Wastewater

Municipal Wastewater Treatment Plant

To make wastewater useable again or to discharge it into the environment, it has to cleaned in a multistage process of a wastewater treatment plant. There are three major cleaning steps, located between inlet and outlet of a plant: mechanical cleaning, biological cleaning, chemical cleaning. An additional part is the treatment of the sludge, which is produced during the cleaning. In all areas, process monitoring is required to take corrective action if needed. This monitoring can be ensured by measuring the respective parameters. The measuring location can be critical for proper monitoring.

Inlet
What parameters to measure at the inlet of a wwtp?
Hence, in the inlet and the within the mechanical cleaning (screen, sand trap, oil filter, etc.) an analysis of the incoming wastewater in necessary, to get initial concentrations of nutrients, organic or salt load. For this, optical probes with ultrasonic cleaning for sum parameters (e.g. SAC, COD, BOD) or sensors for specific parameters (e.g. pH, Cond) can be used. The optimization of the sludge extraction in the pre-clarifier (end of mechanical cleaning), can be reached by a sludge level measurement.

The integrated ultra sonic cleaning for spectral probes reduces your maintenance costs (View on YouTube)

pH calibration in the lab: possible with the smart SensoLyt^® 700 IQ and the SACIQ cable (View on YouTube)

The IFL sludge level sensor: mount, set, measure (View on YouTube)
Biology
What is the working principle of the biological cleaning?
The elimination of nitrogen – mainly chemically bounded in ammonium – happens through biochemical reactions. In aerobe conditions, ammonium is oxidized via nitrite to nitrate by nitrification. After recirculation into an anaerobe tank, nitrate is reduced to elementary nitrogen by denitrification. Hence, the described process takes place very often conversely to the structural arrangement of the tanks. This means that parts of the wastewater passing through twice. This so called activated sludge process requires the recirculation of produced nitrate from the aerobe into the anaerobe basin. Here, process monitoring concentrates on measuring ammonium (NH₄), nitrate (NO₃) and oxygen (O₂). For this, our stable ISE sensor and the calibration free oxygen sensor are advisable. The additional control of total suspended solids (TSS) within the activated sludge is helpful, as an optimal concentrations of solids leads to higher nitrification, denitrification and phosphate elimination. Besides our suspended solids sensor also the turbidity sensor can be used. Both sensors convince by an integrated automatic ultrasonic cleaning. To measure NO₃, TSS and carbon parameters like COD, we recommend our reagent free optical spectral probes.

Cleaning of ISE electrodes easy and simple (View on YouTube)

Simple and fast cap change of the oxygen sensor FDO^® (View on YouTube)

The integrated ultra sonic cleaning of the solids/turbidity sensor reduces your maintenance costs (View on YouTube)

Air pressure compensation of ISE sensors: automatically, effective, visible (View on YouTube)
Bio-P
What is Bio-P?
In case of an applicable biological phosphate elimination, a so called bio-P tank is located upstream of the biological cleaning tanks. Under anaerobe conditions, the phosphorus content is initially increased, as stressed bacteria release their stored phosphate. After transferring into an oxidized tank, bacteria take up more phosphate than they released before. This behavior is called „luxury uptake“. Significant conditions for this process are not only a lack of oxygen, but also a lack of nitrate and the availability of easily degradable organic substrate.
For the entire process of biological cleaning, the respective oxygen concentrations are of vital importance. Hence, measuring this parameter by accurate oxygen sensors is indispensable. Again, in the final post-clarifier the sludge extraction can be controlled by a maintenance free sludge level measurement.

Sloped FDO^® cap: no artificial readings, no additional mounting material (View on YouTube)

Contact free wiper of IFL sludge level sensor prevents incorrect measurement (View on YouTube)
Chem. P elimination
How works chemical phosphate elimination?
The chemical cleaning is based on adding precipitants. To control the dosing of for example aluminum or iron concentration, the Ortho-phosphate remaining after the biological cleaning should be measured. Here, a PO₄ analyzer including filter plate is recommended. Even in case of a very efficient bio-P (see above), this chemical procedure is seen mostly, as Ortho-phosphate cannot be removed completely within the bio-P.

Manual for the filter cleaning of the phosphate analyzer P700 (View on YouTube)
Sludge
Why to measure sludge level?
The treatment of the produced sludge happens in a separate process chain. Here, any raw sludge, which was not recirculated into the biological cleaning stage, is transformed into treated sewage sludge. Process steps are thickening, digestion and dewatering. To monitor the mass fluxes and the cleaning efficiency of the plant, a measurement of total suspended solids and turbidity in needed. As sensor cleaning is important, suspended solids sensors and turbidity sensor including a self-cleaning are recommended.

The integrated ultra sonic cleaning of the solids/turbidity sensor reduces your maintenance costs (View on YouTube)
Outlet
Which parameters need to be monitored at the outlet?
The cleaned water is discharged from the treatment plant into surface waters – also called receiving waters. For this, official permissions are needed and outlet concentrations have to be met. Despite regional or country specific differences, generally the following parameters have to be monitored: COD, BOD₅, NH₄-N, N_tot (NH₄-N + NO₂-N + NO₃-N) and P_tot. To determine these concentrations, measuring locations, sampling procedures, sampling preparations and analytical methods are defined.

The integrated ultra sonic cleaning for spectral probes reduces your maintenance costs (View on YouTube)