Greywater (GW) originates from the kitchen sinks, dishwashers, handbasins, showers, and laundry. GW can account for 70–90% of domestic wastewater volume and contains organics, nutrients, microorganisms, micropollutants, and microplastics. Effective treatment can unlock the potential of GW for non-potable reuse purposes like urban landscaping or irrigation. The overall aim of this thesis was to investigate on-site GW treatment systems which included package-plants, two green walls and a constructed wetland and assess the treatment performance in terms of organic matter, nitrogen (N), phosphorus (P), microorganisms and microplastics (MPs), including the potential resource recovery and safe reuse of GW.
Among the eight package-plants investigated, commercial systems included three type A, two type B and C systems. Type D was a conventional sand filter. After the pre-treatment septic tanks, the treatment unit of type A consisted of a geotextile-fitted trickling filter over a sand bed, type B consisted of a mineral wool filter, and type C had fine plastic mesh filters. The two green wall studies were conducted at a testbed facility, RecoLab, which received GW from a newly developed urban city district (800 P.E.). The treatment efficiency of a pilot-scale indoor green wall with five filter media (pumice, biochar, hemp fiber, spent coffee grounds (SCG), and composted fiber soil (CFS, a paper industry byproduct)) was investigated with vertical flow rates (FRs) of 4.5, 9, and 18 L/d. The real-scale outdoor green wall with four levels filled with biochar and LECA as filter media was investigated for one year, using a subsurface horizontal FR of 430 L/d. A long-term performance evaluation of a constructed wetland for treating GW from a residential building (100 P.E.) in Norway was conducted using GW quality data from 2001–2024. The constructed wetland consisted of a biofilter with Filtralite® media and a horizontal subsurface filter with FiltraliteP® media for enhanced phosphorus removal.
The treatment efficiency of the systems was highly influenced by the filter media and FRs while seasonal temperature changes had a low effect. All the systems demonstrated effective treatment of GW and met the local discharge guideline of 80% BOD reduction and <3mg/L of P in the effluent. However, only the pilot-scale green wall and constructed wetland could produce an effluent with <1 mg P/L, a limit for sensitive regions. Among the filter media, sand, biochar and Filtralite® were the most efficient, up to 4 log10, in removing the microorganisms Escherichia coli, enterococci, Clostridium perfringens, Legionella spp, Pseudomonas aeruginosa and met the European Commission’s guideline for reuse of reclaimed water in agriculture. The quantitative microbial risk assessment (QMRA) on effluent GW from the constructed wetland, for multiple exposure scenario (16 exposures/year) of accidental ingestion of 1 mL, indicated safe reuse in a water cascade during summer season with regards to E. coli and C. perfringens. In addition, using TED-/Pyro-GC/MS, high variability of MPs was observed in GW from different sources of generation while all the filter media of the respective systems effectively retained the MPs, except for mineral wool and hemp fiber.
The findings of this thesis could contribute to the resource-efficient wastewater management and Water-Food-Energy nexus by demonstrating the potential of decentralized GW treatment systems.
Luleå: Luleå University of Technology, 2025.