By Mark Reinsel, Apex Engineering
This article is the second in a series on industrial water treatment focusing on inorganic contaminants. While regulatory limits are being established (see Part 1), the process of identifying a cost-effective treatment process should be undertaken. The goal of this article is to establish the methodology for selecting that process.
The main steps I use in selecting a treatment process are to:
These steps will be explained and elaborated in the remainder of this article.
The three most important design criteria are:
Selecting a treatment process may need to be an iterative process as more information becomes available on influent and effluent concentrations.
Reviewing potential industrial water treatment technologies for this application will be the subject of the next several articles in this series. Chemical, biological, and physical processes are all possibilities. A good water analysis (the influent concentrations in the design) is the key here. Total and dissolved metals analysis is required, with dissolved concentrations particularly important for metals. Dissolved metals concentrations may be a significant factor in deciding whether physical vs. chemical vs. biological treatment is most effective.
Developing possible process flow sheets or process flow diagrams (PFDs) is the third step in the process. These are typically developed for several treatment alternatives. A one- or two-page flow sheet is all that is required initially. These can be expanded later into process and instrumentation diagrams (P&IDs). A typical PFD for biological treatment is shown below.
Next, costs are estimated. Capital costs are developed for equipment based on the design flow. These can be based on similar recent installations, vendor quotes, or a combination. Colleagues in the industry (operating similar facilities or working as consultants) are another great source of information.
Operating costs are based on the average flow. Equipment suppliers can provide information such as horsepower required and recommended chemical dosages, while chemical suppliers can provide budgetary prices for their products.
Bench or pilot testing is the final step in the process. Bench and pilot tests:
Of course, bench testing is simpler, quicker, and less expensive than pilot testing. Several bench tests can often be conducted in a day. Below is a bench test run for metals removal from mine water using a multi-position jar stirrer.
Two types of bench tests are possible: jar tests or column tests. The example shown above is a jar test. Possible jar tests include:
Possible column tests include:
Sometiimes Whole Effluent Toxicity (WET) testing is one of the regulated parameters. A large water volume is required for WET testing, which column tests can more readily provide than bench tests.
Pilot testing is the next step in demonstrating viability of a water treatment process and in determining operating costs. A pilot-scale multimedia filter is shown below. A pilot test is typically run for several weeks.
For more information, contact Mark Reinsel at www.apexengineering.us.