Nutrient treatment of greywater in green wall systems: A critical review of removal mechanisms, performance efficiencies and system design parameters.

Gholami , Moeen
O'Sullivan, Aisling Dominique
Mackey, Hamish

Greywater has lower pathogen and nutrient levels than other mixed wastewaters, making it easier to treat and to reuse in nature-based wastewater treatment systems. Green walls (GWs) are one type of nature-based solutions (NBS) that are evolving in design to support on-site and low-cost greywater treatment. Greywater treatment in GWs involves interacting and complex physical, chemical, and biological processes. Design and operational considerations of such green technologies must facilitate these pivotal processes to achieve effective greywater treatment. This critical review comprehensively analyses the scientific literature on nutrient removal from greywater in GWs. It discusses nutrient removal efficiency in different GW types. Total nitrogen removal ranges from 7 to 91% in indirect green facades (IGF), 48–93% for modular living walls (MLW), and 8–26% for continuous living walls (CLW). Total phosphorus removal ranges from 7 to 67% for IGF and 2–53% for MLW. The review also discusses the specific nutrient removal mechanisms orchestrated by vegetation, substrates, and biofilms to understand their role in nitrogen and phosphorus removal within GWs. The effects of key GW design parameters on nutrient removal, including substrate characteristics, vegetation species, biodegradation, temperature, and operating parameters such as irrigation cycle and hydraulic loading rate, are assessed. Results show that greater substrate depth enhances nutrient removal efficiency in GWs by facilitating efficient filtration, straining, adsorption, and various biological processes at varying depths. Particle size and pore size are critical substrate characteristics in GWs. They can significantly impact the effectiveness of physicochemical and biological removal processes by providing sufficient pollutant contact time, active surface area, and by influencing saturation and redox conditions. Hydraulic loading rate (HLR) also impacts the contact time and redox conditions. An HLR between 50 and 60 mm/d during the vegetation growing season provides optimal nutrient removal. Furthermore, nutrient removal was higher when watering cycles were customized to specific vegetation types and their drought tolerances.

Gholami M, O'Sullivan A, Mackey H (2023). Nutrient treatment of greywater in green wall systems: A critical review of removal mechanisms, performance efficiencies and system design parameters.. Journal of Environmental Management. 345(118917). 1-18.
Decentralized treatment, Nature-based technologies, Nitrogen removal, Phosphorus removal
Ngā upoko tukutuku/Māori subject headings
ANZSRC fields of research
40 - Engineering::4004 - Chemical engineering::400410 - Wastewater treatment processes
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