Civil Engineering Reference
In-Depth Information
Fe and Mn concentrations, color, TOC levels, pH, H
2
S levels,
NH
4
hardness, and dissolved oxygen concentrations can all have an influence on the treat-
ability of the water and the treatment process selected. No one treatment process will
apply to all water sources. In fact, a process that will work in one instance will not
always work in the next. Treatment goals must be established that account for finished
water Fe and Mn levels, color, pH, and trihalomethane formation potential (THMFP),
but these are not the only concerns. Obviously the finished water must meet all current
and projected regulations. Other criteria to consider include capital costs, ease of op-
eration, backwash handling characteristics, cost of operation, regulatory acceptance of
the process, expandability, flexibility, and the potential for phasing of the facilities.
concentration,
Bench-Scale Studies
An important first step in designing or upgrading an iron and manganese removal
facility is a bench-scale study. Such studies can be very useful in the preliminary
determination of the suitability or feasibility of a treatment process train at a fraction
of the cost of a pilot study. The engineer can evaluate iron and manganese oxidation
chemicals, establish chemical dosages, determine sequence of chemical addition, es-
timate oxidation detention times, determine filtration efficiency, and quickly eliminate
several treatment options. Working out some of the details of the iron and manganese
treatment train in the lab is more economical and easier to adjust than during the pilot
study phase of the investigation. It should not be assumed, however, that a bench-scale
study will be a cheap replacement for a pilot study. The bench-scale study is only a
way to eliminate some possible iron and manganese treatment alternatives and make
the pilot study more efficient.
Pilot Studies
The second step in developing an iron and manganese removal system is to conduct
a pilot study. This step is necessary to establish the process design criteria for a
particular water quality, thereby allowing the engineer to size system components. Pilot
studies can provide valuable information on the operating characteristics of the pro-
posed treatment plant. They can determine if a process will work, and they can identify
problems before construction of the full-scale facility, often allowing the utility to avoid
costly repairs or modifications either during or following construction. Depending on
the type and number of processes to be investigated, who operates the pilot plant, who
constructs the pilot unit, and the overall pilot study objectives, pilot studies can require
anywhere from 4 weeks to 6 months to complete and can cost anywhere from $15,000
to $75,000.
An iron and manganese pilot study should be designed to test the limits of the
proposed treatment process, the goal of which is to see how heavy a process can be
loaded before it breaks or fails to meet the stated treatment objectives. Knowing the
limits of a process will allow the engineer to design the system for maximum effect-
iveness and efficiency. In conjunction with this guideline, the pilot test should be
designed to develop the following design and operational criteria:
Full design criteria for all aspects of the proposed iron and manganese removal
process to include but not necessarily be limited to:
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