This engineer manual (EM) was written to provide guidance for determining if precipitation, coagulation, flocculation (PIC/F) systems are applicable and guidance on how to properly design, specify, and operate P/C/F systems to remove dissolved heavy metals from aqueous waste streams.

Chemical precipitation is the most common technique used for treatment of metal-contaminated waters (Patterson and Minear 1975, EPA 625/8-80-003, EPA 600/8-80- 042c, Peters et al. 1985, Patterson 1988). Chemical precipitation of heavy metals has long been used as the primary method of treating wastewaters in industrial applications, such as metal finishing and plating. Owing to this past success, chemical precipitation is often selected to remediate hazardous, toxic, and radioactive waste (HTRW) sites containing ground water contaminated by heavy metals or landfill leachate, or both.

For the precipitation process to be effective, an efficient solids removal process must be employed. To separate the solid and liquid phases of the wastestream, coagulation, flocculation, and clarification or filtration, or both, are typically used along with precipitation. Precipitation/coagulation/ flocculation (P/C/F) systems are often used as a pre-treatment step to stop metals from interfering with subsequent treatment processes (e.g., UV–oxidation or air stripping). Depending on the required treatment standards, a P/C/F system may also be used as the final stand-alone treatment.

This manual is intended to provide guidance and criteria for the design and selection of small-scale wastewater treatment facilities. It provides both the information necessary to select, size, and design such wastewater treatment unit processes, and guidance to generally available and accepted references for such information.

For the purpose of this manual, small-scale wastewater treatment systems are those with average daily design flows less than 379 000 liters per day (L/d) or 100,000 gallons per day (gal/d), including septic tanks for flows less than 18 900 L/d (5000 gal/d), small prefabricated or package plants for flows between 18 900 L/d (5000 gal/d) and 190 000 L/d (50,000 gal/d), and larger prefabricated treatment systems with capacities of no more than 379 000 L/d (100,000 gal/d).

The following manual provides a review of considerations and steps required for the design, construction and operation of constructed wetlands for wastewater treatment in rural applications (i.e. livestock operations, food processing, septic waste treatment, etc). The information provided herein is to be used by practitioners (i.e. professionals with a working knowledge of geotechnical engineering, hydrology, hydrogeology and wastewater treatment) to provide them with enough detailed information to determine if this application is applicable to their needs and if so, to help them develop, implement and operate a constructed wetland treatment system.

The guidelines outlined herein provide a standard system approach for a simple low cost, low maintenance solution. The constructed wetlands discussed in this manual are therefore limited to simple systems such as those found in nature, and do not consider more complex designs such as sub-surface systems and complex mechanical devices. The design examples used in this manual are therefore based on the simpler loading rates methods. This manual can be used by technical staff in provincial agencies, consulting firms, construction companies as well as potential operators and owners of constructed wetland systems.

Most of us take our wastewater (sewer) systems for granted. We flush the toilet or wash the dishes or our clothes, and, with very few exceptions, the dirty water leaves our home. While most of the time our wastewater is out of sight and out of mind, what goes on behind the scenes to carry out this important function is very complex and requires the input of many parts and people. We all generate gallons of wastewater every day and often don’t think about how it is dealt with, yet it often requires so much to provide this service to us—strict health regulations, a knowledge of chemical, biological and technical processes, budgeting to run a business, and miles of infrastructure to make it convenient, to name just a few things.

As a leader in your community, making decisions about your community’s wastewater system is probably part of your role. And it is an important role. You may be on a board or council that is the highest decision-making body for your community’s wastewater system. This means you, along with the other leaders, need to oversee all of the activities that go on in the system—not with an extensive knowledge of each activity, but at least with an awareness of what happens and what is required.

Whatever your role or capacity is, you are to be congratulated for taking an interest in your community’s wastewater treatment processes. You may want more information about what it takes to provide the vital service of treating wastewater. This guide to the operations of wastewater systems for non-technical audiences is designed to explain a typical small-community water system—from the time wastewater leaves a home, through the collection and treatment system, to the final discharge to a receiving body of water or reuse—in an easy-to-understand manner.