% of the total phosphorus and 2.5% of the total nitrogen, was impacted by the struvite precipitation process showing a low collection grade. Substantial total phosphorus and total solids losses were found over the struvite precipitation process in the mass balances. Total nitrogen loss over the struvite precipitation process was mainly deemed to be due to aeration, though a possible overestimated value. Hypothetical calculations of the ammonia stripper showed great potential for nitrogen recovery in the form of ammonium sulphate, where a fully working ammonia stripper would contribute with the largest fraction of nutrient recovery in the RecoLab plant. Overall, the thesis presents an alternative to conventional wastewater treatment methods by possibilities to enhance nutrient recovery and support circular economy principles. However, the study highlights several areas for improving the blackwater treatment at RecoLab, such as optimizing the hydrocyclone to increase the struvite recovery and conducting direct measurements of the aeration process to better understand nitrogen pathways. The implementation of source-separating systems, as demonstrated by RecoLab, can serve as a model for future urban developments, aiming for resource efficiency and minimal environmental impact.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-105809 |
| Date | January 2024 |
| Creators | Gren, Lisa |
| Publisher | Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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