Recycling of Food Waste and Greywater for Sustainable Green Building Infrastructure: Impact of Hydraulic Loading Rate on Pollutant Remediation

Abstract

Urbanization exacerbates water scarcity by increasing demand while reducing the availability of natural water reserves. Food waste is another critical issue that affects urban sustainability. Recycling treated greywater presents a sustainable alternative, particularly for irrigation purposes. This study evaluated the effectiveness of a media blend of spent coffee grounds and date seeds (1:2 ratio) for cultivating five ornamental plants irrigated with treated greywater at two hydraulic loading rates: 200 mL/day and 400 mL/day. Plants irrigated with 200 mL/day of greywater showed significant improvements compared to those supplied with freshwater. Increases were observed in plant height (27.3 ± 11.7 cm), pinnula count (6.3 ± 2.1), leaf number (55.3 ± 6.7, excluding Portulaca grandifolia ), dry shoot weight (13.06 ± 8.83 g), and root length (115.1 ± 10.9 cm). Plant moisture content also increased from 70 ± 4% to 74 ± 3%. In terms of treatment performance, Cyperus alternifolius achieved the highest pollutant removal: 70% TOC, 98% NH 4 + -N, 44% PO 4 3− -P, and 84% isobutyric acid. Portulaca grandifolia showed the best TN removal at 93%. The two loading rates showed no significant difference in pollutant removal (p = 0.19), suggesting rate flexibility in design. Among the tested species, Alternanthera amoena had the highest growth rate, while Cyperus alternifolius showed the greatest biomass yield. These species demonstrate strong potential for use in greenwall systems, offering both effective greywater treatment and robust plant performance. This study supports greywater irrigation as a practical approach to sustainable horticulture and urban water conservation. Graphical Abstract

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