Canadian Municipal Water News & Review - Spring 2012 - (Page 17)
BY ANDR EW NIBLOCK AND JOHN PR IES
Water Treatment Plant
Constructed Wetland for Backwash Water
his is the ﬁrst of two articles concerning the innovative application of a treatment wetland at the Windsor Lake WTP, St. John’s, NL. In this article, the design and technical speciﬁcations of the wetland are presented. The performance results and the owner’s perspective
will be discussed in a subsequent issue of this journal. Overall, the system was designed to achieve a TSS reduction target range of 60–80 percent. The design criteria used to accomplish the TSS reduction is as follows: • Hydraulic Loading Rate: 392 m3/day (300 d @ 365 m3/d; 65 d @ 515 m3/d) • Average Solids Loading: 160mg/l (300 d @ 115 mg/L, 65 d @ 391 mg/L) The constructed wetland system consists of a 500 m2 equalization forebay (EF) and a 0.4 hectare wetted footprint surface ﬂow treatment wetland (SFTW). The following describes the key components of the constructed wetland system.
THE WINDSOR LAKE Water Treatment Plant (WLWTP) supplies the majority of water for the City of St. John’s, NL, using microﬁltration membranes as the main treatment process. The non-chemical backwash water generated by the facility is discharged regularly to a forebay and constructed wetland designed by CH2M HILL Canada. The wetland is designed to reduce the total suspended solids (TSS) concentration in the backwash water by approximately 75 percent before returning that water back to Windsor Lake. This is a unique application of the treatment wetland technology due to the nature of the solids that are typically ﬁne, inorganic particles of combined suspended lake sediment and hydrated lime.
The wetland size was determined based on the available land area. Using the k-C* model, an area-based contaminant loading model, the water quality improvement potential was predicted. Modelling was based solely on TSS values and not other constituents and while they are not being monitored, it is generally accepted that there will be a reduction across the wetland system.
Constructed Wetland Design Components
The EF has a wetted footprint of approximately 500 m2 that consists of a wetland fringe around a portion of its perimeter and a deep pool. The function of the wetland fringe is both functional (wave erosion protection, safety shelf and treatment capability) and aesthetic. The deep pool is 1.5 m deep at the deepest point and provides approximately 180 m3 of storage volume providing a hydraulic retention
FIGURE 1: THE WETLAND FRINGE AND THE DEEP POOL CAN BE SEEN IN THIS PHOTO TAKEN DURING THE CONSTRUCTION OF THE EQUALIZATION FOREBAY.
SPRING | PRINTEMPS 2012 |
Table of Contents for the Digital Edition of Canadian Municipal Water News & Review - Spring 2012
President's Message/ Message du Président
The City of Calgary, BonnyBrook
Lancaster Wastewater Treatment Facility
You Can't Manage What You Don't Measure
Windsor Lake Water Treatment Plant
Product Showcase and Products & Services Marketplace
Index to Advertisers/ Index des Annonceurs
Canadian Municipal Water News & Review - Spring 2012