Nitrogen is present in untreated wastewater effluent and can pose major environmental concern in high concentrations, especially when released into bays and watersheds. Nitrogen is an end-product of the bacterial metabolism of ammonia, which can act to deplete dissolved oxygen in receiving waters. Nitrogen also stimulates aquatic plant and algae growth, which causes hypoxia and, additionally, blocks sunlight from reaching submerged marine life, creating a condition known as eutrophication. Also, nitrogen can exhibit toxicity toward some animals and, in general, presents a significant public health hazard. Furthermore, nitrate compounds are another primary contaminant in drinking water that can cause a human health condition known as methemoglobinemia, which alters the oxygen-carrying capacity of hemoglobin. The levels of nitrogen created during the wastewater treatment process must be significantly reduced before the effluent is discharged into the environment. The primary challenge is to develop a practical method that economically reduces the levels of nitrogen in the effluent.
For low-flow effluent applications, a technology used for decades in medical instrumentation has proven ideal for low and ultra-low volume metering of methanol.
09/03/2015
Image 1. An installation in a non-heated outdoor enclosure at a community college wastewater treatment plant (Images and graphics courtesy of Fluid Metering, Inc.)
Figure 1. The piston is designed with a flat cut into the end closest to the inlet and outlet port.
Diaphragm, bellows and traditional piston pumps typically have four check valves. Even during normal operation, these will wear over time and not seal properly, allowing backflow. When this occurs, accuracy is compromised and the pumps will need periodic recalibration. Eventually, the check valves will need to be serviced.
Figure 3. As the angle of the pump head increases above zero, the piston reciprocates, and fluid is moved through the pump.
Adjustment is infinite between zero and 100 percent, and a flow rate indicator allows for accurate and simple linear calibration. The pump is designed so that at any angle and flow rate, the piston always bottoms for maximum bubble clearance. This is especially important at small dispenses and flow rates, as the presence of even a minute bubble will significantly affect accuracy.
Figure 2. Some valveless piston pumps can maintain a precision of 0.5 percent or better for millions of cycles without recalibration
Valveless piston pumps are also available in several configurations including standalone production dispensing systems and miniature original equipment manufacturer (OEM) models for medical, analytical and process instrumentation. The pump technology is used in a broad range of precision-fluid control applications including adding vitamin D to milk, producing adhesives for medical apparatus assembly and handling monomers that form contact lenses.