ABSTRACT This study evaluated a 23-year-old hybrid treatment wetland (HTW) treating greywater from a residential building in Norway using historic monitoring (2001–2014) and recent sampling campaigns (2023–2024), representing one of the longest documented systems operating in a cold-climate setting. The system consisted of an aerobic vertical flow filter with Filtralite®, and an anaerobic horizontal flow filter with Filtralite®P for enhanced phosphorus removal. Recent findings (2023–2024) show improved organic matter removal, with 98% BOD reduction and effluent BOD consistently 2 mg/L. However, nutrient removal declined over time, with effluent total nitrogen of 3.3–5.6 mg/L (59–74%). Total phosphorus increased from 0.02–0.08 mg/L (2001–2008) to 0.15–0.45 mg/L (2014–2024), indicating partial exhaustion of the Filtralite®P media. The HTW achieved effective log reductions of 1.6–3.4 for E. coli, 2.1–3.4 for enterococci, 1.6–3.1 for Clostridium perfringens, and 2.0 for Pseudomonas aeruginosa. Legionella spp. remained below detection limits, and Campylobacter was not detected. A quantitative microbial risk assessment (QMRA) showed the annual risk of infection was 10−4 for E. coli and Clostridium perfringens. The HTW met Norwegian discharge standards of BOD 20 mg/L, phosphorus 1 mg/L, E. coli 100 MPN/100 mL, and complied with EU standards for agricultural water reuse.
Sami et al. (Wed,) studied this question.
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