Effective Sizing of Natural Systems for Grey Water Treatment Using Locally Derived Parameters

Abstract

When properly managed, grey water can be a valuable resource, which agricultural and horticultural practitioners as well as home gardeners can benefit from using to provide an excellent nutrient sources for vegetation. Natural treatment systems such as constructed wetlands emphasizing on sustainability and wastewater reuse typically for agricultural irrigation/home gardening can be considered as an ideal alternative to close the loop in terms of nutrient capture and water conservation. This paper presents a part of an analysis done to estimate the locally derived treatment wetland parameters based on BOD₅ removal mechanisms of a pilot scale subsurface horizontal flow constructed wetland (SSHF CW) treating greywater. A pilot scale SSHF CW with a surface area of 8.64 m² and a substrate depth (with 20 mm aggregates) of 0.7 m was monitored. This is a part of a long term study carried out to test the viability of SSHFCW for treating grey water for agricultural reuse. The wastewater flow measurements were taken from the inlet and the outlet of the constructed wetland while monitoring the hydraulic (HRT) and organic loading rates. Water samples from four sampling points were collected on a long term basis. Equations based on a kinetic model of a first-order piston flow reactor was used to calculate the relationship among the design parameters appropriate for local conditions. The HRT varied from 3.3 to 4.7 d for maximum and minimum inflow loading rates observed. Using the data from the current study, a resizing exercise for a subsurface horizontal flow constructed wetland was carried out. Accordingly, a household with four people, discharging 720 L/d greywater with an average influent BOD₅ of 300 mg/L could be treated up a BOD₅ concentration of 25 mg/L using an area of 3.60 m² of SSHF CW, implying only 0.975 m² of per capita land usage.