The water requirements for industrial applications are high. Therefore, water must be “reprocessed” or otherwise provided with extended treatment to match the needs of the particular application.
This article reviews the four common treatment requirements in industrial water processing. Most of these solutions are achievable using standard metering pump dosing packages, pre-engineered to match the flow rate, degassing valves for vapor dispersion and tanks and mixers for proper dispersion of the dosing plume when sufficient pipe runs do not exist. Streaming current detectors can greatly assist in coagulation by measuring the overall charge in a process water stream, and maximizing coagulant dosing by providing minimal coagulant addition.
General Needs
In most industrial water applications, the following treatment needs are required in order to match the water
to the application.
- Chemical Disinfection
- BOD Reduction
- Additional Coagulation
- pH Control
Chemical Disinfection
Disinfection is a real need in industrial water use. Although general municipal grade water follows the Safe Water Drinking Act, additional chemical disinfection may be required. If a manufacturing facility does not have access to municipal water, on-site disinfection then becomes necessary to bring the water to manufacturing standards.
Liquid chlorine is still widely used for bulk disinfection. However, the use of liquid chlorine has many drawbacks and unfortunate side effects. Chemicals such as NaOCl and H2O2 are fast becoming the disinfectants of choice for both small- and large-scale applications, especially in industrial environments because of their ready accessibility and ease of application.
Standard metering pumps and tank systems can provide the conveyance of application for these disinfection agents. However, these two chemicals generate gas when pumped as a result of loss of vapor pressure in the pumping action.
This condition can be resolved by using degassing valves inserted between the pump head and check valve to relieve the generated gas within the pump head. Released gas then needs to be returned to the supply tank to prevent release into the atmosphere. However, metering pumps only pump liquid, and not gas; therefore, direct release from the head is the only viable method of providing accurate doses of disinfection to the process water.
From that point on, a standard pre-engineered dosing package system is generally all that is required to dispense the disinfectant of choice. A pre-engineered metering pump dosing package is one where the pump and all its components and accessories are matched by the pump manufacturer to the pressures and flows of the pump. This relieves all of the risk by a systems integrator in system matching or parts checking, shifting this entirely to the pump manufacturer. Degassing is simple and direct and does not require elaborate techniques or timing.
BOD Reduction
Biological Oxygen Demand (BOD) reduction is readily achieved through settling and chemical reduction of the effluent stream. This is achieved using an approved settling agent, appropriate to the application, dosed using a metering pump for accurate and proportionate injection. Many times, a standard tank and mixer with appropriate metering pump dosing under batch applications is appropriate in providing the venue for BOD settling. When the metering pump applies the settling agent, a precipitation of solids from the wastewater suspension will occur. In the upper levels of the tank, the light wastewater at the appropriate BOD level (500–1,000 mg/L) can be withdrawn, and the settled sludge can be disposed at an appropriate landfill or reused in the process.
Metering pumps providing exact doses of settling agents can treat these waste streams in order to maximize chemical application while using the least amount of product. General pre-engineered tank systems along with packaged dosing systems can provide most of the building blocks for these requirements.
Additional Coagulant
Non-organic material (NOM) in a water supply can cause serious disruption to an industrial process if not removed. Many industrial applications require stringent water quality. As a result, additional coagulation is needed to remove NOM.
A quick method to achieve this coagulation in an effective manner is the use of measuring zeta potential, or overall change of the water in the water stream. Zeta potential is measured using a streaming current detector. The streaming current detector samples the water stream and determines the general charge in streaming current units. These unclassified units can be calibrated to the localized water so maximum coagulation can be generated with a minimum of coagulant.
pH Control
A pH controller measures the given pH of a water stream. Water that occurs naturally has a general pH range of 6.7-7.2 barring any known pollutants. The controller probes tend to be quite sensitive and can measure changes in pH to .05 resolution with little difficulty. Therefore it is easy to purchase and install a two-pump dosing system using the pH signals to add an acid or base to balance the water into a desirable pH range.
Commonly, a pH of 7 is most desirable. However, because of the process, shifts close to 6 or 8 are required for the industrial application. Because of the many variables, the pH must be determined by the process manager and the range selected for treatment at the influent, process and effluent stream measurement points. This is commonly accomplished using the standard pH/ORP meter, two pump chemical dosing package using metering pumps and possibly a mixing tank to provide adequate dispersion of the pH adjustment if sufficient pipe runs do not exist.
Although there are many other specific requirements related to a particular industry, each of these four areas discussed become the building blocks where larger and more complex, industry-specific solutions are based.
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