The evolution of horizontal subsurface flow reed bed design for tertiary treatment of sewage effluents in the uk

Abstract

The Horizontal Subsurface Flow (HSSF) reed bed is the most widely used concept of constructed wetland. (Vymazal, 2005). Typically rectangular in design, wastewater is fed at the inlet and passes through the media below the surface in a horizontal path before discharging at the outlet. This basic classification of a HSSF wetland is based on the hydraulic flow pattern through the system. Designed to achieve maximum performance from the system, the optimal design characteristics for HSSF have evolved separately in each country, due to the unique set of conditions (i.e. extremes of temperature, high rainfall, etc), in order to maximise their removal efficiencies and keep the area to a minimum. (Akratos & Tsihrintzis, 2007). Climatic conditions are the main reason for HSSF bed design differences in different parts of the world, with each country having its own set of design guidelines. The Constructed Wetland Association Database lists 1025 reed bed sites in the UK, of which 893 are HSSF. HSSF reed beds have been used for tertiary sewage treatment in the UK since the 1980's. Over this time, the HSSF concept has been widely studied and the design criteria adapted in light of practical experience gained from the operation of numerous systems in order to achieve optimum treatment efficiency. Lessons have been learned from failing systems leading to the designing out of problem areas. As well as achieving maximum performance and reducing the footprint, the most important factor in designing constructed wetlands today is to prolong the life of beds by minimising clogging of systems. © 2011 Springer Science+Business Media B.V.