Water/Wastewater 17
Figure 3: IQ Sensor Net terminal 2020XT by WTW
the plant, or whether there was optimisation potential in the individual phases of the degradation process. In order to be able to measure ammonium and nitrate values online, we installed the WTW ISE combination sensor VARiON (Figure 5) in each of the two reactors. Integration of the sensors into the existing IQ
SENSOR NET system and their start-up was easy. Based on the recorded data, it could quickly be proven that the ammonium was already completely degraded after around half of the aeration time of the two nitrification phases (Figure 6). The one- year trial phase with the ISE sensors confirmed that there was considerable energy saving potential in operating the SBR plant. We decided therefore to change from a simple time control of
the SBR processes to a dynamic control strategy using NH4-N as control parameter.
Process optimisation
Figure 4: FDO 700 IQ optical D.O. sensor by WTW
The engineering office in charge programmed an additional control program named “Energieoptimiert” (energy-optimised) for the dynamic process control, which integrates the ammonium and nitrate measured values into the existing PLC. Ammonium is the control- relevant parameter that
determines the end of the nitrification phases. For the first nitrification process (Phase 3), the control value that switches off the blower
units is at 1.3 mg/l NH4-N and, for the second nitrification process (Phase 6) it is at 0.7 mg/l
Figure 5: VARiON 700 IQ ISE sensor by WTW
NH4-N. The next SBR phase begins after the blowers are switched off. The degradation of the remaining ammonium is
almost complete during the sedimentation phase (NH4-N values < 0.4 mg/l; see Figure 7).
The new dynamic control of the aeration times ensures that the nitrification runs only as long as necessary and the targeted, very low effluent value is reached safely, but without unnecessary energy consumption. The control settings mentioned are based on existing empirical values, but are freely adjustable in the new control program. This ensures a simple optimisation of the degradation process in the future, without having to invest again in costly programming.
The simultaneous measurement of nitrate and ammonium concentrations enables a plausibility check of the ammonium
degradation at any time (via the stoichiometric ratio of NO3-N and NH4-N) and serves as a control for the effluent limit values at the end of the cleaning cycle. The nitrate measurement itself is, however, not used as a control-relevant parameter.
Even today we are using the time-based program as a component of the process control, but it is used mainly as an emergency program in case of measurement faults or implausibility’s. Also, the process management system automatically switches to time-controlled operation, should the energy-optimised program surpass the former fixed times of the nitrification phases.
In consequence, by implementing a dynamic process we could shorten each nitrification phase by up to an hour. Calculating 4 nitrification phases per day (with an overall cleaning cycle of 2 nitrification phases per SBR reactor), the running time of the aeration units could be reduced by up to 4 hours. Extrapolated over a year, we could save up to 1500 operating hours. This not only reduces the energy costs, but also lessens the wear out on the aerator units.
Conclusion
We are very pleased with the new measuring technology which allows us to keep the discharge values stable and at the same time save energy.
The used measurement equipment works with minimum maintenance. The entire degradation process is transparent with regard to the process-relevant parameters ammonium, nitrate and oxygen. The ISE combination sensor and the optical oxygen sensor enable us to simply optimise the degradation process. Thanks to the dynamic control strategy manual adjustments are now practically unnecessary as the plant automatically adjusts to the incoming load of the wastewater.
Pressure Transmitter Resistant to Overload and Condensation
WIKA (Germany) now offers new options with their O-10 OEM pressure transmitter. Under the model designation O-10 (5), the instrument is available with a five-fold overpressure safety and resistance to condensation.
The overload capacity is mainly aimed at applications in the market segments of water supply and irrigation systems. It protects the pressure sensor from possible damage from the water-hammer effect that fast-switching valves can cause.
Furthermore, in the future, the O-10, developed for the global market, will also be available with a condensation-resistant housing. This prevents the formation of condensation in the instrument, which can occur where there is a distinct difference between the fluid and the ambient temperature.
These options increase the durability, and thus the service life, of the O-10 pressure sensor in critical applications.
For More Info, email:
25875pr@reply-direct.com email:
2ad@reply-direct.com
www.envirotech-online.com IET Annual Buyers’ Guide 2013
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